Allen L. Bowman

Neutron Diffraction Study of Ice Polymorphs under Helium Pressure

Neutron diffraction studies of several of the D2O ice polymorphs were made with helium pressures to 3.5 kbar. Volume compressions (ΔVu2009/u2009V) were obtained for ices Ih, Ic, and IX at 2.1 to 2.8 kbar. The equilibrium phase boundaries between ices I–II and I–III in the presence of helium are shifted toward higher pressure values. The crystal structures of ices Ih, Ic, II, and IX at approximately 2.5 kbar are the same as the structures found for these ice forms at atmospheric pressure. A tetragonal structure is indicated for ice III with lattice parameters at −u200923°C and 2.7 kbar of au2009=u20096.674u2009±u20090.015 A and cu2009=u20096.97u2009±u20090.03 A. The cu2009/u2009a ratio for ice IX has been found to be 1.000u2009±u20090.003 both at 1 bar and at 2.8 kbar.

ANISOTROPIC THERMAL EXPANSION OF REFRACTORY CARBIDES BY HIGH-TEMPERATURE NEUTRON DIFFRACTION.

The anisotropic thermal expansion of U2PtC2 (tetragonal), and UMoC2 (orthorhombic) has been measured using a high‐temperature neutron diffractometer. Coefficients of thermal expansion (units of 10−6/°C) are U2PtC2, α11=9.3±0.1, α33=10.1±0.8; UMoC2, α11=8.6±0.2, α22=15.5±0.5, α33=10±3.

High Temperature Neutron Diffraction Furnace

An induction transformer furnace for a neutron diffractometer is described. This furnace has been used for the examination of refractory carbides by neutron diffraction at temperatures up to 2500°C.

The Variation of Lattice Parameter of UC–ZrC Solid Solutions with Temperature and Composition

The variation of lattice parameter of uranium carbide‐zirconium carbide solid solutions with temperature has been measured by high‐temperature neutron diffraction. The cubic lattice parameter, was determined from 800 to 2300°C for samples (UxZr1−x)C plus excess carbon, with x from 0 to 0.181. The lattice parameter of all the samples in this composition range can be approximated by the equation atu2009=u2009a25u2009(1u2009+u20096.6(3);×10−6[t−25]u2009+u20090.7(2)u2009×u200910−9[t−25]2) from room temperature to 2300°C.