Calorimetric measurements of sodium chloride dihydrate NaCl·2H2O (mineral name hydrohalite) were carried out with using DSC. Heat capacity from 190 to 250 K was measured and found to increase from 109 to 137 J mol?1 K?1. The enthalpy of formation of hydrohalite from solid ice and halite at 273.15 K was derived from the thermal effect of melting/decomposition in DSC measurements and found to be close to ??1.8 kJ mol?1. The same DSC results show clearly that the upper temperature limit for the existence of hydrohalite is several degrees greater than the current value of 273.15 K accepted for the peritectic decomposition of hydrohalite. The phase diagram of the NaCl–H2O system needs correction.
相似文献Hydronic snow melting systems are renewable and reliable to eliminate the slippery conditions on the road. In this study, a hydronic snow melting system was implemented in Harbin, China. The characteristics of porous snow were applied to develop a transient two-dimensional model, according to the experimental results. It is the first time that the snow microstructure was considered in the model for the hydronic snow melting system. Three parameters (embedded pipe depth, embedded pipe spacing, and supplied fluid temperature) were compared and analyzed to optimize the design of the hydronic snow melting system in the cold regions. The results indicated that the snow can be cleared in 4.5 h regardless of the fluctuation of parameters. The rank of influence degree was embedded pipe depth?>?supplied fluid temperature?>?embedded pipe spacing when the target was the maximum melting rate. However, the rank of influence degree changed as supplied fluid temperature?>?embedded pipe depth?>?embedded pipe spacing when the target was the average road surface temperature at the heating time of 6 h. The embedded pipe design should be the embedded pipe depth of 80 mm and embedded pipe spacing of 140 mm at the effects of thermal stress and pipe cost. The control strategy was that the supplied fluid temperature should be 298.15 K in the heating period of 0–1 h, then gradually increased to 308.15 K in the heating period of 1–4 h, and eventually decreased to 298.15 K in the heating period of 4–6 h to save energy. This work can offer a good reference for the optimization and design of hydronic snow melting systems in cold regions.
相似文献Polyurethane elastomers (PUR) based on polypropylene glycol and 4,4′-diphenylmethane diisocyanate were prepared with various monoethylene glycol (mEG) contents. The aim of this study is to find a reliable polymer matrix for composites of improved thermal conductivity and testing fully in order to collect knowledge about its structure. Thermal conductivity was improved from 0.255 to 0.329 W m?1 K?1 when increasing chain extender content. This attributed to a high appearance crystalline ordering level when adding high mEG content. Differential scanning calorimetry revealed a low transition temperature of soft segment at the same temperature around ??64 °C, due to constant polyol content. The enthalpy of melting increases with increasing mEG content. This is due to the increasing crystalline phase and hard segment phase separation within the PUR structure. Dynamic mechanical analysis results show the glass transition temperature of soft segment in the same temperature range between ??57 and ??52 °C and intensity peak of tanδ tends to decrease when mEG content was increased. On the other hand, the glass transition temperature of hard segment tends to increase from 10 to 93 °C and has high intensity peak of tanδ with increasing mEG content. Increasing the chain extender content can be enhancing the hard segment length in PUR structure and affecting both soft segment motion and hard segment motion. Increasing hard segment length might be obstructing soft segment motion and influence hard segment motion which is hard to move at low temperatures. Phase separation of soft and hard segment clearly observed using the DMA technique.
相似文献The combustible features of wheat dust easily induce a potential hazard in its processing and application. To clearly reveal the effects of porous mesh parameters on the flame propagation of wheat dust, a vertical combustion pipeline together with the data collecting by the high-speed photography and fine thermocouple was built. Results indicate that with the increase in the mesh scale, the dust combustion and peak temperature are intensified first and then decreased with a darker luminescence. The increasing mesh number shows an inhibition effect on both peak temperature and combustion pressure, but an accelerating first and then weakening effect on flame velocity. A smaller particle size contributes to a more complete combustion, causing a higher peak temperature and flame velocity. At the particle mass of 2.5 g, the maximum value of peak temperature, flame velocity and combustion pressure were obtained during the flame propagation.
相似文献Boron carbide (B4C) is one of the main products from the primary combustion of boron (B)-based propellants and has a significant influence on the secondary combustion of B. To systematically evaluate its effects on the secondary combustion of B, mixtures of B4C and B in different mass ratios were prepared. To study the ignition temperatures and combustion flames of the samples, a xenon lamp ignition experimental system and a flame shape test system were designed, respectively. A thermogravimetry–differential scanning calorimetry–Fourier transform infrared spectroscopy combined thermal analysis system was used to study the thermal oxidation characteristics and analyze the gaseous products of the samples. The results indicate that B4C reduces the heat absorption at the beginning of the ignition, but subsequently prevents the rapid rise of sample temperature. During the stable combustion stage, the maximum flame length under optical density 10−4 (OD4) filter was 20.4 mm, and the maximum flame length under 580 nm + OD4 filters (represents the combustion of B element) was 16.7 mm. The samples contained a small amount of HBO2 and H3BO3, which led to slight mass loss during the low temperature section of the thermal oxidation process. During the high temperature section, the oxidation of B and B4C caused considerable mass gain. The gaseous products of the thermal oxidation process include CO2, CO, and H2O. In general, the B content of 60% was the most beneficial to decrease the oxidation temperature, increase the combustion intensity, and improve the heat-releasing ability of the samples.
相似文献The factors affecting the ignition temperatures of two low-rank coals were experimentally studied using thermogravimetric analysis. The experiments were conducted with coal powders of four different particle size distributions. The thermogravimetric analyzer was operated at three heating rates, 10, 20, and 30 °C min?1 and four oxygen concentrations of 3, 6, 9, and 12%. The results showed that the ignition temperature decreased by about 25 °C as the oxygen concentration increased from 3% to 12%. The standard deviation of the activation energy was 16.75% at a conversion degree of less than 0.4, and it decreased to 1.35% at the end of the combustion process. At a heating rate of 10 °C min?1, the ignition temperature increased by about 8 °C as the coal particle size increased by 100 μm. At a heating rate of 30 °C min?1, the effect of the particle size on the ignition temperature was enhanced and the ignition temperature increased to 15 °C.
相似文献Differential scanning calorimetry (DSC) technique has been applied for the experimental determination of temperature and heat of phase transition of pure silicon (7 N) during heating and cooling cycles at the rate of 10 K min?1. The measurements were carried out in the temperature range of 25–1450 °C in a flow gas atmosphere (Ar, 99.9992%) using three types of crucibles made of alumina, h-BN and alumina covered with h-BN coating. The following characteristics were estimated from DSC curves: melting point of silicon—1414 °C, the heat of fusion—1826 J g?1 and the heat of solidification—1654 J g?1. It was found that the silicon evaporation phenomenon accompanying the tests had no effect on the measurements of temperature during solid-to-liquid and liquid-to-solid transformations and on the measurement of the latent heat of fusion. The effect of crucible type on the DSC measurements is discussed.
相似文献New poly(aryl ether ketone)s (PAEKs) with a low melting temperature (relative to PEEK) are of interest in order to simplify the manufacturing of high-performance polymers or composites. In this study, we propose to investigate the physical properties of a new PAEK from Victrex, namely PAEK LM. Combinations of thermal analyses were used as follows: standard and modulated temperature differential scanning calorimetry, dynamic mechanical analysis, dynamic dielectric analysis and guarded hot plate technique. We found that the global mechanical, dielectric and thermal properties are very similar to the PEEK reference. The glass transition temperature was observed in the same range than PEEK (∼ 150 °C) while the melting temperature Tm was measured at 307 °C for PAEK LM which is about 35 °C below the melting temperature of PEEK. The degree of crystallinity of PAEK LM was found to be 27% while for PEEK it is 38%, depending on the processing conditions. This work explored crystalline structure–property relationships to explain the behaviour of PAEK LM.
相似文献In this study, tetradecanol–palmitic acid/expanded perlite composites containing carbon fiber (TD-PA/EP-CF CPCMs) were prepared by a vacuum impregnation method. Binary eutectic mixtures of PA and TD were utilized as thermal energy storage material in the composites, where EP behaved as supporting material. X-ray diffraction demonstrated that crystal structures of PA, TD, EP, and CF remained unchanged, confirming no chemical interactions among raw materials besides physical combinations. The microstructures indicated that TD-PA was sufficiently absorbed into EP porous structure, forming no leakage even in molten state. Differential scanning calorimetry estimated the melting temperature of TD-PA/EP-CF CPCM to 33.6 °C, with high phase change latent heat (PCLH) of 138.3 kJ kg−1. Also, the freezing temperature was estimated at 29.7 °C, with PCLH of 137.5 kJ kg−1. The thermal cycling measurements showed that PCM composite had adequate stability even after 200 melting/freezing cycles. Moreover, the thermal conductivity enhanced from 0.48 to 1.081 W m−1 K−1 in the presence of CF. Overall, the proposed CPCMs look promising materials for future applications due to their appropriate phase change temperature, elevated PCLH, and better thermal stability.
相似文献Solution-state nitroso monomer-azodioxide equilibria and conformational freedom of several aromatic dinitroso derivatives, differing in the spacer group between the aromatic rings, were studied by one- and two-dimensional variable temperature 1H NMR spectroscopy and by quantum chemical calculations. The proton signals of nitroso monomer-azodioxide mixtures revealed by low-temperature NMR were assigned and validated using B3LYP-D3/6-311+G(2d,p)/SMD level of theory. In almost all cases, a preference towards the formation of only one azodioxy isomer of aromatic dinitroso compounds was found, which was assigned to Z-dimer according to computational data. Nevertheless, the computed small energy difference between the Z- and E-isomer could not account for the extreme preference for Z-dimer formation, indicating an influence of entropic or solvent effects. The formation of shorter oligomers in solution was excluded based on integrated 1H NMR signal intensities. The experimental results indicated an average dimerization Gibbs energy of about ??5 kJ/mol at 223 K and were found to be in very good correlation with dimerization energies obtained by solution-phase optimization.
相似文献The present work presented a synthesis of silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) using the aqueous extract of waste banana stem (WBS), Musa paradisiaca Linn. The reduction and formation of MNPs have been characterized by several analysis techniques such as X-ray diffraction (XRD), Fourier transmission infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The techniques showed that average particle size of WBS-AgNPs and WBS-AuNPs in crystalline nature was in ranges of 7–13 nm and 11–14 nm, respectively. The synthesized nanoparticles were used to evaluate antibacterial activity and catalysis. The WBS-AgNPs showed strong antibacterial activity against B. subtilis and E. coli. The largest zone of inhibition against B. subtilis (14.2 mm) and E. coli (9.3 mm) was found at concentrations of 4.0 ppm and 2.0 ppm, respectively. The excellent catalytic application of both the nanoparticles for the reduction of 4-nitrophenol was confirmed via study on their kinetics. The normalized kinetic constants (knor) of WBS-AgNPs and WBS-AuNPs were found to be 1.72?×?10–3 s?1 mg?1 and 2.45?×?10–3 s?1 mg?1, respectively.
相似文献A kind of pavement crack repairing material with temperature regulation property was successfully prepared through one-step method, in which the paraffin was incorporated into the polyurethane/epoxy resin-interpenetrating polymer networks. Differential scanning calorimeter results indicated that the phase-change latent heat of sample A was 14.4 kJ kg?1, and the phase transition temperature was ??0.3 °C. FTIR and thermogravimetry measurements verified that the paraffin was successfully incorporated into the interpenetrating polymer network without leakage and reacted with the carrier, which exhibited high thermal stability above 300 °C. After 1 year of road test, there was no breakage for the repairing pavement with paraffin–polyurethane/epoxy resin-interpenetrating polymer networks, and there was almost no change for the accumulated attenuation of phase-change latent heat. Therefore, the materials of paraffin–polyurethane/epoxy resin-interpenetrating polymer networks have good chemical stability and thermal stability.
相似文献The thermal stability of HMT under dynamic, isothermal and adiabatic conditions was investigated using differential scanning calorimeter (DSC) and accelerating rate calorimeter (ARC), respectively. It is found from the dynamic DSC results that the exothermic decomposition reaction appears immediately after endothermic peak, a coupling phenomenon of heat absorption and generation, and the endothermic peak and exothermic peak were indentified at about 277–289 and 279–296 °C (Tpeak) with the heating rates 1, 2, 4 and 8 °C min−1. The ARC results reveal that the initial decomposition temperature of HMT is about 236.55 °C, and the total gas production in decomposition process is 6.9 mol kg−1. Based on the isothermal DSC and ARC data, some kinetic parameters have been determined using thermal safety software. The simulation results show that the exothermic decomposition process of HMT can be expressed by an autocatalytic reaction mechanism. There is also a good agreement between the kinetic model and kinetic parameters simulated based on the isothermal DSC and ARC data. Thermal hazards of HMT can be evaluated by carrying out thermal explosion simulations, which were based on kinetic models (Isothermal DSC and ARC) to predict several thermal hazard indicators, such as TD24, TD8, TCL, SADT, ET and CT so that we can optimize the conditions of transportation and storage for chemical, also minimizing industrial disasters.
相似文献Dechlorination of eutectic LiCl–KCl based electrorefiner (ER) salt is reported via ion-exchange reaction with protonated ultrastable Y-type (USHY) zeolite bound into mechanically fluidized 45–250 μm diameter particles. Evidence of exchange of cations from the salt (Li+, K+, and fission product cations) into the zeolite lattice replacing H+ ions was found based on a change in unit cell size, ICP-MS, XRD and TEM–EDS in addition to detection of HCl off gas. Ion exchange reaction was carried out at 625 and 650 °C, temperatures above the melting point of eutectic LiCl–KCl. Experiments were carried out to optimize zeolite drying temperature, estimate maximum ion-exchange capacity, and determine the thermal stability of USHY zeolite. The results indicate over 90% dechlorination can be achieved without zeolite structure collapse at 625 °C. This provides a promising route to stabilizing waste from radioactive chloride salts into dechlorinated waste forms for permanent geologic disposal.
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