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.     

Natural convection during directional solidification of an Al?Zn eutectic

A study was made of the buoyancy convection of melt provoked by temperature gradient of an orientation identical to that of the gravity vector. The convection was assessed on the basis of temperature fluctuations in the melt. The critical Rayleigh numbers for periodic and turbulent flow were determined. Both periodic and turbulent flow gives rise to transverse “bands” in the structure of the eutection obtained by directional solidification. The intensity of unstable flow affects the number of eutectic crystallites in the sample.     

The Johari-Goldstein β-relaxation of glass-forming binary mixtures

The present paper shows, by means of broadband dielectric measurements, that the primary α- and the secondary Johari-Goldstein (JG) β-processes in binary mixtures are strongly correlated. This occurs for different polar rigid probes dissolved in apolar glass-forming solvents, over a wide temperature and pressure range.We found that the coupling parameter n = 1 − β_KWW and the ratio between α- and β-relaxation time reduce on increasing the size of the solute solved within the same apolar matrix. Moreover, such a ratio is invariant when calculated at different combinations of P and T maintaining either the primary or the JG relaxation times constant. Dielectric spectra measured at different T-P combinations but with an invariant α-relaxation time are well superposed in both the α- and β-frequency ranges. Experimental results can be rationalized by Coupling Model equation.     

Simulation of the spinodal phase separation dynamics of the Bi–Zn system

In the phase separation occurring at the miscibility gap (at the spinodal region) of an alloy a discrete symmetry is spontaneously broken and a domain wall network is formed. Field theory simulations are often used to study the dynamics of topological defects networks appearing in different physical contexts. In this work, we focus on the dynamics of the two immiscible liquids appearing on the phase diagram of the Bi–Zn system, one of the basic systems of lead free solders. We use phase field simulations to quantitatively simulate the dynamics of the two liquids separation in the Bi–Zn system, at different temperatures and for different concentrations. We obtain the miscibility gap curve and the domain morphologies of the system as a function of time, temperature and component concentrations using simulations.     

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.     

Experimental determination of the solid–liquid equilibrium,metastable zone,and nucleation parameters of the flunixin meglumine–ethanol system

Measurements of the metastable zone and solubility for flunixin meglumine–ethanol system were obtained. The solubility was measured within the temperature range from 288.15 to 328.15 K. The mole fraction solubility was correlated satisfactorily with the temperature by the equation: x_eq=2.35×10^?12e^0.07121T. The value of enthalpy of dissolution, enthalpy of fusion and enthalpy of mixing were determined to be 49.04, 64.03 and ?14.99 kJ mol^?1 respectively. The metastable zone width of flunixin meglumine was measured by an electric conductivity method. A comparison of the nucleation temperatures from electric conductivity measurement and from focused beam reflectance measurement (FBRM) shows that both detection techniques give almost the same results for flunixin meglumine. The nucleation parameters of flunixin meglumine in ethanol were determined from the metastable zone data. Over the equilibrium temperature range from 312.28 to 325.55 K, the nucleation rate constant was varied from 0.00001 to 0.00120 #/m² min, whereas the nucleation order was varied from 2.23022 to 3.39299. The obtained high values of nucleation order indicated a high rate of nucleation.     

Solvothermal synthesis of micron-sized spherical particles in TiO2–ZrO2 binary system

We prepared TiO₂–ZrO₂ binary oxide particles with various Ti/(Zr+Ti) mole ratios (x) from the solutions containing Ti(OC₃H₇ⁱ)₄, Zr(OC₃H₇ⁿ)₄ and acetylacetone (acac). The spherical particles of 1–5 μm in diameter were obtained via solvothermal treatment at 150 °C. The spheres were anatase at x=1 and amorphous at x=0–0.8. The spheres were thought to be formed through the moderate hydrolysis and nucleation provided by the chelation of the alkoxides by acac. Crystalline TiO₂–ZrO₂ particles were obtained by the heat treatment of the as-precipitated spheres, and the crystalline phase changed with the Ti/(Zr+Ti) mole ratios. Pure ZrO₂ and TiO₂, ZrO₂ doped with Ti⁴⁺, TiO₂ doped with Zr⁴⁺ and ZrTiO₄ phases were produced, and the spherical shape remained after the heat treatment at 500–750 °C.     

The effect of TiO2 on phase separation and crystallization of glass-ceramics in CaO–MgO–Al2O3–SiO2–Na2O system

The experiments were carried out on studying the effect of phase separation on nucleation and crystallization in the glass based on the system of CaO–MgO–Al₂O₃–SiO₂–Na₂O. In the experiments, TiO₂ was chosen as nucleating agent. Three batches of 5, 8 and 10 wt% TiO₂ substitution were investigated by the techniques of DSC, XRD, FTIR and FESEM equipped with EDS. XRD and FTIR analysis indicated that the super cooled glasses were all amorphous, the heat treatment leading to nucleation would cause a disruption of silica network which followed phase separation. The phase separation followed the generation of crystal seeds Mg(Ti, Al)₂O₆. FESEM observation and EDS analysis revealed that the more TiO₂ content of glass, the more droplet separated phase and crystal seeds after nucleation heat treatment. The main crystal phase is clinopyroxene, Ca(Ti, Mg, Al)(Al, Si)O₆, of crystallized glass.     

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.     

The leaching behavior of PbOSiO2 glasses

The leached layer of PbOSiO₂ glasses formed by diluted nitric acid solution has been investigated by ellipsometry and Auger electron spectroscopy (AES). The leaching behavior of PbOSiO₂ glasses in 10^?4 N aqueous solution of NHO₃ at 30°C was measured in real time using a Nikon auto-ellipsometer.The results were applied by curve fitting to the two-layer model from the concentration profile obtained by AES, and the refractive index profile against the film thickness was determined.The leached layer is inhomogeneous and consists of a low refractive index region and a transition region. The gradient of the refractive index in the former region is extremely small and the refractive index becomes nearly constant between 1.42 and 1.44. The shape of latter region becomes stable with its thickness at 100–310 Å, and moves in the direction of depth without changing the shape as the leaching proceeds.     

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.     

The composition dependence of electrical switching behavior of Ge7Se93−xSbx glasses

Bulk Ge₇Se_93?xSb_x (21 ? x ? 32) glasses are prepared by melt quenching method and electrical switching studies have been undertaken on these samples to elucidate the type of switching and the composition and thickness dependence of switching voltages. On the basis of the compressibility and atomic radii, it has been previously observed that Se-based glasses exhibit memory switching behavior. However, the present results indicate that Ge₇Se_93?xSb_x glasses exhibit threshold type electrical switching with high switching voltages. Further, these samples are found to show fluctuations in the current–voltage (I–V) characteristics. The observed threshold behavior of Ge₇Se_93?xSb_x glasses has been understood on the basis of larger atomic radii and lesser compressibilities of Sb and Ge. Further, the high switching voltages and fluctuations in the I–V characteristics of Ge–Se–Sb samples can be attributed to the high resistance of the samples and the difference in thermal conductivities of different structural units constituting the local structure of these glasses. The switching voltages of Ge₇Se_93?xSb_x glasses have been found to decrease with the increase in the Sb concentration. The observed composition dependence of switching voltages has been understood on the basis of higher metallicity of the Sb additive and also in the light of the Chemically Ordered Network (CON) model. Further, the thickness dependence of switching voltages has been studied to reassert the mechanism of switching.     

Influence of crystallisation conditions on the microtexture of the directionally solidified eutectic of the MgF2?CaF2 system

The influence of high-frequency (HF) and resistive (R) heating of a vertical crystallizer furnace on the directional solidification process of the MgF₂ CaF₂ system eutectic has been compared. The turbulent flow induced by HF heating given rise to inhomogeneities in microtexture, which do not occur under R heating conditions. Variations in the growth rate (v) and temperature gradient (ΔT) lead to characteristic changes of the eutectic microstructure: from lamellar to rod-like. Quantitative analysis of these changes was advantageously performed using a digital image analysis of the area (AR), maximum cross-section (D-MAX), direction of the maximum cross-section (ANGLE D-MAX) of MgF₂ particles of the microtexture. This was recorded on SCAN images of transverse cuts through the given directionally solified samples as well as the analysis of the shape of MgF₂ particles.     

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.     

Glass formation and properties of chalcogenide systems (XXII) the phase diagram of the system PbSe?GeSe2 and on the compound Pb2GeSe4

The phase diagram of the system PbSe GeSe₂ is studied by X-ray analysis and DTA. Pb₂GeSe₄ is the only compound which is formed in the system. It melts incongruently at 590 ± 4°C. The formation of Pb₂GeSe₄ as a definite compound is supported by studying the phase relations in the corresponding area of the ternary system PbSe GeSe GeSe₂.     

Metalorganic vapor phase epitaxy of III–V-on-silicon: Experiment and theory

The integration of III–V semiconductors with Si has been pursued for more than 25 years since it is strongly desired in various high-efficiency applications ranging from microelectronics to energy conversion. In the last decade, there have been tremendous advances in Si preparation in hydrogen-based metalorganic vapor phase epitaxy (MOVPE) environment, III–V nucleation and subsequent heteroepitaxial layer growth. Simultaneously, MOVPE itself took off in its triumphal course in solid state lighting production demonstrating its power as industrially relevant growth technique. Here, we review the recent progress in MOVPE growth of III–V-on-silicon heterostructures, preparation of the involved interfaces and fabrication of devices structures. We focus on a broad range of in situ, in system and ex situ characterization techniques. We highlight important contributions of density functional theory and kinetic growth simulations to a deeper understanding of growth phenomena and support of the experimental analysis. Besides new device concepts for planar heterostructures and the specific challenges of (001) interfaces, we also cover nano-dimensioned III–V structures, which are preferentially prepared on (111) surfaces and which emerged as veritable candidates for future optoelectronic devices.     

Molecular and crystal structure ofβ-isosparteine monoperchlorate

The crystal structure; determined by X rays, and the¹³C-NMR spectra of-isosparteine perchlorate are presented. The quinolizidine moieties are present in acis ring-juncture; all piperidine rings are in a chair conformation. The two nitrogen atoms are linked by a hydrogen bond of 2.704(5) Å. The proton at N(16) is also involved in a weak hydrogen bond with the O(2) of the perchlorate anion. The two quinolizidine moieties-protonated and unprotonated-differ only slightly in conformation; the protonation caused small but significant changes in the length of the bonds about the nitrogen atoms. The title compound was obtained by chemical transformations of 17-oxosparteine and protonation with an equimolar amount of HClO₄ in methanol.¹³C-NMR spectra in DMSO-²H₆ revealed the presence of the symmetricalcis-cis bis-quinolizidine structure of the salt in solution.     

Optical and dielectric properties of an isothiocyanato liquid crystal compound and comparison of its behavior with that of a homologous member

The properties of an isothiocyanato liquid crystal compound (code name S1) has been studied with a view to compare its behavior with that of another member of its homologous series (code name S5). Optical properties, such as refractive index, polarisability, and their anisotropies, have been evaluated with varying temperature and the orientational order experimentally determined from the study of polarisability anisotropy and compared with theoretically computed values. Dielectric studies have been conducted to determine not only the dielectric anisotropy but also the effective molecular dipole moment and its temperature dependence. The temperature variation of the angle of inclination (β) of molecular dipole moment with the director direction has also been determined and compared with that of S5. In order to determine the nature of molecular association in the mesophase, the molecular correlation factor (g) has been estimated from the measurements of dipole moments of compound in solution and compared with the values obtained for S5.