由L-J流体的FMSA状态方程计算流体的PVT性质

运用Tang等提出的Lennard-Jones (L-J)流体两参数的一阶平均球形近似(FMSA)状态方程, 计算了流体的汽液共存相图和饱和蒸汽压曲线, 以及非饱和区的PVT性质, 并与文献数据进行比较. L-J参数由Tr＜0.95的汽液相共存数据回归得到. 计算结果表明, 对于分子较接近球形的流体, 除临界点附近外, 该方程可以在较大的温度和压力范围内计算真实流体的PVT性质, 结果满意. 对于球形分子, 该方程的精确度随分子尺寸的变大基本保持稳定. 该方程不适用于强极性物质. 在高密度区, 该方程的计算结果明显优于P-R方程. 对于分子偏离球形较远的流体, 该方程的适用性变差, 此时要考虑分子形状的影响, 可采用三参数的FMSA状态方程进行计算.     

Annealing behaviour of arsenic implants in silicon

Abstract

The annealing behaviour of 80 keV room temperature arsenic implants in silicon below the amorphization dose has been studied by comparing the physical profile and the electrical profiles following different isochronal anneals.

It is shown that the electrically active fraction, which is about 0.4 after 30 min annealing at 600°C, increases continuously until 100% electrical activation of the arsenic ions is reached at about 900°C.

The activation energy for the annealing process has been found equal to 0.4 eV. A tentative interpretation of the mechanism involved is given.

From the analysis of the physical profiles obtained after isochronal annealing, an effective diffusion coefficient at 900°C equal to 5 × 10^?16 cm² s^?1 has been calculated.     

Equation of state for high density solid and melt polyethylene

Pressure‐volume‐temperature (PVT) measurements for high‐density linear polyethylene (LPE) are studied experimentally over a temperature range of 290 to 470 K and pressures up to 3.1 kbar. For melt, the results can be represented by the Tait equation within the precision of the data. It is noticed that for each isotherm, an abrupt departure from the Tait representation occurs at a particular pressure. This is ascribed to onset of solidification due to pressure. Further, variation of the degree of crystallinity with pressure at various temperatures has been investigated. Finally, the PVT data has been analyzed in terms of the LJD cell theory in its original form without any modifications or simplifications of the cell potential. Satisfactory agreement is obtained between experiment and theory over the entire range of PVT data both in solids and melt states. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1618–1623, 2005     

Prediction of polymer PVT behavior using the group contribution lattice-fluid EOS

A scheme has been developed using the group contribution lattice-fluid equation of state (GCLF-EOS) to predict the pressure-volume-temperature (PVT) behavior of polymers in the amorphous state. The model requires only the structure of the molecule as input information. Prediction results with an average error of 2% have been obtained for a wide variety of polymers. A table of 23 different group contributions is presented. With this set of group parameters, the GCLF-EOS can be applied in the prediction of equation of state properties of a wide variety of homopolymers, random copolymers, and polymer blends. © 1995 John Wiley & Sons, Inc.     

高温高压湿空气的维里方程

本文针对湿空气透平循环和压缩空气贮能系统中对高温高压湿空气热力学性质参数的需求,依据统计热力学理论,采用分子动力学模拟研究方法,探讨了高温高压湿空气中水分子与氧分子和氮分子的相互作用特性。通过对比研究,确定了合理的计算湿空气性质的分子动力学模型,模拟计算了最高温度达600℃、压力40 MPa、含湿量0．445下湿空气的PVT参数,并拟合得到了一定条件下的高温高压湿空气的维里方程。     

聚丙烯结晶行为的PVT研究

通过受限液体PVT测量技术对等规聚丙烯的结晶行为进行了研究,采用PVT等压测量模式描述了不同压力场下半结晶聚合物的结晶过程.结果表明,随着压力的升高,等规聚丙烯分子链间的相互作用增强,使得等规聚丙烯分子链段更容易排入晶格中,这是结晶温度和结晶速度升高的主要因素.通过对数据拟合,建立了压力对等规聚丙烯结晶过程参数的影响公式.对Jeziorny结晶动力学模型进行改进,并研究了压力对等规聚丙烯结晶动力学的影响,结果发现,当结晶度大于0.08时,结晶动力学拟合曲线呈较好的线性,分析结果可以对结晶过程的变化机理进行合理地预测,在小于200 MPa压力环境下,等规聚丙烯的结晶生长方式仍是球晶生长模式,晶体的生长符合二维片晶生长方式,自由体积的减小是结晶速率加快的主要原因之一.     

Free volume dependence of polymer viscosity

The Simha–Somcynsky (S–S) equation of state (eos) was used to compute the free volume parameter, h, from the pressure–volume–temperature (PVT) dependencies of eight molten polymers. The predicted by eos variation of h with T and P was confirmed by the positron annihilation lifetime spectroscopy; good agreement was found for h(P = constant) = h(T) as well as for h(T = constant) = h(P). Capillary shear viscosity (η) data of the same polymers (measured at three temperatures and six pressures up to 700 bars), were plotted as logη vs 1/h, the latter computed for T and P at which η was measured. In previous works, such a plot for solvents and silicone oils resulted in a “master curve” for the liquid, in a wide range of T and P. However, for molten polymers, no superposition of data onto a “master curve” could be found. The superposition could be obtained allowing the characteristic pressure reducing parameter, P*, to vary. The necessity for using a “rheological” characteristic pressure reducing parameter, P*_R = κP*, with κ = 1 to 2.1 indicates that the free volume parameter extracted from the thermodynamic equilibrium data may not fully describe the dynamic behavior. After eliminating possibility of other sources for the deviation, the most likely culprit seems to be the presence of structures in polymer melts at temperatures above the glass transition, T _g. For example, it was observed that for amorphous polymers at T ≅ 1.52T _g the factor κ = 1, and the deviation vanish.     

PP/POE共混物的P-V-T属性及压力对结晶温度的影响

采用PVT膨胀仪研究了PP/POE共混物的P-V-T属性, 利用Tait方程预测其比容和热膨胀系数(α), 研究了压力对结晶温度(Tc)的影响. 结果表明, Tait状态方程可用来预测部分相容的、半结晶PP/POE共混物的PVT行为. PP结晶前后的比容变化比POE的大得多, 随着POE含量的增加, PP/POE共混物结晶前后比容的变化均逐渐减小. PP在熔融状态下的α比固体状态的大, 而POE正好相反. PP/POE共混物的α随温度和压力的变化与其组成密切相关. 随着压力的增高, PP, POE及其PP/POE共混物的结晶温度均呈线性增高的趋势.     

Equation-of-state properties and surface tension of ethylene-vinyl alcohol random copolymers

Pressure-volume-temperature (PVT) data were studied for ethylene-vinyl alcohol random copolymers (EVOH) and served to determine bulk reduction parameters for the equation-of-state by Flory-Orwoll-Vrij. The compressibility factor as a function of copolymer composition displays positive deviation from additivity. Sessile drop method yielded surface tensions of EVOH melts at different temperatures. To a good approximation linear variation of surface tension with respect to copolymer composition was observed. It indicates that conformational restrictions prevent surface excess of the low-energy units. Results on surface tensions are discussed in terms of different theoretical approaches. It turns out that the parachor approach is in excellent agreement with experimental data. The corresponding state approximation revealed decreasing surface energy with ascending ethylene content whereas the surface entropy remains approximately constant as long as vinyl alcohol units are in excess.