Solid–liquid interface energies in the succinonitrile and succinonitrile–carbon tetrabromide eutectic system

The equilibrated grain boundary groove shapes for the commercial purity succinonitrile (SCN) and succinonitrile–carbon tetrabromide (CTB) eutectic system were directly observed. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficients for the solid SCN–liquid SCN and solid SCN–liquid SCN CTB have been determined to be (5.43±0.27)×10⁻⁸ Km and (5.56±0.28)×10⁻⁸ Km, respectively, with numerical method. The solid–liquid interface energies for the solid SCN–liquid SCN and solid SCN–liquid SCN CTB have been obtained to be (7.86±0.79)×10⁻³ J m⁻² and (8.80±0.88)×10⁻³ J m⁻², respectively from the Gibbs–Thomson equation. The grain boundary energies in the SCN and SCN rich phase of the SCN–CTB system have been calculated to be (15.03±1.95)×10⁻³ J m⁻² and (16.51±2.15)×10⁻³ J m⁻², respectively, from the observed grain boundary groove shapes. The thermal conductivity ratios of the liquid phase to the solid phase for SCN and SCN–4 mol% CTB alloy have also been measured.     

Single-crystal growth of Ti–Nb–Ta–Zr–O alloys and measurement of elastic properties

Single crystals of β-type Ti alloy system Ti–Nb–Ta–Zr–O have been grown successfully in an Ar gas flow by a floating zone method. The growth orientations were determined approximately by using seed crystals with the desired orientations. The various growth conditions were realized by choosing the gas purity, the gas flow rate, and the growth rate as variables. Composition analysis of the grown crystals was done to check any variation from the values of the raw material along with the bulk homogeneity, followed by measurements of the lattice parameter and the hardness, which provides the following results: (1) the composition of oxygen varies with respect to the flow rate, or is increased as the purity is degraded, (2) the lattice parameter is increased with increasing composition of oxygen, (3) which is also the case with the hardness. Measurements of Young's moduli were performed to investigate the elastic properties. The results indicate that the crystals exhibit the anisotropy which was expected previously. The elastic constants were estimated from the moduli, giving the ideal stress 1.7–1.9 GPa which is on a level with the real strength. Additionally, the tensile stress–strain curve for the crystallographic direction 〈1 1 0〉 exhibited nonlinear elasticity and hysteresis.     

Formation of a blocky ferrite in Fe–Cr–Ni alloy during directional solidification

Formation and evolution details of a blocky microstructure in AISI 304 stainless steel are studied by quenching method during directional solidification. Results show that a coupled growth microstructure, consisting of lathy ferrite and austenite, forms first from the melt. At solid-state transformation stage, most lathy ferrite disappears due to the phase transformation from ferrite to austenite. With further decreasing of the temperature, plenty of fine ferrite colonies occur in the original austenite region. The formation of the blocky ferrite indicates that reverse solid-state transformation from austenite to ferrite takes place. This transformation is due to the segregation and the instability of austenite during the growth of austenite under low cooling rate. The fine ferrite colonies transform into blocky ferrite at room temperature. TEM and EDS analyses were carried out to identify the phases and determine the phase composition, respectively.     

Determining the primary nucleation and growth mechanism of cloxacillin sodium in methanol–butyl acetate system

The primary nucleation and growth mechanism of cloxacillin sodium in methanol–butyl acetate system are determined on the basis of induction time measurements. The induction time of cloxacillin sodium is experimentally determined by the laser scattering method at different supersaturations and temperatures. The measured induction times are then treated using the models of mononuclear and polynuclear mechanisms. It is discovered that the primary nucleation mechanism of cloxacillin sodium is identified as polynuclear mechanism, which relates the induction time and the supersaturation for various growth mechanisms. On the basis of these analyses, the growth mechanism of cloxacillin sodium is two-dimensional nucleation-mediated growth at 285 K, and changes into spiral growth with increasing temperature (at 291 and 297 K).     

Influence of growth temperature on growth of InGaAs nanowires in selective-area metal–organic vapor-phase epitaxy

Indium-rich InGaAs nanowires were grown on an InP (111)B substrate by catalyst-free selective-area metal–organic vapor phase epitaxy, and the growth-temperature dependence of growth rate and composition was studied. In particular, nanowire growth rate rapidly decreases as growth temperature increases. This tendency is opposite (for a similar temperature range) to that found in a previous study on selective-area growth of gallium-rich InGaAs nanowires. This difference between indium-rich and gallium-rich nanowires suggests that the influence of growth temperature on the growth of InGaAs nanowires is dependent on the group-III supply ratio. On the basis of previous experimental observations in InAs and GaAs nanowires, temperature dependence of nanowire growth rate and its dependence on group-III supply ratio are predicted. A guideline to determine the optimum growth conditions of InGaAs nanowires is also discussed.     

Self-assembly of LiFePO4 nanodendrites in a novel system of ethylene glycol–water

In this work, a novel system of ethylene glycol/water (EG/W) was employed to synthesize LiFePO₄, in which dodecyl benzene sulphonic acid sodium (SDBS) was used as soft template to control particle morphology. The samples were characterized by X-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX). The LiFePO₄ sample obtained by the reported method displays interesting hierarchical nanostructure (i.e. nanodendrites), which was constructed by nanorods of 3–5 μm in length and ∼50 nm in diameter. The EG/W ratio, amount of SDBS added, hydrothermal temperature and duration played important roles in the assembly of the hierarchical nanostructures. A formation mechanism was proposed and experimentally verified. It is concluded that the nanodendrites were formed due to the end-to-end self-assembly of nanorods. Compared to previously reported methods, the reported approach shows obvious advantages of one-step synthesis, environmental friendliness and low cost, to name a few. The nanodendrites as a cathode material have a higher capacity, compared with the other samples.     

The structure of Al–Cu and Al–Si eutectic melts

The structure of Al₈₃Cu₁₇ and Al₈₈Si₁₂ liquid eutectic alloys has been studied using the X-ray diffraction (XRD) and reverse Monte-Carlo (RMC) methods. The total and partial structure factors and pair correlation functions as well as structure parameters obtained therefrom have been analyzed. Chemically ordered Al–Cu groups significantly effect the structure in Al₈₃Cu₁₇, while a tendency to chemical ordering between atoms of an unlike kind is negligible in Al₈₈Si₁₂.     

Morphotropic phase boundary,segregation effect and crystal growth in the NBT–KBT system

Lead-free piezoelectric materials of sodium–potassium bismuth titanate, (1−x)NaBi(TiO₃)₂–xKBi(TiO₃)₂, ceramics and single crystals were prepared and their crystallographic and dielectric properties were measured. Single crystals with dimensions of several centimeters were grown by using the melt growth technique. The morphotropic phase boundary between rhombohedral and tetragonal symmetry determined by X-ray diffraction and Raman spectra was found at x=0.2. No coexistence of rhombohedral/tetragonal phases was found in the NKBT system. Compositions analyses showed that severe phase segregation occurred during the crystallization of the solid solution. From the segregation point, a homogeneous NKBT crystal near the MPB composition is difficult to grow.     

Glasses in the system of MnNbOF5–BaF2–BiF3–ErF3

The glasses in the MnNbOF₅–BaF₂–5BiF₃–ErF₃ system were obtained and their thermal and optical properties were studied. The specialties of crystallization depending on system composition are showed. The glass structure is discussed based on results of the IR and Raman spectra study. During the studies of inelastic light scattering, there revealed a strong photoluminescence, produced by erbium emission, whose intensity depends not only on the erbium trifluoride content in glass, but also on the glass network structure.     

Measurements of dendrite tip growth and sidebranching in succinonitrile–acetone alloys

Experiments are carried to investigate free dendritic growth of succinonitrile–acetone alloys in an undercooled melt. The measurements include the steady dendrite tip velocity and radius, the non-axisymmetric amplitude coefficient of the fins near the tip, and the envelope width, projection area, and contour length of the sidebranch structure far from the tip. It is found that the measured dendrite tip growth Péclet numbers agree well with the predictions from a stagnant film model that accounts for thermosolutal convection in the melt. The measured tip selection parameter, σ^?, is verified to be independent of the alloy composition, but shows a strong dependence on the imposed undercooling. The universal amplitude coefficient, A₄, is measured to be equal to 0.004, independent of the undercooling, but the early onset of sidebranching prevents its accurate determination for more concentrated alloys. For the self-similar sidebranch structure far from the tip, scaling laws are obtained for the measured geometrical parameters. While melt convection causes some widening of the sidebranch envelope, and the early onset of sidebranching for alloy dendrites results in a 25% upward shift of the envelope width, the projection area and, hence, the mean width of a sidebranching dendrite, as well as its contour length in the sidebranch plane, obey universal power laws that are independent of the convection intensity and the alloy composition.     

The solidification behavior and phase equilibrium of o-Nitroaniline-β-Naphthol binary eutectic system

Phase diagram studies of o-nitroaniline-β-naphthol system have been made by the thaw melt method. Simple eutectic type phase diagram was formed. Formation of eutectic mixture occurred at 0.7222 mole fractions of o-nitroaniline and melted at 326.85 K. The heat of fusion of components and eutectic mixtures were determined with the help of DSC technique and excess thermodynamic functions were calculated. Experiments were performed to study the undercooling, microstructure and linear velocities of crystallization. Flexural strength measurements were also made. Eutectic mixture showed higher flexural strength as compared to the components.     

Nucleation and growth of needle-like fluorapatite crystals in bioactive glass–ceramics

The nucleation behaviors of glass–ceramics with different Ca–mica (Ca_0.5Mg₃AlSi₃O₁₀F₂)/fluorapatite ratios were investigated. By using differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscope with an energy dispersive spectrometer (SEM/EDS), the effect of CaO and P₂O₅ addition on the nucleation behaviors was studied. Results showed that the addition of CaO and P₂O₅ promoted nucleation process and led to the formation of different nucleation phases. After further heat treatment, Ca₅(PO₄)₃F crystals were of needle-like morphology, instead of particle-like reported in previous studies. This can be attributed to the one-dimensional rapid growth of fluorapatite along the c-axis. The values of the Avrami parameter, n, and the dimensionality of crystal growth, m, are found to be 2 and 1, respectively, which indicated that the bulk nucleation is the dominant mechanism in crystallization, and one-dimensional growth of fluorapatite is preferred. Since needle-like fluorapatite crystals are of the same morphology to hydroxyapatites in human bones, the glass–ceramics thus prepared show excellent bioactivity in vivo.     

An experimental investigation of the columnar-to-equiaxed grain transition in aluminum–copper hypoeutectic and eutectic alloys

Providing benchmark data of the thermal and metallographic parameters during the columnar-to-equiaxed transition (CET) in a wide range of alloy concentrations is of fundamental importance for understanding this phenomenon as well as for metallurgical and modeling purposes. The aim of this study was to investigate the columnar-to-equiaxed transition (CET) in aluminum–copper alloys of different compositions covering a wide range from 2 to 33.2 wt%Cu (eutectic composition), which were directionally solidified from a chill face. The thermal parameters studied included recalescence, cooling rates, temperature gradients and interphase velocities. We found that the temperature gradient and velocity of the liquidus interphase reached critical values at the CET; these critical values were between −0.44 and 0.09 K/mm and between 0.67 and 2.16 mm/s, respectively. The metallographic parameters analyzed were grain size, primary and secondary dendritic arm spacing and also eutectic spacing. The results obtained were compared with previous experimental studies, published predictions and models of the CET for similar alloys.     

Peculiarities of the behavior of the W–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system in a controlled reducing atmosphere

The W–Al₂O₃ system at T = 2400 K and standard pressure (controlled Ar + H₂ atmosphere) has been calculated by stochastic simulation. It is shown that the presence of hydrogen leads to the formation of aluminum hydrides, hydrogen oxides, and aluminum hydroxides; the compounds from the two latter groups (except for water) can interact directly with tungsten. The main chemical reactions occurring in the system are determined, based on which a conclusion about the cyclic character of the processes is drawn. Some recommendations on the composition and pressure of controlled atmosphere for growing sapphire crystals are given.     

Solid–liquid interfacial energy of neopentylglycol solid solution in equilibrium with neopentylglycol–(D) camphor eutectic liquid

The grain boundary groove shapes for equilibrated solid neopentylglycol (NPG) solution (NPG–3 mol% D-camphor) in equilibrium with the NPG–DC eutectic liquid (NPG–36.1 mol% D-camphor) have been directly observed using a horizontal linear temperature gradient apparatus. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient (Г), solid–liquid interfacial energy (σ_SL) of NPG solid solution have been determined to be (7.5±0.7)×10^?8 K m and (8.1±1.2)×10^?3 J m^?2, respectively. The Gibbs–Thomson coefficient versus T_mΩ^1/3, where Ω is the volume per atom was also plotted by linear regression for some organic transparent materials and the average value of coefficient (τ) for nonmetallic materials was obtained to be 0.32 from graph of the Gibbs–Thomson coefficient versus T_mΩ^1/3. The grain boundary energy of solid NPG solution phase has been determined to be (14.6±2.3)×10^?3 J m^?2 from the observed grain boundary groove shapes. The ratio of thermal conductivity of equilibrated eutectic liquid to thermal conductivity of solid NPG solution was also measured to be 0.80.     

Structural role and coordination environment of Fe in Fe2O3–PbO–SiO2–Na2O composite glasses

The structural role, coordination geometry and valence of Fe in a series of Fe₂O₃–PbO–SiO₂–Na₂O glasses are studied by means of Fe-K-NEXAFS and EXAFS spectroscopies. Parameters for the study are the concentration of the Fe and Pb-oxides, the SiO₂/Na₂O ratio and the cast temperature. The EXAFS and NEXAFS results reveal that the role of Fe³⁺ depends on the concentration of Fe₂O₃. More specifically, in most of the studied quaternary systems, the Fe³⁺ ion is a glass former, i.e. the Fe atoms belong to FeO₄ tetrahedra that participate in the formation of the glassy network. The role of Fe as an intermediate oxide is identified only in one sample with 20 wt% Fe₂O₃, where ～80 at.% of the Fe atoms are tetrahedrally coordinated with O atoms, while the remaining ～20 at.% of the Fe atoms occupy octahedral sites. It is also revealed that the tetrahedral coordination of Fe in the vitreous matrix is destroyed when a number of parameters is altered, such as the T_cast, the (Fe + Si)/O and the SiO₂/Na₂O ratio.     

Dielectric properties of keratin–water system in diabetic and healthy human fingernails

Dielectric measurements as a function of temperature (22–200 °C) and frequency (100 Hz–100 kHz) are reported for the healthy and the diabetic nail plate. The plots of the relative permittivity versus temperature at the same frequency are higher in the healthy than in the diabetic nail. These results are interpreted as caused by the damage of the polar sites in the keratin–matrix–water system of the diabetic nail. The activation energy of the β-relaxation is higher for the diabetic nail than for the healthy nail, suggests that advanced glycation end products (AGEs) may form cross-links by interaction with keratin. The results of this work indicate that the dielectric measurements of the nail could be used in detection of diabetes.     

Crystallization kinetics in Se–Te glassy system

Differential scanning calorimetry measurements were used to study crystallization in the Se_yTe_(1 ? y) glassy system under non-isothermal conditions. The examined compositions were y = 0.1, 0.2 and 0.3. The crystallization kinetics was described in terms of the Johnson–Mehl–Avrami nucleation–growth model. It was found that with the addition of tellurium into the selenium matrix the apparent activation energy of the crystallization process monotonically increases and, more importantly, the parameter of the JMA model m decreases. This change in the crystallization mechanism was interpreted as a gradual crossover from surface to bulk process. Both processes are competitive and proceed simultaneously in glasses with low tellurium content, while in the case of increased Te content the surface crystallization mechanism recedes. The transition between mechanisms was discussed in terms of changes in molecular structure of the material.