Relationship between Melting Thermodynamics and Strength for Ultradrawn Polymers

Abstract

With the help of DSC, WAXS, and SAXS techniques highly oriented PE samples produced in six different ways in the range of draw ratios from 25 up to 300 have been investigated. The decrease of melting interval up to zero and the significant increase of melting temperature up to its equilibrium value are observed with draw ratio. The analysis of DSC data enabled us to calculate the thermodynamical parameter of intrachain cooperativity of melting which was found to be equal to v?2×10³ nm. Although the observed thermodynamical characteristics corresponded to those expected for hypothetical macroscopic single crystals of PE, the combining of DSC and X-ray data allow to consider ultraoriented PE as consisting almost entirely of very extended (up to v?2×10³ nm) straightened chain sections, each of which going through dozens of small crystallites and intercrystalline regions containing defects of disclinational type. As a result, the linear correlation between the parameter v and the mechanical strength [sgrave] of oriented PE has been revealed.     

高温高压下氯化钠水溶液的热力学(I)——在373—573K及0.1—100MPa条件下NaCI-H_2O体系的热力学性质

本文提出了一个简易的热力学方程式,式中仅包含一个表示长程作用力的静电项,再加上一个表示两粒子间的短程作用项,即可用以计算温度为373—573K,压力为0.1—100MPa、氯化钠浓度为0—10.4mol/kgH_2O的水溶液中氯化钠和水两者的活度系数,计算简便,易于推广使用.     

Compressibility of Binary Alkaline-Earth Borate Glasses at High Pressures

Compression data to 10,000 atm. were obtained for a series of barium, strontium, and calcium borate glasses at 21°C. The compressibility was found to be in the order Ba > Sr > Ca at corresponding molar concentrations and was not appreciably affected by pressure in the experimental pressure range. Comparison of data on alkali and alkaline-earth borate glasses shows that the compressibility at corresponding molar concentrations is smaller in the alkaline-earth glasses. Numerical comparisons at appropriate compositions show that a large part of the decreased compressibility produced by the alkaline-earth oxides arises from electrovalent sources.     

高压下液氨的pVT关系计算

介绍了一个普遍化的Tait型高压液体的状态方程,并将它应用于高压下液氨的pVT数据的计算。对照2组文献数据(一组温度253～313K,最高压力180MPa;另一组温度310～350K,最高压力110MPa),计算结果表明,平均绝对偏差分别为0.20%和0.94%。本方程适合用来描述液氨的pVT行为。     

Studies of the Combustion of Solid Propellants at High Pressures

To determine burning velocities of solid propellants at high pressures, a new type of manometric bomb of 0.1 1 volume has been designed. Tightening is provided by a cartridge section from a 30 mm HS 831 steel case. 3 0 to 50 ms after the maximum, the pressure is automatically released by erosion of a 1 mm nozzle, this time lag being given by the electric igniter placed before the nozzle and by blocking it for a short time. The bomb has been applied to measure pressures p in a range up to 7000 bar as a function of loading density A for a double base propellant. The curve p(A) shows a change of slope at about 5000 bar for which explanation is still lacking.     

Crystallization and Phase Relations of Boron Trioxide at High Pressures

Crystalline B₂O₃ was readily obtained from the glassy phase at high pressures and temperatures. Single crystals 0.3 mm. in dimension of both α-B₂O₂ (ordinary hexagonal) and β -B₂O₃ (dense monoclinic) were prepared. The difference in the density of the two forms was about 20%. Crystals of β -B₂O₃ were only slowly attacked by H₂O and dilute HF. At atmospheric pressure, transitions between the α- , β -, and liquid phases were extremely sluggish. A tentative phase diagram was constructed up to 1100°C. and 90,000 atmospheres, the probable melting curve being calculated by the use of the Simon melting equation.     

The Structure of High Molecular Weight Linear Polyethylene Injection Moulded at High Pressures

Abstract

High density polyethylene with a low melt flow index (0.1 g/10 min) was injection moulded at pressures ranging from 100 to 500 MPa. The tensile modulus and strength in the flow direction increased substantially with the injection pressure. Three regions are characteristic of the specimens produced; a thin layer near the surface, a transition layer beneath the skin, and a core. DSC, wide angle X-ray scattering (WAXS), scanning and transmission electron microscopy were used to study the structure of the different layers. It was concluded that the skin was slightly oriented containing primarily chain-folded lamellae; the transition layer had a fibre texture and was oriented in the flow direction; the orientation of the core was similar to that of the transition layer but contained extended chain-morphologies similar to those found by Porter et al. in capillary extruded specimens. The composite structure gives rise to the improvement of mechanical properties and the increase in modulus is due to the core material. A monoclinic phase in the core was found by X-ray diffraction.     

Real Gas Corrections in Shock Tube Studies at High Pressures

Reaction kinetics studies at high pressure in shock tubes can be significantly affected by the influence of real gas effects on state variables. The effect on the temperature, pressure, and density can be calculated by solving the shock wave equations using real gas equations of state (EOS). We present a method to solve the shock wave equations in a straightforward way by taking advantage of the recently-developed real gas properties package by Schmitt et al. (U. of Iowa Rep. UIME PPB 93–006, 1994). The solutions of these equations for shock waves in pure argon are presented. We find that the reflected shock temperatures and densities can be significantly different from those predicted by using an ideal gas EOS. Using the Peng-Robinson EOS, for example, the calculated real gas reflected shock temperature is less than the ideal gas temperature by 83 K per 1000 atm. An illustrative example of the effect of real gas corrections on a rate coefficient determination is also presented.     

HAN基液体发射药高压热物理性质的估算

为了系统地研究HAN基液体发射药在高压下的热物理性质,考虑其特有的分子结构,利用估算液体极性物质热物理性质的理论或经验公式,计算了HAN基液体发射药LP1845在高压下的密度、比热容、饱和蒸气压、蒸发潜热、摩尔相变热、黏度、导热系数、扩散系数等热物理性质,并绘制了各热物性参数随温度和压力的变化关系曲线。计算结果表明,HAN基液体发射药的高压热物理性质与一般液体燃料的性质不同。     

在高温高压下测定液体导热系数的方法

本文描述了在高温高压下快速测定液体导热系数的方法.温度和压力分别达到250℃和25.0MPa,以玻璃包封的热敏电阻作为加热元件,用桥路测定热敏电阻的dV/dt,由dV/dt计算介质的导热系数,每次测量时间为1.5秒,用六个已知导热系数的参考液体标定了装置,平均偏差小于±2%.该装置不仅可以测量有机液体,而且也可以测量导电液体或溶液.     

Surface Tensions of Hydrocarbons and Bitumens at High Temperatures and Pressures

A maximum bubble pressure apparatus, described in a previous publication, has been used at pressures to 13.9 MPa (2000 psig) and temperature to 623 K (350°C) to measure the static surface tension of several alkanes and paraffinic petroleum fractions, and two types of Alberta bitumens in contact with hydrogen, helium and hydrogen/methane mixtures. With hydrogen, the surface tensions of alkanes or mixtures of alkanes were nearly independent of pressure, whereas with helium surface tension increased significantly. With hydrogen/methane mixtures, the surface tension decreased in value as pressure increased, with the effect increasing at the higher methane concentrations. For the two bitumens used, the surface tension with hydrogen showed a 10–15% increase as pressure increased at constant temperature. Some discussion is also given concerning methods of predicting the effects of pressure and temperature in hydrogen/hydrocarbon systems.     

Compressibility of Binary Alkali Borate and Silicate Glasses at High Pressures

Isothermal compressibility data at 21°C. at pressures between 1000 and 10,000 atmospheres are reported for the binary alkali borate and silicate glass systems. In general, a decreasing compressibility is noted with increasing alkali content in both silicates and borates, the effect being much greater in the borates in the range of compositions studied. A maximum compressibility appears to be indicated for the potassium silicates at low potassium concentrations. In silicates and at high alkali contents in the borates, the order of compressibility is K > Na > Li. At low alkali contents in the borates, this order appears to be reversed. Possible interpretations of these data are discussed in terms of the concepts of the structura of glasses.     

Deflagration of HMX‐Based Explosives at High Temperatures and Pressures

We measure the deflagration behavior of energetic materials at extreme conditions (up to 520 K and 1 GPa) in the LLNL High Pressure Strand Burner, thereby obtaining reaction rate data for prediction of violence of thermal explosions. The apparatus provides both temporal pressure history and flame time‐of‐arrival information during deflagration, allowing direct calculation of deflagration rate as a function of pressure. Samples may be heated before testing. Here we report the deflagration behavior of several HMX‐based explosives at pressures of 10–600 MPa and temperatures of 300–460 K. We find that formulation details are very important to overall deflagration behavior. Formulations with high binder content (≥15 wt%) deflagrate smoothly over the entire pressure range regardless of particle size, with a larger particle size distribution leading to a slower reaction. The deflagration follows a power law function with the pressure exponent being unity. Formulations with lower binder content (≤10 wt% or less) show physical deconsolidation at pressures over 100–200 MPA, with transition to a rapid erratic deflagration 10–100 times faster. High temperatures have a relatively minor effect on the deflagration rate until the HMX β→δ phase transition occurs, after which the deflagration rate increases by more than a factor of 10.     

Observations of Accelerated Silicon Carbide Recession by Oxidation at High Water-Vapor Pressures

A study of the exposure of SiC at 1200°C and high water-vapor pressures (1.5 atm) has shown SiC recession rates that exceed what is predicted based on parabolic oxidation at water-vapor pressures of less than or equal to ∼1 atm. After exposure to these conditions, distinct silica-scale structures are observed; thick, porous, nonprotective cristobalite scales form above a thin, dense silica layer. The porous cristobalite thickens with exposure time, while the thickness of the underlying dense layer remains constant. These observations suggest a moving-boundary phenomenon that is controlled by the rapid conversion of dense vitreous silica to a porous, nonprotective crystalline SiO₂.     

高压下甲烷在乙醇-正已烷混合溶剂中的溶解度测定与研究

Solubility data were first presented for methane in the mixture of ethanol-hexane at temperatures from 291.15K to 318.15K and pressures up to 12.00MPa. The experimental data were correlated by PR and PRSV equations of state with rms errors of about 0.051. The A-K and Y-W-A-K models were both used to estimate liquid molar volume under high pressure. The results were satisfactory.     

应用PSRK状态方程预测高压汽液平衡

为预测高压汽液平衡,将过量吉布斯自由能混合规则和UNIFAC活度系数模型与SRK状态方程相结合,建立基团贡献状态方程PSRK。利用该状态方程对5个体系在不同压力和温度下的汽液平衡数据进行了关联实验测定的汽相压力和汽相组成与计算结果相比所得的相对平均偏差分别为2．16％和1．01％。结果表明,PSRK状态方程可以成功地预测高压下汽液平衡,其精度高于MHV1和MHV2模型。     

高压下甲烷在乙醇-正己烷混合溶剂中的溶解度测定与研究

Solubility data were first presented for methane in the mixture of ethanol-hexane at temperatures from 291.15 K to 318.15K and pressures up to 12.00MPa. The experimental data were correlated by PR and PRSV equations of state with rms errors of about 0.051. The A-K and Y-W-A-K models were both used to estimate liquid molar volume under high pressure. The results were satisfactory.     

甲烷在汽油中高压溶解度的测定与研究

建立了一套采用循环法测定气体在液体中高压溶解度的测定装置，该装置可以测定气体在纯溶剂和混合溶剂中的溶懈度。在较详细地描述了实验装置及其操作之后，对装置的可靠性进行了验证，并在15～30℃和压力2．0～12．0MPa的条件下，测定了甲烷在汽油、汽油-甲醇、汽油-乙醇混合体系中的溶解度，并用PR方程计算了甲烷的气相逸度。实验结果充分证明了该装置的可靠性，同时也揭示出甲烷在汽油、汽油-甲醇、汽油-乙醇混合体系中的溶解度规律。