Morphology of cold-drawn polyethylene

Small-angle studies suggest the presence of either a 1000- or a 100-Å periodicity in cold-drawn polyethylene. A 1000-Å periodicity is shown in cold-drawn polyethylene thin films to be due to regular placements of portions of two or three lamellae which stayed together during deformation by interlamellar ties. The 100-Å periodicity is shown by dark-field electron microscopy and, in particular, by bright-field diffraction-contrast microscopy to be due to alternating crystalline and noncrystalline units aligned in 100-Å diameter microfibrils. At lower draw ratios, a lateral alignment of the 100-Å units is observed, resulting in the formation of “wavy lamellae.” Although the wavy lamellae are destroyed at higher draw ratios, the 100-Å units remain present throughout the sample. These observations suggest the possible presence of a grain structure of the order of 100 Å in the original crystal.     

Note retraction of cold-drawn polyethylene and polypropylene

Observations on the free retraction of cold-drawn polyethylene and polypropylene as functions of time and temperature are reported and discussed in relation to possible origins of long-range retractive forces in crystalline polymers.     

The effects of thermal annealing on the relaxation of rubbing-induced birefringence in polystyrene

We have conducted a systematic study on the effects of post rubbing annealing on the relaxation of rubbing-induced birefringence of polystyrene. It is found that annealing at T₀ only affects the relaxation up to T₀ + T_Lag, where T_Lag is proportional to the logarithm of the annealing time t_A. A theoretical model based on the distribution of relaxation times due to the individual birefringence elements is proposed. To remove its contribution to the net birefringence each element must overcome an energy barrier E = (317 + 1.17ξ)×10³ J/mol, and therefore must have a characteristic relaxation time τ which depends on temperature T and a barrier height which ranges from 340.4 kJ/mol to 445.7 kJ/mol. The relaxation of birefringence is expressed by the equation NB(T, t) = N(ξ)e^-t/τ(T,ξ)dξ, in which both the relaxation time τ(T,ξ) and the distribution function N(ξ) can be extracted from experimental data. The predictions of the model agree well with all the experimental results presented in this work. The differences and similarities of the relaxation of birefringence with respect to the physical aging of quenched PS are discussed. In particular, similarities in terms of the general temperature lag phenomena are noted.     

Experimental determination of the fracture time of polymethylmethacrylate and polystyrene behind the shock wave excited by a high-current pulsed electron beam

The time ranges of the fracture of polymethylmethacrylate and polystyrene during the action of a shock wave generated by a high-current pulsed electron beam are experimentally determined using laser probing in combination with electron-optical chronography. It is shown that fractures occur during unloading of a material, i.e., after the passage of the shock wave. Although the characters of fracture of these polymers near the surface irradiated by electron beam are different, the fracture wave velocities in them are found to be close.     

Deformation and annealing behavior. III. thin films of polycarbonate,isotactic polymethyl methacrylate,and isotactic polystyrene

The morphology of thin films of polycarbonate (PC), isotactic polymethyl methacrylate (i-PMMA), and isotactic polystyrene (i-PS) were studied by bright field, diffraction, and dark field transmission, electron microscopy. The films were thermally annealed both before and after uniaxial deformation. The undrawn i-PMMA did not develop a crystalline texture upon annealing whereas the undrawn i-PS developed a random arrangement of lamellae. Thermal crystallization of undrawn PC has been shown to occur through the growth and merging of a nodular structure into fibrillar spherulites. Deformation of gold-decorated samples indicated a nonhomogeneous structure in the amorphous polymer on the 200-500 A scale. Thermal annealing of drawn samples resulted in fibrillar lamellae arranged perpendicular to the draw direction for all three polymers, indicating the straining has a marked influence on the crystalline morphology. This morphology is compared to similar morphologies reported in the literature for crystallization from stressed melts. High-resolution dark field micrographs confirm this morphology and indicate variations in crystallite size, depending upon the polymer and deformation conditions.     

Effect of thermal history on Tg and corresponding Cp changes in PVC of different stereoregularities

Samples of poly(vinyl chloride) polymerized at temperatures from ?60°C to +90°C, and therefore of different degrees of syndiotacticity and crystallinity, have been thermally treated in an attempt to reduce their content of ordered structures. Changes in order have been monitored by measuring Tg and the corresponding specific heat increment Δc_p. Partially syndiotactic samples have higher T_g and lower Δc_p than samples that are nearly atactic. After thermal treatment the differences decrease but do not vanish, even for samples heat-treated to about 250°C. This seems to indicate that some ordered structures are very stable even at relatively high temperatures. A quantitative estimate of the ordered structure content, based on Δc_p data, is proposed.     

The monoclinic form of crystal in cold-drawn PE and deformation mechanism

The monoclinic form of crystal in cold-drawn high-density polyethylene has been examined by infrared spectroscopy and x-ray diffraction. The IR results show that the monoclinic form of crystal exists in samples drawn at room temperature at high rates up to 8.5 mm/s. The x-ray diffraction photographs also show that the monoclinic form exists in the high-rate cold-drawn PE samples. The quantitative determination shows that the draw ratio has a primary effect on the content of the monoclinic form in cold-drawn PE samples. The results are explained by a “localized melting” model.     

Nanocomposites based on polymethylmethacrylate and silica

Nanocomposites based on polymethylmethacrylate and silica were synthesized by means of bulk polymerization. The morphology of the obtained polymer composites was studied by scanning electron microscopy. It was established that silica influences the mechanical and tribological properties of nanocomposites.     

刻蚀与退火对GaN欧姆接触的影响

使用干法刻蚀在GaN LED晶片上刻蚀n区,用电子束蒸发方法在n型GaN表面上淀积Ti/Al双金属层作为接触电极,在N2环境中进行退火.探讨不同的刻蚀方法和刻蚀条件及不同的退火条件对Ti/Al-n型GaN间欧姆接触的影响.     

退火对AlTiN多层薄膜结构及力学性能影响

使用TiAl合金靶,利用中频反应磁控溅射系统,通过交替改变氮气流量的方法,在高速钢(W18Cr4V)基体上沉积了一组氮含量周期性改变的AlTiN多层薄膜,并分别在600,700和800 ℃下真空退火热处理. 利用X射线衍射仪、场发射扫描电镜和高分辨透射电镜等方法研究了沉积态和退火态AlTiN多层薄膜组织和微观结构;AlTiN多层薄膜的力学和膜基结合性能用纳米压痕硬度仪、摩擦磨损仪以及划痕试验仪得到. 研究表明,采用沉积过程中周期改变氮气流量的方法,可以制备出稳定的、力学性能良好的AlTiN多层薄膜. 80 关键词： AlTiN多层薄膜 退火 微观结构 力学性能     

Effect of KOH molarity and annealing temperature on ZnO nanostructure properties

In this work, ZnO nanorods (NRs) were fabricated using a low cost chemical bath deposition (CBD) method. The effect of the potassium hydroxide concentration on the fabricated ZnO nanostructures was studied in depth. The optical, structure, and surface morphology properties of the fabricated ZnO nanostructures were investigated using Uv-vis spectroscopy, XRD, and SEM. The results indicate that the formation of hexagonally structured ZnO nanorods with different lengths and diameters was dependent on the KOH concentration. The sample prepared with 2 M of KOH was the best one for optoelectronic applications, since it has the smallest diameters. This sample was annealed at different temperatures (473 K–1073 K). Positron Annihilation Lifetime Spectroscopy was used to determine the defects in the ZnO nanorods. The results show that the positron mean lifetime (τ_m) decreased as the annealing temperature increased, which means that the overall defects in the ZnO nanorods decreased with increasing temperature. Consequently, higher performance semiconductor devices based on ZnO nanorods could be fabricated after high annealing of the ZnO nanorods.     

Effect of thermal treatments on the structure of syndiotactic polystyrene

Syndiotactic polystyrene films were prepared from the melt with different thermal treatments. Amorphous or crystalline films were obtained; x-ray analysis shows that in the crystalline samples two crystalline forms can be present and that the phase composition depends on the thermal conditions. The two forms show a different stability to liquid methylene chloride, one being stable while the other can be dissolved or transformed to a completely different crystalline structure. In all the analyzed samples the study of transport properties of CH₂ Cl₂ at low activity indicates that the amorphous component behaves as atactic polystyrene. This allows the determination of the crystallinity in the different samples.     

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As the ITER first wall Be/CuCrZr hot isostatic pressing (HIP) bonding intermediate transition layer, Ti/Cu layer can form a multi-layer intermediate metal phase, and defects such as cracks occur between the Ti/Cu metal phases. CuCrZr was used instead of Be, and a number of CuCrZr/Ti/Cu/CuCrZr joints were fabricated by the same HIP process as Be/CuCrZr to analyze the Ti/Cu joints. The effects of stress relief annealing on joint strength and defect distribution of the joints unannealed, annealed at 400°C and 500°C respectively were studied. The results show that three layers of Ti/Cu diffusion layers are formed on both sides of the intermediate titanium layer, namely Cu₄Ti, CuTi and CuTi₂. The thickness of Cu₄Ti on the pure copper side is thicker than that on the CuCrZr side, so that the crack is almost entirely distributed at the junction of Cu₄Ti and CuTi on the pure copper side where brittle fracture is easy to occur in the tensile samples. As the annealing temperature increases, the generation and propagation of cracks decreases.     

退火对钛/铜热等静压扩散连接界面的影响

钛/铜(Ti/Cu)作为ITER 第一壁Be/CuCrZr 热等静压连接中间过渡层,形成了多层中间金属相结构,容易在Ti/Cu 金属相之间产生裂纹等缺陷。采用CuCrZr 代替Be,经过与Be/CuCrZr 相同的热等静压工艺,制作了多个CuCrZr/Ti/Cu/CuCrZr 连接件,对Ti/Cu 连接接头进行深入分析。对连接件分别进行未退火、400℃和500℃ 退火处理,去应力退火后对接头强度和缺陷分布的影响进行了研究。研究结果表明,中间钛层的两侧都形成了三层Ti/Cu 扩散层,分别为Cu₄Ti、CuTi 和CuTi₂。纯铜侧的Cu₄Ti 厚度比CuCrZr 侧的厚,使得裂纹几乎全部分布于铜侧的Cu₄Ti 与CuTi 交界处,拉伸样品极易在此处发生脆性断裂。随着退火温度升高,裂纹的产生和扩展减少。     

Structural,magnetic and electrical transport properties in cold-drawn thin Fe-rich wires

Microstructural (X-ray diffraction), magnetic properties (hysteresis loop), electrical resistivity, magneto-impedance and stress impedance effects have been investigated in cold-drawn Fe_77.5B₁₅Si_7.5 amorphous wire. Initial amorphous wire (obtained by the in-rotating-water technique) with diameter of 125 μm was submitted to cold-drawn process decreasing the diameter to 50 μm. Such cold-drawn wire was treated by current annealing (currents of 190, 210, 220 and 230 mA during times between 1 and 45 min) for tailoring the magnetic and electrical transport properties. A qualitative analysis of the magnetoimpedance and stress impedance effects is given by considering the influence of the magnetoelastic anisotropy and frequency of the AC driving electrical current on the circular permeability.     

Effect of doping on thermally stimulated discharge current in polystyrene

TSC spectra of PS exhibit one peak at 105°C. Doping with organic molecular compounds in PS lowers the peak temperature and enhances the peak current and activation energy. Doped samples show one more peak at higher temperature. The results are discussed on the basis of different theoretical models.     

Crack propagation upon dynamic failure of polymethylmethacrylate

Crack propagation in polymethylmethacrylate shock-stressed by a pulsed magnetic field is experimentally investigated. The failure type as a function of the distance from the crack tip is analyzed, and the failure diagram is constructed. The surface failure energy is estimated. The tilt angles of mesocracks are correlated to the failure type.     

Effect of annealing on the structure and morphology of nylon 6 fibers

Changes in the structure of nylon 6 fibers annealed in dry and wet atmospheres were studied by small-and wide-angle x-ray diffraction. In the presence of water or saturated steam, fibers can be annealed to the same strucutral state at temperatures 70°C lower than in dry atmosphere. This is due to the enhanced mobility of the molecular segments in the amorphous region, a mechanism which is also known to lower the T_g by the same amount. Upon annealing under unconstrained conditions, lamellar spacing, crystallite size in the equatorial plane, crystalline as well as fiber density, and the chain-axis repeat increase with annealing-temperature; whereas crystalline orientation and the Van der Waals separation of the hydrogen-bonded sheets decrease. The monoclinic angle 8 remains constant at 66.7° (σ = 0.3°) and might depend on the starting fiber rather than on the treatment of the fiber. Most of these changes occur above a critical temperature of 170°C if dry, or 100°C if wet; rate of crystallization is also the highest under these conditions in nylon. The effect of these changes on such fiber properties as dyeing and the role of micro voids in dye diffusion and in dye uptake are discussed. Surface premelting and the accompanying changes in the surface structure of the lamellae, selective melting, and more importantly, the longitudinal motion of the nylon 6 chains and the resulting folding of interfibrillar extended amorphous chains are invoked to explain the shrinkage of the fiber, disorientation of the crystallites, increase in crystalline perfection, and the increase in lamellar spacing.