Influence of heat-insulating polymer coating on surface-cementite formation in chill casting

The influence of heat-insulating polymer coatings on the cementite formation at the surface of chill castings for oil-industry equipment is studied. Four types of coatings are considered.     

Study of the oxygen content uniformity and stability in BrO10S1.5Ts bronze powder

Results are presented of a study of the BrO10S1.5Ts bronze powder developed as an oxygen standard. It is shown that the powder homogeneity, in terms of its oxygen content and concentrational stability over time, make it suitable for use as a standard.Kiev University. Translated from Poroshkovaya Metallurgiya, No. 2(362), pp. 8–10, February, 1993.     

Cathodoluminescence of ZnO/GaN/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> heteroepitaxial structures grown by chemical vapor deposition

The cathodoluminescent properties of ZnO films in ZnO/GaN/α-Al₂O₃ and ZnO/α-Al₂O₃ heteroepitaxial structures grown by chemical vapor deposition in a low-pressure flowing-gas reactor were studied and compared. A superlinear dependence of the excitonic-band intensity in the cathodoluminescence spectrum of the ZnO/GaN/α-Al₂O₃ structures on the electron-beam current is ascertained, which indicates that the emission is stimulated for relatively low thresholds of the excitation intensity. It is shown that the ZnO films grown on the GaN substrates exhibit a much more effective cathodoluminescence compared to the cathodoluminescence in the films grown on α-Al₂O₃. It was observed that the luminescent properties of ZnO layers in the ZnO/GaN/α-Al₂O₃ structures subjected to long-term heat treatment at 750°C in an oxygen atmosphere exhibit a high thermal stability.     

Plasma polymerization of some silicon- and tin-containing monomers

Plasma polymerization of several selected saturated and unsaturated silicon- and tin-containing monomers, such as vinyltriethoxysilane (VTES), 3-aminopropyltriethoxysilane (APTS), hexamethyldisiloxane (HMDS), hexabutyldistannoxane (HBDS) and tetraethylstannane (TES), were examined in terms of the following selected plasma operational parameters: discharge time (t), flow rate of monomer (F) and power input (W). For the initial deposition rates (DR), the following empirical equation was proposed: DR = k t^a F^b W^c, from which the experimental values of the kinetic power factors (a,b,c and k) were calculated. The value of k calculated for VTES was the highest, indicating the high activity of the monomer in plasma in contrast to HBDS, which was about two orders of magnitude smaller. A modified Arrehnius equation was employed in the form of yield of deposition (DR/F) versus the specific energy (W/F), which showed that silicon-containing monomers are more active than their organotin analogues in the chosen plasma conditions. Plasma polymers of HMDS, TES and HBDS prepared at low conversions were highly crosslinked and their structures were similar to those of crosslinked poly(dialkylsiloxane) or poly(organostannoxane) while those of VTES and APTS were primarily linear.     

Oxidative dehydrodimerization of methane on Bi-Mn oxides: Catalyst active component and reaction mechanism

A series of Bi-Mn-O catalysts has been studied as a function of bismuth content (from 0 to 100 atom.%). The fresh-prepared samples are found to be a heterophasic mixture of the Bi₂Mn₄O₁₀ compound with the individual manganese or bismuth oxide, the surface of which is enriched in bismuth. At initial period of catalytic work, a part of Bi₂Mn₄O₁₀ decomposes to ga-Bi₂O₃ and -Mn₂O₃ resulting in the formation of rather effective catalyst for methane oxidative coupling. It is postulated that the catalyst active component consists of a Bi₂O₃ phase lying at the surface of a Bi₂Mn₄O₁₀ compound. At a steady state, the oxidative dehydrodimerization reaction occurs via both redox and associative mechanisms whilst the deep oxidation proceeds mainly according to the redox one.     

Micro ball-end milling of freeform titanium parts

Micro machining has growing number of applications in various industries such as biomedical,automotive,aerospace,micro-sensor,micro-actuator and jewelry industries.Small-sized freeform titanium parts are frequently needed in the biomedical applications,especially in the implantations such as mini-blood pumps and mini left-ventricular assist devices,finger joint replacements and small bone implants.Most of the small-sized titanium parts with freeform geometries are machined using micro ball-end milling before polishing and other surface treatments.Decreasing the cycle time of the machining parts is important for the productivity.In order to reduce the cycle time of the roughing process in the micro ball-end milling,this paper investigates the implementation of a previously developed force-based feedrate scheduling(FFS) technique on micro milling of freeform titanium parts.After briefly introducing the instantaneous micro milling forces in micro ball-end milling of titanium parts with freeform surfaces,the FFS technique is implemented in the rough machining of a freeform titanium surface to demonstrate the cycle time reduction potentials via virtual micro milling simulations.     

Electrical properties of MnIn2Se4

Semiconductors - The temperature dependence of conductivity and current-voltage characteristics of MnIn2Se4 crystals have been studied. It is shown that the current in the nonlinear part of the...     

Thermal and calorific properties of six aromatic hydrocarbons

Experimental p, v, and T data are used to derive standard-form equations of state for six aromatic hydrocarbons giving their thermal and calorific properties over a temperature range of 298–673°K and a pressure range of P_s to 500 bars with errors not exceeding the experimental ones.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 4, pp. 705–712, April, 1976.