Reaction kinetics at linearly increased temperature. IV. Relationships between dta curves,rate curves and adiabatic calorimetry

A general concept is presented for the kinetic interpretation of DTA curves. This is based on the limiting conditions of a DTA measurement: either the kinetic cell constant is zero (adiabatic conditions), or infinite (rate curve). On the other hand, the self-heating effect (thermal feedback), based on the product of the reaction enthalpy with the reactant feed, may be absent (“ideal” kinetic DTA curve) or infinite (impulse reaction). Our recent formulae for the correction of the kinetic classification parameters, shape index and reaction type index, as well as other relationships and their utility, are successfully tested by application to ca. 2000 experimental DTA curves obtained in stirred solutions.The expressions reveal the influence of the activation parameters, heating rate, maximum signal height and cell constant and, therefore, allow a general discussion of the kinetics, independent of the experimental conditions.     

Limiting cases of DTA curves of one-step reactions and their application to the study of complex processes

Useful relationships are discussed for DTA studies of reactions in solution which are based on two proved concepts:1.For missing thermal feedback, i. e. linear increase of the reaction temperature, the influence of the kinetic cell constant, c, appears exclusively as a product with the specific time of the reaction, u.2.Interference of temperature feedback by the reaction heat is considered by the ratio of the maximum temperature difference (DTA peak height) over the specific temperature difference of the reaction. This can be understood from the Semenov Theory of Thermal Ignition of Gases under Adiabatic Conditions.     

Mechanistic Analysis of Solution Reactions by Non-Isothermal Calorimetry

For the rapid kinetic and energetic analysis of reactions in solution (τ_20°C > 10^-4s) by differential thermal analysis (DTA), the following thermogram parameters are defined as characterizing the start of the reaction: 1. initial temperature, 2. activation energy of the initiation reaction. In conjunction with the shape index (asymmetry of the DTA curve) and the half width of the DTA curve referred to standard physical conditions (cell constant, heating rate, and temperature difference), these quantities allow a simple distinction between one-step reactions of first and second order and composite reactions. It is possible to recognize whether a process involves parallel, successive, or equilibrium reactions, or combinations of these. The reaction mechanism can be clarified in many cases by measurements at various concentrations and heating rates and by discussion of the enthalpy values. The shortened method described in this report for the evaluation of the thermograms was derived with the aid of an analog computer and checked experimentally.     

α-三氢化铝的热分解动力学

用差热分析(DTA)研究了a-三氢化铝在氦气流下的热分解动力学。建立了A-E方程中动力学参数与DTA曲线的特征温度之间的关系式, 用序贯法对竞争模型进行最佳判别和参数估算, 确定a-三氢化铝的热分解曲线可用方程[-In(1-x)]~(1/4)=r_0e~(-E/RT_t)来描述, 表观活化能E为121.4±6.3 kJmoL~(-1), 指前因子r_0为8.1×10~(11±1)(sec-1), 模型计算结果与实验结果吻合较好。     

用Diamond TG/DTA热重/差热综合热分析仪在外加磁场下研究磁性材料相转变

介绍综合热分析仪Diamond TG/DTA在磁性材料研究中的应用.提出在外加磁场作用下,得到样品的热重曲线(TG),由TG曲线分析样品磁性相变及样品居里温度变化的原因,看到稀土铁基金属间化合物样品替代的Co元素的站位和元素之间相互作用对居里温度有很大影响.作为一种测量居里温度的方法,拓展Diamond TG/DTA热分析仪应用研究领域.     

A new apparatus for simultaneous differential thermal analysis and gas evolution analysis

A new apparatus is described which permits the simultaneous recording of the differential thermal analysis and gas evolution curves for a given sample from ambient to 900°. The sample is pyrolyzed in a dynamic helium gas atmosphere using a conventional DTA furnace and sample holder assembly. The evolved decomposition products are detected in the helium gas stream by means of a thermistor thermal conductivity cell. From a knowledge of the GE curve and an analysis of the decomposition products, a more accurate interpretation of the DTA curve can be made.     

马瑞原油在空气和氮气中的热解-氧化性能

低温氧化是注空气采油及原位燃烧采油技术中的重要化学反应,为深入认识原油在有氧环境下复杂热反应过程中的低温氧化特性,我们采用热重/差热分析法(TG/DTA)研究了线性升温和等温条件下马瑞(Merey)原油的热反应行为。 结果表明,Merey原油在空气及线性升温条件下的受热过程分4个阶段:气化段、低温氧化段、热解段和高温氧化段;相邻阶段的物理、化学主导过程的重叠增加了分析原油热反应特征的难度。 升温速率提高,气化段和低温氧化段的终止温度不变;热解段和高温氧化段的终止温度以及热解段的峰温随升温速率的增加而升高。 N₂气与空气下Merey原油的热重/微分热重(TG/DTG)数据对比表明,升温速率越高,空气下的高温氧化段与热解段重叠程度越大,这有利于燃烧但会降低原油采收率。 空气下等温时的TG/DTA结果表明随升温速率增加,升温至300 ℃时的失重率降低,不利于原油轻组分的气化。 反应温度越高,气化过程时间越长,失重分数越大。 Merey原油在低于300℃时低温氧化反应不是主导反应。     

Thermal stabilities of polynitroaromatic compounds and their derivatives

The thermal stabilities of 33 polynitroaromatic compounds and their derivatives were determined using non-isothermal differential thermal analysis (DTA). For twelve of these, the thermal stabilities of their mixtures with 1,3,5-trinitrobenzene was also determined. The results obtained are discussed from a molecular structural point of view.The results obtained from DTA measurements are compared with the published data which were derived from the results of the application of the manometric method to the study of the thermal reactivity of polynitroaromatic compounds. The differences which exist between the conclusions reached on basis of DTA application, on the one hand, and those obtained on the basis of the application of the manometric method, on the other hand, are discussed.Using the published relationship for the calculation of the temperature limit (T_max) for the use of polynitroaromatic compounds as secondary thermostable explosives, T_max values are calculated for the compounds being measured. A relationship is derived between T_max and T_D the initial exothermal decomposition temperature obtained from the DTA of the studied compounds.     

Dynamic dielectric analysis. A new thermal analysis technique

Applications of dynamic dielectric analysis (DDA) in studies on the thermal decomposition and phase transformations of solid materials are discussed. Three illustrative examples are presented for (a) a system undergoing a chemical reaction or thermal alteration on application of heat, (b) a system undergoing a crystallographic transformation and (c) detection of moisture in naturally occurring materials. The advantages derived by applying a combination of DDA and a conventional thermal analysis technique such as DTA to studies on thermal processes are demonstrated. It is shown that the information obtained from techniques such as DTA or TG is limited in scope unless used in conjunction with a method which sheds light on the mechanistic aspects of the physical or chemical process of interest.     

Thermal reactions by automated mass spectrometric thermal analysis

Combination of differential thermal analysis (DTA) with time-of-flight mass spectrometry and data storage on magnetic tape is used to study thermal decompositions.A modified Du Pont 900 DTA cell is used for reactions at atmospheric pressure with evolved gas sampling into a small time-of-flight spectrometer.For fast reactions a specially developed DTA cell is operated within the mass spectrometer and operates at high vacuum.A combination of both operational modes yields pressure dependencies of chemical decomposition.Examples studied include inorganic compounds and complexes, organometallics and organic chemicals such as fire retardants.The data are presented as intensity/temperature curves for each observed fragment, which not only yields decomposition temperatures but also—by the curve shapes—information on the mode of decomposition.     

DTA和XRD用于(14-x)SrCO3-xCaCO3-24CuO系统合成spin-ladder化合物Sr14-xCaxCu24O41的研究

The (14-x)SrCO3xCaCO324CuO system was investigated by means of differential thermal analysis (DTA) technique combined with the powder Xray diffraction (XRD) technique, and the relationship of its thermal behavior with the synthesis of spin-ladder compound Sr14-xCaxCu24O41 was first analyzed in detail. It is found that the DTA curve (x≤5.6) exhibits two endothermic peaks and could be divided into three reaction stages, corresponding to the solid state reaction to synthesize single-phase Sr14-xCaxCu24O41. The DTA curve (x≥8.4) shows three big endothermic peaks below 1000 ℃. The intensity and the position of the first endothermic peak around 800 ℃ is depending on the content of CaCO3 in the system, while the third endothermic peak is the crucial factor of the synthesis of single-phase compound.     

Thermal Analysis and X-ray Diffraction of Synthesis of Scheelite

Scheelite (calcium tungstate)is the product of one of the processing methods of wolframite by its roasting with calcium oxide or limestone or its fusion with calcium chloride, followed by acid processing of calcium tungstate with the formation of tungstic acid. Scheelite occurs in contact metamorphic deposits, hydrothermal veins and pegmatites. The present work illustrates a thermal analysis study of synthesis of scheelite by sintering of wolframite with calcite and sintering of tungsten oxide with calcite or calcium oxide using a derivatograph. The reaction products were identified microscopically and by using a Siemens Crystalloflex diffractometer. The DTA curve of sintering of wolframite with calcite shows the beginning of the reaction at 560°C with the formation of scheelite. The intensive formation of scheelite is represented by the medium and wide endothermic peak at 740°C. This is followed directly by a large and sharp endothermic peak at 860°C, representing the dissociation of unreacted calcite. The DTA curve of tungsten trioxide shows three thermal effects. The sharp exothermic peak at 320°C represents the oxidation of tungsten oxide content of lower valency. The endothermic peaks at 750 and 1090°C are related to polymorphic changes of tungsten trioxide. The beginning of its sublimation is observed at temperature higher than 800°C. The DTA curves of sintering of tungsten trioxide with calcite or calcium oxide indicate that the intensive formation of scheelite takes place by endothermic reactions at 660 and 545°C respectively. The medium and small endothermic peaks at 520 and 730°Con the DTA curve of tungsten trioxide with calcium oxide represent the dehydration of calcium oxide and the loss of carbon dioxide due to some carbonatization of calcium oxide with carbon dioxide from air, respectively. The produced scheelite is colorless in thin sections, has distinct cleavage (101), crystallizes in the tetragonal system in the form of tabular crystals and is optically positive. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal analysis,effect of dopants,spectral characterisation and growth aspects of KAP crystals

Potassium acid phthalate (KAP) which is also known as potassium hydrogen phthalate (KC₈H₅O₄), a semi-organic compound was grown from its aqueous solution only by slow evaporation method at room temperature. The effect of metallic salts HgCl₂ and PbCl₂ as dopants in the growth aspects, thermal properties and SHG efficiency of KAP were determined using UV-VIS, FTIR spectral studies, thermal (TG and DTA) analysis and NLO test. There is only one significant mass loss step on TG curve of pure and doped KAP crystal. DTA curve exhibit a higher peak temperature in case of doped KAP crystal compared to those of pure KAP crystals.     

Anwendung der Differential-Thermoanalyse zur Bestimmung der Zündtemperatur von Schwel- und Hochtemperaturkoks

The application of differential thermal analysis to the determination of the ignition temperature of coke from low-temperature and high-temperature carbonization is treated. The sample mixed with NaNO₂ was heated at a rate of 10?/min, using kaolin as inert substance. As ignition temperature, that of the high exothermic peak on the DTA curve was taken. It has been stated that the ignition temperature of the untreated coal increases from 310 to 365? as the degree of carbonization increases. The ignition temperature of coke from low-temperature carbonization was found to vary between 350 and 370?, and that of coke from high-temperature carbonization between 380 and 400?.     

DTA中升温速率及样品热导率对T_g测量值影响的模拟研究

就不同升温速率和实际样品的不同热导率对差热分析 (DTA)中高分子材料的玻璃化转变曲线的影响进行了MonteCarlo模拟研究 ,发现当所有样品刚完成玻璃化转变时 ,在Tg 曲线中该特征点要低于Tg 的转变中点。转变中点所对应的样品温度肯定要高于实际的玻璃化转变温度。如果以玻璃化转变曲线的转变中点所对应的样品温度作为该材料的玻璃化转变温度 ,那么 ,升温速率越快、样品的热导率越小 ,所测得的玻璃化转变温度就越大 ,反之亦然。DTA测得的玻璃化转变温度与升温速率间有很好的线性依赖关系 ,但与样品热导率间的关系是非线性的     

Electrical conductivity measurements during the thermal decomposition reaction of ammonium metavanadate

Electrical conductivity vs. temperature curve shows all characteristic peaks due to individual stages of the thermal decomposition reaction of NH₄VO₃, including the stage of formation of the anhydrous ammonium divanadate at ～150°, obtainable only under special experimental conditions on TG, DTG, and DTA curves. It is suggested that such measurements can be used for detecting and/or confirming the existence of intermediate solid products of decomposition in case they are difficult to be identified.     

Growth and characterization of 0.1 and 0.25 zinc magnesium ammonium sulphate

Mixed crystals of 0.1 and 0.25 zinc magnesium ammonium sulphate were grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterized by thermal (TG–DTA), FTIR and XRD analyses. A fitting decomposition pattern for the compound was formulated on the TG curve which shows two stage mass losses between 133 and 478.75 °C. In this temperature range, DTA curve shows exothermic peaks supporting the formulated decomposition pattern. The FTIR spectra show the vibration frequencies due to the formation of zinc magnesium ammonium sulphate mixed crystals. Detailed structural analysis of the compound is under progress.     

Thermoanalytical investigation of the aluminothermic reduction of iron(III) oxide

Differential thermal analysis technique has been applied to determine the heat of reduction of iron oxide by aluminium. It has been observed that the DTA curve can be used for quantitative determination of heats of reactions at high temperature ranges where differential scanning calorimetry is not applicable. The experimental results obtained agree closely with the theoretical value of the heat of reaction.

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Zusammenfassung Unter Anwendung von DTA wurde die Bestimmung der Reaktionswärme der Reduktion von Eisenoxid mit Aluminium durchgeführt. Es konnte festgestellt werden, daß DTA zur quantitativen Bestimmung von Reaktionswärmen bei hohen Temperaturen geeignet ist, bei denen DSC nicht mehr angewendet werden kann. Die ermittelten experimentellen Ergebnisse stimmen gut mit dem theoretischen Wert für die Reaktionswärme überein.

     

TG–DTA, UV and FTIR spectroscopic studies of urea–thiourea mixed crystal

A mixed crystal of urea–thiourea was grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterized by thermogravimetric–differential thermal analysis (TG–DTA), UV and FTIR spectroscopic analyses. A fitting decomposition pattern for the title compound was formulated on the TG curve which shows a two stage weight loss between 200 and 750 °C. In this temperature range DTA curve shows exothermic peaks supporting the formulated decomposition pattern. The UV and FTIR spectra show the characteristic absorption, vibration frequencies due to urea–thiourea mixed crystals. Detailed structural analysis of the compound is under progress.     

Thermal and FTIR spectral studies of various proportions of zinc magnesium ammonium sulfate

Mixed crystals of various proportions of zinc magnesium ammonium sulfate were grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterized through thermal (TG–DTA) and FTIR spectral analyses. A fitting decomposition pattern for the compound was formulated on the TG curve which shows two stage mass losses between 133 and 478.75 °C. DTA curve shows exothermic peaks in this temperature range supporting the formulated decomposition pattern. The FTIR spectra show the vibration frequencies due to the formation of zinc magnesium ammonium sulfate mixed crystals. Detailed structural analysis of the compound is under progress.