Journal of the American Ceramic Society

ELKINGTON, W. E.; THOMAS, G.; WASHBURN, J.

doi: 10.1111/j.1151-2916.1963.tb11736.xpmid: N/A

The dislocation substructures in single crystals of MgO deformed in four‐point bending at temperatures from –196° to 1300°C have been observed by transmission electron microscopy. Elongated edge dislocation pairs were found at all deformation temperatures. The majority of pairs originated where screw dislocations intersected grown‐in dislocations. Grown‐in dislocations always contained impurity precipitates along their length and often did not lie exactly in a slip plane. Because of either one or both of these factors, grown‐in dislocations remained immobile during deformation. The stability of dislocation pairs depended on the separation of the two dislocations and on the deformation temperature. Narrow pairs broke up into small prismatic loops at 750°C and above. The width of the largest observed pairs approached but never exceeded the calculated value:

DOMAN, R. C.; BARR, J. B.; McNALLY, R. N.; ALPER, A. M.

doi: 10.1111/j.1151-2916.1963.tb11737.xpmid: N/A

The liquidus, solidus, and subsolidus of the system CaO–MgO have been redetermined. X‐ray diffraction and optical techniques show that the maximum solid solution of MgO in the CaO lattice is approximately 17 wt% at 2370°C and the maximum solid solution of CaO in the MgO lattice is approximately 7.8 wt% at 2370°C. The extent of solid solution in each case is substantially greater than previously reported. Magnesium oxide and calcium oxide solid solutions exist at temperatures above 1600°C. The liquidus values closely agree with those previously reported by Rankin and Merwin.

HULSE, C. O.; COPLEY, S. M.; PASK, J. A.

doi: 10.1111/j.1151-2916.1963.tb11738.xpmid: N/A

Stress‐strain data for single crystals of MgO tested in compression with 〈110〉 and 〈111〉 loading axes are presented for temperatures ranging from 26〉 to 1250°C. Stress‐strain data for polycrystalline MgO are also presented over the same temperature range. Single crystals with a 〈111〉 loading axis were found to deform plastically on the {100}〈110〉 slip systems at temperatures above 350°C. The total strain at fracture for polycrystalline MgO at room temperature was about 0.6%; above 600°C it was about 2%. The general inability of the {110}〈110〉 slip systems of this structure to satisfy the Taylor requirement, i.e., the necessity of five independent slip systems, ease of cleavage, and slip nonuniformity, limits polycrystalline ductility at low temperatures. At higher temperatures, slip can occur on {100}〈110〉 slip systems, thus providing the additional slip, systems necessary to satisfy Taylor's criterion; also, stress‐induced climb and high dislocation mobility inhibit cleavage fracture.

CHIKALLA, T. D.

doi: 10.1111/j.1151-2916.1963.tb11739.xpmid: N/A

The melting points of UO2 and PuO2 in a helium atmosphere were found to be 2730°× 30° C and 2280°× 30° C, respectively. With the exception of a melting maximum at the composition 90 UO2–10 wt% PuO2, the liquidus exhibits good continuity and agrees well with that calculated from thermodynamic data. X‐ray diffraction data on melted PuO2 and UO2‐PuO2 solid solutions indicate that oxygen is evolved during melting but that no reduction to a second‐phase plutonium suboxide occurs. The oxygen‐plutonium atomic ratio of melted PuO2 is 1.62, so that the 2280° C temperature reported here is the result of a dissociation reaction and is considered to be a pseudo melting point. Lattice parameters of melted UO2–PuO2 samples vary linearly with composition but are approximately 0.2% greater than anticipated because of an oxygen deficiency.

HAMMOND, M. L.; RAVITZ, S. F.

doi: 10.1111/j.1151-2916.1963.tb11740.xpmid: N/A

The fracture strength of fused silica rods was determined in vacuum and in the saturated vapors of water, ethyl alcohol, n‐butyl alcohol, n‐propyl alcohol, acetone, ethyl acetate, undried benzene with “less than 0.02% water,” and dried benzene. The relation between the lowering of the fracture strength of the fused silica caused by the vapor and the corresponding decrease in surface free energy of quartz was found to be consistent with the Griffith theory of brittle fracture.

RIGBY, G. R.; HUTTON, R. F.; HAMILTON, B. G.

doi: 10.1111/j.1151-2916.1963.tb11741.xpmid: N/A

Possible reactions occurring in basic brick were first explored by studying (a) binary mixtures of sesquioxides or magnesia spinels and (b) three silicates, namely forsterite, monticellite, and di‐calcium silicate. Compositions ranging from 10 to 90% of each constituent were pressed into cylinders and heated at 100°C intervals between 800°C and a maximum of 1700°C or until melting occurred. Bulk density and volume changes were recorded and X‐ray diffraction was used to explore chemical reactions. Reactions between the three silicates and three chrome ores were also studied. Since the most refractory specimens were those containing magnesiochromite as the spinel constituent, the effect of free magnesia as a third component in these series was finally explored.

WlLCOX, DAVID L.; COOK, RALPH L.

doi: 10.1111/j.1151-2916.1963.tb11742.xpmid: N/A

An intermediate antiferroelectric phase was observed in both the systems (Pb,Ba)HfO3 and (Pb,Sr)HfO3 whereas the intermediate antiferroelectric phase has been reported to be observed only in the system (Pb,Sr)ZrO3 of the analogous zirconate systems. A ferroelectric phase was observed in the system (Pb,Ba)HfO3. This ferroelectric phase was determined to be rhombohedral with the angle between the rhombohedral axes slightly less than 90°. The differences which were observed between the hafnate systems investigated and the analogous zirconate systems are attributed to the lower electronic polarizability of the hafnium ion.

BAILEY, DONALD

doi: 10.1111/j.1151-2916.1963.tb11743.xpmid: N/A

A method is presented for the microscopic examination of asbestos‐cement products. The use of petrographic thin sections and polished sections in determining composition, texture, grain size, and cement‐silica reaction is described. The preparation of thin sections and polished sections, using epoxy resin as an impregnant, is outlined.