GB2129416A

GB2129416A - Shaped sintered porous ceramic body

Info

Publication number: GB2129416A
Application number: GB08324019A
Authority: GB
Inventors: Hans Lennart Slycke; Gote Valdemar Norrbrand
Original assignee: ANTIPHON AB
Current assignee: ANTIPHON AB
Priority date: 1982-09-08
Filing date: 1983-09-07
Publication date: 1984-05-16
Also published as: DE3331613A1; SE8304683D0; ES525444A0; IT8322800A1; SE8205096D0; IT8322800A0; BR8304837A; ES8404965A1; GB8324019D0; JPS5969461A; IT1169462B; SE8304683L; FR2532644A1

Abstract

A sintered porous ceramic shaped body is prepared from a composition comprising: a) one or more basic minerals such as calcium silicate and/or calcium aluminate b) an aqueous solution of one or more compounds of the formula X.(Al2O3).Y.(P2O5).Z.(H2O> wherein 0.3</=X</=3, 1</=Y</=6 and 1</=Z</=10 c) clay or kaolin d) felspar e) silica and/or aluminium phosphate, and optionally f) water which composition is permitted to harden, by chemical reaction, to a porous shaped body, with the introduction of gas bubbles into the mixture before the same has hardened, whereupon the shaped body is dried and finally sintered.

Description

SPECIFICATION Improvements in or relating to a method of forming shaped sintered porous ceramic body The present invention relates to a method of forming shaped sintered porous ceramic body.

U.S. Patent Specification No. 3148996 discloses a method of preparing porous ceramic materials, from a mixture comprising wollastonite (calcium silicate), aluminium hydrogen phosphate and water. However, several problems are associated with preparing porous ceramic materials by way of this prior acid-base system.

Firstly, the complicated process of drying and burning which is described leads to extensive cracking of the ceramic body. Secondly, on sintering the material, further deformation of the material occurs. In certain cases the cracking and deformation can lead to failure of the final product.

As a result of these difficulties it is not commercial practice to sinter the products.

Products which are only dried have too low a strength to be of commercial value. In addition many of the products that are burnt have to be rejected due to the presence of drying cracks caused by the process outlined above.

Consequently products manufactured by the acidbase system disclosed in U.S. Patent Specification No. 3148996 are not commercially attractive.

There is a need for a satisfactory method of preparing sintered porous ceramic materials, for use primarily in heat and sound insulation at elevated temperatures.

Sintered ceramic materials have several useful properties. For example, they can withstand high temperatures and are not degraded by common chemicals which are often very corrosive to other materials.

The present invention seeks to provide a method of preparing shaped sintered porous ceramic bodies which overcomes the above difficulties present in the prior proposed acid-base system.

According to this invention there is provided a method of preparing a shaped sintered porous ceramic body, said method comprising the steps of preparing a mixture comprising: a) one or more basic minerals, b) a solution of one or more compounds of a formula: X.(AI2O3)Y (P2O5).Z (H2O) wherein 0.3 < X < 3, 1 < Y < 6 and 1 < Z < 10, c) clay and/or kaolin d) felspar e) silica and/or aluminium phosphate, and optionally f) water; permitting the mixture to harden to form a porous shaped body by chemical reaction, and incorporating gas bubbles into the mixture before the mixture has fully hardened; drying the shaped body and finally sintering the shaped body.

Preferably the basic minerals are calcium silicate or calcium aluminate for example wollastonite, and conveniently the solution is an aqueous solution.

Advantageously the values of X, Y and Z correspond to the values 1, 3 and 3 respectively.

Conveniently component b) of the mixture is a hydrogen phosphate solution prepared by dissolving aluminium hydroxide in ortho phosphoric acid. The reaction proceeds in aqueous solution, according to the following reaction: AI(OH)3+3H3PO4AI(H2PQ)3+3H2O+heat In most cases water is added to the resultant solution after the reaction has gone to completion in order to prevent the viscosity of the final mixture being too high. It will be appreciated, therefore, that in one embodiment of the invention the substance a) consists of wollastonite which is reacted with an aluminium hydrogen phosphate solution b) and water.

Wollastonite is a calcium silicate having a basic reaction. In the chemical reaction occurring when the composition hardens, Al(H2PO4)3 and calcium phosphate precipitate because of the reaction entered into by the calcium ions. It is to be understood that instead of calcium silicate it would be possible to use calcium aluminate or a mixture of calcium silicate and calcium aluminate.

The components c) d) and e) of the mixture outlined above make it possible for the mixture to be dried and burned without problems, in a manner simliar to porcelain pastes.

In one preferred embodiment of the invention the component c) consists of clay and the component e) consists of silica, preferably in the form of quartz. These components, together with the felspar d) form a glass phase on sintering. The glass phase tends to bind the quartz particles together, so that very strong bonds are formed between the grains of quartz.

Other crystal forms of SiO2, such as an amorphous SiO2 can be used instead of quartz. In addition the silica can, as mentioned above, be completely or partly replaced by aluminium phosphate.

In the glass phase, tricalcium phosphate Ca3(PO4)2 is formed on burning.

Preferably component d) is potash felspar.

In one embodiment of this invention gas bubbles are at least partially incorporated in the mixture by a mechanical process. Said mechanical process may comprise stirring and/or injection of air, to form a good cell system.

In another embodiment of this invention a gas forming additive is included in said mixture, the gas forming additive leading to the creation of at least some of said gas bubbles. Said gas forming additive may comprise one or more carbonates and/or one or more metals. These metals could for example comprise aluminium or iron.

Alternatively or additionally the gas forming additive may comprise a fermentation agent.

The compounds present as a) and b) in the above mixture are preferabiy selected such that they react to allow the porous body to harden by chemical reaction at room temperature, usually within thirty minutes after initial mixing. Thus, no additional heat supply is required.

Suitably sintering is conducted in the temperature range 800-1 5000 C. Preferably sintering is conducted in the temperature range 1000-1 3O00C.

Advantageously said mixture contains a surfactant.

Preferably the mixture comprises 1065% calcium silica and/or calcium aluminate, 5-40% by weight of one or more components of the formula: X (Al203) Y (P205) Z (H20) wherein 0.3 < XS3, 1 sYs6 and 1 SZS 10 530% clay and/or kaolin, 1-10%felspar, and 10-40 % silica and/or aluminium phosphate, all percentages being by weight on a dry basis.

Preferably the percentage of calcium silicate and/or calcium aluminate is 1040% or 2065%.

As has alreadly been broadly outlined above it is possible to provide the air bubbles that contribute to the porosity of the resultant body by utilising various different methods. For example, it is possible to utilise a fermentation method in which a fermentation agent is added to the mixture to provide the desired porosity by fermentation process. It is also practicable to inject air, and/or stir the mixture. Additionally, or alternatively, foaming agents may be added to the mixture. It is also possible to utilise a gas forming agent such as a carbonate, in the form of magnesium carbonate for example, or metals such as aluminium and iron.

It has been found that a good cell system can be created in the final shaped body if a carbonate additive, for example magnesium hydroxide carbonate, is utilised with the addition of a foaming agent and a foam stabilizer, especially if the mixture is then stirred heavily. The cell volume and the cell size can be changed by modifying the foaming method in various different ways.

It is to be appreciated that the particular foaming method utilised in performing the invention is not critical. However, it is necessary to take steps to ensure that the desired cell formation is terminated before the mixture had hardened.

Before the sintering process has been completed the shaped body obtained by the preliminary steps of a method in accordance with the invention has a green strength which is sufficiently high that bodies in this state can be transported on belts, can be piled in furnaces or on carriages without undue problems arising.

However, the mechanical strength is not sufficient for the body to be utilised in a commercial application without being sintered, and also the unsintered body does not have a high resistance to corrosive chemical attack. It has been found, however, that after the completion of the sintering process a porous body in accordance with the present invention has extremely good properties. In addition to having excellent mechanical properties, the body has an extremely good resistance to chemicals and other substances that might tend to degrade the body in question. It has also been found that such bodies have good sound absorbing and heat insulating properties.

Bodies made in accordance with the invention may be utilised for many purposes, especially having regard to the good qualities of such bodies as outlined above. One or more bodies made in accordance with the invention can, for example, be used as sound absorbing elements in a silencer for a motor vehicle. However, the bodies made in accordance with the invention can, of course, also be used for other sound absorbing purposes.

Bodies made by a method in accordance with the present invention may find many applications and may thus be used as building blocks, filters, and heat insulating elements.

The invention will be explained further in relation to the following working examples, which describe the preparation of sintered porous ceramic shaped bodies using different initial mixtures.

Example 1 800 g of an aluminium hydrogen phosphate solution, prepared from 1 56 g of Al(OH)3,400 ml of 85% phosphoric acid and 200 g of water were mixed with 800 g of quartz. The mixture of quartz in the solution is called mixture A. 400 g of calcined wollastonite, 200 g of uncalcined wollastonite, 500 g of glacial clay, 150 g of potassium felspar, 30 g of magnesium hydroxide carbonate (MgCO3xMg(OH)2x3H20), 800 g of water and 0.5 g each of a foaming agent and a foam stabilizer were thoroughly mixed. The mixture obtained is called mixture B below.

The mixture A was poured into the mixture B with vigorous stirring. After stirring for one minute the mixture was cast in a mould to form a ceramic body. After 20 minutes the ceramet body formed by this method was removed from the mould, covered, and thereafter kept at room temperature for 24 hours. The ceramet body was then placed in a drying chamber at a temperature of 7O0C for a period of 100 hours, the relative humidity in the drying chamber being reduced successively from 100% to 10%. Finally, the body was burned at 126O0C+150C, and a sintered porous body was obtained.

Example 2 300 g of calcined wollastonite, 300 g of uncalcined wollastonite, 500 g of clay, 1 50 g of potash felspar, 40 g of magnesium hydroxide carbonate, 850 g of water and 0.5 g of a surfactant were thoroughly mixed. The mixture obtained is called mixture C with below. 1600 g of mixture A from Example 1 was poured into the mixture C with vigorous stirring. After stirring for 1 minute the mixture was cast in a mould. After 20 minutes the ceramet body produced in this manner was removed from the mould and was covered and was thereafter kept at room temperature for 24 hours. The ceramet body was then dried in a drying chamber at temperature of 800C for a period of 90 hours, the relative humidity in the drying chamber being reduced successively, from 100% to 10%.Finally, the body was burned at 1 240 C+1 5 C, a sintered porous body being obtained.

Example 3 1385 g of calcined wollastonite, 1115 g of uncalcined wollastonite, 750 g of felspar, 2400 of clay, 200 g of magnesium hydroxide carbonate, 3750 g of water and 5 g of surfactant were thoroughly mixed. The mixture obtained is called mixture D below. 7500 g of the mixture A from Example 1 was poured into the mixture D with vigorous stirring. After stirring for 1 minute the mass was cast in a mould. After 20 minutes the ceramet body formed in this manner was removed from the mould and covered and was thereafter kept at room temperature for 24 hours.

The ceramet body was then dried in a drying chamber at a temperature of 500C for a period of 120 hours, the relative humidity in the drying chamber being reduced successively from 100% to 10%. Finally, the body was burned at 12900C+1 50C, a sintered porous body being obtained.

Example 4 800 g of an aluminium hydrogen phosphate solution, prepared from 1 56 g of Al(OH)3, 350 ml of 85% phosphoric acid and 250 g of water were mixed with 700 g of quartz. The mixture of quartz and the solution is called mixture E below. 600 g of wollastonite, 600 g of clay, 100 g of potash felspar, 25 g of magnesium hydroxide carbonate, 900 g of water and 0.5 g of each of a foaming agent and a foam stabilizer were thoroughly mixed. The mixture obtained is called mixture F below. The mixture E was poured into mixture F with by vigorous stirring. After stirring for 1 minute the mass was cast in a mould. After 20 minutes the ceramet body produced in this manner was removed from the mould and was covered and was thereafter kept at room temperature for 24 hours. The ceramet body was then dried in a drying chamber at a temperature of 750C for a period of 95 hours, the relative humidity in the drying chamber being reduced successively from 100% to 10%. Finally, the body was burned at 12500C+1 50C a sintered porous body being obtained.

The invention is not limited to the described embodiments, since the same can be modified in various ways within the scope of the invention.

Claims

1. A method of preparing a shaped sintered porous ceramic body, said method comprising the steps of preparing a mixture comprising: a) one or more basic minerals, b) a solution of one or more compounds of a formula: X (Al203) Y (P2O Z (H2O) wherein 0.31X13, 1 < Y < 6 and 1 < Z < 10, c) clay and/or kaolin d) felspar e) silica and/or aluminium phosphate, and optionally f) water; permitting the mixture to harden to form a porous shaped body by chemical reaction, and incorporating gas bubbles into the mixture before the mixture has fully hardened; drying the shaped body and finally sintering the shaped body.

2. A method according to claim 1 wherein calcium silicate constitutes one of said basic minerals.

3. A method according to claim 1 or 2, wherein calcium aluminate constitutes one of said basic minerals.

4. A method according to any one of the preceding claims wherein X=1,Y=3 and=3.

5. A method according to any one of the preceding claims wherein component b) of the mixture is a hydrogen phosphate solution prepared by dissolving aluminium hydroxide in ortho phosphoric acid.

6. A method according to any one of the preceding claims wherein the said solution is an aqueous solution.

7. A method according to any one of the preceding claims wherein said felspar is potash felspar.

8. A method according to any one of the preceding claims wherein said gas bubbles are at least partially incorporated in the mixture by a mechanical process.

9. A method according to claim 8 wherein said mechanical process comprises stirring and/or the injection of air.

10. A method according to any one of the preceding claims wherein a gas forming additive is included in said mixture, the gas forming additive leading to the creation of at least some of said gas bubbles.

11. A method according to claim 10 wherein said gas forming additive comprises one or more carbonates.

12. A method according to claim 10 or 11 wherein said gas forming additive comprises one or more metals.

13. A method according to claim 12 wherein said metals are Al or Fe.

14. A method according to any one of claims 10 to 13 wherein said gas forming additive comprises a fermentation agent.

15. A method according to any one of claims 1 to 14 wherein said hardening is by chemical reaction and proceeds without the external addition of heat.

16. A method according to any one of claims 1 to 15 wherein said sintering is conducted in the temperature range of 800-1500 C.

17. A method according to claim 16 wherein said sintering is conducted in the temperature range of 1000 C-1300 C.

18. A method according to any one of the preceding claims wherein said mixture contains a surfactant.

19. A method according to any one of the preceding claims wherein said mixture comprises: 10-65% calcium silicate and/or calcium aluminate 540% by weight of one or more compounds of the formula X (Al203) Y(P2O5) Z(H2O) wherein 0.3#X#3, 1 < Y < 6 and 1 < Z < 10 530% clay and/or kaolin 110% felspar and 1040% silica and/or aluminium phosphate, all percentages being by weight on a dry basis.

20. A method according to claim 19 wherein the percentage of calcium silicate and/or calcium aluminate is 20-65%.

21. A method according to claim 19 wherein the percentage of calcium silicate and/or calcium aluminate is 10-40%.

22. A shaped sintered porous ceramic body whenever made by a method according to any one of the preceding claims.

23. A method of preparing a shaped sintered porous ceramic body substantially as herein described in Example 1.

24. A method of preparing a shaped sintered porous ceramic body substantially as herein described in Example 2.

25. A method of preparing a shaped sintered porous ceramic body substantially as herein described in Example 3.

26. A method of preparing a shaped sintered porous ceramic body substantially as herein described in Example 4.

27. A shaped sintered porous ceramic body whenever made by a method substantially as described in Example 1.

28. A shaped sintered porous ceramic body whenever made by a method substantially as described in Example 2.

29. A shaped sintered porous ceramic body whenever made by a method substantially as described in Example 3.

30. A shaped sintered porous ceramic body whenever made by a method substantially as described in Example 4.

31. Any novel feature or combination of features disclosed herein.