查看更多>>摘要：The effects of Iodixanol contrast medium were studied on human blood samples with differential scanning calorimetry (DSC). Measurements on anticoagulated and non-anticoagulated samples revealed that the components of the plasma and serum turned into a thermodynamically less stable state in the presence of Iodixanol. The thermal parameters of the main transition peak changed in the same way for both the plasma and serum erythrocyte samples in the presence of Iodixanol. The T-max1 values of the main thermal transition were not dramatically different (similar to 70 degrees C). The T-max2 value of the peak at higher temperature range (similar to 80-85 degrees C) shifted considerably (by 3.97-4.89 degrees C) towards the lower temperature range, while the Delta H value showed a significant drop (similar to 61%) in the presence of higher concentration of Iodixanol. The results suggest that Iodixanol in blood samples can induce specific changes in the structure of blood components by altering the fundamental thermodynamic properties of the underlying biological system.
查看更多>>摘要：A new adamantane-based dicyanate ester has been synthesized. The kinetics of its thermal polymerization is studied by means of conventional and temperature-modulated differential scanning calorimetry. The kinetics is analyzed comprehensively by a combination of an advanced isoconversional and model-fitting method. Polymerization proceeds via transition from a kinetic- to diffusion-control regime, which becomes operative at the later stages of the process. The kinetically-controlled regime manifests itself as a quasi-one-step auto-catalytic reaction. A contribution of diffusion to the overall kinetic is accounted for by means of the Fournier model. The polymerization product possesses excellent thermal properties (the glass transition temperature of similar to 370 degrees C and 5% mass loss temperature of similar to 480 degrees C), which makes it a promising candidate for application in hot-section components for aerospace and military industry.
Nagrimanov, Ruslan N.Samatov, Aizat A.Solomonov, Boris N.
8页
查看更多>>摘要：In this work, an additive scheme for the estimation of solvation enthalpy of halogenated aliphatic hydrocarbons in n-heptane was developed. The proposed structural fragments for halogen group contributions are dependent on the nature of neighbouring atoms. A linear relationship between solvation and vaporization enthalpy at 298.15 K for mono- and di-alpha,omega-halogen aliphatic compounds was found. These relationships can be used for the quick estimation of standard vaporization and solution enthalpies at 298.15 K. Proposed approaches for estimation of solvation, solution and vaporization enthalpies at 298.15 K were verified by conventional methods. In most cases, absolute deviations between experimental and estimated values for halogenated aliphatic hydrocarbons do not exceed 1-2 kJ mol(-)(1).
查看更多>>摘要：The thermal behavior of bischofite waste and MgCl2 center dot 6H(2)O was investigated by thermogravimetric analysis-derivative thermogravimetry (TGA-DTG) and X-ray diffraction (XRD). TGA-DTG results showed that the pyrolysis behavior and weight loss of bischofite were different from those of MgCl2 center dot 6H(2)O due to large number of impurities. The effects of temperature, atmosphere, and heating rate on the pyrolysis mechanism and products of bischofite were studied in detail by using XRD. The pyrolysis temperature remarkably affected the pyrolysis products. The mixture of MgO and Mg(OH)Cl coexisted at high temperatures of 550 and 600 degrees C. However, the presence of MgCl2 was confirmed by calcination at 650 and 700 degrees C for 0.5 h except MgO. Through calcination at 700 degrees C for up to 2.0 h, the pyrolysis products of bischofite and MgCl2 center dot 6H(2)O were predominantly MgO, and the atmosphere had no effect on the content of MgO. Low heating rate was favorable for pyrolyzing bischofite into MgO, and the content of MgO reached 94.1% at the heating rate of 5.0 degrees C/min. After further purification by washing, the content of MgO in the final product increased to 99.0%. This study provided an effective route for the comprehensive utilization of bischofite resources in salt lakes.
查看更多>>摘要：Poly(ethylene glycol) (PEG) is used as phase change materials while the low thermal conductivity restricted the thermal storage efficiency. Incorporation of the metal particles (MPs) into PEG could enhance the thermal conductivity while the crystallization kinetic mechanism of the MP-filled PEG composites is altered. Flake MPs are characterized with layer structure and a large aspect ratio, while there are few research works related to the effect of flake MPs on the crystallization kinetic mechanism of flake MP-filled polymer composites. In this work, different micro flake copper (Cu) particles contents were introduced into the PEG matrix via the physical blending method. The Fourier transform infrared instrument (FT-IR) was used to characterize the chemical compatibility of the PEG/Cu composites. The differential scanning calorimetry (DSC) method was to characterize the crystalline kinetic mechanism of the micro flake Cu particle-filled polymer composites by using the isothermal model and non-isothermal model. It was found that the COC conformation of the confined PEG in the composites was altered, and more helical conformations were transferred from the zigzag conformations. The addition of the Cu particles in the PEG matrix enhanced the heterogeneous nucleation meantime hindered the diffusion of the PEG molecular chains. As a result, the crystallization rate of the PEG/Cu composites was optimized only when there was a middle Cu content in the PEG matrix (14.89 wt% in this work). Additionally, the PEG/Cu composites had 3D PEG crystal growth geometry in the isothermal crystallization process while the stronger dependence of the PEG crystal growth geometry on the temperature was found in the non-isothermal crystallization especially when the Cu amount was higher than 14.89 wt%.
查看更多>>摘要：The effect of Al and Ti ratio on glass forming ability and crystallization characteristics of the ball milled Zr-Al-TiCu amorphous alloy composite powders are systematically investigated. The evolution of crystallization phases for the studied alloys during ball milling is CuZr2 +Al2Zr+Ti(Al,Cu)(2) -> Al2Zr+Ti(Al, Cu)(2)+Fe1.945C0.055+Amorphous -> Amorphous+Fe1.945C0.055. However, the duration for the formation of amorphous phase is longer for high Al and Ti ratio alloy than for low Al and Ti ratio alloy. The thermal stability of low Al and Ti ratio amorphous alloy composite powders is lower than that of high Al and Ti ratio ones. The crystallization is more difficult for high Al and Ti ratio alloy composite powders than for low Al and Ti ratio ones. The crystallization mechanism for the two alloys nearly depends on the heating rates and the annealing temperatures. The detailed crystallization mechanism of isochronal and isothermal modes are discussed.
查看更多>>摘要：Accurate measurements of specific heat capacity for lipids as a function of temperature, C-p (T), are needed for modeling their crystallization behavior. Differential Scanning Calorimetry, DSC, has been the main technique to determine C-p (T) for numerous materials, including lipids. Key experimental conditions (heating/cooling ramps, sample size, purge gas, and temperature modulation) that affect the measured heat flow, from which C-p (T) is calculated, have been extensively discussed in the literature. Usually, DSC manufacturers provide procedures of what they consider to be the best experimental conditions to measure accurate C-p (T) values with the least uncertainties. The successive nature of these procedures requires the user to perform each step separately, which means that the user needs to take out the empty pan from the DSC furnace to load either the standard material (usually sapphire) or the sample and place it back again into the furnace. Following this method will result in a different pan placement on the sensor each time the DSC furnace is opened, which consequently will influence the heat flow signals. Utilizing the Guide to the Expression of Uncertainty in Measurements (GUM),this paper is intended to quantitatively evaluate the uncertainties in C-p (T) measurements due to the pan position on a heat-flux DSC sensor. Due to this effect, relative expanded uncertainty U values were similar to 1.5%, and at least 15-25% as a result of pan placement. The sapphire uncertainty values were much smaller than those from the trimyristin (MMM) sample. With the assistance of FEM simulation, the effect of the different thermal diffusivity of MMM and sapphire on the C-p (T) measurements is elucidated.
查看更多>>摘要：In this study we provide a multi-physical and multi-scale characterization of an organic Phase Change Material (PCM), i.e. hexadecane, for both its liquid and solid phase and during the phase transition. Macroscopic thermal and physical properties provided are density and viscosity in the liquid phase and thermal conductivity and heat capacity in each phase. Further macroscopic measurements were done by differential scanning calorimetry (DSC), which was used to obtain a first estimation of temperatures at which the solid/liquid phase transition occurs. DSC results present a thermal hysteresis between melting (T-m) and solidification (T-s) temperature. A similar hysteresis was also collected during rotational and oscillatory rheometry at the phase change, where T-s is found to depend on the applied cooling rate. Moreover, near T-s the forming solid structure is continuously affected by conditions imposed by the rheometer (i.e. applied shear rate or stress) and the breakage of crystals takes place even at the weak imposed stress tested (0.001 Pa). Beside the bulk behavior, the local melting and solidification were studied at microscopic scale through Raman spectroscopy. The local melting temperature is very close to what found by DSC and by rheometry. On the other hand, crystallization onset is found at higher temperatures for long waiting times, thus considerably reducing the thermal hysteresis. Finally, we highlight a key influence of interfaces on the phase transition. Variations in boundary conditions (thermal and/or kine-matical conditions) are found responsible for the way hexadecane's solidification occurs.
查看更多>>摘要：Thermal impedance spectroscopy (TIS) measurement was developed for thermal analysis of supercapacitors. Compared with previously reported TIS measurement methods, the specific heat flux path through the supercapacitor device can be manipulated under the experimental system equipped with cold and heat sources. Using complex notation, the thermal impedance was defined as the ratio of the measured temperature difference across the tested device to the imposed heat flux. Different from the performance of Li-ion batteries, the thermal impedance spectra of the tested supercapacitor showed two semicircles with different diameters. The negative real part of the thermal impedance in the high frequency region could be considered as a frequency-related phase delay caused by the time response of the thermocouples in the temperature measurement. In addition, heat capacities and thermal resistances of the active materials and the casing of the tested supercapacitor were derived by equivalent thermal RC circuit. Furthermore, the effect of environmental humidity on the thermal characterization of active materials was isolated from the thermal impedance spectra.
查看更多>>摘要：Benzoxazine is widely used in halogen-free copper clad laminate, printed circuit board and other fields in electronic information industry. However, its high curing temperature (about 250 degrees C) limits its future application. The effectiveness of benzoxazine catalyzed by transition metal p-toluenesulfonate(M(OTs)(n)) and linear phenolic resin(PF), separately and mixed, were studied by DSC. The curing mechanism, structural changes and curing kinetics of different catalytic systems was studied by In-situ FT-IR and nonisothermal Differential Scanning Calorimeter(DSC).The results show that M(OTs)n and PF can simultaneously exist in benzoxazine as catalyst, and the catalytic ability is the strongest. The kinetic data shows that the introduction of catalyst can change the curing reaction mechanism of benzoxazine from autocatalytic curing reaction model to n-order reaction model. It follows the n-order reaction kinetic model based on Malek and Friedman method, and the theoretical calculation curve is in perfect accordance with the experimental data.
NSTL
Elsevier