Crystal pulling apparatus

Note that we have not shown the R.F. generator. However, we have shown one design of the pulling apparatus (there are many). Here, we have shown the mechanical parts of the apparatus in addition to the arrangement of the crucible and melt already shown in 4.2.6. A reversing motor is used to turn a precision screw to move the pull rod away from the melt in a precise manner. The function of the puU-motor" is to turn the crystal so that it grows in a regular manner. You will note that we did not show a temperature sensor at the bottom of the crucible. This control is optional and can be used to monitor the bottom temperature of the... 

The apparatus consists of a normal Czochralski melt with an anvil at the surface of the melt. Once the crystal has started to grow, we pull it through the anvil, thus defining its size. Once it is in the form of a strip. 

The apparatus must be completely dry and protected from atmospheric moisture. The filter o is pulled up and the tube closed by a pinch-clamp e. The reaction mixture evolves heat on agitation and crystals of Si(Ac) precipitate at once. The mixture is allowed to stand for several days. It is then cooled with Dry Ice, and filter o is lowered until it reaches the supernatant liquid, which is siphoned into the suction flask. Acetic anhydride (100 ml.) is now added to the residue in a, the crystals are dissolved by heating at 100°C and allowed to recrystallize by cooling to 0°C, and the mother liquor is removed as above. A second re-crystallization proceeds in the same manner, but with 75 ml. of acetic anhydride. The solution adhering to the crystals is removed by evaporation, first at room temperature and then at 100°C (several hours). The yield is 335 g. or about 85%, based on SiCl. ... 

Glass fibers, up to 0.5 m in length and 5 to 30 jjm in diameter were pulled from the apparatus at rates of 1.0-1.5 m/s before crystallization terminated the process. The fibers had a homogeneous appearance and smooth surfaces. They were transparent, highly flexible, and x-ray amorphous. Glass fibers of this kind, which were also made from erbium- or neodynium-doped yttria alumina compositions, would therefore expand the range of fiber lasers into the mid-infrared. 

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