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.     

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.     

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.     

Physical chemistry of binary organic eutectic and monotectic alloys; 1,2,4,5-tetrachlorobenzene−β-naphthol and 1,2,4,5-tetramethylbenzene-succinonitrile systems

Phase diagrams of 1,2,4,5-tetrachlorobenzene–β-naphthol and 1,2,4,5-tetramethylbenzene–succinonitrile systems which are organic analogues of a nonmetal–nonmetal and a nonmetal–metal system, respectively, show the formation of a simple eutectic (melting point 103.7°C) with 0.71 mole fraction of β-naphthol in the former case and a monotectic (melting point 76.0°C) with 0.07 mole fraction of succinonitrile and a eutectic (melting point 52.5°C) with 0.97 mole fraction of succinonitrile in the latter case. The growth behaviour of the pure components, the eutectics and the monotectic studied by measuring the rate of movement of the solid–liquid interface in a capillary, suggests that the data obey the Hillig–Turnbull equation, v=u(ΔT)ⁿ, where v is the growth velocity, ΔT is the undercooling and u and n are constants depending on the nature of the materials involved. From the values of enthalpy of fusion determined by the DSC method using Mettler DSC-4000 system, entropy of fusion, interfacial energy, enthalpy of mixing and excess thermodynamic functions were calculated. The optical microphotographs of pure components and polyphase materials show their characteristic features.     

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。     

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.     

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.     

Isotope Effects in Liquid Crystal Systems: I: Phase Relationships in the Dodecylamine-H2O,Dodecylamine-D2O Systems

The phase diagrams and heats of fusion and transition have been determined for the dodecyl amine (-NH₂)/H₂O and dodecyl amine (-ND₂)/D₂O systems using direct optical observation and differential scanning calorimetry.     

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.     

Structural characterization of anthracene-picric acid eutectic system

The eutectic composition has been derived from phasediagram studies and the nature of eutectics has been established by thermal and spectral studies. Diffraction studies reveal the establishment of preferential ordering and the crystalline character of eutectics.     

Crystal growth of KTiOPO4 isomorphs from tungstate and molybdate fluxes

Large inclusion-free crystal of KTiOPO₄, RbTiOPO₄, KTiOAsO₄ and RbTiOAsO₄ have been grown from the tungstate and molybdate fluxes. In this paper, we report the typical growth parameters, the solubilities, and the heats of solution (δH_sol) for these crystals, and briefly comment on their optical quality. In addition to being nonvolatile and of low viscosity, the tungstate and the molybdate fluxes also have significantly faster dissolution kinetics than the pure phosphate or arsenate self-flux. This makes them especially versatile for the exploratory crystal growth of the KTP isomorphs and their solid solutions. Using these fluxes, single crystal boules of up to 2.5×3×5 cm³ have been grown from a 250 ml melt. We have also observed a modification in the crystal growth habit, which in the case of KTiOAsO₄, results in the formation of stable, singular {111} faces.     

Chemistry of organic eutectics: Phenanthrene — benzoic acid and phenanthrene — cinnamic acid systems

Solid-liquid equilibrium data for binary systems of phenanthrene with benzoic acid and cinnamic acid, expressed in the form of temperature-composition curves, show the formation of a simple eutectic in each case. Linear velocity of crystallisation (v), studied by capillary method at different undercoolings (ΔT), suggests the applicability of Hillig-Turnbull equation, v = u(ΔT) ⁿ, where u and n are constants depending on the nature of solidification. Data on heats of fusion of pure components and eutectics, determined by the DTA method, infer appreciable interaction among the components in the eutectic melts. To highlight the nature of interactions among the components forming the eutectic melt, the excess thermodynamic functions such as h^E, s^E, and g^E were computed. Microscopic studies reveal that the structure of eutectic is different from those of the parent components. Infrared spectra, recorded in the region, 4000 —625 cm⁻¹, indicate weak interactions among the components in the eutectic.     

Developments and future directions of phase diagram,physicochemical and optical studies of binary organic complexes

The aim of this review is to emphasize solvent free or green synthesis, a most efficient utilization of starting materials to give maximum yield, and an alternative route to producing novel promising materials. In this regard the phase diagram study has shown applications in the determination of the precise composition of binary compounds of a specific nature and in the identification of the parameters that affect the crystal growth. To provide an overview worthy of phase diagram, physicochemical, thermal and structure investigations; studies of eleven systems, namely, urea–m-nitrobenzoic acid, urea–p-nitrophenol, urea–resorcinol, benzoin–o-phenylenediamine, pyrene–m-dinitrobenzene, vanillin–p-anisidine, resorcinol–p-dimethylaminobenzaldehyde, benzophenone–diphenylamine, anthracene–picric acid, 8-hydroxyquinoline–salicylic acid and 8-hydroxyqunoline–1,2,3-trihydroxybenzene forming organic complexes, have been reported. In addition, the original data of a newly synthesized complex of m-hydroxybenzaldehyde (HB) and p-chloroaniline (CA) is being reported for the first time. The phase diagram of HB–CA system also shows the formation of a complex in 1:1 M ratio, and two eutectics on either side of the complex. The complex's formation was studied using FTIR, NMR, DSC and powder X-ray diffraction techniques. The thermodynamic parameters such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions were calculated using the heat of fusion values. The single crystal growth and the atomic packing studies of some of the complexes have confirmed the formation of complexes. The optical transmittance efficiency and transparency of novel HB–CA complex crystal were found to be 70% and 399 nm, respectively.     

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.     

Spectroscopy of transition metal ions in inorganic glasses

Transition metal (TM) ions have been used as colouring agents in the glass industry for a long time. Recently, great attention has been paid to the TM ion doped glasses for the development of new lasers or luminescence materials. The absorption spectra of TM ions in different kinds of glasses have been studied extensively, but little work has been done for fluorescence and relaxation spectra. In this paper emphasis is laid on analysing the influence of chemical bond characteristics of the base glass on the spectra and the site structure of transition metal ions in glasses. Recent experimental results about the luminescence characteristics of low valence ions (such as Ti³⁺, Cr³⁺, V²⁺, Mn²⁺, Cu⁺, Mo³⁺) in glasses are also reported.     

Properties of (Ga0.47In0.53)As epitaxial layers grown by metalorganic vapor phase epitaxy (MOVPE) using alternative arsenic precursors

In this study, the use of novel, liquid, organic arsenic precursors as substitutes for the highly toxic hydride gas arsine (AsH₃) in low pressure metalorganic vapor phase epitaxy (LP-MOVPE) of (GaIn)As lattice matched on InP has been investigated. The model precursors out of the classes of (alkyl)3-nAsH_n (n = 0,1,2) are tertiarybutyl arsine (TBAs), ditertiarybutyl arsine (DitBAsH) and diethyltertiarybutyl arsine (DEtBAs). The MOVPE growth has been investigated in the temperature range of 570–650°C using V/III ratios from 2 to 20. The obtained epitaxial layer quality as examined by means of optical and scanning electron microscopy (SEM), high resolution double crystal X-ray diffraction, temperature-dependent van der Pauw-Hall, as well as photoluminescence (PL) measurements, will be compared for the different source molecules. Under optimized conditions almost uncompensated n-type (GaIn)As layers with carrier concentrations below 1 × 10¹⁵ cm⁻³ and corresponding mobilities above 80 000 cm²/V · s have been realized. For TBAs and DitBAsH in combination with the corresponding P sources TBP and DitBuPH, respectively, we have worked out a process parameter area for the growth of layers with device quality, as proven by the realization of a pin-detector structure.     

Optical third-harmonic generation from some high-index glasses

Optical third-harmonic generation from some high-index glasses was investigated. The highest χ⁽³⁾ was obtained from As₂S₃ glass 2.2 × 10⁻¹² esu/ This value was 100 times higher than that of pure SiO₂ glass and comparable with that of the polymer with monomer-doping, which are known as organic materials with quite high χ⁽³⁾. From the relationship between χ⁽³⁾ and composition, sulfide glasses were found to have higher χ⁽³⁾ than oxide or semiconductor-doped oxide glasses with similar refractive indices.     

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.     

An investigation of the structural effects of Fe in the alkali-silicate glasses

The coordination states of Fe³⁺, B³⁺ and Al³⁺ ions in the alkali-silicate glasses have been determined. The structural effects of these cations coexisting in the glass, and the effects of the iron and boric oxide anomaly on glass density, are also analysed.     

Formation of oxygen-deficient type structural defects and state of ions in SiO2 glasses implanted with transition metal ions

The properties and concentrations of oxygen-deficient type structural defects in type III SiO₂ glasses implanted with Ti⁺, Cr⁺, Mn⁺, Fe⁺, or Cu⁺ to doses from 0.5×10¹⁶ to 6×100¹⁶ ions/cm² at an energy of 160 keV have been measured by using vacuum UV and EPR spectroscopies. An intense absorption band centered around 7.5 eV is observed in all the samples except for Cu-implanted ones and is attributed primarily to Si---Si homo-bonds with the bond distance close to that of the Si₂H₆ molecule. The homo-bond and implanted ion concentrations are of the same order of magnitude in the implanted layers. An E′ type center associated with the homo-bond is observed in all the samples except for Cu-implanted ones. Anomalous behaviors of the Cu-implanted samples are attributed to the formation of Cu-colloids. An enhanced formation of metallic particles or colloids is suggested for the samples implanted with Cr, Mn or Fe to doses higher than 3×10¹⁶ ions/cm².