Preparation And Research On The Polycrystal Transparent Alumina

Polycrystal transparent alumina is the better base material used in the fields of optics and illumination and laser etc. In the work, the performance of the high purity alumina powders as material making for transparent alumina are researched and prepared; By adopting solid-state sinter method, the factors effecting on the crystal structures of the transparent alumina are also investigated and the transparent alumina productions with uniform crystal structures are developed successfully; Finally the high purity alumina powders and transparent alumina productions are produced in the industrialization.1 Through research on dynamics and thermodynamic of the process of vitriol salt decomposed in the heating for prepared the alumina powder, the new technics of control crystallization and grain growth speeds by three heating procedures in the non-pressure air is offered and worked out, the 99.99% purity's powder with characteristic of activity and round-like and grain distributing narrow is obtained in the industrialization.2 The properties of the high purity powder prepared of vitriol salt decomposed in the industrialization is researched and token by X-ray diffraction qualitative analysis and scanning electron microscope and specific surface area test etc., the new phases transfer equation is offered as follows:The soft agglomerates caused by gravitation existing among molecules is the main badly phenomenon in the purity alumina powder, But the alumina powder of original grains' size over 450nm (specific surface area less than 3.33m²/g) is dispersal area.3 The firing characteristic is that the densification and grain growth are carried out simultaneity less than 1420℃and the densification is sharp in the 1420-1600℃range , the grain growth is mainly over 1700℃. Based on data of firing densification , the densification curves and equations are described.4 By analysis on the apparent properties of alumina powder effecting on the crystal structures of the transparent alumina ceramics, it is founded that the round-like powders is benefit of making the hexagon crystals, its size is inverse ratio with the specific surface area; the alumina powder of lower specific surface area is more in favor of the stabilization of the crystal shape and structures; Al₂O₃ slurry of the Newton type with better dispersing properties is the need condition of forming the uniform crystal structures of the transparent alumina ceramics.5 By Research on different additives effecting on the crystal structures of transparent alumina ceramics, it is founded that MgO-doped is in favor of forming the uniform crystal structures due to the Al₂MgO₄ phase restraining to non-{0001} side with higher interface energy , and it's content can control the size of the crystals; ZrO₂ and TiO₂ -doped can promote solid-state reaction and form uniform structures , but may reduce the strength and optical transmittance of ceramics in a certain due to forming solid-solutions with lower melting point; Y₂O₃ and La₂O₃-doped may disturb crystal structures due to chroma's non-equably, but may increase optical transmittance due to enhancing the the green body's pores eliminating.6 By adopting the high purity alumina powder with like-round grain and appropriate the technics routes and parameters, and sintering in the kiln with non-pressure hydrogen gas, the transparent alumina productions with uniform crystal structures are obtained in the industrialization. The optical transmittance of single light in 600nm is up to 50% and is the best level of used solid-state sinter method .