Power-compensated Differential Scanning Calorimetry Research Articles

Heat capacities of active pharmaceutical ingredients nifedipine, griseofulvin, probucol and 5,5-diphenylhydantoin

The isobaric condensed-phase heat capacities of selected pharmaceutical active ingredients (APIs), namely nifedipine (CAS RN: 21829-25-4), griseofulvin (CAS RN: 126-07-8), probucol (CAS RN: 23288-49-5) and 5,5-diphenylhydantoin (CAS RN: 57-41-0), were determined over a wide temperature range starting from 2 K by combination of relaxation (heat pulse) calorimetry, Tian-Calvet calorimetry and power-compensated differential scanning calorimetry. Heat capacity measurements were taken for clearly specified polymorphs, a liquid phase (including subcooled liquid) and a glassy amorphous phase, if feasible. For 5,5-diphenylhydantoin, a heat capacity anomaly was detected in the temperature range 160 to 190 K and interpreted based on additional calorimetric and temperature-variable crystallographic measurements as a sequence of two phase transitions, which are reported for the first time in this work. Based on the determined phase behavior and heat capacity data from near 0 K, standard thermodynamic functions for crystalline and liquid phases were calculated for all APIs studied. This work significantly extends the availability of reliable heat capacity data and related thermodynamic properties for APIs required for modeling their solubility and other applications involving thermodynamic modeling.

Calorimetry characterization and crystallization modelling of wax-based mixtures under isokinetic and non-isokinetic cooling

Characterization and modelling of wax crystallization must be carefully addressed to understand wax-oil organogels formation. During casting process of wax-based mixtures, wax crystallization occurs under concomitant non-constant and high cooling rates. In this study, the crystallization kinetics of two representative wax-based materials were studied by power-compensated Differential Scanning Calorimetry (DSC) with moderate-high cooling rates (from − 20 to − 200 °C min−1) in constant cooling rate (isokinetic) conditions and in simplified non-constant cooling rate (non-isokinetic) conditions. Analyses based on the evolution of the mass fraction of solid wax calculated from heat flow (DSC signal) show similar kinetics trend and enthalpy of crystallization for the different isokinetic conditions, but with a significant influence on the supercooling effects. Considering the limits of the classic Avrami kinetics modelling for high aspect ratio crystals and complex mixtures, a semi-empirical modelling approach of non-isokinetic cooling conditions in a differential form is proposed. The modelling shows a good correlation with experimental results.

Heat capacities of selected active pharmaceutical ingredients

Condensed-phase heat capacities of selected pharmaceutical active pharmaceutical ingredients (APIs), namely (RS)-ibuprofen (CAS RN: 15687-27-1), (S)-ibuprofen (CAS RN: 51146-56-6), (S)-naproxen (CAS RN: 22204-53-1), indomethacin (CAS RN: 53-86-1), and carbamazepine (CAS RN: 298-46-4), were determined using Tian-Calvet calorimetry and power-compensated differential scanning calorimetry in the temperature range 216 to 471 K. In most cases, previously published heat capacities of the studied APIs are in significant disagreement both with each other and our measurements. By analyzing the literature values, many previously published data sets were shown to be erroneous. The heat capacities of supercooled liquid, an important parameter in the modeling of API solubility, were also measured in a wide temperature range when feasible. The phase behavior study of carbamazepine suggests that its thermal stability is lower than previously thought, which is in accordance with the most recent studies on carbamazepine decomposition. This work significantly extends the availability of reliable API heat capacity data for clearly defined polymorphic forms and liquid phase.

Heat Capacities of l-Histidine, l-Phenylalanine, l-Proline, l-Tryptophan and l-Tyrosine.

In an effort to establish reliable thermodynamic data for proteinogenic amino acids, heat capacities for l-histidine (CAS RN: 71-00-1), l-phenylalanine (CAS RN: 63-91-2), l-proline (CAS RN: 147-85-3), l-tryptophan (CAS RN: 73-22-3), and l-tyrosine (CAS RN: 60-18-4) were measured over a wide temperature range. Prior to heat capacity measurements, thermogravimetric analysis was performed to determine the decomposition temperatures while X-ray powder diffraction (XRPD) and heat-flux differential scanning calorimetry (DSC) were used to identify the initial crystal structures and their possible transformations. Crystal heat capacities of all five amino acids were measured by Tian–Calvet calorimetry in the temperature interval from 262 to 358 K and by power compensation DSC in the temperature interval from 307 to 437 K. Experimental values determined in this work were then combined with the literature data obtained by adiabatic calorimetry. Low temperature heat capacities of l-histidine, for which no literature data were available, were determined in this work using the relaxation (heat pulse) calorimetry from 2 K. As a result, isobaric crystal heat capacities and standard thermodynamic functions up to 430 K for all five crystalline amino acids were developed.

Heat Capacities of l-Alanine, l-Valine, l-Isoleucine, and l-Leucine: Experimental and Computational Study

This work is part of the effort on establishing reliable thermodynamic data for amino acids and, in a broader context, benchmarking first-principles calculations of thermodynamic properties of molecular crystals against reliable experimental data. In this work, crystal heat capacities of l-alanine (CAS RN: 56-41-7), l-valine (CAS RN: 72-18-4), l-isoleucine (CAS RN: 73-32-5), and l-leucine (CAS RN: 61-90-5) were newly measured in the temperature range 262–450 K by Tian–Calvet calorimetry and power-compensation differential scanning calorimetry (DSC) and combined with the critically assessed literature data to obtain the reference data from near 0 to 450 K. The heat capacity measurements were accompanied by thermogravimetric analysis to determine the decomposition temperatures of the studied amino acids and phase behavior studies by X-ray powder diffraction and heat-flux DSC to identify the initial crystal structures and their possible transformations. The crystal heat capacities calculated by combining the...

Quantitative determination of the spring entropy effect and its indication of the conformational change of polymer coils with varying concentration in aqueous poly(N-isopropylamide) solutions.

The lower critical solution temperature (LCST) phase separation behaviors of thermosensitive poly(N-isopropylacrylamide) (PNIPAM) aqueous solutions were investigated by power-compensation differential scanning calorimetry (DSC). The entropic effect and hence the change of swelling state of PNIPAM polymer coils in homogeneous concentrated aqueous solutions with varied solution composition was elucidated by the isothermal enthalpy demixing recovery behaviors in distinct concentration regions.

Time dependence of phase separation enthalpy recovery behavior in aqueous poly(N-isopropylacrylamide) solution

Thermosensitive LCST phase separation behaviors of poly(N-isopropylacrylamide) (PNIPAM) aqueous solutions have been investigated by a power compensation differential scanning calorimetry which can be subjected to relatively high cooling and heating scanning rates. Significant difference in the thermal properties is observed in four different concentration regions. The typical demixing enthalpy recovery behavior is observed in region III and IV, but cannot be observed in region II. In concentration region I, only one concentration-dependent glass transition behavior can be observed. The distinct thermal features in different concentration regions were interpreted by the complexity of chemical structure, and there are more than one polar groups in the repeating unit of PNIPAM, hydrogen bonded with different numbers of water molecules in different concentration regions. The endothermic phase separation process involved both a chemical process of the breakage of hydrogen bonding between polymer and water molecules and a physical process of the coil-to-globule transition of swelling polymer chains.

Relationship between the Cu content and thermal properties of Al–Cu alloys for latent heat energy storage

Current Al alloys still have shortcomings in their volumetric latent heat (LHV), compatibility and high-temperature inoxidizability, which limit their applications in the field of latent heat energy storage (LHES). The performance of aluminum alloys can be improved by the addition of Cu. The effects of the Cu content on the phase change temperature, mass latent heat (LHM), LHV, supercooling degree and microstructure of Al–Cu alloys were first studied by means of power-compensated differential scanning calorimetry, density, composition analysis and metallographic analysis. The measured values of the latent heat of Al–Cu alloys have been compared with the theoretically predicted values. The results show that for Al–Cu alloys with 7.3–52.8% Cu, the melting/freezing temperature is 540–655 °C/510–637 °C; the LHM and the LHV are 290–340 J g−1 and 877–1224 J cm−3, respectively; and the degree of supercooling is within 10 °C. The LHM and LHV of Al–Cu alloys decrease with the increase in the Cu content; when the content of Cu is over 16.6%, the difference between the theoretical value of the LHM and the measured average of the Al–Cu alloys is within 5%. The LHES phases in Al–Cu alloys are the α-Al and theta phases. Quantitative relationships of the Cu content and metallurgical microstructure with the LHM and LHV of Al–Cu alloys are established, and both theoretical and empirical equations are obtained for the estimation of the latent heat for Al–Cu alloys.

Mathematical analysis of the heat measured by a power-compensated differential scanning calorimeter during the solidification of a multiphase alloy

The determination of the solidification characteristics of alloys using differential scanning calorimetry (DSC) is difficult because of the unknowns associated with the kinetic of phase transformations and the thermal resistance between the sample and the temperature measuring device. This paper shows how appropriate assumptions coupled with a thermodynamic software package and an accurate mathematical analysis of a power-compensated DSC, can enable a direct comparison between the experimental and the theoretical heat evolutions obtained during the solidification of a multiphase alloy. This comparison is helpful in order to assess the thermodynamic database and to validate the different assumptions made in the solidification model.

Parallel nano-Differential Scanning Calorimetry: A New Device for Combinatorial Analysis of Complex nano-Scale Material Systems

ABSTRACTA new device is presented for the combinatorial analysis of complex nano-scale material systems. The parallel nano-differential scanning calorimeter (PnDSC) is a micro-machined array of calorimetric cells. This new approach to combinatorial calorimetry should expedite the analysis of nano-scale material thermal properties. A power compensation differential scanning calorimetry measurement, not yet performed on a device of this type, is described. A NiTi specific heat measurement demonstrates the scanning calorimetry capability of the PnDSC.

Isothermal and nonisothermal crystallization of polymers: Analysis with a shear differential thermal analyzer

The working principle of an instrument developed for studying the effects of controlled shear pulses on the isothermal and nonisothermal solidification of polymers is presented. The device combines a capillary rheometer and a differential thermal analyzer (DTA). The capillary rheometer part of the system allows the production of shear pulses with controlled duration and intensity at any prescribed temperature up to 300°C, and the DTA records the thermal effects resulting from the solidification. Results obtained for quiescent isothermal and nonisothermal crystallizations compare well with those obtained from power compensation differential scanning calorimetry. The effect of controlled shear pulses on the overall isothermal crystallization kinetics enables the evaluation of a critical strain responsible for the saturation of crystallization in sheared polymer melts. Additional shear (increase of the shear rate or of the shearing time) does not accelerate the crystallization kinetics. The shear-induced nonisothermal crystallization of polyethylene filled with talc shows the acceleration of the crystallization kinetics with the shear rate increase, thus confirming this device as a valuable experimental tool for studying the effect of shear on the solidification of fast crystallizing materials.

DSC study of precipitation in an Al–Mg–Mn alloy microalloyed with Cu

Power compensation differential scanning calorimetry (DSC) has been employed to detect and analyse precipitation reactions in an Al–1.3Mg–0.4Mn and an Al–1.3Mg–0.4Mn–0.07Cu alloy in which very small amounts of precipitate, less than 0.3 at.%, are expected to form. Due to the very small heat effects, baseline instability and drift significantly interfere with the measurements. After repeated experiments and careful baseline correction it is demonstrated that in the Cu containing alloy, ageing at 170 °C causes the appearance of two endothermic effects: for 2 days ageing a small dissolution effect appears at about 230 °C, whilst for 7 and 21 days ageing a dissolution effect peaking appears at about 300 °C. The temperature range of the latter is consistent with S phase dissolution.

Thermophysical properties of dental filling materials. Part I: thermal properties

The thermal properties of three light-curable filling materials were determined. The materials under test were: compomer Compoglass® F, and two hybrid composites, Tetric® and Valux tm Plus. The heat capacity measurements were conducted by power-compensated differential scanning calorimetry. The thermal diffusivity was investigated with the use of a laser-flash apparatus. Measurements were based on the modified Parker method. In both cases basic experiments were carried out within a narrow temperature range around 35 °C, ie from about 20 °C to about 50 °C, which corresponds to estimated typical operating temperatures for dental fillings. The obtained thermal characteristics of the specific heat and the thermal diffusivity were used for calculation of the thermal conductivity of the investigated materials.

Observation of two kinds of phase transitions of ZrW 2O 8 by power-compensated differential scanning calorimetry and high-temperature X-ray diffraction

Two kinds of phase transitions were observed for ZrW 2O 8 at 123 and 164°C with power-compensated differential scanning calorimetry. An endothermic peak was observed at 123°C in the DSC curve, indicating that the phase transition at this temperature is of the first order. The variation of enthalpy, Δ H, at the phase transition was estimated to be ∼290 J/mol. The base-line shift of the DSC curve, corresponding to the second-order phase transition, was observed at 164°C. The change in the heat capacity, Δ C p , at 164°C was calculated to be ∼20 J/(mol K), showing good agreement with the result of adiabatic calorimetry. The X-ray diffraction patterns of ZrW 2O 8 below 120°C and above 164°C could be explained by using models with space groups of P2 13 (No. 198) and Pa 3 ̄ (No. 205), respectively. Changes of the linear thermal expansion coefficients were observed at around 123 and 164°C, showing good agreement with the phase transition temperatures measured with DSC.

Determination of heat capacity with a sawtooth-type, power-compensated temperature-modulated DSC

The determination of the heat capacity in sawtooth-type, power-compensated temperature-modulated differential scanning calorimetry (TMDSC) by evaluation of the first harmonic of the Fourier transformation of the sample temperature and heat-flow rate is analyzed with experiments and model calculations. At modulation periods below 100 s, the measured, uncorrected, absolute value of the complex heat capacity deviates exponentially from the true heat capacity, while the steady state within the linear heating and cooling segments is reached after about 50 s. The errors increase with the heat capacity of the sample and vary for different samples and configurations of the measurement. An empirical equation for correction is suggested. It uses a sample-mass and instrument-dependent time constant τ( m) and permits measurements down to periods of 15 s, i.e., much before steady state is reached within the linear segments of the modulation experiment.

Undercooled liquid-to-glass transition during continuous cooling in Pd–Cu–Ni–P alloys

The glass-transition behavior from the supercooled liquid of a Pd40Cu30Ni10P20 alloy was investigated by employing a power-compensated differential scanning calorimetry under continuous cooling. At cooling rates of 0.83, 1.17, and 1.67 K/s, the transition was clearly detected as an abrupt decrease in heat capacity. From the difference in heat capacity between the undercooled liquid and glass, the alloy obtained at the lower cooling rate was found to have a more relaxed structure. The thermodynamic parameters determined in the present study enable us to interpret the reason for the outstandingly high glass-forming ability of the alloy.

Nucleation and Growth of the First Phase in Sputter-Deposited Nb/Al Multilayer Thin Films

ABSTRACTThe formation of the first phase in the reaction of sputter-deposited Nb/Al multilayer thin films has been studied by power-compensated and heat-flux differential scanning calorimetry, x-ray diffraction and transmission electron microscopy. The modulation periods of the films are in the range of 10-500 nm. Both types of calorimetrie measurements, performed at a constant heating rate, show the presence of two peaks (A and B) for the formation of the single product phase, NbAl3. Isothermal calorimetrie scans show that peak A is associated with a nucleation and growth type transformation. The formation of NbAl3 is thus interpreted as a two-stage process of nucleation and lateral growth to coalescence (peak A) followed by normal growth until the consumption of one or both reactants (peak B). Transmission electron microscopy investigations of samples annealed into the first stage of NbAl3 formation show the presence of this phase at the Nb/Al interface and its preferential growth along the grain boundaries of the Al layer. The latter highlights the role of reactant phase grain structure in product phase formation.

Differential scanning calorimetry: A useful tool for studying protein denaturation

Power-compensated differential scanning calorimetry is applied to the determination of the thermodynamic parameters of protein denaturation. The heating of relatively high mass samples (≈40 mg) is programmed at relatively high scan rates (10°C min −1). For these dynamic thermal measurements, attention is paid to the problems of sample thermal lag and to the construction of the baseline under the calorimetric curve. Simplified mathematical models are applied to the case of the denaturation transition of β-lactoglobulin and α-lactalbumin dispersed in distilled water at relatively high concentration (≈5% w/w). The effects of Na + and Ca 2+ addition on the conformational stability of the proteins upon thermal treatment are compared at pH 3.5 and 7, where these two major whey proteins display different thermal behaviours.

Kinetics and mechanism of the dehydration of α-NiSO4·6H2O

A study of the thermal dehydration of α-NiSO4·6H2O has been performed by power compensation differential scanning calorimetry in flowing nitrogen. No significant differences in behaviour were observed using either uncrushed crystalline powders or single crystal slabs cleaved parallel to {001}. In good agreement with previous findings, the kinetic analysis of the thermal curves confirms the validity of an=2 Avrami-Erofeev equation (AE2) in isothermal experiments at low (338–343 K) temperatures or in the initial portions of variable temperature runs. The kinetic obedience is however of an ‘order of reaction’ type for the main portion of the variable temperature runs and, for isothermal experiments, in the upper part of the temperature range investigated. Values of activation energies and frequency factors are reported. Parallel studies by optical microscopy showed relevant changes of surface texture when partially (thermally or vacuum) dehydrated {001} cleaved surface were submitted to rehydration. This phenomenon (named orange peel formation) indicates that a dehydrated layer forms on the crystal surfaces preceding the appearance of product crystals (germination or nucleation). Microscopy also revealed that reaction goes on inside the crystal and that product formation takes place in the bulk phase, following lattice collapse in experiments at high heating rates. Combined with previous results, these new experimental findings allow us to formulate a mechanism for the present transformation, comprising three main rate processes:

Kinetics and Thermodynamics of Amorphous Silicide Formation in Metal/Amorphous-Silicon Multilayer Thin Films

AbstractFormation of intermetallic phases upon heating of films composed of alternating layers of metal and amorphous silicon has been studied using power-compensated differential scanning calorimetry, crosssectional transmission electron microscopy, and thin film x-ray diffractrometry. Results for Ni/amorphous-Si (Ni/a-Si), Ti/a-Si, V/a- Si, and Co/a-Si are reviewed. In the first three cases, an amorphous silicide is the first phase to form. Further heating leads to thickening of the amorphous silicide and eventually to formation and growth of layers of crystalline silicides. In the case of Co/a-Si multilayer films, a crystalline silicide (CoSi) appears to be the first phase to form. In these systems calorimetric measurements suggest that there are barriers to nucleation of the crystalline phases, even though the energy reduction that would accompany their formation from pure components is large. It is suggested that interdiffusion may precede the formation of new phases at the original metal/a-Si interfaces, resulting in a significant decrease in the driving force for nucleation of the crystalline phases.