JPH0577624B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing alumina ceramics, and particularly to a method for producing alumina ceramics having excellent mechanical strength and thermal shock resistance. [Prior Art] Alumina-based ceramics have excellent mechanical properties, electrical properties, etc., and are widely used as constituent materials of various industrial products by utilizing these properties. Conventionally, various additives have been used to improve strength, thermal shock resistance, reduce firing temperature, etc., and research has been conducted on additives for improving properties. One example of these studies is the improvement of the strength, toughness, and thermal shock resistance of alumina ceramics by adding zirconia;
The publication discloses that the addition of zirconia improves thermal shock resistance. Also, JP-A-55-
In Publication No. 158173 and Japanese Patent Application Laid-open No. 61-26558,
It is disclosed that thermal shock resistance is improved by adding zircon (ZrSiO ₄ ) as a zirconia-containing oxide to alumina, and the reason for this is that zircon reacts with alumina and mullite (3Al ₂ O _{3 2} ) is produced, and the zirconia produced has a large amount of monoclinic crystals, which causes microcracks. Further, Japanese Patent Publication No. 59-24751 discloses adding zirconia to improve toughness and bending strength. Furthermore, JP-A-53-
Publication No. 126008 discloses adding flux and a zircon compound. [Problems to be Solved by the Invention] As described above, it is a known technique to improve the properties of alumina by adding zirconia or zircon, but none of the above methods can achieve all the required properties. Satisfactory alumina ceramics have not been obtained. That is, the method described in Japanese Patent Application Laid-Open No. 52-86413 is as follows:
Specifically, about 15% by weight of unstabilized zirconia is added to alumina to improve fracture toughness due to fine microcracks, but the microcracks reduce bending strength. The method described in Japanese Patent Application Laid-Open No. 55-158173 is as follows:
Specifically, 45 to 60% by weight of zircon is mixed with 55 to 60% by weight of alumina, and the method described in Japanese Patent Application Laid-open No. 61-26558 mixes 5 to 25% by weight of zircon. It is to be blended. Since all of these contain a large amount of zircon, high-temperature firing at 1600°C or higher or pressure firing is required to make them densified. Therefore, strength deterioration occurs due to grain growth of alumina due to high temperature firing, and further strength deterioration occurs due to monoclinic zirconia produced. Moreover, using a large amount of zircon is disadvantageous from a cost standpoint. In particular, in the method disclosed in JP-A-55-158173, since a large amount of zircon (45 to 60% by weight) is blended, a large amount of mullite (2Al ₂ O ₃ .2SiO ₂ ) is produced, which deteriorates the properties of alumina ceramics. I can't get it. In the sintered body described in JP-A No. 59-24751,
Since no flux component is used, there is a drawback that the firing temperature is extremely low (1600°C or higher). Furthermore, the method described in JP-A No. 53-126008 specifically uses alumina with CaO, MgO, SiO ₂
4 to 6% by weight of flux, and zirconia or zirconium acid chloride as a zircon compound,
Zirconium hydroxide etc. converted to ZrO ₂ from 1 to
This method also uses 15% by weight.
ZrO ₂ remains as a monoclinic crystal in the sintered body, and compressive stress remains inside. In other words, ZrO ₂ undergoes a phase transition to form microcracks and becomes monoclinic.
Although ZrO ₂ imparts thermal shock resistance, there is a problem of decreased bending strength due to the formation of microcracks. An object of the present invention is to solve the above-mentioned conventional problems and provide a method for manufacturing alumina ceramics that has excellent mechanical strength and thermal shock resistance and can be sintered at a low sintering temperature. . [Means for Solving the Problems] The method for producing alumina ceramics of the present invention includes 1 to 4 parts by weight of zircon with an average particle size of 0.1 to 5 μm;
By molding and sintering a raw material consisting of 1 to 14 parts by weight of a silicate flux having the composition shown below and the remainder being substantially alumina for a total of 100 parts by weight, the grain boundaries of alumina are It is characterized by obtaining a sintered body in which tetragonal zirconia is dispersed in a glassy binder phase. _SiO2 : 40-95% by weight CaO: 5-60% by weight MgO: 0-55% by weight _B2O3 , BaO, SrO, NiO, CdO, _ZnO , MnO
and CrO: 0 to 5% by weight The present invention will be described in detail below. In the present invention, the blending amount of zircon (ZrSiO ₄ ) is 1 to 4 parts by weight, and the average particle size is 0.1
~5 μm is used. If the amount of zircon added is less than 1 part by weight, sufficient improvement effects such as strength and toughness cannot be obtained by adding zircon. If the amount of zircon exceeds 4 parts by weight, high temperatures are required to decompose the zircon, which increases the firing temperature and deteriorates the properties of the resulting alumina-based ceramics. Therefore, the blending amount of zircon is 1 to 4 parts by weight. In addition, when the average particle size of zircon exceeds 5 μm,
The zirconia in the alumina ceramics obtained does not become tetragonal zirconia, but the monoclinic component increases, resulting in a decrease in strength. Zircon with an average particle size of less than 0.1 μm has no difference in its properties improvement effect, and is poor in price and ease of handling due to its fine particle size. Therefore, the average particle size of the zircon used is 0.1 to 5 μm. The silicate flux used in the present invention is SiO ₂ ,
In the ternary composition diagram shown in Figure 1, the ratio of MgO and CaO is A (95, 0, 5), B (40, 55, 5) and C (40, 0, 60) (all weight%). Preferably, it is in the area surrounded by each point. Particularly preferred is a SiO ₂ content of 50% by weight or more, for example, SiO ₂ :MgO:CaO=7:2:1 SiO ₂ :MgO:CaO=6:3:1 SiO ₂ :MgO:CaO=6: A formulation with a ratio of 2:2 may be mentioned. Such silicate flux forms a glassy binder phase at the alumina grain boundaries and improves the strength of the resulting alumina-based ceramic. If the composition of each component of the silicate flux used is outside the range specified by the present invention, a good glass phase having an excellent strength-improving effect cannot be formed. If the amount of silicate flux is less than 1 part by weight, too little glass phase will be formed and sufficient strength will not be obtained. Conversely, if the amount of silicate flux is 14
If it exceeds the weight part, the alumina content will be relatively small and the properties of alumina will be impaired. Therefore,
The amount of silicate flux blended is 1 to 14 parts by weight. In the present invention, there is no particular restriction on the addition form of silicate flux, and SiO ₂ , CaCO ₃ , MgCO ₃
It may be added in the form of reagents such as talc,
It may be added in the form of natural raw materials containing components of silicate flux such as kaolin and lime. In producing the alumina-based ceramics of the present invention, zircon, silicate flux, and alumina are mixed in a predetermined amount by adding water and, if necessary, an organic binder such as polyvinyl alcohol. This is shaped and fired according to conventional methods.
For molding, first, the slurry obtained by mixing the raw materials is spray granulated. Spray granulation improves the fluidity of the raw material and improves the filling properties into the mold. A molded body (green compact) is obtained from this raw material powder by a mold press or the like. In the present invention, the molded body is fired at 1475 to 1550
It can be carried out at a relatively low temperature of °C, and the firing time may be about 1 to 3 hours. If the firing temperature is less than 1475°, the sintering reaction will be insufficient, which is not preferable. Further, high temperature firing exceeding 1550° C. is not only unnecessary but also undesirable as it leads to deterioration of properties such as strength and toughness due to growth and coarsening of crystal grains. [Function] The zircon-added alumina ceramics of the present invention have much better properties than conventional products, even though the amount added is very small compared to conventional zircon-added alumina ceramics. Furthermore, sintering can be performed at a lower firing temperature than conventional methods. If zircon is used in excess as in the conventional method, sinterability is poor because sintering proceeds through a solid phase reaction in which mullite crystallizes due to the reaction between alumina and zircon. Furthermore, due to its poor sinterability, it requires high-temperature firing at 1,600°C or higher, which results in coarse grains, making it impossible to obtain sufficient properties corresponding to the amount of zircon added. Furthermore, most of the zirconia produced from zircon exists as a monoclinic crystal, and although this monoclinic zirconia contributes to improving impact resistance, it causes a decrease in bending strength. On the other hand, in the present invention, zircon decomposes into zirconia and silica during the firing process, which is the same as in conventional products, but the silica produced does not react with alumina, but with silicate added separately. Together with the flux, a glass phase is formed to firmly bind the alumina particles. That is, the sintering in this case is liquid phase sintering, and therefore it is possible to significantly reduce the firing temperature. The zirconia produced by the decomposition of zircon is uniformly dispersed as very fine zirconia particles in the glass phase formed by the reaction between silica and silicate flux, which strengthens the glass phase. The effect of further improving strength and toughness can be obtained. Moreover, in the present invention, most of the zirconia produced by the decomposition of zircon exists as metastable tetragonal zirconia (partially stabilized zirconia) and is restrained by the glass layer, so the phase transition (However, some parts may become monoclinic.) Since no microcracks occur, the strength is extremely high. The effect of improving such characteristics in the present invention is as follows:
With a specific amount of silicate flux of a specific composition,
This is achieved by adding a small amount of 1 to 4 parts by weight of extremely fine zircon with an average particle size of 0.1 to 5 μm. [Examples] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. Examples 1 to 3, Comparative Examples 1 and 2 Raw materials were mixed so that the amounts of zircon, silicate flux, and alumina were as shown in Table 1 (However, in Comparative Example 1, zircon was not added. (In Comparative Example 2, silicate flux was not added.), 1000 g of water per 1000 g of raw material powder, and polyvinyl alcohol (Shin-Etsu Chemical Co., Ltd.) as an organic binder.
Add 20g of solids (10% by weight aqueous solution)
A slurry was obtained by mixing by ball milling for 70 hours. The average particle size of the zircon powder used is
It is 1.0 μm. As a silicate flux,
A mixture of SiO ₂ , CaCO ₃ and MgCO ₃ was used so that SiO ₂ :60% by weight, MgO: 25% by weight, CaO: 15% by weight. The obtained slurry was spray granulated to obtain a raw material powder, and this raw material powder was molded into a size of 5.0 x 5.0 x 40 mm using a mold press at 1000 kgf/ ^cm2 , and then molded into the shapes shown in Table 1 in an electric furnace. Firing was carried out at the indicated firing temperature for 2 hours. Various properties of the obtained alumina-based sintered body were investigated, and the results are shown in Table 1. As is clear from Table 1, according to the method of the present invention, a dense sintered body can be obtained at a low firing temperature, and the resulting alumina ceramics have extremely high bending strength and excellent thermal shock resistance. In particular, Comparative Example 2, in which only zircon was added without adding silicate flux, had a porosity of about 30%.
It was not densified and was significantly inferior in bending strength and thermal shock resistance.

[Table] *1: Three-point bending strength [Effects of the invention] As detailed above, according to the method for manufacturing alumina ceramics of the present invention, the bending strength is high at a low sintering temperature, and the thermal shock resistance is also improved. It is also possible to produce excellent alumina ceramics.

[Brief explanation of the drawing]

FIG. 1 is a ternary composition diagram showing the composition of the silicate flux used in the present invention.

Claims (1)

[Claims] 1 Zircon with an average particle size of 0.1 to 5 μm 1 to 4 parts by weight Silicate flux having the following composition 1 to 14 parts by weight SiO ₂ : 40 to 95% by weight CaO: 5 to 60% by weight MgO: 0 ~55wt% _{B2O3 ,} BaO, SrO, NiO, CdO, ZnO, MnO
One or more selected from the group consisting of: A method for producing alumina-based ceramics, characterized by obtaining a sintered body in which tetragonal zirconia is dispersed in a glassy binder phase at the grain boundaries of alumina.