GB2254608A

GB2254608A - Alumina-based insulating materials

Info

Publication number: GB2254608A
Application number: GB9204591A
Authority: GB
Inventors: Kenichi Shibata; Kouichi Kimura; Yuji Kanamori
Original assignee: Nichias Corp
Current assignee: Nichias Corp
Priority date: 1991-03-04
Filing date: 1992-03-03
Publication date: 1992-10-14
Anticipated expiration: 2012-03-03
Also published as: DE4206800A1; GB9204591D0; GB2254608B; DE4206800C2; JPH04349177A; JPH0794347B2

Description

1 1.

2 2.3 4 63 8 10, HEAT INSULATING MATERIAL BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a molded heat insulating material which can be used as a heat insulating material in a furnace at temperatures of 1400 - 16000C.

Description of the Related Art

Various heat insulating materials have been used in high-temperature furnaces. Recently.. porous molded bodies using poly-crystalline alumina fibers have been utilized because they have excellent properties such as low heat conductivity and capacity due to their light weight, high heat resistance, high durability, and the like. Moreover, porous molded bodies are easily applie4.

The conventional alumina fibrous body, however, contains at least 2t of io 2 from raw material alumina fibers... When the temperature is 14000C or more, the SiO, evaporates and contaminate!'-material burned in the furnace. The SiO, deposits- on the surface of the furnace which can cause failure of the furnace equipment. Furthermore, the conventional alumina fibrous molded body is extremely likely to be reduced in..a hydrogen atmosphere which can increase the evaporation of Si02.

SUMMARY OF THE INVENTION is An object of the present invention is to eliminate the defects in the conventional polycrystalline alumina fibrous insulating material, and to provide an alumina fibrous insulating material which is less likely to contaminate a material to be burned in the furnace or damaging the furnace equipment, even if the heat insulating material is used in high- temperature vacuum, oxidizing or reducing atmosphere.

This invention provides a heat insulating material in which alumina fibers or mixtures of alumina fibers and alumina powder are mutually -bonded with an alumina binder to form a porous molded body having a bulk specific gravity of 0.2 - 1.2. The whole content of A1,0, in the moldedbody is not less than 99.0 weight percent.

The content of A1,0, in the whole of the heat insulating material is made tobe 99.0 weight percent or more by using alumina fibers having an alumina content higher than that of poly-crystal alumina fibers which have been used in producing a conventional'-alumina heat insulating material. Preferably, alumina fibers containing Al,O, by 99 weight percent or more are used, and the alumina powder and the binder contain as much Al,O, as possible.

- 2 DETAILED DESCRIPTION OF THE EMBODIMENTS is The method of producing the heat insulating material according to the present invention is described in detail as follows.

The alumina fibers are the main raw material and preferably have an Al,O, purity of 99 weight percent or more. The alumina fibers may be crystalline or not. Such high-purity alumina fibers may be produced by thoroughly removing silica and components other than alumina from the fiber producing raw material. Alternatively, high-purity alumina fibers may be produced by removing Sio, by reduction f rom ordinary alumina fibers containing a small quantity (generally, about 4 - 5%) of silica.

Although the diameter of the fibers is not partidularly limited, it is preferable that the diameter be within a range of about 1 to 5 pm.

1 The alumina powder to be used as the filler is a high-purity alumina powder such as burned alumina powder, fused alumina powder, aluminum hydroxide, or the like. Preferably, the quantity of alumina powder is not greater than about 9 times the quantity of the alumina fibers (by weight).

The alumina binder used'can be colloidal alumina, aluminum sludge (aluminum hydroxide gel generated in the aluminum anodic oxide coating treatment), aluminum hydroxide obtained by reacting aluminum sulfate with alkali, or the like. Preferably the quantity (the equivalent quantity of Al,O,) of the binder is about 2-30% by weight relative to the mixture of the alumina fibers and alumina powder. Excessive use of the binder has the same harmful effect as excessive use of the filler powder.

The foregoing raw materials are mixed with each other in the foregoing ratio, and a proper quantity of water is poured into the materials before and after the mixing so that the whole mixture is made wet or in a state of slurry. Next, the raw material mixture is molded by a usual method of dehydration molding. At this time, it is desirable that the molding be performed under a condition that the bulk specific gravity of a final molded product is about 0.2 1.2. The thus_obtained molding is dried and burned at about 1400 - 1700 OC so that the binder is hardened to thereby obtain the heat insulating material according to the present invention.

The refractory material according'to the present-invention can be used in a state as it is or after it has been cut as a heat insulating 20material for a high-temperatureburiling furnace.

EXAMPLES

The following raw materials were dispersed into water in the ratio of Table 1, and the.thus obtained slurry was subject to suction dehydration molding. Then, the thus obtained molding was dried with hot air and burned at., 1500-11C for 3 hours.

alumina fibers A:

alumina fibers B:

alumina powder: binder:

Raw material composition (weiqht portion) poly-crystal alumina fibers fiber diameter 3:A12 03 99.9?-.:SiO2 0.1% poly-crystal alumina fibers fiber diameter 3:A15 05 95.0-:SiO25.0-0. sintered alumina colloidal alumina Table 1

Example Example comparison Comparison 1 2 Example 1 Example 2 alumina fibers A 50 40 30 alumina B 10 20 50 alumina powder 50 50 50' 50 1 colloidal alumina 10 1-0 10, 10 Chemical composi tion of product A1203 99.9 99.5 99.0 97.7 (weight percent) Si02 0.1 0.5 1.0 2.3 (weight percent) Performance value of Product bulk specific 0.60 0.55 0.50. 0.45 gravity normal state 17 15 13 12 (flexural strength) shrinkage (%) by heating in oxidation atmosphere after heating 0.0 0.1 0.2 0.0 of 14001C - 24H after heating 1.0 3.0 4.0 0.8 - 5 of 16001C. 24H after heating of 10-4mmHg 15000C. SH flexural strength 14.8 13.2 8.5 4.3 (kgf / cm) size change 0.4 1.0 2.0 3.8 ratio% after heating of 15000C - 5H in flow of nitrogen flexural strength 16.3 14.5 10.5 7.5 (kgf /pm2) size change 0.3 0.7 1.0 2.6 (ratio after heating of 15000C - 5H in flow of hydrogen 1 1 flexural-strength. 15.6 13.8 9.1 6.4 (kgf ICM2) size change ratio (-0,-)' 0.4 0.8. l,.2 2.9--- As described above, the heat insulating material substantially containing only alumina according to the present invention shows an excellent heat resisting property not only in an oxidation atmosphere but in a reduction atmosphere and a vacuum. Further, when the heat insulating material is heated to a high temperature, there is little possibility that silica is free to contaminate a material to be burned or to damage the furnace equipment. Using the heat insulating material according to the present invention prolongs the life of a furnace in comparison with furnace using conventional heat insulating material.

While the invention has been described in detail and with reference to specific embodiments thereof, it is apparent to one skilled in the art that various qhanges and modifications can be made therein without departing from the spirit and scope thereof. The heat insulating material of the claimed invention can be used wherever high heat resistance, low heat conductivity and capacity, ot"high durability is needed.

Claims

WHAT IS CLAIMED IS:

2 3 4 1 1.

comprising:

alumina fibers; and an alumina binder, wherein said molded material has a bulk specif ic gravity of 0. 2 to"_ 1.2, the whole content of alumina in said molded material is not less than 99.0 wt%.

6 7 1 A molded heat insulating material 2. A molded heat insulating material -2. according to claim 1, further comprising an 3- alumina powder.

1 2 3 4 4. A molded heat insulating material 2 according to claim 2, wherein the-quantity of said alumina binder is about 2.to 30 wt% relative to. the amount of said alumina fibers and alumina powder.

3 45 3. A molded heat insulating material according to claim 2, wherein the quantity of said alumina powder.,is less than about 9 times the quantity af said alumina fibers, by weight.

1 3 1 2 3 1 2 5. A molded heat insulating material according to claim 1, wherein the diameter of said alumina fibers is about 1 to 5 gm.

6. A molded heat insulating material according to claim 1, wherein said alumina fibers have an alumina purity of at least 99.0 wt%.

7. A method of making a molded heat insulating material comprising the steps of:

1 3 4 5 6 mixing together alumina fibers, an alumina binder and water to form a slurry; molding said slurry by dehydration to form said molded material; and 7 -drying and burning said molded material at a 8 temperature of about 1400 to 17000C until said.

9 alumina binder is hardened, wherein said molded article has a bulk specific gravity of about 0.2 11 to 1.2, the whole content of alumina in said 12 molded material is not less than 99.0 wt%.

1 8. A method of making a molded heat 2 insulating material according to claim 7, wherein 3 an alumina powder is mixed with said alumina 4 fibers, alumina binder and water to form a slurry.

1... 2 3.

1 2 3 4 1., 2. 3 4 9.. A method of making a molded heat insulat ing material according to claim 8, wherein the quantity of said alumina powder is-.less -than 4- about 5 times the quantity of said alumina fibers.,,. 5 by weight.

10. Amethod of making a molded heat insulating material according to claim 8, wherein the quantity of said alumina binder is about 2 to 30 Wt% relative to the amount of said alumina fibers and alumina powder.

11. A method of making a molded heat insulating material according to claim 7, wherein said alumina fibers have an alumina purity of at least 99.0 wt% 12. A heating insulating material substantially as described herein.

13. A method of making a heating insulating material as claimed in any one of claims 1 to 6 or 12 substantially as described herein.

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