Eutectic Melting Temperature Research Articles

Silicification of Evaporites in Permian (Guadalupian) Back-Reef Carbonates of the Delaware Basin, West Texas and New Mexico

ABSTRACT Outcrops of the Seven Rivers, Yates, and Tansill Formations contain widespread evaporites replaced by quartz and calcite. The original evaporites consisted of discrete horizons, scattered nodules, enterolithic layers, and individual crystals or crystal fragments of gypsum and/or anhydrite within a finely crystalline dolomite matrix. Based on field and petrographic observations, silicification of evaporites proceeded from the exterior to the interior of the nodules. The earliest replacement was by euhedral, black megaquartz that contains abundant fluid inclusions (water and hydrocarbons) and solid inclusions (mainly anhydrite and dolomite). The siliceous replacements were followed by precipitation of equant, blocky calcite spar, which filled pores left by latestage dissolution of evaporites. The fluid inclusions in the replacive megaquartz are primary, and many contain both hydrocarbons and water. Daughter minerals of halite, gypsum, or possibly antarcticite (CaCl2·6H2O) are also found within the aqueous inclusions. Homogenization-temperature data for hydrocarbon and aqueous fluid inclusions average 67.7°C and 67.1°C, respectively. Hydrocarbonbearing and aqueous inclusions are thus interpreted to have formed simultaneously from the same fluids. Eutectic melting and final melting temperatures for aqueous inclusions indicate that the fluids were concentrated brines consisting of CaCl2 and NaCl. Oxygen-isotope values for the megaquartz replacements averaged 28.4 (SMOW), indica ing precipitation from evaporative waters with an isotopic composition of +2.9 (SMOW). Evaporite silicification was coeval with or slightly postdated hydrocarbon migration. The fluid-inclusion data provide a record of the fluid temperatures and compositions that prevailed during silica precipitation. These data, coupled with regional stratigraphy and published geothermal gradients, suggest a burial depth of approximately 1.3 km during silicification. The source of the silica for evaporite replacement is problematic. We postulate, however, that silica may have been derived from dissolution of siliciclastics in back-reef units. Organic acids that form from breakdown of hydrocarbons increase the solubility of quartz by bonding with silicic acid. As these products (and associated brines) moved into cooler oxidizing zones, the organic acids broke down, releasing silica into solution. This organically mobilized silica eventually precipitated as megaquartz replacements of preexisting evaporites.

Use of subambient thermal analysis to optimize protein lyophilization

Subambient thermal analysis with differential scanning calorimetry and thermomechanical analysis has been used successfully to optimize the lyophilization of proteins based on the thermal behavior of solution components. In deionized water, frozen protein solutions exhibit two glass transition temperatures ( T gs): the first ca. − 80 °C ( T g″), and a second ca. − 10 °C ( T g′); the latter appears to be related to the collapse phenomenon. Proteins lyophilized in buffers with low T g values such as Tris (− 81 °C) or sodium acetate (− 80 °C) are collapsed during primary drying at − 20 °C. Substitution of salts which crystallize readily during freezing and have eutectic melting temperatures ( T es) above − 20 °C, e.g., sodium carbonate ( T e = 3 °C), prevents the protein solutions from being collapsed during the same process. The crystallization of these salts during freezing, which may lead to undesirable changes in pH, can be prevented by use of excipients such as sugars. To remove the amorphous fraction in partially crystallizable eutectic salts which exhibit very low glass transition temperature values, an adequate annealing at temperatures between devitrification and eutectic melting is necessary. Annealing is not effective for wholly amorphous glass-forming salts. However, the final T g′ of protein solutions which contain such salts can be raised by adding excipients or by increasing the protein concentration.

Formation Region of K-Al-Priderite (K<sub><i>x</i></sub>Al<sub><i>x</i></sub>Ti<sub>8-<i>x</i></sub>O<sub>16</sub>)

Pseudobinary phase relations relevant to K-Al-priderite (KxAlxTi8-xO16) have been given with the incongruent melting temperature of priderite and the eutectic melting temperature between priderite and rutile. From the lattice parameter change K-Al-priderite has been proved to occur in the range of 1.47<x<1.80 at 1200°C. With increasing x the a-axis decreases from 10.064 to 10.042A, while the c-axis expands from 2.937 to 2.939A. The formation range becomes narrow with increasing temperature and finally converges at x=1.5. The stability of K-Al-priderite with x=1.5 was discussed in connection with the formation of a super structure.

Fluid inclusions and hydrothermal alteration on the Dixie Valley Fault, Nevada

Footwall rocks of the 1954 rupture segment of the Dixie Valley fault show extensive hydrothermal alteration related to fluids that were present on the fault during tectonic events. Hydrothermal alteration of granitic host rocks consists of temporally and spatially overlapping mineral assemblages. An early, biotite‐feldspar assemblage is followed by later Fe‐chlorite and epidote. Both chlorite and epidote are replaced by hydrothermal sericite and cross‐cut by calcite‐hematite and quartz‐calcite veins. Biotite is partially replaced by prehnite. The latest hydrothermal minerals are stilbite, laumontite, kaolinite, alunite, smectite, illite, and pervasive replacement of rock units with fine grained quartz, chalcedony, and opal. Secondary fluid inclusions trapped in healed microfractures in igneous quartz include type I inclusions that contain a moderate salinity aqueous liquid and vapor, type II inclusions that contain a moderate salinity aqueous liquid and CO2; type III inclusions that show eutectic melting temperatures below the NaCl‐H2O eutectic and contain substantial CaCl2, and type IV inclusions containing halite and other daughter minerals. Microthermometric measurements on these inclusions yield variable compositions and homogenization temperatures. Salinities of type I inclusions vary from 0.1 to 12.9 wt % NaCl with the mode in the interval 0 to 1%. Salinities of type II CO2 bearing inclusions range from 0.62 to 6.81 wt % NaCl relative to H2O, and salinities of type III inclusions with low eutectic melting temperatures are 12.9 to 25.3 NaCl equivalent wt %. Salinities of halite‐bearing inclusions are 30.1 to 39.2 wt % NaCl. Homogenization temperatures span the range 120° to 400°C. The processes of isochemical cooling with upward displacement of the footwall, mixing of cool low‐salinity water with hotter components, and mixing of cool, evaporite brine with hotter components could be responsible for variable fluid inclusion compositions, homogenization temperatures, and densities. The P‐T path of the fault fluids is established by mineral equilibria and fluid inclusion characteristics. The path includes a lithostatic fluid pressure at 305°C and 1570 bars. Along with cooling and escape of CO2 from fluids, the fluid P‐T path probably approaches hydrostatic pressure conditions at lower temperatures. Hydrothermal alteration product minerals, fluid temperatures, pressures, and compositions in the footwall of the Dixie Valley fault constrain minimum fault age to 20 to 25 Ma, displacement to 6 km with about 3 km of pre‐10 to 13 Ma and 3 km of post‐10 Ma uplift. Fluid compositions and P‐T data suggest the following mechanism for rupture initiation and arrest. Ruptures may be initiated as a result of high fluid pressures, then opening of dilatant fractures causes drastic decrease in fluid pressure, separation of steam and CO2. The drastic reduction in fluid bulk modulus that accompanies volatile phase separation permits propagation of the ruptures even though fluid pressure is reduced. In areas where fluid pressure reduction is not accompanied by phase separation, fractures are arrested by dilatant hardening.

Application of DTA and TG to studies of the CaCO3-CaF2 phase diagram

A new method (based on DTA and TG) for the determination of the eutectic composition is proposed for systems in which one of the components is unstable in the vicinity of the eutectic melting temperature. The eutectic composition established by means of this method for the CaCO3-CaF2 system is in very good agreement with the results obtained in a classical way.

Interaction of Al-Si, Al-Ge, and Zn-Al eutectic alloys with SiC/Al discontinuously reinforced metal matrix composites

Interactions between Al-Si, Al-Ge, and Zn-Al eutectic alloys with SiC whisker-reinforced aluminium metal matrix composites were studied as a function of temperature above the eutectic melting temperature. Penetration extended several millimetres into the composite for the Al-Si and Al-Ge alloys but was restricted to a thin surface layer (50 μm) for the Zn-Al alloy. The extent of the penetration zone for the aluminium alloys containing silicon and germanium was also affected by the thermal-mechanical treatment of the composite: limited penetration was observed for hot-pressed material whereas extensive penetration was observed for mechanically worked material. Mechanisms for the observed phenomena are discussed in terms of the wettability of the SiC whiskers by the eutectic alloys, the formation of channels during mechanical working as well as the fine grain size of the composite.

Contact structure formed in the Ni/Al/Si system due to rapid thermal melting

The interface reaction induced by means of rapid thermal melting (RTM) of the Ni(30 nm)/Al(10 nm)/Si system, using heat treatment times of a few seconds at temperatures around the aluminum melting point, has been investigated. The RTM occurred at the Al-Si eutectic melting temperature (577 °C). As a result of this melting a polycrystalline intermediate layer, 60 nm thick, composed of NiSi and Ni2Si was formed adjacent to the Si substrate with a relative smooth interface while the Al was repelled to the outer region of the contact and two successive separate layers of polycrystalline Al3Ni and Ni(Al0.5Si0.5) were formed, both 10 nm thick. The results indicate that RTM can be used to obtain a unique interface reaction in a controlled manner.

Crystallization of amorphous Ni 35Zr 65 and Fe 40Ni 40P 14B 6 under proton irradiation

Two amorphous alloys, Ni 35Zr 65 and Fe 40Ni 40P 14B 6, were irradiated using 400 keV protons at several temperatures below the crystallization temperature, T x , to peak doses in the neighborhood of 3.5 to 4.5 dpa. Irradiation at 250°C resulted in the crystallization of both alloys, which were examined by transmission electron microscopy of samples electrolytically polished to various distances from the irradiated surface to study the effect of dose. Samples masked from the proton beam remained amorphous during irradiation. In the Ni 35Zr 65 alloy crystallization of the equilibrium phases propagated throughout the entire sample, while the in the Fe 40Ni 40P 14B 6 alloy crystallization was observed only in those parts of the samples lying within the proton range. Neither alloy crystallized during irradiation at 100°C. In both these alloys the amorphous phase is therefore evidently stable at irradiation temperatures below approximately 0.6 T x . An examination of the literature on irradiation damage of binary alloys and intermetallic compounds suggests that there is a tendency for initially amorphous alloys to remain amorphous at irradiation temperatures, T irr < 0.3 T L, where T L (≈ T x) is the “melting” temperature (either a eutectic, peritectic or congruent melting temperature). Also, these same alloys, even when they are initially crystalline, transform to the amorphous state during irradiation at T < 0.3 T L. Some other crystalline alloys have also been shown to transform to the amorphous state at T irr < 0.3 T L even though they have never been prepared in this condition by rapid quenching techniques. The temperature 0.3 T L appears to be a lower limit, however, since the crystalline to amorphous transformation occurs in many of these alloys at temperatures greater than 0.3 T L. It is suggested, by analogy with results on void formation in irradiated metals, that this low temperature limit is related to the low mobility of vacancies in these materials, although the mechanism of crystallization, or conversely amorphization, is not fully understood.

More accurate determination of the quantity of ice crystallized at low cooling rates in the glycerol and 1,2-propanediol aqueous solutions: Comparison with equilibrium

It is generally assumed that when cells are cooled at rates close to those corresponding to the maximum of survival, once supercooling has ceased, above the eutectic melting temperature the extracellular ice is in equilibrium with the residual solution. This did not seem evident to us due to the difficulty of ice crystallization in cryoprotective solutions. The maximum quantities of ice crystallized in glycerol and 1,2-propanediol solutions have been calculated from the area of the solidification and fusion peaks obtained with a Perkin-Elmer DSC-2 differential scanning calorimeter. The accuracy has been improved by several corrections: better defined baseline, thermal variation of the heat of fusion of the ice, heat of solution of the water from its melting with the residual solution. More ice crystallizes in the glycerol than in the 1,2-propanediol solutions, of which the amorphous residue contains about 40 to 55% 1,2-propanediol. The equilibrium values are unknown in the presence of 1,2-propanediol. With glycerol, in our experiments, the maximum is first lower than the equilibrium but approaches it as the concentration increases. It is not completely determined by the colligative properties of the solutes.

General crystallization behaviour of poly( l-lactic acid) PLLA: 2. Eutectic crystallization of PLLA

The solidification and melting behaviour of quasi-binary systems formed by poly( l-lactic acid) (PLLA) and respectively the diluents parahydroxybenzoic acid (PHBA) and hexamethylbenzene (HMB) have been investigated. For both quasi-binary systems the effect of diluent concentration on the measured melting temperatures was in reasonable agreement with the theoretical values calculated according to the Flory-Huggins theory of melting point depression. The PLLA-PHBA system formed an eutectic composition for 84% w/w of PLLA in the mixture. Its eutectic melting temperature is 437K. For the PLLA-HMB system the eutectic composition was 65% w/w of PLLA in the mixture and the eutectic melting temperaturre of 432K. The morphology of the PLLA-diluent mixtures was strongly dependent on the diluent concentration. Fracture surfaces of the mixtures of PLLA and PHBA exhibited faceted crystals of various shape, formed by the diluent. They could not be removed from the polymer by sublimation, probably because of the intermolecular hydrogen bonds formed by PHBA itself and/or PHBA and the PLLA matrix. Sublimation of diluent from PLLA-HMB quasi-binary system led to a highly porous material of varying morphology.

The Long Term Structural Stability of the Eutectic Composites Cd-Zn and Pb-Cd

ABSTRACTIt is shown that marked microstructural coarsening can occur when eutectic composites are exposed for relatively short periods to temperatures approaching 0.9 TM (where TM is the eutectic melting temperature in °K). Less well known and, perhaps, of more practical importance, are the microstructural changes and consequent changes in properties which result from prolonged exposure at 'safe' operating temperatures, e.g. 0.5 Tm.Cd-Zn and Pb-Cd eutectic specimens of various thermal histories were examined immediately on preparation and subsequently re-examined after storage at ambient laboratory temperatures for up to 1000 days. In general, microstructural changes from the as-grown and heat-treated conditions were observed. In some cases for the Pb-Cd alloy this consisted of only slight thickening of the already coarse larnellae terminations. However, in the more rapidly frozen, and therefore microstructurally finer, specimens marked discontinuous coarsening was observed, but confined to eutectic-cell-wall regions. There the coarse precipitates grew at many angles, including being perpendicular to the eutectic habit plane but were not separated by any well-defined large angle grain boundaries.It was concluded that high temperature degradation occurs mainly by continuous coarsening, whereas at lowtemperatures, microstructural changes are effected mainly by discontinuous coarsening.

Effect of heat treatment temperature on tensile strength and hardness of isostatically compacted aluminum alloy blend

The strength and density of powder metallurgy (P/M) parts are influenced by powder characteristics, consolidation technique and sintering conditions. In the case of an alloy the properties are further improved by heat treatment. However, the properties of such P/M parts, which are not subsequently subjected t o a forging operation, are always lower than those obtained by conventional techniques for wrought metals and alloys. The objective of this study is t o investigate the effect of one of the processing variables, heat treatment, on the tensile strength and hardness of an isostatically compacted aluminum alloy corresponding t o 6061 (1.0 pct Mg, 0.6 pct Si, 0.25 pct Cu and 0.25 pct Cr). Although aluminum powder metallurgy is now practiced quite extensively, relatively few r e s e a r c h papers on this subject have been published.1"4 Aluminum-copper alloys (2xxxs e r i e s and A1-Mg-Si alloys (6xxx s e r i e s ) are usually solution heat t r e a t e d for dissolving maximum amounts of solute elements such as copper, magnesium and silicon in the aluminum solid solution at the highest possible temperature below the eutectic melting point . Homogenization of the solid solution thereby achieved increases the strength and hardness properties of the component with increasing solution heat treating temperature. For heat treatable alloys in the 2xxx and 6xxx s e r i e s , this treatment is conventionally done at temperatures in the range of 940 t o 970°F (777 to 794 K) which is close t o the eutectic melting temperature for most alloys in the s e r i e s except the alloy 6061. This aluminum-magnesium-silicon alloy contains 1.0 pct magnesium and 0.6 pct silicon, whichforms 1.5 pct magnesium silicide. Since some of the magnesium silicide remains undissolved when heat treating the alloy at the conventional temperature of 970°F (794 K) which is below the complete dissolution temperature of 1025°F (824 K), the strength of the alloy should be improved further by heat treating at higher temperatures.%° Therefore, the purpose of this study was to investigate the effect of solution heat treatment temperature on the tensile strength and hardness of 6061 components made from isostatically compacted powder of this blend. The commercial grade powderblend, 601AC, containing 1.0 pct magnesium, 0.6 pct silicon and 0.25 pet copper and which is similar in composition to commercial 6061 alloy, was processed in the following manner. The blend was isostatically compacted at a pressure of 40,000 ps i (276 MN/m2) in a

Melting behaviour of nickel—chromium—silicon alloys

With regard to developing low melting NiCrSi alloys used as joint materials in high temperature brazing technics, especially in reactor technique, the melting behaviour of nickel—rich NiCrSi alloys was investigated systematically by differential thermal analysis. The dependence of the liquidus temperatures on alloying concentration ranges from 0 to 28 at. -% Si and 0 to 60 at.-% Cr shows a ternary eutectic melting temperature minimum of 1077°C at 20 at.-% Cr and 21.3 at.-% Si. The melting behaviour of the alloys in the indicated concentration range will be characterized in a reaction scheme. The dependence on temperature of the solubility of Si and Cr in Ni will be discussed.

Phase relationships and crystal chemistry in the systems USCaS, USSrS and USBaS

Phase equilibria in the systems USCaS, USSrS and USBaS have been investigated by X-ray diffraction, metallography and electron-probe microanalysis. New ternary sulphides, CaUS 2, SrUS 2 and BaUS 2, which appeared in the corresponding systems, formed eutectic mixtures with primary solid solutions. Eutectic melting temperatures were determined for the systems USCaS and USSrS and tentative phase diagrams constructed. Detailed crystal structure analyses of CaUS 2 and SrUS 2 were carried out.

Thermo microindentification of amino acids: Refractive index

The use of a range of constants related to refractive index for the identification of amino acids is described. These constants may be determined microscopically and, combined with eutectic melting temperatures, permit identification of a range of 39 amino acids examined in this study.

Identification spécifique des acides aminés et des vitamines par l'indice de réfraction et la température eutectique: Application a la chromatographie sur papier et au contrôle

Refractive index and eutectic melting temperature of binary systems, together lead to specific identification of organic individuals and isomers. A number of vitamins and amino acids have been experimented with to that purpose. The result is that analysis of an entire spot of amino acids on paper becomes easy owing to these properties. An example using glumatic acids shows that better results on the composition of an entire spot on paper can be obtained by this analysis than by Chromatographie R F values.