Study On The Properties Improvement Of Alumia

Fine grain alumina and its tabular alumina toughened one are the focal points in the research field of alumina materials. In the work, the development of alumina ceramics is briefly surveyed, following the summing up of the development together with the toughening and the reinforcement mechanism and theory of the aforesaid materials, many an effort has been stressed on the study of the starting powder preparation, the technology in preparing a fine-grained alumina fired body, and the mechanical properties at ambient temperature of alumina ceramics toughened by tabular alumina have been observed.Applying aluminium nitrate with amonia as the starting materials, the technology in the preparation of a super fine material through wet-chemical way has been discussed. The result indicated that the remaining amonium nitrate decomposes during the calcination and, adding a number of alumina fine seeds, it will promote the transformation of the metastable alumina and decreases remarkably the transformation temperature. By applying the technic, a super fines of 20 and 30 nm have been obtained. In the study of fine grain alumina materials, it has clearly shown that under protective hydrogen atmosphere of pressureless sintering, a result of end material with bending strength of 210Mpa can be obtained. It is, however, the maximum strength and the maximum toughness of the material will not occur simultaneously.To get an understanding of dopants on the effect of the sinterability of alumina, two commonly dopants which are widely used in industries, i.e. MgO and Y₂O₃ have been applied. The experiment has shown that MgO can enhance remarkably the sinterability of alumina, and it shows a favourable effect in the formation of fine-grained end product, while Y₂O₃ has not shown a marked effect on the sintering temperatuer of alumina. This might evidently indicate that different dopants show a different effect on the sinterability of alumina. The experiment of tabular alumina toughened alumina ceramics has shown that the tabular alumina added having a critical grain size, exeeding this value it will lose the toughening and reinforsement effect. In the precent work an addition of 10% tabular alumina has given rise to a favourable bending strength. As the coated tabular alumina will enhance the properties of the slip, some tests have been carried out in the precent work, the experiment has shown that the addition of coated tabular alumina gives rise to a better result, however, owing to the limitation of the experimental condition, the coating technic giving no ideal result.