Crystal Habits of Silicon Crystallized in Al-Si Alloys

Al-20 per cent silicon alloys containing none or only one of the following additional elements, viz. sodium, magnesium, zinc, chromium, manganese, copper, cadmium, tin, lead, antimony, bismuth, iron, nickel, and cobalt, were cooled very slowly or cast in sand molds. Then, the alloys were electrolized in hydrochloric acid solution by using lead-plate as the cathode. Silicon crystals thus obtained as the anode slime were collected and subjected to goniometry, X-ray and chemical analyses. From the above experiments, following three types of crystal habits of silicon have been detected : (1) Granular crystal, caused by addition of sodium and forming with {111} and {001} faces. (2) Prismatic crystal, caused by the addition of magnesium or zinc to the alloy and forming essentially with {111} face growing in the[011]direction. (3) Platy form crystal, which is most common and is formed in plain binary alloy or alloys containing one of the additional elements, chromium, manganese, copper, cadmium, tin, lead, antimony, bismuth, iron and cobalt, and forming with {111} faces in which one pair of the face {111} being parallel to each other is developed best. Although a small quantity of the added element was found to be contained in silicon crystals, no marked difference in the lattice constant has been found according to the crystal habit