Thermochimica Acta最新文献

Organic compounds can be used as temperature calibrants in fast scanning calorimetry. Their advantages include ease of surface cleaning of the calorimetric chip and good thermal contact with the chip surface. Among several compounds tested, benzoic acid was identified as a convenient and reliable calibrant for temperatures below approximately 130 °C. However, organic calibrants often exhibit unusual heating rate dependencies of the onset temperatures of melting. This phenomenon can be semi-quantitatively explained by considering different heat flows within the sensor. Notably, the thermal resistance between the heater and thermopile, often overlooked, introduces an additional time constant that can sometimes result in a negative apparent thermal lag. In addition, the onset temperatures are influenced by factors such as sample position, thickness, surface wetting, and spreading. These factors limit the accuracy of transition temperature determinations to approximately ±1 K below 130 °C and ±5 K up to 220 °C.

This study aimed to clarify the secondary crystallization process of low-isotacticity polypropylene (LT-PP). LT-PP demonstrates an exceptionally low crystallization rate at room temperature, which is approximately 1/5000 lower than that of isotactic PP (iPP). During the secondary crystallization of LT-PP at 30 °C, the thickness of lamellar (c-axis) and a- and b-axes of crystallite size remained constant. In addition, no significant change was observed in the CC-C bending vibration. It seems that the direction of the CC-C molecular order is similar to the thickness direction. This vibration mode may be associated with changes in the thickness of the lamellae. To explain the log(t) dependence of crystallinity, the Seto–Frank model was employed.

The primary objective of this research is to explore the feasibility of synthesizing phase-pure perovskite SrSnO₃ doped with transition metals and to evaluate the potential of these products as high-temperature inorganic pigments. The initial step in preparing perovskite powders with the general formula SrSn_0.95M_0.05O_3-δ (M = Mn, Fe, Co, Ni) involved synthesizing SrSn_0.95M_0.05(OH)₆ followed by its thermal decomposition. The thermal decomposition processes and the reaction pathway for perovskite formation were analyzed using thermal analysis and X-ray diffraction analysis. Single-phase products of beige SrSn_0.95Fe_0.05O_3-δ and brown SrSn_0.95Co_0.05O_3-δ were successfully obtained by calcining the precursors at 1,100 °C. In contrast, brown SrSn_0.95Mn_0.05O_3-δ contained a phase impurity of SnO₂ and doping with Ni ions resulted in a phase mixture of SrSnO₃ and NiO. The pigment quality of the powders was assessed based on their color parameters, described using the CIE Lab system.

Epoxy/multilayer graphene (ML-graphene) composites were prepared using different curing agents to control the graphene dispersion by changing the curing reactivity. With increasing initial reactivity, the aggregation size of the ML-graphene decreased and their thermal conductivity increased. In particular, the thermal conductivity of the composite prepared with p-phenylenediamine showed a maximum value of 1.46 W/(m·K) at 25 wt% ML-graphene loading because of the highest initial curing reactivity. The application of a magnetic field led to graphene alignment along the applied field, resulting in two times higher thermal conductivity than that of the corresponding system without magnetic field. The relationship between the interfacial affinity for epoxy/graphene and thermal conductivity was also investigated. As a result, resulting in a biphenyl epoxy composite showed higher thermal conductivity (6.17 W/(m·K)) than that of the bisphenol-A epoxy composite. This is derived that the π-conjugated and planar structure of biphenyl epoxy can easily interact with the surface of graphene.

Ethanol is a promising sustainable fuel for its environmental friendliness and renewability. Due to the association effect in ethanol molecules, the particular behavior in isobaric heat capacity was explored by combining experimental and theoretical methods. Experimental isobaric heat capacity measurements of ethanol were performed over the temperature range from (298.15 to 573.15) K and at pressures up to 15 MPa in both liquid and vapor phases by a flow calorimeter. Different association schemes were combined respectively with PC-SAFT equation of state and SAFT-VR Mie equation of state to compare their accuracy in isobaric heat capacity prediction, and it could be concluded that two-site (2B) model was better than three-site (3B) model. It was also found that PC-SAFT equation of state was able to yield good results in predicting the isobaric heat capacity far from the saturated state and critical region, however, SAFT-VR Mie equation of state showed better prediction performance near the saturated state and critical region.