Rechnergestützte DTA- und DMC-messungen: Apparatur und methodische aspekte

The evaluation of data from DTA and calorimetric measurements is still, in most cases, made by hand. This is not only a highly time-consuming procedure, but also includes subjective errors. This is especially true for the determination of starting points and end points of DTA peaks. Via integration between these limits, errors are introduced into the calculation of peak areas, i.e. thermal energies. Since many research groups possess high-performance microcomputers or desktop computers, which are able to perform measurements with subsequent data evaluation by suitable software, we developed a computer-controlled DTA/DMC equipment.In the present paper, we first describe the hardware coupling of a desktop computer to a DTA/DMC apparatus. We proceed with a discussion of the capabilities of both the apparatus and the data evaluation methods. A calorimetric measurement of the melting point of tin is the basis for a rating of the proposed numeric procedure for finding the peak limits and for peak integration in contrast to the evaluation of data by hand. With the argyrodite—cuprodite system. Ag_8?xCu_xGeS₆, O?x?4, as an example, we present a proposed method for obtaining phase diagrams.     

Determination of High Pressure Phase Diagrams of the Ternary Alloy System

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A high pressure electrical conductivity apparatus

A high pressure electrical conductivity (EC) apparatus. capable of operation at pressures from 1 to 170 atm in the temperature range from 25 to 500°C, is described. The effects of the sample holder geometry, pressure, and sample packing on the resulting EC curves are given. Operation of the apparatus is illustrated by the deaquation reactions of BaCI₂·2H₂0.     

Differential-Thermoanalyse von Ölen und Fetten im Temperaturbereich −100° bis +150°

A DTA apparatus is described which is suitable for investigations by thermal analysis in the temperature range from ?100° to +150°. While the system of measuring is a recent development, modified models of the DTA 02 Universal Apparatus manufactured wholesale in the German Democratic Republic are used. The experimental results demonstrate that this apparatus permits high-sensitivity oil and fat investigations by differential thermal analysis, with good zero-line behaviour. The problem of analysing oils and fats is also dealt with.     

Evaluation of thermal analysis equipment for the determination of vapor pressure and heat of vaporization

A rapid, relatively simple method for determining vapor pressure and heat of vaporization on small amounts of organic compounds is described. A DuPont 900 differential thermal analyzer (DTA), a Perkin—Elmer Model DSC-1B differential scanning calorimeter (DSC), and a Thomas—Hoover (TH) melting point apparatus were evaluated in this work. Vapor pressure data for a wide variety of organic liquids were obtained by measuring the boiling points of the liquids at pressures ranging from 20 to 735 torr. A computer was used to rapidly plot the experimental data. The average deviations of boiling points from the literature values were 2.3°C for the DTA 1.2°C for the DSC, and 1.5°C for the TH. The vapor pressure data were used to solve the Haggenmacher equation for heat of vaporization (ΔH_v). The deviations of the experimental values for ΔH_v. from the literature values were 5.5%, 8.3%. and 3.3% for the DTA, DSC, and TH methods, respectively.     

On the method of bae for the determination of kinetic parameters from DTA curves

The mathematical error in the method proposed by Bae for the determination of kinetic parameters from DTA curves has been corrected. The proposed equation does not contain thermal constants of the apparatus, and can be applied to DTA curves by an iterative method. The results obtained by the application of this equation to experimental DTA curves for the decomposition of sodium bicarbonate compared well with those from isothermal measurements, even when the DTA sample holder assembly was of the isolated cup-type instead of the block-type assembly recommended by Bae.     

A high pressure differential thermal analysis apparatus

A high pressure differential thermal analysis apparatus is described which is capable of operation in the pressure range from 1-600 atm of nitrogen gas and at temperatures from 25 to 500°C. Use of the apparatus is illustrated by the deaquation reactions of CuCl₂·2H₂0 and CoSO₄·7H₂O at pressures from 1 to 69 atm.     

The thermal analysis of polymers at high pressures

The extension of two techniques of thermal analysis into the region high pressures (50–100 MPa) are discussed. One is the extension of dilatometry (thus becoming pressure-volume-temperature measurements, PVT). This technique has been well established over the past few years. Some results obtained on typical polymer systems are presented and discussed. The second is the extension of the differential thermal analysis (DTA) principle to high pressures, trying to maintain some of the advantages of the DTA technique when compared to the PVT method, such as small sample size and productivity. DTA determinations of the pressure dependence of the melting points of pure metals and polymers are presented and compared with results from the PVT technique. Satisfactory agreement is obtained. The advantages and limitations of our current high-pressure DTA method are discussed.We gratefully acknowledge the partial financial support of the high-pressure DTA development by Metler Instrumente AG, Switzerland.     

The detection of ignition temperatures of various materials by photothermal analysis

The ignition temperatures of various common materials were detected by means of a photothermal analysis apparatus. The sample is heated in a tube furnace which is programmed at a linear heating rate; a photomultiplier tube located at the end of the furnace tube is used to detect the ignition process. This technique is potentially useful and is most advantageous when used to supplement DTA or TG data. The instrumental factors which influence the ignition temperature, such as heating rate, furnace atmosphere, and so on. were investigated. Factors such as the sample surface area, mass. density, and others can affect the reproducibility of the curves even if the instrumental factors are held constant.     

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.     

The α-β inversion in submilligram particles of natural quartz

The bacground to the supposed development of the ‘Beilby layer’ on fine-grinding quartz is briefly reviewed. It is shown, using single crucible thermal analysis and sub-milligram DTA, that grinding quartz can cause a dispersion of the α-β inversion over a temperature range of several degrees; this is a crystallographic effect rather than an impurity effect. The sub-milligram DTA apparatus used is described and some thermal effects, such as impurity zoning, are illustrated.     

High-pressure studies of polymerization in sulfur

By x-ray and optical studies of thermally quenched products and by differential thermal analysis under pressure the effect of high pressure on the melting and polymerization of sulfur has been investigated to 31 kb and 500°C. At least four different liquid fields have been identified. DTA experiments indicate that pressure shifts the 159°C polymerization transition first toward higher temperatures and then toward lower temperatures until it finally coincides with the melting point at a pressure of about 0.7 kb. The depolymerization temperature was found by the same technique to increase with increasing pressure up to 0.4 kb. A liquid P—T boundary that may constitute the higher-pressure extension to the depolymerization transition has been traced up to 7.5 kb and 480°C. A very sharp, practically temperature-independent reaction in the liquid state has been located at about 9 kb extending from the liquidus to at least the limits of the apparatus at about 450°C. Evidence has been found for a possible second-order phase transformation extending from about 10 kb at 400°C to the liquidus at approximately 360°C.     

The ternary system propyl propanoate+ hexane+chlorobenzene at 298.15 k

Differential thermal analysis shows many interesting properties that allow for prompt finding the place (p,T) and characteristics (endothermic, exothermic) of a phase transition or chemical reaction. In application to reactive sintering under active gas atmosphere at high pressure despite of numerous technical problems encountered during DTA measurements we found its unique possibilities. That allows for quantitative estimation of nitrogen involved in reaction of phase transition from the hexagonal phase to the cubic phase of MoN, and vice versa, in high gas pressure condition. DTA high gas pressure measurement system has the maximum operate temperature 2000°Cat pressure 2 GPa. This revised version was published online in August 2006 with corrections to the Cover Date.     

The study of hydrothermal processes by the differential thermal analysis method

A DTA apparatus has been developed which can operate up to pressures of 500 atm and temperatures of 500°C. A coated thermocouple (thermocoax) is used for the measurement of temperature differences. Thermograms for the dehydration of gypsum, hydration of cement paste and hydrothermal synthesis of calcium silicates hydrates are shown to demonstrate the capability of the apparatus.     

The deaquation reactions of some metal salt hydrates at elevated pressures

The deaquation reactions of BaCl₂·2H₂O, BaBr₂·2H₂O and CoCl₂·6H₂0 were studied by the thermal analysis techniques of thermogravimetry, differential thermal analysis (DTA), and electrical conductivity in the pressure range from one to 170 atm. In general, the effect of pressure on the TG curves increased the T_i and T_f values and also the reaction interval, (T_t—T_i). The DTA curves exhibited splittings into multiple peaks as a result of the increased pressure. These splittings were interpreted as due to the evolution of a liquid water phase followed b     

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.     

Effect of atmospheric pressure on the phase transitions of α,α-trehalose dihydrate DTA study of the dehydration behavior in open systems

The phase transitions of α,α-trehalose dihydrate (T _h) were investigated by either differential thermal analysis (DTA) with an in-house apparatus of variable-pressure type equipped with an open sample holder or commercially available TG (thermal gravimetry)-DTA apparatus for comparison under the same experimental conditions as to the heating rate (2°C min⁻¹), the type of pan (open), and the particle size of T _h (63 μm). The former DTA measurements were carried out under five different total pressures, 101, 75, 61, 48 and 35 kPa, which provided quite helpful information necessary for confirmative assignments of the endothermic peaks due to either melting or dehydration of T _h. The usage of largely different amount of T _h, 126 and 14 mg for the DTA and TG-DTA measurements respectively, led to their different DTA traces, showing that there were largely different extents of the influence by the measured sample surface exposed to the surrounding atmosphere on its dehydration behavior. In addition the high thermal sensitivity achieved with such mass of T _h gave rise to an interesting discovery of an unidentified thermal event at 92°C prior to either melting or dehydration of T _h.     

Study of the phase equilibrium of the oligo(ethylene oxide)-water system by differential thermal analysis

A DTA apparatus suitable for measuring polymer solutions has been constructed. With the use of this apparatus, the phase equilibrium was studied for various concentrations of the oligo(ethylene oxide)-water system. In the region of dilute solutions, the precipitation temperature was determined from the DTA curve, which exhibits a sigmoidal shape. Estimates were made of the thermodynamic parameters for entropyΨ ₁=?1.89 and enthalpyk ₁=?1.86 (at 380 K), and the theta temperatureΘ=101 °C. In concentrated solutions the thermodynamic quantities characterizing the fusion of oligomers depend on the molecular weight, and the values estimated from DTA peak areas and from the equation for the melting point depression agree fairly well.     

Thermal characterisation of the non-stoichiometry and catalytic activity of BaxLn1−xCoO3 (Ln = La,Nd, Sm and Dy) compounds

The compounds Ba_xLn_1?xCoO₃ (Ln = La, Nd, Sm and Dy) were prepared by ceramic technique. They were characterised for oxygen non-stoichiometry using isothermal DTA under varying oxygen partial pressure and TG in air. Isothermal DTA was also employed to study the catalytic activity of the compounds towards CO oxidation. For a given compound, the oxygen deficiency increases with increasing temperature and decreasing oxygen partial pressure. For a given Ba_xLn_1?xCoO₃ series, in general barium-rich compounds were more oxygen deficient. Isothermal DTA study of CO oxidation over Ba_xLa_1?xCoO₃ compounds at 600 K suggested that the carbon monoxide takes up lattice-labile oxygen from the sample and is oxidised to CO₂, the percent CO conversion being higher for barium-rich samples.     

DTA and x-ray studies on extended-chain crystals of polyethylene under high pressure

The relation between the thermal behavior of extended-chain crystals (ECCs) of polyethylene and the phase transitions, i.e., orthorhombic ? hexagonal ? melt, of polyethylene at high pressures above about 400 MPa has been studied by high-pressure differential thermal analysis (DTA), and with a high-pressure and high-temperature x-ray diffraction apparatus equipped with a position-sensitive proportional counter measuring system. The original sample used in this study consists mainly of two kinds of ECC, which we designate as “ordinary extended-chain” crystals (OECCs) and “highly-extended-chain” crystals (HECCs). Experimental results at pressures below 300 MPa substantiate the results previously reported: i.e., the phase diagram indicating the relation between the melting temperatures and pressure for the OECCs and HECCs can be determined for pressures up to 500 MPa. In heating at pressures above about 500 MPa, the peak intensity of the (100) reflection of the hexagonal structure decreases in two stages with increasing temperature. The phenomenon corresponds to the thermal behavior determined by high-pressure DTA in which two small endothermic peaks can be observed at temperatures above that of the crystal transition evidenced by the strong peak. This phenomenon suggests melting in two stages of hexagonal structures with different thermal stabilities, and that the change at higher temperature may be due to fusion of the hexagonal phase annealed either below or above the transition temperature.