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  • Author or Editor: M. Schubnell x
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Abstract  

Thermoanalytical instruments are extensively used in R&D as well as in industrial quality control. A quantitative analysis of the data of a thermoanalytical measurement requires a careful calibration of the instrument. In differential scanning calorimetry (DSC) the quantities that have to be calibrated are the temperature and the heat flow. These two quantities are usually calibrated by evaluating melting or solid-solid transitions of some reference materials with well known transition enthalpies and temperatures. In this contribution we investigate temperature and heat flow calibration in the temperature range between −100 and 160C. We included 9 different samples for the analysis and established some general rules for the calibration process. As a result we found that with a well calibrated instrument the heat flow can be measured with 90% confidence to about 3% accuracy in this temperature range. With respect to temperature calibration we find that accuracies of 0.8C (90% confidence) may be expected. These values represent general accuracy limitations of DSC’s due to varying heat transfer conditions within the samples.

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Abstract  

Recently, model free kinetic analysis of sinusoidal modulated TG-curves has been presented. In this contribution we compare the activation energies resulting from model free analysis of modulated TG-curves and from Vyazovkin's model free kinetic analysis of non-modulated TG-curves. We used polytetrafluorethylene and manganese oxide as samples. As a result we find, that both methods deliver similar activation energies for polytetrafluorethylene. However, the activation energies of manganese oxide deviate substantially. The main purpose of kinetic analysis is its potential for predictions of the temporal behavior of materials under certain thermal conditions. Analysis of modulated TG-curves allows a model free determination of the temperature dependence of the activation energy. However, in order to make predictions, one still has to rely on kinetic models such as e.g. first order kinetics. This is in contrast to Vyazovkin's approach, which allows a model free description of kinetic processes in terms of a conversion dependent activation energy. This function can then be used to make kinetic predictions without any further assumptions with respect to reaction models. In this paper we further discuss this fundamental difference.

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Abstract  

DSC measurements in open pans are often disturbed by mass losses such as sublimation during melting or release of water during chemical reactions. By simultaneous DSC and TG measurements the DSC signal can be corrected. For this purpose, a temperature dependent calibration function has to be determined by which the SDTA signal from the TGA/SDTA851e measuring cell can be converted into a heat flow curve (DSC). By this procedure, accurate heat of melting can be determined despite ongoing sublimation in open pans. This method is illustrated with reference of the melting of anthracene. Additionally, condensation reactions were investigated and analyzed by DSC/TG even under ambient pressure, knowing the heat of evaporation. Using phenol formaldehyde resins the influence of the presence or the release of volatile reaction products on the reaction rate and kinetic parameters were studied. In general, the method can be used to correct DSC curves for thermal effects related to mass change.

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