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Upon application of nano-sized metallic Ni particles as catalyst, the in-situ synthesis mechanism of spinel whiskers in MgO-C refractories was studied. Their phase composition and morphology were determined by means of X-ray diffractionand scanning electron microscopy supported by energy dispersives pectroscopy. The results show that when the catalyst of nano-sizedNiwas addedinMgO-C refractories, the granular MgAl 2 O 4 (MA) spinels transformed into the shapeofwhiskers at 1200 8 C. The presence of Ni catalyst can accelerate the generation of Mg vapor,w hich can react with Al vapor to form MA spinel whiskers. Through dissolution and precipitation, MA spinelc rystals nucleate directlyand grow intowhiskers from the catalytic droplets of nano-sized metallic Ni particles. The growtho fs pinel whiskersf ollows at ypical vapor-liquid-solid( V-L-S) growthmechanism.

Rare earth iodides are commonly used in ceramic metal halide (CMH) lamps, a kind of high intensity discharge (HID) lamp. Rare earth metals in the discharge plasma inside the arc tube contribute to the superb performance of CMH lamps. On the other hand, however, polycrystal alumina (PCA) arc tube corrosion due to its reaction with rare earth iodides causes the deterioration of parameter maintenance, and constrains lifetime of the lamps. In this study, PCA arc tubes with specific rare earth iodides are prepared. Aging tests up to 2000 hours are conducted to evaluate the effects of single rare earth iodides on lamp performance. Also X-ray analysis shows the corrosion content of PCA arc tube by different rare earth iodides. The result shows that PCA tubes with single rare earth iodides are more corrosive than the mixture of various rare earth iodides.