The amount of light-emitting-diodes（LEDs）using gallium（Ga）for lighting unit is now increasing and the amount of disposal of lighting unit using LEDs is also increasing. It is important to establish a recovery method of Ga from used LEDs, because Ga is regarded as rare metals. It is known that Ga compounds are vaporized in a high temperature reducing atmosphere. Using this reaction, we proposed a method to deposit the vaporized Ga compound on a heat resistant plate with moderate gas permeability. In this research, the optimum reaction conditions were examined and the mechanism of recovery of Ga was investigated. As a result, we showed that it is possible to recover the Ga compound in a yield of about 16% by vaporizing the Ga compound.

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Thermal stablilty of polycrystalline wool（PCW）heated in hydrogen atmosphere were investigated. Two types of PCW samples, namely, PCW block and PCW bulk-fiber were used in this study. The samples were set in the tube electric furnace. Hydrogen gas introduced from inlet of the tube furnace at the rate of 200 ml/min. The temperature was raised at the rate of 5 ºC/min up to 1600 ºC. The samples were soaked for 5 h at 1600 ºC and then cooled down at the rate of 5 ºC/min. In the case of PCW block, the weight loss of samples added silica as a binder was higher than that of sample added alumina as a binder. This result suggested that a part of SiO2 added as a binder was reduced to SiO by hydrogen and SiO volatilized outside as gas. In the case of PCW bulk-fiber, amount of weight loss which was calculated from change of SiO2 concentration measured by EDX was in good agreement with observed one. The results of weight loss and XRD indicated that reduction reaction of mullite phase by hydrogen was occurred during heat treatment for mullite-based wool.

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