Phase Diagram Study of Succinonitrile-Vanillin Organic Alloy System

Phase diagram studies of succinonitrile-vanillin system show the formation of 2:1 congruent melting type compound. Crystallization velocities of pure components, succinonitrile-vanillin complex, and two eutectics have been determined at different undercoolings. On the basis of heat of fusion measurements, excess thermodynamic functions have been calculated. Microstructural studies revealed that impurities modify the morphology. FTIR spectral studies and computer simulation have shown the existence of hydrogen bonding in the eutectics and the congruent melting compound. On the basis of experimental results, the mechanism of formation of eutectics and its solidification behavior are discussed.     

Some Physicochemical Studies on Binary Organic Eutectics and 1:2 Molecular Complexes

Benzidine-m. aminophenol system gives a double simple eutectic type phase-diagram showing the formation of a 1:2 addition compound with congruent melting point surrounded by two eutectics on either side. The linear velocity of crystallization data on pure components, eutectics, and addition compound suggest square relationship between growth velocity and undercooling. From the X-ray diffraction studies it can be inferred that the eutectics are not a simple mechanical mixtures of two components. Whereas microstructural investigations suggest faceted growth of the addition compound and a typical characteristic growth of the eutectics, spectral studies indicate the formation of intermolecular hydrogen bonding between two components forming the molecular complex.     

Heat of fusion and excess thermodynamic functions of organic eutectics

Phase diagrams and heats of fusion of some organic eutectics have been studied. An empirical equation is proposed for the determination of heats of fusion of eutectics. Excess thermodynamic functions such as h^E, S^E and g^E have been calculated. The heats of fusion of various organic eutectics have been compared with values obtained from the mixture law. The results have been explained on the basis of the fact that clusters are formed during melting. The cluster formation tendency is greater in systems in which hydroxyl groups are present.     

Eutectic Crystallization of Aluminium Copper Alloys

The directional freezing of Al-Cu eutectic alloys under molten salts has been studied. The value of the specific interphase boundary energy σ_αβ is found to be smaller than CHADWICK 'S and of the same order as for other eutectics. An attempt has been made to appreciate the influence of the growth rate on the interlamellar spacing and tensile strength of alloys investigated.     

Some physicochemical studies on organic eutectics

The phase diagrams of phenothiazine with each of m-nitrobenzoic acid (m-NBA) and m-dinitrobenzene (m-DNB) have been studied by thaw-melt method. These materials have been characterized by X-ray diffraction. Growth behavior of the parent components, eutectic and charge transfer complex (CTC) studied by measuring the rate of movement of the growth front in a capillary suggests the applicability of Hillig–Turnbull equation for the system. Microstructure and electrical conductivities of congruent melting complexes and eutectics have been determined. The low electrical conductivities of these materials have been due to weak interaction and mixed stacking of donor and acceptor. Excess thermodynamics functions of the charge-transfer (CT) materials and eutectics have been determined.     

Solidification behaviour of organic eutectics and 1:1 addition compound: p-Phenylenediamine-resorcinol system

The phase diagram of p-phenylenediamine-resorcinol system, determined by thaw-melt method, shows the formation of a 1:1 molecular compound and two eutectics. The linear velocity of crystallization, determined by measuring the rate of movement of growth front in a capillary, indicates that crystallization data obey Hillig-Turnbull equation: Where u and n are constants and ΔT is undercooling. X-ray diffraction data of the molecular compound, eutectics and pure components infer that these eutectics are not simply the mechanical mixture of the two components and there is preferential ordering of atomic planes during their formation. The infrared studies carried out on this system reveal the intermolecular hydrogen bonding between two components forming the molecular compound. Using experimental values of heats of fusion, entropy of fusion and excess thermodynamic functions were also calculated.     

Peculiarities of aluminium interaction with Ga85In15 eutectics as evidenced by X-ray synchrotron diagnostics

A set of X-ray synchrotron techniques, viz., diffraction, EXAFS/XANES spectroscopy and microtomography, is applied to elucidate microstructural changes in a technical aluminium alloy treated with GaIn eutectics. Such a treatment gives rise simultaneously to a prominent enbrittlement of the material and its activation towards reaction with water with the hydrogen evolution. The latter fact makes the activated aluminium a promising energy carrier for the small-scale hydrogen energetics. It is demonstrated that both phenomena are caused by the fast diffusion of the eutectics along intergrain boundaries and microcracks throughout the bulk of polycrystalline Al. The diffusion is promoted by the formation of (Al-Ga-In) solid solution in near-surface regions of Al crystalline grains. The progressive loss of activity of aluminium treated with GaIn eutectics upon a prolonged storage in humid air is due to the decomposition of the eutectics accompanied by the segregation of indium metal and partial gallium oxidation.     

Solidification behaviour of binary organic eutectic alloys

The phase diagrams of binary organic faceted-faceted systems of p-dibromobenzene with acenaphthene, p-chloronitrobenzene and acetanilide show the formation of a simple eutectic with 0.53, 0.61, and 0.64 mole fraction of p-dibromobenzene, respectively. Crystallization data, determined by the capillary method, suggest that the eutectics of p-dibromobenzene with acenaphthene and p-chloronitrobenzene solidify with alternate nucleation mechanism and the crystallization of the eutectic of p-dibromobenzene-acetanilide system takes place by the side-by-side growth of the phases involved. With a view to throw light on the thermodynamic behaviour of eutectic alloys of non-metals, heats of fusion of their transparent organic analogues and their eutectics were determined, and using these values different thermodynamic parameters were calculated. The microstructures of the eutectics show their typical characteristic features.     

Increasing the growth velocity of coupled eutectics in directional solidification of off-eutectic alloys

A simple and effective approach of employing an abrupt increase in growth velocity is presented to obtain entirely coupled eutectics in directional solidification of off-eutectic alloys. Using the proposed approach, the velocity required for the growth of entirely coupled eutectics in off-eutectic alloys can be increased remarkably. In directionally solidified Al–40 wt% Cu hypereutectic alloys with a thermal gradient of 250 K/cm, primary Al₂Cu dendrites appeared at constant growth velocities ranging from 5 to 100 μm/s and entirely coupled eutectics formed at 1 μm/s. Employing the abrupt increase in growth velocity, the growth velocity of purely coupled eutectics could attain 100 μm/s.     

Struktur und Energie der Phasengrenzen in gerichtet erstarrten NiAl-Cr-Eutektikum

Morphology, crystallography and interface structure of the rod-like directionally solidified NiAl–Cr eutectic were examined by transmission electron microscopy. Regular arrays of misfit dislocations of pure edge type on the cylindrical interface between the chromium rods and the NiAl matrix has been observed. The spatial arrangement and the Burgersvectors of the dislocation networks were analysed. Measurements of the distances between the misfit dislocations yielded a mean value of 1480 Å and a mean misfit of 0.195% in 〈100〉 directions. The experimental results were used to calculate the misfit-dependent part of the interfacial energy in different ways and to prove the applicability of the interfacial theory proceeding from the work of van der Merwe to the case of directionally solidified eutectics.     

Microstructure and spacings of directionally solidified metal-semiconductor eutectic alloys

Directionally solidified metal-semiconductor eutectic alloys, representing nonfacetted facetted eutectics, show a variety of microstructures caused by the great differences in semiconductor volume fraction (Zn Ge 7,8 %; Ge ZrGe₂ 98.6 %), the influence of growth rate and temperature gradient at the solid-liquid interface. The Al Si, Ag Si, Ag Ge, Zn Ge, Cu₃Si Si, NiGe Ge, CoGe₂ Ge, Mn₃Ge₂ Ge, FeGe₂ Ge, Mn₁₁Si₁₉ Si, Cu₃Ge Ge, Ge TiGe₂ and Ge ZrGe₂ eutectics habe been investigated. The following three models are applicable for the calculation of the spacings as a function of growth rate and temperature gradient at the solid-liquid interface to certain microstructures: diffusion-determined growth, branchinglimited growth and phase-lead-determined growth.     

Influence of various conditions of convective mixing of melt on the structure and magnetoresistance of eutectic InSb-NiSb alloys obtained by directional crystallization

The microstructures are analyzed of the eutectic alloys solidified in the quasi-binary InSb-NiSb system under different conditions of convective mixing of melts grown in an ampoule by the Czochralski and directional crystallization methods under earth and microgravity conditions. It is established that growth of the phases in directional solidification of the InSb-NiSb eutectics is determined not only by the diffusion mechanism of the component redistribution at the crystallization front but also by the diffusion-convection mechanism. The comparative analysis of the influence of the crystal microstructure on the value of the magnetoresistance, R _M , is performed for the first time. It is shown that the R _M value of directionally crystallized InSb-NiSb eutectics depends on the density of the NiSb needles, disorder of the eutectic structure, and electrophysical parameters of the matrix.     

Mixed Dimer Formation in Binary and Ternary Mixtures of Liquid Crystalline 4-Substituted Benzoic Acids

Mixed dimer formation is studied for a wide variety of 4-substituted benzoic acids that form liquid crystalline phases. The solid-mesophase transitions can show double eutectics when mixed dimer formation occurs, but in many cases the equilibrium constant for such a mixed dimer is extremely small. The mesophase-isotropic transitions are essentially linear over the entire phase diagram. Ternary mixtures can be created having nematic ranges of over 80° by virtue of eutectization.     

Influence of doping on the microstructure and kinetic parameters of GaSb-FeGa1.3 eutectics

Electron microscopy and X-ray spectroscopy analysis of GaSb-FeGa_1.3 eutectic composite doped with tellurium atoms is performed. It is established that doping changes the GaSb-FeGa_1.3 eutectics microstructure; sizes, shape, and density of FeGa_1.3 metallic inclusions; and the interface regions between the matrix and inclusions. Influence of doping on the anisotropy of kinetic parameters is shown.     

Search for low-temperature solvents using nonplanar tie-lines

The technique of searching for the point of quaternary eutectics is imitated by constructing a series of two-dimensional vertical cross sections (method of tie-lines) by the example of a model of eutectic-type T-x-y-z diagram without solid-phase solubility. Errors that arise when mapping cross sections of experimentally studied diagrams are analyzed.     

添加剂对超重力下燃烧合成Al_2O_3/ZrO_2(4Y)的影响

基于超重力下燃烧合成Al2O3/ZrO2(4Y),通过调整SiO2引入量,研究添加剂对材料显微结构、形态与性能的影响。结果表明:添加SiO2不改变复合陶瓷相组成,但随SiO2引入量增加,陶瓷共晶团发生胞状向棒状形态的转变,且其长径比增大、体积分数下降。陶瓷致密性随SiO2引入量增加而增大,陶瓷硬度与弯曲强度则在SiO2引入量为6%时均呈现最大值,而陶瓷断裂韧性在SiO2引入量为4%时,因裂纹偏转与桥接增韧效应显著而获得最高值。     

GdAlO3∶Tb3+-Al2O3有序共晶生长及其微结构研究

两相有序共晶材料由于具有不同折射率的两晶相呈现有序排列,可降低荧光在共晶材料内部的散射而实现导光功能,可被应用于高分辨探测成像器件中。本工作根据定向凝固原理,用微下降法生长技术制备得到了直径为3 mm的GdAlO₃∶Tb³⁺-Al₂O₃两相有序共晶。通过SEM和元素分析,探究了GdAlO₃∶Tb³⁺-Al₂O₃共晶内部的微结构,结果显示,所得共晶中GdAlO₃∶Tb³⁺晶相均匀有序地分布于基质Al₂O₃晶相中,GdAlO₃∶Tb³⁺晶相直径的大小受生长速率的影响,速率越快,直径越小。所制备得到的GdAlO₃∶Tb³⁺-Al₂O₃有序共晶在X射线辐照下发射出明亮的绿色荧光,并在GdAlO₃∶Tb³⁺晶相中定向传播,有望被用作X射线探测成像材料,提高探测器的空间分辨率。     

A kinetic treatment of glass formation. VIII: Critical cooling rates for Na2OSiO2 and K2OSiO2 glasses

The critical cooling rates required to form glass have been measured for Na₂OSiO₂ compositions containing 15.4, 20.6, 29.9 and 34.0 wt% Na₂O and for K₂OSiO₂ compositions containing 15.3, 21.7, 34.3, 41.8 and 43.9 wt% K₂O. Pronounced minima in critical cooling rate are observed in the ranges about 25 wt% Na₂O and 33 wt% K₂O. The locations of these minima correlate with regions of low liquidus temperatures (near eutectics) in the phase diagrams.Calculations of critical cooling rates have been carried out using the analysis of crystallization statistics and the simplified model of glass formation. In both cases, the models predict well the measured critical cooling rates and their variation with composition.     

Some Physicochemical Studies on Organic Analog of Metal-Nonmetal Eutectics

Phase diagram, growth behaviour, thermochemistry and microstructure of organic analog of metal-nonmetal systems, namely, urea-succinonitrile system and diphenyl-neopentyl alcohol system, were studied. While phase diagram study shows the formation of simple eutectic in each case, the growth kinetics investigations suggest the applicability of Hillig-Turnbull equation to these systems. The values of entropy of fusion, enthalpy of mixing, Jackson's roughness parameter, interfacial energy and excess thermodynamic functions were calculated using enthalpy of fusion values determined by the DSC method. The microstructure of eutectics were found to be significantly different from those of the parent components.