abstracts: technology 381 



TECHNOLOGY. — Silica refractories. Factors affecting their quality 

 and methods of testing the raw materials and finished ware. Donai^d 

 W. Ross. Bur. Stand. Tech. Paper No. 116. Pp. 84. 1919. 



The quartz or amorphous siHca of raw sihca brick is gradually 

 transformed to crystal forms of lower specific gravity when the bricks 

 are burned during manufacture, and when subsequently heated in 

 use. Dr. C. N. Fenner, of the Geophysical Laboratory of the Carnegie 

 Institution, laid the foundations for the study of the silica refractories 

 by working out the physico-chemical properties of the silica minerals. 

 Mr. Spotts McDowell applied the results of this work in a study of 

 the permanent, crystal changes taking place in silica refractories on 

 being heated to temperatures usually attained in manufacture. He 

 also studied the effect of such changes on the strength of the brick, and 

 its tendency to spall (fly apart) when rapidly heated or cooled. 



The writer took up the work at this point, in the hope of obtaining 

 some practical applications. He has studied the changes in volume, 

 porosity, and true specific gravity of most of the leading commercial 

 brands of silica brick, and of the raw materials from which they are 

 made, in conjunction with the crystal changes. The volume, porosity, 

 and specific-gravity changes were obtained by computation from the 

 dry weight of a piece, its weight when saturated with water, and its 

 weight when suspended in water. 



The porosities of the quartzites in conjunction with their appearance 

 under the microscope, indicate that impervious, highly metamorphosed 

 quartzites, having tightly interlocking grains, are more apt to be suit- 

 able for the manufacture of silica brick than porous quartzites which 

 have rounded grains. The changes taking place on heating indicate that 

 the best bricks would be produced in manufacture by an extended 

 heating between 1250° C and 1350° C. and a final gradual rise to 

 higher temperatures. From the studies on commercial brick, it has 

 been determined that the true specific gravity of a silica brick is a direct 

 measure of the degree to which the brick has been burned, and in con- 

 junction with the porosity, indicates approximately what the subse- 

 quent expansion of the brick in use will be. Thus, by a simple pro- 

 cedure, the manufacturer can keep an accurate check on the nature of 

 the silica brick he is turning out, and in the same way the consumer 

 can determine what to expect from them in use. D. W. R. 



