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doi: 10.1111/j.1151-2916.1948.tb14287.xpmid: N/A
Abstract Some evidence leading to the supposition that certain borosilicate glasses containing a high percentage of silica are made up of two‐component glasses is presented. One of these components, which consists mainly of silica and has a low expansivity, forms a rigid network throughout the body of the glass while the temperature is still high enough to maintain the other component in a liquid state. At lower temperatures, the latter component also forms a rigid network that is intricately entwined with that of the high‐temperature component. The composition of the network that forms at relatively low temperatures is presumably not unlike that of a borosilicate glass containing a moderate percentage of silica. Consequently, the expansivity of this low‐temperature component is definitely higher than that of the other. Because of the difference between the expansivities, the low‐temperature component, as soon as it behaves as a rigid network on cooling, compresses the high‐temperature network and is correspondingly distended. By cooling very rapidly, these elastic strains are developed at temperatures within and even above the upper part of the annealing range of the low‐temperature component. When such strains are developed at high temperatures, they are relaxed by heat‐treatments at lower annealing temperatures, and this relaxation causes an expansion of the undercooled glass while at a constant temperature. However, in the early stages of the treatment, the expansion caused by the relaxation of the strains may be overshadowed by a contraction that results from the shrinkage of the low‐temperature component as it approaches equilibrium from its undercooled condition. These concepts concerning the constitution of borosilicate glasses that contain a high percentage of silica are used to explain the very unusual density changes that are observed when these glasses are subjected to heat‐treatments at different annealing temperatures.
Petersen, F. A.; Jones, Rodney A.; Allen, A. W.
doi: 10.1111/j.1151-2916.1948.tb14288.xpmid: N/A
Abstract A process is described which locates microscopic cracks in an enamel layer. This method shows great promise in the study of different types of fractures of porcelain enameled specimens. An analysis of the stress conditions in the enamel‐iron‐enamel system before, during, and after thermal shock is also included.
Johnson, A. L.; Hughes, George B.
doi: 10.1111/j.1151-2916.1948.tb14289.xpmid: N/A
Abstract Two red‐firing Iowa brick clays were analyzed for sulfate (SO4−) content by a method suitable for plant‐control tests. From this datum the amount of barium carbonate required to react with this ion can be calculated. Plasticity measurements on (1) samples treated with the amount of barium carbonate indicated by SO4− analysis, (2) untreated samples, and (3) samples treated with normal plant additions show significant differences in this property. These differences can be explained using the modern concepts of the factors which influence the zeta potential.
doi: 10.1111/j.1151-2916.1948.tb14290.xpmid: N/A
Abstract Viscosity data are presented covering those compositions in the CaO‐Al2O3‐SiO2 system which are liquid at 1500°C. The pattern of isokoms on the CaO‐Al2O3‐SiO2 face of the compositional tetrahedron which represents the CaO‐MgO‐Al2O3‐SiO2 system is a system of lines which roughly parallel the lines along which the lime content is constant. There are, however, considerable deviations from this parallelism in regions of very low and very high alumina content.
Shelton, Gborge R.; Creamer, Ansel S.; Bunting, Elmer N.
doi: 10.1111/j.1151-2916.1948.tb14291.xpmid: N/A
Abstract Dielectrics having compositions in the system BaTiO3‐‐4MgO:TiO2‐TiO2 were matured (<0.1% of absorption) at temperatures from 1275° to 1425°C. Data are given for dielectric constant, K, and the reciprocal of the power factor, Q, at 25°C. and frequencies of 50, 1000, 20,000 kc. per sec. and 3000 me. per sec.; also K at a frequency of 1 mc. per sec. and at various temperatures from —60° to 85°C. Values of K (1 mc. per sec. and 25°C.) ranged from 12 to 1550 and those of Q from 9 to 10,000. Values of K decreased and those of Q increased for several weeks after specimens were matured, when the content of BaO was greater than 30% and that of TiO2 less than 50%. Partial restoration of the original values of K and Q resulted from Beating these specimens at various temperatures for brief periods. Linear thermal expansion (25° to 700°C.) ranged from 0.46 to 0.71%. A few specimens of barium‐strontium titan ate were tested for the effects of thermal history on the properties.
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