Temperature dependence of the viscous flow of glass-forming melts in a broad temperature range

An equation which is able to describe the temperature dependence of the viscous flow of glassforming melts in a broad range, including the glass-transition range and elevated temperatures has been obtained. The equation contains three parameters; one of them is the preexponential multiplier, which is defined by the extension of the viscosity curve to elevated temperatures (using the Lagrange polynomial), and the other two, the delocalization energy of the atom and the transition potential of the particle, are adjustable parameters. The delocalization energy of the atom that is determined by adjustment is in sufficient accordance with the calculation according to the model of delocalized atoms. The nature of the viscous flow of glass and its melts is discussed.     

The effect of temperature on the water electrolysis reactions on nickel and nickel-based codeposits

Usually, an increase in the temperature of operation leads to a reduction in the voltage of operation of commercial water electrolyzers. The present work analyzes this effect in connection with the overpotential of the hydrogen and oxygen evolution reactions on electrodeposited nickel and some nickel-based codeposits which under normal operational conditions have shown good electrocatalytic characteristics. Results on pure nickel are also presented for comparison. A pressure chamber, adequate for electrochemical studies at high temperatures and pressures is described.     

Peculiar transition observed on the temperature dependence of water permeability of a novel hydrophilic polyamide membrane

Summary The relationship between the logarithmic hydraulic permeability and the reciprocal absolute temperature for a novel hydrophilic polyamide membrane peculiarly refracted at about 27°C, which was inferred to be some kind of transition point of the poly(BOL) in water. Some participation mode of water molecules in polar sites, including inter- and intramolecular hydrogen bonds through amide and ether groups, along poly(BOL) chains may vary discontinuously at the temperature.     

The effect of temperature on the observed flow-induced structure in semidilute solutions of gently solubilized starches

The effect of temperature on the unexpected shear-thickening behavior exhibited by semidilute solutions of waxy maize starch during a repeated shear-loop experiment was evaluated. Shear-thickening behavior, characterized using power law models, was observed for waxy maize starch, but not for normal maize starch at the same concentration. The shear-thickening region was observed for waxy maize starch at temperatures ranging from 25°C to 80°C and shear rates from 2–100 s^?1 during the initial part of the shear-loop experiment. For waxy maize starch, the power law exponent, n, was found to be 0.539 ± 0.017 in the shear-thinning region. For normal maize starch, the value of n was found to be equal to 0.751 ± 0.015 and only shear-thinning behavior was observed. The values of n for both waxy maize and normal maize starch were found to be temperature independent within the precision of the experimental measurements. The differences in n indicate the differences in the conformational dynamics of waxy maize and normal maize starches in solution.     

The effect of heating rate on porosity production during the low temperature reduction of graphite oxide

We studied the relationship between the thermal conditions and the evolution of the porosity in thermally reduced graphite oxide (TH-rGO) and found that the heating rate, rather than reduction temperature and atmospheric condition, played a crucial role in the evolution of porosity during the thermal reduction of GO at low temperatures. Higher heating rates increased the porosity of the TH-rGO. A slow heating rate facilitated the evolution of H₂O and CO₂ whereas a higher heating rate released CO₂ and CO gases with the concurrent development of a folded and crumpled morphology. We further demonstrated that the higher heating rate resulted in a highly porous texture with lower reduction temperature (below 140 °C) and shorter reduction time (less than 5 min), indicating that the reduction time and temperature are found to be dependent on the heating rate.     

The effect of gamma irradiation on the pressure dependence of the room temperature transition in PTFE

Some of the effect of gamma irradiation on the pneumatic pressure dependence of the well established room temperature transition (ca. 19 °C) in polytetra(fluoroethylene) are described. The experiments, conducted up to a maximum gamma dosage of 60 Mrad and a superimposed nitrogen pressure of 48.3 MPa indicate a significant reduction in the room temperature transition as well as its pressure dependence with the increasing of the gamma dosage. These data, combined with the observed and reported reduction in the free volume (actually net volume) are consistent with the proposition that irradiation process results in a reduction in the ‘effective internal pressure’ due to extensive bond scission. The latter process is manifested in an observed dramatic decrease in the molecular weight. Data on the compressibility and coefficient of thermal expansion, accompanied by thermodynamic arguments, indicate that the room temperature transition more closely resembles a second order transition as gamma dosage increases. This is consistent with a change in system behaviour progressing from a viscoelastic to that of a brittle glassy polymer as confirmed by monitoring the polymer creep behaviour following rapid pressurisation. Data for the ‘freshly’ irradiated specimens indicate highly transient post-irradiation induced changes in the polymer morphology.     

The effect of mechanochemical degradation on processability and porperties of PVC

The morphology and mechanical properties of PVC after vibro- or jet-milling as well as the rheological behavior of the mechanochemically degraded PVC were studied. The effect of vibro or jet-milling on the crystalline structure of PVC was examined through the crystalline absorption bands of FTIR spectra. The intensity of the crystalline absorption bands becomes weaker and indistinct with milling time. The PVC after milling results in improved melting efficiency, lower melt viscosity, shorter plasticizing time and higher tensile strength in comparing with those of the undegraded PVC due to the destruction of the crystalline structure and the decrease of molecular weight.     

The effect of fluid decoupling on viscous mixing

Flow in a three-dimensional channel with a sinusoidally-wavy, vertical wall is examined for the case of applied down- and cross-channel velocity components. An important parameter for the analysis of the nature of laminar mixing in the flow field occurs when the changes in the downstream direction can be decoupled from the changes in the cross-channel direction, thereby allowing for a two-dimensional solution of the system of equations. This paper shows the effect on the nature of laminar mixing when the decoupling of the momentum equations from a fully three-dimensional case to one where a two-dimensional solution can be performed. Experiments are performed on a channel with sinusoidally varying vertical walls that cover the range of decoupling criteria. Silicone pigmented either white or black was run in the apparatus, cured, and cross-sectioned. The cross sections embody a local, detailed history of the state of mixing as it proceeds down the mixer. The amount of mixing is presented as a function of position at each cross section for the different channel configurations. The nature of mixing changes from a linear growth rate in the amount of interfacial area to an exponential rate as the amplitude of the wave is increased. Results demonstrate the existence of chaos, islands, and the factors affecting the mixing behavior.     

The effect of heating temperature on the properties of vermiculites from Tanzania with respect to potential agronomic applications

This study was carried out to assess the properties of vermiculites from Tanzania with respect to the temperature used to expand them. Vermiculites from five locations in the Mozambique Belt of Tanzania were sampled and heated at 15, 200, 400, 600 and 800 °C in a muffle furnace. Palabora Europe Ltd provided one sample for comparison from their South Africa deposit which provides vermiculite used worldwide as a soil amendment. Water release characteristic, cation exchange capacity, pH, mass loss, and bulk density were among the properties assessed. All six vermiculites responded differently on heating, and had a significant variation in their agronomic properties. Water release characteristic varied with the degree of exfoliation and phase composition. Although vermiculites from Tanzania expanded on heating, their capacity to retain plant available water was relatively low as compared to vermiculite from Palabora. Disintegration on heating and the presence of a high amount of iron could be among the factors affecting their water release characteristic. Loss of hydroxyl water was higher in vermiculites than in hydrobiotites. Dehydroxylation enhanced the availability of exchangeable K⁺ and reduced significantly the cation exchange capacity of vermiculites. The optimum exchangeable K⁺ was obtained on heating at a temperature of 600 °C. The pH was unaffected by heating to a temperature of less than 600 °C. At higher temperature, the pH increased in some samples and was accompanied by substantial amounts of exchangeable Mg²⁺. Thus, it was concluded that initial characterization of vermiculites is essential prior to potential agricultural applications in order to optimize their agronomic potential.     

Lowering the sintering temperature of Gd-doped ceria by mechanochemical activation

Two kinds of Ce_0.8Gd_0.2O_2?δ pellets were synthesized by a solid-state reaction using two types of commercial CeO₂ and Gd₂O₃. In contrast to previous reports, pellets with a sintered density of 99% at 1300 °C were obtained regardless the powder used. Mechanochemical activation of the starting materials by 7 h of high energy milling, which resulted in particles several tens of nanometer in size, was effective in reducing the sintering temperature. Ce_0.8Gd_0.2O_2?δ pellets could be synthesized by direct sintering without calcination due to the homogeneous distribution of fine starting materials. The final phase was confirmed by the ionic conductivity, X-ray diffraction patterns and lattice parameters.     

The temperature dependence of micellar solubilization

The temperature dependence of micellar solubilization was determined in the 180°–140°F. temperature range by using a dye solubilization technique with built and unbuilt solutions of three high-eloud point, commereial surfactants, one anionic of the alkylaryl sulphonate type and two types of nonionic agents. It was found that the logarithm of solubilization in both built and unbuilt solutions was directly proportional to temperature (solubilization was an exponential function of temperature) and that the log solubilization-temperature slopes of the built and unbuilt solutions of each surfactant were approximately parallel.