A study of reinforced refractory concretes

Results of a laboratory study of the properties of corundum concrete with metallic fibers of five compositions are presented. It is shown that some of the fibers affect favorably the strength and heat resistance of the concrete. Industrial tests of parts made of the suggested reinforced concrete have proved these conclusions.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp. 22–24, November, 1996.     

Dehydrocyclization of 1-hexene to benzene on Cu3Pt(111)

The disproportionation ofn-butane (and of isobutane) was catalyzed by sulfated zirconium oxide containing 1.5 wt% Fe, 0.5 wt% Mn, and 4.0 wt% sulfate at 2.0 atm and temperatures in the range of 30–60C. The reaction accompanies isomerization, which under some conditions is as much as one or two orders of magnitude faster than disproportionation. The conversion to each of the products increased with time on stream in a flow reactor, and then declined. The time on stream for maximum conversion was the same for each product. The results suggest that the disproportionation and isomerization reactions proceed through a common C₈ intermediate. Rates of the disproportionation reaction were determined at the time on stream corresponding to the maximum conversion at each temperature; for example, the rate of conversion ofn-butane into isopentane at 60C with ann-butane partial pressure of 0.58 atm was about 1×10^–7 mol/(g of catalyst s).     

Stresses in a bed beneath rigid and flexible foundations under initial and repeated loadings

Conclusion The experiments indicated that repeated loading of flexible foundations (in contrast to rigid foundations) may result in significant variation in the stresses beneath them, which will lead to an appreciable increase in bending moments, elongations in reinforcement, and even to failure of the flexible foundation under a loading that did not give rise to dangerous deformations during the initial loading.Scientific-Research Institute of Bases and Underground Structures. Giproniiaviaprom. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 29–31, January–February, 1987.     

Direct fluorination of the polyimide matrimid® 5218: The formation kinetics and physicochemical properties of the fluorinated layers

Fluorinated polymers have a set of unique properties, including improved chemical stability and thermal stability and good barrier and membrane parameters, which are mainly defined by their surface properties. This article presents systematic data on the direct fluorination of the polyimide Matrimid® 5218, a commercially available polymer suitable for the formation of gas‐separation hollow fibers. Changing the fluorination conditions (i.e., the fluorinated mixture composition, fluorine partial pressure, and treatment duration) allows the rate of formation of the surface‐fluorinated layer over the 0.1–10 μm range to be kept under control. The physicochemical properties of modified layers (i.e., the chemical composition, formation of radicals, refractive index, IR and UV spectra, density, and surface energy) are examined. The thickness of the fluorinated layer (δ_F) depends on the fluorination duration (t): δ_F ～ t^0.5. During fluorination, hydrogen atoms are replaced with fluorine, double bonds are saturated with fluorine, and at least one CN bond in the five‐member ring is disrupted. Fluorination results in a significant increase in the polymer density, transparency in the visible and ultraviolet regions of spectra, and a reduction of the refractive index. A high concentration of long‐living radicals (up to ～5 × 10¹⁹ radicals/cm³ of the fluorinated layer) is generated under fluorination. This can be used for subsequent grafting (e.g., with acrylonitrile). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 6–17, 2004     

Structure and gas permeability of nanoporous metal oxide coatings produced by the alkoxide method

Peculiarities of the preparation of selective nanoporous metal oxide coatings on the surface of macroporous rutile support (pore size 0.1 μm and mixed aluminum and titanium oxides (pore size 0.05 μm) are presented. Gas selective coatings of empirical formula of P _x Ti_{1 ? 0.5x} O_{2 ± δ} with uniform distribution of nanosized pores have been obtained with the alkoxide method using titanium alkoxide and ettriol phosphite (precursor of the phosphorous-containing component) at their various total concentrations. Surface morphology of the obtained membranes has been investigated and major parameters of gas selective coatings have been determined. It has been shown that the dependences of the He, N₂, CO₂, and C₃H₈ gas permeability on temperature and pressure drop are consistent with the molecular regime of gas flow. The reproducible effect of permeability anisotropy of ～502?60% is observed when the integral vacuum method is used.     

Noble gases as indicators of molecular-selective gas transport in polymeric membranes

Methods of estimation of molecular-selective gas transport parameters in polymeric membranes and explanation of separation selectivity evolution for ‘small’ and ‘large’ molecules up to inversed selectivity are proposed based on comparative analysis of diffusion and solubility of noble gases as isotropic diffusion probes in different classes of polymers and block copolymers on their basis. Two approaches are considered in this work: (1) analysis of diffusional migration of permanent gases, lower hydrocarbons, and alcohols (vapor) in glassy polymers and rubbers relative to the diffusion of noble gases including radon; (2) adaptation of the ‘hard sphere’ theory developed for gas solubility in liquids to the calculation of the solubility of gases in the polymer matrix. In the latter case, noble gases as isotropic probes are used for calculating the required fitting parameters of the polymer medium.     

Modification of the surface of cross-linked oligophenylene based on 4,4''-diacetyldiphenyloxide and acetophenone by IR laser radiation

The influence of quasi-momentum IR laser radiation (CO₂ laser; wavelength λ = 10.6 μm; power density W = 70 W cm⁻²) on the physicochemical and mechanical properties of the surface of articles made from oligophenylene has been investigated. These oligomers were produced by the reaction of 4,4'-diacetyldiphenyl oxide and acetophenone and were filled with graphite. The measurements of the interfacial wetting angle demonstrated the influence of the irradiation dose on the surface energy. The relations between the coefficient of friction, wear and microhardness and the IR radiation dose were established. It was found that quasi-momentum IR laser radiation makes it possible to change significantly the structure of surface layers and to improve the tribological properties of polyphenylene without changing its chemical structure and initial physical properties as a whole.