Zone refining of semiconducting elements

The method of zone refining which was first used in the production of very pure germanium depends for its success on the difference between the thermodynamic properties of an impurity, present as a dilute constituent dissolved in 

The removal of impurity in one pass can be calculated by making a mass balance for the advancing liquid phase. If the original impurity content of the bar is Co, and CL is the impurity content of the liquid, then for an advance Sx of the liquid, the amount dissolved into the advancing liquid minus the amount deposited behind the liquid is equal to the increase in the impurity content of the liquid 

In order to calculate the effect of several passes an iterative calculation is needed using the initial profile at each pass to represent Cq. Clearly for the second pass, die concentration profile given in the right-hand side of tire above equation must be used. It is clear that tire partition constant of the impurity between the solid and liquid is the most significant parameter in tire success of zone refining. 

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