Features of formation of cylindrical packs of mineral fibres

The danger of the appearance of fibre segments of increased linear density over the ends of cylindrical packs in winding of mineral fibres was substantiated. Dependences were obtained that allow determining the helix angle of the loops at which the linear density of the fibre will not exceed the acceptable values when the direction of movement changes. __________ Translated from Khimicheskie Volokna, No. 6, pp. 44–45, November–December, 2007.     

Vibratory densification of thermal insulation corundum products

Conclusions During vibratory densification, the bulk density and the angle of repose of the corundum bodies based on hollow granules and a porous filler depend on the type of the filler used and the size of its grains. The relative settling and the relative density of the bodies obtained after densification are related to their bulk density and the angle of repose.We established the dependence of the shrinkage during firing, the apparent density, and the strength of the fired products on the bulk density, the degree of settling, and the relative density of the specimens after vibratory densification. At a given density, the products based on the corundum granules exhibit higher strength.We developed large-sized corundum products of complex shape for thermal insulation at 1800°C under reducing conditions.Translated from Ogneupory, No. 4, pp. 28–32, April, 1986.     

Modeling of Filtration Combustion of Carbon

The kinetics of the overall reactions of carbon gasification at temperatures up to 1600 K is studied. The kinetic characteristics of the reactions are taken into account in a distributed mathematical model of filtration combustion of carbon. By computational experiment at different values of process control parameters (the gas flow rate, the fraction of the oxidant in the gas, and the mass ratio of carbon to the inert material in the combustible mixture), it is found that, in the wave of filtration combustion of carbon under superadiabatic conditions, carbon gasification can predominately yield either CO₂ or CO.     

Production of zinc ferrite in a mechano-chemical reaction by grinding in a ball mill

Zinc ferrite was obtained by prolonged dry grinding of stoichiometric powder mixtures of ZnO + -Fe₂O₃ or ZnCO₃ + -Fe₂O₃. The kinetics of transformation was studied by X-ray diffraction, Mössbauer spectroscopy and DTA. Crystallite size reduction followed the process, and defect structures resulted. The carbonate decomposed as a necessary step in the process. In the mixture of NiO + -Fe₂O₃, nickel ferrite was not obtainable, although considerable grain size reduction was observed. This was attributed to the inverse spinel configuration of the nickel ferrite, differing from the normal spinel configuration of the zinc ferrite. In the -Fe₂O₃ and the zinc ferrite, iron ions occupy octahedral sites, while in ZnO and the ferrite, zinc ions occupy tetrahedral sites, and metal ion—oxygen distance is almost identical. These facilitate the transformation. In the nickel ferrite, iron ions occupy both sites, which calls for high strains of -Fe₂O₃ before it can undergo transformation. Further implications of the processes are discussed.     

Ignition and Combustion of Dust-Gas Suspensions

The ignition and combustion of dust-gas suspensions are considered. It is shown that the ability of these systems to accumulate heat is determined not only by their kinetic and thermal properties but also by the relation between their reaction surface and the heat-removal surface (f). Experimental information on flame temperatures, ignition delays, and flame propagation over gas suspensions is processed using the parameter f, and the postulate on the stimulating role of the developed reaction surface in activating these processes is validated. It is shown that during overall burning, diffusion combustion of particles occurs only for rather small values of f. The ambiguous effect of the parameter f on the ignition and combustion processes leads to the necessity of optimizing the fuel size distribution and concentration for the effective operation of the power devices. The role of the macroparameters of two-phase flames of refractory metals in the synthesis of combustion nanoproducts is analyzed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 6, pp. 3–14, November–December, 2005.     

Polyelectrolyte swelling of polyamidobenzimidazole

Conclusions An extreme character of the swelling of PABI fibres in DMAc-water mixtures has been detected. The maximum is observed in the region of a 10% water content.The peculiarity in swelling has been explained by the manifestation of a polyelectrolyte nature of the polymer.Translated from Khimicheskie Volokna, No. 5, pp. 34–35, September–October, 1987.     

Efficiency,recovery and productivity of continuous reverse osmosis systems: new closed expressions

Numerical and approximate analytical solutions for salt concentration polarization in hyperfiltration with laminar flow in a flat sheet configuration are presented. The analysis accounts for the variation of the water flux in the longitudinal direction. Approximate solutions were obtained with an integral method which was found to provide good agreement with the numerical solution. The integral method allows one to obtain closed expressions for the productivity Q, the recovery R and the efficiency E of a reverse osmosis system which can be applied relatively quickly in design calculations.In this analysis the physical properties of the solution are taken to be constant.     

Thermal properties of poly(tetramethyl-p-silphenylene siloxane) and (tetramethyl-p-silphenylene siloxane-dimethyl siloxane) copolymers

Some physical properties of poly(tetramethyl-p-silphenylene siloxane) homopolymer and random block copolymers of tetramethyl-p-silphenylene siloxane-dimethyl siloxane have been determined and correlated with polymer structure. Differential scanning calorimetry (d.s.c.), differential thermal analysis (d.t.a.), density gradient column measurements and optical hot stage melting point determination and diluent techniques were used. The thermodynamic melting temperature of the homopolymer was estimated to be 160°C and its heat of fusion, ΔH_u, found to be 54.4 J/g (13 cal/g or 2710 cal/mol of monomer repeat units). Its limiting glass transition temperature, T_g, was ?20°C. T_g of the copolymer was found to vary almost monotonically with increasing dimethyl siloxane (DMS) content ranging from ?20° (0% DMS) to just above ?123°C, for pure DMS polymer. The copolymer melting temperature was found to increase as the fraction of the crystalline (hard) TMPS constituent was increased. Based upon copolymer theory and extrapolated melting point data, it was estimated that the block size of soft DMS component in the copolymer most probably consists of twelve monomer units distributed amongst TMPS sequences of varying length.