Results of neutron and X-ray diffraction studies on I-If and Ti hydrogen systems are reported. It is shown that the first single-phase hydride formed is a non-stoichiometric compound with a CaF2-type structure. It deforms to a face-centered tetragonal structure as the composition approaches MX 2. From the crystal-structure data of these hydrides the positions of hydrogen atoms, the nearest-neighbor atoms and their interatomic distances are determined. It is indicated that the size of the 'hole' for the hydrogen atom in the hydride is such that it must enter as an ion. The effect of metal-hydrogen bonds on the physical properties of hydrides, such as characteristic temperature and vibration frequency, is given. Evidence and explanation for the embrittlement of metals by hydrogen are offered.
Neutron diffraction patterns have been obtained for the alkali metal liquids; lithium (180°C), sodium (100°C), potassium (65°C), rubidium (40°C, 160°C, 240°C, and 360°C), and cesium (30°C, 300°C, and 575°C). It was found necessary to correct intensities for scattering by a free atom for lithium and sodium but not for the heavier atoms. Atomic distribution curves were computed for all the above cases, and compared with results from x-ray diffraction. Just above melting temperatures the nearest-neighbor distances are for lithium 3.15 A, sodium 3.82 A, potassium 4.64 A, rubidium 4.97 A, and cesium 5.31 A, the number of nearest neighbors is, within one-half atom, about 9.0 to 9.5 atoms in each case. At elevated temperatures with rubidium and cesium, a weak subsidiary concentration of atoms appears between the usual first and second neighbor concentration.
Titanium and zirconium alloy system consists of a continuous series of random substitutional solid solutions of solvent and solute atoms. Titanium scatters thermal neutrons in the opposite phase from those scattered by zirconium, the scattering amplitudes being: bTi=−0.38×10−12 cm and bZr=0.62×10−12 cm. An alloy containing 62 atomic percent titanium and 38 atomic percent zirconium is developed that gives no coherent scattering reflections in its neutron diffraction pattern, and is extremely useful in constructing devices in which scattering of thermal neutrons is not desired. Based on negative and positive scattering amplitudes of different isotopes of the same element for thermal neutrons, development of isotopic alloys is suggested.
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