Reaction Sintering of ZnO‐AI₂O₃

Abstract

The reaction sintering of equimolar mixtures of ZnO and A12O3 powders was investigated as a function of primary processing parameters such as the temperature, heating rate, green density, and particle size. The powder mixtures were prepared by two different methods. In one method, the ZnO and A12O3 powders were ball‐milled. In the other method, the ZnO powder was chemically precipitated onto the A12O3 particles dispersed in a solution of zinc chloride. The sintering characteristics of the compacted powders prepared by each method were compared with those for a prereacted, single‐phase powder of zinc aluminate, ZnAl2O4. The chemical reaction between ZnO and A12O3 occurred prior to densification of the powder compact and was accompanied by fairly large expansion. The mixing procedure had a significant effect on the densification rate during reaction sintering. The densification rate of the compact formed from the ball‐milled powder was strongly inhibited compared to that for the single‐phase ZnAl2O4 powder. However, the densification rate of the compact formed from the chemically precipitated mixture was almost identical to that for the ZnAl2O4 powder. The difference in sintering between the ball‐milled mixture and the chemically precipitated mixture is interpreted in terms of differences in the microstructural uniformity of the initial powder compacts resulting from the different preparation procedures.

Thermoelectric Properties of Solution Combustion Synthesized Al-Doped ZnO

“…In future studies, the effect of this aspect on the thermoelectric properties of Al-doped ZnO should be avoided by improving the SCS process by, for example, adjusting the amount of urea to control the amount of exhaust heat and optimizing the heating temperature of the SCS process. Second, according to a previous study, the spinel phase of ZnAl 2 O 4 can be easily formed from Al 2 O 3 and ZnO when the temperature is higher than 1073 K. 23) In this study, although we did not detect any impurity phases by the XRD analysis, the impurity of ZnAl 2 O 4 was probably formed at the grain boundaries of no PBM samples during SPS, because the powders formed in the absence of PBM were inhomogeneous, which deteriorated the sintering condition, thereby facilitating the synthesis of ZnAl 2 O 4 . Therefore, the second phase of no PBM samples decreased the electrical conductivity.…”

Synthesis and characterization of spinel-type CuAl2O4 nanocrystalline by modified sol–gel method

“…Transition metal aluminates are commonly prepared by a solid state reaction [7], coprecipitation method [8,9], hydrothermal [10][11][12], combustion [13] and sol-gel [14][15][16][17][18][19][20][21][22]. The disadvantages of solid-state routes, such as inhomogeneity, lack of stoichiometry control, high temperature and low surface area, are improved when the material is synthesized using a solution-based method.…”

Enhancement of Hydrophilic Properties of Alumina-Based Ceramics

“…[7][8][9] However, few studies have addressed oxide ceramics, in particular, alumina ceramics. None have examined their water-wettability to improve frictional properties under water lubrication.…”