Nano-alumina Powder And Its Mineral Phase Study

Firstly this paper summarizes the current status of nanomaterial applications and opportunities opened by nanotechnology to many fields , such as new materials , environmental protection , energy , health care , IT and other traditional industries that need upgrade their products . The preparation of ultrafine alumina powder is of far reaching importance to the development of electronic and material industry . Hydrochemical preparation techniques are the important methods to make ultrafine powder of a -AliOs with its intrinsical advantage . It also summarizes the development of the current nanotechnology and nanomaterrial characteries .The optimum technic conditions have been gotten in in preparaing high dispersive A1(OH)3 colloid by controlling reactant concentration , pH value , reaction temperature , matured time . They are the prereguisite to prepare nanopoder of a -A1203 .This paper entirely and systematically studies the following three kinds of drying stages : oven drying , dehydration with alcohols and azeotropic distillation stage . The results show that all of them have little different effect on the crystalline size of ultrafine powder of a -AhC^ ,but they have greatly different effect on the secondary partical size .The azeotropic distillation is the most effective processing , it can prevent the formation of hard agglomerates and improve the sinter-ability of powder .The mechanism of drying stages preventing the formation of hard agglomerates has investigated . Azeotropic distillation stage and dehydration with alcohols can prepare nanocry stalline powders with extremely small crystallite size (40nm). Oven drying only gets powders with 100-200 nm .The effect of calcination precess on the ultrafine of the alumina powder has been studied . The results show that the condition of 11 OO'C and 1.5h is the best to prepare the a -A12O3 powders . Below 1100癈 , the Y- Al^Oj may be prepared from A1(OH)3 powders , when the time is below 1.5h ,a little Y - AljOj may be fond among the powders . If the calcination time is too long , much more energy will be wasted , and the hard agglomerates may be formed .This paper studies the effect of dispersant on the properties of alumina powders . The results show that the adding time of dispersant is important to the fabrication properties of alumina powders . it also shows that the dispersant is added before reaction will be better than after .So the dispersant is an effective way to eliminate water from the gel . Therefore , the agglomeration state in the obtained powder was well controlled by adding dispersant . Ultrafine a -AhOa powder with average crystalline size of 27nm and spherical secondary partical shape of 40nm has been prepared by the method of adding dispersant before reaction .After discussing the agglomeration mechanism , the paper studies the way to eliminate the hard agglomeration . It thinks that main reasons to lead to agglomeration are larger specific surface area and high reactivity of nanopowder .