The absence of convective stability in incongruent crystal growth on Earth

It is often assumed that convection can be excluded in materials processing by avoiding horizontal temperature gradients, and employing top-heating and horizontal interfaces. Model calculations for vapor transport processes show that this supposition holds only for strictly congruent vapor-solid transitions. This result can be generalized to all fluid-solid phase transitions. Due to the omnipresence of impurity segregation, it is concluded that convective stability is practically unattainable in materials processing on Earth.