アナターゼ型TiO₂ナノ粒子造粒粉末を適用した光触媒TiO₂溶射皮膜の相変態挙動と粒子成長制御

抄録

The phase transformation of anatase to rutile and the growth of nano primary particle in agglomerated TiO₂ powder in heat treatment and HOVF spraying processes were investigated systematically. The 200nm, 30nm and 7nm primary particles were agglomerated by spray dry method for the feedstock powders of P₂₀₀, P₂₀ and P₇, respectively. From the heat treatment results of feedstock powders, it was found that the phase transformation temperature of P₇ was 100K and 150K lower than that of P₃₀ and P₂₀₀, respectively. The growth of primary particles of P₇ and P₃₀ happened earlier than their phase transformation, and increased drastically with increasing the heat treat temperature. Under various fuel pressure HVOF conditions, the anatase phase content was between 86% and 5% for sprayed P₇ coating, whereas it was higher than 50% for P₃₀ coating. The particle sizes of P₇ and P₃₀ grew during spraying processes.
The anatase content of collected particles was lower than that of HVOF sprayed coatings in all conditions if phase transformation happened. Although the particle size had not significant change for P₂₀₀, it grew obviously for P₇ and P₃₀. It was considered that the phase transformation and growth of primary particles were frozen for the rapid cooling effect due to the low temperature substrate. Therefore, it was concluded that the coating with high anatase ratio (approximately 100%) and primary particle size of single nano might be developed using the substrate with high thermal conductivity and large heat capacity.