Maximum Melting Temperature Research Articles

Evolution of the hydrothermal system at Los Azufres, Mexico, based on petrologic, fluid inclusion and isotopic data

The Los Azufres geothermal reservoir, formed in a fractured, Upper Miocene to Pliocene andesite and basalt base complex, is sealed to the surface by a silicic, mainly rhyolitic sequence of Pleistocene age. Almost the entire sequence is affected by hydrothermal alteration to varying extent. Petrological and fluid inclusion studies confirmed vertical zonation of the reservoir by secondary processes: Hydrothermal alteration processes under low temperature conditions (<170°C) caused argillitization of the shallow zone of the reservoir (depth <500m). Smectite, zeolite, calcite, and chlorite predominate the mineral assemblage in the shallow zone.At a depth of 1200–1500m, the maximum ice melting temperatures (Tmi) values of −0.7 to −4°C and salinities of 6.4wt% NaCl eq. indicate boiling conditions of the geothermal brine in a vapor-rich zone. Chlorite, calcite, quartz, zeolite, anhydrite, albite, sphene, pyrite, hematite, and illite form the hydrothermal mineral paragenesis with maximum temperatures of 250°C and pressure conditions of 150bar. Below 1500m, Tmi reach maximum values of −0.1°C and low salinities of 0.2wt% NaCl eq. The minerals epidote, amphibole, prehnite, and garnet indicate temperatures above 250°C and pressure conditions between 150 and 200bar. The measured homogenization temperatures (Th) of fluid inclusions (FI) are consistently higher than the in-situ measured temperatures, which indicates retrograde cooling of the Los Azufres geothermal reservoir since the time of the hydrothermal mineral formation.Updoming temperature isotherms at the center of the geothermal field (below well Az-9, Az-23, and Az-25) indicate the heating up of the fluids by a shallow magma chamber. Stable isotope data (δ18O, δD) of the geothermal brine indicates mixing processes between meteoric water and a minor magmatic component. Secondary reactions forming sericite may have caused a further positive shift in 18O in the shallow part of the geothermal reservoir.

Solubilization and Emulsification of Perfume in Discontinuous Cubic Phase

Solubilization of three typical perfume compounds, d-limonene (LN), β-ionone (IN), and geraniol (GL), in the discontinuous micellar cubic (I1) phase of the water−polyoxyethylene dodecyl ether (C12EO25) system was investigated by phase study and small-angle X-ray scattering (SAXS). The hydrocarbon perfume LN increases the maximum melting temperature of the I1 phase, whereas GL decreases it. This phenomenon is related to their solubilization location in the micelle. LN tends to be solubilized inside the aggregates and makes a perfume core (swelling). On the other hand, GL is solubilized in the surfactant palisade layer and expands the effective cross-sectional area per surfactant, aS (penetration). The penetration tendency is in the order GL, IN, and LN, judging from the SAXS analysis. The change in repulsion between hydrophilic moieties of surfactant upon addition of perfume is evaluated by calculating an optimum cross-sectional area, aS,opt, at which the EO chain is neither compressed nor expanded. It is found from the calculation of aS/aS,opt that the repulsion considerably increases in the LN system whereas it decreases in the GL system.

Cubic-Phase-Based Concentrated Emulsions

The effect of different types of added oil on the formation of a discontinuous micellar-type cubic phase was investigated in water–polyoxyethylene dodecyl ether (C12EO25) systems by phase study and small-angle X-ray scattering. The thermal stability of the cubic phase increases upon addition of oil, especially short-chain hydrocarbons. However, in the heptane system, the maximum melting temperature of the cubic phase is lower than that for decane due to the formation of a different liquid crystal phase. The effect of polyols on C12EO25 cubic phases was also investigated. It was found that the thermal stability of the cubic phase decreases with polyol concentration. The destabilizing effect becomes large as the polyol molecule penetrates further into the surfactant palisade layer. Although the solubilization of oil in the cubic phase is very low, a large amount of excess oil can be incorporated and a transparent cubic-phase-based concentrated emulsion is formed. The transparency is attributed to the very small difference in the refractive indices between the cubic and excess-oil phases.

Melting of the blends between syndiotacticity-rich and atactic poly(vinyl alcohol)s

A highly syndiotacticity-rich ( s-) poly(vinyl alcohol) (PVA) of a 66 s-dyad% [s(66)-PVA] was blended by a solution method with atactic ( a-) PVA of a 55 s-dyad% and another s-PVA of a 61 s-dyad%. The s(66)-PVA was shown to be able to produce cocrystallized phases with the other PVAs by investigating the melting behavior. The melting temperature and heat of fusion changed with the average syndiotacticity that was controlled by blending two PVAs with various compositions. As a result, the maximum melting temperature and the maximum heat of fusion appeared when the average rr triad value was 0.40, indicating that the high nucleation rate due to the high syndiotacticity component decreased the morphological factors such as the crystal size or the order of molecular packing.

Mechanism of Surface Quality Improvement in Continuous Cast Slab with Rectangular Cold Crucible Mold.

The control of the initial stage of solidification for continuous casting of steel is extremely important in producing high surface quality products. The surface quality is strongly influenced by the oscillation mark on the solidifying shell, which could be improved by applying alternating electromagnetic field in the mold. A 50×200 mm rectangular cold crucible mold has been designed by numerical simulation and used for measuring the meniscus contour and local heating of molten metals using tin and lead. It has also been used in continuous casting experiment with Sn and Sn-10%Pb alloy to study the effects of frequency, input power, melt level in the mold, casting speed, mold cooling water flow rate, and mold oscillation frequency on the oscillation mark. The maximum melt temperature was observed near the triple point where the mold wall, melt free surface and the atmosphere meet all together. It has also been found that the local Joule heating density has strong influence on the oscillation mark formation.

Phase equilibria in the ternary system Sc−Cr−C at subsolidus temperatures

Phase equilibria in the ternary system Sc−Cr−C were investigated by metallography, differential thermal analysis, x-ray diffraction, and electron probe microanalysis. A projection of the solidus surface was constructed for the first time. The nature of phase equilibria in the system is defined by the presence of two thermodynamically stable phases based on the compounds Sc2CrC3 (whose existence was confirmed) and ScC1−x. The melting point of the alloys increases with increasing carbon concentration. Compositions in the 〈Cr〉+〈ScC1−x〉+〈Sc〉 range have a minimum melting temperature equal to 1018±2°C, and the maximum melting temperature in the system, 1660±2°C, is found in alloys containing 〈Cr3C2〉+〈Sc2CrC3〉+C.

Effects of chain flexibility of chitosan molecules on the preparation, physical, and release characteristics of the prepared capsule

The effects of chain flexibility of chitosan molecules on the preparation, physical, and release characteristics of the prepared capsule were studied. The chain flexibility of chitosan molecules in solution was manipulated by using chitosans with different degrees of deacetylation (DD) (67.9%, 81.3%, 90.5%, 92.2%), different pHs (2.0, 3.0, 4.0), and NaCl concentrations (0, 0.3%). The solutions were then used to encapsulate hemoglobin or dextran by the orifice method to make the capsules. Axial ratios and break strengths were used to characterize the appearance and mechanical properties of the prepared capsules. D. S. C. was employed to measure enthalpies and maximum melting temperatures to be used as a quantitative index of hydrogen bond formation in the walls of the capsules. Release rate was used as a pore size indicator. The results show axial ratios of the capsules increased with a decrease in molecular weight and also with an increase in DD of chitosan used. Axial ratios also increased when 0.3% NaCl was added to the solutions used. The effects of solution pH show that capsules prepared from pH 3.0 solutions were smaller than those from pH 2.0 and/or pH 4.0 solutions. Capsules of lower break strengths had higher axial ratios. The enthalpies of the chitosan capsules increased with increasing DD of chitosans used, and also with increasing NaCl concentration in the solutions used. However the maximum melting temperatures showed no linear relationship with the DDs of chitosan used. Maximum melting point temperatures of capsules also increased with an increase in NaCl concentrations in solutions used. The hemoglobin and dextran release percentages from the capsule at 25 °C for 24 h increased with an increase of DD of chitosan used. The release rate also increased with the addition of NaCl in the chitosan solution used. The release percentages of capsules prepared from pH 4.0 solutions were higher than those from pH 2.0 and/or pH 3.0 solutions. Release percentages of dextran of different molecular weights from capsules of 81.3% DD chitosan and pH 3 solutions were 52.7% for 19600 Da dextran, 26.3% for 87000 Da dextran and 12.4% for 162000 Da dextran.

Crystallization of the one-component plasma at finite temperature.

We have determined the coexistence at positive temperature between a Wigner crystal and a fluid plasma using path integral Monte Carlo. The total energies are significantly different from classical and semiclassical predictions. The location of the phase transition between liquid and solid is higher in temperature than predicted by a generalized Lindemann criterion. Some features of the phase diagram can be understood using a novel application of the Clausius-Clapeyron equation. We find a maximum melting temperature of $6.0(5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\mathrm{Ry}$ at ${r}_{s}\ensuremath{\simeq}180(20)$.

Effect of molecular weight of chitosan with the same degree of deacetylation on the thermal, mechanical, and permeability properties of the prepared membrane

Different molecular weight, 90% deacetylated chitosans were obtained by ultrasonic degradation on 90% deacetylated chitosan at 80 °C for various times. Ninety percent deacetylated chitosan was prepared from alkali treatment of chitin that was obtained from red shrimp waste. Number average-, viscosity average- molecular weights were measured by gel permeation chromatography and the viscometric method, respectively. Degree of deacetylation was measured by the titration method. Enthalpy, maximum melting temperature, tensile strength and elongation of the membranes, flow rate of permeates and water are properties measured to elucidate the effect of molecular weight of chitosan on the above thermal, mechanical, and permeation properties, respectively of the prepared membranes. Results show tensile strength, tensile elongation, and enthalpy of the membrane prepared from high molecular weight chitosans were higher than those from low molecular weight. However, the permeability show membranes prepared from high molecular weight chitosans are lower than that from those of low molecular weight.

Chondrules as products of dust collisions with totally molten droplets within a dust-rich nebular environment: An experimental investigation

Chondrules are usually interpreted as the products of incomplete melting of mineral aggregates in the solar nebula and have textures controlled by the number of residual nuclei present after melting. If barred olivine (BO) chondrules formed by nearly total melting at their respective liquidi, i.e., over a wide temperature range, it is surprising that there are so few totally glassy chondrules. The occurrence of fine-grained, accretionary rims on chondrules suggests mineral dust in the chondrule-forming environment which might have collided with totally molten droplets to produce chondrule textures. We have, therefore, conducted experiments in which mineral dusts encounter molten droplets during their cooling at 500°C/h and cause nucleation. Our experiments reproduce the majority of common chondrule textures. The production of textures in our experiments is a function of the temperature at which dust is encountered, the number of dust grains encountered and, to a lesser extent, the mineralogy of the encountered mineral grains. Crystal growth rates increase with lower dust encounter temperatures giving a textural range with increasingly skeletal or elongated crystals for lower temperature encounters. We have produced some less commonly discussed types of chondrule textures, e.g., barred-olivine-porphyritic-olivine pyroxene (BO/POP) by dust seeding that have not been reproduced by the incomplete melting of starting materials. The reproduction of BO/POP and excentroradial textures by dust collisions, and the scarcity of natural totally glassy chondrules, suggest that formation by seeding of total melts was common for chondrules with the lowest liquidus temperatures, e.g., FeO-rich chondrules. From these seeding experiments we suggest that the maximum melting temperature chondrules experienced is limited only to the temperature at which evaporation of chondrule liquid occurs. However, we have reproduced the very fine-grained microporphyritic textures characteristic of Type IA chondrules only by incomplete melting. Such chondrules could not have reached average internal temperatures above their liquidus temperatures. The conclusion, that at least some chondrules formed from total melts that collided with mineral dust during cooling, indicates that chondrule formation occurred within a region of the nebula rich in mineral dust.

Relationships between the chain flexibilities of chitosan molecules and the physical properties of their casted films

Relationships between the chain flexibilities of chitosan molecules in solutions and the physical properties (gel swelling index, maximum melting temperature, and tensile strength) of their casted films were studied in order to manipulate the conditions to tailor the physical properties of the films made. The chain flexibilities of chitosan molecules in solutions were manipulated by using chitosans with different degrees of deacetylation (DD), pH and ionic strength of the media, and solvent systems. The results show the gel swelling index was independent of the media pH, and decreased with increasing DD of chitosans used, whereas maximum melting temperature and tensile strength increased with the increase of DD of the chitosan molecules. The differences were attributed to different crystalline regions in the films.

Self-diffusion of magnesium in spinel and in equilibrium melts: Constraints on flash heating of silicates

We have measured Mg self-diffusion in spinel and coexisting melt at bulk chemical equilibrium using an isotopic tracer. The diffusion coefficients were calculated from the measured isotope profiles using a model that includes the complementary diffusion of 24Mg, 25Mg, and 26Mg in both phases with the constraint that the Mg content of each phase is constant. This model also permits the calculation of the diffusion coefficient in one phase from the measured data in a coexisting phase. The activation energy and pre-exponential factor for Mg self-diffusion in spinel are, respectively, 384 ± 7kJ and 74.6 ± 1.1 cm 2/s. These data indicate Mg diffusion in spinel is much slower than previous estimates, probably because earlier measurements included grain boundary transport. The activation energy for Mg self-diffusion in coexisting melt is 343 ± 25 kJ and the pre-exponential factor is 7791.9 ± 1.3 2cm/s. The results from this study were applied to evaluate cooling rates of Plagioclase-Olivine Inclusions (POI) in the Allende meteorite. Given a maximum melting temperature for POIs of ~ 1500°C, these results show that a 10 μ radius spinel would equilibrate isotopically with a melt within about 60 min. To preserve Mg isotopic heterogeneity, the POIs must have initially cooled faster than 15 to 250°C/h depending on the initial temperature of flash heating. The cooling rate must also be slow enough to generate the observed basaltic textures. The inferred cooling rate appears to be comparable or up to ten times greater than those inferred from experimental and textural studies of synthetic CAI systems. The nature of the heating process is thus required to be short with relatively rapid cooling, such as flash heating. However, the relatively rapid cooling cannot be due to radiation into a cold, ~400°K nebula but would require radiation into a rather stable hot environment.

Dynamic cyrstallization of chondrule melts of porphyritic olivine composition: Textures experimental and natural

Melts of the same composition as has been defined for porphyritic olivine chondrules have been crystallized under controlled cooling conditions, dynamic crystallization. The full range of textures observed in such chondrules has been duplicated in the experimentally produced analogs. The primary controlling factor in producing this range of textuures is the heterogeneous nucleation behavior. In general, if nuclei are present when cooling begins, growth starts immediately at low degrees of supercooling and porphyritic textures result. The shapes of the phenocyrsts depend on the growth rate, which in turn depends on the cooling rate. With high nucleation densities and modest to low cooling rates, the textures are microporphyritic with generally equant, euhedral phenocrysts. As the nucleatio density decreases, the phenocrysts become larger, and as the cooling rate increases, they become increasingly skeletal. If nuclei are not present when cooling begins, growth is delayed until subcritical-sized embryos graduate to supercritical nuclei. Growth usually begins at some significant degree of supercooling depending on the cooling rate and how long it takes the embryos to become nuclei. The shapes of the crystals depend on the degree of supercooling when growth is initiated and on the subsequent cooling rate. The resulting textures vary from plate dendrites (barred olivine chondrules) to randomly oriented, elongated, skeletal crystals as the degree of supercooling and cooling rates decreases. The results of a matrix of experiments set limits on the maximum melting temperatures of chondrule forming materials and the subsequent cooling rates. Based primarily on crystal shape, the porphyritic textures develop best for this composition at melting temperatures less than 1590°C and cooling rates near 100°C/hr and definitely less than 1000°C/hr. At cooling rates significantly less than 100°C/hr, the phenocrysts are generally larger than observed in chondrules, and as cooling rates approach 1000°C/hr, they become more skeletal. Barred olivine chondrule textures form best from materials melted at higher temperatures and cooling rates in the range 1000 to 3000°C/hr.

Endothermic reaction aided crystal growth of 2-methyl-4-nitroaniline and their electro-optic properties

We investigated relationships between the electro-optic properties and the growth conditions for 2-methyl-4-nitroaniline (MNA) thin-film crystals. The crystal is grown by melt growth between two quartz substrates with a newly developed automatic control of the crystal growth, which utilizes an endothermic reaction. The electro-optic effect decreases with increases in the maximum melt temperature. When MNA thin-film crystals are grown from the melt at temperatures near the melting point, the figure of merit for electro-optic phase retardation is the greatest. The value is twice that of the LiNbO3 crystal. By annealing, the figure of merit becomes three times as large as that of the LiNbO3 crystal. This is consistent with the expectations from second-harmonic generation measurements. We also investigated the purity dependence of the electro-optic effect. The electro-optic effect drastically decreases with impurity, especially for purities &amp;lt;99.9%.

P-T-X phase diagram aho homogenity range of CdAs2

Abstract DTA, X-ray diffraction and total vapour pressure measurements were used to investigate P-T-X phase equilibria for the system Cd-As at T=770-950 K and P=10 2 -10 5 Pa. The co-ordinates of two eutectic points were determined as well as the maximum melting temperatures of Cd 3 As 2 and CdAs 2 . By geometrical analysis of the vapour pressure reiults both arsenides were shown to melt congruently. Sublimation of Cd 2 As 2 was shown to be a congruent process while CdAs 2 sublimes incongruently. Non-stoichiometry of CdAs 2 was estimated.

Adsorption of CCl4 on graphite.

We have performed a comprehensive x-ray scattering study of ${\mathrm{CCl}}_{4}$ adsorbed on exfoliated graphite. We observe the following features. At low coverages, there is an incommensurate triangular monolayer solid, with a gas-liquid-solid triple point at 195 K. Below a temperature of 215 K the graphite is partially wet by only one monolayer. The monolayer solid has a maximum melting temperature of \ensuremath{\sim}246 K. A two-layer solid phase, which melts at 236 K, does not have a simple triangular structure. There is a liquid prewetting film of at least ten layers thickness at 246 K, 4 K below the bulk ${\mathrm{CCl}}_{4}$ triple point.

The maximum melting temperatures in strain-crystallized van der waals networks

A theory of strain-crystallization of random networks comprised of stereoregular chains is developed. The crosslinks are assumed to be expelled from crystal cores. For this reason, the rubber is considered to be represented as a random eutectoid copolymer, the thermodynamics of strain crystallisation of which is described by the use of the van der Waals model of networks. The strain dependence of the maximum melting temperatures, the degree of crystallinity and the average thickness of the crystallites calculated are shown to be in fair accord with experimental data.

Phasenbeziehungen und intermediäre Verbindungen in Systemen GaX3 – Ga2S3 und InX3 – In2S3 (X = Cl, Br, I) / Phase Relations and Intermediate Compounds in Systems GaX3 – Ga2S3 and InX3 – In2S3 (X = Cl, Br, I)

The systems GaX3-Ga2S3 and InX3-In2S3 (X = Cl, Br, I) are quasi-binary and contain the intermediate phases GaSX and InSX with incongruent melting behaviour. Stability regions of GaSCl and GaSBr at elevated temperatures are shifted towards the respective binary halides and include compositions Ga9S8X11 which in an earlier work were reported as separate crystalline phases. InSCl and InSBr (CdCl2-type structure) also show a significant phase width towards the respective binary halides, but with the maximum melting temperature remaining at stoichiometric compositions. Cell parameters and symmetry of InSI are related to InSeI, but do not confirm the proposed isotypic relationship

Melting behavior of ultrahigh modulus linear polyethylene

AbstractThe differential‐scanning calorimetry (DSC) behavior of drawn linear polyethylene (LPE) has been investigated as a function of draw ratio and molecular weight. All the samples examined showed a dependence of the melting temperature on heating rate, an effect generally known as superheating. The magnitude of this effect, as well as the maximum melting temperatures, increased markedly at high draw ratio and high molecular weight. The highest melting temperature recorded was 145°C for a tape of draw ratio 25 and weight‐average molecular weight of 312,000. The results were first considered in terms of the information which might be provided regarding crystal thickness. It was concluded that the DSC data are consistent with previous wide‐angle x‐ray diffraction results in confirming that an extended chain morphology similar to that observed in pressure crystallized LPE is not present in these samples. Secondly, the superheating effects were examined in the light of the possible configurational constraints on the amorphous regions of drawn polymers, along the lines proposed by Zachmann. It is possible to understand the effects of draw ratio and molecular weight very well on this basis, in a manner consistent with previous structural results on these materials.

High‐Temperature Phase Diagram for the System Zr.

The melting, eutectic, peritectic, solidus, and liquidus temperatures in the system Zr‐O have been measured directly by a simple optical pyrometric technique requiring only a few hundred milligrams of sample. The saturation solubility of oxygen in α‐Zr(s) between 1270° and 1980°C and the lower phase boundary of the ZrO2–α phase between 1900° and 2400°C have been measured by an isopiestic equilibration method. The oxygen solubility limit in α‐Zr(s) agrees well with previous low‐temperature studies and reaches a maximum solubility of 35°1 at.% O at the eutectic temperature, 2065°°5°C. The maximum melting temperature of α‐Zr(ss) is 2130°°10°C and corresponds to a composition of 25°1 at.% O. Both of these temperatures are approximately 150° higher than previously reported. Liquidus compositions above the eutectic temperature were obtained via mass spectrometry from the kinetic behavior of the liquid solution‐ZrO2–x(s) mixture as it approached equilibrium at 2125°°5°C. The lower phase boundary or solidus of the ZrO2–x phase departs appreciably from ideal stoichiometry above 1900°C and smoothly reaches its most reduced composition, 61 at.% (ZrO1.56), near 2300°C. The solidus is retrograde at higher temperatures. The melting temperature of the stoichiometric dioxide is 2710°°15°C.