固相反応法により合成したコバルトブルーの色調に及ぼす原料混合時間と焼成温度の影響

摘要

コバルトブルー(CoO・nAl_2O_3)は,アルミン酸コバルト(CoAl_2O_4)を主成分とする鮮明な青色無機顔料で,その化学的および熱的安定性から陶磁器,ガラス,プラスチックなどの着色顔料として幅広く用いられている.また,特殊な用途として,有価証券の偽造防止ィンキゃ青色蛍光体のコントラスト向上にも利用されている.アルミン酸コバルトの合成法として,ゾルーゲル法,水熱合成法,共沈法,低温燃焼法などさまざまな合成法が報告されているが,原料を乾式混合して焼成する固相反応法が最も一般的な合成法である.%Cobalt blue is widely used as coloring agents in ceramics, glassware, and plastic products, etc., due to the chemical and thermal stability. In this study, the influence of mixing time and calcination temperature on the color tone of cobalt blue was investigated. Cobalt blue particles were synthesized by the solid phase reaction method with cobalt oxide (Co_3O_4) as Co source and aluminium hydroxide (Al(OH)_3) as Al source, respectively. The obtained powders were characterized by CIE-L~*a~*b~* color space, particle size distribution, SEM-EDX, and XRD. The chromaticity coordinate b~* of the calcinated powder was shifted to blue direction, and the chroma represented by c~* became vivid with increasing calcination temperature. This means the color tone of the cobalt blue powder becomes vivid blue. However, the color tone of the calcinated powder barely changed even if the mixing time of raw materials was increased. XRD analysis of the calcinated powder revealed the formation of the single-phase CoAl_2O_4 at 1200 ℃. These results indicate that the color tone of cobalt blue is mainly controlled by the calcination temperature in the solid phase reaction method.