Single-Step Synthesis of Chemically Cross-Linked Polysilastyrene and Its Conversion to β-Silicon Carbide

A new method for chemically cross-linking polysilastyrene using divinylbenzene as the cross-linking agent is reported. The procedure involves a single-step synthesis using the alkali-metal sodium to promote the polymerization of dimethyldichlorsilane in the presence of the comonomers phenylmethyldichlorosilane and divinylbenzene. The cross-linked polymer can be readily converted to β-SiC on pyrolysis at 1500°C. The β-SiC obtained by this procedure is nanocrystalline and has a grain-size distribution of 8–20 nm.     

New lipophilic cyclo- and poly-phosphazenes containing surfactant substituents

The reaction of the sodium salt of the commercially available surfactant Igepal CA 210^™ with hexachlorocyclotriphosphazene, N₃P₃Cl₆ (1) and poly(dichlorophosphazene), [—P(Cl₂)=N—]_n (Publisher's note: for graphical representation please see printed journal or the Acrobat PDF version on this website.) affords lipophilic cyclo- and poly-phosphazenes SSCP (2) and SSPP (4), respectively. These materials, containing a short chain oligo etheroxy side group while being completely insoluble in water, are soluble in a wide range of solvents ranging from hexane to chloroform. The polymer, SSPP (4) forms polymer–metal salt complexes with lithium salts. DC conductivity measurements by a complex impedance method have been carried out. The maximum conductivity observed for SSPP–LiClO₄ (O: Li ratio, 6:1) is 1·0×10^-6Scm^-1 at 348K. © 1998 SCI.     

A new family of Cayley graph interconnection networks of constantdegree four

We propose a new family of interconnection networks that are Cayley graphs with constant node degree 4. These graphs are regular, have logarithmic diameter, and are maximally fault tolerant. We investigate different algebraic properties of these networks (including fault tolerance) and propose optimal routing algorithms. As far as we know, this is the first family of Cayley graphs of constant degree 4     

Experimental study and analysis of lubricants dispersed with nano Cu and TiO<Subscript>2</Subscript> in a four-stroke two wheeler

The present investigation summarizes detailed experimental studies with standard lubricants of commercial quality known as Racer-4 of Hindustan Petroleum Corporation (India) dispersed with different mass concentrations of nanoparticles of Cu and TiO₂. The test bench is fabricated with a four-stroke Hero-Honda motorbike hydraulically loaded at the rear wheel with proper instrumentation to record the fuel consumption, the load on the rear wheel, and the linear velocity. The whole range of data obtained on a stationery bike is subjected to regression analysis to arrive at various relationships between fuel consumption as a function of brake power, linear velocity, and percentage mass concentration of nanoparticles in the lubricant. The empirical relation correlates with the observed data with reasonable accuracy. Further, extension of the analysis by developing a mathematical model has revealed a definite improvement in brake thermal efficiency which ultimately affects the fuel economy by diminishing frictional power in the system with the introduction of nanoparticles into the lubricant. The performance of the engine seems to be better with nano Cu-Racer-4 combination than the one with nano TiO₂.     

Experimental studies on a metal hydride–based single bed sorption cryocooler

The present work deals with the development of a MmNi_4.5Al_0.5‐based single bed sorption precooled Linde‐Hampson cryocooler. The working substance and the precooling refrigerant used in this investigation were hydrogen and liquid nitrogen, respectively. The gaseous hydrogen could be compressed merely in the metal hydride reactor in comparative ease and thus an MmNi_4.5Al_0.5‐based metal hydride reactor was used to develop a single bed sorption compressor. The hydrogen is allowed to compress at two different supply pressures of 5 and 10 bar at a constant absorption temperature of 20°C. Desorption temperatures were varied at 65°C, 75°C, and 80°C. Maximum discharge pressures were obtained at a desorption temperature of 80°C as 21 and 27 bar, respectively. The entire cryocooler was designed, fabricated, and tested on the sorption cryocooler. Furthermore, compressed high‐pressure gaseous hydrogen was allowed to flow in the cryocooler at a flow rate of 40 standard cubic centimeter per minute. The minimum temperatures obtained in the evaporator at discharge pressures of 21 and 27 bar were 111 K and 107 K, respectively.     

Chemically Cross-linked Polysilanes as Stable Polymer Precursors for Conversion to Silicon Carbide

Cross-linked polysilanes were prepared by the co-polymerization of Me₂SiCl₂ or PhMeSiCl₂ with varying amounts of divinylbenzene (2–15% by weight) using molten sodium as the dehalogenating agent. All the cross-linked polysilanes were stable to air and could be processed thermally for conversion to silicon carbide. Polymers containing from 5–15% of the cross-linking agent underwent a uniform shrinkage during thermal treatment (1500 °C) to afford β-SiC in good yields. The ceramic was characterized by a variety of techniques including Raman and infrared spectroscopy, powder XRD, as well as Scanning Electron Microscopy (SEM). Dedicated to Prof. C. W. Allen in recognition of his outstanding contributions to inorganic polymers. Deceased in a tragic car accident in July 2004.     

Nanodimensional organostannoxane molecular assemblies

Organooxotin cages, clusters, and coordination polymers containing [Sn 2(mu-O)], [Sn 2(mu-OH)], [Sn 2(mu-O) 2], [Sn 2(mu-OH) 2], and [Sn 3(mu 3-O)(mu-OR) 3] building blocks have been assembled by the reactions of organotin precursors with phosphonic, phosphinic, carboxylic, or sulfonic acids. Various synthetic methodologies including Sn-C bond cleavage reactions and solventless procedures have been utilized to generate several nanodimensional organostannoxane assemblies. The synthesis, structure, and structural interrelationship of these diverse organostannoxane compounds are discussed. The synthetic knowledge gained to prepare specific organostannoxane structural forms in high yields has been utilized for the construction of dendrimer-like molecules. These contain a central stannoxane core and a functional periphery. The functional periphery can be readily modulated to assemble photoactive, electroactive, or multisite coordinating molecules. The synthesis, structure, and potential uses of these compounds are discussed.     

Fate of sulphate removed during the treatment of circumneutral mine water and acid mine drainage with coal fly ash: Modelling and experimental approach

The treatment of acid mine drainage (AMD) and circumneutral mine water (CMW) with South African coal fly ash (FA) provides a low cost and alternative technique for treating mine wastes waters. The sulphate concentration in AMD can be reduced significantly when AMD was treated with the FA to pH 9. On the other hand an insignificant amount of sulphate was removed when CMW (containing a very low concentration of Fe and Al) was treated using FA to pH 9. The levels of Fe and Al, and the final solution pH in the AMD–fly ash mixture played a significant role on the level of sulphate removal in contrast to CMW–fly ash mixtures. In this study, a modelling approach using PHREEQC geochemical modelling software was combined with AMD–fly ash and/or CMW–fly ash neutralization experiments in order to predict the mineral phases involved in sulphate removal. The effects of solution pH and Fe and Al concentration in mine water on sulphate were also investigated. The results obtained showed that sulphate, Fe, Al, Mg and Mn removal from AMD and/or CMW with fly ash is a function of solution pH. The presence of Fe and Al in AMD exhibited buffering characteristic leading to more lime leaching from FA into mine water, hence increasing the concentration of Ca²⁺. This resulted in increased removal of sulphate as CaSO₄·2H₂O. In addition the sulphate removal was enhanced through the precipitation as Fe and Al oxyhydroxysulphates (as shown by geochemical modelling) in AMD–fly ash system. The low concentration of Fe and Al in CMW resulted in sulphate removal depending mainly on CaSO₄·2H₂O. The results of this study would have implications on the design of treatment methods relevant for different mine waters.