The mechanism of the formation of enantiotropic polymorphs of carisbamate in solution crystallization

The nucleation kinetics, as a function of supersaturation level, was studied for carisbamate, a polymorphic crystalline compound, in methanol, ethanol, 2-propanol and water. The induction times in nucleation kinetics varied markedly with respect to relative supersaturation in the range 1.3–2.3. At the same relative supersaturation, the induction time for carisbamate in methanol is the shortest, increasing in order from ethanol, 2-propanol, and then water. The interfacial tensions γ between carisbamate and methanol, ethanol, 2-propanol, and water were estimated from their induction times based on nucleation theory and were found to be about 3.6, 4.1, 4.5, and 5.7 mJ/m², respectively. These values were of same order of magnitude as those obtained from solubility data. The equation that displays the influence of interfacial tension, supersaturation and temperature on crystallization kinetics was derived, and found to be consistent with experimental observations. The mechanism of enantiotropic polymorphism for carisbamate in the solvents is illustrated. Using interfacial tension values determined for single solvents, the polymorphic form resulting from crystallization in mixed and pure solvent systems could be predicted with good accuracy.     

Crystal growth and characterization of GaCrN nanorods on Si substrate

GaCrN nanorods were grown on GaN nanorods by RF-plasma-assisted molecular beam epitaxy. GaN nanorods were grown on Si (0 0 1) substrates with native SiO₂. Cr doping into GaCrN nanorods was conducted at substrate temperatures of 800 and 550 °C. Cross-sectional transmission electron microscopy images revealed that the diameter of GaCrN nanorod gradually increases with growth proceeding at 550 °C, while the growth at 800 °C does not change the nanorod diameter. Low-temperature growth enhances the growth perpendicular to the c-axis and decreases the growth along the c-axis. It was found that the solubility limit of Cr atoms in GaCrN is much higher for the low-temperature growth than for the high-temperature growth. It was also found that the highest saturation magnetization is obtained at some optimum Cr cell temperature.     

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.     

Solubility of GaN in supercritical ammonia with ammonium chloride as a mineralizer

The solubility of GaN in supercritical ammonia with ammonium chloride as a mineralizer was measured with a weight-loss method. Temperature-, pressure-, and mineralizer concentration-dependence of the solubility of GaN were investigated. The solubility increased with increase in temperature, and its pressure dependence was very low. The solubility behavior was quite different from the case of using the mineralizer KNH₂ as a basic mineralizer.     

Fabrication of (1 1 1)-oriented Si layers on SiO2 substrates by an aluminum-induced crystallization method and subsequent growth of semiconducting BaSi2 layers for photovoltaic application

We have prepared (1 1 1)-oriented Si layers on SiO₂ (fused silica) substrates from amorphous-Si(a-Si)/Al or Al/a-Si stacked layers using an aluminum-induced crystallization (AIC) method. The X-ray diffraction (XRD) intensity from the (1 1 1) planes of Si was found to depend significantly on growth conditions such as the thicknesses of Si and Al, deposition order (a-Si/Al or Al/a-Si on SiO₂), deposition technique (sputtering or vacuum evaporation) and exposure time of the Al layer to air before the deposition of Si. The crystal orientation of the Si layers was confirmed by θ−2θ, 2θ XRD and electron backscatter diffraction (EBSD). The photoresponse properties of semiconducting BaSi₂ films formed on the (1 1 1)-oriented Si layers by the AIC method were measured at room temperature. Photocurrents were clearly observed for photon energies greater than 1.25 eV. The external quantum efficiencies of the BaSi₂ were also evaluated.     

Isothermal crystallization kinetic of ZnO thin films

Zinc oxide (ZnO) thin films deposited by DC magnetron sputtering were annealed in nitrogen atmosphere at different temperatures ranging from 100 to 500 °C with a step of 100 °C; the annealing time was 6 h. In order to study the film’s crystallization kinetic, their structures were monitored by means of X-ray diffraction (XRD) analysis each hour. Variation in grain size, calculated from the XRD patterns, with annealing time and temperature, obeys the classical parabolic law of grain growth. Exponent n was found to be dependent on the annealing temperature; it ranged from 5.13 to 3.8 with increase in annealing temperature. From the obtained exponent n values we inferred that the grain growth mechanism is mainly governed by the atom jumping across the grain boundary. We have found that the grain growth is characterized by a low activation energy ranging from 22 to 24 kJ/mol.     

Electrical conductivity of NbN-SiO2 films obtained by ammonolysis of Nb2O5-SiO2 sol-gel derived coatings

The studies of electrical conductivity of NbN-SiO₂ films are reported. To obtain these films, sol-gel derived xNb₂O₅-(100 − x)SiO₂ (where x = 100, 90, 80, 70, 60, 50 mol%) coatings were nitrided at 1200 °C. The nitridation process leads to the formation of some disordered structures, with NbN metallic grains dispersed in insulating SiO₂ matrix. The structure of the samples was studied using X-ray diffraction (XRD) and atomic force microscopy (AFM). The electrical conductivity was measured with the conventional four-terminal method in the temperature range from 5 to 280 K. The superconducting transition was not observed even for the sample that does not contain silica. All the samples exhibit negative temperature coefficient of resistivity. The results of conductivity versus temperature may be described on the grounds of a model proposed for a weakly disordered system.     

Growth of InxGa1−xN quantum dots by nitridation of nano-alloyed droplet method using MOCVD

In_xGa_1−xN quantum dots (QDs) were grown on GaN/sapphire (0 0 0 1) substrates by employing nitridation of nano-alloyed droplet (NNAD) method using metal-organic chemical vapor deposition (MOCVD). In+Ga alloy droplets were initially formed by flowing the precursors TMIn and TMGa. Density of the In+Ga alloy droplets was increased with increasing precursors flow rate; however, the droplet size was scarcely changed in the range of about 100–200 nm. Two cases of In_xGa_1−xN QDs growth were investigated by varying the nitridation time and the growth temperature. It was observed that the In_xGa_1−xN QDs size can be easily changed by controlling the nitridation process at the temperature between 680 and 700 °C for the time of 5–30 min. Self-assembled In_xGa_1−xN QDs were successfully grown by employing NNAD method.     

Solubility of glasses in the system P2O5-CaO-MgO-Na2O-TiO2: Experimental and modeling using artificial neural networks

Phosphate glasses in the system P₂O₅-CaO-MgO-Na₂O-TiO₂ for use as degradable implant materials were produced. In order to classify their solubility behavior, dissolution experiments were performed in deionized water for 60 min at 98 °C. Resulting solutions were analyzed using ICP-OES. In addition, pH measurements were carried out in physiological NaCl solution. With increasing phosphorus oxide content, the glasses showed a higher solubility and gave lower pH values in aqueous solution. This was caused by changes in the glass structure, as long phosphate chains are more susceptible to hydration than smaller phosphate groups. These changes in glass structure were followed by ³¹P MAS-NMR experiments. Increasing sodium oxide concentrations in exchange for calcium or magnesium oxide also increased the glass solubility by disrupting ionic cross links between chains. By contrast, addition of titania made the glasses more stable towards dissolution by cross linking smaller phosphate groups. The aim of this study was to find a relationship between glass composition and solubility behavior. As classical linear methods of data analysis were unsuitable due to the complexity of the relationship, preliminary artificial neural networks analyses were performed and were found to be an interesting tool for modeling the solubility behavior of phosphate glasses.     

Ammonothermal epitaxy of wurtzite GaN using an NH4I mineralizer

Purely wurtzite phase needle crystals and epitaxial layers of GaN were grown by the ammonothermal method using an NH₄I mineralizer. The inclusion of zincblende phase GaN was effectively eliminated by increasing the growth temperature higher than 500 °C. Accordingly, an approximately 20-μm-thick GaN epitaxial layer was achieved on the Ga-polar face of a c-plane GaN seed wafer at 520 °C. Although the characteristic deep state emission band dominated the room temperature photoluminescence spectrum, the near-band-edge emission of GaN was observed for both the needle crystals and the epitaxial layers. These results encourage one to grow better quality GaN crystals at a high growth rate under high-temperature growth conditions.     

Zr-based bulk metallic glass with super-plasticity under uniaxial compression at room temperature

Commonly, bulk metallic glasses exhibit very limited plastic deformation (<2%) at room temperature. In this letter, through appropriate composition choices, rods of Zr_62.55Cu_17.55Ni_9.9Al₁₀ and Zr_64.80Cu_14.85Ni_10.35Al₁₀ bulk metallic glasses (BMGs) were prepared by using copper-mold suction-casting. X-ray diffraction and differential scanning calorimetry were utilized to determine their structures and thermal stabilities, and uniaxial compression tests were adopted to study their plastic deformation behaviors (PDBs) at room temperature. The results showed that T_g and T_x of the former are 651.5 K and 748 K, respectively, while those of the latter are 646 K and 750 K, respectively. Micro-hardness values are 693 ± 7 Hv and 595 ± 5 Hv for T1 and T2, respectively. During the compression tests, the former underwent about 2.5% engineering strain, i.e., 2.8% true strain, then fractured. While the latter was compressed into a flake-like form, of which, engineering strain values are larger than 70%, i.e., true strain exceeds 120%, showing super-plasticity at room temperature. It can be concluded that micro-hardness and PDBs of BMGs are very sensitive to composition.     

Water diffusion into a silica glass optical fiber

The diffusion coefficient and solubility of water in silica glass optical fiber cladding were measured in the temperature range of 600-800 °C and were compared with the corresponding values of bulk silica glasses. It was found that the diffusion coefficient was slightly lower and the solubility was appreciably higher in optical fiber, especially at low temperatures, compared with those in bulk silica glasses. The observed trend was consistent with the expected effect of fictive temperature.     

Influence of tempereature on Struvite precipitation by CO2‐deagassing method

The present study explores struvite precipitation by degassing method under different temperature (14.5‐35 °C). It is shown that an increase of temperature does not affect the nucleation kinetics but strongly influences the growth rate and the efficiency of the phosphate removal. This was attributed to the effect of temperature on the struvite solubility and then the reached supersaturation coefficient. It was also shown, by using degassing method, that the determined solubility constant (pK_s) values of struvite, at 14.5, 20, 25 and 35 °C are 13.00, 12.82, 12.63 and 13.20, respectively, are close to those presented in the literature. The results show that temperature influences the kinetics of precipitation. First‐order kinetics were found to be sufficient to describe the rate data. The rates decreased with increasing temperature and the apparent rate constants for the reaction were determined. Arrhenius plots yielded a relatively apparent high activation energy E_a = 31.0 kJ·mol^–1. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bulk single-crystal growth of ternary AlxGa1−xN from solution in gallium under high pressure

We have successfully grown bulk, single crystals of Al_xGa_1−xN with the Al content x ranging from 0.5 to 0.9. Samples were grown from Ga melt under high nitrogen pressure (up to 10 kbar) and at high temperature (up to 1800 °C) using a gas pressure system. The homogeneity and Al content of the crystals were investigated by X-ray diffraction and laser ablation mass spectrometry. On the basis of the high-pressure experiments, the corresponding pressure–temperature (p–T) phase diagram of Al–Ga–N was derived. The bandgap of the material was determined by the femtosecond two-photon absorption autocorrelation method and is equal to 5.81±0.01 eV for the Al_0.86Ga_0.14N crystals.     

On the temperature dependence of the enthalpies of mixing in liquid binary (Ag, Cu, Ni)-Sn alloys

The partial and integral enthalpies of mixing of liquid binary alloys in the systems Ag-Sn, Cu-Sn and Ni-Sn were determined at different temperatures from 500 to 1500 °C using drop calorimetry techniques. Generally, our measured values fit well to most of the hitherto reported results. The data were fitted using a Redlich-Kister polynomial and the binary interaction parameters were evaluated. For all three systems the enthalpy curves at various temperatures are discussed focusing on the association theory. C^ass,C^A₁,B₁,C^A₁,A_iB_j,C^B₁,A_iB_j, the interaction parameters and K_AiBj were determined. The general shape and supposed temperature dependence of the enthalpy of mixing in Ag-Sn and Cu-Sn could be confirmed. No significant temperature dependence could be found experimentally for Ni-Sn at temperatures above 1100 °C. Extrapolations into the metastable liquid regions based on the association theory, however, indicate a small drop of Δ_MixH with temperature. A second series of measurements limited to low concentrations of Ag, Cu, or Ni, respectively in Sn has been performed in order to determine the partial enthalpies of mixing at infinite dilution at 500, 600, 700, and 800 °C. Temperature dependence could be observed for all three binary systems, most developed for Ni-Sn.     

Effects of pH and temperature on CaCO3 crystallization in aqueous solution with water soluble matrix of pearls

Water soluble matrix (WSM) was extracted from pearls originated from Hyriopsis cumingii in Zhuji, Zhejiang province, China. WSM was regarded as an additive in mineralization experiments in order to study the effect of WSM on CaCO₃ crystallization. The experiments were carried out at different pH and temperatures by gas diffusion method and solution titration method, respectively. Scanning electron microscopy (SEM) and Raman spectroscopy (Raman) were used as powerful techniques to analyze the co-effect of pH value, temperature and WSM on crystal growth of CaCO₃. The results showed that WSM could induce aragonite at different pH values of mineralization solution, and the pH value had remarkable influence on morphology of calcite rather than aragonite due to distinct supersaturation and ionic strength related to various pH values. At different solution temperatures, WSM had little effect on crystal growth of calcium carbonate while the solution temperature had notable effect on polymorph and morphology of CaCO₃ crystals. This work can provide some basic information for the polymorph and morphology control of calcium carbonate.     

Coexistence properties of phase separation and CuPt-ordering in InGaAsP grown on GaAs substrates by organometallic vapor phase epitaxy

CuPt-ordering and phase separation were directly investigated in In_1-xGa_xAs_yP_1-y with a low arsenic content grown by organometallic vapor phase epitaxy on GaAs substrates. CuPt-ordering and phase separation in samples grown at the substrate temperatures of 630 and 690 °C were characterized by transmission electron diffraction and transmission electron microscopy. Although the immiscibility of InGaAsP was enhanced at the lower substrate temperature, the sample grown at 630 °C showed less phase separation than the 690 °C-grown sample. The degree of CuPt-ordering was significantly enhanced in the sample grown at 630 °C. The results demonstrated that the CuPt-ordering originating from surface reconstruction of P(2×4) suppressed the phase separation even in the miscibility gap. The detailed characterization of the phase separation clearly revealed a vertical composition modulation (VCM) in InGaAsP for the first time. The mechanism of the VCM formation is discussed based on the modulated-strain field on the surface.     

Effect of cooling rate on enthalpy and volume relaxation of polystyrene

This paper presents the results of measurements of physical aging on polystyrene with a narrow molecular weight distribution (M_w/M_n = 1.03). The evolution of the aging process was followed by recording the relaxed enthalpy and the accompanying decrease in volume, using differential scanning calorimetry and mercury-in-glass dilatometry, respectively. The measurements were carried out after cooling the sample at constant rate to the aging temperature. The cooling rate varied between 0.0037 and 1 °C/min. The aging data were fitted with the KWW and the TNM functions. The differences in the time scales of enthalpy, h, and volume, v, relaxation were relatively small. From the h(v) graphs the derivative dh/dv was found to amount to about 1.8 GPa, a value significantly exceeding the predictions of the thermodynamic model containing an additional internal variable.     

Isobaric heating of polystyrene and evaluation of the Narayanaswamy parameter x from volume recovery data

Structure parameter x, defining the relative contributions of temperature and structure to the relaxation times, which is applied in Tool-Narayanaswamy-Moynihan (TNM) equation, was evaluated from volume heating isobars for polystyrene (PS) applying the peak shift method. The peak shifted with changing structural state of PS prior heating, which was reached by different period of aging time at 89 °C < T_g up to 2544 h. In this novelized procedure for volume data, originally tested only for enthalpic measurements, high sensitivity of peak temperature (position of inflection point of the heating isobar) was shown, together with high linearity of data. This allows to directly and sensitively calculate the shift and consequently structure parameter x. The value found in the research, x = 0.40 ± 0.02, is in good agreement with published results obtained by the peak-shift method from enthalpy data of PS.     

Physicochemical studies of phosphate based P2O5-Na2O-CaO-TiO2 glasses for biomedical applications

Glasses P₂O₅-Na₂O-CaO-TiO₂ with different TiO₂ contents and fixed P₂O₅ (45 wt%) and CaO (24 wt%) have been prepared employing the normal melting and annealing technique. Measurements such as ultrasonic velocity, attenuation, solubility and pH have been carried out in all the compositions of the glasses. It is interesting to note that the above measured ultrasonic parameters exhibit an abnormal behavior (minimum) at 0.5 wt% of TiO₂ content, beyond which an increase in these parameters with increasing TiO₂ content is observed. The maximum pH values and Ca²⁺ ion release have been observed for the TiO₂ free glass those compositions with and the low TiO₂(?1.0 wt%) content. As the content of the TiO₂ increases, the solubility of the glasses decreases. The observed weight loss reveals two stages of phosphate dissolution kinetics i.e. the first stage, in which the weight loss is proportional to t^1/2, and a second stage in which a linear behavior is observed.