METHODS FOR LOW ENERGY INORGANIC MATERIAL SYNTHESIS
20250296843 ยท 2025-09-25
Assignee
Inventors
Cpc classification
International classification
Abstract
The present invention relates to methods for low energy solvothermal vapor synthesis in an unsaturated vapor-phase reaction medium. By regulating the amount and pressure of carbon dioxide in the reaction medium, the product composition can be controlled.
Claims
1. A method of synthesizing a metal silicate, or a metal silicate hydrate, or a metal silicate hydrate carbonate comprising: providing a silicon precursor and a metal oxide precursor in a reactor; providing in the reactor a reaction medium comprising a vapor phase of unsaturated water, wherein the vapor phase is an equilibrium unsaturated water vapor, wherein the unsaturated water vapor has a partial pressure of greater than 1 atm; providing carbon dioxide (CO.sub.2) is in gaseous form; and reacting the silicon precursor and the metal oxide precursor in the reaction medium at a predetermined temperature to form the metal silicate or the metal silicate hydrate; wherein the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected to reduce the non-standard state change in Gibb's free energy of the reaction for the formation of the metal silicate or the metal silicate hydrate to less than or equal to zero kJ/mol.
2. The method of claim 1, wherein the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected so that the synthesis is selective for the metal silicate over the metal silicate hydrate.
3. The method of claim 1, wherein the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected so that the synthesis is selective for the metal silicate hydrate over the metal silicate.
4. The method of claim 1, wherein the temperature is higher than 100 C.
5. The method of claim 1, wherein the temperature is higher than 400 C.
6. The method of claim 1, wherein the CO.sub.2 ranges from about 100 ppm to about 10 atm in the reactor, and the temperature ranges from about 150 C. to about 800 C.
7. The method of claim 1, wherein the partial pressure of CO.sub.2 is higher than 0.01 atm.
8. The method of claim 1, wherein the partial pressure of CO.sub.2 is selected so that the metal silicate is thermodynamically most stable phase.
9. The method of claim 1, wherein the partial pressure of CO.sub.2 ranges from 400 ppm to 800 ppm.
10. The method of claim 1, wherein the metal silicate is CaSiO.sub.3, Ca.sub.2SiO.sub.4, Ca.sub.3SiO.sub.5, Ca.sub.3Si.sub.2O.sub.7, MgSiO.sub.3, MgCaSi.sub.2O.sub.6 or Mg.sub.2SiO.sub.4.
11. The method of claim 1, wherein the metal silicate hydrate is Ca.sub.6Si.sub.6O.sub.17(OH).sub.2, Ca.sub.3(SiO.sub.4).sub.2(OH).sub.2, Ca.sub.4Si.sub.3O.sub.9(OH).sub.2, Mg.sub.3Si.sub.2O.sub.5(OH).sub.4 (Serpentine or Chrysotile), or Mg.sub.3Si.sub.4O.sub.10(OH).sub.2.
12. The method of claim 1, wherein the metal oxide precursor is selected from the group consisting of metal oxide, metal hydroxide, metal carbonate, and any combination thereof.
13. The method of claim 1, wherein the metal oxide precursor comprises a member selected from the group consisting of CaO, Ca(OH).sub.2, CaCO.sub.3, MgO, Mg(OH).sub.2, MgCO.sub.3, MgCO.sub.3, an oxygen-containing compound of Table 7, hydrate thereof, and any combination thereof.
14. The method of claim 1, wherein the silicon precursor comprises SiO.sub.2.
15. The method of claim 1, wherein the metal oxide precursor comprises CaCO.sub.3 and the silicon precursor comprises SiO.sub.2.
16. The method of claim 1, wherein CO.sub.2 is introduced into the reactor after the silicon precursor and the metal oxide precursor begin to react with each other.
17. The method of claim 1, wherein the unsaturated water vapor is produced by filling less than 5% volume of the rector with liquid water and then heat it to a predetermined temperature.
18. The method of claim 1, wherein the reactor is a closed system.
19. The method of claim 1, wherein the reactor is an open system.
20. The method of claim 1, wherein the metal silicate or metal silicate hydrate is a powder, which is capable for hydrating or carbonating to form a cementitious product.
21. A method of changing the amount of a metal silicate, metal silicate hydrate or a metal silicate carbonate hydrate in a composition, comprising providing in a reactor a reaction medium comprising a vapor phase of unsaturated water, wherein the vapor phase is an equilibrium unsaturated water vapor, wherein the unsaturated water vapor has a partial pressure of greater than 1 atm; contacting the composition with gaseous carbon dioxide (CO.sub.2) at a predetermined temperature; wherein the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected to change the amount of the metal silicate hydrate or the metal carbonate hydrate.
22. (canceled)
23. (canceled)
24. (canceled)
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0030]
[0031]
[0032]
[0033]
[0034]
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0035] The present invention provides versatile methods of synthesizing inorganic products at relatively low temperatures and pressure. In particular, the present invention provides a method of solvothermal vapor synthesis (SVS) for facilitating the crystallization of a phase from a mixture of precursors in the unsaturated vapor phase of a reaction medium containing a predetermined amount of gaseous carbon dioxide. In some embodiments, the reaction medium is water, and the method is referred to as hydrothermal vapor synthesis (HVS).
[0036] The methods of the present invention allow for convenient and efficient manipulation of pressure and temperature and can be utilized in the synthesis of materials such as scawtite, wollastonite, xonotlite, and quartz.
[0037] The following non-exclusive list of materials can be synthesized according to the HVS method of the present invention: [0038] 1. MgAl.sub.2O.sub.4 [0039] 2. Mg.sub.6Al.sub.2CO.sub.3(OH).sub.16*4H.sub.2O [0040] 3. CaSiO.sub.3 [0041] 4. Ca.sub.6SiO.sub.7(OH).sub.2 [0042] 5. Ca.sub.7Si.sub.6CO.sub.3O.sub.18.Math.2(H.sub.2O) [0043] 6. 2Y.sub.3Al.sub.5O.sub.12 [0044] 7. SrZrO.sub.3 [0045] 8. ZnAl.sub.2O.sub.4 [0046] 9. CaTiO.sub.3 [0047] 10. Ba.sub.2Ti.sub.9O.sub.20 [0048] 11. LiMn.sub.2O.sub.4 [0049] 12. Li.sub.2MnO.sub.3 [0050] 13. Co.sub.3O.sub.4 [0051] 14. LiCoO.sub.2 [0052] 15. Y.sub.2Ti.sub.2O.sub.7 [0053] 16. Li.sub.2Mn.sub.2O.sub.3 [0054] 17. LiV.sub.3O.sub.8
[0055] Other multi-cation compounds include but are not limited to magnesium silicate, calcium-magnesium silicate, all oxides containing one or more alkaline earth cations combined with any suitable cation, all oxides containing aluminum ions in combination with any suitable ion, and all oxides that contain silicon and any suitable ion.
[0056] Throughout this patent document, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the disclosed matter pertains. While the following text may reference or exemplify specific elements of a composite or a method of utilizing the composite, it is not intended to limit the scope of the invention to such particular reference or examples. Various modifications may be made by those skilled in the art, in view of practical and economic considerations, such as the temperature and pressure of the reaction conditions and the ratio between the calcium and silicon precursors.
[0057] The articles a and an as used herein refers to one or more or at least one, unless otherwise indicated. That is, reference to any element or component of the present invention by the indefinite article a or an does not exclude the possibility that more than one element or component is present.
[0058] The term about as used herein refers to the referenced numeric indication plus or minus 10% of that referenced numeric indication.
[0059] The terms vapor and gas are used interchangeably throughout this document. When referring to the solvothermal or hydrothermal vapor atmosphere, this means the vapor is unsaturated gas.
[0060] The term reaction catalyst as used herein refers to a material (liquid, solid, gas, ionic, or supercritical) that is added to the raw material mixture prior to or during the reaction. The catalyst typically does not change the thermodynamics of the reaction system, but does typically change the reaction rate (faster or slower).
[0061] The term metal silicate hydrate refers to a metal silicate compound in hydrate form. Alternatively, the formula of the metal silicate hydrate contains one or more OH groups. Likewise the term metal carbonate hydrate is a metal carbonate compound in hydrate form or the formula of the compound contains one or more OH groups.
[0062] The term precursor as used herein refers to any material leading to the formation of the target product. A precursor may be in the form of a solid, liquid, gas, ionic, or supercritical species. Examples of solid precursors include metals (Aluminum, Iron, Cobalt, Copper, Zinc, Magnesium, Titanium etc.), ceramics (carbonates, hydroxides, oxides, carbides, bromides, borides, nitrides, fluorides, iodides, arsenides, selenides, phosphides, sulfides, tellurides, hydrides, etc.). Additional examples for oxides includes MgO, Al.sub.2O, CaO, and Mn.sub.2O.sub.3. Additional examples for Hydroxides include Mg(OH).sub.2, Al(OH).sub.3, AlO(OH), Ba(OH).sub.2. Additional examples for Carbonates include MgCO.sub.3, CaCO.sub.3, BaCO.sub.3, and Na.sub.2CO.sub.3. The term metal oxide precursor includes metal oxide, metal hydroxide, and metal carbonate. Additional examples for Nitrides include Si.sub.3N.sub.4, Mg.sub.3N.sub.2, (AlN).sub.x.Math.(Al.sub.2O.sub.3).sub.1-x. Additional examples for Carbides include SiC, B.sub.4C, WC, MgC.sub.2, and CaC.sub.2. A material or precursor may be in a liquid state. Examples include inorganic materials (MgO (l), NaCl (l), H.sub.2O (l), NaClKCl (Eutectics), Ga (l), and NH.sub.3 (l), etc.) and organic materials (C.sub.2H.sub.6O.sub.2 (Ethylene Glycol), C.sub.4H.sub.6O.sub.3 (Propylene Carbonate), (Methanol), C.sub.2H.sub.5OH (Ethanol), C.sub.3H.sub.7OH (isopropanol), etc.). A material may be an inorganic gas (e.g. CO.sub.2, H.sub.2O, N.sub.2, Cl.sub.2, F.sub.2, NH.sub.3) or an organic gas (CH.sub.2O (Formaldahyde), CHCl.sub.3 (Chloroform)). An ionic material may be inorganic (containing for example H+, OH, Ca.sub.2+, Mg.sub.2+, Na+, Cl, K+, NH.sub.4+) or organic (containing for example CH.sub.3COO (Acetate), HCOO (Formate) or CN (Cyanide)). A supercritical material may also be inorganic (for example CO.sub.2, CH.sub.4, N.sub.2O, NH.sub.3, N.sub.2) or organic (e.g. C.sub.2H.sub.5OH (Ethanol), CH.sub.3OH (Methanol), C.sub.3H.sub.6O (Acetone)).
[0063] The term solvothermal Vapor Synthesis (SVS) refers to a method for facilitating the crystallization of a phase from a mixture of selected inorganic or organic precursors in a gaseous solvent reaction medium (subcritical). By adjusting the temperature and the partial pressures of the solvent and monitoring any relevant partial pressures of other gasses, phases can be selectively partitioned out. In the case of water being the solvent, the reaction method is labeled Hydrothermal Vapor Synthesis (HVS). The role of the gaseous solvent is to enhance the kinetics of a thermodynamically favorable reaction system. In some cases, the gaseous solvent could participate in the thermodynamics of a reaction (e.g. 6CaCO.sub.3+6SiO.sub.2+H.sub.2OCa.sub.6S.sub.16O.sub.17(OH).sub.2+CO.sub.2 in unsaturated gaseous H.sub.2O (g)). The departure temperature point at which the liquid-phase no longer exists, may be important in optimizing the reactivity of several systems. This temperature can be changed by modifying the solvent with addition of various solute or increasing/reducing vessel liquid fill fraction. The solvent phase is generally in the form of a subcritical unsaturated gaseous phase. SVS should be substantially free from liquid-phase in the reaction zone. In any SVS reaction, the main reaction medium (e.g., water, acetone, ammonia) is in the subcritical gaseous regime. For example, if the solvent is pure H.sub.2O, the pressure cannot exceed 22.06 MPa (3199.308 psi) at temperatures >374 C. (In the case of pure NH.sub.3, the pressure cannot exceed 11.3 MPa (1638.6 psi) at temperatures >132 C. In all cases, the reaction medium is unsaturated gas, meaning no liquid-phase is present in the reaction zone. Examples of solvent in SVS include water, ammonia, ethanol, methanol, acetone, toluene and benzene. Additional gaseous vapors might be introduced (precursor, or catalyst) to enhance the reaction.
[0064] The terms vapor and gas are used interchangeably throughout this document. When referring to the solvothermal or hydrothermal vapor atmosphere, this means the vapor is unsaturated gas.
[0065] The term liquid refers to a material that is above its melting temperature and pressure, but below its boiling temperature and pressure.
[0066] The term gas refers to a material that is above its boiling temperature and pressure, but below its supercritical temperature and pressure.
[0067] The term ionic material refers to a material that has undergone speciation into its elemental components. The ionic material may be complexed by the solvent.
[0068] The term supercritical material refers to a material that has exceeded its supercritical temperature and pressure.
[0069] The term inorganic material or inorganic reaction product or product refers to a material represented by the formula A.sub.a B.sub.b C.sub.c Z.sub.z Y.sub.y X.sub.x ().sub.f().sub.g().sub.h.Math.i().Math.j().Math.k(), wherein A, B, C are single or multi-elemental cations, Z, Y, X are single or multi-elemental anions, , , are charged molecules, and , , are neutral molecules. The material can be either crystalline (ordered), amorphous (disordered), or a mixture of both. (A), (B), and (C) can comprise of a single or multi-elemental cation (positively charged alkali, alkali-earth, transition metal, semi-metal, non-metal, halogen, noble gas, lanthanide, or actinide species) with a concentration of [a], [b], and [c] between ppb (parts per billion) and 100%. (Z), (Y), and (X) can comprise a suitable single or multi elemental anion (negatively charged elemental species, e.g., Oxygen, nitrogen, carbon, fluorine, chlorine, etc) with a concentration of[Z], [Y], and [X] between ppb and 100%. (), (), and () can comprise a variety of charged molecules and ligand groups (organic or/and inorganic) with concentrations of [f], [g], and [h] between ppb and 100%. These molecules could be positively or negatively charged (e.g. OH.sup., CO.sub.3.sup., NH.sub.4.sup.+, NR.sub.4.sup.+). (), (), and () can comprise of a variety of neutral molecules and ligand groups (e.g., H.sub.2O) with concentrations of [i], [j], and [k] between ppb and 100%. In some embodiments, a, b, c, d, e, f, g, h, i, j, and k are each a value equal to or greater than 0.
[0070] The term standard-state pressure refers to a system pressure equal to 1 atm.
[0071] The term non standard-state pressure refers to a system pressure above or below 1 atm.
[0072] The term non-standard state change in Gibb's free energy refers to a change in Gibb's free energy associated with the formation of a reaction product at a system pressure above or below 1 atm.
[0073] The term stable in describing a product or compound refers to its energetic state that has a Gibb's free energy of reaction lower than any other favored reaction products.
[0074] The term metastable in describing a product or compound refers to its energetic state that has a Gibb's free energy of reaction less than zero, but not lower than other thermodynamically favored reaction products.
[0075] The term supercritical describes material that has exceeded its supercritical temperature and pressure.
[0076] The following abbreviations are used: HVS: Hydrothermal Vapor Synthesis; LPH: Liquid-phase hydrothermal; VPH: Vapor-phase hydrothermal; SCW: Supercritical water.
[0077] Unlike LPH, VPH, and SCW synthesis, HVS is conducted at any temperature (>100 C.) and pressure where liquid water no longer exists. The pressurized water vapor atmosphere acts as a reaction catalyst for the synthesis of inorganic materials at relatively low temperatures (<500 C.). This means that HVS enhances the kinetics of a thermodynamically favorable reaction between the selected precursors. Specifically, the main equation governing whether a reaction between precursors is thermodynamically favorable is the Gibb's free energy of reaction:
[0078] If the G.sup.o.sub.rxn is negative, positive, or zero, then the reaction will proceed, not proceed, or remain in equilibrium respectively. The .sup.o refers to standard state conditions: i.e., Total Pressure=1 atm. The pressure increase inside a hydrothermal vessel is dictated by the water liquid-vapor equilibrium curve and also by any volatile substance that could be adding gaseous products to the mix. Accordingly, any gaseous reactant or product can also contribute to the overall thermodynamics of the reaction system via the following non-standard-state relationship:
where R is the molar gas constant (8.314 J/mol.Math.K), T is the temperature (Kelvin), K is the reaction equilibrium constant, a is the activity component of the reactants and products, and P is the partial pressure (atm) of the present gases (Subscripts p=product, r=reactant, s=solid, g=gas). If the G.sub.total (non standard-state change in Gibb's free energy for a particular reaction) is negative, positive, or zero, then the reaction will proceed, not proceed, or remain in equilibrium respectively. The present disclosure details how to apply the thermodynamics of a system in the solvothermal vapor environment to predict product formation. In particular, one or more of the temperature, unsaturated vapor pressure, and partial pressure of any gases added or produced are selected to reduce the non-standard state change in Gibb's free energy of the reaction system to less than or equal to zero. In some embodiments, the non-standard state change in Gibb's free energy of the reaction system may be reduced to below zero, or below 10, or below 100, or below 1,000 [kJ/mol]. In some embodiments, the non-standard state change in Gibb's free energy may be reduced down to 10,000 [kJ/mol]. The non-standard state change in Gibb's free energy may also be reduced by the addition of a gaseous, liquid, or solid species, or by the production of a gaseous, liquid, or solid species within the reaction system. The non-standard state change in Gibb's free energy may also be reduced by removal of any of these species from the reaction system.
[0079] The solvothermal method deviates from the liquid-vapor equilibrium by eliminating the vessel liquid volume fraction. The utilization of unsaturated vapor increases the versatility of this process by introducing another synthesis variable and one additional degree of freedom; where any pressure (P) can be selected at a given temperature by control of the amount of reaction medium added to the vessel. Tuning this variable can optimize reaction kinetics, phase-purity, crystallite size, and morphology.
[0080] In the case of water being the reaction medium, the reaction method is labeled Hydrothermal Vapor Synthesis. However, methods of the present disclosure may utilize other reaction mediums such as organic or inorganic species, or mixtures thereof. In some embodiments, the reaction medium may be one or more of ammonia, ethanol, methanol, acetone, toluene and benzene. If the reaction medium comprises more than one species, then at least one the species may in an unsaturated vapor state at the temperature and pressure of the reaction conditions. In some embodiments, the other species may be saturated, subcritical, or critical pressures.
[0081] The precursors utilized can be crystalline, amorphous, liquid, or aqueous. The precursors may be well-mixed to ensure a high degree of reaction completion. Precursor mixtures can be suspended above or dispersed in the water residing in the reactor prior to the beginning of the reaction. Each material system will dictate the pressure and therefore liquid fill percent necessary for reaction to proceed.
[0082] There are several considerations that make the HVS method possible and unique: (1) Adequate understanding of pressure control within a reactor and (2) Thermodynamic understanding of reaction between selected precursors. The process of HVS in general is explained in US patent application NO. 20190010628, the entire disclosure of which is hereby incorporated by reference. The methods of this patent document facilitate the crystallization of a phase from a mixture of selected inorganic or organic precursors in a water vapor-phase reaction medium. By adjusting the temperature and the partial pressures of water and monitoring any relevant partial pressures of other gasses (e.g., CO.sub.2), phases can be selectively partitioned out. The reaction generally proceeds at a temperature above 100 C. with higher than 1 atm pressure and the water is in the vapor phase (unsaturated vapor).
[0083] Gaseous or dissolved CO.sub.2 is typically used to create carbonate phases from inorganic oxide and hydroxide materials. For example, exposing CaO, MgO, or CaSiO.sub.3 to gaseous and dissolved CO.sub.2 will create CaCO.sub.3, MgCO.sub.3, and CaCO.sub.3/SiO.sub.2 under certain thermodynamic conditions. In this patent document, CO.sub.2 is no longer used to create a carbonate, but rather to suppress the formation of a hydroxide phase and resultantly enable the formation of an oxide phase. By modifying the pressure of unsaturated water-vapor and CO.sub.2, an anhydrous oxide at a low temperatures can be produced.
[0084] It is suggested in US20190010628 that a product yield limitation exists due to CO.sub.2 evolving in a closed-batch system, with the thermodynamics describing that any presence of CO.sub.2 will begin to stabilize the precursors (CaCO.sub.3 and SiO.sub.2) and no longer favor the formation of CaSiO.sub.3. Thus, it would be intuitive to conclude that removing all presence of CO.sub.2 from the system would result in greater product purity. However, it is surprisingly discovered that CO.sub.2 should not always be considered as a precursor (e.g., CaCO.sub.3) stabilizer, and in-fact can be used to induce the formation of an oxide product phase instead of a carbonate one. This is not intuitively realized in the patent literature, where the role of CO.sub.2 in the formation or partitioning of an oxide product phase is completely ignored.
[0085] Specifically, this patent document provides that a thermodynamically prescribed quantity of CO.sub.2 can be introduced into the reaction system to selectively crystallize a hydroxide or an oxide phase. In the method disclosed herein, the Gibb's Free Energy of a synthesis reaction is modified via the introduction of gaseous CO.sub.2. For example, a chemical reaction between CaO or Ca(OH).sub.2 and SiO.sub.2 in an unsaturated water vapor reaction medium as reported in literature will produce xonotlite (Ca.sub.6Si.sub.6O.sub.17(OH).sub.2) if no gaseous CO.sub.2 is introduced into the system. However in the methods of this patent document, if gaseous CO.sub.2 is introduced at a thermodynamically prescribed concentration, then the hydroxide (i.e., Ca.sub.6Si.sub.6O.sub.17(OH).sub.2) phase is energetically suppressed and CaSiO.sub.3 crystallizes.
[0086] One aspect of the invention provides a method of synthesizing a metal silicate, or a metal silicate hydrate. The method includes [0087] providing a silicon precursor and a metal oxide precursor in a reactor; [0088] providing in the reactor a reaction medium comprising a vapor phase of unsaturated water, wherein the vapor phase is an equilibrium unsaturated water vapor, wherein the unsaturated water vapor has a partial pressure of greater than 1 atm; [0089] providing carbon dioxide (CO.sub.2) is in gaseous form; and [0090] reacting the silicon precursor and the metal oxide precursor in the reaction medium at a predetermined temperature to form the metal silicate or the metal silicate hydrate.
[0091] In some embodiments, the Gibb's free energy at a particular temperature and unsaturated water vapor pressure of the material mixture will favor the metal silicate to form. In other embodiments, the favored phase will be the metal silicate hydrate. In another embodiment, both the metal silicate and the metal silicate hydrate will be favored to form. In yet another embodiment, both the metal silicate and the metal silicate hydrate will form, but one of the phases will be energetically more favorable than the other. In these embodiments, it may be possible to insert a gaseous species into the reaction chamber that will selectively affect the Gibb's free energy of reaction of the material mixture and promote the formation of either a metal silicate, metal silicate hydrate, or a mixture of the two. Table 7 lists some examples of metal silicates, metal silicate hydrates/hydroxides, and metal silicate hydroxide carbonates that are possible to synthesize with this invention.
[0092] Various approaches, including procedures based on HVS can be adopted to implement the methods of this patent document. The reactor can be a closed or sealed system such as a batch-style autoclave. This reactor can also be configured as a semi-batch, continuous, or semi-continuous reaction vessel where precursor feeding and product removal is occurring in a continuous or semi-continuous manner. Where a continuous, semi-continuous, or semi-batch reaction vessel is used, unreacted reactants may be removed and recycled back into the reaction vessel, Nonlimiting examples are provided as follows.
[0093] In a first example, the method includes liquid water being added to a batch-style autoclave prior to beginning the reaction process. Specifically, water is placed on the bottom of a batch-style autoclave. The selected mixture of precursors is also placed inside the batch reaction vessel. Two embodiments of placing the material inside the autoclave exist: (1) placing the material into a sample holder that prevents the liquid water from touching the material mixture, or (2) placing the material directly into the liquid water, allowing the liquid water to wet, hydrate, and/or hydroxylate the precursor mixture. CO.sub.2 can be introduced into the reactor before or during the reaction. The amount of water used is determined by the volume of the autoclave. For instance, in the case of a 1-L autoclave, the amount of water can be chosen to be 30 mL to have an approximate volume fill-percent of 3% in order to achieve an unsaturated water partial (also referred to as super-heated steam) pressure of about 58 atm at 350 C. The autoclave is heated for a suitable period of time to induce the precursor mixture to react to form a product; after which it is depressurized. After depressurization, the reactor is cooled to room-temperature. After cooling, the reaction product is removed from the autoclave.
[0094] In a second example of a modified version of HVS, the batch-style reaction vessel is pressurized with water vapor. In this embodiment, the selected material is placed into the autoclave, and the autoclave is sealed. CO.sub.2 can be introduced into the reactor before or during the reaction. The autoclave is preheated, for example, to 350 C. The autoclave is then pressurized to 58 atm with unsaturated water vapor (also referred to as super-heated steam). The unsaturated water vapor can be produced by a steam generator, water boiler, or other preheating systems. The autoclave remains pressurized at for example 350 C. for 12 h; after which it is depressurized. After depressurization, the reactor is cooled to room-temperature. After cooling, the material is removed from the autoclave.
[0095] In a third example of a modified version of HVS, the batch-style reaction vessel is converted to a semi-continuous reactor. In this embodiment, the selected material is placed into the semi-continuous reactor. CO.sub.2 can be introduced into the reactor before or during the reaction. The reactor is preheated to, for example, 350 C. The autoclave is then pressurized to 58 atm with unsaturated water vapor (also referred to as super-heated steam). The unsaturated water vapor can be produced by a steam generator, water boiler, or other preheating systems. This reactor is configured in such a way that precursor feeding and product removal is occurring in a semi-continuous manner. The precursor remains in the reaction zone, for example, at 350 C. for 12 h; after which it is removed from the reactor, with fresh precursor taking its place. This cycle continues in a continuous/semi-continuous manner.
[0096] In a fourth example of a fully continuous version of HVS. In this embodiment, the selected material is placed into the continuous reactor. This reactor may have multiple zones with liquid water, gaseous water (unsaturated/superheated), saturated water vapor, wet gaseous water, dry gaseous water, and partially wet/dry gaseous water. The reactor may have multiple zones with zero water species at all (dry). The reaction zone is a location inside the reaction chamber where the crystallization reaction occurs. CO.sub.2 can be introduced into the reactor before or during the reaction. The unsaturated water vapor can be produced by a steam generator, water boiler, or other preheating systems. Unsaturated water vapor can also be produced by microwave heating of solid, microwave heating of liquid, microwave heating of gas, microwave heating of plasma, solar heating (e.g., solar thermal), solar-electric, waste-heat, and geothermal. This reactor is configured in such a way that precursor feeding and product removal is occurring in a continuous/semi-continuous manner. The precursor remains in the reaction zone, for example, at a predetermined temperature for a certain period; after which it is removed from the reactor, with fresh precursor taking its place. This cycle continues in a continuous/semi-continuous manner.
[0097] The partial pressure of the unsaturated water vapor can be regulated via the initial fill of liquid water in the reactor. The amount of water as a liquid ranges from about 0.1 to about 40 vol %, all subunits and sub-ranges included, of the total volume of the reaction vessel. In non-limiting exemplary embodiments, the water content is about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40% of the total volume of the reaction vessel. For example, in the case of a reaction at 374 C., the water fill percent may be less than 15.6% to achieve an all-gas (steam) reaction medium. All other cases can be numerically computed and experimentally confirmed. The numeric computation involves equating the pressure values obtained by surveying concentration of water in the Vander-Waals or Redlich-Kwong equations with the pressure in the water liquid-vapor equilibrium curve. One or more additional inert organic solvent may be added to further fine tune the total or partial-gas pressure in the vessel.
[0098] After a desirable temperature is reached, the water inside the reaction vessel is substantially in the gaseous state. In some embodiments, more than about 98% or 99% of the water in the vessel is in the gaseous state. In some embodiments, the water in the vessel is in gaseous state and no liquid water exists.
[0099] The partial pressure of water in the reactor ranges from about 10 psi to 50000 psi or higher, all subunits and sub-ranges included. Non-limiting ranges include from about 10 psi to about 500 psi, from about 500 psi to about 700 psi, from about 700 psi to about 1000 psi, from about 1000 to about 1500 psi, from about 1500 to about 2000 psi, from about 2000 psi to about 2500 psi, from about 2500 psi to about 3000 psi, from about 2500 psi to 5000 psi, from about 2500 psi to 10000 psi, from about 2500 psi to 20000 psi, from about 5000 psi to 20000 psi and from about 2500 psi to 20000 psi. In other exemplary embodiments, the lower limit of the pressure range is about 150, about 200, about 250, about 300, about 350, about 400, about 450, about 500, about 550, about 600, about 650, about 700, about 750, about 800, about 850, about 900, about 950, about 1000, about 1200, about 1400, about 1600, about 1800, about 2000, about 3000, about 4000, about 5000, about 6000, about 8000, about 10000, about 12000, or about 14000 psi. In some embodiments, the upper limit of the pressure range is about 1000, about 1200, about 1400, about 1600, about 1800, about 2000, about 2200, about 2400, about 2600, about 2800, about 3000, about 3200, about 3400, about 4000, about 5000, about 6000, about 8000, about 10000, about 15000, about 20000, about 25000, or about 30000 psi. In some embodiments, the partial pressure of water in the reactor vessel is about 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400, 2600, 2800, 3000, 3200, 3400, about 4000, about 5000, about 6000, about 8000, about 10000, about 12000, about 14000, about 16000, about 20000, or about 25000 psi.
[0100] In some embodiments, the unsaturated water vapor is a pressurized superheated steam, which is a steam having a temperature greater than 100 C. and not in equilibrium with liquid water.
[0101] The partial pressure of CO.sub.2 in the reactor vessel needs to be regulated to control the reaction outcome. The regulation of the partial pressure of other gases may be accomplished by the introduction or removal of CO.sub.2 from the reaction vessel through, e.g., outgassing the reaction vessel. In some embodiments, the partial pressure of CO.sub.2 added or produced are independently between 0.0000001 and 10,000 atm, all subranges and subunits included. In some embodiments, the partial pressure of carbon dioxide ranges from about 0.00000001 to about 1000, from about 0.0000001 to about 0.00001, from about 0.000001 to about 0.0001, from about 0.00001 to about 0.001, from about 0.0001 to about 0.01, from about 0.001 to about 0.1, from about 0.01 to about 0.1, from about 0.1 to about 1, from about 0.1 to about 10, from about 1 to about 10, from about 1 to about 20, from about 1 to about 50, from about 1 to about 100 psi, all subranges and subunits included. Non-limiting examples of the partial pressure of CO.sub.2 include about 0.0005, about 0.001, about 0.005, about 0.01, about 0.05, about 0.1, about 0.5, about 1, about 5, about 10, about 15, about 20, about 25, about 30, about 40, about 50, about 80 and about 100 psi. In some embodiments, the amount of CO.sub.2 ranges from about 50 ppm to about 1000 ppm, from about 100 ppm to about 800 ppm, from about 200 ppm to about 800 ppm, from about 400 ppm to about 800 ppm or from about 200 ppm to about 600 ppm in the reactor. In some embodiments, the amount of CO.sub.2 ranges from about 100 ppm to about 10 atm, from about 100 ppm to about 5 atm, from about 100 ppm to about 1 atm, from about 200 ppm to about 10 atm, from about 500 ppm to about 5 atm, or from about 500 ppm to about 1 atm. In some embodiments, the CO.sub.2 is in the supercritical state. In some embodiments, CO.sub.2 is partially in the liquid state. In some embodiments, CO.sub.2 is completely in the gaseous state.
[0102] A significant advantage of the present invention over traditional method is the much lower temperature range and net-energy required in the crystallization process. Not only is the process cost-efficient, it is also environmentally friendly in terms of generating less side reaction products. The temperature of the reaction ranges from about 100 C. to 1000 C., from about 150 C. to 1000 C., from about 150 C. to 800 C., from about 200 C. to 800 C., from about 200 C. to 600 C., from about 400 C. to 600 C., from about 600 C. to 800 C., all subunits and sub-ranges included. In some exemplary embodiments, the lower limit of the temperature range is about 200 C., 250 C., 300 C., 350 C., 400 C., 500 C., 600 C., 700 C., 800 C. or higher, and the upper limit of the range is about 350 C., 400 C., 500 C., 600 C., 700 C., 800 C., 900 C., 1000 C., 1200 C., 1400 C., 1600 C., 1800 C., or 2000 C. More non-limiting examples of temperature include about 150 C., 200 C., 250 C., 300 C., 350 C., 400 C., 450 C., 500 C., 550 C., 600 C., 650 C., 700 C., 750 C., 800 C. 850 C., 900 C., 950 C. and 1000 C.
[0103] For example, the CaSiO.sub.3 phase selection according to the methods of this patent document, the partial pressure of CO.sub.2 can range from 100 ppm to 10 atm, and the temperature can range from about 150 C. to about 800 C. In further examples For Mg.sub.2SiO.sub.4 phase selection according to the methods disclosed herein, the partial pressure of CO.sub.2 can range from 100 ppm to 1000 atm, and the temperature ranges from about 150 C. to about 800 C.
[0104] The reaction temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected to reduce the non-standard state change in Gibb's free energy of the reaction for the formation of the metal silicate or the metal silicate hydrate to less than or equal to zero kJ/mol. As illustrated in the examples, the three factors directly impact the identity of the products. In some embodiments, the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected so that the synthesis is selective for the metal silicate over the metal silicate hydrate. In some embodiments, the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected so that the synthesis is selective for the metal silicate hydrate over the metal silicate. In some embodiments, the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected so that metal silicate is sole or main thermodynamically stable phase in the product. In some embodiments, the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected so that metal silicate hydrate is sole or main thermodynamically stable phase in the product. In some embodiments, the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected so that metal silicate is sole or main thermodynamically metastable phase in the product. In some embodiments, the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected so that metal silicate hydrate is sole or main thermodynamically metastable phase in the product. When a compound is the main thermodynamically stable phase in the product, it is more than 50%, more than 60%, more than 70%, more than 80% or more than 90, or more than 95% by weigh in the product.
[0105] Nonlimiting examples of metal silicates in the methods disclosed herein include calcium silicate CaSiO.sub.3, Ca.sub.2SiO.sub.4, Ca3SiO5, Ca3Si2O7, MgSiO3, MgCaSi2O6 and Mg2SiO4. Nonlimiting examples of metal silicate hydrates include Ca6Si6O17(OH)2, Ca5(SiO4)2(OH)2, Foshagite, Serpentine, Chrysotile, Talc, and alike. Nonlimiting examples of metal silicates include one or more of those oxygen containing compounds listed in Table 7. Depending on the specific conditions, these metal silicates can be reaction precursors or reaction products.
[0106] Precursors include for example metal oxide, metal carbonate, metal hydroxide, and a silicon source. The silicon source can be derived from SiO.sub.2, or any other silicon source, for example, SiCl.sub.4 or TEOS (Tetraethyl Orthosilicate, Si(OC.sub.2H.sub.5).sub.4, or orthosilic acid (Si(OH).sub.4), or any water soluble or non-soluble silicate, for example, NaSiO.sub.3, Na.sub.2Si.sub.2O.sub.5. The Si source can also be any multicomponent silicate, for example alkali silicates, alumino silicates, feldspars. Additional examples of silicon dioxide (amorphous or crystalline) as a precursor include quartz, silica flour, siliceous sand, diatomaceous earth, clays, silica gel, and combination thereof. Meanwhile, the metal oxide precursor such as calcium oxide source include calcium carbonate, calcium oxide, calcium hydroxide, calcium silicate, other single/multi cation species and any combination thereof. In some embodiments, metal oxide precursors are in the formula of A.sub.a B.sub.b C.sub.c Z.sub.z Y.sub.y X.sub.x ().sub.f().sub.g ().sub.h.Math.i().Math.j().Math.k(), the components of which are as defined above. Nonlimiting examples of metal oxide precursors include one or more those oxygen containing compounds listed in Table 7. Further examples of metal oxide precursor include CaO, Ca(OH).sub.2, CaCO.sub.3, MgO, Mg(OH).sub.2, MgCO.sub.3, MgCO.sub.3hydrates thereof and any combination thereof.
[0107] In some embodiments, the precursors include SiO.sub.2 and at least one of CaO, Ca(OH).sub.2, and CaCO.sub.3. In some embodiments, the precursors include Ca(OH).sub.2 and SiO.sub.2. In some embodiments, the precursors include CaO and SO.sub.2 CaCO.sub.3 and SiO.sub.2.
[0108] The ratio between the silicon in the silicon source and the calcium oxide in the calcium oxide source ranges from about 0.5:1 to 10:1, all sub-ratio included. Non-limiting examples include about 0.6:1, 0.8:1, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1:2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, and 9:1. The precursors should be thoroughly mixed to create desirable particle contact and avoid reaction limiting particle separation.
[0109] The amount of calcium hydroxide or calcium carbonate in the calcium source may be adjusted to modify the composition of the product and the rate of the reaction. In some embodiments, the calcium oxide source comprises more than about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of calcium hydroxide or calcium carbonate. In some embodiments, the calcium source comprises mainly calcium hydroxide in order to obtain a pellet configuration. In some embodiments, the calcium source comprises mainly calcium carbonate in order to obtain a powder configuration.
[0110] The particle size of the above reaction precursors is preferably less than about 600 mesh to ensure a thorough mixing of the precursors and promote a fast crystallization process. In some embodiments, the particle size of one or more of the precursors including the silicon source and the calcium oxide source is less than about 500, 400, 350, 300, 250, 200, 150, or 100 mesh. In some embodiments, the particle size of one or more of the precursors including the silicon source and the calcium oxide source is less than 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 200, 300, 400, 500, or 1000 microns. In some embodiments, the particle size of the precursors may be within a range, e.g., between 1 and 5 microns, 8 and 10 microns, 25 and 35 microns, 50 and 100 microns, etc. The techniques used to mix the precursors and obtain a desired particle size are known to those of ordinary skill in the art, and may include, e.g., attrition milling, ball milling, ultrasonic de-agglomeration, etc., or combinations thereof.
[0111] An additional material such as an acid, a base or a salt may be added to the above reaction precursors to facilitate the crystallization process. In some embodiments, the reactant mixture consists essentially of a silicon source, a calcium oxide source and a salt. Exemplary salts include potassium chloride, potassium bromide, sodium chloride, and sodium bromide. In some embodiments, the salt is sodium chloride. In some embodiments, basic or acidic additives may be introduced to enhance or modify the reaction. In some embodiments the basic additive is sodium hydroxide. In some embodiments the acidic additive is magnesium chloride. The exact amount of salt depends on the specific salt additive and the product and can be determined by one of ordinary skill in the art without undue experiments.
[0112] The composition or mixture of the reactants can be exposed to water steam or dispersed in liquid water. In some embodiments, the exposure is limited to water steam only. In some embodiments, the composition is exposed to the steam after initially being dispersed liquid water.
[0113] The silicon source, the calcium oxide source and other additives may be exposed to the desirable pressure and temperature for any period of time depending on the specific composition of the target product. In exemplary embodiments, the reaction condition is maintained for about 10 minutes, 20 minutes, 40 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 30 hours, 35 hours, 40 hours or longer before the product is collected.
[0114] Also provided is a compound prepared according to the above described methods. The compounds synthesized through methods disclosed herein are of crucial importance to anyone that has interest in the field of calcium silicate synthesis, carbon dioxide emissions, and manipulation of hydrothermal reactions for the synthesis of inorganic oxide materials. A variety of metal inosilicate minerals or related compounds including scawtite, xonotlite, wollastonite, alite, and belite can be represented by Ca.sub.aSi.sub.bO.sub.c(CO.sub.3).sub.d(OH).sub.e. In some embodiments, a, b, and c are each greater than 0, and d and e are each equal or greater than 0. In some embodiments, the formula is Ca.sub.aSi.sub.bO.sub.c.Math.(H.sub.2O).sub.f, wherein f is a value equal or greater than 0. In some embodiments, the formula is Ca.sub.aSi.sub.bO.sub.c. In some embodiments of the formulas, a+2b=c. In some embodiments, the values of a, b and c are independently selected from 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In some embodiments, the values of d, e and f are independently selected from 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. Non-limiting examples of compounds under the formula include Xonotlite (Ca.sub.6SiO.sub.17(OH).sub.2), Scawtite (Ca.sub.7Si.sub.6O.sub.18(CO.sub.2).Math.2(H.sub.2O)), wollastonite (CaSiO.sub.3), belite (Ca.sub.2SiO.sub.4), and alite (CaSiO.sub.5). Additional examples of compounds that can be prepared with the methods of this patent document are provided in Table 7.
[0115] In some embodiments, the product is a powder. In some embodiments, the powder can hydrate to form a cementitious product. In some embodiments, the powder can carbonate to form a cementitious product.
[0116] Another aspect of the patent document provides a method of forming a cementitious product. The method includes hydrating or carbonating the metal silicate or metal silicate hydrate prepared according to the method disclosed herein. In some embodiments, the metal silicate or metal silicate hydrate is a powder.
[0117] Another aspect of the patent document provides a method of changing the amount of a metal silicate hydrate or a metal carbonate hydrate in a composition. The reaction conditions can be adjusted similarly as in the methods described above. The method includes: [0118] providing in a reactor a reaction medium comprising a vapor phase of unsaturated water, wherein the vapor phase is an equilibrium unsaturated water vapor, wherein the unsaturated water vapor has a partial pressure of greater than 1 atm; [0119] contacting the composition with gaseous carbon dioxide (CO.sub.2) at a predetermined temperature; [0120] wherein the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected to change the amount of the metal silicate hydrate or the metal carbonate hydrate.
[0121] In some embodiments, the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected to convert the metal silicate hydrate to a metal silicate. In some embodiments, the temperature, the pressure of the unsaturated vapor pressure, and the pressure of CO.sub.2 are selected to convert the metal carbonate hydrate to a metal oxide. In some embodiments, the metal carbonate hydrate is Mg.sub.6Al.sub.2CO.sub.3(OH).sub.16*4(H.sub.2O) and the metal oxide is MgAl.sub.2O.sub.4. Nonlimiting examples of the metal silicate hydrate and metal silicate are provided in Table 7.
[0122] CO.sub.2 Source: the gaseous CO.sub.2 can be provided to the reaction zone from the following sources: (1) direct from atmosphere, (2) desorption of adsorbate, (3) thermal, hydrothermal, hydrothermal vapor (unsaturated water vapor), or chemical decomposition of an organic or inorganic compound to form CO.sub.2 gas, (4) Oxidation of hydrocarbons and elemental carbon by water or air to form carbon monoxide and then catalyzed oxidation of CO to form CO.sub.2 (e.g., Platinum on titania or zirconia, and other systems), (5) Direct oxidation of carbon to form carbon dioxide, () decomposition of calcium carbonate, or any other carbonate or CO.sub.2-bearing materials, (7) combustion of fuel, (8) direct CO.sub.2 release from a metal silicate carbonate, (8) The exothermic Boudouard reaction where CO disproportionates into carbon dioxide and elemental carbon, (9) pressurized CO.sub.2 gas, (10) insertion of liquid CO.sub.2, (11) insertion of solid CO.sub.2, (12) any method of gaseous CO.sub.2 sourcing, and (13) any combination of the above. These sources may be used to generate the desired gaseous CO.sub.2 pressure and concentration within the reaction chamber. These sources may also be used to generate the desired gaseous CO.sub.2 pressure and concentration outside of the reaction chamber. This CO.sub.2 would be subsequently injected into the reaction chamber.
EXAMPLES
Example 1Ca.SUB.6.Si.SUB.6.O.SUB.17.(OH).SUB.2 .Synthesis from CaO and SiO.SUB.2
[0123] 6 grams of SiO.sub.2 precursor was thoroughly mixed with 5.6 g of CaO precursor. The mixing process was completed by dry mixing the two components inside a small ceramic (ZrO.sub.2) jar (SPEX mill) with 2 spherical zirconia balls (3 mm) for 10 min. The amount of each precursor was chosen to achieve a 1:1 molar mass mixture. This precursor mixture was placed into a sample holder that prevents any liquid water from touching the material mixture. The sample holder was placed on the bottom of a batch-style 1-L autoclave that is capable of housing temperatures and pressures up to 500 C. and 5000 psi, respectively. De-ionized liquid water (18 M-ohm) was placed on the bottom of the autoclave outside of the sample holder to ensure that the precursor mixture is not in contact with the liquid water. The amount of water used is determined by the volume of the autoclave. In the case of a 1-L autoclave, the amount of water is chosen to be 50 mL to have an approximate volume fill-percent of 5% in order to achieve an unsaturated water partial pressure of about 81 atm at 400 C. The autoclave was heated for 12 h; after which it was depressurized. After depressurization, the reactor was cooled to room-temperature. After cooling, the reaction product was removed from the autoclave.
[0124] According to the computed chemical equilibrium, gaseous CO.sub.2 in any concentration can affect the purity and identity of the product phase. Further, any CO.sub.2 partial pressure can alter the chemical reaction's Gibb's free energy and create zones of stability and metastability of particular phases. These zones of stability and metastability can be computed by calculating the equilibrium temperatures of selected reaction products and comparing the Gibb's free energy of the selected reaction product to other thermodynamically favored phases. Stability and metastability zones are thus a function of temperature, CO.sub.2 pressure, and water partial pressure. For instance, under certain conditions, Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 is never the sole thermodynamically stable phase, and CaSiO.sub.3 always accompanies it in stable or metastable form.
[0125] In the case of this example, the raw material mixture was >99% pure and had negligible adsorbed CO.sub.2. Therefore, it can be assumed that the CO.sub.2 concentration inside the autoclave at room-temperature was approximately 400 ppm (atmospheric). This concentration does not favor the formation of a carbonate, and instead stabilizes the calcium silicate hydrate. The CaSiO.sub.3 phase is metastable under these conditions.
[0126] The powder retrieved was analyzed via x-ray diffraction which revealed that the only new phases formed were Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 (Xonotlite, Eq. 1) and CaSiO.sub.3 (Wollastonite) (Eq. 2). A small amount of Foshagite (Ca.sub.4(Si.sub.3O.sub.9)(OH).sub.2) was also detected.
6CaO+6SiO.sub.2+H.sub.2OCa.sub.6Si.sub.6O.sub.17(OH).sub.2Eq. 1
CaO+SiO.sub.2CaSiO.sub.3Eq. 2
[0127] The extent of reaction (i.e., how much of the precursor was consumed) depended on the mixedness of the initial powder blend. If the mixedness was low, unreacted phases such as CaO, SiO.sub.2, and hydrated CaO (Ca(OH).sub.2) formed. Additionally, if mixture was not-uniform, precursor excess regions may favor the formation of a non 1:1 molar compound. This can be evidenced by the formation of the Foshagite (Ca.sub.4(Si.sub.3O.sub.9)(OH).sub.2) phase.
[0128] Additionally, this example was based on a thermodynamic model that is based on calcium silicate hydrate (Ca.sub.6Si.sub.6O.sub.17(OH).sub.2) and calcium silicate (CaSiO.sub.3). In other scenarios, there may be different phases that exist. For example, other hydrates and other oxides, that may form as metastable or stable phases. Therefore, this example is just one possible phase configuration that is possible. Many other calcium-silicate based phase assemblages are possible.
Example 2CaSiO.SUB.3 .Synthesis from CaO and SiO.SUB.2
[0129] 6 g of SiO.sub.2 was thoroughly mixed with 5.6 g of CaO. The mixing process was completed by dry mixing the two components inside a small ceramic (ZrO.sub.2) jar (SPEX mill) with 2 spherical zirconia balls (3 mm) for 10 min. The amount of each precursor was chosen to achieve a 1:1 molar mass mixture. This precursor mixture was placed into a sample holder that prevents any liquid water from touching the precursor mixture. The sample holder was placed on the bottom of a batch-style 1-L autoclave that was capable of withstanding temperatures and pressures up to 500 C. and 5000 psi, respectively. De-ionized liquid water (18 M-ohm) was placed on the bottom of the autoclave outside of the sample holder to ensure that the material mixture was not in contact with the liquid water. The amount of water used was determined by the volume of the autoclave. In the case of a 1-L autoclave, the amount of water was chosen to be 50 mL to have an approximate volume fill-percent of 5% in order to achieve an unsaturated water partial pressure of about 81 atm at 400 C. The autoclave was assembled and sealed.
[0130] To avoid the hydrate phase (Ca.sub.6Si.sub.6O.sub.17(OH).sub.2) identified in example 1, gaseous CO.sub.2 was introduced into the autoclave at a very specific pre-selected partial pressure. At 25 C., the partial pressure of CO.sub.2 introduced was at least 0.68 atm. This CO.sub.2 partial pressure increased by heating the autoclave to 400 C. to achieve a partial pressure of 1.54 atm (Redlich-Kwong, Equation of state for non-ideal gas). According to computed chemical equilibrium diagram and the computed stability and metastability diagrams, this CO.sub.2 partial pressure created conditions in which CaSiO.sub.3 was the sole thermodynamically stable phase.
[0131] Once the CO.sub.2 gas was introduced, the autoclave was heated for 12 h; after which it was depressurized to atmospheric pressure. After depressurization, the reactor was cooled from 400 C. to room-temperature. After cooling, the material was removed from the autoclave. The powder retrieved was analyzed via x-ray diffraction which revealed that the only new phase formed is CaSiO.sub.3 (Wollastonite) (Eq. 3). A small amount of unreacted SiO.sub.2 and newly formed CaC.sub.03 (from the reaction between CaO precursor and CO.sub.2 overpressure) was also detected in x-ray diffraction.
CaO+SiO.sub.2CaSiO.sub.3Eq. 3
The purity of the CaSiO.sub.3 will depend on the degree of mixture homogeneity (mixedness) of the original material mixture. If the mixedness was low, unreacted phases such as CaO, SiO.sub.2, and hydrated CaO (Ca(OH).sub.2) will have formed. If the mixedness was high, then all of the precursor phases will be consumed and only the product phase will be present.
Example 3Phase Selection
[0132] The information in Tables 1-5 was derived from the computed diagrams and describes examples of reaction conditions that create a thermodynamic condition in which CaSiO.sub.3 or Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 is the unstable, stable, or metastable phase.
[0133] The shift of the metastable region can be observed depending on the reaction condition. For instance, under certain conditions a shift towards the lower temperatures creates a large field in which CaSiO.sub.3 is metastable and Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 is stable.
TABLE-US-00001 TABLE 1 Thermodynamically favored phases from the reaction between CaO, SiO.sub.2, H.sub.2O, and CO.sub.2 at a P.sub.H2O of 0.1 atm. CaSiO.sub.3 refers to Wollastonite. Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 refers to Xonotlite. Temp P.sub.CO2 P.sub.H2O ( C.) (atm) (atm) Stable Metastable 400 0.0004 0.1 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 200 CaSiO.sub.3 150 CaSiO.sub.3 400 0.01 0.1 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 CaSiO.sub.3 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 200 CaSiO.sub.3 150 CaCO.sub.3 and SiO.sub.2 400 0.1 0.1 CaSiO.sub.3 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 300 CaSiO.sub.3 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2 400 1 0.1 CaSiO.sub.3 300 CaSiO.sub.3 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2 400 10 0.1 CaSiO.sub.3 300 CaCO.sub.3 and SiO.sub.2 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2
TABLE-US-00002 TABLE 2 Thermodynamically favored phases from the reaction between CaO, SiO.sub.2, H.sub.2O, and CO.sub.2 at a P.sub.H2O of 1 atm. Temp P.sub.CO2 P.sub.H2O ( C.) (atm) (atm) Stable Metastable 400 0.0004 1 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 200 CaSiO.sub.3 150 CaSiO.sub.3 400 0.01 1 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 CaSiO.sub.3 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 200 CaSiO.sub.3 150 CaCO.sub.3 and SiO.sub.2 400 0.1 1 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 CaSiO.sub.3 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2 400 1 1 CaSiO.sub.3 300 CaSiO.sub.3 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2 400 10 1 CaSiO.sub.3 300 CaCO.sub.3 and SiO.sub.2 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2
TABLE-US-00003 TABLE 3 Thermodynamically favored phases from the reaction between CaO, SiO.sub.2, H.sub.2O, and CO.sub.2, at a P.sub.H2O of 10 atm. Temp P.sub.CO2 P.sub.H2O ( C.) (atm) (atm) Stable Metastable 400 0.0004 10 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 200 CaSiO.sub.3 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 150 CaSiO.sub.3 400 0.01 10 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 200 CaSiO.sub.3 150 CaCO.sub.3 and SiO.sub.2 400 0.1 10 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 CaSiO.sub.3 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2 400 1 10 CaSiO.sub.3 300 CaSiO.sub.3 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2 400 10 10 CaSiO.sub.3 300 CaCO.sub.3 and SiO.sub.2 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2
TABLE-US-00004 TABLE 4 Thermodynamically favored phases from the reaction between Cao, SiO.sub.2, H.sub.2O, and CO.sub.2 at a P.sub.H2O of 100 atm. Temp P.sub.CO2 P.sub.H2O ( C.) (atm) (atm) Stable Metastable 400 0.0004 100 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 200 CaSiO.sub.3 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 150 CaSiO.sub.3 400 0.01 100 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 200 CaSiO.sub.3 150 CaCO.sub.3 and SiO.sub.2 400 0.1 100 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 CaSiO.sub.3 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2 400 1 100 CaSiO.sub.3 300 CaSiO.sub.3 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2 400 10 100 CaSiO.sub.3 300 CaCO.sub.3 and SiO.sub.2 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2
TABLE-US-00005 TABLE 5 Thermodynamically favored phases from the reaction between Cao, SiO.sub.2, H.sub.2O, and CO.sub.2 at a P.sub.H2O of 1000 atm. Temp P.sub.CO2 P.sub.H2O ( C.) (atm) (atm) Stable Metastable 400 0.0004 1000 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 200 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 150 CaSiO.sub.3 400 0.01 1000 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 200 CaSiO.sub.3 150 CaCO.sub.3 and SiO.sub.2 400 0.1 1000 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 300 Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 CaSiO.sub.3 200 CaSiO.sub.3 150 CaCO.sub.3 and SiO.sub.2 400 1 1000 CaSiO.sub.3 300 CaSiO.sub.3 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2 400 10 1000 CaSiO.sub.3 300 CaCO.sub.3 and SiO.sub.2 200 CaCO.sub.3 and SiO.sub.2 150 CaCO.sub.3 and SiO.sub.2
Example 4Mixed Reaction Study (Ca.SUB.6.Si.SUB.6.O.SUB.17.(OH).SUB.2 .and CaSiO.SUB.3.)
[0134] For crystallizing a product from CaCO.sub.3 and SiO.sub.2, equal molar ratios (1:1) of CaCO.sub.3 (calcite, 98%, CAS #471-34-1, Fisher Scientific, Fair Lawn, NJ) and SiO.sub.2 (quartz, Min-u-sil 40, CAS #14808-60-7, U.S. Silica Co., Berkley Springs, WV,) were attrition wet mixed (Szegvari Attritor System, Type: 01 HDDM, Union Process Inc, Akron, OH) for 10 min with spherical zirconia media (6.5 mm, YSZ, Product #4039GM-S065, Inframat Corporation. Manchester, CT). The mixed powder was dried at 90 C. overnight. After drying, 3 g of powder was suspended over a bath of de-ionized (18.2 M, Rios 5/MilliQ water purification system, Billerica, MA) liquid water in a 1-Liter (Actual volume=1.11 L) Hastalloy (C-276 alloy) hydrothermal reaction vessel (HAST C 1807H.sub.04, Parr Instruments, Moline, Illinois). The amount of liquid water placed into the autoclave was 2.88 and 3.15 volume fill % in order to maintain a constant P.sub.H2O of 58 atm at the set temperature (350 and 390 C., see Table. 6). The vessel was then sealed according to manufacturer specifications (30 ft-lb of torque per bolt). Afterwards, it was placed into a heater (Cart Heater, 340 atm, 500 C., HT/HP 21571, Parr Instruments, Moline, Illinois), heated to the desired temperature (refer to Table. 4), and held isothermally for 12 h. After 12 h, the vessel was automatically de-pressurized using a computer (Matlab-based software, Kopp Acquire v2.1, Rutgers University, Piscataway, NJ) controlled gas-outlet valve. The gas outlet valve consisted of a stepper motor that was mechanically coupled to gas outlet-valve. A microcontroller (Mega 2560, Arduino) established the connection between the computer and the stepper motor. After depressurization, the reactor was cooled to room-temperature. The dry reaction product was then retrieved from the reactor and fully characterized as described below.
TABLE-US-00006 TABLE 6 Experimental parameters for the HVS of CaSiO.sub.3 Temperature Pressure Experimental Fill Reaction ( C.) (atm) (%) CaCO.sub.3 + SiO.sub.2 350 58 3.15 CaCO.sub.3 + SiO.sub.2 390 58 2.88
[0135] X-ray diffraction (XRD) patterns were obtained by scanning the reacted powdered samples (Silicon zero background holder) with a Bruker D8 Discover x-ray diffractometer (Cu-K radiation, =1.514 , 40 kV/40 mA, Parallel beam, Vantec 1 Detector, Karlsruhe, Germany) in the 10-80 2 range (step size=0.018*, dwell time=0.5-s). The NIST inorganic crystal structure database (NIST ICSD, FIZ Karlsruhe, Germany) was accessed using the Jade v9.1 pattern analysis software (Materials Data Inc., Livermore, CA) to determine the identity of the constituent phases. Microstructural analyses were conducted on gold sputter coated (20 nm Au) powdered samples (Model EMS150T ES, Electron Microscopy Sciences, Hatfield, PA) with the Field Emission Scanning Electron Microscope (FE-SEM, Carl Zeiss Microscopy GmbH, Jena, Germany) at an accelerating voltage of 5 kV (Working distance 8.5 mm). Thermogravimetric analysis (TGA, Q5000IR, TA Instruments, New Castle, DE) was conducted on the reacted samples to quantify reaction progression by decomposing any remaining CaCO.sub.3 in the product mixture. This analysis consisted of heating the samples from room temperature to 1000 C. at a heating rate of 20 C./min in a flowing N.sub.2 atmosphere (50 mL/min). The amount of remaining CaCO.sub.3 directly corresponds to the amount of calcium silicate product formed. The general relationship shown in Eq. 4 relates the reaction yield (, mol %) with the mass fraction lost during CaCO.sub.3 decomposition (M.sub.L).
[0136] This relationship assumes the only solid-reaction product to be CaSiO.sub.3 (Eq. 5), and as such, the 1/0.379 factor represents the molar mass ratio between CaSiO.sub.3 and CO.sub.2, which is the amount of CO.sub.2 corresponding to a 0 mol % CaSiO.sub.3 yield reaction. This relationship is more complicated if Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 was also formed (Eq. 6) since there is an additional mass-loss at higher temperatures (>700 C.) from the dehydroxylation of Ca.sub.6Si.sub.6O.sub.17(OH).sub.2.
CaCO.sub.3+SiO.sub.2CaSiO.sub.3+CO.sub.2Eq. 5
CaCO.sub.3+6SiO.sub.2+H.sub.2OCa.sub.6Si.sub.6O.sub.17(OH).sub.2+6CO.sub.2Eq. 6
[0137] For this system, accounting of both carbonate content and hydroxide content is necessary to adequately confirm total reaction yield and concentration of individual products. First, the amount of Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 was determined by determining the mass-loss associated with dehydroxylation. This mass-loss was then converted to a molar quantity to describe the molar concentration of carbonate that was utilized to form the Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 phase. Second, the carbonate decomposition was determined from the thermogravimetric decomposition of any remaining CaCO.sub.4. This mass-loss was converted to a molar quantity to describe the total amount of CaCO.sub.3 consumed. Comparing the moles consumed with the moles utilized to form Ca.sub.6Si.sub.6O.sub.17(OH).sub.2, the concentration of the remaining CaSiO.sub.3 phase was determined. It is worth noting that high resolution x-ray diffraction, FTIR analysis, Carl-Fisher Titration, and other techniques not mentioned can also be suitable methods to determine phase formation and corresponding concentration.
[0138] According to the developed thermodynamic diagrams, a P.sub.H.sub.
[0139] The amount of formed CaSiO.sub.3 and Ca.sub.6Si.sub.4O.sub.17(OH).sub.2 was determined by analysis of the thermogravimetric decomposition profile of the reaction products, in which unreacted CaCO.sub.3 and formed Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 was decomposed. It was found that 0.06 g (2.3 wt %) and 0.86 g (32.3 wt %) of CaSiO.sub.3 and Ca.sub.6Si.sub.6O.sub.17(OH).sub.2, respectively, formed in the 350 C. reaction. The 350 C. thermodynamic reaction limit, derived (ideal-gas law) from the chemical equilibria was found to be 0.44 g of Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 and 17.53 g of CaSiO.sub.3 in a 1.11-L reaction volume. The anomaly of exceeding the thermodynamically computed phase ratio for Ca.sub.6Si.sub.6O.sub.17(OH) formation is believed to be due to temperature gradients that caused the reaction temperature to be higher than 350 C. at various times in various sections of the autoclave. A closer look at the developed phase diagram reveals that this reaction was predominately in the Ca.sub.6Si.sub.6O.sub.7(OH).sub.2 and CaSiO.sub.3 stability and metastability phase-field, respectively. Thus, due to the lower than expected concentration of the CaSiO.sub.3 phase, it may be concluded that the formation of Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 halted once the evolved P.sub.CO.sub.
Example 5Mg.SUB.3.Si.SUB.2.O.SUB.5.(OH).SUB.4 .Synthesis from MgO and SiO.SUB.2
[0140] 2 grams of SiO.sub.2 precursor is thoroughly mixed with 2.02 g of MgO precursor (3:2 molar ratio). The mixing process was completed by dry mixing the two components inside a small ceramic (ZrO.sub.2) jar (SPEX mill) with 2 spherical zirconia balls (3 mm) for 10 min. The amount of each precursor was chosen to achieve a 3:2 molar mixture. This precursor mixture was placed into a sample holder than prevents any liquid water from touching the material mixture. The sample holder was placed on the bottom of a batch-style 1-L autoclave that is capable of housing temperatures and pressures up to 500 C. and 5000 psi, respectively. De-ionized liquid water (18 M-ohm) was placed on the bottom of the autoclave outside of the sample holder to ensure that the precursor mixture is not in contact with the liquid water. The amount of water used is determined by the volume of the autoclave. In the case of a 1-L autoclave, the amount of water is chosen to be 3.5 mL to have an approximate volume fill-percent of 0.35% in order to achieve an unsaturated water partial pressure of about 10 atm at 400 C. The autoclave is heated for 12 h; after which it is depressurized. After depressurization, the reactor is cooled to room-temperature. After cooling, the reaction product is removed from the autoclave.
[0141] According to the computed chemical equilibrium diagrams, gaseous CO.sub.2 in any concentration can affect the purity and identity of the product phase. Further, any CO.sub.2 partial pressure can alter the chemical reaction's Gibb's free energy and create zones of stability and metastability of particular phases. These zones of stability and metastability can be computed by calculating the equilibrium temperatures of selected reaction products and comparing the Gibb's free energy of the selected reaction product to other thermodynamically favored phases. For this example, stability and metastability zones of Forsterite (Mg.sub.2SiO.sub.4) and Chrysotile (Mg.sub.3Si.sub.2O.sub.5(OH).sub.4) have been shown as a function of temperature, CO.sub.2 pressure, and water partial pressure. These figures only describe the thermodynamic conditions for phase formation, and do not include additional phases that may form as a result of mixture inhomogeneity. These figures also specifically look at the Mg.sub.2SiO.sub.4 and Mg.sub.4Si.sub.2O.sub.5(OH).sub.4 phases. There are additional MgSi oxide, hydroxide, and carbonate phases that may exist in these conditions. Furthermore, thermodynamic illustrations in
[0142] In the case of this example,
[0143] The powder retrieved after the reaction was analyzed via x-ray diffraction which revealed that the formed phases were Mg.sub.3Si.sub.2O.sub.5(OH).sub.4 (Chrysotile) (Eq. 7) and Mg.sub.2SiO.sub.4 (Forsterite)(Eq. 8).
3MgO+2SiO.sub.2+2H.sub.2OMg.sub.3Si.sub.2O.sub.5(OH).sub.4Eq. 7
3MgO+2SiO.sub.2Mg.sub.2SiO.sub.4+MgO+SiO.sub.2Eq. 8
[0144] The purity of the Mg.sub.3Si.sub.2O.sub.5(OH).sub.4 depended on the mixedness of the initial powder blend. If the mixedness was low, unreacted phases such as MgO, SiO.sub.2, and hydrated MgO (Mg(OH).sub.2) formed. It is important to note that other phases may exist as kinetic intermediary ones and co-exist for a period of time with the desired products. Additionally, other thermodynamically favorable phases may form/exist during the autoclave heating and pressurization stages, during which the exact thermodynamic conditions have not yet been set. Obtaining phase pure Mg.sub.3Si.sub.2O.sub.5(OH).sub.4 is possible by operating in thermodynamic zone described in zone B (
[0145] Additionally, this example is based on a thermodynamic model that is based on magnesium silicate hydrate (Mg.sub.3Si.sub.2O.sub.5(OH).sub.4) and magnesium silicate (Mg.sub.2SiO.sub.3). In other scenarios, there may be different phases that exist. For example, other hydrates and other oxides, that may form as metastable or stable phases. Therefore, this example is just one possible phase configuration that is possible. Many other magnesium-silicate based phase assemblages are possible. Finally, it is also worth noting that the partial pressure of the unsaturated water vapor will also affect the phase equilibria.
Example 6Mg.SUB.2.SiO.SUB.4 .Synthesis from MgO and SiO.SUB.2
[0146] 3 grams of SiO.sub.2 precursor was thoroughly mixed with 4.03 g of MgO precursor (2:1) molar ratio). The mixing process was completed by dry mixing the two components inside a small ceramic (ZrO.sub.2) jar (SPEX mill) with 2 spherical zirconia balls (3 mm) for 10 min. The amount of each precursor was chosen to achieve a 1:1 molar mass mixture. This precursor mixture was placed into a sample holder than prevents any liquid water from touching the material mixture. The sample holder was placed on the bottom of a batch-style 1-L autoclave that is capable of housing temperatures and pressures up to 500 C. and 5000 psi, respectively. De-ionized liquid water (18 M-ohm) was placed on the bottom of the autoclave outside of the sample holder to ensure that the precursor mixture is not in contact with the liquid water. The amount of water used was determined by the volume of the autoclave. In the case of a 1-L autoclave, the amount of water was chosen to be 3.5 mL to have an approximate volume fill-percent of 0.35% in order to achieve an unsaturated water partial pressure of about 10 atm at 400 C. The autoclave was heated for 12 h; after which it is depressurized. After depressurization, the reactor was cooled to room-temperature. After cooling, the reaction product was removed from the autoclave.
[0147] According to the computed chemical equilibrium diagram, gaseous CO.sub.2 in any concentration can affect the purity and identity of the product phase. Further, any CO.sub.2 partial pressure can alter the chemical reaction's Gibb's free energy and create zones of stability and metastability of particular phases. These zones of stability and metastability can be computed by calculating the equilibrium temperatures of selected reaction products and comparing the Gibb's free energy of the selected reaction product to other thermodynamically favored phases. For this example,
[0148] To avoid the hydrate phase Mg.sub.3Si.sub.2O.sub.5(OH).sub.4 identified in example 5, gaseous CO.sub.2 was introduced into the autoclave at a very specific pre-selected partial pressure. At 25 C., the partial pressure of CO.sub.2 introduced was 35 atm. This CO.sub.2 partial pressure increased by heating the autoclave to 96 atm (Redlich-Kwong, Equation of state for non-ideal gas) at 400 C. According to the computed stability and metastability diagrams shown in
[0149] Once the CO.sub.2 gas was introduced, the autoclave was heated for 12 h; after which it was depressurized to atmospheric pressure. After depressurization, the reactor was cooled from 400 C. to room-temperature. After cooling, the material was removed from the autoclave. The powder retrieved was analyzed via x-ray diffraction which revealed that the only new phase formed is Mg.sub.2SiO.sub.4 (Forsterite) (Eq. 9).
2MgO+SiO.sub.2Mg.sub.2SiO.sub.4Eq. 9
[0150] The purity of the Mg.sub.2SiO.sub.4 will depend on the mixedness of the original material mixture. If the mixedness was low, unreacted phases such as MgO, SiO.sub.2, and hydrated MgO (Mg(OH).sub.2) will have formed. If the mixedness was high, then all of the precursor phases will be consumed and only the product phase will be present. Finally, it is also worth noting that the partial pressure of the unsaturated water vapor will also affect the phase equilibria.
Example 7Asbestos Remediation
[0151] Examples 5 and 6 detail how unsaturated water vapor conditions can be used, in conjunction with additional gaseous species, to promote a chemical reaction. It is worthy to note, that the operator can select the unsaturated water vapor conditions and additional gaseous species partial pressures to promote or prevent certain phases. For example, it is possible to convert Chrysolite (asbestos) into non-hazardous form, for example, forsterite or magnesium carbonate by simply adjusting the CO.sub.2 partial pressure, while at unsaturated water vapor conditions. Thus, to convert Chrysolite to Forsterite, the operator can adjust to P.sub.CO2 in accordance with the phase equilibria shown in
Example 8Universal Application
[0152] Examples 1-7 highlight the utility of the invention but do not encompass the breadth of the potential material phases in other material systems that can be achieved through a similar route. The introduction of a gaseous species can change the free energy of the reaction system and resultantly promote the crystallization of a phase that would be intuitively expected. For example, gaseous CO.sub.2 can be used to promote the formation of anhydrous MgAl.sub.2O.sub.4 instead of the hydrate carbonate phase, hydrotalcite (MgaAl.sub.2CO.sub.3(OH).sub.16*4(H.sub.2O)). It can also be used to promote the formation of anhydrous Mg.sub.2SiO.sub.4, or promote the formation of any hydrated MgSiO phase. One of ordinary skill would expect that an external pressure of CO.sub.2 would create a carbonate product, however, thermodynamics says that you can convert hydroxide to oxide, or vice-versa.
[0153] The purity of the product phase in the examples above also depend on the mixedness of the initial precursors. If the mixedness was low, unreacted precursor phases such as MgO, SiO.sub.2, and hydrated MgO (Mg(OH).sub.2) will have to be unchanged, or hydrated, or carbonated. If the mixedness was high, then all of the precursor phases will be consumed and only the product phase will be present. Furthermore, the degree of mixedness may modify the stoichiometric proportions of the precursor mix. For example, the intention may be to create a 1:1 molar mixture of CaO and SiO.sub.2, however, a poorly mixed particle system may have regions of CaO or SiO.sub.2 excess. As a result, these excess regions will behave as localized systems whose composition differs and thus forms phase products consistent with those predicted by thermodynamic calculations of a system having the same composition. The size of these localized regions that possess deviations in compositions will vary based on precursor particle size and diffusion path lengths. It is possible that a mixture of 0.5 m particles could have a localized region of 10 m. It is also possible that a mixture of 5.0 m particles could have a localized of 100 m. For example, the intent may be to synthesize CaSiO.sub.3, but the precursor mixture produces non-uniform concentration zones with a CaO:SiO.sub.2 molar ratio of 2:1, resulting in the formation of Ca.sub.2SiO.sub.4 due to a poorly mixed and distributed precursor particles. Another example is the formation of Ca.sub.6Si.sub.6O.sub.17(OH).sub.2: the intent may be to synthesize Ca.sub.6Si.sub.6O.sub.17(OH).sub.2, but the precursor mixture produces non-uniform concentration zones with a CaO:SiO.sub.2 molar ratio of 4:3, resulting in the formation of Ca.sub.4(Si.sub.3O.sub.9)(OH).sub.2 due to a poorly mixed and distributed precursor particles. In all examples and practices of this patent document, the mixture homogeneity can directly impact the final product phase and purity.
[0154] Several of the examples above describe the formation of CaSiO.sub.3 and Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 from a precursor mixture of CaO and SiO.sub.2. These examples are applicable to Ca(OH).sub.2 and CaCO.sub.3 calcium sources as well. Additional examples are included that describe the formation of Mg.sub.2SiO.sub.4 and (Mg.sub.3Si.sub.2O.sub.5(OH).sub.4) from a mixture of MgO and SiO.sub.2. These examples are applicable to Mg(OH).sub.2 and MgCO.sub.3 magnesium sources as well. It is worth noting that the examples are a non-exclusive list of possible phases that be produced with this invention. In-fact, this invention is applicable to all metal-silicate phases. Furthermore, the examples listed focus on the production of an oxide or a hydroxide silicate phase. It is worth noting that numerous oxide and hydroxide phases (e.g., xonotlite & foshagite) can co-exist at the prescribed thermodynamic conditions. Furthermore, a slight partial pressure of CO.sub.2 may disable one hydroxide phase in favor of the other. The same may exist for oxide silicate phases (e.g., CaSiO.sub.3 & Ca.sub.2SiO.sub.4). Table 7 provides a non-exclusive list of Calcium Silicate and Calcium Silicate Hydrates that may be formed using the invention described in this application. Additional examples of Calcium Silicates are provided in Table 8. Furthermore, it is worth noting that each described example is utilizing the first HVS configuration. In this configuration, a batch style autoclave is loaded with all needed ingredients (precursors, water, gases (CO.sub.2)) and heated to desired temperature. Upon heating the reactor to the desired temperature, the water vapor pressure increases autogenously to get to the desired temperature. During this time, it may be possible to form stable thermodynamic phases that inhibit or contaminate a particular reaction to proceed. While these phases be thermodynamically unstable/unfavorable at the set reaction conditions, the pathway to obtaining those conditions must also be considered.
TABLE-US-00007 TABLE 7 Calcium Silicate and Calcium Silicate Hydrates Name Formula (a). Wollastonite group Foshagite Ca.sub.4(Si.sub.3O.sub.9)(OH).sub.2 Hillebrandite Ca.sub.2(SiO.sub.3)(OH).sub.2 Nekoite Ca.sub.3Si.sub.6O.sub.157H.sub.2O Okenite Ca.sub.3Si.sub.6O.sub.156H.sub.2O Pectolite NaCa.sub.2Si.sub.3O.sub.8 Xonotlite Ca.sub.6Si.sub.6O.sub.17(OH).sub.2 (b). Tobermorite group Clinotobermorite c Ca.sub.5Si.sub.6O.sub.175H.sub.2O Clinotobermorite d Ca.sub.5Si.sub.6O.sub.175H.sub.2O Clinotobermorite Ca.sub.5Si.sub.6O.sub.16(OH).sub.2 9 c Clinotobermorite Ca.sub.5Si.sub.6O.sub.16(OH).sub.2 9 d Oyelite Ca.sub.10Si.sub.5B.sub.2O.sub.2912.5H.sub.2O 9 tobermorite Ca.sub.5Si.sub.6O.sub.16(OH).sub.2 (riversideite) c 9 tobermorite Ca.sub.5Si.sub.6O.sub.16(OH).sub.2 (riversideite) d Anomalous 11 Ca.sub.4Si.sub.6O.sub.15(OH).sub.25H.sub.2O tobermorite c Anomalous 11 Ca.sub.4Si.sub.6O.sub.15(OH).sub.25H.sub.2O tobermorite d Normal 11 Ca.sub.4.5Si.sub.6O.sub.15(OH)5H.sub.2O tobermorite d 14 tobermorite Ca.sub.5Si.sub.6O.sub.16(OH).sub.27H.sub.2O (plombierite) c 14 tobermorite Ca.sub.5Si.sub.6O.sub.16(OH).sub.27H.sub.2O (plombierite) d (c). Jennite group Jennite Ca.sub.9Si.sub.6O.sub.18(OH).sub.68H.sub.2O Metajennite Ca.sub.9Si.sub.6O.sub.18(OH).sub.64H.sub.2O (d). Gyrolite Group Fedorite (Na,K).sub.2-3(Ca.sub.4Na.sub.3)Si.sub.16O.sub.38(OH,F).sub.23.5H.sub.2O Gyrolite NaCa.sub.16Si.sub.23AlO.sub.60(OH).sub.814H.sub.2O K-phase Ca.sub.7Si.sub.1-5O.sub.38(OH).sub.2 Reyerite (Na,K).sub.2Ca.sub.14(Si,Al).sub.24O.sub.58(OH).sub.86H.sub.2O Truscottite (Ca,Mn).sub.14Si.sub.24O.sub.58(OH).sub.82H.sub.2O Z-phase Ca.sub.9Si.sub.16O.sub.40(OH).sub.214H.sub.2O (e). y-C2S group Calcium chondrodite g Ca.sub.5[SiO.sub.4].sub.2(OH).sub.2 Kilchoanite Ca.sub.6(SiO.sub.4)(Si.sub.3O.sub.10) (f). Other calcium silicate phases Afwillite Ca.sub.3(SiO.sub.3OH).sub.22H.sub.2O a-C.sub.2SH Ca.sub.2(HSiO.sub.4)(OH) Cuspidine h Ca.sub.4(F.sub.1.5(OH).sub.0.5)Si.sub.2O.sub.7 Dellaite Ca.sub.6(Si.sub.2O.sub.7)SiO.sub.4(OH).sub.2 Jaffeite Ca.sub.6[Si.sub.2O.sub.7](OH).sub.6 Killalaite Ca.sub.6.4(H.sub.0.6Si.sub.2O.sub.7).sub.2(OH).sub.2 Poldervaartite i Ca(Ca.sub.0.67Mn.sub.0.33)(HSiO.sub.4)(OH) Rosenhahnite Ca.sub.3Si.sub.3O.sub.8(OH).sub.2 Suolunite CaSiO.sub.2.5(OH)0.5H.sub.2O Tilleyite Ca.sub.5Si.sub.2O.sub.7(CO.sub.3).sub.2 (g). Other high temperature cement phases Bicchulite Ca.sub.2(Al.sub.2SiO.sub.6)(OH).sub.2 Fukalite Ca.sub.4[Si.sub.2O.sub.6][CO.sub.3](OH).sub.2 Katoite Hydrogamet 1 Ca.sub.1.46AlSi.sub.0.55O.sub.6H.sub.3.78 Rustumite Ca.sub.10(Si.sub.2O.sub.7).sub.2(SiO.sub.4)(OH).sub.2Cl.sub.2 Scawtite Ca.sub.7(Si.sub.3O.sub.9).sub.2CO.sub.32H.sub.2O Stratlingite Ca.sub.2Al.sub.2SiO.sub.78H.sub.2O Ca.sub.2Al(AlSi).sub.2.22O.sub.2(OH).sub.122.25H.sub.2O
TABLE-US-00008 TABLE 8 Calcium Silicates (a). Nesosilicate Subclass (single tetrahedrons) Forsterite Mg.sub.2(SiO.sub.4) Andradite Ca.sub.3(Fe.sup.3+).sub.2(SiO.sub.4).sub.3 Grossular Ca.sub.3Al.sub.2(SiO.sub.4).sub.3 Pyrope Mg.sub.3Al.sub.2Si.sub.3O.sub.12 Olivine (Mg,Fe.sup.2+).sub.2(SiO.sub.4) Sphene/Titanite CaTiSiO.sub.5 Larnite Ca.sub.2SiO.sub.4 Hatrurite (alite) Ca.sub.3SiO.sub.5 (b). Sorosilicate Sublcass (double tetrahedrons) Danburite CaB.sub.2(SiO.sub.4).sub.2 (c). Inosilicate Subclass (sinf!le and double chains) Augite (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al).sub.2O.sub.6 Diopside MgCaSi.sub.2O.sub.6 Enstatite MgSiO.sub.3, Mg.sub.2Si.sub.2O.sub.6 Hedenbergite CaFeSi.sub.2O.sub.6 Hypersthene (Mg,Fe)SiO.sub.3 Rhodonite (Mn.sup.2+,Fe.sup.2+,Mg,Ca)SiO.sub.3 Wollastonite 1A CaSiO.sub.3 (d). Cyclosilicate Subclass (rings) Cordierite (Mg,Fe).sub.2Al.sub.4Si.sub.5O.sub.18 Osumilite-(Mg) (K,Na)(Mg).sub.2(Al,Fe).sub.3(Si,Al).sub.12O.sub.30 Osumilite-(Fe) (K,Na)(Fe).sub.2(Al,Fe).sub.3(Si,Al).sub.12O.sub.30 Pseudo Wollastonite Ca.sub.3Si.sub.3O.sub.9 (e). Tectosilicate Subclass (frameworks) Andesine (Ca,Na)(Al,Si).sub.4O.sub.8 Anorthite CaAl.sub.2Si.sub.2O.sub.8 Bytownite (Ca,Na)[Al(Al,Si)Si.sub.2O.sub.8] Labradorite ((Ca,Na)(Al,Si).sub.4O.sub.8) Oligoclase (Ca,Na)(Al,Si).sub.4O.sub.8
Example 9
[0155] This example illustrates a temperature-gradient-based continuous reactor as shown in
[0156] It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described. Rather, the scope of the present invention is defined by the claims which follow. It should further be understood that the above description is only representative of illustrative examples of embodiments. The description has not attempted to exhaustively enumerate all possible variations. The alternate embodiments may not have been presented for a specific portion of the invention, and may result from a different combination of described portions, or that other un-described alternate embodiments may be available for a portion, is not to be considered a disclaimer of those alternate embodiments. It will be appreciated that many of those un-described embodiments are within the literal scope of the following claims, and others are equivalent.