The use of magnetic transitions in temperature calibration and performance evaluation of thermogravimetric systems

Norem, S. D.; O'Neill, M.J.; Gray, Allan P.

doi:10.1016/0040-6031(70)85026-2

Cited by 67 publications

(8 citation statements)

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“…At the Curie point a significant apparent mass loss in the specimen occurs. 16 Five metals have been certified as ICTAC certified reference materials for TG, GM761, as shown in Table 1. 17 The materials cover the temperature range 200 -800°C.…”

Section: Measurement Of Temperature and Methods Of Calibrationmentioning

confidence: 99%

Thermogravimetry

Dunn

2000

Encyclopedia of Analytical Chemistry

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Thermogravimetry (TG or TGA) is a technique in which the mass of a substance is measured as a function of temperature whilst the substance is subjected to a controlled temperature program.1, 2 Commonly materials can be heated or cooled in the temperature range from −160 to 1600°C at rates of fractions of a degree per minute up to 100°C min −1 . Sample sizes are from 10–100 mg, although apparatus is available which can take larger sample masses. Different atmospheres can be used, from inert gases such as nitrogen, to reactive gases such as oxygen, hydrogen and vapors. The sensitivity of the apparatus is usually in the microgram range, with an accuracy of ±1% and a similar level of precision. The results obtained from TG experiments are subject to a variety of experimental variables, and an understanding of the effects of these is essential to a correct interpretation of the results. TG can be used to study any physical or chemical reaction which gives a mass change, and includes absorption and desorption of gases, sublimation and vaporization, the thermal decomposition of a wide range of materials from inorganic compounds to polymers, the reaction between a gas and a solid, and solid–solid reactions. TG has also been widely used to carry out kinetic studies on solid materials, with the aim of determining the reaction model and the kinetic parameters of activation energy ( E ) and frequency factor ( A ). However, considerable care is required in the interpretation of the results obtained.

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Section: Measurement Of Temperature and Methods Of Calibrationmentioning

confidence: 99%

Thermogravimetry

Dunn

2000

Encyclopedia of Analytical Chemistry

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“…With the magnet in place, scans of the reference material over the desired temperature range, using multiple references, which can be loaded simultaneously if they do not react or melt together, generate a very high accuracy temperature correction curve [11]. It is important to note that this measurement is sensitive to scan rate and flow conditions, but in a way that is smaller, more repeatable, and easy to correct for during analysis.…”

Section: Methodsmentioning

confidence: 99%

“…Older studies [11] used the derivative of the T g signal but this is very unreliable when the T g signal pre-and post-Curie point is subject to other simultaneous processes. The number of confounding terms such as sample decomposition, buoyancy and oxidation are capable of generating a variety of profiles above and below the Curie transformation.…”

Section: Methodsmentioning

confidence: 99%

“…Curie temperature measurement is accomplished in some DSC-TGA geometries by the placement of a high strength permanent magnet just outside the temperature controlled chamber [10,11]. With the magnet in place, scans of the reference material over the desired temperature range, using multiple references, which can be loaded simultaneously if they do not react or melt together, generate a very high accuracy temperature correction curve [11].…”

Section: Methodsmentioning

confidence: 99%

“…Systems supplementing differential scanning calorimeter and thermogravimetric analyzers with a permanent magnet to create a similar magnetic balance are popular for Curie temperature measurements [9,10]. This is done not only to enable measurement of Curie transformations in unknown materials, but also to increase the accuracy of the instrument by correcting temperature profiles using the very sharp Curie point instead of or in addition to melting point reference temperatures [11,12].…”

Section: Introductionmentioning

confidence: 99%

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Curie temperature determination via thermogravimetric and continuous wavelet transformation analysis

2017

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A cost effective method for conversion of a vertical tube thermogravimetric analysis system into a magnetic balance capable of measuring Curie Temperatures is presented. Reference and preliminary experimental data generated using this system is analyzed via a general-purpose wavelet based Curie point edge detection technique allowing for enhanced speed, ease and repeatability of magnetic balance data analysis. The Curie temperatures for a number of Heusler compounds are reported.

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Thermogravimetric Analysis

Dunn

2002

Characterization of Materials

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The formal definition of thermogravimetry (TG is the preferred abbreviation, although TGA is also used) has been given by the Nomenclature Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC) as “a technique in which the mass of a substance is measured as a function of temperature whilst the substance is subjected to a controlled temperature programme”. In the above definition, a controlled temperature program means heating or cooling the sample at some predetermined and defined rate. Although it is common to have just one constant heating or cooling rate, it is also advantageous in some cases to have different rates over different temperature ranges and in some cases even a varying rate over a specific temperature range. An apparatus called a thermobalance is used to obtain a thermogravimetric curve. By means of a thermobalance the temperature range over which a reaction involving mass change occurs may be determined. The sample is usually a solid, or more rarely a liquid. Thermogravimetric data can be presented in two ways. The TG curve is a plot of the mass against time or temperature, with the mass loss on the ordinate plotted downward and mass gains plotted upward relative to a baseline. Alternatively, data can be presented as a derivative thermogravimetric (DTG) curve, which is a plot of the rate of change of mass with respect to time or temperature against time or temperature. The DTG mass losses should also be plotted downward and the gains upward. Conventionally, thermal analysis experiments are carried out at a constant heating rate, and a property change is measured as a function of time. An alternative approach is to keep the change in property constant by varying the heating rate. For TG, the rate of mass loss is kept constant by variation in heating rate. To achieve this, the mass change is monitored and the heating rate decreased as the mass loss increases, and vice versa. At the maximum rate of mass loss, the heating rate is a minimum. This gives mass losses over very narrow temperature ranges and sometimes enables two close reactions to be resolved. This method has the advantage of using fast heating rates when no thermal event is taking place and then slowing down the heating rate when a mass change is in progress. Thermogravimetry does not give information about reactions that do not involve mass change, such as polymorphic transformations and double‐decomposition reactions. Also, it is not useful for identification of a substance or mixture of substances unless the temperature range of the reaction has already been established and there are no interfering reactions. However, when a positive identification has been made, TG by its very nature is a quantitative technique and can frequently be used to estimate the amount of a particular substance present in a mixture or the purity of a single substance. The types of processes that can be investigated by TG are given.

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The use of magnetic transitions in temperature calibration and performance evaluation of thermogravimetric systems

Cited by 67 publications

References 0 publications

Thermogravimetry

Thermogravimetry

Curie temperature determination via thermogravimetric and continuous wavelet transformation analysis

Thermogravimetric Analysis

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