Heat Exchange Method

Heat exchange method referred HEM method.Heat exchange method is a method for

a schematic diagram of the heat exchanger method

growing large sapphire crystal growth technology and invention.1970 Schmid and Viechnicki first heat exchange method using a large piece of sapphire crystal growth.The principle is to use a heat exchanger to dissipate the heat , so that crystal growth region is formed at the cold temperature of the hot longitudinal,gradient , and then by controlling the gas flow in the heat exchanger (He cooling source ) to change the size of the heating power level to control the temperature gradient within the crucible to reach a molten metal from the bottom up slowly solidified into crystals of the objective Figure shows a schematic diagram of the heat exchanger method.Main features of the method :

1)The temperature gradient opposite to the field of gravity , crucibles , crystals, and neither heat movement crystal growth
Long interface stability, no mechanical perturbations , buoyancy convection is small, eliminating the mechanical movement caused by crystal defects ;

2)Remain after the crystal growth in the hot zone , the control temperature of the helium flow rate can slow, the crystallization temperature
Reduced , to achieve in-situ annealing , to reduce the crystal and the resulting thermal stress cracking and crystal dislocations and other defects;

3)Solid-liquid interface in the melt inclusions , the thermal disturbance before reaching the solid-liquid interface can be reduced or even
Excluded , the interface obtained a uniform temperature gradient ;

4)Heat exchange method is the most suitable for the growth of various shapes and sizes sapphire crystal ;

5)Equipment demanding conditions , the entire complex process, crystal growth cycle is long, requires a lot of cold helium,coolant,high cost. Heat exchange method is mainly applied in the United States and developed the process for the United States Crystal Systems company's patented technology.Crystal Systems Corporation heat exchange with sapphire crystal grown by more than 30 years of history, represents the highest international standards .

Chandra , who use heat exchange has grown out of the diameter ¢ 200mm, ¢ 340mm ¢ 380mm diameter and height ratio 2:1 high quality crystal , as shown in 13b, c shows,and hopes to eventually be able to grow in diameter ¢ 750mm optical grade sapphire crystal.

Note:

(a) Schematic crystal furnace ;
(b) sapphire crystal ¢ 380mm;
(c) sapphire crystal ¢ 340mm