The use of infra-red light-modulated temperature in DSC created by pulse-width modulation

• Published in: Thermochimica acta Vol. 381; no. 2; pp. 139 - 146
• Main Authors: Kamasa, P., Buzin, A., Pyda, M., Wunderlich, B.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 10.01.2002; Elsevier Science
• Subjects: Analytical chemistry; Chemical and thermal methods; Chemistry; Exact sciences and technology; Infra-red-modulated temperature; Pulse-width modulation; Temperature-modulated DSC; Temperature-modulated DSC; Infra-red-modulated temperature; Pulse-width modulation; Differential scanning calorimetry; Aluminium Oxides; Pulse width; Melting; Sapphire; Heat capacity; Styrene polymer; Thermal analysis; Infrared radiation heating; Indium; Group IIIA metal
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/S0040-6031(01)00649-9

Infra-red light, generated by diodes, is applied to produce a sinusoidal temperature modulation in the standard heat-flux DSC of TA instruments. The temperature of the sample and reference are controlled by both, the original temperature controller of the instrument, and by the radiant energy generated by two high-power infra-red light-emitting diodes (LEDs). This allows for isothermal or quasi-isothermal experimentation in the standard mode of operation of the calorimeter. The additional infra-red irradiation is provided only for temperature modulation. The radiant energy transferred to the specimens is controlled by pulse-width modulation (PWM) which provides a high linearity in the temperature modulation program. This feature enables to obtain any arbitrary temperature profile with the limits of frequency set by the calorimeter response and speed of the computer. Simple electronics and a computer algorithm for the PWM control are described. The method was tested in the melting range of indium and by measurement of the heat capacity of sapphire (Al 2O 3) and polystyrene. The problem of frequency correction arising from a wide frequency range is analyzed and discussed.