Studies of the Composition for Graphite Crucibles Consisting of Graphite, Silicon Carbide, Ferrosilicon, Borosilicate Glass and Fluoride

Abstract

In the present paper effects of the composition consisting of graphte, silicon carbide, ferrosilicon, borosilicate glass and fluoride upon the quality of graphite crucibles were studied.In order to confirm these effects, L16(215) type orthogonal array experiment was carried out, in which 5 factors with 2 levels were examined, A: type of borosilicate glass (T-20, T-51), B: borosilicate glass content (10 parts, 15 parts), C: type of fluoride (cryolite, fluorite), D: fluoride content (little, much), E:SiC:FeSi (20:25, 25:20), F: type of graphite (Amo, Cylon), and the water absorption of newlyfired test pieces and both the water absorption and the weight change of above pieces after the oxidation test were measured as characteristic values with results as follows.1) Amo crystalline graphite produced in Japan showed better quality than that from Ceylon.2) The lower silicon carbide composition (SiC:FeSi=20:25) showed better quality than that of the richer (25:20).3) The graphite crucible of the lower borosilicate glass content (10 parts, total being 84 parts) showed better result than that of the higher one (15 parts), and borosilicate glass of the lower alkali content (Na2O+K2O, 4.1%) showed better result than that of the higher one (6.5%).4) Cryolite gave better effect upon the quality of graphites crucibles than fluorite, and the graphite crucible of the 3 parts cryolite content (total being 84 parts) showed better result than that of the 1.5 parts content.5) Finally, cryolite flux containing borosilicate glass showed the best quality of those in the present studies.In this studies it was found that the positive correlation exists among above three characteristic values, so that the quality of graphite crucibles can be judged by any one of these characteristic values.