Effect of void location on segregation patterns in microgravity solidification

Effects of void-induced convection on interface morphology and segregation during low-g solidification

“…The relevant thermophysical properties of gallium arsenide are available in the literature [12,13] and are listed along with some system parameters [9] in Table 1.…”

“…Results suggested that dopant transport was dominated by convection rather than diffusion during growth. Kassemi et al [12,13] have hypothesized that this convective mixing of solute was due to the thermocapillary flow generated by voids in the gallium arsenide melt. Thermocapillary convection is driven by surface tension gradients, which are generated by temperature variations along a free surface.…”

“…Pimputkar and Ostrach [14] first called attention to the importance of understanding thermocapillary flows especially as it pertains to crystal growth. In this context, Kassemi et al [12,13] showed how a typical microgravity crystal growth process can be affected by thermocapillary convection. Their results indicated that void-generated convection can have a significant impact on interfacial segregation patterns especially if the void is located close the growth interface.…”

“…Their results indicated that void-generated convection can have a significant impact on interfacial segregation patterns especially if the void is located close the growth interface. In these studies [12,13] attention focused on the melt region alone by invoking a simplifying assumption that the interface shape is fixed. The interface shape in previous models was extracted from space experiments [9].…”

Contamination of microgravity liquid diffusivity measurements by void-generated thermocapillary convection

“…Examination of the samples in all three experiments revealed the existence of rather large bubbles and voids in the melt region during the growth process. Numerical simulations of the Matthiesen and Majewski [24] experiment by Kassemi et al [32,33] have shown that the transformation of growth conditions from the expected diffusion-dominated regime in microgravity to a fully mixed regime could have been caused by void-driven thermocapillary convection.…”