Granular-structure chromium-bearing refractories: Properties and uses

Results are presented on the corrosion resistance of chromium-bearing refractories of granular structure acted on by corrosive molten slags, metals, and glasses. It is possible to recommend these refractories to customers for particular conditions of use. Chromium-bearing refractories increase the working lives of furnaces considerably. __________ Translated from Novye Ogneupory, No. 1, pp. 55–61, January, 2008.     

Formation of the complex oxide NaNdTiO<Subscript>4</Subscript>

The processes of phase formation in the Na₂CO₃-TiO₂ and Na₂CO₃-TiO₂-Nd₂O₃ systems are investigated in the temperature range 600–900°C. The high-temperature solid-phase reactions underlying the process of formation of complex oxide NaNdTiO4 are studied. It is established that the synthesis of the NaNdTiO₄ compound occurs through the reaction of the intermediate product Na₈Ti₅O₁₄ with neodymium oxide in the temperature range 720–780°C. The optimum method is proposed for synthesizing NaNdTiO₄, which makes it possible to reduce the temperature of the synthesis, to avoid the formation of impurities, and to obtain the product in a finely dispersed state.     

Features of phase transitions in electrolyzer hearth block material between joints

Phase transitions are considered for silicon oxycarbide material between joints in hearth blocks under aluminum electrolyzer operating conditions. It is established that in the electrolyzer there is formation of aluminum subcarbide, and also there is conversion of silicon carbide polytypes as a result of impurities of aluminum, sodium, magnesium, copper and iron. Due to phase transitions there is a reduction in joint strength, and therefore it is undesirable to use material based on corundum and black silicon carbide in hearth joints between blocks for aluminum electrolyzers. Use of pure α-SiO₂ free from impurities is recommended for this purpose. Translated from Novye Ogneupory, No. 4, pp. 47–52, April 2008.     

Synthesis of nanocrystalline solid solutions based on zirconia and hafnia

Nanosized (2–8 nm) amorphous powders of the solid solution based on zirconia and hafnia are synthesized through back coprecipitation upon treatment of gels at temperatures from +20 to −77°C. Heat treatment of these powders at temperatures up to 1000 and above 1100°C leads to the formation of cubic (fluorite type, O _h ⁵ = Fm3m) and tetragonal phases of the Zr₈₂Hf₁₀Y₃Ce₅O _x composition, respectively. It is revealed that a decrease in the synthesis temperature (from +20°C to −6°C) results in a decrease in the size of gel agglomerates from 30 to 1 μm. Recrystallization processes in the gels prepared using cryochemical treatment are developed very slowly in the temperature range 500–1200°C (the crystallite size does not exceed 25 nm). Original Russian Text ? T.I. Panova, V.B. Glushkova, A.E. Lapshin, 2008, published in Fizika i Khimiya Stekla.     

Dynamic modes of Ti combustion in a coflow of N<Subscript>2</Subscript>-Ar mixture

Combustion of bulk density Ti powder (containing 20 wt % TiN as a diluent) in a coflow of N₂-Ar mixture was investigated upon variation in the nitrogen content of the gaseous mixture. The obtained data are believed to open up new horizons for fabrication of layered and composite ceramics by infiltration-mediated combustion.      

A fragmentary model of vitreous As<Subscript>2</Subscript>S<Subscript>3</Subscript>

The X-ray scattering intensity curves for vitreous As₂S₃ are experimentally measured using soft (copper) and hard (molybdenum) X rays. The inclusion of all the specific features revealed in the experimental scattering intensity curves makes it possible to obtain the experimental atomic radial distribution function (ARDF) in the ordering range up to ～1 nm. The experimental ARDF is interpreted in the framework of the fragmentary model. A comparison of the experimental ARDF with the model ARDF calculated from the crystal structure data obtained for orpiment demonstrates that the corrugated layers inherent in crystalline As₂S₃ are retained in the glass structure but the characteristic interlayer interatomic distances are absent. The layers are joined together through the As₄S₅ molecular clusters. Microcrystals consisting of several unit cells are absent in the glass structure, which involves only the structural fragments of both crystalline analogs. One of the possible variants of their joining is proposed.     

Reproducibility of plastic measurements: The need to modify State Standard GOST 1186-87

A very important characteristic of coking coal is its clinkering ability, i.e., its ability to form a nonvolatile solid residue, consisting of disparate grains, on heating in specific conditions. The clinkering ability of the coal is determined by the properties of its plastic mass. Various methods may be used to evaluate the plastic-ductile properties of the coal. However, since the 1930s, the main method used to evaluate the clinkering properties of coal, within the nations of the former Soviet Union, has been the Sapozhnikov-Bazilevich plastometric method, because it provides more information than competing approaches. For the same reason, the thickness of the plastic layer, which is one of the parameters determined by this method, is used for coal classification in State Standard GOST 25543-88 (Lignite, Coal, and Anthracite: Genetic and TEchnological Classification) and its Ukrainian counterpart DSTU 3472-96 (Lignite, Coal, and Anthracite: Classification). This explains the strict requirements on the accuracy and reliability of the plastometric characteristics.     

Swift and Selective Reduction of Nitroaromatics to Aromatic Amines with Ni–Boride–Silica Catalysts System at Low Temperature

Various nitroaromatics are successfully reduced to amines with 100% conversion and selectivity in methanol at low temperature (≈5 °C), by using versatile system of 5% Ni–SiO₂ catalyst and NaBH₄ and in situ generation of Ni boride. The catalytic efficiency of Ni loading (5%, 10% and 15%) with silica or titania as support materials is investigated for reduction of nitrobenzene. The Ni–titania/NaBH₄ system recorded lower conversion and selectivity. The IR studies indicate that silica support does not have free –OH group on its surface. Thus the nickel boride is anchored to the silica to facilitate the catalytic process.