DC electrical conduction in solution-grown pure and iodine-doped poly(butylene terephthalate) films

DC electrical conduction in poly(butylene terephthalate) films sandwiched between planar aluminium electrodes was investigated. The films were grown by the isothermal immersion technique. The conduction process was studied in the temperature range 300–450K, with an applied electric field of 0.22 × 10⁷?6.66 × 10⁷ Vm^?1. It was found that the Richardson-Schottky type of conduction mechanism was dominant throughout the temperature range of study. The values of the Schottky field lowering constant β, the effective metalinsulator potential barrier and the activation energy were evaluated. The value of the activation energy (U = 0.7 eV) indicates the predominance of electronic conduction. The effect of impurities like iodine on electrical conduction was also investigated.     

Modelling of long-term diffusion–reaction in a bentonite barrier for radioactive waste confinement

Bentonites have been proposed as buffer material for barriers in geological disposal facilities for radioactive waste. This material is expected to fill up by swelling the void between the canisters containing the waste and the surrounding ground. However, the bentonite barriers may be submitted to changes of humidity, temperature variation, fluid interaction, mass transport, etc. This could modify the physico-chemical performance of the barrier, mainly on the interface with the steel container and with the geological barrier. The engineered barrier development necessitates thus the study of the physico-chemical stability of its mineral component as a function of time under the conditions of the repository in the long-term.The purpose of the present study was two-fold. Firstly, it was hoped to simulate the chemical transformations (geochemical and cation exchange reactions) coupled with diffusion of chemical-elements into the engineered barrier under repository conditions by applying a thermokinetic hydrochemical code (KIRMAT: Kinetic Reactions and Mass transport).Secondly, it was hoped to apply a simplified method to estimate the swelling capacity evolution by a volume balance in the fluid-saturated engineered barrier, considering that the decay of swelling capacity is directly proportional on the volume of transformed montmorillonite and, taking into account that it may be partially compensated by the volume of neo-formed swelling clays.The system modelled herein was considered to consist of 1-m thick zone of water-saturated engineered barrier. This non-equilibrated system was placed in contact with a geological fluid on one side, which was then allowed to diffuse into the barrier, while the other side was kept in contact with a source of metallic iron. Reducing initial conditions(P_O2 0; Eh = − 200 mV) and a constant reaction temperature (100 °C) were considered.The results showed that the EB in contact with the geological fluid was highly transformed after 10,000 years, whereas the most significant chemical processes were illitization, cation exchange and saponization, extending up to 20 cm into the EB. Chemical transformations of minor importance in the EB were identified as well, such as a neo-formation of silicates (quartz, cristobalite), anhydrite, laumontite, magnetite and chlorite in the system.A simplified method based on volume balance showed that the swelling capacity of the bentonite barrier is slightly affected after 10,000 years of diffusion–reaction (D close to 1) because the volume of neo-formed swelling-clays is almost directly proportional to the volume of transformed Na/Ca-montmorillonite, except for a strong illitization and/or neo-formation of non-swelling clays. In the present study, this simple approach predicted that the decay of swelling capacity of the engineered barrier is drastically affected close to the geological barrier-engineered barrier interface. Out this zone the swelling capacity decay lies between 5% and 11%.     

Effect of organic vapour interaction on permeation rate through polymer films

The permeability coefficients (P) of linalool, citral ethyl butyrate, d-limonene and octanal permeating through LDPE and ionomer films were measured alone as individual and as a component of a mixture at a temperature of 23 °C and in saturated water vapour. Values of P for ionomer film were approximately two orders of magnitude below those for LDPE for the compounds tested. Both PET and PETG films were found to be much better barriers against the compounds tested than LDPE and ionomer films. In general, the permeability, diffusion and solubility coefficients (P. D, and S) values measured in mixture were substantially less than the values obtained individually. Permeability behaviour of these compounds at low concentrations in the mixture was similar to that of permanent gases. Reduction of solubility coefficients in mixture permeation was greater with the higher solubility coefficients. These results provide a better understanding of the mechanism of vapour diffusion through polymers.     

A screen-printed interdigitated back contact cell using a boron-source diffusion barrier

A low-cost approach to fabricating interdigitated back contact cells is carried out on the principle of screen-printing a material that serves both to dope the rear surface and as a diffusion barrier to the dopant species of the opposite polarity. With this technique, an interdigitated pattern of n⁺ and p⁺ regions is formed on the cell back. Shunt-free rear interdigitated junctions are achieved. This work produced a cell with confirmed conversion efficiency of 10.5%. Areas for further efficiency gains are discussed.     

Insulation characteristics of perfluorocarbon liquid/solid insulation for nonflammable large power transformer

A new type nonflammable large power transformer system is proposed in which the excellent cooling characteristics and insulation properties of nonflammable perfluorocarbon (PFC) liquid is utilized. In the system, transformer windings are put in an insulating cylinder filled with PFC liquid. The core includes cooling panel through the liquid. The space between the insulating cylinder and tank is filled with compressed SF⁶ gas. This paper describes the insulation characteristics of main insulation and inter-winding insulation models which simulate the transformer. It is found that (1) higher withstand voltage is expected by means of insulation barriers in the main insulation model; (2) partial discharge in inter-winding insulation model is beginning to behave in a constant electric field strength on the point of 0.1 mm liquid gap length.     

份菁／铝肖特基势垒光生伏特的温度效应

测定了１６０－３２０Ｋ范围内铝／份菁／银有机太阳电池的光电流、光电压的温度效应。光电流和转换效率随温度的上升而上升；光电压在低于２２３Ｋ时呈下降，高于２２３Ｋ时呈上升．当温度高于２９３Ｋ时，三者均趋于饱和，在温度低于２２３Ｋ时热离子发射电流起主导作用，高于２２３Ｋ时杂质离子复合电流起主导作用。     

高速半导体激光器等效参数的提取

本文克服了背地共面线谐振现象的有害影响，制作了国产高速半导体激光器非匹配微波封装组件，测试了组件的频响特性，由此提取了器件的等效参数，讨论了改善国产器件性能的技术途径。     

平面栅静电感应晶体管阻断状态解析模型

给出的这一解析模型,是在合理近似基础上,通过求解二维Poisson方程获得的。其计算值与数值模拟结果相符,而且该模型也是分析平面栅静电感应晶体管特性的基础。     

High-temperature corrosion of dilute chromium-lanthanum alloys

The kinetics of oxidation in air of chromium-lanthanum alloys have been investigated in the temperature range 1100–1400°C. The positive effect of lanthanum on the heat resistance of chromium was established and is explained as a result of the formation of a barrier oxide film consisting of Cr₂O₃ and LaCrO₃. The dispersed particles of lanthanum chromite distributed on grain boundaries form diffusion barriers that change the oxidation law from parabolic to logarithmic. An empirical equation which quantitatively describes masstransport processes with decreasing effective diffusion area and simultaneous sublimation of scales is proposed.     

Structural properties of ZnSy Se1−yZnSe/GaAs (001) heterostructures grown by photoassisted metalorganic vapor phase epitaxy

ZnS_ySe_1−yZnSe/GaAs (001) heterostructures have been grown by photoassisted metalorganic vapor phase epitaxy, using the sources dimethylzinc, dimethylselenium, diethylsulfur, and irradiation by a Hg arc lamp. The solid phase composition vs gas phase composition characteristics have been determined for ZnSy_ySe_1−y grown with different mole fractions of dimethylselenium and different temperatures. Although the growth is not mass-transport controlled with respect to the column VI precursors, the solid phase composition vs gas phase composition characteristics are sufficiently gradual so that good compositional control and lattice matching to GaAs substrates can be readily achieved by photoassisted growth in the temperature range 360°C ≤ T ≤ 400°C. ZnSe/GaAs (001) single heterostructures were grown by a two-step process with ZnSe thicknesses in the range from 54 nm to 776 nm. Based on 004 x-ray rocking curve full width at half maximums (FWHMs), we have determined that the critical layer thickness is h_c ≤200 nm. Using the classical method involving strain, lattice relaxation is undetectable in layers thinner than 270 nm for the growth conditions used here. Therefore, the rocking curve FWHM is a more sensitive indicator of lattice relaxation than the residual strain. For ZnS_ySe_1−y layers grown on ZnSe buffers at 400°C, the measured dislocation density-thickness product Dh increases monotonically with the room temperature mismatch. Lower values of the Dh product are obtained for epitaxy on 135 nm buffers compared to the case of 270 nm buffers. This difference is due to the fact that the 135 nm ZnSe buffers are pseudomorphic as deposited. For ZnS_ySe_1−y layers grown on 135 nm ZnSe buffers at 360°C, the minimum dislocation density corresponds approximately to room-temperature lattice matching (y ∼ 5.9%), rather than growth temperature lattice matching (y ∼ 7.6%). Epitaxial layers with lower dislocation densities demonstrated superior optical quality, as judged by the near-band edge/deep level emission peak intensity ratio and the near band edge absolute peak intensity from 300K photoluminescence measurements.