JPH0336959B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention has sufficient mechanical strength and is extremely chemically stable even in an extremely high temperature atmosphere.
Moreover, the present invention relates to a zirconia powder-containing sheet that is easy to handle at room temperature and a method for producing the same. [Prior art] Zirconia is known as a ceramic raw material with a high melting point of approximately 2700°C, and has high resistance to thermal shock, extremely low thermal conductivity, low electrical resistance at high temperatures, and low electrical resistance at low temperatures. It has high electrical resistance and extremely low chemical reactivity, and has characteristics not found in ceramics, such as being basic, not wetted by acidic slag, having low volatility, and having a Mohs hardness of 7 or more. Utilizing these properties, zirconia is used as a raw material for refractory materials, polishing and abrasive materials, electronic materials, pigments for ceramics, glass additives, and materials for sensors. However, conventionally used zirconia molding methods do not allow large quantities of zirconia sheets to be obtained at low cost. [Problems to be Solved by the Invention] In view of the above-mentioned circumstances, the present invention provides a method for manufacturing uniform sheets with a high zirconia content in large quantities at low cost without losing the properties of zirconia. It is. [Means for Solving the Problems] The present inventors have discovered that a zirconia sheet having sufficient strength can be obtained by using a zirconia powder instead of a sheet manufacturing method using zirconia fibers, and have arrived at the present invention. That is, the present invention is particularly a method for producing a zirconia sheet using zirconia powder, and in detail,
Slurry consisting mostly of 95 to 99.5 parts by weight of zirconia powder and 5 to 0.5 parts by weight of cellulose fibers
To 100 parts by weight (solid content), add 2 zirconia sol or/and zirconia salt aqueous solution as solid content.
This is a method for producing a zirconia powder-containing sheet, which is characterized in that it is obtained by a conventional wet papermaking method by adding ~15 parts by weight, 1 to 5 parts by weight of an organic binder, and 0.001 to 5 parts by weight of a flocculant. The zirconia powder-containing sheet obtained by the present invention is chemically stable even at high temperatures, has excellent corrosion resistance, has low vapor pressure, and hardly reacts with molten metal or glass. In addition, it has sufficient strength, flexibility, and abrasion resistance for handling. The zirconia powder used in the present invention is a powder of zirconium compounds such as zirconium oxide, zirconyl carbonate, and zirconyl hydroxide, and one or more of these is appropriately selected. Zirconia powder may be used alone, but it may also be used in combination with a very small amount of zirconia fiber.
That is, zirconia powder alone can provide the strength necessary for handling the sheet, but adding zirconia fibers improves tear strength and flexibility. However, if a large amount of zirconia fiber is used, the cost will increase, so the blending ratio of these fibers is determined depending on the purpose of use. What is zirconia fiber? 100% zirconia fiber,
Calcium oxide stabilized zirconia fiber, yttrium oxide stabilized zirconia fiber, magnesia oxide stabilized zirconia fiber, etc., and the fiber length is
The fiber diameter used is 0.1 to 50 mm and the fiber diameter is 0.1 to 20 μ. 5 to 0.5 parts by weight of cellulose fibers are blended to 95 to 99.5 parts by weight of zirconia powder. Cellulose fibers are used for the purpose of separating the wet paper from the papermaking wire during papermaking or preventing paper breakage, but if added in excess of the above range, harmful substances will be generated in a high temperature atmosphere and the chemical damage of the sheet will occur. This results in loss of stability. Accordingly, experimentally, it is preferable to use about 3 parts by weight. As is well known, cellulose fibers include wood pulps such as NBKP and LBKP that are commonly used in the paper industry, vegetable fibers such as kozo, mitsumata, hemp, and cotton, modified pulps such as cationized pulp, and microfibrillated cellulose. Therefore, those having high toughness and flexibility are more preferable. A zirconia sol or/and a zirconium salt aqueous solution is added to a slurry consisting of zirconia powder and cellulose fibers in the above-mentioned proportions, and in the present invention, the zirconia sol and/and zirconium salt aqueous solution are essential components. The addition maintains the strength of the sheet in a high temperature atmosphere and after firing for the first time. That is, the zirconia sol and/or the aqueous solution of zirconium salt strengthens the bond between the zirconia powders and forms a tough film itself, so it has heat resistance equivalent to that of zirconia fibers. Therefore, the sheet obtained has high mechanical strength and excellent chemical stability. The particle size of the zirconia sol used in the present invention is
It is a milky white colloidal liquid in which zirconia of around 70μmm is suspended in water. The zirconium salt aqueous solution is a colloidal solution of zirconia using water as a solvent, and zirconyl acetate, zirconyl nitrate, zirconyl acid chloride, zirconyl sulfate, zirconyl ammonium carbonate, etc. are used. These zirconia sol and/or zirconium salt aqueous solution are added to the slurry as described above, but they can also be added by spraying or impregnation during the papermaking process or after papermaking, or they may be added in combination. good. However, the amount added must be in the range of 2 to 15 parts by weight (solid content) per 100 parts by weight (solid content) of the slurry consisting of zirconia powder and cellulose fibers. Experiments have shown that if the amount added is less than 2 parts by weight, the mechanical strength of the sheet in a high-temperature atmosphere or after firing will be weakened, and if it is more than 15 parts by weight, the sheet will harden, break, crack, etc., and become difficult to handle. A range of 3 to 10 parts by weight is optimal. The organic binder in the present invention is involved in binding zirconia powder, zirconia fibers, cellulose fibers, zirconia sol, etc., and is used for the purpose of imparting strength, flexibility, and abrasion resistance to the sheet and making it easier to handle the sheet. Ru. Suitable organic binders include synthetic rubber latex, synthetic resin emulsions, water-soluble polymers, and the like, which form a flexible and tough coating. The smaller the amount of these organic binders added, the less harmful substances are generated in a high-temperature atmosphere, and the strength decreases less even after firing. Therefore, in order to maintain chemical stability in a high-temperature atmosphere to a level that does not cause any practical problems and to facilitate handling at room temperature, the organic binder must be added to a slurry of zirconia powder and cellulose fibers (100 parts by weight (solid content)). ), a range of 1 to 5 parts by weight (solid content) is optimal. The flocculant used in the present invention acts on flocculation of zirconia powder, zirconia fiber, cellulose fiber, zirconia sol or/and zirconium salt aqueous solution, and organic binder, and is composed of a polymer flocculant or a trivalent metal salt. Examples of polymer flocculants include polyacrylamides, modified polyacrylamides, sodium polyacrylates, strong polymers of acrylamide and sodium acrylate, and polyethylene glycols, and trivalent metal salts include aluminum sulfate and aluminum chloride. Examples include aluminum salts such as, ferric salts such as ferric chloride, and ferric nitrate. These flocculants are a slurry consisting of zirconia powder and cellulose fibers.
It is added in an amount of 0.001 to 5 parts by weight based on the weight part (solid content). That is, if the amount is less than 0.001 parts by weight, aggregation will be insufficient and turbidity will remain, and if it is more than 5 parts by weight, the amount of aggregates will be too large, which will have an adverse effect on the formation of the resulting sheet. In carrying out the present invention, first, zirconia powder and cellulose fibers are poured into water and stirred to easily obtain a fiber-dispersed slurry. Next, a slightly colored transparent zirconia sol or/and zirconium salt aqueous solution and an organic binder such as synthetic rubber latex are added to this dispersion, and after thorough mixing, the pH of the slurry is adjusted to the alkaline side with ammonia, etc. After adding a flocculant such as anionic polyacrylamide or anionic polyacrylamide to form an agglomerated slurry, the slurry is made into a paper using a known paper machine such as a fourdrinier paper machine or cylinder paper machine. [Operations and Effects] As described above, the present invention makes it possible to form zirconia powder into a sheet without losing the excellent properties of zirconia, and the zirconia powder-containing sheet obtained by the present invention has flexibility and strength. It is extremely easy to handle, has mechanical strength even in high-temperature atmospheres or after firing, and has excellent chemical stability. In particular, the content of metal ions and metal oxides is extremely low, so it is difficult to react with metals even at high temperatures. The sheets obtained by this method can be used in a variety of applications by taking advantage of their properties, such as reaction prevention materials during ceramic firing, packing materials for special alloy casting equipment, gaskets, special filters, catalyst carriers, insulation materials for high-temperature furnaces, and separation materials. Can be used for a wide range of purposes such as mold materials. [Example] Zirconia powder, zirconia fibers, and hemp fibers were dispersed in the proportions shown in Table 1, and then zirconia sol and synthetic rubber latex were added and mixed thoroughly. Then, a coagulant was added, and the resulting coagulated slurry was mixed. The paper was made using a square hand paper machine to a weight of approximately 400 g/m ² . As a comparative example, a sheet mainly made of zirconia fibers was produced. Table 2 shows the characteristics of the obtained sample.

【table】

【table】

[Table] From Table 2, the sheet based on the present invention exhibits substantially the same melting point and tensile strength as the zirconia fiber sheet under normal conditions. Furthermore, even after heating to 1000°C, it exhibits approximately the same tensile strength and flexibility as a zirconia fiber sheet.

Claims (1)

[Claims] 1 Slurry solid content consisting of 95 to 99.5 parts by weight of zirconia powder and 5 to 0.5 parts by weight of cellulose fibers
For 100 parts by weight, 2 to 15 parts by weight of zirconia sol or/and zirconium salt aqueous solution as solid content, 1 to 5 parts by weight of organic binder, and flocculant.
A sheet containing zirconia powder, characterized in that it is wet paper-made with the addition of 0.001 to 5 parts by weight.