The Nature of the Alumina‐Rich Phase in the System La 2 O 3 ‐Al 2 O 3ROPP, R. C.; LIBOWITZ, G. G.
doi: 10.1111/j.1151-2916.1978.tb16119.xpmid: N/A
Of the two formulas previously reported for the compound on the alumina‐rich side of the system La2O3‐Al2O3, present experimental results indicate that LaAl11 O18 is correct. This compound melts congruently at ∼2000°C and has a hexagonal structure with lattice parameters of a0= 5.561± 0.007 Å and c0=22.041± 0.004 Å. Compositions fired at 1650° showed invariant powder diffraction patterns whereas those fired at 1450°C exhibited X‐ray patterns which varied both in numbers and relative intensities of lines. When the samples which had been initially fired at 1450° were refired at 1650°, the X‐ray patterns changed to the invariant 1650°C pattern. This behavior appears to be related to an ordering mechanism in which the La3+ cations are distributed between two types of cation sites in the hexagonal lattice.
Ionic Conduction of Li 2 O‐2SiO 2 Glass Under DC PotentialTAKIZAWA, KAZUTAKA
doi: 10.1111/j.1151-2916.1978.tb16120.xpmid: N/A
A charging current flows under a dc potential applied to electrodes on Li2O 2SiO2 glass, producing effects that cannot be ignored. These effects aid in understanding the behavior of the charging current when charges are transported across the boundaries between the electrodes and the glass and are more important, even at room temperature, for glasses with relatively good conductivities, e.g. Li2O‐2SiO2 glass. The current for lithium ion penetration into the cathode was estimated from the amount of the lithium in the cathode material. The phenomenological comparison of the current determined by subtracting the penetration current from the charging current indicates that this resultant current is not only attributed to accumulation of the lithium ions transported from the bulk of Li2O 2SiO2 glass into the surface layer adjacent the cathode, but also to displacement (toward the anode) of the oxygen ions in the lithium‐depleted region developed near the anode. This conclusion is qualitatively confirmed by the observed depth concentration profiles of oxygen distributed in the surface layers adjacent the electrodes.
Yttria Hydroxy‐Salt BindersHOLCOMBE, C. E.
doi: 10.1111/j.1151-2916.1978.tb16122.xpmid: N/A
Binder phase (primarily chloride or nitrate) formation was examined in YX3‐NaOH‐H2O, Y2O3‐acid‐H2O, and Y2O3‐salt‐H2‐O systems. The cementitious phase consisted mostly of plate‐ (or needle‐) shaped hydroxy salts of the general formula Y2(OH)6‐m XmnH2O, where m and n normally equal one. These binders were examined by X‐ray diffraction and thermal analysis techniques. Nitrate binders decompose to Y2O3 by 600°C, whereas chloride binders form oxychlorides that sublime or convert to Y2O3 after oxygen replacement of chlorine (in air) at >1000°C. Although nitric and hydrochloric acid solutions form porous (< 50% dense) plasterlike bodies in 2 to 10 min of reaction with Y2O3 powder, salt solutions (i.e. NH4NO3 Mg(NO3)2, NH4Cl, and YCl3‐ ∼6H2O) slow the reaction considerably (48 h to 4 weeks), allowing 70‐ to 80%‐dense cements to form. The effects of formation conditions on physical properties of binders were studied. Examination of scandium and lanthanide oxides showed that several behave in the same way as yttria.
Microcracking of Monoclinic HfO 2DOLE, S. L.; HUNTER, O.; CALDERWOOD, F. W.; BRAY, D. J.
doi: 10.1111/j.1151-2916.1978.tb16123.xpmid: N/A
Elasticity, internal friction, and thermal expansion were measured at temperatures up to 1500°C to characterize the micro‐cracking behavior of HfO2. Crack‐free HfO2 showed consistent, typical changes in these properties with temperature. Micro‐cracked HfO2 showed hysteresis in the elastic moduli and thermal expansion on thermal cycling. Internal friction increased with microcrack healing. Repeated thermal cycling and high‐temperature anneals markedly changed the microcrack system and a time‐ and atmosphere‐dependent aging effect in microcrack formation was noted.
Powder Diffraction Patterns and Structures of the Bismuth OxidesMEDERNACH, JOHN W.; SNYDER, ROBERT L.
doi: 10.1111/j.1151-2916.1978.tb16125.xpmid: N/A
The structures of the bismuth oxides are discussed and evaluated. Calculated powder diffraction patterns were made for all reported phases with known crystal structures. Comparing the calculated and experimental patterns indicates that the α and β polymorphs are well characterized. All previous observations concerning δ‐Bi2O3 are explained using a primitive cubic crystal structure model. The existence of an fee Bi2O3 is in doubt. Calculated patterns are given for all reported nonstoichiometric and suboxides of bismuth.
Finite Element Analysis of Stresses in Glass‐to‐Metal Foil SealsVARSHNEYA, A. K.; PETTI, R. J.
doi: 10.1111/j.1151-2916.1978.tb16126.xpmid: N/A
Stresses in glass‐to‐metal foil seals were measured using photo‐elastic techniques and calculated using finite element analysis. Cases considered were one in which the metal remains elastic during cooling and one in which the metal yields under the action of developed stresses at some stage during cooling. Calculated and measured values agreed very well using a coarse spatial resolution limited by the measurements. Spatial resolution of the calculations was then made finer to obtain the stress distribution in the immediate vicinity of the foil tip more precisely. Observed fractures in such seals are discussed in terms of these stresses. The effect of the metal foil geometry on the magnitude of the critical stresses was studied using finite element analysis. The relative merits of using various foil geometries are discussed in relation to lowering the seal failure probability.