Melting of indium by temperature-modulated differential scanning calorimetry

The melting and crystallization of a sharply melting standard has been explored for the calibration of temperature-modulated differential scanning calorimetry, TMDSC. Modulated temperature and heat flow have been followed during melting and crystallization of indium. It is observed that indium does not supercool as long as crystal nuclei remain in the sample when analyzing quasi-isothermally with a small modulation amplitude. For standard differential scanning calorimetry, DSC, the melting and crystallization temperatures of indium are sufficiently different not to permit its use for calibration on cooling, unless special analysis modes are applied. For TMDSC with an underlying heating rate of 0.2 K min^–1 and a modulation amplitude of 0.5–1.5 K at periods of 30–90 s, the extrapolated onsets of melting and freezing were within 0.1 K of the known melting temperature of indium. Further work is needed to separate the effects originating from loss of steady state between sample and sensor on the one hand and from supercooling on the other.On leave from Toray Research Center, Inc., Otsu, Shiga 520, Japan.This work was supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 90-00520 and the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U.S. Department of Energy, under contract number DEACOS-960R22464. Support for instrumentation came from TA Instruments, Inc. and Mettler-Toledo Inc. Research support was also given by ICI Paints.     

The calorimetric calibration of differential scanning calorimetry cells

In this paper it is shown that in many cases enthalpy determinations can be carried out with a precision <1%. The influences of various sample and instrumental properties are described. The enthalpies of 24 compounds with 30 phase changes (polymorphic transitions or melting points) were redetermined. Twelve of the compounds with 15 transitions in the temperature range 0?670°C are selected and recommended for calorimetric DSC calibration. The linearization of the calibration curve as stated by the manufacturer of the instrument employed was fully confirmed.     

Precise determination of melting and boiling points by differential thermal analysis and differential scanning calorimetry

The theory, operation and instrumentation of differential thermal analysis (DTA) and differential scanning calorimetry (DSC) are sufficiently well developed to determine melting and boiling points with a high degree of certainty and reproducibility. However, certain precautions must be taken if data of maximum value are to be obtained. Sampling techniques, encapsulation, instrumental parameters and theoretical considerations will be treated in detail.In addition to the very small amount of material required for a melting or boiling point determination, DTA and DSC have other advantages. If certain precautions are observed it is possible to use several equations from classical thermodynamics to obtain absolute purity. A complete Cox Chart of a pure liquid can be obtained and the heat of vaporization determined in a few hours. Complex solid phase diagrams are easily studied. The success or failure of fractionation techniques can be predicted from single thermograms if several phase transitions are present.     

Phase transformations in sodium molybdate studied by differential scanning calorimetry

Differential scanning calorimetry (DSC) was used to study the thermal behavior of sodium molybdate in the range of elevated temperatures. Parameters (temperatures and enthalpies) of phase transformations in Na₂MoO₄ were determined.     

Solidification behavior of indium droplets embedded in aluminum by differential fast scanning calorimetry

Journal of Thermal Analysis and Calorimetry - Indium droplets embedded in aluminum matrix were successfully prepared by melt spinning technique. The results showed that an amount of nano-sized...     

Simplification of differential temperature calibration and emittance measurements in scanning calorimetry

The energy emitted by the two sample holders of a Perkin—Elmer Differential Scanning Calorimeter (DSC) can be balanced quickly at any temperature by observing instrument signal as a function of differential temperature control setting. This balance point, depending on the emittance characteristics of the individual sample holders, will correspond closely to the point at which the temperatures of the two sample holders are the same, making rapid differential temperature calibration possible. Deterioration in the characteristics of the sample holders can be detected, and emittance measurements can be greatly simplified.     

A new approach for the estimation of the melting enthalpy of metastable crystalline compounds using differential scanning calorimetry

This article focuses on the development of an innovative method, based on thermodynamic considerations and with the use of Differential Scanning Calorimetry (DSC), for the estimation of the melting enthalpy of crystalline compounds which are metastable near their melting temperature. The curves obtained, at various heating rates, are analysed in two steps. In the first step, the area of a zone generated by the melting endothermic peak is calculated following a specific method. In the second step, the melting enthalpy is extracted from this area through an enthalpy balance. This method is applied to both identified crystallographic forms, named form I and form II, respectively, of Etiracetam (UCB Pharma). The results show that the melting enthalpy of the stable form II compare well with the ones obtained using conventional methods. The curves of the metastable form I present thermal instabilities (partial solid–solid polymorphic transition and beta-recrystallization) near the form I melting peak leading to difficulties for a direct determination of the melting enthalpy by conventional methods. The proposed method is therefore very useful for the estimation of the form I melting enthalpy.     

Morphology characterization of emulsions by differential scanning calorimetry

This article is a review of some results obtained by Differential Scanning Calorimetry (DSC) for characterizing the morphology of emulsions. In a classical DSC experiment, an emulsion sample is submitted to a regular cooling and heating cycle between temperatures that include freezing and melting of the dispersed droplets. By using the thermograms found in the literature for various emulsions, how to get information about the solidification and melting, the presence of solute, the emulsion type, the transfer of matter, the stability and the droplet size is shown.     

Thermal polymerization of acrylamide by differential scanning calorimetry

Thermal polymerization of acrylamide was studied by differential scanning calorimetry. Latent heat of fusion ΔH_f and enthalpy of polymerization ΔH_p values were found to be 36 and ?18.0 kcal mol^?1, respectively. The overall activation energy E for the polymerization was calculated to be 19 k cal mol^?1 up to 60% conversion. The added free-radical inhibitor (benzoquinone) was found to desensitize the thermal polymerization of acrylamide suggesting the polymerization to be a free-radical type. The existing rate equation for the heterogeneous bulk polymerization in the presence of initiators has been modified for the thermally initiated bulk polymerization of acrylamide. The experimental overall E value was found to agree well with the calculated E value when considering only the propagation and termination steps, thereby suggesting the process to be similar to postpolymerization of acrylamide.     

Measurement of thermal conductivity by differential scanning calorimetry

A technique of measurement of thermal conductivity of solid materials by differential scanning calorimetry is presented. It concerns small samples having a diameter less than 8.0 mm, a height less than 2.0 mm and a low thermal conductivity. This method requires many samples with different heights which are heated in such a way that a calibration substance put on their top undergoes a first-order phase transition. The analysis of heat transfer of a such experiment predicts that the slope of the differential power during the transition is proportional to the factor 2 and inversely proportional to the sum of the thermal resistances. A measurement of the thermal conductivity of samples made of polytetrafluoroethylene powder, compressed at the density of 2.10±0.03 g cm⁻³, has been performed; the value obtained is 0.33±0.02 W m⁻¹ K⁻¹. Measurements of thermal conductivity of small metal hydride pellets are also presented. The precision of the measurements are on average 10%.     

Hydration of thermally denatured lysozyme studied by sorption calorimetry and differential scanning calorimetry

We have studied hydration (and dehydration) of thermally denatured hen egg lysozyme using sorption calorimetry. Two different procedures of thermal denaturation of lysozyme were used. In the first procedure the protein was denatured in an aqueous solution at 90 degrees C, in the other procedure a sample that contained 20% of water was denatured at 150 degrees C. The protein denatured at 90 degrees C showed very similar sorption behavior to that of the native protein. The lysozyme samples denatured at 150 degrees C were studied at several temperatures in the range of 25-60 degrees C. In the beginning of sorption, the sorption isotherms of native and denatured lysozyme are almost identical. At higher water contents, however, the denatured lysozyme can absorb a greater amount of water than the native protein due to the larger number of available sorption sites. Desorption experiments did not reveal a pronounced hysteresis in the sorption isotherm of denatured lysozyme (such hysteresis is typical for native lysozyme). Despite the unfolded structure, the denatured lysozyme binds less water than does the native lysozyme in the desorption experiments at water contents up to 34 wt %. Glass transitions in the denatured lysozyme were observed using both differential scanning calorimetry and sorption calorimetry. Partial molar enthalpy of mixing of water in the glassy state is strongly exothermic, which gives rise to a positive temperature dependence of the water activity. The changes of the free energy of the protein induced by the hydration stabilize the denatured form of lysozyme with respect to the native form.     

Determination of the temperature and enthalpy of the solid-solid phase transition of caesium nitrate by differential scanning calorimetry

The equilibrium temperature of the solid-solid phase transition of high purity caesium nitrate has been measured accurately by stepwise heating and by the extrapolation to zero heating rate method. A mean value of 154.3 ± 0.1 °C was obtained using two different heat flux DSC instruments. A value of 3.44 ± 0.04 kJ mol⁻¹ was determined for the enthalpy of transition.     

A new differential scanning calorimetry based approach for the characterization of peracid resin

Differential scanning calorimetry was used to trace the heat of decomposition of the peracid groups (ΔH_d) in the oxidized EVA-g-AA resin. From the correlation between ΔH_d and the oxidation capacity measured by iodometry, it was found that 35 ± 5 cal of energy evolved per miliequivalent of peracid group decomposed. The ΔH_d values are also useful in finding the optimum condition for oxidation of acid groups and can be used to investigate the distribution of active peracid groups across the matrix. The stability and the activation energy of decomposition of grafted type peracid resin were also studied, where the activation energy of decomposition was calculated to be 13.4 kcal/mol.     

Quantitative determination of specific heat by differential scanning calorimetry

The influence of some experimental parameters on the quantitative determination of specific heats by DSC is discussed. Conditions allowing measurement of the specific heat with a maximum relative error of 1.5 % are proposed. The specific heats of NaA zeolite,C _p=0.227±0.003 cal.°C^?1.g^?1, and AgA zeoliteC _p=0.205±0.003 cal.°C^?1.g^?1 have been determined.     

A study of propellant decomposition by differential scanning calorimetry

The decomposition of 12 commercial nitrocellulose propellants was studied by differential scanning calorimetry. In general, heats of decomposition were found to be about 400–475 cal g^? for all the propellants when the reaction produced 12–16% residue. Some samples decompose in a much different way, producing only about 3–4% residue and liberating only 200–250 cal g^?1. Both decomposition patterns were observed for samples of the same propellant run in the same way. In almost all cases, different manufacturing lots of the same propellant do not appear to show a significant difference in heat content. It appears that neither reprecipitation nor prolonged drying materially affects the heat of decomposition of the propellants.     

Thermal behaviour of emulsions studied by differential scanning calorimetry

This article is a review about the ways in which solidification and the melting may occur within emulsions submitted to steady cooling and heating performed in a differential scanning calorimeter. Simple, multiple and mixed emulsions are considered. Due to nucleation phenomena creating supercooled and supersaturated liquids, the DSC curves obtained during cooling and heating are quite different. The influence of a solute in the disperse phase is described in detail. Some implications about the instabilities of emulsions due to mass transfer phenomena are described.