Research On Gel-casting Forming Technology And Pressureless Sintering Densification Mechanism Of Hexagonal Boron Nitride

Hexagonal boron nitride is a kind of ceramic materials with flat structure, having high melting points, low hot expansion coefficient, high thermal conductance rate. But its sintering performance is relatively bad. The main sintering method of hexagonal nitrogen boron ceramics is hot pressing sintering at present, but the geometry of the products is obvious restricted by hot pressing sintering method. And as a lean material, hexagonal boron nitride is difficult to form complex shape, it is difficult to get complex shape green by conventional forming technology. So pressureless sintering process and new forming technology of hexagonal boron nitrogen is necessary to study at present.By introducing the concept of organic monomer polymerization chemistry into the ceramic forming techniques, gel-casting of ceramics has become a novel forming method by which a ceramic green body with good uniformity and high strength can be prepared. In the paper, in order to prepare a concentrated suspension with low viscosity and high solid volume content is studied. The rheological properties of h-BN suspensions with two dispersants, PAA and modified PMAA-NH4, were compared. The results show that PAA is more effective than modified PMAA-NH4 which is used frequently.The complex shape green body of hexagonal boron nitride obtained by Gel-Casting forming technology is studied in this paper, it is focused on effect of organic monomer content and proportion on colloid character, collide gelling behavior of slurry added initiator, effect of activator on gel gelling performance, effect of monomer and initiator content on green body gelling character as well as.Thinking about t-BN has been considered to be the effective method to resolve the h-BN pressureless sintering densification question. We synthesis t-BN (turbostratic boron nitride) powder by urea and boric acid. The t-BN powder was analyzed by XRD, SEM and laser granularity analyzer. The results indicated that the BN powder synthesized was pure t-BN and particle size was sub- micron. The particle shape was globular.This paper has researched the pressureless sintering performance of hexagonal boron nitride,with Al₂O₃, Y₂O₃ and B₂O₃ as the additive, under N₂ atmosphere, pressureless sintering at about 1800 °C degrees. Result of study indicates that with increase of the content of Y2O3 and Al₂O₃, the density and the intensity of sintering body...