Notes on the Constitution of Steatite 443Similar maxima were observed when barium carbonate was progressively substituted for the 50 parts of magnesium carbonate in body I. The maxima in Q and specific resistance illustrated in Fig. 5 occur when half of the magnesium carbonate has been replaced. Not enough values were determined to locate these maxima exactly, and the curves were intended to indicate simply the presence of such maxima. The important observation is that better ceramic products may be produced by the correct combination of two or more alkaline earth oxides as fluxes than by the use of any one by itself.The results of studies on the effects of methods of preparation, firing schedules, additions of small amounts of alkalis, and the nature and quantities of impurities in the raw materials will be discussed in a future paper. X-ray and microscopic studies are also being pursued in an attempt to furnish a theoretical explanation for the results presented in this paper. VI. SummaryVariations of the ratio of talc to kaolin within certain limits have little effect on the dielectric properties of low-loss ceramics whose principal constituent is talc.Large variations in the dielectric properties are caused by variations in the amounts, proportions, and kinds of alkaline earth oxides added as fluxes t o a talckaolin mixture.The conditions in a ceramic favorable to high specific resistance are not necessarily those favorable to low dielectric loss.Differences in dielectric properties of steatite ceramics are more evident in measurements at high temperature than in those at room temperature.(I) (2) (3) (4) BELL TELRPHONE LABORATORIES 463 WEST STRBRT NEW YORK, N. Y. ABSTRACTA review of the literature 'is given. A number of steatite bodies, which were given a varying number of firings, were investigated by autoclaving and determining the water absorption in conjunction with microscopic and X-ray methods.
9considerably greater than that extracted by the dilute acid. This should have been expected because alkaline solutions (such as those in accelerated distilled water tests) are known to corrode glass surfaces considerably more than acidic solutions. The total material extracted by acids (when weighed as sulfates), in general, is between two and three times the amount of titratable alkali calculated as NaOH. The total material extracted in a water test, when weighed as sulfates, is between four and five times the amount of titratable alkali calculated as NaOH. This unquestionably is due to a difference in the mechanism of attack of acidic and alkaline solutions because it is highly probable that of the total amount of material extracted in the accelerated acid test a t least 40 to 50% is alkali oxide, whereas of that extracted in the accelerated distilled water test, only 15 to 20% is alkali oxide. OWENS-ILLINOIS GLASS COMPANY GENERAL RESEARCH LABORATORY TOLEDO. OHIO ABSTRACTPower factor measurements at frequencies of 100,500, 1500, and 5000 kilocycles were made on a series of soda-lime-silica glasses and on another series of glasses, starting with a base glass of the composition of 17.4% NaeO, 10.1% CaO, 72.5% SiOz (or 1.4 NazO to 0.9 CaO to 6.0 %On), to which 0.030 gram-atom of various elements in the form of their oxides were added. In the first series, the power factor for all glasses measured decreased with increasing frequency and increased markedly with increase in NazO content. In the second series, the power factor decreased with increasing frequency as in the case of the first series. An increase in power factor was produced by additions of Zr. Na, and A1 oxides, and a decrease was produced by additions of the oxides of
Phosphate-bonded talc shows advantages over block talc, which indicates that it is a superior substitute for this strategically important raw material. A satisfactory product has been made using talc from domestic sources. It has been formed by various methods, such as dry pressing, hydrostatic pressing, or hot pressing. Some factors that control the properties of the end product have been investigated, and the mechanical and dielectric properties are compared with those of natural block talc.
The requirements of physical properties for high‐frequency insulators arc outlined The three groups of ceramic materials especially suitable for high‐frequency insulation arc steatite, cordierite, and rutile bodies The properties and manufacturing problems in connection with these three groups of materials arc discussed.
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