sintering at 1'750" and G5O"C., respectively. Thermal expansion data were obtained over a temperature range from 100" to lQOO°C. for MgO-W and from 100" to 600°C. for silica glass-41. Data obtained are plotted as the experimental points in Fig. 1. Calculated curves are shown, based on the following: Al, p = 2.i0 gm. per cc., E = 10.1 X lo6 lb. per sq. in.; \IT, p = 19.3. E = 51.5 X lo6; fused silica, D = 2.20, E = 10.1 X l o G ; and MgO, p = 3.58, E = 30 X lo6. The calculated values and the experimentally determined values of expansion coefficient are in good agreement. This leads one to accept with confidence equations (I), (2), and (3) for WhfgO and ALSO2 compositions and for other ceramic systems.Calculations of stresses on this basis leads to values which make grain separation understandable in many systems, and it is known that this process gives expansion hysteresis in systems such as A12Ti051(e) and TiO?.'(f) Similarly, thermal conductivity anomalies in some systems may be explained on this basis. As an example, calculation of stresses on cooling fused silica to room temperature after devitrification to lOyo cristobalite indicates stresses of several hundred thousand pounds per square inch, so it is not surprising that the product should be friable. I n general, it is felt that phenomena based on the microstresses observed in ceramics are more common than has often been recognized.
ConclusionsExperimental data for thermal expansion coefficients in two systems are in good agreement with predictions based on the presence of substantial microstresses. The magnitude of stresses due to differential thermal expansion of body constituents are substantial and these stresses have a large effect on the resultant thermal expansion of the composite body.The total sulfur in glass in the range 0.01 to 1.0% SOI can be rapidly estimated by an induction furnace combustion method using standard commercial equipment. The results compare favorably with the classical barium sulfate precipitation procedure and with X-ray fluorescence analysis. The sulfide sulfur in glass can be determined by solution of the sample with hydrofluoric acid in the presence of silver ion, followed by titration of the amount of silver precipitated.
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