Formation of Color Centers in Glasses Exposed to Gamma RadiationKREIDL, N. J.; HENSLER, J. R.
doi: 10.1111/j.1151-2916.1955.tb14568.xpmid: N/A
Glasses exposed to gamma radiation develop a visible absorption band similar to the F‐band developed in alkali halide crystals. The function of cerium in preventing coloration of glass was studied in detail in an ultraviolet‐transmitting phosphate base glass in which its characteristic absorption could be measured. When visible absorption was thus prevented, radiation still caused a strong absorption in the ultraviolet which was associated with the electronic structure of cerium. On this basis, transition ions of similar electronic structure were introduced. It was found that iron, manganese, cobalt, nickel, vanadium, copper, and, under certain conditions, some other elements do suppress the formation of the visible absorption band formed in the base glass by radiation while forming more or less prominent bands in other spectral regions. Thus the colorless iron phosphate glass remained colorless under radiation and could be considered to be “protected.” Conversely, with cobalt the new band which reached into the visible was relatively intense and stable, suggesting its use to indicate radiation dose.
New Method of Preparing Clay Samples for Differential Thermal AnalysisWALTON, J. D.
doi: 10.1111/j.1151-2916.1955.tb14570.xpmid: N/A
A method of preparing clay samples for differential thermal analysis which permits the analysis to be made with the test and reference samples freely exposed to the furnace atmosphere is described. The data obtained when samples were thus heated are presented, together with those obtained when an Inconel block was used to contain the clay. The sensitivity of the two methods is compared, with particular emphasis on the increased sensitivity in the low‐temperature range which resulted from the use of the new method.
Structural Behavior in the System (Ba, Ca, Sr) TiO 3 and Its Relation to Certain Dielectric CharacteristicsMcQUARRIE, MALCOLM
doi: 10.1111/j.1151-2916.1955.tb14571.xpmid: N/A
The effect of strontium additions on the immiscibility region between barium titanate and calcium titanate was studied and it was found that the two‐phase gap is closed by about 18% strontium titanate when the specimens are fired at 1430°C.; at lower firing temperatures the gap is greater and there is evidence of incomplete reaction. The effect of different firing temperatures on the dielectric properties of bodies in this region is discussed and the theoretical conclusions are supported by experimental data. The strontium titanate‐calcium titanate binary was studied and the phase boundaries (cubic‐tetragonal, tetragonal‐orthorhombic) were located with regard to changing composition and temperature.
Fundamental Study and Equipment for Sintering and Testing of Cermet Bodies: VII, Fabrication, Testing, and Properties of 34 Al 2 O 3 ‐66 Cr‐Mo CermetsSHEVLIN, THOMAS S.; HAUCK, CHARLES A.
doi: 10.1111/j.1151-2916.1955.tb14572.xpmid: N/A
The properties of a cermet solid body containing 34% Al2O3 and 66% 80Cr–20Mo alloy (50Al2O3‐50 alloy by volume) are given as firing shrinkage, density, modulus of rupture, tensile strength, stress‐rupture life, modulus of elasticity, oxidation resistance, thermal‐shock resistance, and thermal expansion. It is shown that substitutions of the 80Cr‐20Mo alloy for Cr in a similar cermet developed earlier substantially improved thermal‐shock resistance.
Clay Particle Dispersion in Organic MediaFOLKERS, CHARLES L.; WELCH, A. PHILIP
doi: 10.1111/j.1151-2916.1955.tb14573.xpmid: N/A
The dispersion of approximately 1.0% kaolin suspensions in various organic liquids was studied. Both individual and family effects were noted. Complete dispersion was found with higher alcohols, such as hexanol, and with glycols and glycerol. Sodium salts of the several alcohols were also employed to advantage as deflocculants. Complex alcohol formations with kaolin are believed to be absent or at least negligible. Results are compared with the typical effects obtained with water. Summary Optimum dispersion of kaolin was obtained in the higher alcohols and in the glycols. Both alcohols and glycols are known to behave similarly toward montmorillonite; the only difference is the degree of exactness of the complex formed. If glycol, which forms the strongest montmorillonite complex, is inert to kaolinite (and there is no evidence to the contrary), it follows that the other alcohols also are inert to kaolinite, at least very nearly so. These results agree with those of MacEwan.33 Although the glycol‐montmorillonite complex is the most stable one formed, the glycol can be completely washed out, restoring the particles to their original condition, and regenerating the expansible lattice. Thus, with kaolinite, even assuming a limited type of complex formation with an alcohol, the particles may be retained unaltered and the alcohol may be removed by washing or by evaporation. Considering kaolinite surfaces as being analogous to montmorillonite edges, only a single‐layer complex flat against the surface can be formed by C‐H.O bonding or by O‐H.O bonding. The maximum adverse effect on particle size under these circumstances would be the addit'on of approximately 3.0 a.u. to the radius of the particle. Applied to a particle 0.05 μ in diameter, this would result in an increase of only 1.2%; and with larger particles this percentage would be considerably reduced. Particle‐size analyses based on Stokes’law and using an alcohol as the suspending medium thus could be expected to yield a more accurate picture of actual particle diameters, on the basis of complex formation alone. In the alcohols the intensity of Brownian motion was reduced from that exhibited in water and in some cases motion was not present at all. This was true even in methanol, with a viscosity much less than that of water. This reduced Brownian motion would tend to give closer adherence to Stokes’law, particularly in the portion of the kaolin particles less than 1.0 μ in diameter, and would result in more accurate particle‐size determinations. A dispersed condition is not always required for handling clays in suspension. For instance, in processing a clay through a fractionation procedure, the several steps involved require at one point or another the development of both flocculation and dispersion. From the appropriate curves it is evident that by the proper selection of the particular alcohol almost any desired condition may be obtained (from complete flocculation to a nearly absolute dispersion). Table VI shows that these conditions may be attained over a wide range of viscosities, volatilities, densities, and many other physical properties. Note that oxygen was present as a part of the molecule of every liquid which gave even moderate dispersion, with the exception of aniline, in which nitrogen can be considered to replace the negative oxygen with the acceptance of an additional hydrogen. The presence of oxygen in the organic structure cannot be considered to ensure successful dispersion; however, without it no other compounds were even moderately successful. At present, the exact significance of the oxygen is not clear.