An analytical equation of state for water and alkanols

An analytical equation of state extended from statistical associating fluid theory (SAFT) is modified to describe the thermodynamic properties of fluids with high polarity such as water and alkanols up to the region close to the critical point. Five terms are used in the equation of state: the term for hard convex body, the term for dispersion energy, the term for the chain formation of hard convex body, the term for the change of the dispersion energy because of chain formation, and the term for dipole-dipole interaction. This equation of state is still called SAFT-CP (across critical points). Six fluids water, methanol, ethanol, 1-propanol, 1-butanol and 1-pentanol are used as examples. The new equation of state reproduces saturated pressures and densities in vapor-liquid equilibrium, critical properties (as temperature, pressure and density), and densities in the one-phase region with rational accuracies. The comparison of the calculated critical exponent β with the experimental one for methanol shows the improvement up to the region only with 20 K difference of temperature to the critical point. The result coincides with the estimation of the critical region on the basis of Ginzburg number and also with the available opinion that crossover methods and renormalization theories are necessary in the near-critical region.     

Application of time–temperature–stress superposition principle on the accelerated physical aging test of polycarbonate

The effect of physical aging on the polymer mechanical properties is very important for long‐term safety assessment of engineering application. In this paper, the physical aging tests of polycarbonate (PC) were conducted systemically under different temperature and uniaxial tensile stress level. It was shown that both temperature and stress have obvious accelerated effect on the physical aging of PC. The higher the temperature and stress level are, the faster the aging process is. To predict the long‐term behavior after physical aging using the short‐term test results of PC, the elongation‐at‐break was chosen as the index of the severity of physical aging. An Arrhenius‐type time–temperature–stress superposition principle (TTSSP) was proposed to evaluate long‐term performance using short‐term test data. Using the proposed method, time and cost can be dramatically reduced for the assessment of long‐term physical aging performance of polymeric material. POLYM. ENG. SCI., 55:2215–2221, 2015. © 2015 Society of Plastics Engineers     

Measurement of concentration profiles using confocal Raman spectroscopy in multicomponent polymeric coatings—model validation

Concentrations of the solvents were measured using confocal laser Raman Spectroscopy for two ternary systems, poly(styrene)—tetrahydrofuran—p‐xylene and poly(methyl methacrylate)—ethylbenzene—tetrahydrofuran, during drying at room temperature. The concentrations were compared with predictions of drying models, which utilize several existing theories for mutual diffusion coefficients for polymer solvent systems. Of the nine free volume parameters required to predict diffusion coefficients of binary systems, four for each of the four pairs studied here were estimated as suggested by the literature. Estimation was done by minimizing the difference between predictions of the model and experimental weight loss data for each binary pair. It is found that the predictions of the models which include cross term diffusion coefficients are in better agreement with measured concentrations than those which ignore the cross terms. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Diamagnetism of pyrolytic carbons

The temperature dependence of the diamagnetic susceptibility (DMS) of pure and boronated carbons has been investigated in the temperature range of 4.2–1000 K. A high DMS at low temperatures as compared to the exponentially small value predicted by available theories is explained by the effects of electron scattering on structural imperfections and their influence on energy spectrum “spreading” near the singular conical point.     

Thermodynamic study of surfaces of liquid polybutadienes and their interfaces with poly(dimethylsiloxane)

Surface tension of liquid polybutadienes (PBD) as well as interfacial tension between them and poly(dimethylsiloxane) (PDMS) were measured in the temperature range from 25 to 150°C. The measured pressure–volume–temperature (PVT) data were used for the determination of reduction parameters of pressure, volume, and temperature in several equations of state for polymers. The reduction parameters were used for the estimates of surface tension and compared with experimental data. Interfacial tensions were used to determine Flory‐Huggins interaction parameters using the Roe and Helfand theories for the system PBD‐PDMS. The results obtained using both the theories were somewhat different; the difference being the least with the segment chosen as a part of molecule containing 4–5 nonhydrogen atoms. Modifications of PBD that were investigated increase the density. Maleic ester end groups increase both surface tension and interfacial tension and bring a positive contribution to the Flory‐Huggins interaction parameter (to its enthalpic component), whereas the pending maleic anhydride groups have shown the opposite effect; their negative contribution to Flory‐Huggins parameters concerns mainly its entropic component. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of temperature,molecular weight,and molecular weight dispersity on the surface tension of polystyrene,polypropylene, and polyethylene. II. Theoretical

Experimental data for the surface tension of polystyrenes of different molecular weights (3400–200,000) and different molecular weight dispersities (1–3) and of different polyolefins are compared with the predictions of the Patterson–Rastogi and Dee–Sauer cell theories, which infer the surface tension from pressure–volume–temperature (PVT) data. PVT data for these polymers were obtained from the literature and experimentally and are fitted to the Flory–Orwoll–Vrij equation of state. Both theories predict that the surface tension will decrease linearly with increasing temperature and increase with molecular weight, thereby corroborating the experimental data. However, both theories underestimate the entropy change in the surface formation per unit area at a constant volume for low molecular weight and polydisperse systems and underestimate the effect of molecular weight dispersity on surface tension. Both theories feature two parameters, m and b, that quantify the enthalpic and entropic contributions to surface tension. The theoretical predictions are fitted to the experimental data for monodisperse polystyrene (with a molecular weight above the molecular weight of entanglement), polypropylene, and linear low‐density polyethylene to quantify the enthalpic contribution to surface tension. b is then evaluated as a function of molecular weight and molecular weight dispersity and is found to decrease with increasing molecular weight and to increase with increasing molecular weight dispersity, showing that end‐group excess at the surface has some effect on surface tension. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2201–2212, 2002     

人体血液灌注和代谢产热对低温手术过程的影响

使用有限元方法研究了人体血液灌注和代谢产热对低温手术过程中组织温度场的影响.结果表明：一旦引入上述两种因素的影响后,即相当于在经典的传热方程中增加了非线性热源项;该热源项的出现,明显减慢了低温手术过程中冷刀附近组织的降温速率,增加了局部位置组织经历的温度梯度;不仅减慢了冷刀周围组织冻结面的生长速度,而且减小了手术过程中冰球的最大半径.该结果对低温手术的临床应用具有参考价值.     

Effect of Creep of Ferritic Interconnect on Long‐Term Performance of Solid Oxide Fuel Cell Stacks

High‐temperature ferritic alloys are potential candidates as interconnect (IC) materials and spacers due to their low cost and coefficient of thermal expansion (CTE) compatibility with other components for most of the solid oxide fuel cells (SOFCs). However, creep deformation becomes relevant for a material when the operating temperature exceeds or even is less than half of its melting temperature (in degrees of Kelvin). The operating temperatures for most of the SOFCs under development are around 1,073 K. With around 1,800 K of the melting temperature for most stainless steel (SS), possible creep deformation of ferritic IC under the typical cell operating temperature should not be neglected. In this paper, the effects of IC creep behaviour on stack geometry change and the stress redistribution of different cell components are predicted and summarised. The goal of the study is to investigate the performance of the fuel cell stack by obtaining the changes in fuel‐ and air‐channel geometry due to creep of the ferritic SS IC, therefore indicating possible changes in SOFC performance under long‐term operations. The ferritic IC creep model was incorporated into software SOFC‐MP and Mentat‐FC, and finite element analyses (FEAs) were performed to quantify the deformed configuration of the SOFC stack under the long‐term steady‐state operating temperature. It was found that the creep behaviour of the ferritic SS IC contributes to narrowing of both the fuel‐ and the air‐flow channels. In addition, stress re‐distribution of the cell components suggests the need for a compliant sealing material that also relaxes at operating temperature.     

Demixing of Oxides under a Temperature Gradient

The microscopic mechanism of a demixing of binary oxide solid solution in an oxidizing atmosphere under a temperature gradient is investigated by the path probability method of irreversibly statistical mechanics. The problem is reduced to a steady-state metal ion transport under the coexistence of an oxygen partial pressure gradient and a temperature gradient. Calculations are performed under two different conditions: (i) demixing in a steady-state diffusion process under the two driving forces and (ii) a redistribution of constituent metal ions in a closed system under a given temperature gradient (Soret effect). The results can be interpreted as the superposition of the contributions of two driving forces plus a cross term which tends to zero as the driving forces become small. The difference between these two cases is discussed in detail and some controversies in the past work with respect to the difference are pointed out.     

Resistive phase transition of the superconducting Si(111)-([... formula ...])-In surface

Recently, superconductivity was found on semiconductor surface reconstructions induced by metal adatoms, promising a new field of research where superconductors can be studied from the atomic level. Here we measure the electron transport properties of the Si(111)-(7×3)-In surface near the resistive phase transition and analyze the data in terms of theories of two-dimensional (2D) superconductors. In the normal state, the sheet resistances (2D resistivities) R_□ of the samples decrease significantly between 20 and 5 K, suggesting the importance of the electron-electron scattering in electron transport phenomena. The decrease in R_□ is progressively accelerated just above the transition temperature (T_c) due to the direct (Aslamazov-Larkin term) and the indirect (Maki-Thompson term) superconducting fluctuation effects. A minute but finite resistance tail is found below T_c down to the lowest temperature of 1.8 K, which may be ascribed to a dissipation due to free vortex flow. The present study lays the ground for a future research aiming to find new superconductors in this class of materials.     

Diffusion of Oxygen in Vitreous Silica

The diffusivity of the oxygen ion in vitreous silica has been directly determined by exchange measurements employing the stable isotope ¹⁸O and mass spectrometer analysis. It was found that over the temperature range 925° to 1225°C the results can be represented by the equation D = 1.51 × 10⁻² exp (-71,200/ RT ) cm² sec⁻¹. These results are compared with other measurements of oxygen diffusion in silicate glasses. It is proposed that the controlling diffusion step in silicate glasses and nonstoichiometric silica is the rupture of a single oxygen bond to silicon and that the diffusion mechanism is interstitial motion through voids in the lattice. An analysis of theoretical expressions for the pre-exponential term D _O shows that present theories are unable to predict D _O for oxygen diffusion in glasses. It is also shown that the mechanism for electrical conduction in vitreous silica or in electrolytically purified quartz is not migration of oxygen ions.     

Prediction of creep of polymer concrete

Polymer concrete possesses viscoelastic properties conditioned by relaxation processes in the polymer binder. Their acceleration with an increase of temperature (principle of time–temperature equivalence) is used in predicting the long‐term creep of polymer concrete. Physical aging of the polymer binder influences the creep of polymer concrete. To predict the long‐term creep accounting for the aging process, an attempt to improve the time–temperature equivalence principle was undertaken. As a result of the experimental study of polyester resin‐based concrete and its structural components (a resin unfilled and filled with diabase flour), it has been established that the changes in the creep compliance of the material follow according to the principle of the time–aging time equivalence with the reduction function depending on aging temperature. To predict the long‐term creep of polymer concrete, a function of the time–temperature–aging time reduction was applied. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1949–1952, 1999     

Nonisothermal electrochemical cell for monitoring hydrogen or oxygen in high temperature water

A nonisothermal, solid state electrochemical sensor for monitoring hydrogen or oxygen dissolved in high temperature (to about 500 K) water is described. Nafion^® in the form of tube was used as the electrolyte. The reference electrode at ambient temperature and pressure was a saturated aqueous solution of Fe²⁺ and Fe³⁺ sulphates. Sensor voltage measurements with dissolved hydrogen showed good reproducibility and long term stability. A regression equation for the hydrogen concentration related to cell voltage and water temperature was derived. Sensor voltage measurements with dissolved oxygen showed relatively poor reproducibility and long term stability. This is attributed to the greater complexity of electrode reactions involving oxygen and water.     

Perturbation techniques for accelerated convergence of cyclic steady state (CSS) in oxygen VSA simulations

Non-isothermal PSA bulk gas separations are notoriously slow to converge to cyclic steady state (CSS). Most numerical simulators that model the slow transient behaviour of these processes share this slow pace of convergence. This difficulty with numerical simulators has long been recognised, and has hampered the optimisation of oxygen VSA.This paper outlines the application of perturbation techniques to enable more rapid determination of CSS temperature profiles. A number of different techniques are proposed. The simplest approach based on experimental observations involves a two-time-scale decomposition of the adsorbent temperature profile. This decomposition of the temperature term enables the rapid numerical determination of the fast (or adsorptive) component of the temperature, followed by the direct determination of an estimated cyclic steady-state slow time-scale (or convective) temperature. It is demonstrated that this approach is the same as a zeroth-order multiple scale analysis (MSA) approach and a simple application of the Krylov-Bogoliubov (K-B) method of averaging. This study compares the results of this acceleration technique for determining CSS with a full numerical model. The results indicate that the proposed acceleration technique based on perturbation methods provides fast and reasonable estimates of the CSS temperature profile with some limitations. Recognising these limitations of the zeroth-order approach, a first-order MSA is developed. This compares better with full numerical simulations, and could be used to augment and complement existing acceleration techniques. It is shown that a first-order MSA approach can also be used to capture the dynamic temperature response of the oxygen VSA process, in addition to the CSS axial temperature profile.The perturbation techniques presented here are limited to a series expansion of the temperature term in the energy balance, and mass balance is ignored in this analysis. A procedure is outlined where a K-B approach can be used to incorporate a perturbation series expansion in the mass balance. We show that these perturbation techniques not only offer potential for simulation acceleration, but also offer useful insights into the thermal convergence to CSS in oxygen VSA.     

Changes in the Mechanical Sensitiveness of Explosives as a Result of Previous Exposure to Elevated Temperatures

The ambient temperature sensitiveness of blackpowder formulations was found to be relatively unaffected by prior elevated temperature storage, whereas the results for pyrotechnic flash composition indicated that there was a significant change in sensitiveness as a result of previous temperature exposure. Both the single and double based propellants became more sensitive to friction after short term storage (1 day) but this trend was reversed at the end of 10 days. The behaviour of the nitroglycerin (NG)-containing explosives was found to depend on their NG concentration; high concentration materials became more sensitive, while lower concentration materials became less sensitive.     

THE ORIGIN, DISTRIBUTION AND COMPOSITION OF LATERITE

The term laterite means a red rock or red earth deposit. Laterites are formed by the decomposition of different kind of rocks, under conditions yielding aluminum and iron hydroxides. The different theories of origin are discussed, as well as the chemical process of laterization, and the geographic distribution of this peculiar type of clay.     

HTPB推进剂的低温力学性能

通过低温和低温恢复常温单轴拉伸试验,考察了低温条件下HTPB推进剂力学性能的变化情况,用SEM扫描电镜观察了推进剂拉伸断面形貌,分析了所得HTPB推进剂的拉伸应力-应变曲线和力学性能特性。结果表明,在低温拉伸条件下,HTPB推进剂主要表现为基体撕裂和颗粒脆断,而在低温恢复常温拉伸条件下,主要以"脱湿"破坏为主。推进剂的低温拉伸曲线具有明显的屈服现象发生,说明推进剂的屈服现象与低温有关。推进剂在低温和低温恢复常温条件下的最大抗拉强度、弹性模量和延伸率等力学性能呈现出不同的变化规律。     

A New Thermo‐, pH‐ and CO2‐Responsive Fluorescent Four‐Arm Star Polymer with Aggregation‐Induced Emission for Long‐Term Cellular Tracing

Development of fluorescent bioprobes for long‐term cell tracking is of great importance to monitor the processes of genesis, development, invasion, and metastasis of cancerous cells. Herein, a new multistimuli‐responsive star polymer of tetraphenylethene‐graft‐tetra‐poly[N‐[2‐(diethylamino)‐ethyl]acrylamide] (TPE‐tetraPDEAEAM) with aggregation‐induced emission (AIE) effect for tracing live cells over a long period of time is synthesized by atom transfer radical polymerization using TPE derivative as initiator. TPE‐tetraPDEAEAM gives both lower critical solution temperature and fluorescence responses to the stimulus of the temperature, pH, and CO₂ by combining the thermoresponsive and pH/CO₂‐responsive moieties of the diethylamino and acrylamide groups. The AIE‐active TPE‐tetraPDEAEAM has the advantages of very low cytotoxicity, efficient cellular uptake, and strong fluorescence of polymer‐treated cells, which ensure its good performance in long‐term cell tracing. This facile tracking of HeLa cells for as long as nine passages exhibits superior performance in long‐term cell tracing as compared with some commercial cell tracing probes.     

Temperature Dependence of Interfacial Tension of Polymer Melts

A unique behavior of interfacial tension of polymer melts is that, in an ordinary temperature region of strong segregation, the entropy effect of chain molecules on the composition-gradient term in the free energy at the interface can make the interfacial tension increase with increasing temperature. To confirm this role of the entropy, interfacial tension of polystyrene/poly(dimethylsloxane) was measured as a function of temperature, and was found to increase with increasing temperature. Using temperature dependence of the segment-segment interaction parameter, which was evaluated from experimental coexistence curves, it was shown that the entropy effect was responsible for this positive temperature dependence of the interfacial tension. The experimental result was also discussed on the basis of scaled expressions of interfacial tension as a function of segregation strength covering weak, strong, and very strong segregation regimes.