Sol-Gel Synthesis of Magnesium Oxide-Silicon Dioxide Glass Compositions

MgO-SiO₂ glasses containing up to 15 mol% MgO, which could not have been prepared by the conventional glass-melting method because of the presence of stable liquid-liquid immiscibility, have been synthesized by the sol-gel technique. The gelling time decreased with increase in magnesium content, water: TEOS ratio, and reaction temperature. The gels were subjected to various thermal treatments and characterized using DTA, TGA, IR spectroscopy, XRD, and surfacearea- and port-size-distribution measurements. No organic groups could be detected in the glasses after heat treatments to ∼800°C, but trace amounts of hydroxyl groups were still present. The overall activation energy for gel formation in the 10MgO·90SiO₂ (mol%) system for the water: TEOS mole ratio of 7.5 was calculated to be 58.7 kJ/mol.     

Heat Extraction from a Diffusely Reflecting Bottom Salt Gradient Solar Pond

This paper presents an investigation of a three zone solar pond with a diffusely reflecting bottom under two modes of heat extraction viz. constant flow rate of the heat removal fluid and heat retrieval zone at constant temperature. At a typical flow rate of 10^-3 kg/s m ² M. S. Sodha , N. D. Kaushika and S. K. Rao , Energy Research , 5 , 321 – 340 , 1981 . [Google Scholar], optimal heat retrieval efficiencies of 32.4% (at non-convective zone depth, l_-2 = 1.25m), 25.2% (at l_-2 = 0.75m) and 21.5% (at l_-2 = 0.6m) are predicted at bottom reflectivities of 0.0, 0.5 and 0.8 respectively. In the mode of heat retrieval at constant temperature, efficiencies of 32.5% and 23.5% are obtained at extraction temperatures of 40°C and 100°C respectively for R = 0.0. However, these values of efficiency go down to 22.3% and 12.4% respectively for a typical value of R = 0.6.     

VISCOELASTICITY OF A SIMULATED POLYMER AND COMPARISON WITH CHICKPEA FLOUR DOUGHS

An integrated approach consisting of compression and stress relaxation is performed with a simulated model system of poly dimethyl siloxane (PDMS), a viscoelastic polymer material when the compressive strain, height of sample and crosshead speed were varied. The parameters derived are the forces at the end of compression and relaxation, energy for compression and the extent of elasticity of the sample based on the ratios of forces as well as the proposed energy values. The results were verified with food doughs undergoing large deformations that show a nonlinear behavior. The proposed extent of elasticity based on the ratios of energy stored and compression can be used as an index for the characterization of viscoelasticity. A nonlinear three‐parameter model had also been proposed to predict the stress decay characteristics as a function of time, which was found suitable for the PDMS system, and was better than the two‐parameter Peleg model as judged by lower variance values (0.0006–0.018 and 0.002–0.048, respectively). Further, an actual system of food doughs in the form of chickpea (Cicer arietinum L.) flour dough was used to verify the proposed model and viscoelastic index at different moisture contents (27–39%) subjected to compressive strains of 25–75%. The nonlinear relaxation characteristics of the food dough are sensitive to moisture content as well as to strain level.     

PROTEIN ADSORPTION AND FOULING OF CERAMIC MEMBRANES AS MEASURED BY SCANNING ELECTRON MICROSCOPY WITH DIGITAL X-RAY MAPPING

A technique for studying fouling in ceramic membranes using the energy dispersive x-ray spectroscopy capability of an electron microscope is described. The location and amount of foulant within the membrane are presented on a digital x-ray map showing elements constituent to or stained on the foulant.

Fouling of alumina membranes during filtration of the protein hemoglobin has been studied as a function of filtration time, pH, and membrane pore size. After each filtration run, the protein within a piece of the membrane was stained with phosphotungstic acid and located on a digital map of either phosphorus or tungsten.

For a 0.2 μm pore size membrane, time dependent fouling was observed consistent with an observed flux decline within the first few minutes of filtration. A pH dependence was also observed indicating much greater fouling at pH 6.9 near the protein isoelectric point than at pH 8.5. This observation is consistent with pH dependent adsorption, flux, and rejection studies. No internal fouling was observed for a 40 Å pore size membrane, which is consistent with the size of hemoglobin in solution being larger than the 40 Å pores and with the fact that the 40 Å membrane can be more easily cleaned after use than can the 0.2 μm membrane.     

Study of obliquely propagating electron acoustic shock waves with non-extensive electron population

Obliquely propagating electron acoustic shock waves in magnetized plasma composed of stationary ions, cold and non-extensive hot electrons are investigated by deriving Korteweg–de Vries Burgers(KdVB) equation. The tangent hyperbolic method is used to solve the KdVB equation in dissipative medium. The dissipation effect is introduced in the model by means of kinematic viscosity term. The analytical calculations of the KdVB equation shows that the structures(amplitude, velocity and width) of the shock waves are modified significantly with kinematic viscosity(η_0), obliqueness(k_z) and magnetic field(ω_c). Since plasmas are ubiquitously permeated with magnetic field, it is pertinent to explore the characteristics of KdVB equation in a magnetized plasmas.     

Precipitation in Partially Stabilized Zirconia

Transmission electron microscopy was used to study the sub-structure of partially stabilized ZrO₂ (PSZ) samples, i.e. 2-phase "alloys" containing both cubic and monoclinic modifications of zirconia, after various heat treatments. Monoclinic ZrO₂ exists as (1) isolated grains within the polycrystalline aggregate (a grain-boundary phase) and (2) small plate-like particles within cubic grains. These intragranular precipitates are believed to contribute to the useful properties of PSZ via a form of precipitation hardening. These precipitates initially form as tetragonal ZrO₂, with a habit plane parallel to the {100} matrix planes. The orientation relations between the tetragonal precipitates and the cubic matrix are
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A Mossbauer effect study of Ni3Fe1-xSix alloys for 0≤x≤0.9

⁵⁷Fe Mossbauer effect studies were carried out on the quasibinary Ni3Fe1-xSix alloy system for x = 0, 0.1, 0.25, 0.5, 0.75 and 0.9 compositions. Single phase alloys are formed upto x = 0.5 whereas a two phase alloy is observed for x = 0.75 composition. The x = 0.9 composition also shows single phase formation with lattice parameters close to Ni3Si. Substitution of Si primarily takes place at the Fe sites and the x = 0.25 composition shows a high degree of L12 order. The magnetic hyperfine field systematics are discussed in terms of first and second neighbour configurations. This revised version was published online in November 2006 with corrections to the Cover Date.     

Fracture Stress as Related to Flaw and Fracture Mirror Sizes

Fractographically observed critical-flaw boundaries in strength-tested specimens of 2 polycrystalline ceramics were used in calculating critical stress-intensity factors ( K_IC )- Each ceramic exhibited a K_IC which had little or no dependence on critical-flaw characteristics and which agreed with the value obtained from independent determinations on artificially precracked specimens. Analyses both of fracture-mirror sizes and of water-enhanced subcritical crack growth data supported the evidence that K_1C is a material constant. The fracture-mirror analysis further indicated that the parameter A/K_IC , where A is the fracture-mirror constant, is a dimensionless, material-independent constant.     

Effect of Hydrogenation on Some Physical Properties of Canola Oil

Canola oil from mixed seeds of cultivars Regent, Tower and Candle and oil from cultivar Regent were hydrogenated under selective (200°C and 48 kPa hydrogen pressure) and nonselective conditions (160°C and 303 kPa) using two different commercial catalysts. The physical properties of the hydrogenated oils determined were dropping point (Mettler), solid fat content by wide-line NMR, solid fat index by dilatometry and melting behavior by differential scanning calorimetry. Hydrogenation conditions had an important effect on physical properties. Differences were also observed between the oils and the catalysts.