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Sapphire Growth Method- Heat Exchanger Method (HEM)

Heat exchanger method (HEM) is one of sapphire growth method, which is used to grow the sapphire with large size. Since 1970s, Schmid and Viechnicki applied HEM to grow a big sapphire crystal, and the method is used popular and popular.
Its basic principle is to apply a heat exchanger to dissipate heat, making the crystal growth region forming a longitudinal cold hot temperature gradient. By controlling the volume of gas flow inside heat exchanger and changing the heating powder, the gradient can be kept. Then the crystal can grow slowly from the bottom to the upper part. Following is a pic to show the structure and principle of the growing method.

Heat Exchanger Method

The specialties of HEM sapphire growth method are:
1)The temperature gradient inside heat exchanger is opposite to gravity direction. During sapphire growing, the crucible, sapphire crystal and heat exchanger are kept un-moved, so that the crystal growth interface is stable, no mechanical perturbation, buoyancy convection is small, and the elimination of the crystal defects caused due to mechanical movement can be decreased a lot.
2) After crystal growth remains in the hot zone, controlled by a helium flow temperature can slow crystallization temperature uniformity, reduced-situ annealing, reduce the thermal stress of crystals and crystal cracking and dislocation resulting defects.
3) The solid-liquid interface in the melt inclusions, the heat disturbance before it reaches the solid-liquid interface can be reduced and even eliminated, uniform temperature gradient can be obtained at the interface.
4) Heat exchange method is most suitable for the growth of various shapes and sizes of sapphire crystal.
5)Device demanding conditions, the entire process complex, long crystal growth cycle, requires a lot of helium as the coolant, high cost.

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