| 摘要 |
PROBLEM TO BE SOLVED: To diminish operation time without damaging fluorite single crystal by specifying heating rate up to a preferred temperature in a specific range. SOLUTION: When heat-treating fluorite single crystal, heating rate up to a preferred temperature lower than that of its melting point is set so as to become >=20 deg.C/h. and <150 deg.C/h. When the heating rate is 100 deg.C/h., the yield of fluorite single crystal is excellent as much as that when the heating rate is <=20 deg.C/h. When the heating rate is >=50 deg.C/h., the heating operation time becomes <=1/2 and is extraordinarily shortened. The preferred temperature is preferably the highest one in the total excursion of heat treatment. The heat treatment of fluorite single crystal is usually conducted at about 1,000 deg.C and the above heating rate for heating the single crystal up to the set temperature is adopted without any problem even when such high temperature is set, which leads to the improvement in efficiency because one-step heating rate up to the highest temperature is adopted.
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