Microstructure of high modulus solid state extruded polyethylene: 2. X-ray scattering studies of 12, 24 and 36 extrusion draw ratio

The microstructure of a series of solid state extruded polyethylene fibres was examined by wide- and small-angle X-ray scattering. By measuring absolute intensities using a two dimensional position sensitive detector, accurate values of the small-angle invariant for anisotropic samples were obtained. This measurement coupled with wide-angle X-ray scattering and d.s.c. permitted determination of the density of the noncrystalline component. The use of a two phase model for solid state extruded polyethylene is justified if consideration is given to the effective densities of the crystalline and noncrystalline phases, which change with deformation. The effective density of the crystalline phase decreases by 1% (0.999–0.990 g cm^?3) from the unextruded billet compared to a 36 draw ratio extrudate, while the noncrystalline phase density increases by 6% (0.84–0.89 g cm^?3). These changes lead to an overall decrease in the mean squared electron density fluctuation of 63%. The average axial crystallite length measured by wide-angle X-ray scattering increases with extrusion draw ratio while the SAXS long period decreases and weakens considerably. These observations and the electron microscopy results from the previous paper, (Polymer, 1982, 23, 1069), are fully consistent with the key features of the Peterlin model of fibre microstructure.     

Reactive Hot Melts on the Basis of Polyester and Polyamide

Hot melts show many advantages over other adhesives, for instance, their lack of solvent and their very short setting time just by cooling. The weak point of hot melts in comparison to thermosetting resins is their limited thermal resistance. There is no doubt that the high performance hot melts on the basis of polyester and polyamide show a better heat performance than the widely-used rubbery hot melts. Nevertheless, it is true that the thermal resistance is limited by the melting point of the hot melt. To improve the heat performance, without losing the favourable hot melt properties, crosslinkable hot melts have been created. For the example, copolyamide/blocked isocyanate blends, it can be shown that crosslinkable hot melts are achievable in a wide range of reactivities. After curing, which takes place during the bonding process, these hot melts withstand temperatures of over 220°C even if the melting point of the initial hot melt was 100°C.     

普光气田邻井干扰压降研究

根据普光气田现场资料,分析普光气田关井压降恢复时间和稳定生产时间的关系。建立邻井干扰计算模型,评价邻井干扰压降值及邻井干扰,并对邻井干扰规律进行敏感性分析。     

Intergranular oxidation of silicon in 20Cr-25Ni niobium-stabilized stainless steel at 1140–1230 K

The kinetics of intergranular oxidation of silicon in a 20Cr-25Ni Nb-stabilized stainless steel are reported, at temperatures in the range 1140–1230 K, in CO₂ at 40 bar pressure. The depth of attack increased parabolically with respect to time, with an activation energy of 335±30 kJ/mol. The mechanism of growth is discussed in terms of classical internal-oxidation theories, and an alternative explanation based on an available-space theory is developed. The internal oxidation rates in a number of different alloys are compared with diffusivities of metals in the base alloy. It is proposed that intergranular oxidation in the 20–25 Nb steel is controlled by the rate of outward diffusion of iron or chromium in the alloy.     

电控柴油机分缸均衡控制算法及试验

柴油机各个气缸的进气量、喷油量、燃烧等存在差异,导致气缸间存在做功差异,直接影响柴油机转速的平稳性以及排放性能等。针对位置式电控柴油机,采用PI闭环控制,通过瞬时转速信号识别并计算各缸的工作差异,利用分缸均衡控制算法对油量进行补偿修正。试验结果显示低转速稳态工况转速波动由7 r/min降至3 r/min,各缸工作不均匀度由±5 r/min降至±2 r/min,在瞬态过程和高转速3 400 r/min时该算法仍然适用有效。     

2-（4-氯苯氨基）甲基苯酚降解的动力学研究

采用高效液相色谱技术,开展了Fenton试剂对2-（4-氯苯氨基）甲基苯酚（CMP）的氧化降解动力学的研究。考察了初始双氧水摩尔浓度、亚铁离子摩尔浓度和温度等因素对CMP降解速率的影响,结果表明,当双氧水摩尔浓度、亚铁离子摩尔浓度增大和温度升高时,CMP的氧化速率明显加快。在30~45℃的温度范围内,其氧化降解符合假一级反应动力学模型,反应的表观活化能Ea为102.90kJ/mol。     

Oxidation Performance of Fe-Al/WC Composite Coatings Produced by High Velocity Arc Sprayed at 650 ℃

Fe-Al intermetallics with remarkable high-temperatureintensity and excellent erosion,high-temperatureoxidation and sulfuration resistance are potential lowcost high-temperature structural material.ProducingFe-Al/WC composite coating by high velocity arcspraying(HVAS)on structural materials would notonly obviate the problems faced in fabrication of thesealloys into useful shapes,but also allow the effectiveuse of their outstanding high-temperature performance,which might thus promisingly mak…     

Sensitivity analysis based preform die shape design using the finite element method

This paper uses a finite element-based sensitivity analysis method to design the preform die shape for metal forming processes. The sensitivity analysis was developed using the rigid visco-plastic finite element method. The preform die shapes are represented by cubic B-spline curves. The control points or coefficients of the B-spline are used as the design variables. The optimization problem is to minimize the difference between the realized and the desired final forging shapes. The sensitivity analysis includes the sensitivities of the objective function, nodal coordinates, and nodal velocities with respect to the design variables. The remeshing procedure and the interpolation/transfer of the history/dependent parameters are considered. An adjustment of the volume loss resulting from the finite element analysis is used to make the workpiece volume consistent in each optimization iteration and improve the optimization convergence. In addition, a technique for dealing with fold-over defects during the forming simulation is employed in order to continue the optimization procedures of the preform die shape design. The method developed in this paper is used to design the preform die shape for both plane strain and axisymmetric deformations with shaped cavities. The analysis shows that satisfactory final forging shapes are obtained using the optimized preform die shapes.     

High-temperature oxidation of pure titanium in CO2 and Ar-10%CO2 atmospheres

The oxidation behavior of pure titanium has been investigated in the temperature range of 1000 K to 1300 K in CO₂ or Ar-10%CO₂. Optical microscopy, electron probe microanalyses, and X-ray measurements on the oxide scales formed during oxidation indicate that their structures are nearly independent of temperature and the corrosion atmosphere. The scales consisted of two layers, an external one and an internal one, having a rutile (TiO₂) structure. The parabolic rate law was confirmed for growth of the external scale and the permeation depth of oxygen in titanium with apparent activation energies of 266 and 226 kJ/mol, respectively. The rate-determining diffusion species in the oxidation processes are discussed.     

20G高压锅炉管裂纹原因分析

对20G高压锅炉管产生裂纹的原因进行了分析，结果表明是冷拔工艺不当所致。