Growth of Quartz Crystals by the Hydrothermal Reverse TemberatUre Gradient Method

Abstract

The hydrothermal growth of quartz crystals has been carried out generally at high filling such as 75∼85%. The growth rates lessen with a decrease, of, filling, and the seeds which are suspended in the growth zone dissolve at a filling of 40% or below. In this experiment, the growth of quartz crystals with a filling of 40% or less, i. e.10∼40%, was carried out by the hydrothermal reverse temperature gradient method, the method whereby the nutrient material was placed at a low temperature (upper side of autoclave) and the seed crystals 'at a high temperature (lower side of autoclave) in Na'OH and Na₂CO₃ solutions. The growth rates were almost identical at 36% and 40% fill, about 1/2 as fast at 20%fill and extremely slow at 10%fill., The dependence of the growth rates on the filling' showed the same tendency in both solutions. The relative growth rates for the Z, X, 'R and r faces were Z>X>r>R. A cre vice flawing was observed on the Z face which exhibited sawtoothed patterns. But the growth in R, r and X directions was flawless and transparent. Spontaneously nucleated crystals were observed conspicuously on the inner wall of the autoclave, but they decreased with a reduction in temperature difference.