Differential Scanning Calorimetry Heat Flow Research Articles

T-history analysis of aspect ratio effect on subcooling and solidification behaviour of phase change material in vertical glass tubes

The study deals with the effect of the tube aspect ratio on subcooling and the solidification behaviour of phase change material using the T-history method and is compared with the differential scanning calorimetry analysis. Three tubes of different aspect ratios, l/d, and a constant length of 178 mm are chosen for this study. Infrared contour depicts that the inner surface of the glass tube and phase change materia initiate heterogeneous nucleation. The differential scanning calorimetry heat flow graph indicates a higher degree of subcooling than T-history method. The study of aspect ratio with and without insulation shows that the mean value of degree of subcooling is less in the insulated tube than non-insulated tube due to reduced cooling rate. The effect of the high aspect ratio is to increase the degree of subcooling due to increased cooling rate and, however, decrease the sensible heat discharge time to reach the plateau, tplt.

Thermodynamics and kinetic analysis of carbon nanofibers as nanozymes.

PurposeEvaluation of structural features, thermodynamics and kinetic properties of carbon nanofibers (CNFs) as artificial nanoscale enzymes (nanozyme).MethodsSynthesis of CNFs was done using chemical vapor deposition, and transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM) and energy-dispersive x-ray spectroscopy (EDX) were used to provide information on the morphology, elemental monitoring and impurity assay of the CNFs. The thermal features of the CNFs were evaluated using differential thermal analysis (DTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) derivative and TGA. The calculated thermo-physical parameters were melting temperature (Tm), weight loss maximum temperature (Tmax) and enthalpy of fusion (ΔHfusion). Catalytic activity was assayed by a 4-aminoantypyrine (4-AAP)-H2O2 coupled colorimetric system by UV-visible spectroscopy.ResultsFE-SEM and TEM analysis demonstrated parallel graphitic layers and uniformity of atomic orientation and morphology. The EDX spectra approved carbon element as major signal and presence of partial Ti as impurities of CNFs during CVD process. The DTA thermogram showed the endothermic process had a maximum temperature of 82.27°C at −15.48 mV and that thermal decomposition occurred at about 200°C. The TGA-differential gravimetric analysis thermogram showed that Tmax was 700°C. The DSC heat flow curve showed a melting temperature (Tm) of 254.52°C, ΔHfusion of 3.84 J^.g−1, area under the curve of 58.58 mJ and Te (onset) and Tf (end set) temperatures of 246.60°C and 285.67°C, respectively. The peroxidase activity of the CNFs obeyed the Michaelis–Menten equation with a double-reciprocal curve and the calculated Km, Kcat and Vmax kinetic parameters.ConclusionCNFs as peroxidase nanozymes are intrinsically strong and stable nanocatalysts under difficult thermal conditions. The peroxidase activity was demonstrated, making these CNFs candidates for analytical tools under extreme conditions.

Thermal Response and Degressive Reaction Study of Oxo-Biodegradable Plastic Products Exposed to Various Degradation Media

In this work, three plastic film products commonly used as commodity thermoplastic articles were analysed with the aim of characterizing their thermal behaviour and stability. The test specimens were subjected to a series of analytical tests to confirm their biodegradable nature. The specimens ranged between 30 and 70 μm in thickness and showed high concentrations of regulated metals, namely, lead (Pb), postchemical analysis which can lead to its migration to natural sinks. The specimens were also exposed to degressive media, namely, accelerated (UV induced) weathering and soil burial field testing. The weight loss measured exceeded 58% after soil burial indicating deterioration under natural environmental stressors. In addition, the thermal characterization campaign executed with the aim of determining the product’s thermal response followed internationally recognised experimental protocols for the determination of thermal stability. The methodology used followed the International Confederation for Thermal Analysis and Calorimetry (ICTAC) recommendation for thermal stability and the computation of kinetic parameters. The degradation reaction kinetics were also determined postexposure to degressive media. Thermogravimetric analysis coupled with differential scanning calorimetry heat flow analysis and Fourier infrared spectroscopy results was also used in studying the degradation behaviour of the specimens. Analytical kinetic estimation methods relying on model free solutions enabled the determination of the apparent activation energy (Ea) of the specimens postexposure to degradation media. A shift in the degradation mechanism was also detected after studying the kinetic parameters which showed a range of Ea between 86.64 and 226.90 kJ mol-1 depending on the type of specimens and exposure media. It can be concluded that the oxo-biodegradable films are well suited for thermal treatment in the future as discarded plastic solid waste (PSW) articles. This work also paves the way for developing national standards and future plans for societies burdened with PSW accumulation.

Thermodynamic Investigation of the Eutectic Mixture of the $$\hbox {LiNO}_{3}$$ LiNO 3 – $$\hbox {NaNO}_{3}$$ NaNO 3 – $$\hbox {KNO}_{3}$$ KNO 3 – $$\hbox {Ca}(\hbox {NO}_{3})_{2}$$ Ca ( NO 3 ) 2 System

Molten nitrate salt is usually employed as heat transfer or energy storage medium in concentrating solar power systems to improve the overall efficiency of thermoelectric conversion. In the present work, the liquidus curves of the $$\hbox {LiNO}_{3}$$ – $$\hbox {NaNO}_{3}$$ – $$\hbox {KNO}_{3}$$ – $$\hbox {Ca}(\hbox {NO}_{3})_{2}$$ system is determined by conformal ionic solution theory according to the solid–liquid equilibrium state of the binary mixture. The calculated eutectic temperature of the mixture is $$93.17\,{^{\circ }}\hbox {C}$$ , which is close to the experimental value of $$93.22\,{^{\circ }}\hbox {C}$$ obtained from differential scanning calorimetry (DSC). Visualization observation experiments reveal that the quaternary eutectic mixture begins to partially melt when the temperature reaches $$50\,{^{\circ }}\hbox {C}$$ , and the degree of melting increases with temperature. The mixture is completely melted at $$\hbox {130}\,{^{\circ }}\hbox {C}$$ . The observed changes in the dissolved state at different temperatures correlate well with the DSC heat flow curve fluctuations.

The impact of fragility on the calorimetric glass transition in bulk metallic glasses

The glass transition of bulk metallic glasses with various fragilities as well as strong oxide glasses is studied using differential scanning calorimetry (DSC). It is found that the liquid fragility determined from equilibrium viscosity measurements is very well correlated with the scaled maximum slope of the DSC heat flow during the glass transition. We compare the correlation found in this work and those correlations with fragility from previous studies on other classes of glass-formers and find that the slope, which describes the curvature of the enthalpy on a reduced temperature scale, is a quantity better correlated with fragility, as it reflects the timescale of the non-equilibrium relaxation and the distribution of relaxation times in the glassy state. The present findings are supported by a recent theoretical report for calculated enthalpy curves with different fragilities from a model of selenium using the enthalpy landscape approach.

Investigation of heat of biomass pyrolysis and secondary reactions by simultaneous thermogravimetry and differential scanning calorimetry

The heat of pyrolysis reactions is of great importance not only for its impact on biomass pyrolysis process but as a fundamental parameter for modelling biomass thermochemical conversion. Previously frequently-used technique that integrates DSC heat flow curves to determine the heat of pyrolysis actually presented the enthalpy change of pyrolysis within a temperature range. This enthalpy change in effect took no account of the sensible heat of the volatiles leaving the crucible before reaching the upper limit of the temperature range. This work was attempted to determine both the heat of biomass pyrolysis as a function of conversion ratios or temperatures and the heat of secondary reactions. To this end, the conventional simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC) technique was re-examined to investigate thermal behaviour of cellulose, xylan, lignin and four lignocellulosic biomass samples using a TG–DSC analyser. Selected samples around 3.3mg were thermally decomposed in a crucible either with or without a pierced lid at a heating rate of 10°C/min to a maximum temperature of 500°C. Specific heat capacities of all the original biomass and char samples were measured through DSC analyses. Temperature-dependent formulas were developed for extrapolating the specific heat of both biomass and char samples at high temperatures. The heat of pyrolysis as a function of conversion ratios was characterised by the derivative of the enthalpy change versus mass changes during pyrolysis. Thus-obtained heat of biomass pyrolysis represented the difference between the enthalpies of formation of the products and reactants at a specific temperature or conversion ratio instead of a temperature range. The results showed that the heat of pyrolysis reactions changed from high endothermic values, via moderately endothermic values and finally rapidly to high exothermic values as the conversion ratios increased. Linear relations were established between the heat of biomass pyrolysis and conversion ratios ranging from 0.2 to 0.8. The heat of secondary reactions was about 80–280J/g for cellulose and increased with conversion ratios up to 2500–4000J/g for the lignocellulosic biomass samples.

Measurement of kinetics and thermodynamics of the thermal degradation for charring polymers

This work was focused on developing and applying a systematic methodology for the measurement of kinetics and thermodynamics of the thermal degradation of polymeric materials. This methodology employed a simultaneous thermal analysis instrument capable of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). A numerical model was utilized to fit thermogravimetric data to obtain thermal degradation kinetics. This model was subsequently employed to analyze DSC heat flow and extract sensible, melting and decomposition reaction heats. The extracted set of kinetic and thermodynamic parameters was shown to simultaneously reproduce TGA and DSC curves. In the current study, this methodology was applied to polymers that produce a significant amount of carbon rich residue (char) upon thermal decomposition. The analyzed materials were a poly(methyl methacrylate)–poly(vinyl chloride) alloy (Kydex), polymerized diglycidylether of bisphenol A, poly(ethylene terephthalate), poly(paraphenylene terephthalamide) (Kevlar), polymerized bisphenol A cyanate ester, poly(phenylene sulfide), polyetherimide and poly(ether ether ketone). The materials that produced less than 40 wt.% of char upon decomposition were found to decompose endothermically. The materials whose char yield exceeded 40 wt.% were found to undergo an exothermic decomposition.

Measurement of kinetics and thermodynamics of the thermal degradation for non-charring polymers

A quantitative understanding of the processes that occur in the condensed phase of burning materials is critical for the prediction of ignition and growth of fires. A number of models have been developed to simulate these condensed phase processes. The main issue that remains to be resolved is the determination of parameters to be input to these models, which are formulated in terms of fundamental physical and chemical properties.This work is focused on developing and applying a systematic methodology for the measurement of kinetics and thermodynamics of the thermal degradation of polymers. Specifically, the polymers examined in this study are the following seven representative non-charring materials: poly(oxymethylene), poly(methyl methacrylate), high-impact polystyrene, polyamide 6,6, polypropylene, poly(lactic acid), and poly(acrylonitrile butadiene styrene). This methodology employs a simultaneous thermal analysis instrument capable of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). A numerical model is utilized to fit thermogravimetric data and obtain thermal degradation kinetics. This model is subsequently employed to analyze DSC heat flow and extract sensible, melting and degradation reaction heats. The extracted set of kinetic and thermodynamic parameters is shown to simultaneously reproduce TGA and DSC curves.

Inkjet printing of gadolinium-doped ceria electrolyte on NiO-YSZ substrates for solid oxide fuel cell applications

A sol–gel-based precursor solution of gadolinium-doped ceria (CGO) was developed for deposition by inkjet printing. A stable precursor was synthesised by dissolving stoichiometric amounts of cerium (III) acetate hydrate and gadolinium (III) acetate hydrate in propionic acid, and diluted to 0.75 M with 1-propanol. The sintering behaviour of the printed precursor was investigated. Since the commonly used method of dilatometry is only applicable to bulk samples, an alternative approach using Differential scanning calorimetry (DSC) has been explored. The sintering temperature of the printed precursor was estimated by subtracting contributions from energy stored due to heat capacity and activation energy of ionic mobility from the DSC heat flow signal. Based on this modelling it was found that the optimum sintering temperature of the acetate-based CGO precursor was 1100 ± 55 °C, a result independently confirmed by SEM imaging of printed precursor coating on NiO-YSZ cermet. A gadolinium-doped ceria (CGO) thin film was then directly deposited on a porous NiO-YSZ cermet anode composite by inkjet printing. After co-sintering, it was shown that crack-free and continuous coating thinner than 10 μm of CGO can be readily produced. These results suggest that the inkjet printing technique can be successfully implemented to fabricate a thin film of dense electrolyte (>98%) for solid oxide fuel cell (SOFC) applications.

Kinetics of primary crystallization of hypoeutectic amorphous Ni–P alloy studied by in situ ASAXS and DSC

The primary crystallization of amorphous Ni 83P 17 alloy was studied by in situ anomalous small-angle scattering (ASAXS) and differential scanning calorimetry (DSC). ASAXS, DSC and X-ray diffraction experiments show that only one process, the primary crystallization, proceeds at 250 °C for annealing times up to 18 h. The volume fraction and the average composition of the precipitating Ni-rich particles were determined from the ASAXS data. The volume fraction as a function of the annealing time was compared with the transformation rate determined from the DSC heat flow. The two methods differ significantly only for annealing times shorter than 100 min. The average particle composition differs from the final one also for this period. The Avrami plot is not linear for the integrated DSC heat flow, but it is linear for the volume fraction determined by ASAXS. The nucleation rate determined by ASAXS was used to calculate the extended volume in the Kolmogorov–Johnson–Mehl–Avrami theory. The ASAXS results are consistent with the KJMA theory. The primary crystallization of the amorphous Ni 83P 17 alloy proceeds by precipitation of Ni-rich particles by diffusion controlled mechanism and decreasing nucleation rate. The effective diffusion coefficient is close to that of B in the similar amorphous Fe–B alloy.

Solidification Curves for Commercial Mg Alloys Determined from Differential Scanning Calorimetry with Improved Heat-Transfer Modeling

An improved method is presented for determination of solidification curves, i.e., fraction solid vs temperature, for commercial Mg alloys using heat-transfer model (HTM) differential scanning calorimetry (DSC) curves. A better evaluation of the measured DSC heat flow signal is attained through an independent measurement of the time constant as a function of temperature for the applied equipment. A further improvement is achieved through a more impartial interpretation of the measured DSC curves. Both improvements enable a better desmearing of the DSC signal and reduce the error induced by the operator. Challenging Mg alloys could be appropriately handled by optimizing the tantalum encapsulation. Highly reproducible DSC-HTM solidification curves are determined for seven Mg alloys of the AZ and AM series. The results indicate a potential of this method for simple, fast, and reliable determination of solidification curves even for such very reactive alloys with high vapor pressure.

Comparison of TSSD results obtained by differential scanning calorimetry and neutron diffraction

Due to their low absorption cross-section for neutrons, Zr alloys are used for reactor core components. The terminal solid solubility (TSS) for hydrogen in these alloys is very low – in Zr–2.5 wt% Nb, used to fabricate pressure tubes for CANDU (CANDU–CANada Deuterium Uranium is a registered trademark of Atomic Energy of Canada Ltd.) power reactors, the TSS is ∼0.7 at.% H at 300 °C. The mechanical properties of the components may deteriorate when their hydrogen concentration exceeds TSS. Therefore, accurate values of the TSS are needed to assess the operating and end-of-life behaviours of these components. Differential scanning calorimetry (DSC) is used to measure the TSS of hydrogen in Zr alloys. Three distinct features are marked on a typical DSC heat flow curve when the material is being heated and the hydrides are dissolving; ‘peak temperature’, ‘maximum slope temperature’ and ‘completion temperature’. Usually, the maximum slope temperature, being about the average of the three temperatures, is interpreted as the TSS temperature for hydride dissolution ( T TSSD). A set of coordinated DSC and neutron diffraction measurements have been carried out to identify the features of the heat flow signal that closely correspond to the T TSSD. Neutron diffraction was chosen because hydrides generate distinctive diffraction peaks whose intensities approach zero at the transition temperature – an unambiguous indication of dissolution. Neutron diffraction shows that the temperature of hydride dissolution correlates closely with the DSC peak temperature.

Effect of aging on glass transformation measurements by temperature modulated DSC

Differential scanning calorimetry (DSC) is a well established technique for studying the glass transformation behavior of glasses and for measuring the glass transition temperature T g and the relaxation enthalpy Δ H g. However, T g and Δ H g measurements on glasses from DSC heating scans depend on the thermal history and aging (annealing time at a given temperature below T g) which makes it difficult to compare measurements on a given glass from different laboratories and also examine small changes in T g and Δ H g due to small changes in the glass composition. We have performed both temperature modulated DSC (TMDSC) and conventional DSC experiments to study the dependence T g , complex heat capacity C p and relaxation enthalpy Δ H g on aging for vitreous Se alloyed with 0.5% As (a-Se:0.5%As). We have studied the behavior of the TMDSC total, reversing and nonreversing heat flows and the DSC heat flow as the glass is heated from 20 °C to a temperature above the glass transition temperature. We observe that TMDSC T g has a much smaller dependence on the aging time than DSC T g measurements and, therefore, TMDSC results are particularly useful for T g comparisons of glasses with unknown thermal history and aging characteristics. The change in TMDSC T g was almost ten times smaller than the DSC T g change over an aging time of 100 h. We observe that the apparent relaxation enthalpy Δ H g as measured by conventional DSC, reversing and total heat flows in TMDSC increases with the aging time. If we analyze the long time relaxation in terms of stretched exponential behavior we find β values in the range 0.39–0.43.

Aging behaviors of alumina borate whisker reinforced AC8A-AI composite

The aging behavior of alumina borate whisker (Al18B4O33w/AC8A-Al) composite was examined by hardness and differential scanning calorimetry heat flow measurement. Microstructures were investigated by transmission electronic microscope. The results indicated that the interfacial reaction played an important role in the aging precipitation behavior of the composite. As the interfacial reaction between the whiskers and AC8A-Al alloy consumed the Mg atom of the matrix in the composite, the time to the peak aging of the composite was almost same as that of the AC8A-Al alloy. The free precipitation zone can be found nearby some whisker in the composite, duo to Mg content decreased in the matrix.

Anhydride and diamine epoxy–Kevlar composites: thermal and dynamic‐mechanical properties

Differential scanning calorimetry (DSC) and dynamic–mechanical thermal analysis techniques have been used to characterize different Kevlar–epoxy composites. Tetrafunctional aliphatic amine and anhydride–diglycidyl epoxy have been used as matrix, and different quantities of continuous Kevlar fibers as reinforcement. Kevlar fibers had different effects on curing kinetics and final thermal properties depending on epoxy matrix type. As Kevlar content increased DSC heat flow curves shifted to much lower temperatures in the anhydride matrix case, while there was very little difference in the diamine–epoxy one. A significant decrease in the glass transition temperature (Tg) was observed as Kevlar content increased when anhydride matrix was used, while little change was observed in the reinforced diamine systems. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal scans. The main dynamic–mechanical relaxation and its evolution versus frequency with fiber addition was studied. An important shift to high frequencies was observed in the anhydride system. Copyright © 1999 John Wiley & Sons, Ltd.

Anhydride and diamine epoxy-Kevlar composites: thermal and dynamic-mechanical properties

Differential scanning calorimetry (DSC) and dynamic–mechanical thermal analysis techniques have been used to characterize different Kevlar–epoxy composites. Tetrafunctional aliphatic amine and anhydride–diglycidyl epoxy have been used as matrix, and different quantities of continuous Kevlar fibers as reinforcement. Kevlar fibers had different effects on curing kinetics and final thermal properties depending on epoxy matrix type. As Kevlar content increased DSC heat flow curves shifted to much lower temperatures in the anhydride matrix case, while there was very little difference in the diamine–epoxy one. A significant decrease in the glass transition temperature (Tg) was observed as Kevlar content increased when anhydride matrix was used, while little change was observed in the reinforced diamine systems. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal scans. The main dynamic–mechanical relaxation and its evolution versus frequency with fiber addition was studied. An important shift to high frequencies was observed in the anhydride system. Copyright © 1999 John Wiley & Sons, Ltd.

Enthalpy determinations and adsorption behaviour in the coal pyrite-sodium acrylate co-polymer system: effects of pH

Abstract The thermal oxidation of coal pyrite in an air atmosphere has been studied by differential scanning calorimetry (DSC) as a function of Magnafloc 74L addition and system pH. DSC heat flow curves show that the thermal oxidation of coal pyrite between 0° and 500°C is a three-stage exothermic process. Enthalpy data indicate that the adsorption of Magnafloc 74L at the coal pyrite-water interface is fundamentally different at pH 8 to that at pH 6 and 10. When considered in conjunction with electrokinetic (zeta potential) data, it is concluded that the anionic co-polymer adsorbs in an anionic form at pH 6 and pH 10, whereas at pH 8 adsorption is in the form of a non-ionic or charge reduced species.