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[en] Highlights: • Simple oxidation process produces fibrous SiO2/SiC filler for epoxy composites. • Thermal conductivity and electrical insulation increased with treatment temperature (SiO2 thickness). • Thermal conductivity and electrical insulation of oxidized fiber composite higher than that of SiC-epoxy one. • Increased thermal conductivity due to improved interfacial interactions. - Abstract: SiO2/SiC core-shell hybrid was prepared by oxidation of silicon carbide fibers. The material was thermally oxidized to observe the oxidation layer on the surface of the silicon carbide. The electrical and thermal properties of the epoxy composites consisting of SiC or SiO2/SiC were investigated. The thermal conductivity of SiO2/SiC-epoxy composites increased with increasing oxidation temperature. The thermal conductivity of the SiO2/SiC-epoxy composite was higher than that of the SiC-epoxy composite. The surface resistance and breakdown strength of the epoxy composite containing SiO2/SiC increased after the thermal oxidation of SiC. The developed SiO2/SiC could be used for electronic packaging applications.
[en] Highlights: • First time investigation of thermal properties of metallic glass reinforced MMCs. • Flake arrangement within the composites was analyzed by micro computed tomography. • Layered flake arrangement leads to anisotropic thermal expansion behavior. • Measured results were compared with several thermo-mechanical models. - Abstract: Many efforts were made during the last years to utilize the superior properties of metallic glasses as reinforcements in metal matrix composites and several investigations were carried out to characterize composites’ mechanical properties. Since there is a complete lack of knowledge about their thermal properties, this work focuses on the thermal expansion behavior of metallic glass reinforced metal matrix composites produced via gas pressure infiltration. The aluminum alloy AlSi12 was used as matrix material. Metallic glass Ni60Nb20Ta20 flakes with different size ranges were taken as reinforcement and volume fractions in the range of 29–44% were studied. X-ray micro computed tomography (μCT) measurements were performed to investigate the reinforcement 3D-structure within the composite. The thermal expansion behavior depending on flake orientation within the composite was investigated by dilatometric measurements. Four thermal cycles were carried out between room temperature and 500 °C at a constant heating and cooling rate of 5 °C/min. Results show that thermal strain rather depends on flake size and orientation than on volume fraction. Further, the composites exhibit a distinct anisotropic behavior for the thermal expansion coefficient (CTE) due to a layered flake structure within the composite. Finally determined CTEs were compared with several thermo-mechanical models to study the underlying mechanisms of the composite behavior.
[en] Highlights: • The LDTR is a useful diagnostic for characterizing HME thermochemical behavior. • ANNM thermograms indicated sensitivity to varying HME composition. • ANFO measurements demonstrated sensitivity to fuel hydrocarbon volatility. • Mixture preparation time can be defined by studying vaporization effects on mass. - Abstract: Measurements were carried out to obtain thermal signatures of the most commonly used homemade explosive (HME) materials, i.e., ammonium nitrate/nitromethane and ammonium nitrate/No. 2 diesel fuel oil, using a novel laser-heating technique referred to as the laser-driven thermal reactor (LDTR). Experiments were performed for different compositions, initial masses, and steady-state temperatures, along with the effects associated with HME aging. For ammonium nitrate/nitromethane (ANNM), the NM/ANNM mass fractions investigated were 29% (stoichiometric value) and 14%; these experiments were with fresh mixtures. The 29% NM/ANNM mass fraction mixture was also aged to 3%. For ammonium nitrate/fuel oil (ANFO), a fresh stoichiometric FO/ANFO mass fraction of 6% was used initially, and aged mixtures were then investigated for mass fractions of 5.4%, 4.7%, 4.4%, and 3.7%. The results indicated that the LDTR thermograms (i.e., sample temperature change with time) for the mixed ANNM were different than the individual isolated components, and that the technique was sensitive to varying HME composition. In addition, changes in the thermograms as ANFO aged were attributed to the varying volatility of the fuel hydrocarbon fractions, and thus provide important information for forensics analysis as to the HME reactivity
[en] Highlights: • Porous MgO material with ultrahigh surface area was synthesized. • A composite PCM was prepared from PEG-1000 and the porous MgO. • The phase change temperatures and enthalpy of the composite were measured. • The composite PCM performed good shape-stabilized property. - Abstract: Mesoporous magnesium oxide (MgO) material was synthesized using an integration of the evaporation-induced surfactant assembly and magnesium nitrate pyrolysis. The as-prepared MgO material is well crystalline, and possesses three-dimensional interconnected mesopores and a surface area as high as 596 m"2/g. Using the porous MgO as a matrix and polyethylene glycol (PEG-1000) as the functional phase for heat energy storage, a shape-stabilized phase change composite of PEG/MgO was fabricated by an easy impregnation method. In the composite, mesoporous MgO material provides structural strength and prevents the leakage of the molten PEG during the phase change process. The compositions and microstructures of the PEG/MgO composite were determined by Fourier transformation infrared spectroscope (FT-IR), X-ray diffractometer (XRD), scanning electronic microscope (SEM) and thermogravimetric analyzer (TGA), respectively. The phase change properties of the PEG/MgO composite were determined by differential scanning calorimeter (DSC). The high heat-energy storage capability and good thermal stability of the composite enable it extensive applications in the future
[en] Highlights: • Two polymorphic forms of CoQ 10. • CoQ 10 forms eutectic mixture with LA. • Experimental and predicted values of eutectic points are 70% CoQ 10 at 37.93 °C and 87.7% CoQ 10 at 38.98 °C, respectively. • Attraction exists between CoQ 10 and LA molecules. - Abstract: Solid state characterization of coenzyme Q10 (CoQ 10) was carried out using differential scanning calorimetry (DSC), variable temperature X-ray diffractometry (VT-XRD) and hot/cold stage microscopy (H/CSM). It revealed that CoQ 10 exists in two polymorphic forms. The recrystallized samples of CoQ 10 melted at different temperatures either due to the wide crystal size variation or change in crystallinity. Further, the binary mixture of CoQ 10 and lauric acid (LA) formed eutectic mixture in the ratio 70:30 melting at 37.93 °C, which was close to the predicted eutectic composition of 87.7:12.3 melting at 38.98 °C. The values of actual liquidus temperatures for CoQ 10 are higher than the predicted liquidus temperatures. The experimental heat of fusion at eutectic point was less than the calculated heat of fusion. Activity coefficient of CoQ 10 in the binary mixture was less than unity, which indicates the attraction between the components of eutectic mixture
[en] Highlights: • Heat contents of Co_2Hf and CoHf_2 were measured by drop calorimetry. • Enthalpy of formation for Co_2_3Hf_6 was computed via first-principles calculations. • Co–Hf system was assessed by means of CALPHAD approach. • Order–disorder model is used to describe B2 (CoHf) and A2 (βHf). • Glass forming range of the Co–Hf amorphous alloys was predicted. - Abstract: Phase equilibria and thermodynamic properties of the Co–Hf system were investigated via calorimetric measurements, first-principles calculations and thermodynamic modeling. Heat contents of Co_2Hf and CoHf_2 were measured by drop calorimetry from 300 to 1200 °C. The enthalpy of formation for Co_2_3Hf_6 at 0 K was computed via first-principles calculations. Based on the experimental measurements and first-principles calculations from the present work and the literature, the Co–Hf system was assessed by means of CALPHAD (CALculation of PHAse Diagram) approach. The excess Gibbs energy of solution phases was modeled with Redlich–Kister polynomial. Sublattice models were employed to describe the homogeneity ranges of Co_2Hf, CoHf and CoHf_2. The order–disorder transition between B2 (CoHf) and A2 (βHf) phases was taken into account in the current optimization. Using the optimized parameters, glass forming range (GFR) of the Co–Hf amorphous alloys was predicted to be 15–75 at.% Hf, which is in satisfactory agreement with the experimental observation
[en] Highlights: • Vapor pressures of butoxy benzoic acid derivatives were measured. • Vaporization, sublimation and fusion enthalpies were derived. • Molar enthalpies of formation were measured by calorimetry. • Thermochemical data tested for consistency using additivity rules and computations. • Simple additivity method suggested for prediction thermochemical properties. - Abstract: Standard (p° = 0.1 MPa) molar enthalpies of formation at the temperature T = 298.15 K of the 2-, 3-, and 4-iso-butoxybenzoic acids were measured using the combustion calorimetry. Standard molar enthalpies of vaporization and sublimation were derived from the vapor pressure temperature dependencies measured by the transpiration method. Molar enthalpies of the solid state phase transitions were measured by the DSC. Thermodynamic data on alkoxy substituted benzoic acids available in the literature were collected and combined with own experimental results. This data set on alkoxybenzoic acids was evaluated by using quantum-chemical and group-additivity methods
[en] Temperature dependences of saturated vapor pressure for crystalline phases of 2-ethyl-4-pyridinecarbothioamide (ethionamide) and two parent compounds 2- and 4-pyridinecarbothioamide isomers were measured by the transpiration method. The results were used to determine the standard molar enthalpies, entropies and Gibbs energies of sublimation at T = 298.15 K. HYBOT descriptors application has shown an increase in the donor–acceptor ability of the molecules of the studied compounds to form hydrogen bonds to result in their crystal lattice energy growth. The obtained standard molar sublimation enthalpies have been compared with the literature results for 2- and 4-substituted pyridine isomers.
[en] The comment points out several mathematical shortcomings in the published paper by Lisa and coworkers, including the use of an incorrect form for the Redlich–Kister equation for a ternary system.
[en] Highlights: • Quinary LLE phase equilibria involving PEG 6000 + Na_2SO_4 + H_2O + glucose + ethanol. • Favorable partition coefficients of ethanol and glucose. • Satisfactory correlation of the LLE experimental data with the original NRTL model. • Root mean squared deviations (RMSDs) of less than 0.6%. - Abstract: Extractive fermentation processes involving aqueous two-phase systems (ATPSs) are considered as viable means of overcoming the problems associated with product inhibition. Practical development of these processes requires accurate knowledge of the liquid–liquid equilibrium (LLE) of the ATPS forming components alongside the substrate and product of the fermentation process. In this work, the quinary aqueous two-phase LLE of poly(ethylene glycol) 6000 + sodium sulfate + water in the presence of glucose and ethanol have been experimentally determined at 298.15 K using spectrophotometric methods. The resulting LLE data were then satisfactorily correlated by the non-random two-liquid (NRTL) activity coefficient model based on mass fractions. In doing so, the binary energy interaction parameters of the NRTL activity coefficient model were obtained and reported. Calculated RMS deviations below 0.6% demonstrate that the original NRTL activity coefficient model can accurately correlate the LLE data of the quinary aqueous biphasic system of interest.