1530608 Single crystal alumina UNION CARBIDE CORP 18 Dec 1975 [20 Dec 1974] 51773/75 Heading B1S [Also in Division Cl] A massive R-plane α-alumina monocrystal of substantially circular cross-section is made by (a) heating alumina to at least 2040‹C to form a me (b) inserting into the melt a seed rod of unicrystalline α-alumina having an orientation such that its longitudinal axis is normal to an R-plane of the seed rod; (c) maintaining an atmosphere over the melt which is substantially chemically inert to the me (d) withdrawing the seed rod so as to pull a massive unicrystalline product having a growth axis common with the longitudinal axis of the seed and (e) rotating the seed rod at such a speed that the major axis of an elongated end portion facet 64 (Fig. 4), lying in a plane perpendicular to the longitudinal axis of the formed monocrystal, is at an angle of 90Œ15 ‹ to the plane defined by the C-axis and the longitudinal axis of the monocrystal. In Examples, bowls of about 2.4 ins. dia. are pulled using seed rods rotating at 10 rpm.
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