PREDICTION OF THE KINETIC PROPERTIES OF LOW-DENSITY POLYETHYLENE

The curing processing of fatty amine/epoxy resin was studied by non-isothermal differential scanning calorimetry (DSC) at different heating rates. The curing kinetics mechanism function and the kinetic parameters were determined using n order reaction and autocatalytic reaction and the model-free method. The curing processing was determined by extrapolation method. The results indicated that n order reaction model does not accord with the basic reaction characteristics of curing system. While the DSC curves from the autocatalytic model can well agree with that of experiment. The whole curing reaction process accords with the autocatalytic reaction model. The results by using FWO and FR method can also confirm that the curing reaction of resin system belongs to the autocatalytic model.

The Experimental data of Differential Scanning Calorimetry (DSC) under non-isothermal conditions of Xanthan gum biopolymer at different heating rates (2 ≤ β ≤ 10) are reported and discussed. From the heating rate dependencies of the glass transition temperature (Tg),the activation energy for glass transition (Eg) is determined by utilizing well known methods, Piloyan and Coats & Redfern. The methods of Piloyan and Coats & Redfern utilizes only one DSC curve at an arbitrary heating rate and these are compared with the multiple heating rate methods like, Kissinger and Ozawa.

The differential scanning calorimetry (DSC) curves for three commercial dentin and incisal porcelains fused-to metal were measured using high-temperature DSC. The glass transition temperatures (Tg) were determined from the DSC curves at heating rates of 7-20 degrees C/min, and the activation energy was derived from an Arrhenius plot of negative reciprocal Tg vs. logarithm of heating rate. The Tg of the dental porcelains depended on the content of aluminum oxide, whereas the activation energy depended on the content of sodium oxide. The ultra-low fusing type porcelains had a low activation energy due to the higher content of sodium oxide than the other porcelains.

The aim of this study was to determine selected thermal properties of cranberries based on DSC and TGA curves, and to compare the properties of fresh cranberries, the dry matter of cranberries, cranberries processed by hot‐air convective drying (HACD) at 80°C, and cranberries processed by microwave‐vacuum drying (MWVD) at 150 W. Thermal analysis techniques can be used to determine the thermal stability of fruits and indicate the best temperature of processing, which can minimize the thermal‐oxidative damage, as well as extend the shelf life of fruits. Dry matter of cranberries was analyzed at −30°C to 500°C. The first endothermic peak was determined at −14.7°C, the last endothermic peak at 362.3°C. The area under the DSC curve was 874.8 J/g, and mass loss was 64.70%. The temperature of the first and last endothermic peak was determined at 4.8 and 84.6°C (fresh fruits), −10.6°C and 86.0°C (HACD), 2.0°C, and 84.5°C (MWVD), respectively. The area under the DSC curve was determined at 4970.0 J/g (fresh fruits), 525.1 J/g (HACD), and 518.5 J/g (MWVD), and mass loss reached 65.54% (fresh fruits), 1.84% (HACD), and 4.27% (MWVD).Practical applicationsThe results of this study expand our knowledge about the thermal properties of the dry matter of cranberries, fresh cranberries, cranberries processed by hot‐air convective drying (HACD) at 80°C and by microwave‐vacuum drying (MWVD) at 150 W. Differential scanning calorimetry (DSC) proved to be a useful technique for determining the temperature of endothermic phase transition peaks and the area under the DSC curve of cranberries. Thermogravimetric analysis (TGA) supported the determination of mass loss during the measurements. Processing of food products, including drying can change their thermophysical and chemical properties. These changes can affect the thermal stability of dried products, which can be seen in the course of DSC and TGA curves. In this study, the temperature, at which the phase transitions of cranberries occur, was indicated. On this basis, the optimal processing temperature can be selected to preserve the berries content. The best temperature of fruit processing can minimize the thermal‐oxidative damage and extend shelf life of cranberries. Similar thermal stability of cranberries dried by hot‐air convection (HACD) at 80°C, and fruits dried by microwave‐vacuum (MWVD) at 150 W was found. The obtained findings can be further expanded by calculating the specific heat of cranberries.

Structural and thermal behavior of coal combustion and gasification byproducts: SEM, FTIR, DSC, and DTA measurements

Study on the influence of ageing on thermal decomposition of double‐base propellants and prediction of their in‐use time

Investigation on caloric requirement of biomass pyrolysis using TG–DSC analyzer

The melting and crystallization behavior of poly(L‐lactic acid) (PLLA; weight‐average molecular weight = 3 × 105) was studied with differential scanning calorimetry (DSC). DSC curves for PLLA samples were obtained at various cooling rates (CRs) from the melt (210 °C). The peak crystallization temperature and the exothermic heat of crystallization determined from the DSC curve decreased almost linearly with increasing log(CR). DSC melting curves for the melt‐crystallized samples were obtained at various heating rates (HRs). The double‐melting behavior was confirmed by the double endothermic peaks, a high‐temperature peak (H) and a low‐temperature peak (L), that appeared in the DSC curves at slow HRs for the samples prepared with a slow CR. Peak L increased with increasing HR, whereas peak H decreased. The peak melting temperatures of L and H [Tm(L) and Tm(H)] decreased linearly with log(HR). The appearance region of the double‐melting peaks (L and H) was illustrated in a CR–HR map. Peak L decreased with increasing CR, whereas peak H increased. Tm(L) and Tm(H) decreased almost linearly with log(CR). The characteristics of the crystallization and double‐melting behavior were explained by the slow rates of crystallization and recrystallization, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 25–32, 2004

Study on curing kinetics of diallyl-bearing epoxy resin using sulfur as curing agent

N-Nitrodihydroxyethyl dinitrate (DINA) is a useful energetic plasticizer in double-base propellant. To analyze the potential hazards of its thermal decomposition, the differential scanning calorimetry (DSC) was used to test the thermal behavior of DINA under non-isothermal and isothermal conditions. It is found from the non-isothermal DSC results, that the melting point of DINA is about 50 °C, the initial exothermic decomposition temperature (T onset) is between 177.46 and 189.60 °C with the heating rate 2, 4, 8 and 10 °C min−1, and its decomposition enthalpy (ΔH d) is about 3235.63 J g−1. Both the shapes of heat flow curves and activation energy curves, calculated by Friedman method, indicate the exothermic decomposition of DINA contains at least four reactions (P1–P4), which were separated into four curves by AKTS software according to the four peaks. The relatively constant E(α) of P1, P2, P3 and P4 verifies this four peaks are likely to be described by a single reaction model. The method proposed by ICTAC was used to determine the most suitable reaction function and kinetic parameters of DINA decomposition, the results show that P1 and P2 follow the Z–L–T model and the Avrami–Erofeev model, respectively, both of them are autocatalytic models, which is consistent with the isothermal DSC results. The reaction model of P3 cannot be obtained, while P4 corresponds to n-order reaction, f(α) = (1 − α)1.67.

This work estimates the magnitude of the effect of thermal inertia on the value of the activation energy determined from heat‐flux differential scanning calorimetry (DSC) data. The estimates are obtained via analysis of the literature data on crystallization of copper and thermal degradation of isotactic polystyrene (iPS). The copper crystallization data have been obtained for very large masses (200 mg) and fast heating rates up to 80 K min−1. The iPS degradation data have been collected on small masses (3 mg) and at the heating rates up to 20 K min−1. For crystallization of copper, the Kissinger activation energy obtained from the DSC data corrected for thermal inertia is 34% larger than the value estimated from uncorrected data. This difference drops to 8% and becomes statistically insignificant when the fastest heating rate used is decreased to 10 K min−1. For iPS degradation, the difference in the isoconversional activation energies estimated, respectively, from corrected and uncorrected DSC data is less than 3% and is not statistically significant. Overall, the effect of thermal inertia on the activation energy appears negligible provided that DSC measurements are conducted on smaller samples and at slower heating rates, that is, as advised by the International Confederation for Thermal Analysis and Calorimetry (ICTAC) recommendations. It is suggested that the difference in the activation energies should generally be within the typical 5‐10% uncertainty as long as the product of the time constant and the maximum heating rate does not exceed 2‐3 K.

The processing window is important for the semisolid processability of alloys. This study focusses on the kinetics of diffusion. It compares prediction of fraction liquid versus temperature taking into account both thermodynamic and kinetics, with experimental results from Differential Scanning Calorimetry (DSC) and Single Pan Scanning Calorimetry (SPSC). SPSC is a novel technique with an order of magnitude higher accuracy than DSC. A range of Al-Si binary alloys has been investigated. The studies reveal that the simulation results predicted by DICTRA (DIffusion-Controlled TRAnsformations) show the same pattern with experimental results in the relationship of fraction liquid-temperature. However, the SPSC results are closer to the prediction results than DSC curves even with the relatively large sample size associated with SPSC. This is potentially a significant result as conventionally one of the difficulties is predicting the liquid fraction versus temperature for the heating of a billet for semi-solid processing. DSC results are known to be unrepresentative because the heating rates which can be achieved in DSC are much lower than those in induction heating. In addition, the DSC results are dependent on sample size and heating rate. The long term aim is to gain confidence in prediction with software packages which will reduce trial and error.

Structural and calorimetric studies of two crystallization stages of Ag10As30S60 glassy alloys

A powder mixture of Al/TiO2/H3BO3 = 10/3/6 in molar ratio was used in this study to form the Al2O3–TiB2 ceramic composite via thermite reactions (combustion synthesis). As no combustion synthesis occurred for an unmilled sample in a furnace, the mixture was milled in a planetary ball-mill for various milling times, and the as-milled samples were in situ synthesized in the furnace at a heating rate of 10 °C/min. The differential scanning calorimetry (DSC) measurements were performed with the same heating rate on the unmilled and the as-milled samples to evaluate the influences of the milling on the mechanisms and efficiencies of reactions. Although no combustion synthesis occurred for the unmilled sample in the furnace, two exothermic peaks were detected in its DSC curve after the melting of the Al. For the as-milled samples, significant changes revealed in the DSC curves, suggest that the milling process before the combustion synthesis changed the mechanisms and efficiencies of reactions. In addition, the intensity and the temperature of the exothermic peaks in the DSC curves changed by increasing the milling time. According to the XRD analyses, by enhancing the milling time, the purity of the final products would increase, confirming that the efficiency of the reactions increased. Finally, the microstructures of the as-milled and as-synthesized samples were examined by a SEM, and it was shown that the morphology of the reactant powders was altered by increasing the milling time.

Ni/Al reactive multilayer foils were fabricated by cold rolling method and self-propagating reactions in these foils were investigated. A two-stage phase formation process was observed in the ignition experiment. The first step is the lateral growth of Al3Ni phase from isolated nucleation sites and the following coalescence into a continuous layer; the second step is the growth of such Al3Ni layers in the perpendicular direction of the interface until all Al is consumed. As there is still Ni available, Al3Ni will continuously react with Ni until no Ni is left, and the final reaction product turns out to be ordered B2 AlNi compound. X-ray diffraction (XRD) experiments showed that the reaction product of the cold rolled foil was the same as the physical vapor deposition (PVD) foil. The reaction process was studied by differential scanning calorimetry (DSC). Three peaks can be identified from the DSC curve. Cold rolled foils were heated to different peak temperatures obtained from DSC curve with the same heating rate as DSC. XRD results for such foils showed that the first two peaks were the exothermic formation of Al3Ni, while the last one was for the formation of AlNi. The enthalpy of the reaction for the cold rolled foil was calculated to be -57.5 KJ/mol, which was in good agreement with the formation enthalpy of AlNi (-59 KJ/mol). The reaction velocities of the first formation stage were measured to be 7mm/s for cold rolled foils, which were much smaller than the reaction velocities of PVD foils (which range between 1-30 m/s).