Moisture sorption of a three‐dimensional braided carbon fiber–epoxy composite under different media

A three‐dimensional braided carbon fiber–epoxy (C_3D/EP) composite was prepared by the vacuum‐assisted resin transfer molding (VARTM) technique. Its moisture absorption behavior under different media was characterized and compared with a unidirectional composite. Similar to the unidirectional composite, diffusion in the 3D composite obeys Fick's second law of diffusion when immersed in distilled water and phosphate‐buffered saline. In HCl and NaOH solutions, no Fickian behavior was observed. The similarity between the unidirectional and 3D composites suggests that fiber structure does not change diffusion pattern. However, the two composites showed different diffusion parameters (k, D, and M_e) in each medium studied. The 3D composite showed lower k, D, and M_e values because of its stronger hindrance effect to transport of moisture molecules. Diffusion in PBS is slower than that in distilled water because of the presence of heavy ions, but the diffusion pattern remains unchanged. In HCl, the diffusion behavior of the two composites cannot be described by Fick's law. In addition, the k value calculated from the initial linear part of the moisture sorption curve is much lower than that in distilled water. Diffusion in NaOH is unusual; the uptake initially increases rather rapidly but quickly drops, which is likely caused by the extensive solubility of the polymer matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 507–512, 2005     

三(苄基硫醇)锑的合成及其应用性能

以苄基硫醇、三氧化二锑 (或三氯化锑 )等为原料 ,研究了三 (苄基硫醇 )锑的最佳合成工艺条件 ,产率分别达到 90 %和 95 %。用元素分析法及红外光谱技术对产品进行了表征 ,热分析技术 (TG和DSC)研究表明 ,含合成产物的聚氯乙烯 (PVC)制品的初始分解温度在 2 2 0℃以上 ,其热分解效应为 1 1 5 5J/g。热老化研究表明 ,当合成产物添加量达 1 5份 (PVC质量为 1 0 0份 )时 ,PVC树脂的热稳定时间为 1 8min(2 0 0℃ ) ,当其与硫醇钡以质量比 3∶1复配时 ,可显著提高PVC制品的长期热稳定性     

γ-丁内酯制备α-乙酰-γ-丁内酯的探讨

探讨了在醇钠的催化作用下,以γ-丁内酯(GBL)和醋酸乙酯缩合制取α-乙酰-γ-丁内酯(ABL)的可行性。在带搅拌的间隙式反应釜中,用正交试验设计和单因素试验研究了反应温度、进料摩尔比和反应时间以及醇钠用量对ABL收率的影响,获得了主要工艺参数。结果表明:在相同条件下,影响收率的主要因素是反应温度和反应时间。     

Chinese melon (Momordica charantia L.) seed: Composition and potential use

Chinese melon (Momordica charantia L.), also known as bitter gourd, is a tropical crop, grown throughout Asian countries for use as food and medicinals. In 1993, four cultivars of Chinese melon were grown in Mississippi and the seeds were collected. Oil contents of the seeds ranged from 41 to 45% and the oils contained 63–68% eleostearic acid and 22–27% stearic acid. Industrially important tung oil, a “fast-drying oil” used in paints and varnishes, contains 90% eleostearic and 2–3% stearic acid. The ratio of stearic to eleostearic in Chinese melon seed oil is ten times greater than that in tung oil. The higher ratio should reduce the rate of drying and crosslinking and could be advantageous in the paint industry. The defatted meals contained 52–61% protein and would be a good source of methionine.     

Effects of Copper Coating on the Crystalline Structure of Fine Barium Titanate Particles

We have investigated the effect of a metal coating—copper—on the tetragonal structure of fine barium titanate (BaTiO₃) particles. The BaTiO₃ particles were synthesized by a sol-gel method and heat treated at temperatures >900°C for various amounts of time before coating. The copper coating was achieved by an electroless coating technique. The transmission electron microscopy micrographs revealed that the coated powder contained fine BaTiO₃ particles that were embedded in copper patches. The X-ray diffractometry patterns showed that the copper coating increased the c/a ratio of the fine BaTiO₃ particles. For powders that were heat treated at 900°C for 10 h and were initially cubic, the copper coating changed the c/a ratio, from 1 to 1.0034. For powders that were calcined at 900°C for 20 h and were initially tetragonal, the copper coating further enhanced the c/a ratio, from 1.0028 to 1.0043. When the copper-coated BaTiO₃ particles were oxidized, the c/a ratio was reduced to a value that was approximately equal to or below that of the uncoated powders. A conductive coating can eliminate the depolarization energy of an insulating polar particle. The fact that the copper coating promoted the polar tetragonal phase but the nonconductive copper-oxide coating did not was consistent with the interpretation that the presence of the cubic phase (nonpolar) in small BaTiO₃ particles was caused by the depolarization effect.     

W/O型反相微乳法制备纳米材料及其应用

简要介绍了反相微乳液的结构、性质、相行为及微观结构的检测方法；阐述了在W／O型反相微乳液中制备纳米材料的反应原理、制备方法及影响纳米微粒成核、增长的因素；综述了近年来国内外使用该方法制备纳米材料的研究进展。     

Novel Fabrication Route to Al2O3–TiN Nanocomposites Via Spark Plasma Sintering

A novel method for the preparation of Al₂O₃–TiN nanocomposites was developed. A mixture of TiO₂, AlN, and Ti powder was used as the starting material to synthesize the Al₂O₃–TiN nanocomposite under 60 MPa at 1400°C for 6 min using spark plasma sintering. X-ray diffractometry, scanning electron microscopy, and transmission electron microscopy were used for detailed microstructural analysis. Dense (up to 99%) nanostructured Al₂O₃–TiN composites were successfully fabricated, the average grain size being less than 400 nm. The fracture toughness ( K _{I C} ) and bending strength (σ_b) of the nanostructured Al₂O₃–TiN composites reached 4.22±0.20 MPa·m^1/2 and 746±28 MPa, respectively.     

有关网银系统的信息安全问题与措施探索

近年来,我国网上银行的业务量增长迅速,越来越多的商务交易通过网银来实现,由于网络存在缺陷,进而导致针对网银的犯罪情态日益严重,网银的安全问题十分突出,这给网络银行的正常运行造成了一定程度的影响,严重损害了网银的根本利益,阻碍了网上银行的稳定、健康发展。本文主要针对我国网银安全问题进行探讨,阐述了我国网银发展的现状,并提出了几点措施,以有效加固网银安全,降低网银的风险,不断推动网上银行的健康发展。     

纳米CaSO_4晶须改性聚氨酯密封胶的制备

通过三种聚醚制成的密封胶进行对比,具体考察了CaSO4晶须对密封胶力学性能的影响。结果表明,在单组分湿固化聚氨酯密封胶中添加纳米CaSO4晶须后,密封胶的剪切强度得到提高,硬度和弹性变化不大。使用CaSO4晶须替代气相二氧化硅,在降低成本的同时,密封胶的触变性仍然很好。     

银催化剂研究进展(下)

综述了银催化剂的发展历史、催化作用机理、制备方法、助催化剂、载体研究进展，并对用于乙烯环氧化反应的银催化剂在不同时期的发展状况、宏观及微观催化作用机理、从原料到催化剂成品的制备过程、数十种金属及非金属助催化剂的助催作用、载体结构及添加组分的改进等方面的最新研究成果作了阐述。