Thermodynamic modelling of CVD of high-T c superconductors

Thermodynamic modelling of CVD of the superconducting phases in the Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems is reviewed. Both MOCVD and halide CVD are considered. The results are discussed in terms of calculated CVD stability diagrams. The influence of deposition parameters, including selection of precursors, on the existence and extension on those stability regions, where the superconducting phases can be deposited, is described. The results of the thermodynamic modelling are compared with experimental investigations. The agreement between thermodynamics and experiments is satisfactory, indicating that thermodynamic modelling can be used as a guide to predict the optimum deposition conditions.Financial support from the Swedish National Board for Industrial and Technical Development is gratefully acknowledged.     

The application of microbalance technique in study of the high temperature superconductors

Many physical-chemical properties of oxide superconductors depend on oxygen content and its distribution in the sample. Investigations of the thermal decomposition of the oxide superconductors in dynamic vacuum are valuable, particularly in view of the high oxygen diffusion coefficient in these cuprates. Dynamic vacuum protects against the readsorption of oxygen from the environment. Samples of the high-temperature superconductors were synthesised from stoichiometric mixtures of high-purity oxides and carbonates.The lattice parameters of all preparations were controlled, in both initial and final experiments using a Stadi P (Stoe) diffractometer with a positron-sensitive detector (CuK radiation). The oxygen content was measured by iodometric titration with a reproducibility of at least 0.02.DC four probe resistivity measurements were performed on pellets to which copper contacts were attached by using silver paint. Thermogravimetric analyses (TG) were performed by using a Cahn RG ultramicrobalance system.The purpose of the present paper is to show the application of microbalance technique in study of high-temperature superconductors.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermoanalytical studies of the processing of bulk and thin film BSCCO highT c superconductors by the Edita-Gel route

The decomposition of EDTA gel precursors for BSCCO superconductor manufacture has been studied using STA (TG/DTA) and dilatometry in conjunction with FTIR. Ther thermoanalytical data are discussed in relation to the sequence of phase formation necessary for the production of the 2223 BSCCO superconducting phase. Thin film preparation of Bi-based highT _c superconductors have been carried out on MgO (100). Grain orientation of oxide thin films has been investigated. Well orientated 2212 grains have been achieved, with the (001) planes parallel to the substrate. The EDTA-gel method has been modified by the addition of glycerol to achieve the appropriate viscosity for spin coating. STA has been used to study the decomposition of these modified gels for the formation of thin films.     

Microbalance and Related Studies of High-temperature Superconductors

Many properties of oxide superconductors depend on the oxygen concentration and its distribution in the samples. The microgravimetric method is very useful to study of oxide superconductors, as it allows investigations in vacuum and controlled environments in classical applications: thermogravimetric analysis for the study of solid-state reactions, determinations of oxygen contents in redox reactions and the combined measurement of mass and additional parameters, e.g. evolved gas analysis etc. Single-phase samples of high-temperature superconductors were synthesized from stoichiometric mixtures of high-purity oxides and carbonates. Appropriate amounts of the precursor powders were homogenized manually or by a mechanical ball mill and subsequently calcined at temperatures in the 800 to 950°C range with intermediate grinding to ensure homogenous reaction. The lattice parameters of all preparations were controlled, in both initial and final experiments, by the X-ray powder method (CuKα radiation), using a Stadi P (Stoe) diffractometer with a position-sensitive detector. It is well known that temperature and mass can be measured with an accuracy higher by orders of magnitude than it is still possible for the thermoanalyst to determine the transformation temperatures or the mass changes due to overlapping partial reactions. Applications of Cahn microbalance to study of high-temperature superconductors are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal analysis and the processing of electronic and magnetic ceramics

Control of processing parameters, in both conventional ceramic routes and novel gel processing routes, is vital in the production of electronic and magnetic ceramics. The role of thermal analysis in the provision of basic data for the understanding of both types of processing route is discussed with special emphasis being placed upon the production of 1–2–3 YBCO superconductors and MgO-based soft ferrite materials for TV deflection unit applications.     

热分析技术在药物研究中的应用

本文简要介绍了热分析技术在药学领域中的重要性及其应用。由于热分析技术具有试样微量化、快速简便、不用分离试样、不用溶剂、适用范围广、曲线易于解析等优点,在药学研究和药品质量检验等方面,热分析技术将发挥更重要的作用。     

ZnAc2·2H2O在空气中的热分解动力学研究

用TG/DTA,DSC和XRD技术研究了固态物质ZnAc2.2H2O在空气中的热分解过程.结果表明,ZnAc2.2H2O在空气中发生两步分解,其失重率与理论计算失重率相符.XRD结果表明,ZnAc2.2H2O分解的最终产物为ZnO.用Friedman法和Flynn-Wall-Ozawa(FWO)法求得分解过程的活化能E,并通过多元线性回归方法给出了可能的机理函数.ZnAc2.2H2O在空气中两步分解的活化能分别为119.82和66.82kJ/mol.     

Far infrared reflectivity of narrow band materials

The application of a Fourier spectrometer to the study of the electronic structure in the far infrared of some intermediate valence or heavy fermion materials or of highT _c superconductors showed that FT-reflectivity is a powerful tool of investigation at very low energies. A very careful control of the experimental conditions and of the reference measurements is necessary to eliminate spurious reflectivities.The results show optical transitions at very low energy and permit to evaluate the electronic structures and the effective mass of the carriers in the vicinity of the Fermi level.     

Thermal Behaviour of Silver-Filled Epoxy Adhesives. Technological implications in microelectronics

One-component silver-filled epoxy adhesives electrically conductive with low extractable ionic content have been used in microelectronics for attach applications. For the specific application described here there was evidence showing that adhesive polymerisation was not complete with negative consequences for the electronic devices. The present study aimed at understanding the causes of such disadvantages and setting up the best conditions to make the epoxy adhesive perfectly suitable for the required applications. The work was carried out mainly by means of differential scanning calorimetry (DSC) and with the help the dynamic mechanical thermal analysis (DMTA) technique. The study succeeded in determining that the technological problems were due to incomplete polymerisation that caused solvent and monomer retention. These residues produced a leakage of the insulating properties of some capacitors present in the devices jeopardising the sensor working. Moreover, the study also showed that it was possible to avoid these difficulties adjusting the polymerisation temperature to 130°C and respecting curing time of 3 h: with these new curing conditions excellent results were achieved. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sodium and silver phosphate glasses doped with chlorides of Fe,Mn and Zn

A number of samples of sodium and silver phosphate glasses doped with various compositions of some transition metals viz. iron, manganese and zinc chlorides alongwith undoped samples of sodium and silver phosphate glasses were synthesized and characterized by X-ray diffraction, IR spectral, electrical conductivity and differential scanning calorimetry (DSC). The glass transition temperature (T _g) and crystallization temperature (T _c) values obtained from DSC curves were found to increase with increasing concentration of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses and the following sequence is observed: T _g(–FeCl₃)>T _g(–MnCl₂)>T _g(–ZnCl₂) T _c(–FeCl₃)>T _c(–MnCl₂)>T _c(–ZnCl₂) The increase in T _g and T _c values indicate enhanced chemical durability of the doped glasses. The electrical conductivity values and the results of FTIR spectral studies have been correlated with the structural changes in the glass matrix by the addition of different transition metal cations as dopants.     

Thermal characterization of highT c superconductors through the photodeflection method

The photothermal deflection method has been used for thermal diffusivity measurements on bulk YBCO and BISCCO highT _c superconductors. A cryostat set up is used to perform photothermal measurements from room temperature down to 77 K.     

Crystal solvate of C60 with tricloroethylene,C60 · C2HCl3

Extraction of fullerenes from carbon soot by trichloroethylene has been studied. We have found that C₆₀ forms a solvate with trichloroethylene (C₆₀ · C₂HCl₃:a=31.31(1);b= 10.156(4);c=10.146(4) Å;V=3228.6 ų,Z=4,d _calc=1.752 g cm^–3, orthorhombic symmetry). Its thermal stability has been studied using TG and DSC. A phase transition of the first order at 167 K has been detected.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1248–1250, July, 1994.The authors are grateful to V. P. Bubnov and I. S. Krainskii for providing them with the samples of fulle-rene-containing carbon soot, and to M. G. Kaplunov and A. V. Zvarykina for assistance in the work.This work was carried out with the financial support of the Russian Foundation for Basic Research, Project Nos. 93-03-18705 and 93-03-5650.     

Simulation of the condenser of the seawater greenhouse

The BaF₂-YF₃ system was partially investigated, with focus given to the BaY₂F₈ compound and its neighboring phases. In this report, various difficulties that hinder the thermal analysis investigation of this binary fluoride system are described in detail. Samples of various compositions ranging from 58 to 79% YF₃ were prepared and subjected to thermal analysis (DTA, TG and DSC) and X-ray diffraction. Diffraction patterns were analyzed through the Rietveld method for the calculation of phase concentrations in samples and determination of the lattice parameters of monoclinic BaY₂F₈. Thermal results were compared with data from the literature and discrepancies were found.     

Thermal analysis of gel-derived support for metallic catalyst

A series of Al₂O₃-SnO₂ catalysts with the molar ratio of Al₂O₃ to SnO₂ between 1:0 and 0:1 have been characterized by thermal analysis in reductive conditions, TPR and XRD methods. In the reductive conditions in temperatures up to about 1000 K, no reduction of the tin component to the metallic form takes place in the binary gel Al₂O₃-SnO₂. In the temperatures characteristic of the reforming process, only a reduction to SnO occurs in the above binary support. Thermal analysis of the gels in the reductive conditions and TPR results indicate stabilisation of the tin oxide species even in the systems of the molar ratio of Al₂O₃ to SnO₂ of 1:1. The metallic tin appears in the binary gel only after its reduction in the hydrogen atmosphere at temperatures close to ∼1100 K.     

Phase Transition and Thermal Decomposition of [Cd(H2O)6](BF4)2

Phase transition and thermal decomposition of [Cd(H₂O)₆](BF₄)₂ were studied by differential scanning calorimetry (DSC), differential thermal analysis (DTA) and thermogravimetry (TG) methods. The solid-solid phase transition at T _C1=324 K and the melting point atT _melt.=391 K were registered. The thermal dehydration process starts just above T _C1 and continues up to T _melt.,where [Cd(H₂O)₄](BF₄)₂ in the liquid phase is formed. Then, dehydration and decomposition take place simultaneously until CdF₂ is obtained. Final products of the thermal decomposition were identified using quadrupole mass spectrometry (QMS) and X-ray diffraction methods. This revised version was published online in August 2006 with corrections to the Cover Date.     

Emanation Thermal Analysis of Precursors for Ruthenia-based Materials

Emanation Thermal Analysis (ETA) was used to characterize microstructure changes of hydrous ruthenia and hydrous ruthenia-titania as precursors for preparation of RuO₂ and (RuO₂)_0.9-(TiO₂)_0.l by heating in the temperature range of 20–600°C in argon. A good agreement was found between ETA, TG and DTA results, X-ray diffraction patterns and surface area measurements of intermediate products of the thermal treatment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal induced phase separation of E7/PMMA PDLC system

The phase behaviour of thermoplastic polymer-dispersed liquid crystal system is studied with particular emphasis on the various transitions that occur within the system. The extent of plasticization of the polymer(polymethyl methacrylate) by the low molecular weight liquid crystal(E7) along with the several transitions of theLC(Liquid Crystal) are determined by modulated DSC. Optical microscopy was used to construct the temperature versus composition phase diagram. Our study indicates the existence of a limiting temperature of 40°C around which the PMMA matrix turns glassy irrespective of the initial composition within the phase separated region, suggesting the intersection of the glass transition curve with the coexistence curve. A slight depression of theN-I(Nematic to Isotropic) transition of theLC is observed with increasing composition of PMMA whereas theS-M(Smectic to Nematic) transition and theT _g (Glass transition temperature) of theLC remain unaffected. The one phase mixture remains isotropic until phase separation at a lower temperature where theLC rich domains become nematic. The growth ofLC rich domains is studied as a function of temperature and time.     

Thermal properties of lanthanide(III) complexes with 2-aminoterephthalic ACID

The complexes of yttrium(III) and lanthanides(III) with 2-aminoterephthalic acid form the isostructural series of triclinic compounds with a space group P from La to Lu and they have the general formula of Ln₂(C₈H₅O₄N)₃·8H₂O. On heating in air or inert gas atmosphere they lose all water molecules in the temperature range 50–200°C in one or two steps. The anhydrous compounds are stable from 360 to 435°C and then decompose to oxides.     

Thermal properties of a polyimide fiber

A commercially available polyimide fiber was investigated as a possible precursor for the formation of carbon fibers. The thermal response of the fiber was thoroughly investigated using DSC, TMA and TG. These responses were dependent on the atmosphere and tension during scanning. The fiber was stabilized at high temperatures both in inert and oxidative environments and the effect of these stabilization treatments on the structure and properties of the fiber was carefully followed. During heating, the fiber showed shrinkage tendency at small tensions, but at higher tensions the fibers could be stretched. Among the two environments investigated, air was more effective than nitrogen in getting a more stable fiber.The authors would like to acknowledge the Graduate School of the University of Tennessee, Knoxville for financially supporting this work and Lenzing USA Corporation for providing the fiber samples.     

Thermal decomposition of silver cyano complex and characterization its decomposition products by ETA,DSC, DTA and TG

It was found by DTA and TG that [Phenyl₂I][Ag(CN)₂] in the solid state is chemically stable on heating in argon up to 160°C. During heating to higher temperatures it decomposes, forming volatile products such as [Phenyl]I, [Phenyl]NC and (CN)₂ [1]. After heating the sample to 500°C metallic silver resulted. The volatile and intermediate solid products were analysed by IR-spectroscopy.It was found by means of DTA and ETA that an isophase reversible transition takes place when the sample is heated and cooled, not higher than 100°C. At heating higher than 100°C the sample melts (melting pointT _m=135°C). The enthalpy melting was determined by means of DSC (H=–28 kJ·mol^–1).By means of ETA the disorder degree of the final decomposition product was estimated. The value of the activation energy of radon diffusion in the temperature range 720°–500°C equals 32.6 kJ·mol^–1.Dedicated to Prof. I. N. Bekman Moscow State University at the occasion of his 50th birthday