Foamed nitride-bonded silicon carbide refractories

Conclusions We obtained foamed silicon carbide insulating material with a nitride bond. The nitride bond is formed from a mixture of silicon nitride of the- and-modifications upon reaction with nitrogen. The formation of the nitride commences at about 1200°, and is practically complete at 1450°; the rate of nitriding of the foam ceramic is much greater than in dense specimens. The material has a homogeneous phase composition which is an advantage compared with foamed silicon carbide containing a complex bond obtained in carbon fillings.The foamed insulating brick based on nitride bond possesses a high thermal-shock resistance and structural strength at elevated temperatures. The strength is increased with an increase in the apparent density. The material is characterized by moderate mechanical strength, typical for silicon carbide refractories of this type [1, 3, 4].The foamed silicon carbide brick with a nitride bond can be recommended for service at high temperatures in nonoxidizing atmospheres when substantial thermal-shock resistance is required.Translated from Ogneupory, No. 7, pp. 48–51, July, 1970.     

Numerical Simulation of Ignition of a Condensed Substance by a Particle Heated to High Temperatures

The problem of ignition of a condensed substance by single particles heated up to high temperatures is solved within the framework of the twodimensional heattransfer model. Numerical studies are performed for typical materials: polyvinyl nitrate and carbonic particles. Regimes of ignition of a condensed substance by a single particle at relatively low temperatures are adequate in terms of the ignition delay to regimes of heating of the condensed substance by a gas flow without particles; at high temperatures, they correspond to regimes of heating by a metal plate with a fixed temperature. In a certain (rather narrow) range of particle temperatures, the use of the twodimensional heattransfer model yields ignitiondelay values substantially different from other regimes.     

Nanocrystalline CeO2 in SBA-15: Performance of Pt/CeO2/SBA-15 Catalyst for Water-gas-shift Reaction

CeO₂ particles confined within the pores of an SBA-15 mesoporous silica host were prepared by incipient wetness impregnation (IMP) and deposition precipitation (DP) methods. The materials were characterized by XRD, N₂-adsorption and temperature programmed reduction (TPR) to evaluate the structure, texture, and redox properties. The preparation procedure had significant impact on the assembling mode of CeO₂ inside the SBA-15 mesopores. A high dispersion of CeO₂ particles was achieved via DP, whereas the dispersion of CeO₂ prepared by IMP was found to be inhomogeneous and CeO₂ partially blocked the pores. The CO conversion in the water-gas-shift reaction was enhanced over 1 wt% Pt supported on CeO₂-modified SBA-15 obtained by DP.     

Refractories with a Boron nitride base

Conclusions A technique for the reaction sintering of a new refractory made of 82–83% boron nitride and 17–18% graphite has been developed.The refractory possesses high specific resistance up to 1500–1800°, a low coefficient of thermal expansion, a moderative evaporation rate in a vacuum, satisfactory strength and machinability, as well as high resistance to cryolite-aluminum melts, borate, chloride and also silicide and boron-silicon alloy melts (at between 900 and 2000°).     

Synthesis, isolation, spectroscopic and electrochemical characterization of some calcium-containing metallofullerenes

A few Ca-containing mono-metallofullerenes, i.e. Ca@C₇₆, Ca@C₈₈, Ca@C₉₀ (I, II), were synthesized by an improved DC arc discharge method and isolated by a multi-stage HPLC method for the first time. These isomer-separated metallofullerenes were characterized by LD-TOF MS and UV-vis-NIR spectrometry. Their HOMO-LUMO band gaps and possible molecular geometries are discussed according to the absorption spectra in this report. In addition, the cyclic and differential pulse voltammetry of Ca@C₇₆ was conducted in MeCN/C₆H₅CH₃ (1:4 v/v). The voltammograms of Ca@C₈₂ (II, III) and Ca@C₈₄ (II) were also recorded. Their electrochemical behaviors are discussed compared with those of corresponding ytterbium metallofullerenes. The features of the Ca metallofullerenes’ electronic structures are also discussed.     

宁波市高校实践教学档案归档范围思考

宁波市高校实践教学有了长足发展,形成了鲜明的地域特色.企业与高校人才互动互用形式趋向多样,学生在校学习与毕业后的就业结合更加紧密,对高校实践教学档案建设提出了新的要求.认真思考高校实践教学档案的归档范围,加强实践教学档案管理工作,有益于全面提高教育教学质量.     

Investigation of the mechanical properties of low-alloy steels

Technical University, Koice, Czechoslovakia. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 21–24, February, 1991.     

Structural condition of martensite in the surface layer of cold rolling rolls

Conclusions The martensitic base of the surface hardened layer is inhomogeneous in phase composition. Despite complicating concepts post-hardening tempering does not cause homogenization of the martensitic phase. Decomposition of the martensite has a heterogeneous character. In the hardened layer and the transition zone together with the low-carbide constituent there is formed a high-carbon one. The presence of high-carbon -martensite may not inpoint of concepts on homogeneous martensite, the degree of tetragonality of which is close to unity, it is difficult to explain the phenomenon of high hardness of rolling mill rolls. Undoubtedly the high-carbon constituent is one of the factors causing an increase in hardness in tempering of type 9KhMF steel. The two martensites manifest themselves differently in rolling. Concepts of the heterogeneous nature of maratensite may be used for improving the service conditions of rolling rolls.Kramatorsk Industrial Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 10–12, February, 1991.