Studies on Some Physical Properties of Steatite Products

Abstract

Several poor plastic or non plastic refractory materials such as, silica, alumina, magnesia and steatite were studied on their physical properties, effected by their various moulding pressures and quantities of the binder. In this paper, however, some experimental data with only a steatite are reported.The steatite used for electrical insulating materials of vacuum tubes of many kinds was a non plastic material. Therefore, how to mould or how to form the insulators was a very important problem. The raw material was temporarily given various quantities of some organic binders for the purpose of forming green products, and then pressed in an iron mould by a hydraulic press under various pressures. Mechanical strength, thermal expansion coefficients, porosities, densities and moulding pressures of the burned and green products were measured, and their relations to each of them were investigated and explained under some assumptions of distribution of moulding pressures in the specimens, with an aid of some experimental formulas applicable to testing materials, and summarised as following:1 When moulded with no binder, the transvers strength of the burned products could be linearly increased by being increased the moulding pressure.2 In the case of an excess quantity of binder was added, the transvers strength of the burned products showed a rapid approach to the saturating constant value with increasing the moulding pressure.3 In the case of a moderate quantity of binder was used, it was found that there were maximum and minimum values in the process of increasing the moulding pressure.4 The transvers strength of the burned products was found to have a strength of nearly maximum value when they had a saturated mechanical strength in the green state.5 Expansion coefficients of the burned products were constant independently of their moulding pressures, whiles the cristobalite effect at about 270°C (extraordinary expansion due to the transition of α→β cristobalite) had a maximum value for a certain moulding preasure.6 A decrease in porosities were produced by a decrease in the quantity of the binder and an increase in the moulding pressures. The mechanical strength of the burned products of lower porosity was larger than that of higher one.7 The expansion of the green products when knocked out freshly from the mould could be decreased by being increased their moulding pressures and the quantities of the binder.