Highly Monodisperse Colloidal Magnesium Nanoparticles by Room Temperature Digestive Ripening

Nanoclusters of 25 nm sized Mg-THF have been prepared by the solvated metal atom dispersion method. Room-temperature digestive ripening of these nanoclusters in the presence of hexadecylamine (HDA) resulted in highly monodisperse colloidal Mg-HDA nanoparticles of 2.8 ± 0.2 nm. An insight into the room-temperature digestive ripening process was obtained by studying the disintegration of clusters for various Mg:HDA ratios. The Mg colloids are quite stable with respect to precipitation of particles under Ar atmosphere. Using this procedure, pure Mg(0) nanopowders were obtained in gram scale quantities. The Mg powder precipitated from the colloid was fully hydrided at 33 bar and 118 °C. Initial desorption of H2 from samples of MgH2 was achieved at a remarkably low temperature, 115 °C compared to >350 °C in bulk Mg, demonstrating the importance of the size on the desorption temperatures.

Temperature characteristics of the billet and the dies in a small batch forging production

The work reported herein is part of an on-going programme to develop a computer code which, given the geometrical, process and material parameters of the forging operation, is able to predict the die and the billet cooling/heating characteristics in forging production. The code has been experimentally validated earlier for a single forging cycle and is now validated for a small batch production. To facilitate a step-by-step development of the code, the billet deformation has so far been limited to its surface layers, a situation akin to coining. The code has been used here to study the effects of die preheat-temperature, machine speed and rate of deformation the cooling/heating of the billet and the dies over a small batch of 150 forgings. The study shows: that there is a pre-heat temperature at which the billet temperature changes little from one forging to the next; that beyond a particular number of forgings, the machine speed ceases to have any pronounced influence on the temperature characteristics of the billet; and that increasing the rate of deformation reduces the heat loss from the billet and gives the billet a stable temperature profile with respect to the number of forgings. The code, which is simple to use, is being extended to bulk-deformation problems. Given a practical range of possible machine, billet and process specifics, the code should be able to arrive at a combination of these parameters which will give the best thermal characteristics of the die-billet system. The code is also envisaged as being useful in the design of isothermal dies and processes.

Mean-field results of a lattice-gas model of multilayer adsorption

A lattice-gas model of multilayer adsorption has been solved in the mean-field approximation by a different numerical method. Earlier workers obtained a single solution for all values of temperature and pressure. In the present work, multiple solutions have been obtained in certain regions of temperature and pressure which give rise to bysteresis in the adsorption isotherm. In addition, we have obtained a parameter which behaves like an order parameter for the transition. The potential-energy function shows a double minimum in the region of bysteresis and a single maximum elsewhere.

Temperature dependence of the dielectric constant of diamond

The temperature dependence of the dielectric constant of diamond has been measured over the temperature range 50-2OO"c. The value of E-ldc dT over this range is + 1 x 10-j. Details of the method of measuring the temperature coefficient of dielectric constant are also given. The magnitude and sign of c-ldc, dT for diamond has been theoretically calculated using Maxwell's relationship and Kramers-Heisenberg theory. The agreement between theoretical and experimental values is extremely good.

NMR relaxation study of disorder in the mixed system BP x GPI(1-x) and the low temperature transition from classical to quantum rotation

1H NMR spin-lattice relaxation time (T1) studies have been carried out in the temperature range 100 K to 4 K, at two Larmor frequencies 11.4 and 23.3 MHz, in the mixed system of betaine phosphate and glycine phosphite (BPxGPI(1-x)), to study the effects of disorder on the proton group dynamics. Analysis of T1 data indicates the presence of a number of inequivalent methyl groups and a gradual transition from classical reorientations to quantum tunneling rotations. At lower temperatures, microstructural disorder in the local environments of the methyl groups, result in a distribution in the activation energy (Ea) and the torsional energy gap (E01). For certain values of x, the magnetisation recovery shows biexponential behaviour at lower temperatures.

Natural convection from a vertical cone in a porous medium due to the combined effects of heat and mass diffusion with non-uniform wall temperature/concentration or heat/mass flux and suction/injection

An analysis has been carried out to study the non-Darcy natural convention flow of Newtonian fluids on a vertical cone embedded in a saturated porous medium with power-law variation of the wall temperature/concentration or heat/mass flux and suction/injection with the streamwise distance x. Both non-similar and self-similar solutions have been obtained. The effects of non-Darcy parameter, ratio of the buoyancy forces due to mass and heat diffusion, variation of wall temperature/concentration or heat/mass flux and suction/injection on the Nusselt and Sherwood numbers have been studied.

Microprocessor-based temperature indicator using a thermistor as the sensor

A novel microprocessor-based temperature indicator has been developed and described. This indicator provides a linear performance over a wide dynamic temperature range of 0-100°C with an accuracy of ±0-l°C. The interfacing module reduces computing time required by the microprocessor for solving the thermistor equation. Test results are given to support the theory.

The sputtering temperature of a cooling cylindrical rod with an insulated core

By a standard application of Jones's method associated with the Wiener-Hopf technique an explicit solution is obtained for the temperature distribution inside a cylindrical rod with an insulated inner core when the rod is allowed to enter into a fluid of large extent with a uniform speed, and a simple integral expression is derived for the value of the sputtering temperature of the rod at the points of entry. Numerical results under certain special circumstances are also obtained and presented in the form of a table.

Effect of Temperature Variation on Sister Chromatid Exchange Frequency in Cultured Human Lymphocytes

The effect of temperature variation on sister chromatid exchange (SCE) frequencies in human lymphocytes was studied. An increase as well as decrease in incubation temperature of cells leads to a higher frequency of sister chromatid exchanges than in cultures grown at 37°C. In addition, it was observed that mitotic: index and cell cycle duration were affected by low temperature.

High-temperature superconductivity in La- and Lu-substituted YBa2,Cu3,O7, and related oxides

The perovskites, Y0.75La0.25Ba2Cu3O7 and Y0.75Lu0.25Ba2Cu3O7, show high-Tc superconductivity (with zero resistance at or above 80 K), just as the parent compound YBa2Cu3O7. The Lu-substituted oxide, with the smallest unit-cell parameters, shows the highest Tc besides exhibiting a 100% Meissner effect. Hc1, in these oxides is around 25 mT, but the Hc2, is large. The thermopower of YBa2Cu3O7 shows a sharp transition to zero at the superconducting transition, reinforcing the bulk nature of the superconductivity. Preliminary studies show that ErBa2Cu3O7 and Er0.5Y0.5Ba2Cu3O7 are both high-temperature superconductors with zero resistance in the 82-90 K range.

Temperature dependence of 35Cl NQR in 2,6-dichloropyridine

Chlorine NQR in 2,6-dichloropyridine has been investigated in the temperature range 77 K to room temperature and a single resonance line has been observed throughout. Using this data, torsional frequencies of the molecule have been evaluated on the basis of both the Bayer theory and the modified Bayer theory incorporating Tatsuzaki correction.

Reactivities of tetrahalosilanes and silane with sulphur trioxide

Reactions of tetrahalosilanes [SiX4 (X= F, Cl or Br)] and silane (SiH4) with sulphur trioxide (SO3) have been studied under different experimental conditions. Each of the silanes behaves differently in accordance with the bond energy of the Si—X bond. While SiF4 remains unreactive even at 600°C, SiCl4 reacts with SO3 at 500°C giving rise to hexachlorodisiloxane [(SiCl3)2O] as the major product. In contrast SiBr4 and SiH4 react with SO3 at room temperature and below room temperature, respectively, yielding silica as one of the products of reaction. In all cases the SO3 is reduced to sulphur dioxide.

New temperature fluctuation method for direct determination of thermal activation energy of deep levels in semiconductors

A new method is suggested where the thermal activation energy is measured directly and not as a slope of an Arrhenius plot. The sample temperature T is allowed to fluctuate about a temperature T0. The reverse-biased sample diode is repeatedly pulsed towards zero bias and the transient capacitance C1 at time t1 is measured The activation energy is obtained by monitoring the fluctuations in C1 and T. The method has been used to measure the activation energy of the gold acceptor level in silicon.

1H NMR and a study of the anomalous temperature dependence of the 35Cl NQR frequencies in 2-chloro-3-pyridinol

A 35Cl NQR study of 2-chloro-3-pyridinol showed the presence of four NQR signals at 77 K. One of the lines showed a positive temperature coefficient of the NQR frequency. 1H NMR studies showed the presence of intramolecular hydrogen bonding, and the anomalous NQR temperature dependence has been explained in terms of Bayer and hydrogen bond effects. The room temperature x-ray structure and the low-temperature NQR data suggest the presence of a phase transition.

Pressure and temperature dependence of the electrical resistivity of bulk Al23 Te77 glass

Electrical resistivity of bulk amorphous Al23T77 samples has been studied as a function of pressure (up to 80 kbar) and temperature (down to 77 K). At atmospheric pressure the temperature dependence of resistivity obeys the relation = π0 exp(δE/RT) with two activation energies. In the temperature range 300 K T > 234 K the activation energy is 0.58 eV and for 234 >T 185 K the value is δE = 0.30 ev. The activation energy has been measured as a function of pressure. The electrical resistivity decreases exponentially with the increase of pressure and at 70 kbar pressure the electrical behaviour of the sample shows a metallic nature with a positive temperature coefficient. The high pressure phase of the sample is found to be a crystalline hexagonal phase.