Materials Of Machines - 1903 Author:Albert W. Smith Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III REFRACTORY MATERIALS Crucibles and the linings of furnaces, ladles and other apparatus for metallurgical purposes must be made of materials havin... more »g suitable resistance to fusion, to change of form at high temperature and to wasting by chemical or erosive action; also these materials must be so constituted as not to interfere with desired chemical changes, or to cause undesirable chemical changes, in the materials treated by the process. Acid, neutral or basic linings for furnaces. — Temperatures of incipient fusion of pure refractories are approximately as follows: Silica, SiO2 (acid) 3200 F. Aluminum silicate, Al2Si2O7 (neutral). . 3300 F. Chromic oxide, Cr2O3 (neutral) infusible Carbon, coke or graphite (neutral).... infusible Alumina, Al2O3 (basic) 3600 F. Lime, CaO (basic) 4500 F. Magnesia, MgO (basic) 4500 F. This table shows silica to be the least satisfactory material for use as a refractory, considering only the temperature of fusion. But, because of other qualities, it is used very extensively where the temperature to be sustained is safely below fusion point. Lime, CaO, in contact with aluminum silicate at high temperatures yields calcium silicate and calcic aluminate,and the mixture is fusible at a relatively low temperature, probably about 2000 F. If magnesia is substituted for lime there is a similar reduction of fusion temperature. Hence, lime or magnesia would act as a flux upon aluminum silicate; and, conversely, aluminum silicate would act as a flux upon lime or magnesia. Hence, wherever alumina, silica and lime are in contact, or wherever alumina, silica and magnesia are in contact, if the temperature is above 2000 F. fluxing will take place; that is, the material will melt. In certain cases this melting is desirable, ...« less