These characteristics of ceramic materials are superimposed or weakened between each pair of characteristics, so there are technical difficulties in improving all these characteristics. Therefore, the prior art (1) has the following problems. The strength of ceramic body varies with the thermal shock resistance of materials. The green body (hereinafter referred to as glass green body) made of porcelain stone, feldspar and clay through dense sintering has a bending strength of 40-80Mpa.
This glass body consists of a crystalline phase and a glass phase. The crystalline phase contains timely and mullite. The crystalline phase existed in raw materials at first, while mullite was deposited by silica and alumina, which are mainly aluminum silicate minerals, during sintering. The glass phase is mainly made of silicate glass, which mainly includes silicon dioxide and contains alkali metal or alkaline earth metal oxides.
On the other hand, in recent years, corundum has been used to replace the time in the green body to improve the strength, and this high-strength ceramic green body has been used to replace the vitreous green body. This kind of green body, also called alumina porcelain, is used in tableware, insulators and so on.
For example, in Japanese patent publications 41-14, 43- 19866, 2-400 15 and 7-6806 1 and Japanese delayed patent publications 6-20.
Japanese Patent Laid-Open No.41-14914 has a crystal phase ratio of 35-75%, and the crystal phases include cristobalite, timely and mullite; Japanese Patent PublicationNo. 43- 19866 is formed by adding Synchro, alumina and mullite into the crystalline phase of the green body; The crystallization rate of those green bodies disclosed in Japanese Patent Laid-OpenNo. 2-400 15 and Japanese Patent Laid-OpenNo. 7-6806 1 is more than 40%, and the crystal phase contains corundum, mullite and cristobalite, and all components can increase the strength of ceramics and reduce sintering deformation. In addition, Japanese Patent PublicationNo. 6-232970 discloses the application of alumina ceramics in sanitary ware.
The bending strength of alumina porcelain is 150-300MPa, so the strength of glass body can be improved by not less than two times. The principle of this enhancement is as follows.
For the glass green body, due to the stress generated in the cooling process during the sintering process, there is a great difference between the thermal expansion coefficients of the glass phase and the time in the green body, which will lead to the formation of microcracks near the time. The existence of these microcracks reduces the original strength.
On the contrary, for alumina ceramics, the number of microcracks is reduced and the strength is improved because it is replaced by corundum in time.
In addition, because corundum particles smaller and stronger than the corresponding ones are uniformly dispersed in the green body, the crack caused by stress cracking is prevented from developing further, thus further improving the strength.
This kind of alumina porcelain has excellent strength performance, but when it is used under the same conditions as glass body, the following problems will appear.
Although there are many microcracks as mentioned above, the glass body has excellent thermal shock resistance because these microcracks alleviate the stress caused by thermal shock.
On the other hand, for the traditional alumina ceramics, the thermal shock resistance is reduced because of the few microcracks mentioned above, especially for large-scale products such as sanitary ware, the products will crack during the cooling process during sintering.
In addition, the proportion of crystalline phase in the green body is higher than that in the glass body, because the addition of alumina is increased to strengthen the green body by using conventional alumina ceramics. However, due to the high proportion of crystalline phase, the melting amount of raw material particles decreases, which changes the glass phase for further sintering, and as a result, the sintering process is changed.
Therefore, it is necessary to sinter at a higher sintering temperature than the glass body, but considering the sintering cost, it is more suitable to sinter at a lower temperature, and adopting the same sintering temperature as the glass body is beneficial to sintering on the same production equipment as the glass body.
On the other hand, in order to sinter alumina green body at lower temperature, it is necessary to add sodium oxide or potassium oxide as sintering AIDS to accelerate the vitrification of raw materials and crush raw material powder.
However, in the case of adding sintering AIDS, because the viscosity of vitrified raw materials in the green body decreases during the sintering process, the sintering deformation of the green body caused by static weight and other stresses during the sintering process will increase, resulting in an increase in the deformation during the product manufacturing process.
As mentioned above, conventional alumina ceramics have problems of poor thermal shock resistance and sintering performance.
For the deterioration of sintering performance, the method of adding sintering AIDS or further crushing raw material powder can be adopted, but this will lead to a new problem of increasing sintering deformation of green bodies.
(2) The method of reducing sintering deformation and the matching glaze of ceramic body can be applied to a variety of products. In civil use, tableware and sanitary ware are the main uses, while insulation fittings and others are used for commercial purposes. However, in these products, from the point of view of decoration and use function, ceramic bodies should not be used alone, but should be glazed on the surface.
Ceramic glaze, as glaze, is mainly used in sanitary ware. This ceramic glaze is mainly composed of RO2 (acidic oxide, mainly SiO2), R2O2 (amphoteric oxide, mainly Al2O3) or R2O+RO (basic oxide, mainly K2O, Na2O, CaO, ZnO, MgO, BaO and SrO), and may also contain opacifying agents such as zirconia, tin oxide and various dyes if necessary.
As mentioned above, if the raw powder is crushed to reduce the sintering deformation, the deformation will be reduced in the sintering process, but compared with the raw powder, applying glaze, such as ceramic glaze, on the surface of the green body will increase the shrinkage of the green body at the initial temperature of melting the glaze during the sintering process, which will lead to the problem that the glaze will peel off due to deformation. In addition, if the amount of sintering AIDS increases, the viscosity of vitrified raw materials will decrease and the sintering process will proceed rapidly, leading to similar problems.
(3) Sintering density and green strength of materials Generally speaking, the strength of ceramic materials can be improved by dense sintering. However, for some or a large number of ceramic materials containing glazes similar to the subject matter of the present invention, as the sintering process of the materials progresses, the sintering deformation due to the softening of the materials will increase. Therefore, for some or a large number of glazed ceramic materials, if the sintering density is limited to a low level to reduce the sintering shrinkage or sintering deformation of the materials, the strength of the materials will also decrease.
(4) The wet strength, dry strength and dry shrinkage of materials are very important characteristics in the product manufacturing process. Especially in the production process of large products, such as sanitary ware, higher wet strength and dry strength are needed. In addition, the drying shrinkage should preferably be small to prevent tearing in the drying step. For traditional ceramics, these properties are not enough, and considering the breakage or similar strength of products during the processing of production steps, it is necessary to increase the thickness of materials beyond the required level. In addition, due to the large drying shrinkage, gradient drying is needed to prevent tearing, which will lead to the problem that drying takes a lot of time.