Effect of Al2O3 on phase separation and crystallization in ZnO---Al2O3---B2O3---SiO2 glasses

The effect of alumina on the phase separation and the crystallization of the glasses of composition (mol%) 18ZnO·30B₂O₃·52SiO₂ and O-40 Al₂O₃ was studied using an electron microscope and IR spectroscopy. The main crystalline phase appears in the microphase for which the compositions are not nearer to the crystal stoichiometry than the mean. The addition of Al₂O₃ suppresses the immiscibility but enhances the crystallizability.     

Microstructure and Texture Formation in Vacuum-deposited Silver Films

The role of the recystallization in the processes of microstructure and texture formation of silver films is compared for films: 1) deposited at high substrate temperatures (up to 720 K) and slowly cooled or quenched to room temperature; 2) deposited at room temperature and annealed at high temperatures. The grain growth distribution curves and the texture perfection are analysed. It is shown that the recrystallization processes taking place both during the slow cooling and during the annealing of the films lead to a formation of identical film structure with lower degree of texture perfection than in the case of quenched films.     

Transformations in liquid state and microstructure development in immiscible Fe60Cu20P10Si5B5 alloy

A five-component Fe₆₀Cu₂₀P₁₀Si₅B₅ immiscible alloy was arc-melt and melt-spun from various temperatures. The microstructure and chemical composition of the ingot and melt-spun ribbons were analyzed using scanning electron microscope SEM/EDS. The melt-spun ribbon was investigated by transmission electron microscope (TEM). The melting range of the alloy was investigated by means of differential thermal analysis (DTA) and for reference, the temperature change during free cooling of the alloy was controlled by pyrometer in the melt spinning device. Processing with the slow cooling rate produced the fractal surface structures formed by the Fe-rich regions and Cu-rich regions. The arrangement of the regions was characteristic for the liquid immiscible alloys. It was found that the microstructures of the melt-spun ribbons depended on the ejection temperature. The lower ejection temperatures resulted in the formation of the lamellar structures separated into Fe-rich and Cu-rich regions. This was due to rapid cooling within the miscibility gap. Ejection at higher temperatures, above the miscibility gap led to the formation of a uniform amorphous/crystalline composite.     

Nd(III) and Yb(III) ions incorporated in Y4Al2O9 obtained by sol‐gel method: synthesis,structure, crystals and luminescence

The nanocrystalline powders of Y₄Al₂O₉ (YAM) pure and doped by Nd, Yb and codoped by Nd and Yb were obtained via modified sol‐gel method. These powders were characterized by X‐ray diffraction method, scanning electron microscopy and high resolution scanning electron microscopy, luminescence spectroscopy and differential thermal analysis (DTA). We obtained single phase powders of crystalline structure with average size 70 nm exhibiting interesting luminescent properties. Efficient non‐radiative energy transfer between Nd and Yb was found. DTA confirmed the phase transition at about 1400 °C. From these nanocrystalline powders, the crystals YAM:Yb, YAM:Yb,Nd were grown by micro‐pulling down technique. They were cracking during cooling owing to the phase transition. Luminescent properties of YAM:Nd,Yb crystals were identical with properties of corresponding nanopowders within experimental incertitude. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of the annealing process on the microstructure of La2Zr2O7 thin layers epitaxially grown on LaAlO3 by metalorganic decomposition

La₂Zr₂O₇ (LZO) films have been grown by metalorganic decomposition (MOD) to be used as buffer layers for coated conductors. A characteristic feature of LZO thin films deposited by MOD is the formation of nanovoids in an almost single crystal structure of LZO pyrochlore phase. Annealing parameters (heating ramp, temperature, pressure, etc.) were varied to establish their influence on the microstructure of the LZO layers. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for sample characterization. The epitaxial pyrochlore phase was obtained for annealing temperatures higher than 850 °C whatever the other annealing conditions. However, the film microstructure, in particular, nanovoids shape and size, is strongly dependent on heating ramp and pressure during annealing. When using low heating ramp, percolation of voids creates diffusion channels for oxygen which are detrimental for the substrate protection during coated conductor fabrication. From this point of view high heating rates are more adapted to the growth of LZO layers.     

Relationship between phase separation and properties in some non-prototype glasses

The microstructure of different samples concerning the matrices of glass-ceramics and non-prototype glasses including slags, frit of aluminate cement additive, glass ionomer cement as well as dolomite phosphate fertilizer were studied by using an X-ray diffractometer and electron microscope. It was revealed that phase separation occured in most of these samples of non-prototype glasses.

The relationship between phase separation and properties, e.g. viscosity and chemical activity of these melts or amorphous solids are discussed. Factors influencing the mechanism of phase separation are estimated.     

Formation and structure of titanate glasses

The formation of high titanium oxide (30–60 wt%) containing glasses was studied. Stable titanate glasses with high content of TiO₂ and BaO could be obtained even without other glass-forming oxides. It is demonstrated that the coloration of titanate glasses with high content of TiO₂ is due to oxygen loss during the melting. A systematic study of controlling melting and heat treatment conditions led to the successful decoloration of titanium oxide containing glasses. Infrared spectra and X-ray diffraction studies showed that Ti⁴⁺ in titanate glasses is in sixfold coordination. Phase separation was observed by electron microscopy when the titanate glasses were heat-treated at the temperature above T_g. The crystallization of titanate glasses is generally preceded by phase separation. The obtained crystalline phases are mainly different titanates.     

Co掺杂改性CaTi2O4(OH)2纳米片的溶剂热制备及电化学性能

利用无水氯化钙-钛酸四正丁酯-无水乙醇体系,通过掺杂Co元素,用溶剂热法制备了CaTi2O4(OH)2片状结构.利用X射线衍射(XRD)和扫描电子显微镜(SEM)对样品的显微结构进行检测分析,并利用CHI660E电化学工作站测试掺杂样品电化学性能,研究掺入Co元素对CaTi2O4 (OH)2样品的物相结构、微观形貌以及其电化学性能的影响.实验结果表明:随着钴离子掺入量增加样品的比电容先增加后减小,当Co掺杂量为2;样品的电化学性能最优,且在10 mA/cm2的工作电流密度下,其比电容为496.3 F·g-1.     

人造金刚石单晶生长机理的金属包膜研究进展

在高温高压条件下,利用触媒合金合成金刚石单晶过程中,包覆着金刚石单晶的金属薄膜起着极其重要的作用,揭示其本质对解释金刚石合成机理有着重要的意义.本文从金属包膜的形貌、成份、组织结构以及余氏理论和程氏理论在金属包膜研究中的应用等方面阐述了人造金刚石生长机理的研究现状.在此基础上提出了今后的研究方向.     

Characterization of immiscible Ni78Ag2P20 alloy and formation of amorphous/crystalline composite

This paper presents characterization of the ternary Ni₇₈Ag₂P₂₀ alloy that was arc-melt in argon protective atmosphere and melt spun in helium. The microstructure of the arc-melt droplet was investigated in scanning electron microscope with EDS. The microstructural studies of the melt-spun alloy was made using light microscope, transmission electron microscope and X-ray diffraction. A tendency for separation of the alloy was found and the phases were identified. The mechanical properties were evaluated with use of micro-hardness measurements and the results compared with the available data.     

Centrifugal separation of primary silicon crystal in solvent refining of silicon using Al‐30% Si alloy

This study describes the formation of a primary silicon network during separation of an Al‐30% Si melt and the process conditions to make bigger primary silicon crystals. As the crucible rotates in the centrifugal separation, the unfrozen aluminum‐rich phase and small silicon particles are pushed outside through the openings in the silicon network. As a result, primary silicon crystals are separated in the form of a foam after centrifugation. The recovery of the silicon ranged from 13 to 18% depending on the location in the crucible. The size of the primary silicon achieved by changing the cooling rate and quenching temperature during solidification is also measured using a quenching furnace. Primary silicon particles exhibit a coarse, plate‐like morphology, although small star‐like silicon particles are also found in the aluminum‐rich matrix. The fraction of plate silicon decreases, while the fraction of small globular silicon increases with an increasing cooling rate. The thickness of the primary silicon plate also decreases with an increasing cooling rate in the samples quenched at various temperatures during solidification.     

Electron microscopy studies of epitaxial MgB2 superconducting thin films grown by in situ reactive evaporation

The morphology and chemistry of epitaxial MgB₂ thin films grown using reactive Mg evaporation on different substrates have been characterized by transmission electron microscopy methods. For polycrystalline alumina and sapphire substrates with different surface planes, an MgO transition layer was found at the interface region. No such layer was present for films grown on MgO and 4-H SiC substrates, and none of the MgB₂ films had any detectable oxygen incorporation nor MgO inclusions. High-resolution electron microscopy revealed that the growth orientation of the MgB₂ thin films was closely related to the substrate orientation and the nature of the intermediary layer. Electrical measurements showed that very low resistivities (several μΩ cm at 300 K) and high superconducting transition temperatures (38 to 40 K) could be achieved. The correlation of electrical properties with film microstructure is briefly discussed.     

Continuous cooling crystallization kinetics of a molten blast furnace slag

The crystallization characteristics and kinetics of a molten blast furnace slag during continuous cooling were investigated. Samples of molten blast furnace were continuously cooled both in tiny amounts in a differential scanning calorimetry (DSC) equipment and in bulk states in a cooling mold. The mineragraphy and morphology were investigated by means of X-ray diffraction (XRD) and scanning electron microscope (SEM). The continuous cooling crystallization kinetics were studied using different models based on DSC data. The results show that akermanite (2CaO·MgO·2SiO₂) and gehlenite (2CaO·Al₂O₃·SiO₂) are the major minerals in the continuously cooled crystalline blast furnace slag. The mechanism of crystallization of the blast furnace slag during continuous cooling is dominated by both surface nucleation and one-dimensional growth with bulk nucleation, which is significantly different to that during heating. The activation energy of crystallizations of akermanite and gehlenite was determined by Kissinger and Matusita methods. The values obtained are much higher than that yielded during heating.     

Physical properties of Zn‐ 22 wt.% Al‐ x wt.% Ce melt spun eutectoid alloy

Zn‐ 22 wt.% Al (Zn ‐ 40 Al in atomic%) eutectoid alloys with different Cerium (Ce) contents of 0, 1, 2, and 6 (in wt.%), 0.35, 0.70 and 2.1 (in atomic%) were rapidly solidified by melt spun technique. The effects of high cooling rate and alloying element (Ce) on microstructure of the studied alloys were analyzed by X‐ray diffractometry (XRD), scanning electron microscopy (SEM) and electrical resistance measurements. The results showed that the dendrites as well as grains size were refined by the additions of Ce. The main phases in melt spun alloys were α‐Al and η‐Zn, in addition to intermetallic CeZn₅ and Al₄Ce. Additional metastable intermetallic Al_0.71Zn_0.29 phase has been observed only for melt spun alloy of 6 wt.% Ce content. XRD peaks of melt spun alloys demonstrated a considerable broadening with percentage of Ce due to the grain refinement and lattice distortion. Moreover, increase of Ce content results in a decrease of Al lattice constant which could be related to formation of supersaturated solid solution of Zn and/or Ce in α‐Al. Crystallite size of all phases were in the range of nanometer scale which reflects the role of the high cooling rate and the existence of Ce as alloying element for producing nanocrystalline structure. Resistance measurements of melt spun alloys show that the relative resistance rate for the alloys of higher Ce content relaxed faster to lower value than that of lower Ce content. Electrical resistance and microstructure exhibit strongly Ce content dependence.     

Redox freezing temperature and Bartenev equation in a 25Na2O-15B2O3-60SiO2 glass doped with chromium and manganese

In a melt with the base mol% composition 25Na₂O-15B₂O₃-60SiO₂, doped with chromium and manganese, a redox reaction takes place during cooling the melt. This reaction was studied using high temperature UV-vis spectroscopy. Above 600 °C, the reaction is in equilibrium and shifted during cooling to the Cr³⁺ and Mn³⁺ species. At temperatures between 500 and 600 °C, the kinetics of the redox reaction is decisive and the cooling rate plays an important part. At temperatures < 500 °C, the reaction is frozen in. The smaller the cooling rate, the smaller is the Cr⁶⁺ concentration and the lower is the fictive redox temperature.The kinetics of the reaction was described by a differential equation assuming Arrhenian behaviour. The equation was numerically solved and fictive temperatures were calculated. These temperatures depended on cooling rate similar to Bartenev equation. Activation energies calculated hereof were around 38 kJ?mol⁻¹ larger than those inserted into the kinetic equation. The experimentally determined activation energy is 565 kJ?mol⁻¹, a value much larger than the activation energies of diffusion of the polyvalent elements. The rate determining step in the case of the Cr³⁺/Cr⁶⁺/Mn²⁺/Mn³⁺ system is the electron transfer reaction, because a notable structural rearrangement is necessary during the course of the electron transfer reaction (Cr³⁺ and Cr⁶⁺ occur in octahedral and tetrahedral coordination, respectively). The latter leads to a large inner reorganisation energy and to an activation energy similar to that of the viscous flow. In the case of the redox reaction between copper and arsenic, the activation energy is much smaller (210 kJ?mol⁻¹), because here the coordination numbers do not change during the course of the redox reaction.     

The induction time,interfacial energy and growth mechanism of maltitol in batch cooling crystallization

Maltitol is crystallized with seeds by cooling mode in industry, often with large amount of fine crystals and wide crystal size distribution. To eliminate the fine nucleation, it's necessary to understand the nucleation kinetics. In this work, the solubility of maltitol in water was measured by the gravimetric method, the nucleation kinetics of maltitol in batch cooling crystallization was investigated using focus beam reflectance measurement (FBRM), and a novel method was proposed to determine the induction time from the trend of the crystal median chord given by FBRM. Based on the relationship between the induction time and the supersaturation, the nucleation mechanism was obtained, including homogenous nucleation at high supersaturation and heterogenous nucleation at low supersaturation. Additionally, combining the classical nucleation theory (CNT) and Arrhenius’ principle, the crystal‐solution interfacial energy and the energy barrier of homogenous nucleation were calculated. From the scanning electron microscope (SEM) images, the growth mechanism of maltitol was identified as surface nucleation growth and the surface entropy factor calculated from the kinetic analyses of t_ind data corroborated this growth mechanism.     

Blocky and spheroidal growth in Y1.5Ba2Cu3Ox system

Solidification of Y_1.5Ba₂Cu₃O_x system was studied with the aim to find the temperature of self-nucleation. The microstructure after cooling from isothermal dwells in the temperature range 984–995 °C was analysed. It is shown that blocky YBa₂Cu₃O_7?δ crystals were self-nucleated and grown during isothermal dwells below 988 °C and spheroidal multicrystals were formed during cooling from isothermal dwells at higher temperatures. The symmetrical and radial YBa₂Cu₃O_7?δ crystal branches of spheroids grow in the 〈110〉 crystal direction.     

溶胶-凝胶法制备CuAlO2微晶及其合成活化能研究

采用溶胶-凝胶法制备了铜铁矿结构的CuAlO2微晶,利用示差扫描量热法(DSC)对其合成活化能进行了初步研究;通过XRD、TEM等分析方法对CuAlO2微晶的物相组成和显微结构进行表征.结果表明,以乙酸铜、硝酸铝和乙二醇为反应原料,采用溶胶-凝胶法可以成功制备CuAlO2微晶.前躯体在烧结过程中,首先生成了CuAl2O4和CuO中间相,然后继续反应再形成了CuAlO2微晶.DSC分析表明CuAlO2的合成温度在1181 ℃左右,计算得到其合成活化能为88.25 kJ/mol.利用紫外-可见光谱分析,CuAlO2微晶的光学带隙约为3.85 eV.     

The Influence of the Shape and the Incompatibility of Molecular Moieties on the Structure of Smectic Mesophases

For selected compounds with perfluorinated chains the structure of smectic phases was investigated by X-ray diffraction measurements. For rod-like compounds with only one terminal perfluorinated chain the incompatibility of the hydrocarbon and the fluorocarbon moieties leads to a segregation of both parts which can be considered as microphase separation. For swallow-tailed compounds the structure of smectic phases depends on the position and the length of the perfluorinated chains. If the steric interaction dominates an antiparallel packing of the molecules within the smectic layers is favoured. If the incompatibility of the hydrocarbon and fluorocarbon moieties is of importance the smectic layers are distorted and at lower temperatures the layer structure is transformed into a columnar structure.     

Microstructure of high-temperature plastically deformed Zn-doped CdTe; comparison with In-doped GaAs

We investigated the microstructure of CdTe and Cd_0.96Zn_0.04Te samples plastically deformed by uniaxial compression at constant strain rate between 0.6T_m and 0.85T_m (where T_m is the melting temperature, 1365 K). We used scanning electron microscopy (SEM) in the cathodoluminescence (CL) mode to observe dislocation arrangements and transmission electron microscopy (TEM) to measure dislocation dissociation widths. These results are compared to those reported for In doped GaAs, as well as results concerning high temperature plastic deformation of both types of materials. In both cases, isoelectronic doping strongly increases yield stresses and hardening rates. A cell structure appears for larger stresses and strains. The increase of dissociation width in Ga_0.99In_0.01As with respect to GaAs was not observed in Cd_0.96Zn_0.04Te compared to CdTe. On the basis of macroscopic and microscopic studies, a better understanding of the hindering by doping of dislocation multiplication during crystal growth is possible. The involved mechanisms can reduce the as-grown dislocation density in CdTe and GaAs.