No abstract

Carbothermal reduction and nitridation CRN process was utilized to prepare magnesium aluminum oxynitride MgAlON and the influence of reaction variables, such as heating temperature, soaking time and the source of carbon, on the formation of MgAlON was investigated. In addition, the density of samples prepared under different route was compared. The results show that volatile gases, Mg g in chief, lead to variation in lattice constant and chemical composition at high temperature, and decrease the sintering effect. Since high temperature and low CO partial pressure are favorable to the CRN reaction in view of thermodynamic reason and high temperature also favors the transport of gases, the rate of CRN reaction increases with the increasing temperature. Due to the difference in reactivity between graphite and carbon black, CRN reaction may be the rate controlling step when graphite is used and solid solution of AlN may be the controlling step when carbon black is utilized. CRN reaction can increase surface energy of reaction materials and results in higher final density. However, gases in the system retard the densification effect.

Temperature dependence of the electrical resistivity of the Al 4 SiC 4 sintered bodies in the range of 100 1000 C was studied in this paper. Currentvoltage characteristics of the bodies showed a linear relationship, and the characteristics have an ohmic region. Electrical resistivity, obtained from the currentvoltage characteristics, exhibited insulation properties, and decreased with the porosity of the bodies. Further, the electrical resistivity varied signicantly with temperature. However, any dierence in activation energy for electrical resistivity among samples was rarely found despite the dierent porosity of them. Consequently, the porosity of the bodies did not aect the temperature dependence of electrical resistivity.

The composite in Al 4 SiC 4 -AlN and Al 4 SiC 4 -AlN-C system were sintered by a spark plasma sintering method. The powders of metal Al, Si and carbon black and AlN as starting materials were mixed. The mixture was calcined at 1300? C and sintered at 1600? to 1800? C by spark plasma sintering. Shrinkage during sintering, density, microstructure and phase of sintered bodies were measured. X-ray diffraction analysis gave Al 5 SiC 4 N 15R and AlN 2H phases in the bodies sintered at 1750? C. Densification did not occur in some composition in 50 to 80! AlN of the system Al 4 SiC 4 -AlN, but their densification was accelerated by addition of carbon. By the analysis of shrinkage during sintering and SEM observation of microstructure, the grain of Al 5 SiC 4 N 15R and AlN 2H grew, and pore exclusion was obstructed in the system Al 4 SiC 4 -AlN, though the grain did not grow, and pore exclusion was accelerated in the system Al 4 SiC 4 -AlN-C.