Al-20%Si alloys containing none or only one of the following addional 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 moulds. Then the alloys were electrolized in hydrochloric acid solution, using lead-plate as the cathode. Silicon crystals thus obtained as the anode slime were collected and subjected to goniometric, X-ray and chemical analyses. From the above experiments, three types of crystal habits of silicon have been detected as follows: (1) Granular crystal, caused by addition of sodium, consisting of {111} and {100} surfaces. (2) Prismatic crystal, caused by the addition of magnesium or zinc to the alloy, consisting essentially of {111} surface, growing in the [110] direction. (3) Platy form crystal, which is most common and is formed in plain binary alloy or alloys, containing one of the following additional elements, Chromium, manganese, copper, cadmium, tin, lead, antimony, bismuth, iron, nickel, and cobalt, consisting of {111} surfaces in which the (111) and the (\bar1\bar1\bar1) surfaces are most predominant. Although a small quantity of the added element was found to be contained in silicon crystals, no marked difference in the lattice constant have been found according to the crystal habit.
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