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Effect of Additives on Vacuum Sintering of Ceramics

Vacuum sintering and densification of alumina ceramic materials requires a high temperature of 1600 ° C. It is precisely because of high temperature sintering that the process is difficult and the manufacturing cost is high, which has always been the main factor limiting its application. In order to reduce the sintering temperature, people have carried out various methods. try. Studies in recent years have shown that when titanium dioxide reacts with alumina at high temperature, a lattice activity is formed, which can promote vacuum sintering. Alumina is an important ceramic material. The grains of pure alumina are in the form of flakes. In order to improve the performance of alumina, material workers have carried out many studies aimed at changing the microscopic morphology of alumina grains. One of them is The method is to change the grain morphology of alumina itself, use liquid phase sintering, add seeds and other means to enhance the anisotropy of grains, greatly improve the sintering activity of alumina, and make the density and density of alumina ceramic materials after sintering Strength has increased to a certain extent. The anisotropic growth of grains in single-phase alumina bulk materials has been studied. The work shows that the addition of a small amount of titanium dioxide can significantly enhance the anisotropy of alumina grains. The morphology of alumina grains will change significantly with different amounts of AlO, from equiaxed grains to enhanced anisotropy of some grains, and finally to the growth of all grains and the weakening of anisotropy. However, the anisotropic crystal grains generated by simply adding titanium oxide are generally very large, and the microstructure is not uniform enough. The purpose of this paper is to discuss that the density of alumina ceramic materials has also changed significantly through the difference of double doping and addition of titanium dioxide and magnesium oxide, vacuum sintering temperature and holding time, thereby greatly improving the density and strength of alumina ceramics.

1 experiment

Alumina (purity >99.5%), titanium oxide (analytical pure) and magnesium oxide (analytical pure) were used as starting materials.

When simply adding titanium dioxide, the addition amount of titanium dioxide was 0.4wt%, 1.0wt% and 2.0wt% for analysis and research.

When adding in combination: the addition amount of titanium dioxide is fixed at 0.4wt%, and 0.1wt%, 0.2wt% and 0.4wt% of magnesium oxide are added respectively.

Alumina is pre-calcined at a high temperature of 1450°C.

The mixed powder uses pure water as the medium, and agate stones as the grinding balls, according to the ratio of material:water = 1:0.6, put it into the polyurethane ball mill tank, and ball mill for 30 hours. The resulting slurry was dried in an oven, added PVA solution after drying, passed through a 40-mesh sieve, and pressed into a thin disc with a diameter of 35 mm and a thickness of 2 mm under a pressure of 25 MPa. Vacuum sintering is carried out in the RVS vacuum sintering furnace of SIMUWU. Below 300°C, the heating rate is controlled at about 1°C/min; below 300~1000°C, the heating rate is controlled at about 5°C/min; when the temperature exceeds 1000°C, the heating rate is reduced to 2°C/min to ensure sufficient time to get rid of the pores. The vacuum sintering temperatures were 1400℃, 1450℃ and 1500℃ respectively, and the holding time was 2h. Then the samples were left in a box furnace to cool naturally to room temperature.

The density of the ceramic disc samples was determined by the buoyancy method.

2 Experimental results and discussion

Table 1 lists the densities of alumina ceramic materials with different titania additions at different vacuum sintering temperatures. The data in Table 1 show that the density of all the alumina ceramic disc samples added with titania is higher than that of the undoped samples at the same sintering temperature. In addition, except for the addition of 2.0wt% TiO2 samples, the density of the material increases with the increase of vacuum sintering temperature. This shows that both titania and vacuum sintering temperature can promote the sintering of alumina ceramics, but the effect of different additions of titania on the sintering of alumina is significantly different, adding 0.4wt% and 1.0wt%: the oxidation of titania For aluminum, with the increase of vacuum sintering temperature, the density rises faster than that of the sample with 2.0wt% titanium dioxide added. At 1400°C, the density of the former is lower than that of the latter, at 1450°C, the density of the two is approximately equal, and at 1500°C, the density of the former exceeds the latter. In contrast, the density of alumina added with 2.0wt% titania decreases with the increase of vacuum sintering temperature, which may be because too many and too large grains will generate steric hindrance and hinder the densification of the sample. The dual effects of titania addition and sintering temperature on alumina density can be intuitively reflected in Table 1.

Table 1 Effect of different titania additions and vacuum sintering temperature on the density of alumina blocks

When double adding titanium dioxide and magnesium oxide, 1450°C was selected as the sintering temperature, and the addition amount of titanium dioxide was fixed at 0.4wt%. Table 2 gives the bulk densities of alumina samples with addition of titania and magnesia. It can be seen from Table 2 that when magnesia is added to alumina containing titania, the density of the material increases first and then decreases with the increase of magnesia content, indicating that the addition of a small amount of magnesia can inhibit the excessive growth of grains, thereby The steric hindrance of the growth of alumina grains is reduced. In addition, when the addition of magnesia reaches 0.4wt%, the density of the material decreases, which may be because magnesia is pinned through grain boundaries, which reduces the grain growth rate of alumina and affects the sinterability of alumina.

Table 2 The effect of different magnesium oxide additions on the density of alumina containing 0.4wt% titanium oxide

3 Conclusion

In the case of adding titania, different titania addition amount and vacuum sintering temperature will have a certain influence on the density of alumina porcelain. The density changes obviously with the increase of sintering temperature, and the density also changes obviously with the addition of TiO2. It also shows that adding different amounts of titanium dioxide and sintering temperature has a double effect on the density of alumina porcelain.

Adding a small amount of magnesium oxide to the alumina sample with titanium oxide can refine the crystal grains while maintaining the anisotropic morphology of the alumina grains. Experiments show that the atomic content of magnesium should not exceed that of titanium. atomic content. If the atomic content of magnesium is higher than that of titanium, the density decreases instead.