Powder feeder for crystals of large diameter grown by the verneuil technique

Abstract

To grow crystals of large diameter (= 50 mm) by t h e flame fusion process it is necessary t o feed powder with a flow rate of = 2 g/min into the gas stream, the grain size being as small as possible. The properties of vertically and horizontally excitated sieves are compared. A sieve arrangement with horizontal and vertical vibration is described, which at a mesh width of 90 pm has a powder flow of up to 5 g/min. The long range constancy was within f8Y0. Sieves with a mesh width < 90 prn can be used if a n ultrasonic disintegrator is mounted above the feeder sieve. Sapphire and Mg-A1 spinel crystals up to 65 mm in diameter could be grown.