The effect of the size of grog in fire-clay bodies. . ification temperature range, of the temperature of overburning,and hence of the refractoriness of the materials. TABLE 2Porosity of Clays and Bodies Temperature, °C Fireclay Georgiakaolin Grog body 4-8 8-12 12-20 20-40 40-80 80-dust 1150
The effect of the size of grog in fire-clay bodies. . ification temperature range, of the temperature of overburning,and hence of the refractoriness of the materials. TABLE 2Porosity of Clays and Bodies Temperature, °C Fireclay Georgiakaolin Grog body 4-8 8-12 12-20 20-40 40-80 80-dust 1150 1200 1230 1260 1290 1320 1350 1380 1410 1440 12 Technologic Papers of the Bureau of Standards As the curves of Fig. 3 show, the bodies possess quite differentrates of vitrification. At 11500 C the porosity of all the materialswas from 25 to 30 per cent with the exception of the Georgiakaolin, which was per cent. These are characteristic values. 1150 1230 1290 13ZO 13SO 138C> 14-70 74-4C Fig. 3.—Relation between porosity and temperature of burning of clays alone and of bodies containing grog for the types of clays represented. The Georgia kaolin had a highrate of vitrification below 13800 C at which temperature its porositywas only a little lower than that of the fire-brick bodies. Hence,when added to fire-brick mixtures the kaolin decreases the strength, Size of Grog in Fire-Clay Bodies 13 since it decreases the amount of fused or vitrified material in thebrick. The fire clay had an average rate of decrease of porosityamounting to per cent per 300 from 11500 C to 12300 C and cent per 300 from 12300 C to 13800 C. At 13800 C overburningbegan, due to the formation of a vesicular structure. The addition of an equal weight of grog of any of the sizes indi-cated from 4 to 8 mesh to 40 to 80 mesh lowered the rate of decreaseof porosity to an average o
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