Back-Kyu Lee

Preparation of Ti-Mo-Si alloy powders with enhanced high-temperature oxidation resistance using Ti-10Mo scraps

To recycle Ti alloy scraps and enhance the functionality of the recycled scraps, we manufactured low-oxygen contented Ti-Mo-Si powders using two types of ternary Ti alloy ingots which were prepared by vacuum arc melting of Ti-Mo scrap with different amounts of Si. The weight ratio of Ti-Mo scrap was Ti:Mo=9:1 and Si contents in two alloy ingots were 1 and 2 wt%. The alloy powders were prepared by the hydrogenation-dehydrogenation process and the oxygen atoms were removed by the deoxidation in solid state method. We confirmed that the deoxidation process effectively reduced the oxygen content of Ti-Mo-Si alloy powder from 3,350 ppm to 1,700 ppm. In addition, we confirmed that the high-temperature oxidation resistance was increased by adding Si to Ti-Mo alloys. Thermal gravimetric analysis showed that the weight gain of powders by the oxidation was reduced from 8.85% for Ti-Mo to 7.5% for Ti-Mo-Si at 1,500 °C.

Preparation of 6N grade silicon ingot by combined purification processes from waste silicon cutting sludge

Abstract This study is aimed at fabricating ultrahigh-purity silicon ingots from silicon cutting sludge – a byproduct of the ingot for solar cells cutting process. Firstly, silicon powder from the silicon cutting sludge was recovered by 1st purification, such as ultrasonication, centrifugation, and acid treatment before preparation of the silicon ingots. After the 1st purification, the silicon cutting sludge yielded silicon powder with a purity of 99.7612 %. The 1st-purified silicon powder was subjected to 2nd purification – 3 cycles hydrogen plasma arc melting (HPAM), resulting in ultrahigh-purity silicon ingot with a purity of 99.9999 %. HPAM has been verified to be an effective process for removal of B and P – the major impurities of silicon for semiconductors and solar cells – to levels of total ≤ 0.3 ppm.