Effect of pressure on melting temperature and other associated thermodynamic functions of polyethylene

The melting temperature of polyethylene was determined at pressures up to 30 kbar. Using these results and the calculated values of the volume change on melting in the Clausius–Clapeyron equation, the enthalpy and entropy of fusion as a function of pressure were also determined.     

A method for determination of thermodynamic and solubility parameters of polymers from temperature and molecular weight dependence of intrinsic viscosity

An equation using the temperature dependence of intrinsic viscosity of a polymer was proposed for the determination of the partial molar entropy and enthalpy changes of the polymer for mixing in dilute solution. It was found that the partial molar entropy change of a polymer for mixing at a given temperature is proportional to the hydrodynamic volume or segment number of the polymer. The partial molar enthalpy change of the polymer for mixing was determined from the thermodynamic equilibrium property of polymer phases. The solubility or cohesion parameter of a polymer fraction was calculated by using the partial molar enthalpy change and repeat unit volume of the polymer. The solubility parameter of high molar mass polymer at a given temperature was determined by extrapolating solubility parameter values of polymer fractions to high molar mass by using the solubility parameter-segment number relation of polymer fraction. This relation gives a straight line. The solubility parameter of the polymer at a given temperature and the effective interchange energy parameter for polymer-solvent pair were obtained directly from the intercept and the slope of this line, respectively. These equations were applied to the intrinsic viscosity-temperature data of polystyrene fractions in decalin solutions, and polystyrene fractions in decalin, cyclohexane and dioctyl phthalate solutions at the theta temperatures and in toluene solutions at the given temperatures. The results obtained in this study coincide with the literature values. In addition, it was given a relation, which is derived from the blob theory for the temperatures above the theta point, for the estimation of the thermodynamic parameters of polymers for mixing.     

Temperature dependence of some thermodynamic functions for amorphous and semi-crystalline polymers

The temperature dependence of some heat-capacity related functions is evaluated on the basis of experimental data, and a further elaboration is given for polyethylene.     

Chemical model for cement-based materials: Temperature dependence of thermodynamic functions for nanocrystalline and crystalline C-S-H phases

In the context of waste confinement and, more specifically, waste from the nuclear industry, concrete is used both as a confinement and as a building material. Its exposure to high temperatures makes its geochemical behavior difficult to predict over large periods of time. The present work aims to elucidate the solubility constants, as a function of temperature, for the phases of the system CaO-SiO₂-H₂O. For the nanocrystalline phases, the present work investigates the existence of compounds of fixed composition, possibly in a metastable state. The question of whether the nanocrystalline C-S-H phases correspond to a series of phases of discrete composition or a solid solution is discussed and compared to the possible influence of impurities in the solid phases.For the crystalline phases, having established that the currently available values of thermodynamic properties were not consistent, we show that their refinement leads to a better agreement with the literature data. From the refined thermodynamic properties of crystalline C-S-H, a polyhedral decomposition model is developed. It enables to estimate the enthalpy of formation and the heat capacity of nanocrystalline C-S-H phases. Finally, verification shows that such phases remain unstable compared to the crystalline phases, at room or higher temperatures. A comparison, based on reaction enthalpies derived from experimental data indicates that predicted values for nanocrystalline C-S-H are in close agreement with experimental data. By estimating the properties of okenite and truscottite with the model developed in this study, we have been able to complete the CaO-SiO₂-H₂O phase diagram with a reasonable agreement with the literature. The case of jaffeite remains open to discussion. Finally, for the hydrate C2SH,α, the model predicts a transition with hillebrandite at 159 °C, in contradiction with the hypothesis of C2SH,α metastability.     

Numerical evaluation of the thermodynamic equation for the state of polymer melts from pressure-volume-temperature (pVT) data

A refinement of the numerical calculation of reducing PVT parameters has been given by using the Marquardt-Levenberg nonlinear least-squares algorithm. Three different polymers were analyzed and evaluated by the proposed method. The precision of the PVT measurement makes sense for an improvement of the evaluation by applying the Marquardt algorithm.     

Pressure and temperature dependence of second-order elastic constants from third-order elastic constants in TMC (TM=Nb,Ti, V,Zr)

In this paper, we present an efficient and effective method to predict the pressure dependence and temperature dependence of second-order elastic constants (SOECs) by introducing third-order elastic constants (TOECs) in the monocarbide ultrahigh temperature ceramics. The method is validated by comparing with experiments and previous calculations in four TMCs (TM = Nb, Ti, V, Zr). Using this method, we investigate the derivatives of SOECs against pressure and temperature as well as the anisotropic properties of polycrystalline modulus. In addition, we fit the SOECs with pressure and temperature under the framework of CALPHAD for practice usage.     

A test method for determining adhesion forces and Hamaker constants of cementitious materials using atomic force microscopy

A method for determining Hamaker constant of cementitious materials is presented. The method involved sample preparation, measurement of adhesion force between the tested material and a silicon nitride probe using atomic force microscopy in dry air and in water, and calculating the Hamaker constant using appropriate contact mechanics models. The work of adhesion and Hamaker constant were computed from the pull-off forces using the Johnson–Kendall–Roberts and Derjagin–Muller–Toropov models. Reference materials with known Hamaker constants (mica, silica, calcite) and commercially available cementitious materials (Portland cement (PC), ground granulated blast furnace slag (GGBFS)) were studied. The Hamaker constants of the reference materials obtained are consistent with those published by previous researchers. The results indicate that PC has a higher Hamaker constant than GGBFS. The Hamaker constant of PC in water is close to the previously predicted value C₃S, which is attributed to short hydration time (≤ 45 min) used in this study.     

Identification of kinetic and thermodynamic reaction parameters from online calorimetric and IR-ATR data using a new combined evaluation algorithm

In order to identify parameters of a chemical reaction, such as rate constants, reaction orders, activation energies, or reaction enthalpies, a new evaluation algorithm that allows a simultaneous evaluation of online measured infrared and calorimetric data will be investigated. The evaluation of the infrared data neither requires calibration nor the knowledge of pure component spectra. Overlapping absorption bands are allowed. The weighting of the calorimetric and infrared objective functions performs completely automatic using a sensitivity analysis. The performance of this combined evaluation principle was investigated by analyzing the consecutive epoxidation of 2,5-di-tert-butyl-1,4-benzoquinone with tert-butyl hydrogen peroxide. Different reaction models as well as physical constraints were postulated in order to reveal the flexibility and the capability of the approach. The results obtained underline the importance of such a combined evaluation of both analytical signals instead of separate evaluations.     

Noniterative method for evaluation of the complex material constants of piezoelectric ceramics in the radial vibration mode

A new noniterative method, for determining the dielectric, piezoelectric and elastic constants, in complex form, for piezoceramic materials, in the radial mode, was proposed.This method uses the standard procedure to determine the elastic compliance and Poisson factor and the measurement of admittance at two frequencies to calculate the dielectric and piezoelectric constants, by solving a system of two equations.The accuracy of the new method was determined for materials with different planar coupling coefficients (k_p = 2.5-57%) and mechanical quality factors (Q_m = 20-3000). This method proved to be very accurate for all materials especially for those with large coupling factors. The accuracy of standard method was also evaluated for the same materials.     

Kinetic analysis of non-isothermal thermogravimetric analyser results using a new method for the evaluation of the temperature integral and multi-heating rates

A technique using non-isothermal thermogravimetric analyser results was developed for the validation of reaction rate models together with associated parameters suitable for chemically controlled gas-solid reactions. The solution of the temperature integral which occurs in the calculation is achieved by numerical integration with respect to a dimensionless activation energy variable, y=E/RT, following a transformation of the temperature integral equation. The evaluation of the validity of the kinetic model and determination of all the constants is accomplished with a two-step regression procedure with experimental results from several thermogrammes with different linear heating rates. The technique was validated by comparing results obtained for the combustion of two coal-chars with corresponding isothermal results using a shrinking core model with a nth order surface reaction.     

Regression analysis studies of polymer transitions II. TII from specific heat and other data for polyisobutylene

Linear regression analysis studies with residuals of heat capacity vs. temperature (C_p vs. T) data above the glass transition temperature (T_g) for polyisobutylene (PIB) of molecular weights M¯_v = 1,350,000 and M = 4900 show that the data points can be represented by three straight lines in each case. The lower intersection temperature represents the intermolecular T_ll transition (relaxation); the upper one an intramolecular T_lp process. Both processes are confirmed by ultrasonic velocity data in vulcanized butyl rubber, by zero shear melt viscosity data in PIB (M = 4900); and by isothermal specific volume vs. pressure data in PIB (M¯_v = 36,000). T_ll is confirmed by thermal diffusivity, differential scanning calorimetry (DSC), ¹³C nuclear magnetic resonance (NMR) spectroscopy and the T^* temperature of Lobanov and Frenkel based on Arrhenius-type plots log frequency vs. 1/T_g. A comparison of dynamic mechanical loss data, both old and new, reveal that T_ll follows a Vogel-WLF type relation; log f vs. 1/(T₀ ?1/T_o). PIB samples with number average molecular weights between 7100 to 860,000 have been measured on three types of support systems: glass braid (0.3 Hz), filter paper (11 Hz), brass shim stock (14–16 Hz), and give similar values of T^u. A considerable amount of literature data long neglected from the viewpoint of its bearing on T_ll is reviewed. T_ll has been observed in the same way as T_g by both relaxational and quasi-static methods. Some instructive cross comparisons between these two types of methods emerge. With so many diverse methods yielding evidence for T_ll in PIB, it cannot be dismissed as an artifact. A molecular origin for T_ll is plausible in terms of the Frenkel-Baranov phase dualism mechanism. A complete relaxation map (log f vs. 1/T) has been assembled with frequencies from 10^?2 to 10¹⁰ Hz and temperatures from 150 to 500 K. It shows T_β, T_g, T_ll and methyl group rotation, all based on data in the literature. The molecular weight dependence to T_g and T_ll and the low resiliency of butyl rubber as it relates to T_ll are discussed in the appendices.     

固体氧化物燃料电池阳极材料Ni-SDC的稳定性实验及热力学分析

以Ni-SDC作为固体氧化物燃料电池（SOFC）的阳极,研究了该阳极粉末在制备过程中以及5% H2S-N2硫化后的产物,并用热力学软件绘制相图对其在各种温度下的产物变化进行分析。结果表明：NiO-SDC在800 ℃煅烧和在850 ℃还原的产物与热力学分析结果是一致的。对比在5%的H2S-N2中硫化12 h前后的XRD表明Ni已经转化为NiS2,热力学分析验证了该结论。比较Ni-SDC和SDC硫化前后的Raman光谱和XRD结果得到：SDC硫化后主峰型没有发生明显变化,但强度变弱,说明粒径变大,可能因为有Ce-O-S键生成。     

Application of conformational analysis techniques to the prediction of heats of formation and gas-phase thermodynamic functions

Conformational energy calculations based on describing the deformation of chemical bonds by energy functions allow the prediction of molecular geometries, heats of formation, vibrational frequencies, and gas-phase thermodynamic functions of compounds which contain bonds or groups of bonds whose properties are transferable from molecule to molecule.     

蓄顶温度与火道温度关系模型辨识新方法

针对焦炉火道温度与蓄顶温度关系模型的辨识问题,提出了一种基于区间预估最小二乘法的模型辨识方法.此方法可以有效消除煤气交换给火道温度和蓄顶温度带来的趋势不同的影响.使用置信区间的预计算,能够避免辨识数据紧凑带来的拟合数据准确而物理意义不准确的问题.     

New method for the direct analysis of supercritical fluid coal extraction and liquefaction

A new method is described for the direct mass spectrometric analysis of the products of coal supercritical fluid extraction processes. Coal placed in an extraction cell was elevated to supercritical conditions with pressure regulation by a high pressure pump. The extracted products were continuously analysed by direct fluid injection into a mass spectrometer chemical ionization ion source. The extraction process was observed as a function of pressure to determine threshold pressures for individual solutes or as a function of temperature at constant pressure. The method was demonstrated for a supercritical fluid extraction of a bituminous coal by a mixture of n-pentane and 2-propanol at 280 °C and 0.5–10 MPa.     

Generalized method for determination of penultimate model reactivity ratios and analysis of data

Method of determination of penultimate model reactivity ratios has been generalized to take care of specific systems where copolymer composition data are available only in narrow ranges. A number of copolymerization systems reported in literature have been analyzed and applicability of generalized relationship was tested. Most systems are seen to follow penultimate model better than the terminal model. Monomer independent universal relationship of penultimate model reactivity ratios has similarly been generalized and successfully tested.     

Comparative analysis of the thermokinetic constants for drying and pyrolyzing forest fuels

Thermogravimetric measurement in an inert medium and the simplest kinetic equations are used to obtain thermokinetic constants for drying and pyrolizing typical forest fuels. The adequacy of the model is demonstrated experimentally. Materials are identified for which a single value of the kinetic constants can be used. Methods are suggested for using these values in a general mathematical model of forest fires.Tomsk. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 6, pp. 17–24, November–December, 1991.