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additions by conduction calorimetry ’, Ph.D. Tesis, ETS Ings. CCP, Polytechnic University of Madrid-Spain, 12 Dec. 2002 . 13 Larbi , J Fraay , A

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Multicycle differential scanning calorimetry

Thermophysical procedures for research, development, and quality control of substances and materials

Journal of Thermal Analysis and Calorimetry
Authors: E. Marti, E. Kaisersberger, and E. Füglein

Abstract  

Multicycle Differential Scanning Calorimetry (MCDSC) is a procedure where repeated temperature cycles are executed and the measured data are superimposed for a selected number of cycles. Temperature cycles with a single sample are executed under selected experimental conditions in one of these procedures, namely, the MCDSCs. The second one, MCDSCm is a procedure in which every identical temperature cycle starts with a new sample of the same substance of a similar mass. The procedure MCDSCs using the same sample for a number of cycles is only applicable for substances and materials which are chemically and physically stable under the selected experimental conditions. The application of MCDSC enhances two extremely important qualities of a DSC measurement, namely, the sensitivity and the statistical base, both qualities with respect to the final data elucidated. Another possibility by MCDSC also related to the enhanced sensitivity can lead the discovery of a phenomenon which hitherto has not been observed. The most important result of any MCDSC application is the determination of the mean DSC curve within the temperature interval of interest by superimposing the single curves point by point and by the division of the calorimetric values obtained with the number of scans evaluated. The signal-to-noise-ratio (SNR) for the mean curve can be compared with the value determined for one or even for all the single curves measured yielding the improvement factor achieved with a MCDSC measurement. This experimentally determined improvement of the SNR can be compared with the value given on a statistical consideration by Gauss as the square root of the number of cycles evaluated. The main aims of this article are to prove the practical application of the procedure and the efficiency in case of rather small sample masses. Substances were selected with known enthalpy transitions and, in addition, polystyrene was taken for a determination of the data for the glass transition by MCDSC. Rather small sample masses in the order of micrograms as well as the experimental conditions have been selected for the measurements with 4,4′-azoxyanisole and n-hexatriacontane with the expectation to get a value of SNR for the single curves of about unity or even below. Two aims should be achieved with these experiments. First, the multicycle procedures and the data evaluation developed should be capable of establishing, after performing of a certain number of cycles, a mean curve showing an improvement over the SNR with respect to the single curves. Second, we should be able to get a rough estimation of the lower limit of the SNR for a single curve, below the instrumental noise level of the DSC used, necessary to achieve with a MCDSC experiment a mean curve with a clearly visible peak.

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properties of the mixture [ 3 ]. For a determination of the effect of additive on the course of hydration, various methods based on calorimetry proved to be useful for their fastness, simplicity of analysis and high informative value [ 5 ]. From the

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Abstract  

Isothermal titration calorimetry (ITC) and reaction calorimetry (RC) have been used to construct the solid-liquid equilibrium line in ternary systems containing the solute to precipitate and an aqueous mixed solvent, and to study polymerization reactions under real process conditions, respectively. Phase diagrams have been established over the whole concentration range for some benzene substituted derivatives, including o-anisaldehyde, 1,3,5-trimethoxybenzene and vanillin, in {water + alcohol}mixtures at different temperatures. Acrylamide polymerization in aqueous solution using potassium permanganate/acid oxalic redox system as initiator was investigated on a homemade calorimeter, which works according to the isoperibolic mode. A Calvet type differential RC was used to illustrate the applicability of temperature oscillation calorimetry (TOC) for the evaluation of the heat transfer coefficient during the course of reaction.

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Modulated temperature differential scanning calorimetry

Characterization of curing systems by TTT and CHT diagrams

Journal of Thermal Analysis and Calorimetry
Authors: A. Van Hemelrijck and B. Van Mele

Abstract  

Modulated temperature differential scanning calorimetry (MTDSC) is used to study simultaneously the evolution of heat flow and heat capacity for the isothermal and non-isothermal cure of an epoxy-anhydride thermosetting system. Modelling of the (heat flow related) chemical kinetics and the (heat capacity related) mobility factor contributes to a quantitative construction of Temperature-Time-Transformation (TTT) and Continuous-Heating-Transformation (CHT) diagrams for the thermosetting system.

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The results from temperature modulated DSC in the glass transition region of amorphous and semicrystalline polymers are described with the linear response approach. The real and the imaginary part of the complex heat capacity are discussed. The findings are compared with those of dielectric spectroscopy. The frequency dependent glass transition temperature can be fitted with a VFT-equation. The transition frequencies are decreased by 0.5 to 1 orders of magnitude compared to dielectric measurements. Cooling rates from standard DSC are transformed into frequencies. The glass transition temperatures are also approximated by the VFT-fit from the temperature modulated measurements. The differences in the shape of the curves from amorphous and semicrystalline samples are discussed.

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Modulated temperature differential scanning calorimetry

Considerations for a quantitative study of thermosetting systems

Journal of Thermal Analysis and Calorimetry
Authors: G. Van Assche, A. Van Hemelrijck, and B. Van Mele

Abstract  

The influence of temperature modulation and signal treatment (deconvolution procedure) of modulated temperature differential scanning calorimetry is discussed with respect to the investigation of cure kinetics of thermosetting systems. The use of a ‘dynamic’ heat capacity calibration is not important for this purpose due to normalization of the heat capacity signal in all cure experiments. The heat flow phase during isothermal and non-isothermal cure is always small, giving rise to negligible corrections on the heat capacity and reversing heat flow signals in-phase with the modulated heating rate. The evolution of the heat flow phase contains information on relaxation phenomena in the course of the chemical reactions.

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Research developments in titration calorimetry over the past ten years by personnel at the Thermochemical Institute have resulted in new techniques and instrumentation that have greatly increased the usefulness of calorimetry in the study of chemical problems. During this time, problems associated with the components of the calorimeter (i.e., constant temperature bath, constant rate buret, reaction vessel, temperature sensing circuit, and data analysis procedure) have been solved so that the continuous titration method now gives results comparable in accuracy to those obtained with conventional solution calorimeters. These developments have opened new avenues of research in the fields of biochemistry, microbiology, and environmental analysis.

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Experimental progress in adiabatic, cryogenic calorimetry is tersely reviewed and contrasted with other techniques for heat capacity determinations in this temperature region—including DSC. Trends and prognostications of important developmente including scaling down sample size and use of adjuvant thermometry.

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calorimetries, a contact, PPE, and a non-contact one, PTR. As “recent developments and trends” concerning these methods, we will focus on two recent improvements: (i) the increase of the number of the layers of the PPE detection cell (with the final purpose of

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