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doi: 10.1111/j.1151-2916.1947.tb18883.xpmid: N/A
Abstract Experiments, which included the development of methods of measuring the linear rates of crystal growth and crystal solution and a study of surface crystallization, were conducted on commercial‐type glasses. A method of studying interdiffusion of two glasses of similar composition is described but no conclusions were reached. It was found that (a) the rate of crystal growth is constant until the crystallization zones from the opposite surfaces meet and (b) the curve of crystal solution is continuous with that of crystal growth as the temperature is raised above the liquidus temperature. The results indicate that dust in the atmosphere is a major contributing factor promoting surface devitrification.
doi: 10.1111/j.1151-2916.1947.tb18884.xpmid: N/A
Abstract Measurements were made of the rates of crystal growth in a series of glasses with 74% SiO2, 16% Na2O, and 10% (CaO + MgO), the MgO replacing the CaO in 2% steps; and in a series of glasses with 17% Na2O, 12% CaO, and 71% (SiO2+ Al2O3), the alumina replacing the silica in 2% steps up to 8% Al2O3. A study was also made of the rate of crystal solution in the series with variable alumina. The results are explained qualitatively by considering the viscosity and crystallization temperature changes of the glasses as the composition varied. The substitution of MgO for CaO to the composition with the minimum liquidus decreased the maximum rate of crystal growth of cristobalite (primary phase) and devitrite (secondary phase) and further substitutions increased the rate of crystal growth of diopside and Na2O·2MgO·6SiO2. Substitution of Al2O3 for SiO2, decreased the maximum rate of crystal growth of devitrite, and substitutions of more than 4% of Al2O3 increased the rate of crystal growth of wollastonite.
doi: 10.1111/j.1151-2916.1947.tb18885.xpmid: N/A
Abstract The ultraviolet transmission of Vycor brand glass No. 791 is compared with that of certain commercial glasses and fused silica. The loss in transmission after 230 hours of exposure to ultraviolet radiation (2537 a.u.) from a Hanovia arc was 2.5% for No. 791 glass and 32.5% for Pyrex brand glass No. 9741. The loss (approximately 12%), due to the darkened layer which forms on a glass surface in contact with a mercury arc, is smaller for No. 791 glass than for glasses in general. The decrease in 2537 a.u. output of experimental lamps was determined after operation times up to nearly 6000 hours; after 5000 hours, No. 791 glass showed 27% loss in hot cathode lamps and Pyrex brand No. 9741 showed 53%. Vycor brand glass No. 7911, developed for medium‐pressure arcs (such as sunlamps), is discussed. The electrical properties of Vycor brand No. 791 are resistivity at 350°C., 9.2 (log R, ohm‐cm.); loss factor at 1.0 mc., 0.00091; and dielectric constant, 3.8.
doi: 10.1111/j.1151-2916.1947.tb18886.xpmid: N/A
Abstract The effects on the crystal stabilization and other properties of pure zirconia were determined for additions of CaO, MgO, BeO, ThO2, and CeO2 in binary and ternary combinations. Complete stabilization was attained with the following compositions (in mol. %): 10 to 20 CaO, 14 MgO, 26 CeO2, 10 CaO + 5 ThO2, 10 CaO + 5 BeO, or 2 to 7 CaO + 4 to 6 to MgO. Cerium oxide produced partial stabilization, but BeO and ThO2 used alone were ineffective at 1927°C. Some strong, dense bodies were found which had good resistance to thermal shock, namely, those containing (mol. %) 8 to 12 CaO, 6.7 CaO + 3.7 MgO, or 2.3 CaO + 6.4 MgO; all of these compositions still had a small amount of inversion present. This small inversion may be necessary for high resistance to thermal shock in ZrO2 ware because (a) the over‐all thermal expansion is then small and gradual and (b) with complete elimination of inversion, the expansion is large since the expansion curve is a straight line and the coefficient of expansion is rather high, 11 to 12 × 10‐6.
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