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Neutron diffraction data from in situ deuteration and dedeuteration of Li(3)N are presented under different pressure regimes, whereby reaction pathways differing from the widely reported stoichiometric pathway of Li(3)N + 2D(2)<--> Li(2)ND + LiD + D(2)<--> LiND(2) + 2LiD are observed. At sufficiently high pressures, where the deuterium chemical potential is comparable with the heat of amide formation, the reaction appears to be driven straight to the amide plus deuteride phase mixture. At lower pressures, a cubic phase exhibiting a concentration-dependent variation in lattice parameter is observed. In dedeuteration, two sets of reflections from cubic structures with distinct lattice parameters are observed, both of which exhibit a continual decrease in cell volume. The reaction pathways are discussed in terms of the compositional variation.

Highly densified TiC, ZrC and HfC based ultrahigh temperature heteromodulus ceramics (HMC), containing 10-50 vol.-% of low modulus phase in the form of particulate graphite, were prepared by hot pressing at 2700uC and 12 MPa in argon atmosphere. The microstructure, elastic characteristics, flexural and compressive static strength, fracture toughness, impact resistance, hardness and thermal expansion were investigated and compared with those available in earlier works for clear understanding the composition-property correlations and anisotropy of this type of HMC composites. Different thermal shock resistant parameters for the HMC were calculated on the basis of obtained experimental data. A new principle of optimum materials design for the compositions in the refractory carbide-graphite systems is exemplified by the TiC-C HMC materials.