GROWTH OF NaCl CRYSTALS FROM SUBLIMED VAPOR
从昇华的NaCl蒸汽生长单晶体

By sublimation of NaCl crystals of high purity in vacuum at a temperature near its melting point single NaCl crystals of macroscopic size were grown at zones of somewhat lower temperatures. Oriented overgrowths up to 1 mm thick were obtained over the whole cleavage faces of the crystals, but the deposition was muchmore effective on the faees normal to the temperature gradient.The influence of zonal temperature differences and the geometric form of the substrate upon the size and orientation of the crystals have been investigated. The relative importance of faces observed was found of the following sequence: 100> 111>120>122>110. of these the form 122 has not been reported for NaCl crystals growing from the solution. But there is ample evidence from the present experiment that the dominance of 111 over 120 may not be as certain as obsreved for the crystals prepared from solution.In accord with the theory generally held, initial deposition was found to take place statistically more often at the corners of cube faces than elsewhere. New patterns of interpenetration growth and surface structures have been observed and there are features indicating layer growth and screw dislocation.Preliminary experiment was also made on evaporation of a cylindrical NaCl crystal resulting in the exposition of the faces (100) and (120).