Masaaki Mishima

Sulfurization Process of Surface Oxide in Calcium Sulfide Powder

The sulfurization processes of the oxide phase existing on the surface of calcium sulfide powder were studied using thermogravimetric analysis, differential thermal analysis and an X-ray diffraction measurements. According to the results and to thermodynamic considerations, the mixture of calcium oxide and sulfur showed some weight loss starting at a temperature lower than the boiling point of sulfur. An X ray diffraction peak of calcium sulfate was identified in this mixture specimen after heating to 1200•Ž under argon atmosphere. Sulfurization of calcium oxide by sulfur was thought to be occurred at temperatures bet ween 200•Ž and 300•Ž from the viewpoint of thermodynamic considerations. [Received November 4, 1997; Accepted February 20, 1998]

Microstructure and Mechanical Properties of Hot-pressed Silicon Nitride Ceramics

Publisher Summary Silicon nitride (Si3N4) ceramics have excellent properties such as strength, toughness, and wear resistance compared with other ceramics and have been expected to apply many mechanical and structural parts. Densification during sintering process progresses accompanied with α-β phase transformation. Therefore, the transformation rate is affected by states of starting powders and sintering conditions. Also, the addition of oxide sintering aid affect to the phase transformation. It is expected that properties of silicon nitride ceramics are influenced by amounts and kinds of sintering aids. This chapter discusses an experiment wherein starting powder of Si3N4 was Ube SN-E10 and Y203 powder was produced Nippon yttrium (>99.9% purity, 0.4μm in diameter), CeO2 was produced by Shinetsu kagaku (>99.9%, 0.8μm) and MgO was Ube 1000A (>99.98%, 0. ιμm). Microstructure of the ceramics was observed on fracture surface after bending tests using scanning electron microscope (SEM). β-phase fraction of the ceramics was calculated from the intensity of X-ray diffraction peaks.