Surface softening in silicon by ion implantation

Load-variant microhardness tests have been used to investigate the hardness behaviour of ion-implanted (1 1 1) silicon wafers. A variety of ion doses, energies and species, including n-type, p-type and isovalent ions, have been implanted. At the high doses used (1 to 8 x 10¹⁷ ions cm^2–), all implantations resulted in a surface amorphous layer being formed. The microhardness behaviour has been interpreted in terms of the presence of a surface layer of lower hardness than the substrate. The thickness of this layer has been investigated experimentally using Rutherford backscattering and the results correlated with simple theoretical predictions. Finally, the microhardness behaviour of a soft layer on a harder substrate has been modelled in order to try to predict the hardness variations arising from differing layer thicknesses and different indentation sizes. It is concluded that the amorphous layer produced by implantation appears to show no variation of microhardness with load and has a hardness typically between 400 and 700 Vickers (VHN). Further, the previously reported critical dose of 4 x 10¹⁷ ions cm^–2 necessary to observe significant surface softening seems to correspond to the regime in which the amorphous layer shows a rapid increase with dose.     

Determination of parameters used to prevent ignition of stored materials and to protect against explosions in food industries

There are always risks associated with silos when the stored material has been characterized as prone to self-ignition or explosion. Further research focused on the characterization of agricultural materials stored in silos is needed due to the lack of data found in the literature. The aim of this study was to determine the ignitability and explosive parameters of several agricultural products commonly stored in silos in order to assess the risk of ignition and dust explosion. Minimum Ignition Temperature, with dust forming a cloud and deposited in a layer, Lower Explosive Limit, Minimum Ignition Energy, Maximum Explosion Pressure and Maximum Explosion Pressure Rise were determined for seven agricultural materials: icing sugar, maize, wheat and barley grain dust, alfalfa, bread-making wheat and soybean dust. Following characterization, these were found to be prone to producing self-ignition when stored in silos under certain conditions.     

FE-Modelling of cover splitting due to corrosion by use of inner softening band

The splitting of concrete covers due to the expansive action of corrosion has been investigated by a finite element method (FEM) based on an element-embedded crack concept called the inner softening band. Fictive cross-sections, with and without transverse reinforcement, were studied. The concrete composition (plain and fibrous high-strength concrete) and the cover thickness were varied. The model produced credible fracturing behaviour in concrete covers and explained the mechanical origin of the cracks. For cover thicknesses less than two times the bar diameter, fibres do not seem to have any significant effect on occurrence of splitting cracks. However, fibres are effective to arrest the opening of arisen splitting cracks and to redistribute the strains to other cracks. Hence, fibres may postpone or prevent a total spalling of concrete covers. A larger cover is necessary not only to prolong the initiation period, but also for the fibres (2 volume-%) to be effective beyond occurrence of corrosion induced cover cracks.

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Résumé La fissuration de la couche protectrice d'une poutre en béton causée par l'expansion due à la corrosion, a été étudiée à l'aide de la méthode des éléments finis basée sur le concept de fissure élémentaire incluse, appelée bande interne de radoucissement. Des sections transversales fictives, avec et sans armatures transversales ont été étudiées. La composition du béton de haute résistance (avec et sans fibres) et l'épaisseur de la couverture des armatures ont été étudiées. Le modèle a généré un comportement crédible de la rupture dans la zone d'enrobage des armatures, permettant d'expliquer l'origine mécanique des fissures. Pour une épaisseur de recouvrement inférieure à deux fois le diamètre de l'armature, les fibres ne semblent pas avoir d'effet significatif sur l'apparition des fissures. Cependant les fibres sont efficaces pour arrêter l'ouverture de fissures existantes et pour redistribuer les contraintes aux autres fissures. Les fibres peuvent retarder ou éviter la destruction de la couche protectrice en béton de la poutre. Une épaisseur de couverture supérieure est nécessaire non seulement pour prolonger la période d'initiation mais aussi pour que les fibres (2% en volume) soient efficaces lors de l'apparition de fissures d'origine corrosive.

     

有机-无机复合骨重建材料的研究进展

骨组织重建技术的进步与材料科学的发展息息相关，对国内外当前非金属骨植入与骨组织工程材料的种类及其复合技术的研究情况进行了综述与评价，认为对界面结合的研究、新的智能型材料的研究是今后非金属复合骨重建材料的发展方向。     

超声化学法制备无机纳米材料的研究进展

由于纳米材料具有许多不同于本体材料的优良性能,因此纳米材料的制备与应用是近年来材料科学研究的热点。超声化学法是一种制备特异性能纳米材料的有效途径。超声波对反应体系的作用主要表现在:利用超声能量进行分散,利用空化过程进行高温分解,利用剪切破碎机理对颗粒尺寸进行控制,利用机械搅动影响沉淀的形成过程。本文中介绍了超声化学法制备纳米材料的原理,并详细介绍了超声化学法在制备纳米金属及合金、纳米金属氧化物及其它纳米金属化合物方面的应用。     

Strain hardening and softening in a nanocrystalline Ni-Fe alloy induced by severe plastic deformation

The strain response of an electrochemically deposited nanocrystalline Ni-20 wt.% Fe alloy processed by high-pressure torsion (HPT) was investigated by monitoring changes in hardness. Strain hardening was observed in the very early stage of HPT, followed by strain softening before the onset of a second strain hardening stage. Structural investigations revealed that the two hardening stages were associated with an increase in dislocation density, whereas the strain softening stage was accompanied by a reduction in the dislocation and twin densities, thereby demonstrating the main dependence of hardness on the dislocation density in this material. Grain growth occurred during HPT and its role in the hardness evolution is also discussed.     

顶空气相色谱法测定利奥西呱原料药中9种残留溶剂的含量

建立同时测定利奥西呱原料药中残留溶剂甲醇、异丙醇、二氯甲烷、正己烷、乙酸乙酯、六甲基二硅醚、三乙胺、甲苯与N,N-二甲基甲酰胺残留量的方法。采用顶空进样气相色谱法,以二甲基亚砜为溶剂,外标法计算残留溶剂量。9种残留溶剂色谱峰的理论板数均10 000,相邻峰的分离度均1.5,在考察的浓度范围内各溶剂线性关系良好(r=0.998 2~0.999 7);RSD10%;平均加标回收率为90.86%~105.01%。各残留溶剂的检测限和定量限分别为0.000 025%~0.002 6%,0.000 051%~0.008 8%,均低于《中国药典》规定。利奥西呱原料中检出甲醇、正己烷、乙酸乙酯与DMF残留,但均未超过限度,其余溶剂未检出。该方法操作简单、方法灵敏、结果准确,可用于利奥西呱原料药中残留溶剂检测。     

气相法制备纳米铁颗粒新进展

纳米铁颗粒在磁性、催化和吸波等方面都展现了优异的特性,具有广阔的应用前景.在过去的几十年里,国内外许多学者开展了对纳米铁颗粒制备、结构和性能的研究.着重阐述了纳米铁颗粒的气相法制备方法,并指出了这一领域今后的研究方向.     

气相法制备纳米铁颗粒新进展

纳米铁颗粒在磁性、催化和吸波等方面都展现了优异的特性，具有广阔的应用前景。在过去的几十年里，国内外许多学者开展了对纳米铁颗粒制备、结构和性能的研究。着重阐述了纳米铁颗粒的气相法制备方法，并指出了这一领域今后的研究方向。     

Removal of residual stresses by low-temperature annealing to prevent stress-corrosion cracking of carbon steels

The effect of low-temperature annealing on the relaxation of residual stresses and on the stress-corrosion resistance of carbon steels was investigated. It was shown that stress-corrosion cracking of welded joints in carbon steels under the influence of boiling nitrate solutions and alkaline solutions is prevented by annealing at temperatures 450° C and 500° C, respectively.     

Dental application of glass cloth to denture: dimensional accuracy in reinforced resins

Duplicate dentures were made from heat-cured (HC) and microwave-cured (MC) bases, and with these bases reinforced with glass cloth. The clearance as a dimensional change in the resins was measured in relation to duplicate gypsum models from a master denture model. The clearance value in resins stored in distilled water at 37°C demonstrated better dimensional accuracy as compared with base resin replicas stored in air at 37°C. When measured at 1 kg load, MC and HC base resins showed a decrease in the clearance value. MC and HC resins reinforced with glass cloth had no significant difference between the values of dimensional accuracy at each site. The MC base and reinforced resins could be useful, comparable with HC acrylic base resin, for dental applications.     

Electrochemically mediated reduction of horseradish peroxidase by 1,1'-ferrocenedimethanol in organic solvents

Cyclic voltammetry is an efficient means of analyzing the catalytic reduction of H2O2 at immobilized horseradish peroxidase (HRP)-Eastman AQ 55 electrodes in the presence of 1,1'-ferrocenedimethanol as a one-electron reversible cosubstrate. This system was employed to study the kinetics of the reduction of compound II of HRP in a number of organic solvents. An electrocatalytic response was detected in methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetone, 2-butanone, 1,2-propanediol, acetonitrile, ethyl acetate, and ethylene glycol. Unusual bell-shaped variations of the peak or plateau catalytic current with the substrate concentration were observed in all solvents tested. The results obtained in methanol, acetonitrile, and 1-propanol were analyzed using the model developed by Saveant (Limoges, B.; Saveant, J.-M.; Yazidi, D. J. Am. Chem. Soc. 2003, 125, 9192-9203). The values of k3Gamma0 and K3,M, where k3 = k3,1k3,2/(k3,-1 + k3,2), Gamma0 is the surface concentration of active enzyme, and K3,M = (k3,-1 + k3,2)/k3,1, were determined. The values of k3Gamma0 for the mediated reduction of compound II of HRP in methanol, 1-propanol, and acetonitrile (in the presence of 5% aqueous buffer) were not affected by the solvent dielectric constant but decreased with solvent hydrophobicity. The value of K3,M obtained in methanol was similar to that obtained for [Os(bpy)2pyCl]2+ in aqueous buffer.