共查询到20条相似文献,搜索用时 15 毫秒
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A new method of kinetic analysis that allows the combined analysis of data obtained under different experimental conditions, i.e. heating pathway, is presented for the crystallization of non-crystalline solids. The method consists of a two-stage procedure. Firstly, an optimization procedure is applied for the determination of the Johnson, Mehl and Avrami (JMA). This optimization procedure is based on the linearization of the rate equation throw a logarithmic transformation; where the correlation coefficient function is the objective function, and the JMA order is the adjustable parameter. The JMA order obtained from this optimization procedure allows one to determine in a second stage the other kinetic parameters, i.e. activation energy and pre-exponential Arrhenius factor. The method proposed here allows one to analyze in a combined way data obtained under any heating profile, because no assumptions are made on the heating profile for the derivation of the rate equation. The method is tested with computed and experimental curves obtained under different heating conditions. The crystallization kinetics of (GeS2)0.3(Sb2S3)0.7 glass are studied from the combined analysis of several curves. 相似文献
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D. Nataraj K. Prabakar Sa.K. Narayandass D. Mangalaraj 《Crystal Research and Technology》2000,35(9):1087-1094
Bi2Se3 thin films are prepared by thermal evaporation method onto well‐cleaned glass substrates. From the XRD analysis, the film is found to be amorphous in nature. Thermal analysis of Bi2Se3 sample scraped off from the glass substrate is performed using the technique differential scanning calorimetry (DSC) at different heating rates. Kissinger method is used to analysis these constant heating rate spectra and the activation energy 'Ea′ corresponding to the phase transformation is calculated through the examination of the DSC peak temperature shift induced by variation of the heating rate. An analytical equation with three kinetic parameters (activation energy (Ea), transformation order (n) and the frequency factor (v)) is derived from the Johnson‐Mehl‐Avrami (JMA) theory to describe the constant heating rate DSC spectra. Using the activation energy from Kissinger plot, theoretical constant heating rate DSC traces are generated for arbitrary values of 'v' and 'n' using the analytical equation. Finally, theoretically generated DSC spectra is compared with that of the experimental one and the unknown values 'v' and 'n' are determined. 相似文献
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《Journal of Non》2001,279(2-3):110-118
Silica aerogel preparation is analyzed and two different supercritical drying techniques, autoclave drying of the solvent and drying following carbon dioxide exchange of the solvent, are compared in terms of stress formation during the heating step. The model used is a partial differential equation that relates stress to thermal expansion and flow of pore liquid for a radially bounded cylindrical geometry and the model is modified to see the effect of condensation reactions that result in the contraction of the body. The finite element collocation method is used to solve the model for different drying techniques, at several heating rates, and shear moduli. The carbon dioxide exchange method is found to be more advantageous as far as the stress formation in the heating step of supercritical drying is concerned. 相似文献
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Defect characterization of Tl2Ga2Se3S single crystals has been performed by thermoluminescence (TL) measurements at low temperatures between 10 and 70 K with various heating rate ranging from 0.6 to 1.0 K/s. The TL signal due to the luminescence from trap centers revealed one glow peak having maximum temperature of 36 K. Curve fitting and various heating rate methods were used for the analysis of the glow curve. The activation energy of 13 meV was found by the application of curve fitting method. This practical method also established that the trap center exhibits the characteristics of mixed (general) kinetic order. In addition, various heating rate analysis gave a compatible result (13 meV) with curve fitting as the temperature lag effect was taken into consideration. Distribution of traps was also investigated using an experimental method. A quasi‐continuous distribution was attributed to the determined trap centers. 相似文献
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溶胶-凝胶、微波加热合成Li1.3Al0.3Ti1.7(PO4)3粉体 总被引:1,自引:1,他引:0
以钛酸丁酯、硝酸锂、硝酸铝和磷酸为原料,采用溶胶-凝胶、微波加热的工艺合成了Li1.3Al0.3Ti1.7(PO4)3粉体,并研究了热处理温度对粉体结构的影响.用X射线衍射仪(XRD)、傅立叶变换红外光谱仪(FT-IR)、扫描电镜(SEM)对制备的粉体进行了表征.结果表明:溶胶凝胶、微波加热工艺与固相合成工艺相比可以显著地降低热处理的温度,缩短保温时间;前躯体经700~900 ℃微波热处理30 min后均可合成纯相的Li1.3Al0.3Ti1.7(PO4)3粉体,且结晶性良好,粉体的粒度为2~5 μm. 相似文献
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应用Fe/Mo/Al2O3载体载入式催化剂,以CO为碳源,分别通过火焰热解法和电加热热解法合成了碳纳米管.为了探究导致两种方法合成产物异同的原因,分别对两种方法中对应的实验操作和参数进行了对比分析.分析表明:(1)由于热解形式不同-火焰热解形式的剧烈性和电加热热解形式的缓和性,导致两种方法热解区气流扰动强度存在巨大差别,极大影响了产物的产量和质量;(2)由于合成温度不同,火焰热解法合成温度为830℃,可以合成单壁碳纳米管,而电加热热解法合成温度为790℃,仅能合成双壁、三壁碳纳米管. 相似文献
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Chia-Yao Lo Jih-Shang Hwang Xiu-Mi Liu Yung-Yi Zhang Der-Chang Chen Chih-Chiang Wu Tai-Yuan Lin Surojit Chattopadhyay 《Journal of Crystal Growth》2010,312(24):3564-3568
A simple growth technique capable of growing a variety of zinc oxide (ZnO) nanostructures with record growth rates of 25 μm/s is demonstrated. Visible lengths of ZnO nanowires, nanotubes, comb-like and pencil-like nanostructures could be grown by employing a focused CO2 laser-assisted heating of a sintered ZnO rod in ambient air, in few seconds. For the first time, the growth process of nanowires was videographed, in-situ, on an optical microscope. It showed that ZnO was evaporated and presumably decomposed into Zn and oxygen by laser heating, reforming ZnO nanostructures at places with suitable growth temperatures. Analysis on the representative nanowires shows a rectangular cross-section, with a [0 0 0 1] growth direction. With CO2 laser heating replacing furnace heating used conventionally, and using different reactants and forming gases, this method could be easily adopted for other semiconducting inorganic nanostructures in addition to ZnO. 相似文献
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S. Mhmel I. Kurzawski D. Uecker D. Müller W. Geßner 《Crystal Research and Technology》2002,37(4):359-369
Differently synthesised layered double hydroxides (LDH) were characterised by using XRD, N2 adsorption, DTA/TG and 27Al NMR. The results of these investigations are discussed with respect to the crystallinity and purity of the material in dependence on the preparation method (without aging, aging at 20 °C, aging under hydrothermal conditions using microwave heating). It is shown that microwave heating is a suitable method to prepare well crystallised LDH without impurities in the form of e.g. Mg(OH)2 and Al(OH)3 and with a sufficient specific surface area within acceptable times. 相似文献
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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 < Tg 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. 相似文献
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We present a new method of measuring the tilt angle and the optical biaxiality in liquid crystals (LCs). The method uses a fitting procedure of the optical path difference in specially prepared LC cells. Measurements are performed in the SC phase of 4-n-hexyloxyphenyl-4n-decyloxybenzoate (HOPDOB) by means of microscopic observations in a rotary heating stage. 相似文献
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K. A. Kokh Yu. M. Andreev V. A. Svetlichnyi G. V. Lanskii A. E. Kokh 《Crystal Research and Technology》2011,46(4):327-330
The paper describes principal manipulations to prepare single crystals of GaSe and GaS. A new simple method of synthesis with single‐zone heating furnace is proposed. Growth of crystals was performed by modified Bridgman method with the use of rotating heat field. Raman and optical depth spectra show high structural and optical quality of obtained crystals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Co(II)-doped alumina monoliths prepared by the sol-gel method were laser irradiated producing fluorescence. The intensity of this defect-induced fluorescence was exponentially reduced with the irradiation time to practically disappear. The rate the fluorescence intensity decays was modeled as a double exponential function of the irradiation time; the characteristic times associated with the decays are in the range of seconds. The suppression of the luminescence was associated with the local heating produced by the highly focused laser beam in a small area (≈ 2 μm in diameter) on the sample. This heating process reduces physical (grain boundaries and surface states) and chemical (oxygen vacancies) defects present in the sol-gel samples. Some residual fluorescence still remains after long periods of illumination. The characteristic times for alumina samples are compared with those obtained for other metal oxides prepared also by the sol-gel method. 相似文献
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《Journal of Non》2006,352(32-35):3729-3733
Nanoparticles of fcc-NiO phase were obtained by heating the dried resin resultant of a mixture of gelatin and NiCl2 · 6H2O in aqueous solution. The average particle size and microstrain were calculated from the line broadening of X-ray powder diffraction peaks, and these values were between 15 nm and 78 nm, and 0.056% and 0.172%, respectively. The Rietveld refinement method was applied to all diffraction patterns. The particle size, obtained from this procedure, changes as a function of temperature, heating time and the remarkable reduction due to the addition of NaOH to the solution, which can be attributed to the presence of NaCl crystals and carbon encapsulating NiO nanoparticles during the heating. The heating temperature was in the range of 350–700 °C. Thermo-gravimetric analysis showed that the majority of organic fraction starts to disappear after 300 °C. 相似文献
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大尺寸低缺陷碳化硅(SiC)单晶体是功率器件和射频(RF)器件的重要基础材料,物理气相传输(physical vapor transport, PVT)法是目前生长大尺寸SiC单晶体的主要方法。获得大尺寸高品质晶体的核心是通过调节组分、温度、压力实现气相组分在晶体生长界面均匀定向结晶,同时尽可能减小晶体的热应力。本文对电阻加热式8英寸(1英寸=2.54 cm)碳化硅大尺寸晶体生长系统展开热场设计研究。首先建立描述碳化硅原料受热分解热质输运及其多孔结构演变、系统热输运的物理和数学模型,进而使用数值模拟方法研究加热器位置、加热器功率和辐射孔径对温度分布的影响及其规律,并优化热场结构。数值模拟结果显示,通过优化散热孔形状、保温棉的结构等设计参数,电阻加热式大尺寸晶体生长系统在晶锭厚度变化、多孔介质原料消耗的情况下均能达到较低的晶体横向温度梯度和较高的纵向温度梯度。 相似文献
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A simple method for the growth of conventional or reentrant smectic phases from strongly-deformed conventional or reentrant nematics, is proposed. It permits the formation of surface-induced and surface-governed conventional and/or reentrant smectic textures which can be studied from the scientific point of view or can be applied in the laser-addressed thermo-optic smectic liquid crystal storage displays for the creation of static figures. The simple method proposed might be applied for study of many smectics arrising either from conventional or reentrant nematic phases under cooling or heating. 相似文献