Open-pore foam materials with guest phases, procedure for the preparation of these materials and uses thereof

Abstract

The present invention relates to a foam material comprising:—a structural matrix (1),—at least one guest phase (2), and—a fluid, the material being characterised in that the structural matrix (1) comprises a plurality of interconnected pores (3), the one or more guest phases (2) are accommodated inside at least one pore (3) of the structural matrix (1) and the fluid is accommodated inside the pores (3). The present invention further relates to the process for preparing the foam material according to the present invention and to the various uses of the foam material according to the present invention.

Claims

1. A foam material comprising: a structural matrix, one or more guest phases made of a functional material in the form of a particle or a fiber wherein the particles or fibers are stacked one on top of each other and interstitial spaces between the particles or fibers filled with the structural matrix, and a fluid, wherein: the structural matrix is made up of a metal selected from the group consisting of tin, aluminum, copper, titanium, mixture and metal alloys thereof, and comprises a plurality of interconnected pores wherein the pores are in fluid communication with each other by an interconnection opening having a diameter that is not the same or larger than a diameter of the particle or fiber of the one or more guest phases, and wherein a wall of the pore has a shape matching and conforming to a shape of the particle or the fiber, the one or more guest phases are accommodated inside at least one pore of the structural matrix without maintaining any bond with said structural matrix such that between the wall of the pore of the foam material and the surface of the guest phase there is a gauge of space that is occupied by the fluid, and the fluid is accommodated inside the pores and surrounds the entirety of the one or more guest phases in the pore.

2. The foam material according to claim 1, wherein the functional material is selected from the group consisting of an adsorbent material, an absorbent (impacts or radiation) material, a catalytic material, a magnetic material, a supporting or a catalyst-supporting material for releasing chemical and/or pharmaceutical substances, and a material with an electrode function.

3. The foam material according to claim 1, wherein the functional material is selected from the group consisting of: carbon, active carbon, graphite, alumina (Al.sub.2O.sub.3), activated alumina (Al.sub.2O.sub.3), silicon (Si), silicon carbide (SiC), activated SiC, titanium carbide (TiC), activated TiC, aluminium nitride (AlN), cerium oxide (CeO.sub.2), activated CeO.sub.2, titania (TiO.sub.2), activated TiO.sub.2, zeolites, metal-organic frameworks (MOFs), platinum (Pt), rhodium (Rh), palladium (Pd), iron, cobalt, nickel and metal alloys thereof, iron oxides (Fe.sub.xO.sub.y), cobalt oxides (Co.sub.xO.sub.y), and nickel oxides (Ni.sub.xO.sub.y).

4. The foam material according to claim 1, wherein the fluid is a liquid or a gas.

5. A method for preparing a foam material according to claim 1, comprising the following steps: a) coating a continuous layer of at least one sacrificial particulate material on the one or more guest phases made of a functional material in the form of a particle or a fiber, b) compacting the one or more coated guest phases until a porous preform is formed such that the particles or the fibers are stacked one on top of each other and interstitial spaces formed between the particles or the fibers, c) infiltrating the porous preform, with a precursor liquid of the structural matrix, d) solidifying the precursor liquid and machining, e) removing the at least one sacrificial particulate material from the one or more coated guest phases.

6. The method according to claim 5, wherein the at least one sacrificial particulate material is a salt selected from the group consisting of halides, carbonates, fluorides, aluminates, sulphates and silicates.

7. The method according to claim 5, comprising an additional step of compacting the at least one sacrificial particulate material and the one or more coated guest phases.

8. The method according to claim 5, wherein the coating step is performed with two or more sacrificial particulate materials.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIGs. 1(a) and 1(b) showsa diagram showing the interconnection of pores existing in a foam material with structural matrix (1) and with guest phase (2) and the manner wherein a guest particle (2) is accommodated in a pore (3) of the foam material: (a) drawing in two dimensions wherein the lines represent interconnecting openings between pores; and (b) three-dimensional representation of a representative fraction volume containing a guest particle (2) accommodated in a pore (3).

(2) FIG. 2 illustrates the manufacturing process of a foam material with a guest phase filling 100% of the cavities. The fundamental steps are as follows:

(3) A. Manufacture of the preform

(4) (a) guest phase (2) in the finely divided form of particles or fibres; (b) coating of the guest phase (2) with a sacrificial material (4); (c) compaction of the coated guest phase (2) until it forms a porous preform accommodated in moulds (5) suitable for the infiltration;
B. Infiltration (d) infiltration of the porous preform with a liquid precursor (1′) of the foam material, (e) directional solidification of the liquid precursor (1′) of the foam material by means of a cooling system (6) which enables directional cooling; (f) machining of the structural matrix (1) with conventional tools (7) and techniques;
C. Processing of the foam material (g) removal of the sacrificial material (4) either by dissolution (g1) in a liquid phase (8) or by controlled reaction (g2) with a liquid or gas phase (8′) until a foam with interconnected pores (h) with guest phases (2) completely filling the cavities thereof is obtained.

(5) FIG. 3 illustrates different types of foam materials with guest phases which can be achieved depending on the type of porous preform started with. The porous preforms are shown on the left and the different types of foam materials obtained therefrom are shown on the right: a) Porous preform obtained by compaction of a single guest phase (2) coated by a single sacrificial material (4), in order to give rise to a foam material comprising all the pores occupied by the guest phase (2). b) Porous preform obtained by compaction of more than one guest phase (2 and 2′), and coated with more than one sacrificial material (4 and 4′) in order to give rise to a foam material comprising all the pores occupied by the guest phases (2 and 2′). c) Porous preform obtained by compaction of a guest phase (2) coated with more than one sacrificial material (4 and 4′), together with sacrificial material particles (4″) in order to give rise to a foam material comprising only some of the pores occupied by the guest phase (2). d) Porous preform obtained by compaction of more than one guest phase (2 and 2′) coated with by-more than one sacrificial material (4 and 4′) together with particles of sacrificial material (4″) in order to give rise to a foam material comprising some of the pores occupied by the guest phases (2 and 2′).

(6) FIG. 4 shows a diagram of equipment for the coating of finely divided material in the form of particles with NaCI, which was used in the development of the exemplary embodiments presented in the present invention. The equipment consists of a quartz tube (9) having two inlet holes, one (10) for pressurised air—which maintains the particles (11) in suspension forming a fluidised bed—and another (12) for a nebulised NaCI solution. The equipment has a porous filter (13), which does not allow the particles to escape through the lower portion of the tube, and is heated by means of electrical resistances (14).

(7) FIGS. 5(a), 5(b), 5(c), and 5(d) show images of a foam material obtained starting from a metal structural matrix (1), specifically aluminium, the guest phase (2) of which are SiC particles which fill the entirety of the pores, (a), (b) and (c) are images obtained by a scanning electron microscope (SEM) and (d) is an image obtained by conventional photography. Image (a) shows the angular morphology of the SiC particles, with an average diameter of 750 micrometres; image (b) shows these same particles with a sodium chloride (NaCl) coating, as a sacrificial material (4), with a thickness in the interval of 20-50 micrometres achieved with the device of FIG. 4; image (c) shows an image of two SiC particles as a guest phase in the cavities of the aluminium structural matrix; image (d) shows a photograph of a part made of the material.

(8) FIG. 6 shows images of a foam material obtained starting from a ceramic structural matrix (1), specifically mesophase pitch, the guest phase (2) of which are activated carbon particles which partially fill the pores of the foam material. (a), (b) and (c) are images obtained by a scanning electron microscope (SEM) and (d) is an image obtained by conventional photography. Image (a) shows the morphology of the active carbon particles, with an average diameter of 1 millimetre; image (b) shows these same particles with a sodium chloride (NaCl) coating with a thickness in the interval of 70-100 micrometres achieved with the device of FIG. 4; image (c) shows an image of an activated carbon particle as a guest phase (2) in a pore of the foam material made of mesophase pitch; image (d) shows a photograph of a part made of the material.

(9) FIG. 7 shows images of a foam material obtained starting from a metal structural matrix (1), specifically tin, the guest phase (2) of which are spherical cobalt particles which partially fill the pores, (a) is an image obtained by a scanning electron microscopy (SEM) and (b), (c) and (d) are images obtained by optical microscope. Image (a) shows a cobalt particle, with an average diameter of 5 millimetres, coated with sodium chloride (NaCl), as a sacrificial material (4), with a thickness in the interval of 150-200 micrometres achieved with the device of FIG. 4; images (b), (c) and (d) show images of cobalt particles as a guest phase (2) in the pores of the foam material made of tin.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

(10) The foam material of the present invention is configured, in the simplest embodiment thereof, by three phases (see FIG. 1): a structural matrix (1), comprising a plurality of interconnected pores (3), a guest phase (2), in the finely divided form of particles or fibres, which is accommodated in the entirety or in a portion of the pores, and a fluid, the nature of which depends on the environment wherein the material is located, since the pores (3) are connected to the outside through the interconnections between them.

(11) As mentioned in the general description of the invention, the foam material of the present invention can be made up of several guest phases (2 and 2″) with different natures, so that each of them provides a different functionality to the final foam material.

(12) The material making up the guest phase (2) is preferably selected in a finely divided state, in the form of particles or fibres, the dimensions of which can vary in the interval of 0.1 micrometres-1 centimetre in diameter for particles and in the same interval in diameter and in the interval of 0.1 micrometres-5 centimetres long for fibres.

(13) In the simplest embodiment thereof, the method for manufacturing the foam material with at least one guest phase (2) and at least one sacrificial material (4) comprises the following steps (see FIG. 2, FIG. 3 and FIG. 4 for greater detail):

(14) a) continuous coating of the guest phase (2) previously divided into particles or fibres, with at least one sacrificial material (4),

(15) b) compaction of the coated guest phase (2) obtained in step a) until a porous preform is formed,

(16) c) infiltration of the porous preform of step b), with a liquid precursor of the structural matrix (1),

(17) d) solidification of the liquid precursor (1′) of step c) and machining

(18) e) removal of the sacrificial material (4) from the guest phase.

(19) The coating of the guest phase (2) is done with a sacrificial material (4) the nature of which is selected depending on the infiltrating liquid, since the melting/softening point thereof must be higher than that of the other. The sacrificial material (4) is preferably selected from among: saline halides (i.e. NaCl, KCl), saline carbonates (i.e. K.sub.2CO.sub.3, CaCO.sub.3), strontium fluorides (SrF.sub.2) or barium (BaF.sub.2), sodium aluminate (NaAlO.sub.2), saline sulphates (i.e. MgSO.sub.4) and silicon oxide (SiO.sub.2).

(20) The coating of the guest phase (2) with the coating material (4) can have a thickness preferably selected in the interval of 1 micrometre-5 millimetres.

(21) The coating of the guest phase (2) must be continuous. A continuous coating generates foam materials wherein the guest phase (2) and the structural matrix (1) do not maintain any bond.

(22) The guest phase (2) coated with the sacrificial material (4) is compacted in crucibles (5), the nature of which depends on the melting/softening point and the chemical compatibility with the liquid with which the infiltration step will be performed. The nature of the crucible (5) is preferably selected among the following group: glass (for liquids compatible with a melting/softening point less than 400° C.), pyrex glass (for liquids compatible with a melting/softening point less than 600° C.), quartz (for liquids compatible with a melting/softening point less than 1500° C.), alumina (for liquids compatible with a melting/softening point less than 2000° C.), graphite (for liquids compatible with a melting/softening point less than 3500° C.). The compaction of the guest phase (2) coated with the sacrificial material (4) is performed by means of a conventional compaction technique, preferably selected from among the following: compaction by vibration, compaction by mechanical pressure, compaction by impacts or compaction by a combination of impacts and vibrations.

(23) The porous preform generated is subsequently infiltrated with a liquid precursor of the solid phase (1′) which will form the structural matrix of the foam material. The infiltration can be preferably achieved by gas pressure infiltration, microwave-assisted infiltration, centrifugal infiltration or mechanical pressure (squeeze casting). Subsequent to the infiltration, the directional solidification of the liquid infiltrating material is then performed. Then, the demoulding of the material and the machining thereof with conventional tools and techniques (7) are then performed. It is possible that certain precursor materials (1′) may need to be suitably treated to modify the structure thereof (for example, graphite precursors such as mesophase pitch can be thermally treated until graphite material is generated). These treatments can be performed before or after the step of removing the sacrificial material (4) coating the guest phase (2).

(24) The coating material (4) is removed by following different methodologies depending on the nature thereof. The removal method can be based on dissolution in a liquid phase (8) or on a controlled reaction with a liquid or gas phase (8′), preferably selected from among the following group:

(25) a) removal by dissolution in water or aqueous solutions—preferably for alkaline halides (i.e. NaCl, KCl), alkaline and alkaline earth carbonates (i.e. K.sub.2CO.sub.3, CaCO.sub.3), strontium fluoride (SrF.sub.2), barium fluoride (BaF.sub.2), sodium aluminate (NaAlO.sub.2), magnesium sulphate (MgSO.sub.4);

(26) b) removal by dissolution in acids—preferably for silicon oxide (SiO.sub.2);

(27) c) removal by thermal treatment—preferably for alkaline and alkaline earth carbonates (i.e. K.sub.2CO.sub.3, CaCO.sub.3);

(28) d) combustion (thermal treatment in an atmosphere with oxygen present)—preferably for coatings made of carbon or polymers.

(29) The processes based on removing the sacrificial material (4) by dissolution can be preferably carried out by means of the following methods: i) immersion in the solution for a controlled time; ii) immersion in the solution for a controlled time followed by injection of the solution at a certain pressure for a controlled time. This combined method (ii) enables a quicker removal of the sacrificial material (4).

(30) The dimension of the free space between the cavities of the structural matrix (1) and the guest phase (2) is defined by the thickness of the coating material (4).

(31) The interconnection opening between the different pores of the foam material depends on the shape adopted by the particles or fibres of the guest phase (2) after the coating thereof with the sacrificial material (4) and the manner wherein these touch each other in the compacted bed which forms the porous preform. In any case, it must be ensured that the interconnection opening diameter is not the same or larger than the diameter of the particles or fibres of the guest phase (2), since this could cause the outlet of the guest phase (2) from the material and the loss of the functionality of the material, which would transform into a conventional foam of the material which forms the structural matrix (1).

(32) As shown in FIG. 3, the foam material can contain more than one guest phase (2, 2′) and can be made with one or several sacrificial coating materials (4, 4′), apart from containing cavities not occupied by a guest phase (2) generated starting from sacrificial particles (4″) with the same or different nature as the sacrificial material or materials used to coat the one or more guest phases.

Exemplary Embodiments

EXAMPLE 1

(33) This example describes the embodiment of foam material made of aluminium with pores interconnected and with guest phase (2) of silicon carbide (SiC) particles with an average diameter of 750 micrometres which fill up the entirety (100%) of the pores. The particles of the guest phase (2) were coated with NaCl as the sacrificial material (4), by means of the deposition method using forced spray precipitation. To do so, the device shown in FIG. 4 was prepared, which enables the particles to be maintained in suspension by means of a fluidised bed generated by the inlet of an inert gas (argon) through a porous material placed in the lower portion of the device. The system enables the particles to be heated to a maximum temperature of 1000° C. Specifically, the SiC particles were maintained at a temperature of 300° C. Through the inlet hole ((12) in FIG. 4) a mist generated by the vaporisation of a solution prepared with 20 g of NaCl in 100 g of water was allowed to enter. The mist was projected during 5 second intervals, with resting intervals between each misting of 30 seconds. By means of this method, a compact layer of NaCl with a coating thickness of 20-50 micrometres was achieved.

(34) 18 grams of SiC particles thereby coated (SiC—NaCl) were compacted in a crucible made of quartz with a diameter of 17 mm and a length of 150 mm. The compacted bed reached a height of 50 mm inside the tube. A part made of aluminium metal (25 g) was added in the upper portion of the bed and the assembly was transferred to the inside of an infiltration chamber. This was closed and a vacuum was applied at a pressure of 0.1 mbar. Then the temperature was raised to 750° C. by means of a heating rate of 3° C./min. The temperature was maintained at 750° C. for 15 min and then 5 bar of pressure were applied in the chamber.

(35) The pressure was maintained for 2 minutes and immediately afterwards, the crucible was lowered to the bottom of the infiltration chamber, which acts as a cold trap for quick and directional solidification. After the solidification, the sample was demoulded and machined in order to remove the excess metal, until the coated particles were able to be accessed on all the faces of the cylinder. The machining was performed by means of a cutting saw and then by means of a lathe, using cutting tools, in order to finally perform a fine finish by means of successive abrasive sheets of sandpaper with grits of 240 and 400. The removal of the sacrificial material (4) was achieved by means of immersion of the part in water in a glass of precipitates, magnetically stirred for 5 minutes. After this time, the part was fitted to a tube through which water was passed at a pressure of 4 bar, with which the complete dissolution of the salt was achieved in a time of 15 minutes. Details of the final material can be seen in FIG. 5.

EXAMPLE 2

(36) This example describes the embodiment of a foam material made of aluminium with pores interconnected and with guest phase (2) of silicon carbide (SiC) particles with an average diameter of 750 micrometres which fill up half (50%) of the pores. The embodiment is identical to that of EXAMPLE 1 but starting from a mixture of SiC particles with an average diameter of 750 micrometres coated with NaCl (SiC—NaCl) with a coating thickness of 20-50 micrometres and NaCl particles with an average diameter of 750 micrometres. The volume ratio of the mixture used is 1:1 for SiC—NaCl: NaCl, for which 8.88 grams of SiC—NaCl particles and 6.47 grams of NaCl particles are used.

EXAMPLE 3

(37) This example describes the embodiment of foam material made of mesophase pitch with pores interconnected and with guest phase (2) of activated carbon particles with an average diameter of 1 millimetre which fill up the entirety (100%) of the pores. The particles were coated with NaCl by means of the deposition method using forced spray precipitation in the same manner as in EXAMPLE 1. A coating thickness of 70-100 micrometres was achieved. The infiltration with mesophase pitch was performed at 400° C. by means of an infiltration process identical to the one described in EXAMPLE 1. The embodiment is identical to that of EXAMPLE 1 but starting with an amount of 13 grams of active carbon particles. Details of the final material can be seen in FIG. 6.

EXAMPLE 4

(38) This example describes the embodiment of foam material made of tin with pores interconnected and with guest phase (2) of spherical cobalt particles with an average diameter of 5 millimetres which fill up half (50%) of the pores. The particles were coated with NaCl by means of the deposition method using forced spray precipitation in the same manner as in EXAMPLE 1. A coating thickness of 150-200 micrometres was achieved. The infiltration with tin was performed at 400° C. by means of an infiltration process identical to the one described in EXAMPLE 1. The embodiment is identical to that of EXAMPLE 1 but starting from a mixture of cobalt particles with an average diameter of 5 millimetres coated with NaCl (Co—NaCl) and NaCl particles with an average diameter of 3 millimetres. The volume ratio of the mixture used is 1:1 for Co—NaCl: NaCl, for which 23 grams of Co—NaCl particles and 6.5 grams of NaCl particles were used. Details of the end material can be seen in FIG. 7.

EXAMPLE 5

(39) This example describes the embodiment of foam material made of tin with pores interconnected and with two guest phases of activated carbon particles (2) and spherical cobalt particles (2″) with average diameters of 1 millimetre and 5 millimetres, respectively. The guest phase (2) of activated carbon particles fill 25% of the cavities of the foam and the guest phase of cobalt particles (2′) fill another 25% of the pores. The particles were coated with NaCl by means of the deposition method using forced spray precipitation in the same manner as in EXAMPLE 1. A coating thickness of 70-100 micrometres was achieved in the activated carbon particles and 150-200 micrometres in the cobalt particles. The embodiment is identical to that of EXAMPLE 4 but starting from a mixture of particles in a volume ratio of 1:1:2 for carbon-NaCl:Co—NaCl:NaCl, for which 3.27 g of activated carbon particles, 11.48 g of cobalt particles and 6.47 g of NaCl particles were used.