Microstructure of silicon nitride ceramics sintered with rare-earth oxides

Microstructures of Si₃N₄ with crystallized grain boundaries of rare-earth silicates were investigated. β-Si₃N₄ grains in samples sintered with Yb₂O₃ were more elongated than those sintered with Dy₂O₃. Amorphous thin layers between crystallized grain boundaries of silicate and Si₃N₄ grains were recognized for both specimens sintered with Dy₂O₃ and with Yb₂O₃. In the sample sintered with Dy₂O₃, very clean grain boundaries between Si₃N₄ grains which did not contain the heavy elements were frequently recognized, while samples with Yb₂O₃ had an amorphous grain boundary phase containing Yb. Unusual structures with distorted lattice images in regions rich in Si and O were discovered in crystalline Dy-silicate phases.     

Interaction of copper sulfides with copper oxides in the molten state

Reactions of Cu₂S with Cu₂O, CuS with Cu₂O and CuS with CuO in the molten state were examined in the presence of one atmosphere of argon at 1200°C. A rate law of the form,r _SO2 =kN_SN_O was applicable for each reaction system studied. Comparison of the rate constants for the systems, under conditions of similar initial mole fraction of sulfur to mole fraction of oxygen ratios, showed that Cu₂O was much more reactive than CuO in its reaction with copper sulfides. These results are incorporated in a mechanism in which Cu₂O reacts with the sulfide in the rate determining step. Experiments carried out in the presence of oxygen indicated the importance of a CuO-Cu₂O equilibrium in the overall reaction mechanism.     

Thermionic properties of tungsten with additions of oxides of rare-earth elements

Translated from Poroshkovaya Metallurgiya, No. 5(305), pp. 42–44, May, 1988.