Differential Scanning Calorimetry Heating Rate Research Articles

Nuances in the Calculation of Amorphous Solubility Enhancement Ratio

The theoretical amorphous solubility enhancement ratio (Rs) can be calculated based on the free energy difference between amorphous and crystalline forms (ΔGx→a), using several experimentally determined input parameters. This work compares the various approaches for the calculation of Rs and explores the nuances associated with its calculation. The uncertainty of Rs values owing to experimental conditions (differential scanning calorimetry heating rates) used to measure the input parameters was determined for 3 drugs (indomethacin, itraconazole, and spironolactone). The calculated value of Rs was most influenced by the measurement of heat of fusion. The range in values of Rs using the various equations in the literature was within the calculated uncertainty of the theoretical Rs value. Still, all equations appear to overpredict the experimental value of Rs, sometimes by more than a factor of 5, when an experimental value is attainable. Methods for the calculation of ΔGx→a for molecules undergoing additional phase transitions (other than glass transition and melting) were developed, employing itraconazole as a model drug. In addition, the influences of enthalpy relaxation and entropy of mixing for racemic compounds on Rs were also considered. These additional corrections improved agreement between theoretical and experimental Rs.

State of cure in silicone/clay nanocomposite coatings: The puzzle and the solution

Properties of a rubber/clay nanocomposite coating depend on rubber network formed in the presence of clay platelets. Not surprisingly, however, a few is known about the state of cure in silicone nanocomposites. In this work, nanoclay flakes are modified with trifunctional silane, fully characterized, and then added to silicone coatings. The resulting nanocomposites are underwent nonisothermal differential scanning calorimetry (DSC) varying heating regime. Fourier-transform infrared spectrophotometry, X-ray diffractometry, and thermogravimetric analysis (TGA) techniques were employed to quantify grafting reaction efficiency and thermal stability of modified nanoclay. Cure characteristics of nanocomposites (exothermal peak temperature as well as cure enthalpy) containing pristine and silane-modified nanoclays were discussed in terms of clay content under different DSC heating rates. The mysterious state of cure in silicone/clay nanocomposite coatings was unraveled and then explained by solving curing puzzle for silicone/clay systems through comparison between newly defined T* and ΔH* dimensionless indexes dedicated to the crosslinked nanocomposite networks with respect to blank silicone coating. The progressive/diffusional crosslinking and complete/partial/imperfect curing were respectively evaluated by analyzing fluctuations in T* and ΔH* values, where the effects of clay content and surface chemistry were satisfactorily quantified.

Thermal stability of ε-Ga2O3 polymorph

The thermal stability of ε-Ga2O3 polymorph was studied by complementary methods. Epitaxial films of ε-Ga2O3 grown on c-oriented sapphire were annealed at temperatures in the range 700–1000 °C and then investigated by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). In addition, Differential Scanning Calorimetry (DSC) up to 1100 °C was carried out on fragments of pure ε-Ga2O3 taken from a very thick layer. The results clearly indicate that ε-Ga2O3 initiates modifying its crystallographic structure above 650 °C, as demonstrated by a mild endothermic bent of the DSC curves. However, the effective transition to β-phase occurs quite suddenly at 880–920 °C, depending of the DSC heating rate. XRD and TEM results confirm this evidence. TEM investigation in particular shows that after annealing at 1000 °C and rapid cooling the film is completely made of β-Ga2O3 grains, most of them with orientation (310) respect to the sapphire substrate. However, if the cooling rate is substantially reduced, the converted β-Ga2O3 layer assumes the standard orientation (−201) parallel to (00.1) of the Al2O3 substrate. Based on the results of this study we conclude that ε-Ga2O3 may conveniently be used for device fabrication, exploiting its higher crystallographic symmetry and better matching to sapphire. However, all fabrication steps must be carried out at temperatures below 700 °C.

Differential Scanning Calorimetry (DSC) and Thermodynamic Prediction of Liquid Fraction vs Temperature for Two High-Performance Alloys for Semi-Solid Processing (Al-Si-Cu-Mg (319s) and Al-Cu-Ag (201))

There is a need to extend the application of semi-solid processing (SSP) to higher performance alloys such as 319s (Al-Si-Cu-Mg) and 201 (Al-Cu-Ag). The melting of these two alloys was investigated using differential scanning calorimetry (DSC) and thermodynamic prediction. The alloys had been processed by magneto-hydrodynamic (MHD) stirring before receipt to produce a microstructure suitable for SSP. The DSC results for the as-received MHD material were compared with those for material which has been taken through a complete DSC cycle and then reheated for a second DSC run. The effects of microsegregation were then analyzed. A higher liquid fraction for a particular temperature is found in the second DSC run than the first. Microstructural observations suggest this is because the intermetallics which form during the first cooling cycle tend to co-located. Quaternary and ternary reactions then occur during the second DSC heat and the co-location leads to enhanced peaks. The calculated liquid fraction is lower with 10 K/min DSC heating rate comparing with 3 K/min at a given temperature. The DSC scan rate must therefore be carefully considered if it is to be used to identify temperature parameters or the suitability of alloys for SSP. In addition, the starting material for DSC must represent the starting material for the SSP. With thermodynamic prediction, the equilibrium condition will provide better guidance for the thixoforming of MHD stirred starting material than the Scheil condition. The Scheil mode approximates more closely with a strongly microsegregated state.

Impact of the enthalpy function on the simulation of a building with phase change material wall

Recent studies concerning phase change material (PCM) characterization show that important errors occur if differential scanning calorimetry (DSC) experiments are misinterpreted. Therefore, it is important to know the influence of such misinterpretation on system modeling. The present work deals with phase change materials integrated in building structure to reduce overheating. The objective is to evaluate the discrepancies consequences (temperatures, heat fluxes), due to the use of the misinterpreted DSC experiments at different heating rates to determine the enthalpy, in comparison with those determined with the actual value of the enthalpy of the PCM determined by a proven inverse method. A numerical model of a single-family house with a phase change material mortar is developed to evaluate the thermal comfort in the building. The results show that for free-running temperature, none of the enthalpy curve deduced directly from DSC can predict correctly the thermal behavior of the house and the thermal comfort. Moreover, the more the DSC heating rate and the more the discrepancy with the results from the reference inverse method.

Crystallisation kinetics of MgO during the reconstruction process of steel slag

After high temperature reconstruction of converter steel slag, the content distributions of MgO are determined by chemical phase separation, and the decrystallisation degree of steel slag is tested by X-ray diffraction. The exothermic temperature of MgO crystallisation is measured combined with differential scanning calorimetry under heating rates of 5, 10, 15 and 20 K min−1, respectively. The results show that exothermic peak temperature of the MgO crystallisation increases with the increase of differential scanning calorimetry heating rates, mainly in the range of 1523–1618 K. The existence of mineraliser, manganese and phosphorus during the steel slag reconstruction can increase the crystallisation activation energy of free MgO, thus inhibit the crystallisation of MgO. The crystallisation reaction order of MgO increases with the increase of heating rates, but it still belongs to the first-order solid-state reaction. A mathematical model of the MgO crystallisation kinetics during the reconstruction process of steel slag is built.

Probing the effects of experimental conditions on the character of drug-polymer phase diagrams constructed using Flory-Huggins theory.

Amorphous drug-polymer solid dispersions have been found to result in improved drug dissolution rates when compared to their crystalline counterparts. However, when the drug exists in the amorphous form it will possess a higher Gibb's free energy than its associated crystalline state and can recrystallize. Drug-polymer phase diagrams constructed through the application of the Flory Huggins (F-H) theory contain a wealth of information regarding thermodynamic and kinetic stability of the amorphous drug-polymer system. This study was aimed to evaluate the effects of various experimental conditions on the solubility and miscibility detections of drug-polymer binary system. Felodipine (FD)-Polyvinylpyrrolidone (PVP) K15 (PVPK15) and FD-Polyvinylpyrrolidone/vinyl acetate (PVP/VA64) were the selected systems for this research. Physical mixtures with different drug loadings were mixed and ball milled. These samples were then processed using Differential Scanning Calorimetry (DSC) and measurements of melting point (Tend) and glass transition (Tg) were detected using heating rates of 0.5, 1.0 and 5.0°C/min. The melting point depression data was then used to calculate the F-H interaction parameter (χ) and extrapolated to lower temperatures to complete the liquid-solid transition curves. The theoretical binodal and spinodal curves were also constructed which were used to identify regions within the phase diagram. The effects of polymer selection, DSC heating rate, time above parent polymer Tg and polymer molecular weight were investigated by identifying amorphous drug miscibility limits at pharmaceutically relevant temperatures. The potential implications of these findings when applied to a non-ambient processing method such as Hot Melt Extrusion (HME) are also discussed.

Effect of functional group on thermal stability of cellulose derivative energetic polymers

This paper describes thermochemical properties and decomposition characteristics of cellulose acetate nitrate, azidodeoxy cellulose and azidodeoxy cellulose nitrate as three cellulose derivatives which are proper candidates for usage as novel binders in propellant compositions. Differential thermal analysis (DTA), differential scanning calorimetry (DSC) and thermogravimetry (TG) techniques have been employed to elucidate the reaction process of these energetic polymers. The results of the experiments showed that azidodeoxy cellulose nitrate decomposes exothermally during three continuous steps at temperature range of 180–500°C. Also, azidodeoxy cellulose polymer decomposes exothermally at about 206°C in a single step. However, cellulose acetate nitrate decomposition occurs exothermally in a single step at about 208°C. Furthermore, the effect of DSC heating rate on the thermal decomposition of interested energetic polymers was investigated. The apparent activation energy (E), ΔG#, ΔH# and ΔS# of the decomposition processes were obtained from the non-isothermal DSC experiments. Based on these thermokinetic data, the relative thermal stability of investigated energetic polymers was found to obey the following order: azidodeoxy cellulose>cellulose acetate nitrate>azidodeoxy cellulose nitrate.

Pharmaceutical physical form characterisation with fast (>200 °C min−1) DSC heating rates

Differential scanning calorimetry (DSC) has many applications during preformulation screening of new drug candidates, but definitive assignment of peaks to specific events in the sample is difficult without supplementary data from other techniques. To some extent these problems can be overcome by running multiple experiments at different heating rates. Typically 2 and 20 °C min−1 are indicated. However, modern instruments are capable of achieving much faster heating rates (up to 750 °C commercially); with this extended range comes a new capacity for investigating the physical form of materials. Here, the use of fast DSC heating rates for materials characterisation is explored, focussing on determination of melting temperatures, glass formation and polymorph screening.

Estimation Method for Liquidus Temperature of Lead-Free Solder Using Differential Scanning Calorimetry Profiles

It is usually complicated to analyze the liquidus temperature of lead-free solder, because unlike Sn-Pb eutectic solder, supercooling easily occurs during the cooling process of lead-free solder, and common lead-free solders contain only a small fraction of a primary phase. In order to determine the melting temperature range of lead-free solder easily, an estimation method using differential scanning calorimetry (DSC) profiles is proposed. The purpose of this study is to show the applicability of the newly proposed DSC-based approach. DSC profiles using several heating rates were measured and analyzed. As a result, it was found that the extrapolated onset temperature, the peak temperature, and the extrapolated end temperature of the endothermic peak were proportional to the square root of the DSC heating rate. For lower heating rate, the temperature–axis intercept of the relationship between the square root of the heating rate and the peak temperature can be regarded as the liquidus temperature under equilibrium conditions with better accuracy. For higher heating rate, the temperature–axis intercept of the relationship between the square root of the heating rate and the extrapolated end temperature can be approximately estimated as the liquidus temperature of noneutectic lead-free solder under equilibrium conditions.

Physical Aging of Amorphous Fructose

ABSTRACT: Physical aging of amorphous anhydrous fructose at temperature 5 °C and at 22 °C was studied using differential scanning calorimetry (DSC). The dynamic glass transition temperature, Tg0 for unaged samples was 16 °C and 13.3 °C for heating rate of 10 °C/min and 1 °C/min, respectively. The fictive temperature, Tf0 for unaged samples calculated by Richardson and Savill method was 12 °C, which is close to the dynamic value obtained from the lower DSC heating rate. The fictive temperature Tf of the aged fructose glasses at temperatures both below and above the transition region was fitted well by a non‐exponential decay function (Williams‐Watts form). Aging above the transition region (22 °C) for 18 d increased both the dynamic glass transition temperature Tg and the fictive temperature Tf. However, aging below the transition region (5 °C) for 1 d increased the dynamic glass transition temperature Tg but decreased the fictive temperature Tf.

Macromolecular Characteristics of Natural Organic Matter. 1. Insights from Glass Transition and Enthalpic Relaxation Behavior

This is the first of a series of papers focusing on an experimental investigation of mechanisms contributing to the sequestration of hydrophobic organic compounds (HOCs) by macromolecular natural organic matter (NOM). It presents the results of a detailed study by differential scanning calorimetry (DSC) of NOM-related glass transition and enthalpic relaxation phenomena. Parallel measurements for model synthetic organic macromolecules of well characterized structure provide a basis for interpretation of the observed behaviors of the structurally heterogeneous and relatively ill-characterized natural organic materials investigated. The effects of varied DSC heating rates reveal transition temperature and enthalpic relaxation responses consistent with the Gibbs-Dimarzio glass transition theory, thus providing definitive evidence to support our earlier reports of the occurrence of glassy/rubbery state transitions in NOM macromolecules. Quantification of maximum changes in heat capacity for enthalpic relaxatio...

Study of multiple melting behaviour of syndiotactic polystyrene in ?-crystalline form

A series of syndiotactic polystyrene (SPS) samples in β-crystalline form were prepared by cooling from the melt at various rates. The effects of cooling rate from the melt, DSC heating rate and annealing on the multiple melting behaviours of β crystals were investigated by differential scanning calorimetry (DSC) and temperature modulated differential scanning calorimetry (TMDSC), from which the nature of the multiple melting behaviour was determined. The two melting endotherms of β-form crystals were considered to arise from the occurrence of simultaneous melting, recrystallization and remelting processes in the melting region. It is suggested that the lower melting endotherm is due to the melting of imperfect β crystals originally present in the sample, whereas the higher melting endotherm comes from the melting of recrystallized SPS crystals, ie more perfect β crystals that formed during the DSC scanning process. © 2000 Society of Chemical Industry

Melting behavior of poly(butylene succinate) during heating scan by DSC

The melting behavior of isothermally crystallized poly(butylene succinate) (PBS) has been investigated using differential scanning calorimetry (DSC) and wide-angle X-ray analysis. The samples crystallized between 80°C to 100°C show middle endotherm at the position just before the high exotherm, while the others under 80°C show two endotherms (low and high). From the results of the melting peak vs. crystallization temperature plot, it was suggested that the middle endotherm corresponds to the melting process of the original crystallites and the high endotherms to the melting process of the recrystallized ones. As the DSC heating rate was increased, the peak temperature of the low and middle endotherms increased and that of the high endotherm decreased, indicating that the low endotherm was due to the original crystallites as well as the middle endotherm. Consequently, in the heating scan of PBS, the existence of two kinds of morphologically different crystallites as well as the process of melting and recrystallization becomes evident. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1357–1366, 1999