First Cycle Of Heating Research Articles

Effect of magnesium and silver doping on the thermoelectric performance of cast Mg2Sn alloys

High quality undoped and silver (Ag) doped Mg2Sn cast products with relatively less cracking were obtained using radio-frequency (RF) induction method under argon atmosphere. The thermoelectric properties of cast alloys were studied as a function of magnesium added up to ∼10.8 wt. % in the temperature range of 323 K (50 °C) to 723 K (450 °C). It was observed that the electrical and thermal conductivity at 323 K (50 °C) was increased by approximately 12 and 4 times as the magnesium concentration changed from 2 to 10.8 wt.%. The lattice thermal conductivity of the near stoichiometric alloy decreased by at least 2 times due to silver doping. However, such effect is faded with an increase in magnesium concentration. This was attributed to the probable increase in the electronic contribution due to metallic magnesium phase. Interestingly, the electrical (and thermal) conductivity was irreversible during the first cycle of heating and cooling. The irreversibility in the conductivity was attributed to the inhomogeneous distribution of tin (Sn) in the Mg phase prior to heating. The Seebeck coefficient of the Ag doped alloy with 10.8 wt. % Mg was ∼120 μV/K and it was reduced to 55 μV/K after the first cycle of heating. However, the decrease in the Seebeck coefficient following cooling was not systematic across all the alloys investigated here. The inability to obtain a unique Seebeck coefficient in the cast alloys at ∼323 K (50 °C) was primarily due to the coarse grain size of Mg2Sn and Mg phases and their respective grain orientations. Consequently, a maximum ZT of 0.055 was obtained at 323 K. However, a ZT of the order of 0.015 can be readily obtained in near stoichiometric silver doped cast Mg2Sn alloys at high temperatures ∼723 K.

The re-entrant cholesteric phase of DNA

The character of packing of double-stranded DNA molecules in particles of liquid-crystal dispersions formed as a result of the phase exclusion of DNA molecules from aqueous salt polyethylene glycol solutions has been estimated by comparing the circular dichroism (CD) spectra of these dispersions recorded at different osmotic pressures and temperatures. It is shown that the first cycle of heating of dispersion particles with hexagonally packed double-stranded DNA molecules leads to the occurrence of abnormal optical activity of these particles, which manifests itself in the form of a strong negative CD band, characteristic of DNA cholesterics. Moreover, subsequent cooling is accompanied by a further increase in the abnormal optical activity, which indicates the existence of the “hexagonal → cholesteric packing” phase transition, controlled by both the osmotic pressure of the solution and its temperature. The result obtained can be described in terms of “quasi-nematic” layers composed of orientationally ordered DNA molecules in the structure of dispersion particles. There are two possible ways of packing for these layers, which determine their hexagonal or cholesteric spatial structure. The second heating → cooling cycle confirms these results and is indicative of possible differences in the packing of double-stranded DNA molecules in the hexagonal phase, which depend on the osmotic pressure of the solution.

Study on Characterization of River Sand as Heat Storage Medium

The article focuses towards the study and characterization of the river sand suitability for high temperature thermal energy storage. The study is carried out preferably on the specific heat capacity of the river sand. A river sand sample from the banks of cauvery having the smallest grain size has been chosen. The sample undergoes the tests namely; Thermal Gravimetric Analysis (TGA), Fourier Transform Infrared Analysis (FTIR) and Differential Scanning Calorimeter (DSC). Detailed analysis is carried out to observe the sample’s change in weight when subjected to heating. FTIR analyzes the chemical groups present in the sample and DSC helps to identify its specific heat capacity which could justify the effect of thermal storage. TGA analysis showcased 1.013% of change in the sample weight during the first cycle of heating. However, during further heating cycle’s negligible change in weight is observed. Therefore, same sample could be used for several heating cycles without the need for replacement. The reason behind the weight loss was later examined by FTIR analysis. It is observed that the carbonate compound present in the sample was missing after heating. This test justifies the absence of carbonate compound presence after the heating process. The specific heat capacity of sand was found to be 1041 J/Kg/K by DSC analysis. The observed value of specific heat capacity of sand shows its superiority over the conventionally used high temperature thermal storage medium mainly molten salt and synthetic oils. The observation shows the heated sample with agglomeration due to the presence of other impurities and a considerable color change was observed. River sand is tested for its thermal characteristics and studied for the first time to the best of knowledge which the researchers are still at the finding stage. The specific heat capacity observed in the river sand makes its suitable for high temperature thermal energy storage in Concentrated Solar Power Plants (CSP).

An old dog with new tricks: Schiff bases for liquid crystals materials based on isoxazolines and isoxazoles.

AbstractSchiff bases are in action again showing an exuberant mesophase range despite their chemical and thermal weakness. Two series of Schiff bases (SB), based on isoxazolines 9 a–f and isoxazoles 10 a–f, are described. 9 a–f were synthesized by a [3+2] cycloaddition 1,3‐dipolar of arylnitrile oxide from p‐nitrobenzaldehyde (1) and alkenes. And, subsequently oxidized to 10 a–f by MnO2. The isoxazolines and isoxazoles thus obtained were reduced to aniline derivatives and condensed with appropriated arylaldehydes. The SBs series isoxazolines 9 a–f presented a narrow mesophase range, while SBs series isoxazoles 10 a–f showed a large mesophase range. Nematic mesophase was observed for SBs with short and non‐polar groups, while SmA and SmC mesophase for SBs with long and more polar terminal groups. The stability of the SBs is also dependent on the clearing temperature. For 10 a–f with high clearing temperature, decomposition induced by heat was observed during the first cycle of heating and in solutions of CDCl3. Series 9 a–f was more resistant to the thermal decomposition.

Thermal Deformation of Cement-Asphalt Mortar under Repetitive Heating and Cooling

Cement-asphalt mortar interlayer plays an important role in ballast-less track in high speed railway. Cement-asphalt mortar undergoes repetitive changes in temperature when it is exposed to its service environment. Change in temperature has a significant effect on the thermal deformation of cement-asphalt mortar, and even affects directly the durability of ballast-less track. In the paper, length and mass of the specimens of cement-asphalt mortar were continuously measured during the heating and cooling cycles within the range of temperatures of -10~60°C. The results indicate that there is an evidently irreversible shrinkage at the end of the first cycle of heating and cooling. The shrinkage taken place at the end of cycles of heating and cooling decreases with the increase in cycle numbers. Apart from the curve for the first heating, deformation curves of cement-asphalt mortar either for heating or for cooling are nearly lines. After being heated and cooled for 5 times, the temperature-deformation curve for heating nearly overlaps the curve for cooling. The percent of moisture loss at the end of every cycle decreases with the increase in cycle numbers. Thermal shrinkage occurs at about 0°C in the first heating.

Stress Evolution During Annealing of Cu/Au, Cu/Ag and Au/Ag Bilayers

Experimental observations of the measurements of the average force F per width (i.e., F/w) during annealing of Au/Cu, Cu/Au, Ag/Cu, Cu/Ag, Au/Ag and Ag/Au bilayers attached to silicon substrate are reported. Systems with total thickness of 12 nm and thicknesses of films of 6 nm are investigated. The total force per width in a system was determined in-situ by the substrate curvature measurement method with the laser scanning technique during deposition and annealing. Significant stress evolution during the first cycle of heating was observed for all samples. It was found that during the first annealing cycle, irreversible changes occur in layers and increases the interface roughness. An increase in the interface roughness modifies the coefficients of elastic deformation of layers. Subsequent annealing cycles do not cause major changes in the stress in a bilayer.

Stress evolution of Au/Cu/Au tri-layer systems during annealing

Experimental observations of the measurements of the average force per width (i.e. F/w) during deposition and annealing of Au/Cu/Au tri-layers attached to silicon substrate are reported. Systems with constant thickness of Au films (5nm) and with different thickness of Cu films (5–20nm) are investigated. The total force per width in a system was determined in situ by the substrate curvature measurement method with the laser scanning technique during deposition and annealing. Significant stress evolution during the first cycle of heating was observed for all samples. It was found that during the first annealing cycle, irreversible changes occur in layers. The beginning of deviation from linear part of stress curve can identify the temperature at which plastic deformation processes occurring in materials of the multilayer. Subsequent annealing cycles do not cause major changes in the stress in Au/Cu/Au tri-layer systems.

Effect of annealing on the mechanical behaviour of Au/Cu and Cu/Au bilayers on silicon

AbstractThe realtime evolution of stress during deposition of Cu/Au and Au/Cu bilayers was studied by an in‐situ curvature measurement optical technique and annealing in the temperature range from room temperature to 400 °C. The Au/Cu and Cu/Au bilayers attached to silicon substrate with total thickness equal 12 nm and individual film thicknesses equal 6 nm Cu and 6 nm Au; 4 nm Cu and 8 nm Au; and 8 nm Cu and 4 nm Au, respectively, were examined. During deposition, an increase in tensile stress with increasing the total thickness of a system for both Au/Cu and Cu/Au bilayers were observed. Deposition of Au layer on Cu layer resulted in a change in compressive direction, whereas no change was observed for Cu deposition on Au. This difference is explained by lattice parameter mismatch. Significant stress evolution during the first cycle of heating was observed for all samples. It was found that irreversible modifications occur in systems during the first cycle of annealing. A change in the slope of the elastic part of stress curve during heating indicates a change in the coefficient of thermal expansion of metallic layers. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Damage of the unalloyed-plutonium structure as a result of phase naklep and self-irradiation: An electrical-resistance study

Damage of the structure of the α phase of plutonium as a result of repeated α ↔ β phase recrystallization and prolonged self-irradiation was estimated based on the changes in the electrical resistance measured at room temperature before and after phase recrystallization. Samples with different time of storage were used. An analysis of the results showed that the electrical resistance of samples grows linearly depending on the number of cycles of phase recrystallization. It has been established that the slope of the dependences obtained is determined by the maximum temperature of the sample in the cycle. At a maximum temperature in the cycle equal to 170°C, an increase in the relative electrical resistance of the samples was ∼2.5%/cycle; when heating to 125°C, ∼0.3%/cycle. The variation of the electrical resistance of the samples stored for ∼20 years depending on the number of cycles of phase recrystallization exhibited a single feature, namely, a decrease in resistance in the first cycle of heating to 170°C rather than an increase observed in the experiments with the samples stored for ∼2.5 year. This decrease is connected with the influence of the possible beginning of migration of radiogenic helium. In the subsequent cycles, the change in the electrical resistance of samples upon prolonged storage was analogous to that of the samples with a short time of storage.

Thermal, structural and morphological assessment of PVP/HA composites

Composites of poly(vinyl pyrrolidone)/hydroxyapatite (PVP/HA), at variable proportions (100/0; 80/20; 50/50; 20/80 wt%) were prepared and characterized by Fourier transformer-infrared spectroscopy (FT-IR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and thermogravimetry/differential thermogravimetry (TG/DTG). PVP carbonyl stretching was slightly shifted to lower frequency in composites indicating the formation of hydrogen bonding with HA hydroxyl groups. At the first cycle of heating, the calorimetric curves revealed a broad peak the intensity of which was reduced insofar as the amount of PVP decreased in the composites. This peak was attributed to the PVP enthalpy relaxation. According to the TG/DTG curves, PVP degraded into two steps sharply perceivable in the composites. The first decay was ascribed to the release of the pyrrolidone pendant groups and the following one concerned the burning of the hydrocarbon chains. The HA molecules seem to exert a catalytic action on the PVP degradation.

Young’s modulus defect for the solid solution of hydrogen in palladium (PdH x )

We use the internal friction method in the free vibration mode to study the temperature dependence of the spectra of dissipative losses and shear modulus in the Pd polycrystalline system, the PdHx penetration solid solution, and in the dehydrogenized Pd system. Studying the spectra and shear moduli, we discovered that the hydrogen desorption from the α- and β-phases of the PdHx system occurs completely after the first cycle of heating of this system. The temperature dependences of the shear modulus of the original and dehydrogenized systems coincide. The existence of dissipative processes in the solid solution is related to the mobility of hydrogen atoms in the face-centered cubic lattice of the Pd structure and provokes the appearance of peaks of losses on the modulus defect spectrum in the temperature region. We consider the possibility of describing the modulus defect in the framework of phenomenological models of elasticity.

Spectral reflectivity of ceramics of cubic zirconium oxide on the wavelength of 0.63 μm under intense surface heating above the melting point and subsequent cooling

The experimental data on the normally hemispherical reflectivity of zirconium oxide ceramics are obtained for the wavelength of 0.63 μm in the course of the first cycle of heating by concentrated laser radiation up to temperatures above the melting point and free cooling in ambient air. The obtained data are compared with analogous results of the second and subsequent cycles of heating and cooling. Analysis is made of the effect of the temperature field in the heated layer on the reflectivity and on the “effective” temperature measured by a pyrometer.

Coking propensity of Athabasca bitumen vacuum bottoms in the presence of H-donors — formation and dissolution of mesophase from a hydrotreated petroleum stream (H-donor)

The effect of H-donors (hydrogenated aromatic hydrocarbons — HHAP) derived from a petroleum stream on mesophase formation during thermal hydrocracking of Athabasca bitumen vacuum bottoms (ABVB, +525°C) was investigated using real time high pressure and temperature microscopy (hot-stage) under a nitrogen atmosphere. When ABVB was treated alone, mesophase formed at a relatively fast rate after only 66–70 min (at 440°C). When HHAP was treated alone under the same conditions, it showed a highly fluid behavior. This material did not develop any mesophase even after a prolonged first cycle of heating (>140 min), but eventually formed mesophase during a second cycle of prolonged heating. Two distinct mesophase types were observed during thermal treatment of HHAP. One type of mesophase dissolved upon heating at moderate temperatures and re-appeared upon cooling, an indication of “thermotropic transformation” typical of true liquid crystalline material derived from low molecular weight components. The other type of mesophase that was most likely derived from high molecular weight components did not dissolve but formed bulk mesophase. ABVB was then mixed with 5 wt.% HHAP to observe the effect of an H-donor on mesophase formation from bitumen. In the presence of HHAP, both the rate and the amount of mesophase formed from ABVB were reduced significantly. Furthermore, the mesophase appearance time (induction period) was prolonged by as much as 20 min. This paper demonstrates the usefulness of hot-stage microscopy as a tool for screening potential additives in visbreaking and fouling operations.

Immediate and delayed thermal expansion of hardened cement paste

Experiments are reported in which the thermal deformations were measured of thin tubular specimens of hcp conditioned to various relative humidities between 0 and 100%. Attention was concentrated on the first cycle of heating and cooling and on a second heating; the level of temperature was also an experimental variable. It was found that the thermal movement could be considered as the sum of two deformations, the immediate (taking place during the temperature change) and the delayed (taking place after temperature equilibrium was reached). The immediate deformation was approximately the same for all three temperature changes, was approximately linear with temperature, and exhibited a maximum value at an intermediate conditioning humidity towards 100%. The delayed deformation had a smaller reversible component, and a larger irreversible component which was associated only with the first heating. With only a few exceptions all the measurements of delayed deformation were of the same sense as the preceding immediate deformation. Measurements were made of two distinct types of evaporable water. There were no significant changes in the quantities of either as a result of temperature cycling.

Effect of substrate temperature during growth on defect density in bismuth thin films

Bismuth thin films of thickness 720±10 Å have been vacuum deposited on clean glass substrates held at various substrate temperatures ranging between 30 ° and 185 °C at a constant deposition rate 0f 3±0.3 Å s. Immediately after the formation of the films, the heat treatment was given to the films in situ. For each film, the resistance was recorded as a function of temperature during the heat treatment. It has been found that the resistance of the films decreases when the temperature increases during the first cycle of heating, and this has been attributed to the removal of defects. During the first cycle of cooling and the next cycle of heating and cooling, it is observed that the resistance first decreases when the temperature increases and then increases as the temperature increases. Using Vand’s theory, from the resistance–temperature data during heat treatment, both defect density and the initial lattice distortion energy spectra have been evaluated. It is observed from these spectra that as the substrate temperature increases the defect density decreases. It is also found that the defects have a mild preference for energies in the range between 1.30 and 1.35 eV. The results have been interpreted on the basis of the influence of the substrate temperature on the nucleation and growth phenomena in thin films.