关于定量界定设备修理周期若干问题的研究

本文通过对确定设备修理周期经验公式的讨论,指出了两点不足。对此笔者提出了:在生产过程中运用单位产品维修成本与产量的量化模型,从经济效益的角度动态界定最佳修理周期的设想,以期在设备维修管理方面,为企业提供最佳经济效益。并由此得出了几点有益的启示。     

Calcium Silicate Hydrates Studied by Small-Angle Neutron Scattering (SANS)

Small-angle neutron scattering (SANS) was used to study calcium silicate hydrate (C-S-H) formed via pozzolanic reaction between calcium oxide and ultrafine silica in water or polymer solutions at a temperature of 20°C. The SANS profile of this product was consistent with a structure that consisted of platelets with maximum diameters of ∼20 nm (± 5 nm) in the x – y plane, which was similar to a structure that had been deduced in previous work via X-ray diffractometry. The presence of two different types of superplasticizer in solution (at a concentration of 10 g/L) had no significant effect on its formation kinetics or its SANS profile.     

Temperature of nanometer-scale structure appearance in glasses

The structural network of glass is known to be partitioned into quasiordered nanometer regions (clusters). It is considered that the formation of nanometer-scale inhomogeneities occurs still in a liquid state in the process of cooling and substantially affects the ability of the substance to glass transition. In this work, we discuss the problem of determining the temperature at which a glass nanometer-scale structure is formed. Based on the analysis of the inhomogeneous broadening of Raman spectrum lines and the Landau-Placzek ratio, we show that the formation of an inhomogeneous structure starts near the temperature of the transition from the Arrhenius behavior of the relaxation time (viscosity) to non-Arrhenius behavior. This temperature can be determined using the derivative analysis.     

Structure and conductivity of carbon materials produced from coal pitch with carbon additives

Attention focuses on the structure and electrical conductivity of carbon materials obtained by the carbonization of coal pitch in the presence of additives (nanotubes, graphite foam, and graphite), at temperatures up to 900°C. In some cases, ultrasonic mixing is used on introducing the additives to the pitch. Ultrasonic mixing is found to change the properties of the pitch and affect the properties of the carbon material produced. In particular, the proportion of carbon with an ordered structure is increased; the electrical conductivity at temperatures below 40 K is increased; and the energy barrier E _g between individual crystallites is reduced almost fourfold. At higher temperatures, the electrical conductivity is practically unchanged. Adding nanotubes to the pitch reduces the content of ordered carbon structures in the carbon material produced and lowers its electrical conductivity. Adding graphite foam and graphite to the pitch increases the order and electrical conductivity of the carbon material produced and lowers the energy barrier E _g between individual crystallites in the samples. The electrical conductivity of all the carbon materials below 16 K is described by the characteristic formula for fluctuation-induced tunneling conduction. This indicates that contacts between individual crystallites are mainly responsible for the electrical conductivity.     

Ceramics based on partly stabilized zirconium dioxide: technology,structure, properties,and behavior under dynamic action

Technology is described for manufacturing dense ceramic from very fine powder based on zirconium dioxide partly stabilized with yttrium oxide. Some engineering properties of the manufactured ceramic are defined. Its microstructure and phase composition are studied. Ceramic properties with impact-wave loading are studied, and values of dynamic elastic limit and spalling strength are obtained.     

A study of physicochemical properties of modified carbon nanomaterials intended for sorption extraction of radionuclides I. The influence of the porosity of carbon nanomaterials on their sorption properties with respect to Tc(VII)

The influence of the porous structure of samples of FAS and VSK carbon adsorbents on their sorption properties with respect to Tc(VII) is studied in this work. Complex research on the porous structure of the chosen samples is conducted. It is found that FAS sample no. 6 (distribution coefficient K _d = 4.3 × 10⁴ cm³/g) and sample of VSK coal no. 5 (K ^d = 2.2104 cm³/g) possess the highest sorption activity relative to Tc(VII). It is established that the presence of a considerable quantity of mesopores with sufficient width promotes sorption of Tc(VII) ions. The kinetics of ionic exchange on surface of FAS carbon adsorbents samples is studied, and it is established that sorption on these samples occurs by a mixed diffusion mechanism.     

Optimization of heat-treatment conditions of aluminum-silicon alloys

Dnepropetrovsk Metallurgical Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 31–33, November, 1992.