Room Temperature Lattice Parameters Research Articles

The BeO — MgO system

X-ray powder diffraction and melting-point studies provide no evidence of the existence of any compound or solid solution in the BeO-MgO system. Samples investigated by X-ray diffraction were (a) powders of various stoichiometric compositions and powders of high BeO content, calcined at 1400° C for 87 hours, (b) powders containing up to 4 mole per cent MgO, quenched from above 2100° C, and (c) powders derived from quenched melts at near the eutectic composition. In all cases examined, the room temperature lattice parameters of BeO conformed to the limits a o = 2.698 ± 0.002 Å, and c o = 4.378 ± 0.004 Å. A determination of the liquidus confirmed the existence of a single eutectic in the system, located at 69 ±2 mole per cent BeO and 1838 ± 13° C.

Some observations on uranium-molybdenum-niobium alloys

The constitution of U-Mo-Nb alloys at 1100°, 1200°, and 1300°C has been studied, mainly by metallographic and X-ray methods, and isothermal sections have been obtained. The decomposition of the body-centred cubic γ-phase in alloys containing 5 at. % Mo and approximately 50 at. % U occurred very slowly at temperatures near the maximum of the miscibility gap. Additions of Mo have been found to decrease the rate of the monotectoid reaction γ1 → α + γ2. Room temperature lattice parameters of quenched homogeneous γ alloys were obtained and a hardness survey of the same alloys showed that a maximum occurred at approximately 50 at. % Nb and a minimum at 85 at. % U. The effect of Mo on the maximum temperature of the miscibility gap has been discussed in terms of the strain energy in the solid solution from which it is formed.