Studies on Magnesium Silicates, “Steatite”, Part II

Abstract

The authors, in continuing their previous studies, reported in the present paper the further studies on fine refractory and electric insulating material “steatite”. The results were reported in Japanese, which are here briefly abstracted, as following:(a) The effects of serveral plastisers on moulding, shrinkages of drying and burning, strengths, densities, etc., were systematically studied and the following results were obtained.Table 1. Results of Comparative Studies on Effects of Various Plastisers (I)* These specimens cracked in water and could not be tested on strengthIt is clearly seen that sodium silicate and borax have no good effects on burning and other physical properties of steatite.(b) F. Reinhard (Tonindustrie-Zeitung, 1932, 56, 323) reported that alkali silicate or chloride has good effect on to produce magnesium orthosilicate (2MgO⋅SiO2) and to make good refractories. Hautefeuille (Ann. Chim. Phys., 1865, 4, 175) also reported that magnesium chloride has the same effect. The next table shows the results of studies on the effects of addition of magnesium chloride, which are better than those of sodium silicate and borax shown in the above table 1.Table 2. Results of Comparative Studies on Effects of Various Plastisers (II)It is seen from these results that magnesium chloride gave slightly good effect.(c) Nextly, it was studied that the relation between the compressive strength of the products and the moulding pressure, the amount of moulding water. The results were tabulated in the following table 3.Table 3. Relations between Moulding Pressures, Amounts of Moulding Water, etc. and Compressive Strengths of SteatiteFrom these results, it is clear that the compressive strength of the products depends li early on the moulding pressure, and the greater the moulding pressure is, the better the physical strength of the steatite. Relating to the amount of moulding water, E. A. Schoenberg (Elektrochem. Zeitschrift, 1933, 23, 545) reported on the dry moulding (Trockenpressung). The authors studied also on this point, which will be reported hereafter.(d) Compressive strengths of the specimens during heating at high temperatures (600°C and 10000C) were tested by the small cylindrical test pieces (Dia: 2cm and Length: 2.5cm) and compared the results with those of chamotte refractory materials (S. Nagai and S. Mannami, this Journal, 1930, 38, 788). The compressive strengths of steatite at high temperatures (600°C, 1000°C, etc.) were lower than that at the room temperature, this fact being quite contrary to that of chamotte refractories, as shown in the following table 4.Table 4. Results of Compressive Strength Testing at High Temperatures(CL-211 was the sample moulded by 2% solution od magnesium chloride)The steatite has far greater compressive strengths than those of chamotte refractories and it must be tested on at higher temperatures, which is now being studied and will be reported hereafter.(e) Spalling test was carried out by treating the small cyliindrical test pieces (Dia: 2cm and Length: 2.5cm) heating at 1200C for 30 minutes, throwing into cold water, and then compressive strengths, densities and porosities were compared to those before heat treatment. The results are shown in the following table 5.Table 5. Results of Spalling Tests of SteatiteFrom these results, it can be clearly seen that compressive or transverse srength decreases about 50-60% by heating at 1200°C for 30 minutes and quick cooling, and densities and porosities increase in every cases.The authors are now further studying on various points, e.g., change of molar ratio (MgO/SiO2) of steatite by adding magnesia or silica, thermal expansion, electrical properties, etc., which will be reported in the following reports.