Guna S Selvaduray

AbstractAbstractSeveral technologies have been reported for the synthesis of AlN. These are reviewed and described in detail. The processes are classified according to the principle of synthesis, and the AlN product characteristics for each method of synthesis are identified. Only two of the methods reported, direct nitridation and carbothermal reduction, are currently used industrially. Due to the requirement for higher quality AlN powders, several other methods are being developed. The level of development, the principle of synthesis, the raw materials used, the reaction products, and the powder characteristics of the synthesis methods are discussed. Where appropriate, environmental or safety concerns are identified. Process flowcharts for each of the technologies were developed on the basis of information available.MST/1794

Alloys of NiTi have gained popularity in biomedical applications; however, Ni is known to cause toxic and allergic reactions in the body, and concerns have been expressed regarding the material's biocompatibility. In this study, coupons of equiatomic NiTi were prepared by four methods, namely, mechanically polishing to a mirror finish, electropolishing, chemical etching and argon plasma etching, to produce various levels of roughness, and then examined by atomic force microscopy (AFM), XPS and AES. The resulting surface chemistry depended upon the method of preparation and was found not to be a function of surface roughness. The mechanically polished samples, although having the smoothest surface, showed the highest level of Ni in the near-surface region. The other preparation methods produced surfaces that were predominantly TiO2, with the electropolished surfaces showing the next smoothest surface and the least Ni in the near-surface region. The correlation between method of preparation, surface roughness and surface chemistry may be important in the preparation of NiTi for biomedical applications. © 1998 John Wiley & Sons, Ltd.

Shape memory and superelastic capabilities coupled with good biocompatibility give Nitinol the ability to provide functionality seldom possible with traditional engineering alloys. In this study the effect of heat treatments of 300 ∼ 550°C for 2 ∼ 180 minutes on Ti-50.8%Ni (at.%) wire of 30% and 50% cold work was investigated. Transformational and mechanical properties were characterized through the bend and free recovery (BFR) method and tensile testing. Thermally activated precipitation and annealing processes occurred. Annealing processes tended to increase the slope and the total strain recovery of the BFR plots. Two TTT diagrams were constructed illustrating the trends in the Austenite Finish Temperature (Af) of the wires. A maximum precipitation rate occurred at approximately 450°C. Precipitation strengthening was evident in both 30% and 50% cold-worked wires. However, only in the former did an increase in UTS occur. Recrystallization began at approximately 450°C for both wires.