COMPACTED CERAMIC MATERIALS WITH LOW POROSITY

Abstract

The invention relates to a high-performance compacted ceramic material, comprising between 40%-85% by weight of glassy phase, having a density between 2.3 and 3.0 g/cm3, and characterized in that it has an internal porosity of less than 4% by volume. This material is highly resistant to mechanical and chemical action, sparingly permeable and prevents staining, so it is ex tremely suitable as a building material, particularly for kitchen countertops.

Claims

1. A compacted ceramic material comprising between 40%-85% by weight of glassy phase, having a density between 2.3 and 3.0 g/cm.sup.3, and an internal porosity of less than 0.5% by volume of the total volume of the material, wherein the starting materials comprise potassium feldspar in a range of 15-25% by weight out of the total raw materials, and sodium feldspar in a range of 35-45% by weight out of the total raw materials, and wherein at least 95% of the feldspar particles have a size of less than or equal to 40 m.

2. (canceled)

3. A compacted ceramic material according to claim 1, having an internal porosity between 0.01% and 0.5% by volume.

4. A compacted ceramic material according to claim 1, comprising between 50%-70% by weight of glassy phase.

5. A compacted ceramic material according to claim 1, having a density between 2.5 and 2.8 g/cm.sup.3.

6. A compacted ceramic material according to claim 1, wherein the starting materials comprise an amount of feldspars between 50% and 70% by weight of the total starting materials.

7. (canceled)

8. A building material comprising a compacted ceramic material according to claim 1.

9. Use of the building material according to claim 8 for covering floors, walls or facades.

10. Use of the building material according to claim 8 for a kitchen countertop.

11. Use according to claim 10 wherein the kitchen countertop has a length exceeding 3 meters.

12. A method for obtaining the compacted ceramic material according to claim 1, comprising the following steps: a) Grinding the raw materials to reduce them to a particle size of less than 100 microns; b) Shaping and compacting the raw materials at pressures exceeding 400 kg/cm.sup.2; c) Firing at a maximum temperature comprised between 1,000 C. and 1,200 C.

13. A method according to claim 12, where the grinding step a) reduces the raw materials to particle sizes of less than 50 microns.

14. A method according to claim 12, wherein the compacting step c) is performed by applying a pressure exceeding 450 kg/cm.sup.2.

15. A method according to claim 12, which comprises applying a firing cycle c) until reaching a temperature comprised between 1,100 C. and 1,160 C.

16. A method according to claim 12, which includes a preparation step for preparing the ground raw material composition, where the composition comprises between 20% and 35% by weight of clays and between 50% and 70% by weight of feldspars.

17. A compacted ceramic material according to claim 1, wherein at least 99% of the feldspar particles have a size of less than or equal to 40 m.

18. A compacted ceramic material according to claim 3, having an internal porosity between 0.01% and 0.3% by volume.

19. A compacted ceramic material according to claim 4, comprising between 55%-65% by weight of glassy phase.

20. A compacted ceramic material according to claim 6, wherein the starting materials comprise an amount of feldspar between 55% and 70% by weight of the total starting materials.

21. A method according to claim 13, where the grinding step a) reduces the raw materials to particle sizes of less than 45 micrometers.

22. A method according to claim 14, wherein the compacting step c) is performed by applying a pressure exceeding 500 kg/cm.sup.2.

23. A method according to claim 15, which comprises applying a firing cycle c) until reaching a temperature comprised between 1,120 C. and 1,150 C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0024] The term ceramic material refers to a material consisting of inorganic, polycrystalline, non-metallic compounds, the fundamental characteristic of which is that they are consolidated in solid state by means of high-temperature heat treatments (firing) and are formed by a combination of crystalline and glassy phases. The inorganic compounds are formed by metallic and non-metallic elements bound by ionic or covalent bonds.

[0025] In the context of the present invention, the term ceramic material or compacted ceramic material or ultra-compacted ceramic material refers to ceramic materials that have been compacted at pressures exceeding 400 kg/cm.sup.2.

[0026] In the present invention, glassy phase is understood to mean the amorphous, non-crystalline phase between the crystalline phase grains. The percentage by weight of glassy phase is determined by means of the usual methods in the field of ceramics, such as by means of x-ray diffraction, for example.

[0027] Internal porosity is understood to mean the empty space within the ceramic material and is expressed in % by volume. The methods of measuring porosity in ceramic materials are known by the person skilled in the art. Among said methods, the following are included: mercury porosimetry, porosity measurements in an autoclave based on impregnating with water or simply using the Archimedes' principle. Internal porosity has been determined at room temperature. In an embodiment, it refers to the internal porosity measured at room temperature and a pressure of 600 mmHg.

[0028] In a particular embodiment, the internal porosity is less than 2% by volume, preferably less than 1% by volume, more preferably less than 0.5% by volume, even more preferably less than 0.1% by volume.

[0029] In an embodiment, the internal porosity is comprised between 0.00 and 2% by volume or between 0.01 and 2% by volume, preferably between 0.01 and 0.5% by volume, preferably between 0.01 and 0.3% by volume, more preferably between 0.01 and 0.1% by volume, even more preferably between 0.01 and 0.05% by volume.

[0030] In another embodiment, the internal porosity is comprised between 0.05 and 0.5% by volume, preferably between 0.1 and 0.3% by volume.

[0031] The internal porosity values of the present document refer to values measured in an autoclave based on impregnating with water.

[0032] The ceramic materials of the invention that may be obtained from very pure raw materials, in the form of micrometric particles, and by means of high shaping pressures and consolidated in solid state at high sintering temperatures, with a glassy phase of between 40%-85% by weight, are almost completely densified bodies, with virtually no internal pores, cracks and flaws, giving them excellent technical features: high mechanical, thermal, abrasion and chemical etching resistances.

[0033] The compacted ceramic material provided by the present invention has a density comprised between 2.3 and 3.0 g/cm.sup.3, preferably between 2.4 and 2.7 g/cm.sup.3. In a particular embodiment, the density of the compacted ceramic material is comprised between 2.5 and 2.7 g/cm.sup.3. More preferably, the compacted ceramic material has a density of 2.6 g/cm.sup.3. The density measurements provided in the present invention have been taken by immersion in water applying Archimedes' principle. Density has been determined at room temperature.

[0034] In one aspect of the invention, the mineral particles used in manufacturing the ceramic materials of the invention are substances with a particle size of less than 200 micrometers, preferably less than 100 micrometers, a size in the order of tens of microns, between 10-90 micrometers, is particularly preferred. More preferably, a particle size between 10 and 50 micrometers is used. The particle size is statistical and refers to the mean size determined by means of sieves, as is usual in the materials field, determining the % of particles that go through a specific sieve. Preferably, at least 95% of the particles of the materials used to prepare the ceramic material of the invention go through a 45 m sieve, more preferably at least 98% of the particles of the materials used to prepare the ceramic material of the invention go through a 45 m sieve.

[0035] These particles are preferably obtained by wet grinding the starting raw materials and spray drying, which techniques are known in the field of ceramics.

[0036] The starting materials can have different compositions, although there is preferably an amount of non-siliceous melting materials which allow obtaining 40-85% of glassy phase.

[0037] The high glassy phase content of the ceramic material of the invention gives it special properties, because it is capable of closing internal pores. This phase occurs as a result of the semi-liquid state solidification phase which easily closes pores as a result of the low viscosity.

[0038] The compacted ceramic material according to the invention may contain from 40% to 85% by weight of glassy phase, preferably between 40 and 75% by weight, even more preferably between 45 and 70% by weight, even more preferably between 50 and 65% by weight of glassy phase based on the total weight of the compacted ceramic material.

[0039] In an embodiment of the invention, the starting materials comprise the following materials in the indicated ranges: [0040] Clays, 20-35% by weight [0041] Kaolins, 5-15% by weight [0042] Feldspars, 50-70% by weight

[0043] Preferably, the feldspars have a particle size of less than 40 micrometers.

[0044] According to the present invention, the term clays may refer to clay, shales, and other natural or synthetic brickmaking material. The clays provide plasticity for shaping the starting product. Since they are mixtures of minerals that usually have particle sizes in the range of tens of micrometers, they generally do not have to be subjected to an intensive grinding process, which allows maintaining the plastic properties of the clay. The clays used are very plastic so as to allow correct shaping of the overall mixture because the large amount of feldspars contained in the formula hinder the pressing thereof.

[0045] Clays according to the present invention are principally selected from hydrosilicates of alumina and may include clay minerals such as smectites (such as montmorillonite, nontronice, sapolite, and the like), kaolins (such as kaolinite, dickite, halloysite, nacrite, and the like), illites (such as illite, clay-micas and the like), chlorites (such as clinochlore, chamosite, nimite, pennantite, and the like), attapulgites, sepiolites, and the like. Further, clays may also contain minerals such as quartz, sylvine or siderite in its composition along with other various trace components.

[0046] In a particular embodiment, the clays comprise montmorillonite, illite and kaolinite. Preferably, the clays comprise at least 60% by weight of montmorillonite, illite and kaolinite based on the total weight of the clays. More preferably, at least 65% or at least 70% by weight.

[0047] The term kaolins refers to a clay containing the mineral kaolinite as its principal constituent. Preferably, kaolinite is the only plastic component in kaolins. Kaolins may further contain other impurities, such as quartz, mica, phosphates, fine clay impurities such as certain smectite clay constituents and various other species, e.g. compounds containing transition elements such as iron.

[0048] In a particular embodiment, kaolins comprise at least 60% by weight of kaolinite based on the total weight of kaolins.

[0049] Feldspars give special properties to the ceramic material of the invention. They provide quartz content in addition to sodium and potassium oxides. They act as melting in the firing process and reduce porosity in the final material. They represent over 50% of the materials, preferably 50-70%, more preferably 55-60% by weight.

[0050] Feldspars are aluminosilicates containing sodium, potassium, calcium or barium. In a particular embodiment, the feldspars comprise sodium and potassium feldspars.

[0051] In an embodiment of the invention, the feldspars contain potassium feldspar in a range of 15-25% by weight out of the total raw materials, and sodium feldspar in a range of 35-45% by weight out of the total raw materials.

[0052] Preferably, at least 95%, more preferably at least 99%, even more preferably at least 99.7% of the feldspar particles have a size less than or equal to 40 m.

[0053] Sodium feldspar acts as a lower viscosity melting, quickly creating bridges for binding particles together, particularly as a result of the small sizes of the particles and of feldspar itself. It eliminates the internal porosity of the material during the sintering process.

[0054] Potassium feldspar provides greater viscosity to the melting, which helps maintain the stability and shape of the product during the firing process.

[0055] In the present invention, the size of feldspar particles is also reduced by micronizing to tens of microns. By reducing the size of the feldspar particles, the specific surface, and therefore the reactivity of said particles, increases. As a result of this effect, bridges are generated between particles resulting in a compacted material where the pores are isolated from others, generating a closed porosity throughout the entire volume. Furthermore, the increase in the reactivity of the particles allows reducing the firing temperature from 1,180 C. to 1,140 C., preventing pyroplastic deformation.

[0056] Preferably the starting materials have a high purity, which allows precise control of the compositions and prevents flaws in the material. For example, an undetermined organic matter content can cause the occurrence of considerable pores and flaws during firing due to combustion thereof. The presence of unwanted mineral materials can affect glassy phase formation, bring about internal stresses or issues of planarity or generation of residual porosity.

[0057] In one embodiment, the purity of the selected materials exceeds 90% by weight in the feldspathic compounds.

[0058] Once the starting materials are selected and reduced to the desired size, they can be stored in order to be used at the appropriate time. Preferably, the different materials are mixed uniformly and to a suitable moisture content that allows shaping and pressing prior to firing.

[0059] Preferably the material is mixed with water, or dried if it was obtained through a wet process, so that the amount of water is between 4 and 12% by weight, preferably between 4%-9% by weight, more preferably between 6% and 9% by weight.

[0060] After preparing the mixture of particles forming the raw material, in an embodiment of the invention the method includes a compacting step using a continuous pressing station, comprising compacting means in the form of a compacting roller and belt. In a particular embodiment, the mixture of particles of raw materials are compacted at a pressure of between 30 and 110 kg/cm.sup.2, preferably between 40 and 100 kg/cm.sup.2, more preferably between 60 and 80 kg/cm.sup.2. If required, the product is cut into the desired shape after compacting, for example in the form of a rectangular slab.

[0061] After compacting, and optionally cutting, the method includes a pressing step carried out at very high pressures, which generates ultra-compacting of the material prior to firing. This step contributes to reducing the porosity in the end product and makes the sintering process easier. In this pressing, pressures can exceed 400 kg/cm.sup.2, preferably exceeding 450 kg/cm.sup.2, and more preferably exceeding 500 kg/cm.sup.2. In a particular embodiment, the pressure is comprised between 400 and 450 kg/cm.sup.2, more preferably between 410 and 440 kg/cm.sup.2, even more preferably between 410 and 430 Kg/cm.sup.2.

[0062] Once the product is shaped and the materials ultra-compacted, drying and firing can be performed.

[0063] Before drying, the product may have a water content of up to 10% by weight. Drying reduces the water content without deforming the piece, so that the final content of water in the product is of up to 0.7% by weight, preferably of up to 0.5% by weight, more preferably of up to 0.3% by weight. Drying can be done in a specific installation, which allows storing the dried pieces before firing them, making it easier to manage the pieces in stock. Alternatively, drying can be done in the firing kiln, as a step immediately prior to firing.

[0064] During firing, the glassification and sintering process generates a viscous liquid phase that contributes to reducing porosity when firing the product of the invention. The formation of a viscous glassy phase which surrounds the most refractory particles, and under forces of the surface tension created by the fine pores of the piece, tends to bring the particles closer to one another, increasing shrinkage and reducing the porosity of the product, takes place during firing. The high density of the starting product resulting from the ultra-compaction process and the selection of the particle size (preferably between 10 and 50 m) give the product specific characteristics that make the glassification and sintering process faster, and it results in a smaller pore volume and in the maintenance of suitable technical characteristics in the end product; these properties can be seen when the material is polished.

[0065] Preferably the firing in the firing cycle the material is heated to maximum temperatures comprised between 1,000 C. and 1,200 C., more preferably between 1,000 C. and 1,180 C. A maximum temperature range comprised between 1,120 C. and 1,160 C. is particularly preferred, even more preferably a range comprised between 1,140 C. and 1,150 C. Melting and sintering occur at these temperatures, but deformation of the pieces, for example due to the action of gravity, is prevented. Preferably, the time at the maximum firing temperature is comprised between 5 and 60 min.

[0066] In a particular embodiment, the firing cycle to which the material is subjected (including heating the material, residence time at the maximum temperature and cooling) has a duration of up to 9 hours. Preferably, the firing cycle has a duration between 1 and 9 hours, preferably between 90 and 500 min, depending on the thickness of the piece. For instance, 90 min might be sufficient for pieces of 8 mm thickness, whereas longer times such as 500 min might be necessary for pieces of 3 cm thickness.

[0067] The method of manufacturing the ceramic material of the invention can include additional conventional steps, such as, for example, the addition of coloring substances, for example after the grinding step, the formation of decorative veins using mineral powders of different colors, elimination of metallic particles, etc.

[0068] In addition to a low porosity, high density and glassy phase content, the product of the invention has unique mechanical properties allowing it to be manufactured in large sized pieces, even exceeding 3 meters in length and 1.5 meters in width, and with a thickness that can reach up to 3 cm or more if required.

[0069] In a particular embodiment, the compacted ceramic material has lateral dimensions of up to 42 m.sup.2, preferably of up to 3.201.44 m.sup.2, more preferably comprised between 31 m.sup.2 and 42 m.sup.2. In a preferred embodiment, the compacted ceramic material has lateral dimensions of 3.201.44 m.sup.2.

[0070] In another particular embodiment, the compacted ceramic material has a thickness of at least 0.7 cm, preferably of 1 cm, 2 cm or 3 cm. Preferably, it has a thickness between 0.7 and 3 cm. Preferably, the compacted ceramic material has lateral dimensions of up to 42 m.sup.2 and a thickness of at least 0.7 cm. More preferably, the compacted ceramic material has lateral dimensions of at least 3 meters in length and 1.4 in width or of 3.201.44 m.sup.2 and a thickness of at least 0.7 cm, preferably at least 1 cm, preferably at least 2 cm, more preferably at least 3 cm.

[0071] Preferably the compacted ceramic material is in the form of a slab with lateral dimensions of 3.201.44 m.sup.2 and a thickness of between 0.7 and 3 cm.

[0072] These properties mean that the compacted ceramic materials of the invention are excellent for use thereof as a building material. The high chemical and physical resistance, and the large manufacturing dimensions allow the use thereof in the covering of floors and facades, where they are inert to the action of solar radiation, chemical agents, have a high degree of hardness and controlled internal stress level allowing the pieces to be cut and handled without breaking.

[0073] A particularly preferred application for the ceramic materials of the invention are kitchen countertops. The high chemical resistance and hardness thereof allow contact with food, food colorants, and drinks such as wine or coffee without generating stains and without affecting the properties thereof. Furthermore, the possibility of manufacturing thicknesses of 3 cm or more gives the countertop an appearance similar to that of natural stones.

[0074] The invention is illustrated below by means of examples, which must not be interpreted as being limiting of the invention, which is defined by the claims.

EXAMPLES

Example 1

[0075] The following starting materials and amounts by weight were used in the following example: [0076] 30% clay (comprising at least 60 wt % of montmorillonite, illite and kaolinite and wherein the reject at a 125 m sieve is about 4.5%), [0077] 15% kaolin (comprising at least 60 wt % of kaolinite and wherein the reject at a 53 m sieve is less than 1%), [0078] 38% sodium feldspar (wherein the particles have an average size of less than 300 m, and the content of sodium is of at least 10% by weight), [0079] 17% potassium feldspar (wherein 75% of the particles have an average size of less than 100 m, and the content of potassium is of at least 14% by weight),

[0080] A first grinding of the clay materials is performed in an industrial grinder, generating a slip with a particle size below 45 m with the following characteristics: [0081] Density=1.600 g/cm.sup.3 [0082] Viscosity=20 s [0083] Reject at 40 m=0.1%

[0084] The resulting slip is stored in a reservoir where it is kept under continuous agitation.

[0085] In a second grinding the size of the feldspathic materials and the remaining materials is reduced until achieving a particle size below 45 m. [0086] Density=1.690 g/cm.sup.3 [0087] Viscosity=24 s [0088] Reject at 40 m=0.9%

[0089] This second slip is unloaded in the reservoir where the slip resulting from the first grinding is located and it is all subjected to agitation.

[0090] Spray drying is then performed until achieving a product with a water content of 8% by weight.

[0091] The wet material is subjected to shaping and ultra-pressing at 450 kg/cm.sup.2.

[0092] It is then dried by means of heat in a drying line until achieving a product with a water content of 0.5% by weight.

[0093] The dry product is subjected to firing at a cycle of 180 min, reaching a maximum temperature of 1,155 C.

[0094] The resulting product has the following characteristics: [0095] 2 cm thickness, 3.2 meters in length and 1.44 in width. [0096] 9% shrinkage [0097] 0.00% internal porosity measured by means of an autoclave by impregnating with water at room temperature and 600 mmHg [0098] 2.500 g/cm.sup.3 measured by immersion in water applying Archimedes' principle at room temperature [0099] 79% of glassy phase.

Example 2

[0100] The following starting materials and amounts by weight were used in the following example: [0101] 29% clay (comprising at least 60 wt % of montmorillonite, illite and kaolinite and wherein the reject at a 125 m sieve is about 4.5%), [0102] 8% kaolin (comprising at least 60 wt % of kaolinite and wherein the reject at a 53 m sieve is less than 1%), [0103] 38% sodium feldspar (wherein the particles have an average size of less than 300 m, and the content of sodium is of at least 10% by weight), [0104] 15% potassium feldspar (wherein 75% of the particles have an average size of less than 100 m, and wherein the content of potassium is of at least 14% by weight), [0105] 10% by weight of an alumina and zircon pigment

[0106] A first grinding of the clay materials is performed in an industrial grinder, generating a slip with a particle size below 45 m with the following characteristics: [0107] Density=1.600 g/cm.sup.3 [0108] Viscosity=20 s [0109] Reject at 40 m=0.1%

[0110] The resulting slip is stored in a reservoir where it is kept under continuous agitation.

[0111] In a second grinding the size of the feldspathic materials and the remaining materials is reduced until achieving a particle size below 45 m. [0112] Density=1.690 g/cm.sup.3 [0113] Viscosity=24 s [0114] Reject at 40 m=0.9%

[0115] This second slip is unloaded in the reservoir where the slip resulting from the first grinding is located and it is all subjected to agitation.

[0116] Spray drying is then performed until achieving a product with a water content of 8% by weight.

[0117] The wet material is subjected to shaping and ultra-pressing at 450 kg/cm.sup.2.

[0118] It is then dried by means of heat in a drying line until achieving a product with a water content of 0.5% by weight.

[0119] The dry product is subjected to firing at a cycle of 180 min and achieving a highest temperature of 1,155 C.

[0120] The resulting product has the following characteristics: [0121] 2 cm thickness, 3.2 meters in length and 1.44 in width. [0122] 9% shrinkage [0123] 0.01% internal porosity measured by means of an autoclave by impregnating with water at room temperature and 600 mmHg [0124] 2.46 g/cm.sup.3, measured by immersion in water applying Archimedes' principle at room temperature [0125] 71% of glassy phase.