Differential thermal analysis

Differential thermal analysis (DTA) is a thermoanalytic technique that is similar to differential scanning calorimetry. In DTA, the material under study and an inert reference are made to undergo identical thermal cycles, (i.e., same cooling or heating programme) while recording any temperature difference between sample and reference.[1] This differential temperature is then plotted against time, or against temperature (DTA curve, or thermogram). Changes in the sample, either exothermic or endothermic, can be detected relative to the inert reference. Thus, a DTA curve provides data on the transformations that have occurred, such as glass transitions, crystallization, melting and sublimation. The area under a DTA peak is the enthalpy change and it's not affected by the heat capacity of the sample.

Differential Thermal Analysis
AcronymDTA
ClassificationThermal analysis
Other techniques
RelatedDifferential scanning calorimetry
Isothermal microcalorimetry
Dynamic mechanical analysis
Thermomechanical analysis
Thermogravimetric analysis
Dielectric thermal analysis

Apparatus

A DTA consists of a sample holder, thermocouples, sample containers and a ceramic or metallic block; a furnace; a temperature programmer; and a recording system. The key feature is the existence of two thermocouples connected to a voltmeter. One thermocouple is placed in an inert material such as Al2O3, while the other is placed in a sample of the material under study. As the temperature is increased, there will be a brief deflection of the voltmeter if the sample is undergoing a phase transition. This occurs because the input of heat will raise the temperature of the inert substance, but be incorporated as latent heat in the material changing phase.[2] It consist of inert environment with inert gases which will not react with sample and reference. Generally helium or argon is used as inert gas.

Today's instruments

In today's market most manufacturers don't make true DTA systems but rather have incorporated this technology into thermogravimetric analysis (TGA) systems, which provide both mass loss and thermal information. With today's advancements in software, even these instruments are being replaced by true TGA-DSC instruments that can provide the temperature and heat flow of the sample, simultaneously with mass loss.

Applications

A DTA curve can be used only as a finger print for identification purposes but usually the applications of this method are the determination of phase diagrams, heat change measurements and decomposition in various atmospheres.

DTA is widely used in the pharmaceutical[3] and food industries.[4][5][6][7]

DTA may be used in cement chemistry,[8] mineralogical research[9] and in environmental studies.[10]

DTA curves may also be used to date bone remains[11] or to study archaeological materials.[12][13] Using DTA one can obtain liquidus & solidus lines of phase diagrams.

References
  1. Bhadeshia H.K.D.H. “Thermal analyses techniques. Differential thermal analysis”. University of Cambridge, Material Science and Metallurgy. www.msm.cam.ac.uk/phase-trans/2002/Thermal1.pdf
  2. Robert Bud, Deborah Jean Warner (1998). Instruments of Science. pp. 170–171. ISBN 9780815315612.
  3. Ferrer S., Borrás J., Martín Gil J. and Martín Gil F.J. "Thermal studies on sulphonamide derivative complexes”. Thermochim. Acta, 1989, 147, 321 330; 1989, 153, 205 220; 1991, 185, 315 333.
  4. Berger K.G., Akehurst E.E. “Some applications of differential thermal analysis to oils and fats”. International Journal of Food Science & Technology, 1966, 1, 237–247.
  5. Ramos Sánchez M.C., Rey F.J., Rodríguez M.L., Martín Gil F.J. and Martín Gil J. "DTG and DTA studies on typical sugars". Thermochim. Acta, 1988, 134, 55 60.
  6. F.J. Rey, M.C. Ramos-Sánchez, M.L.Rodríguez, J. Martín-Gil, F.J. Martín-Gil. "DTG and DTA studies on sugar derivatives". Thermochim. Acta, 1988, 134, 67 72.
  7. Rodríguez Méndez M.L., Rey F.J., Martín Gil J. and Martín Gil F.J. "DTG and DTA studies on amino acids". Thermochim. Acta, 1988, 134, 73 78.
  8. Ramachandran V.S. “Applications of differential thermal analysis in cement chemistry”. Chap. V, Chemical Publishing Co., Inc., New York (1969), 92.
  9. Smykatz-Kloss W. “Application of differential thermal analysis in mineralogy”. J. Therm. Anal. Cal., 1982, 23, 15-44.
  10. Smykatz-Kloss W., Heil A, Kaeding L. and Roller E. “Thermal analysis in environmental studies”. In: Thermal analysis in Geosciences. Springer Berlin / Heidelberg, 1991.
  11. Villanueva, PrE, Girela F. y Castellanos M. “The application of differential thermal analysis and thermogravimetric analysis to dating bone remains”. Journal of Forensic Sciences, 1976, 21,
  12. Misiego-Tejeda J.C., Marcos-Contreras G.J., Sarabia Herrero F.J., Martín Gil J. and Martín Gil F.J. "Un horno doméstico de la primera Edad del Hierro de "El Soto de Medinilla" (Valladolid) y su análisis por ATD". BSAA (University of Valladolid) 1993, LIX, 89 111.
  13. Kingery W.D. “A note on the differential thermal analysis of archaeological ceramics”. Archaeometry, 1974, 16, 109–112.
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