Abstract:
The effects of forced convection on the microstructure, macrostructure and macrosegregation of impurities in cylindrical ingots obtained by directional solidification of metallurgical grade silicon were examined. Two experiments were carried out, one without and another with the forced convection induced by a disk at the melt top rotating at 120 rpm during solidification. In the two resulting ingots, two regions exist: (1) a lower region extending from the bottom of the ingot up to 8 mm (without rotation) or 75 mm (with rotation) of columnar grains with straight boundaries, aligned in the heat extraction direction and free from intermetallic particles (except SiC); (2) an upper region of columnar grains with serrated boundaries and intermetallic particles. The lower region, which increases from 8 to 75 mm with disk rotation, is purified and displays concentrations of metallic impurities (except Al) below the recommended limits for solar grade silicon feedstock. The macro/microstructures suggest that the lower region solidified with a planar solid–liquid interface, which changed to cellular/dendritic in the upper region. A mathematical model indicates that, although forced convection increases the growth velocity and decreases the temperature gradient in the liquid, which are detrimental to the stability of a planar solid–liquid interface, convection also decreases the concentration gradient in the liquid, increasing stability.
Referência:
NASCIMENTO, Denir P.; MARTORANO, Marcelo E.; LIMA, Moyses Leite; FERREIRA NETO, João Batista; PADILHA, Angelo F. Effect of forced convection on the purification of metallurgical silicone by Direction solidification. Silicon, 21p., nov., 2023.
Acesso ao artigo no site do Periódico:
https://link.springer.com/article/10.1007/s12633-023-02742-7
