AcknowledgmentThe authors gratefully acknowledge the capable assistance of Miss Agnes Forster ( x -r a y diffraction) and Mr. T. R. McKinney (electron diffraction) of the General Motors Research Laboratories, and the encouragement and active participation in m a n y aspects of this w o r k provided by personnel of the Delco Radio

%) . . UC + 0 . 1 w t % Ni 0.127 5 MOz-,t 0.083 8 90 W t % M(Oo.34C0.66) + 10 W t % MOz uoz 0.064 2 0.036 2 -* Uncorrected for porosity. t M = (Uo.sPua.i). relations plotted by McAdams" for a semi-infinite solid. I n UC and UOz, thermal conductivities were calculated using reported heat capacity values16 of 0.048 cal/g-OC and 0.060respectively. An assumed value of 0.048 cal/g-OC was used for the monoxide-type materials because of the similarity of their molecular structures with that of carbide.The calculated values presented in Table V show that the monoxide-type compositions have higher room-temperature conductivities than those of (U,PU)OZ and UO,. Although the absolute values for UC and UO, are lower than expected, the relative values are reasonably good. These data, therefore, are believed to be useful for qualitative comparison.

Single crystals of AI,(P,, (sapphire) were grown from PbO-PbFz and MoO,-PbFn fluxes; they varied from flat plates (PbRrich melts) to equidimensional crystals (PbO-or Moo,-rich melts).The primary growth planes are basal {OOOl}, first-order rhombohedral { lOjl}, and second-order rhombohedra1 { 0172). The habit change is interpreted on the basis of F-contamination and Pb2+ surface adsorption. Possible ion species in the melts and their relative importance on crystal growth from these systems are discussed.

The LAboratory Operations of The Aerospace Corporation is conducting experitnental and theoretical Investigations necessary for the evaluation mand application of scientific advances to new military concepts and systems. Versatility and flexibility have been developed to a high dog ree by tbe laboratory personnel in dealing with the many problems encountered In the nation's rapidly developing space and missile systems. Expertise in the latest scientific daevdopments is v~tal to the accomplishmant of tasks related to these p~roblems. The laboratories that contribute to this research are:Aerodynamics and Propul Ion Research Laboratnry: launch and reentry aerodynanifcs, ceat trnfr enry physics, propulsion, high -temperature chemistry a.nd chemicnl kinetic,,, structural mechanics, flight dynamics, atmospheric pollution, and high-power gas lasers. Single crystals of phenacite (Be 2 SiO 4 ), bromellite (BeO), and tridymite (SiO1 2 ) were grown from a MoO 3 -Li 2 MoO 4 flux. Phenacite, with rhombohedral symmetry, grew in three distinct shapes .with aspect ratios (length/ width) as follows: needles ( > 3), rods(-> it. i to 1. 5), and rhombohedral-faced crystals (=.1). The latter grew as single crystals; the others were twinned on the (1.010). 'For most experiments the temperature was held constant at 1i65"C and the Li 2 MoO4/MoO 3 ratio at 1/16. The growth mechanism for crystallization was the evaporation of MoOThe system produced one to three phases depending on the BeO/SiO ralio. Bromellite grew until a BeO/SiOt ratio of 0. 8 was attained. It grew as a hemipyramidal crystal. that had a short prism with a curved (0001) top or as a hexagonal plate. The pyramid-and prism-shaped crystals were twianed, although a few hexagonal plates were single. Tridymite grem in small hexagonal plates when the BeO/SiOý ratio was less than 1. 5. The effect of temperature, nucleation, and flux composition on crystal shape, twinning, and occurrence is discussed. The pyramid-and prism-shaped crystals were twinned, although a few hexagonal plates were single. Tridymite g-ew in small hexagonal plates when the BeO/SiO 2 ratio was less than t. 5. The efiect of temperature, nucleation, and flux composition on crystal shape, twinning, and occurrence is discussed.

Einkristalle von Phenakit (Be,SiO4), Bromellit (BeO) und Tiidymit (SiO,) werden aus einem LizMoOfMoOa‐Schmelzfluß erhalten.