Structural transition and enhanced phase transition properties of Se doped Ge2Sb2Te5 alloys

Amorphous Ge2Sb2Te5 (GST) alloy, upon heating crystallize to a metastable NaCl structure around 150 degrees C and then to a stable hexagonal structure at high temperatures (>= 250 degrees C). It has been generally understood that the phase change takes place between amorphous and the metastable NaCl structure and not between the amorphous and the stable hexagonal phase. In the present work, it is observed that the thermally evaporated (GST)(1-x)Se-x thin films (0 <= x <= 0.50) crystallize directly to the stable hexagonal structure for x >= 0.10, when annealed at temperatures >= 150 degrees C. The intermediate NaCl structure has been observed only for x, 0.10. Chemically ordered network of GST is largely modified for x >= 0.10. Resistance, thermal stability and threshold voltage of the films are found to increase with the increase of Se. The contrast in electrical resistivity between the amorphous and crystalline phases is about 6 orders of magnitude. The increase in Se shifts the absorption edge to lower wavelength and the band gap widens from 0.63 to 1.05 eV. Higher resistance ratio, higher crystallization temperature, direct transition to the stable phase indicate that (GST)(1-x)Se-x films are better candidates for phase change memory applications.

Molecular dynamics insight to phase transition in n-alkanes with carbon nanofillers

The present work aims to investigate the phase transition, dispersion and diffusion behavior of nanocomposites of carbon nanotube (CNT) and straight chain alkanes. These materials are potential candidates for organic phase change materials(PCMs) and have attracted flurry of research recently. Accurate experimental evaluation of the mass, thermal and transport properties of such composites is both difficult as well as economically taxing. Additionally it is crucial to understand the factors that results in modification or enhancement of their characteristic at atomic or molecular level. Classical molecular dynamics approach has been extended to elucidate the same. Bulk atomistic models have been generated and subjected to rigorous multistage equilibration. To reaffirm the approach, both canonical and constant-temperature, constant-pressure ensembles were employed to simulate the models under consideration. Explicit determination of kinetic, potential, non-bond and total energy assisted in understanding the enhanced thermal and transport property of the nanocomposites from molecular point of view. Crucial parameters including mean square displacement and simulated self diffusion coefficient precisely define the balance of the thermodynamic and hydrodynamic interactions. Radial distribution function also reflected the density variation, strength and mobility of the nanocomposites. It is expected that CNT functionalization could improve the dispersion within n-alkane matrix. This would further ameliorate the mass and thermal properties of the composite. Additionally, the determined density was in good agreement with experimental data. Thus, molecular dynamics can be utilized as a high throughput technique for theoretical investigation of nanocomposites PCMs. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Phase dependent photocatalytic activity of Ag loaded TiO2 films under sun light

Well-crystallized anatase and mixed (anatase-rutile) phase TiO2 thin films were deposited by DC magnetron sputtering technique at various DC powers in the range of 80-140 W. Pure anatase phase was observed in the TiO2 films deposited at low power of 80 W. Films deposited at 120 W were composed of both anatase and rutile phases. At higher power of 140 W, the films are rutile dominated and the rutile percentage increased from 0 to 82% with increase of DC power. The same results of phase change were confirmed by Raman studies. The surface morphology of the TiO2 films showed that the density of the films increased with increase of sputter power. The optical band gap of the films varied from 3.35 to 3.14 eV with increase of DC power. The photocatalytic activity of the TiO2 films increased with increasing DC power up to 120 W and after that it decreases. We found that the TiO2 films deposited at 120 W with 48% of rutile phase, exhibited high photocatalytic activity (43% of degradation) under UV light compared with other TiO2 films. After loading the optimized Ag nanoparticles on the mixed phase TiO2 films, the photocatalytic activity shifted from UV to visible region with enhancement of photocatalytic activity (55% of degradation). (C) 2015 Elsevier B.V. All rights reserved.

Phase dependent photocatalytic activity of Ag loaded TiO2 films under sun light

Well-crystallized anatase and mixed (anatase-rutile) phase TiO2 thin films were deposited by DC magnetron sputtering technique at various DC powers in the range of 80-140 W. Pure anatase phase was observed in the TiO2 films deposited at low power of 80 W. Films deposited at 120 W were composed of both anatase and rutile phases. At higher power of 140 W, the films are rutile dominated and the rutile percentage increased from 0 to 82% with increase of DC power. The same results of phase change were confirmed by Raman studies. The surface morphology of the TiO2 films showed that the density of the films increased with increase of sputter power. The optical band gap of the films varied from 3.35 to 3.14 eV with increase of DC power. The photocatalytic activity of the TiO2 films increased with increasing DC power up to 120 W and after that it decreases. We found that the TiO2 films deposited at 120 W with 48% of rutile phase, exhibited high photocatalytic activity (43% of degradation) under UV light compared with other TiO2 films. After loading the optimized Ag nanoparticles on the mixed phase TiO2 films, the photocatalytic activity shifted from UV to visible region with enhancement of photocatalytic activity (55% of degradation). (C) 2015 Elsevier B.V. All rights reserved.

Phase transformation in the surface region of zirconia and doped zirconia detected by UV Raman spectroscopy

The phase evolution of yttrium oxide and lanthanum oxide doped zirconia (Y2O3-ZrO2 and La2O3-ZrO2, respectively) from their tetragonal to monoclinic phase has been studied using UV Raman spectroscopy, visible Raman spectroscopy and XRD. UV Raman spectroscopy is found to be more sensitive at the surface region while visible Raman spectroscopy and XRD mainly give the bulk information. For Y2O3-ZrO2 and La2O3-ZrO2, the transformation of the bulk phase from the tetragonal to the monoclinic is significantly retarded by the presence of yttrium oxide and lanthanum oxide. However, the tetragonal phase in the surface region is difficult to stabilize, particularly when the stabilizer's content is low. The phase in the surface region can be more effectively stabilized by lanthanum oxide than yttrium oxide even though zirconia seemed to provide more enrichment in the surface region of the La2O3-ZrO2 sample than the Y2O3-ZrO2 sample, based on XPS analysis. The surface structural tension and the enrichment of the ZrO2, component in the surface region of ZrO2-Y2O3 and ZrO2-La2O3 might be the reasons for the striking difference between the phase change in the surface region and the bulk. Accordingly, the stabilized tetragonal surface region can significantly prevent the phase transition from developing into the bulk when the stabilizer's content is high.

Phase transformation in the surface region of zirconia detected by UV Raman spectroscopy

The phase transformation of zirconia from tetragonal to monoclinic is characterized by UV Raman spectroscopy, visible Raman spectroscopy, and XRD. Electronic absorption Of ZrO2 in the UV region makes UV Raman spectroscopy more sensitive at the surface region than XRD or visible Raman spectroscopy. Zirconia changes from the tetragonal phase to the monoclinic phase with calcination temperatures elevated and monoclinic phase is always detected first by UV Raman spectroscopy for the samples calcined at lower temperatures than that by XRD and visible Raman spectroscopy. When the phase of zirconia changes from tetragonal to monoclinic, the slight changes of the phase at very beginning can be detected by UV Raman spectroscopy. UV Raman spectra clearly indicate that the phase transition takes place initially at the surface regions. It is found that the phase change from tetragonal to monoclinic is significantly retarded when amorphous Zr(OH)(4) was agglomerated to bigger particles and the particle agglomeration of amorphous zirconium hydroxide is beneficial to the stabilization of t-ZrO2 phase.

Modeling of ingot development during the start-up phase of direct chill casting

Direct chill (DC) casting is a core primary process in the production of aluminum ingots. However, its operational optimization is still under investigation with regard to a number of features, one of which is the issue of curvature at the base of the ingot. Analysis of these features requires a computational model of the process that accounts for the fluid flow, heat transfer, solidification phase change, and thermomechanical analysis. This article describes an integrated approach to the modeling of all the preceding phenomena and their interactions.

Heat and mass transfer in two-phase porous materials under intensive microwave heating

Computational results for the intensive microwave heating of porous materials are presented in this work. A multi-phase porous media model has been developed to predict the heating mechanism. Combined finite difference time-domain and finite volume methods were used to solve equations that describe the electromagnetic field and heat and mass transfer in porous media. The coupling between the two schemes is through a change in dielectric properties which were assumed to be dependent both on temperature and moisture content. The model was able to reflect the evolution of both temperature and moisture fields as well as energy penetration as the moisture in the porous medium evaporates. Moisture movement results from internal pressure gradients produced by the internal heating and phase change.

A new computational approach to microwave heating of two-phase porous materials

Computational results for the microwave heating of a porous material are presented in this paper. Combined finite difference time domain and finite volume methods were used to solve equations that describe the electromagnetic field and heat and mass transfer in porous media. The coupling between the two schemes is through a change in dielectric properties which were assumed to be dependent on both temperature and moisture content. The model was able to reflect the evolution of both temperature and moisture fields as well as energy penetration as the moisture in the porous medium evaporates. Moisture movement results from internal pressure gradients produced by the internal heating and phase change.

The effect of phase-correlated returns and spatial smoothing on the accuracy of radar refractivity retrievals

Radar refractivity retrievals have the potential to accurately capture near-surface humidity fields from the phase change of ground clutter returns. In practice, phase changes are very noisy and the required smoothing will diminish large radial phase change gradients, leading to severe underestimates of large refractivity changes (ΔN). To mitigate this, the mean refractivity change over the field (ΔNfield) must be subtracted prior to smoothing. However, both observations and simulations indicate that highly correlated returns (e.g., when single targets straddle neighboring gates) result in underestimates of ΔNfield when pulse-pair processing is used. This may contribute to reported differences of up to 30 N units between surface observations and retrievals. This effect can be avoided if ΔNfield is estimated using a linear least squares fit to azimuthally averaged phase changes. Nevertheless, subsequent smoothing of the phase changes will still tend to diminish the all-important spatial perturbations in retrieved refractivity relative to ΔNfield; an iterative estimation approach may be required. The uncertainty in the target location within the range gate leads to additional phase noise proportional to ΔN, pulse length, and radar frequency. The use of short pulse lengths is recommended, not only to reduce this noise but to increase both the maximum detectable refractivity change and the number of suitable targets. Retrievals of refractivity fields must allow for large ΔN relative to an earlier reference field. This should be achievable for short pulses at S band, but phase noise due to target motion may prevent this at C band, while at X band even the retrieval of ΔN over shorter periods may at times be impossible.

Heat Conduction Equation Solution in the Presence of a Change of State in a Bounded Axisymmetric Cylindrical Domain

The heat conduction problem, in the presence of a change of state, was solved for the case of an indefinitely long cylindrical layer cavity. As boundary conditions, it is imposed that the internal surface of the cavity is maintained below the fusion temperature of the infilling substance and the external surface is kept above it. The solution, obtained in nondimensional variables, consists in two closed form heat conduction equation solutions for the solidified and liquid regions, which formally depend of the, at first, unknown position of the phase change front. The energy balance through the phase change front furnishes the equation for time dependence of the front position, which is numerically solved. Substitution of the front position for a particular instant in the heat conduction equation solutions gives the temperature distribution inside the cavity at that moment. The solution is illustrated with numerical examples. [DOI: 10.1115/1.4003542]

Population dynamics, sex ratio and size at sex change in a protandric simultaneous hermaphrodite, the spiny shrimp Exhippolysmata oplophoroides

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The influence of heat treatment on the phase relations in mineral growth systems

ABSTRACT Corundum is one of the most famous gems materials. Different heat treatment methods for enhancement purposes are commonly applied and accepted in the gem market. With this reason, the identification of the natural, unheated corundum is intensively investigated. In this study, aluminium hydroxide minerals and zircon are focused to observe the crystallization and phase change of these minerals during heat treatment procedures. Aluminium hydroxide minerals can be transformed to alumina with the corundum structure by heating. The reaction history of aluminium hydroxide minerals containing corundum was investigated comparing it with diaspore, boehmite, gibbsite and bayerite by TG and DTA methods. These hydroxide minerals were entirely transformed to corundum after heating at 600°C. Zircon inclusions in corundums from Ilakaka, Madagascar, were investigated for the influence of different heat-treatment temperatures on the recovery of their crystalline structure and on possible reactions within and with the host crystals. The host corundum was heated at 500, 800, 1000, 1200, 1400, 1600 and 1800°C. The crystallinity, the trapped pressure, and the decomposition of the zircon inclusions within the host corundum have been investigated by Raman spectroscopy. Radiation-damaged zircon inclusions may be used as an indicator for unheated Ilakaka corundum crystals. They are fully recrystallized after heating at 1000°C influencing the lowering of the 3 Raman band shift, the decreasing of FWHM of the 3 Raman band and the decreasing of the trapped pressure between the inclusion and the host corundum. Under microscopic observation, surface alterations of the inclusions can be firstly seen from transparent into frosted-like appearance at 1400°C. Then, between 1600°C and 1800 °C, the inclusion becomes partly or even completely molten. The decomposition of the zircon inclusion to m-ZrO2 and SiO2-glass phases begins at the rim of the inclusion after heating from 1200°C to 1600°C which can be detected by the surface change, the increase of the 3 Raman band position and the trapped pressure. At 1800°C, the zircon inclusions entirely melt transforming to solid phases during cooling like m-ZrO2 and SiO2-glass accompanied by an increase of pressure between the transformed inclusion and its host.

Local Heat Application for the Treatment of Buruli Ulcer: Results of a Phase II Open Label Single Center Non Comparative Clinical Trial.

BACKGROUND Buruli ulcer (BU) is a necrotizing skin disease most prevalent among West African children. The causative organism, Mycobacterium ulcerans, is sensitive to temperatures above 37°C. We investigated the safety and efficacy of a local heat application device based on phase change material. METHODS In a phase II open label single center noncomparative clinical trial (ISRCTN 72102977) under GCP standards in Cameroon, laboratory confirmed BU patients received up to 8 weeks of heat treatment. We assessed efficacy based on the endpoints 'absence of clinical BU specific features' or 'wound closure' within 6 months ("primary cure"), and 'absence of clinical recurrence within 24 month' ("definite cure"). RESULTS Of 53 patients 51 (96%) had ulcerative disease. 62% were classified as World Health Organization category II, 19% each as category I and III. The average lesion size was 45 cm(2). Within 6 months after completion of heat treatment 92.4% (49 of 53, 95% confidence interval [CI], 81.8% to 98.0%) achieved cure of their primary lesion. At 24 months follow-up 83.7% (41 of 49, 95% CI, 70.3% to 92.7%) of patients with primary cure remained free of recurrence. Heat treatment was well tolerated; adverse effects were occasional mild local skin reactions. CONCLUSIONS Local thermotherapy is a highly effective, simple, cheap and safe treatment for M. ulcerans disease. It has in particular potential as home-based remedy for BU suspicious lesions at community level where laboratory confirmation is not available. CLINICAL TRIALS REGISTRATION ISRCT 72102977.