纳米SiC表面接枝修饰的XPS研究

聚合物在纳米粒子表面接枝后,可在其表面建立起空间位阻稳定层,提高纳米粒子的分散稳定性及其与树脂基体的相容性.本文采用缩聚法在纳米SiC表面接枝了聚缩醛,X射线光电子能谱(XPS)的分析结果表明,经过聚缩醛接枝改性的纳米SiC表面Si2p峰明显降低,而C1s峰和O1s峰明显地增长,对C1s、Si2p峰精细扫描及分峰拟合表明,纳米SiC表面碳元素中有38.4%属于接枝物聚缩醛的有机碳,而79.8%的Si元素结合能增加了2.5eV,由此表明,纳米SiC表面形成了良好的表面修饰层,接枝物聚缩醛以化学键结合于纳米SiC表面;对比XPS和热失重分析(TG)的数据结果,可以推测,聚缩醛主要分布在纳米SiC的表面,而在体相中独立存在的几率较小.     

Fracture from inherent flaws in polymers

Fracture data on polymethyl methacrylate, polyvinyl chloride, polyacetal and polypropylene in both tension and bending are given for a range of temperatures using unnotched specimens. It is concluded that all the failures occur at the gross crazing or yield stress and are thus stress-controlled, and the flaw size has little effect. The propagation behaviour of the flaws under these conditions is discussed in terms of stability criteria.     

Anions effect on the low temperature growth of ZnO nanostructures

Seed mediated aqueous chemical growth (ACG) route was used for the growth of ZnO nanostructures on Si substrate in four different growth mediums. The growth medium has shown to affect the morphology and the size of the different nanostructures. We observed that the medium containing zinc nitrate anions yields the nanorods, in a medium containing zinc acetate anions nano-candles are obtained. While in a medium containing zinc chloride anions ZnO nano-discs were obtained and in a medium containing zinc sulfate anions nano-flakes are achieved. Growth in these different mediums has also shown effect on the optical emission characteristics of the different ZnO nanostructures.     

Effect of polishing conditions on terminating optical connectors with spherical convex polished ends

Increased demand for fiber-optic technology has created significant growth in the sales of interconnection devices such as fiber-optic connectors, cable assemblies, and adapters. To ensure good connector performance during actual use, several process parameters related to geometric and optical characteristics of the connector must be thoroughly understood during the manufacturing stage. The experimental design has been used here to see the influence of applied pressure and time on the fiber end geometry as well as optical performance. The mathematical model is also applied to explain the phenomena of the present fiber undercut-reflectance relation. By a proper choice of polishing film grit size and processing conditions, it is possible to obtain fiber connectors with less fiber undercut and better return loss. Influences of film grit size and rubber-pad thickness on the reflectance and the fiber undercut are also presented.     

In-fiber strain characterization of fiber-optic connector assemblies by Bragg grating sensors

In-fiber Bragg grating sensors were used to study mechanical strain in optical fibers that were terminated in standard-termination and ribbon connectors. Our findings indicate that terminated sensors experience a compressive strain whose magnitude depends on the cure profile of the epoxy encapsulant used in these connectors. Anneal treatments on these connectors generally reduce the mechanical stress by inducing stress relaxation in the encapsulant layer. These experiments demonstrate the viability of in-fiber sensors to characterize fiber-optic connector assemblies during and following termination.     

Higher Order Assembly of Virus‐like Particles (VLPs) Mediated by Multi‐valent Protein Linkers

Two‐ and three‐dimensional assembly of nanoparticles has generated significant interest because these higher order structures could exhibit collective behaviors/properties beyond those of the individual nanoparticles. Highly specific interactions between molecules, which biology exploits to regulate molecular assemblies such as DNA hybridization, often provide inspiration for the construction of higher order materials using bottom‐up approaches. In this study, higher order assembly of virus‐like particles (VLPs) derived from the bacteriophage P22 is demonstrated by using a small adaptor protein, Dec, which binds to symmetry specific sites on the P22 capsid. Two types of connector proteins, which have different number of P22 binding sites and different geometries (ditopic linker with liner geometry and tetratopic linker with tetrahedral geometry) have been engineered through either a point mutation of Dec or genetic fusion with another protein, respectively. Bulk assembly and layer‐by‐layer deposition of P22 VLPs from solution was successfully achieved using both of the engineered multi‐topic linker molecules, while Dec with only a single binding site does not mediate P22 assembly. Beyond the two types of linkers developed in this study, a wide range of different connector geometries could be envisioned using a similar engineering approach. This is a powerful strategy to construct higher order assemblies of VLP based nanomaterials.     

Simulation of methylene blue adsorption by salts-treated beech sawdust in batch and fixed-bed systems

Batch and column kinetics of methylene blue adsorption on calcium chloride, zinc chloride, magnesium chloride and sodium chloride treated beech sawdust were simulated, using untreated beech sawdust as control, in order to explore its potential use as a low-cost adsorbent for wastewater dye removal. The adsorption capacity, estimated according to Freundlich's model, the Langmuir constant K(L) and the adsorption capacity coefficient values, determined using the Bohart and Adams' bed depth service model indicate that salts treatment enhanced the adsorption properties of the original material. Since sawdust is an industrial waste/byproduct and the salts used can be recovered as spent liquids from various chemical operations, this process of adsorbent upgrading/modification might be considered to take place within an 'Industrial Ecology' framework.     

Cement-based biocide coatings for controlling algal growth in water distribution canals

The germicidal effectiveness of various additives when blended within a microstructure of a cement based system was studied. The relationship between the chemical and physical characteristics of concrete surfaces and their ability to have an enhanced resistance to algal growth was documented through a novel set of laboratory and field testing. The main potential areas of application for these new cement composite systems involve the lining of canal surfaces where fixed-surface biocides are desirable to control biofouling. Different biocide formulations containing class F fly ash, silica fume, Zn oxide, copper slag, ammonium chloride, sodium bromide, and cetyl-methyl-ammonium bromide were evaluated for the mitigation of algal growth on concrete surfaces. Mortar coupons treated with these formulations were tested under laboratory and field conditions.These new cement composite systems were compared with proprietary products that are commercially available and applied using a latex paint. Laboratory scale screening experiments showed that various concentrations of zinc oxide significantly inhibited algal growth even after nine months. It was observed that 20% zinc oxide in concrete produced optimal algal inhibition compared to other additives. Copper slag, ammonium chloride, sodium bromide, and fly ash, when added singly, also showed algal inhibition capabilities. Addition of zinc oxide and ammonium chloride (10% each) in mortar mix was as effective as expensive proprietary chemicals in reducing algal growth on concrete surfaces under laboratory and field conditions.     

电网设备线夹开裂原因

某电力公司变电站用铝合金设备线夹在运行过程发生批次开裂事故,通过宏观观察、断口分析、化学成分分析、力学性能测试、冷冻模拟试验等方法,对设备线夹的开裂原因和开裂机理进行了分析.结果表明:设备线夹焊缝存在焊接缺陷,导致焊缝强度下降;设备线夹接线管底部存在积水空间,寒冷天气下积水结冰,体积膨胀,使焊缝承受设计工况外的负载而过...     

Bulk ZnO nanorod assemblies fabricated by spin coating of organo-precursor gels on CuO nanowires

Bulk ZnO nanorod assemblies have been successfully fabricated on CuO nanowires through spin coating of organoprecursor gels. A thin film of CuO nanowires was first generated by direct heating of a metallic Cu-foil at 500 °C in an air atmosphere. A stable colloidal organo-precursor sol synthesized by dissolving equimolar zinc acetate dihydrate and monoethanolamine in 2-methoxyethanol was subsequently repeatedly deposited onto the CuO nanowires by spin coating. The formation of ZnO nanorod assemblies was controlled by varying the number of coatings. The average diameter of the ZnO rods was determined to be ～600 nm.     

低碳钢丝焊网热镀锌工艺的改进

根据低碳钢热镀锌原理,分析了低碳钢钢丝焊网热镀锌工艺中存在的问题,包括工艺不完善、锌液成分不合理、镀后抹拭材料及方法不当等而导致的热镀锌层质量不稳定、锌耗高.针对上述问题,提出了相应的改进方法,包括采用复合除锈剂进行酸洗除锈,强化除锈效果;以氯化锌与氯化铵比例为1.2～1.6、总浓度为12%～15%的混合溶液代替单一的氯化铵作为助镀剂;增加助镀后的烘干工序;采用无机物和珍珠岩混合材料作为抹拭剂等改进措施.通过改进与完善工艺,所得镀锌层表面光滑,焊接点处无积锌,锌耗比工艺改进前降低2%.     

增韧聚甲醛共混合金的自润滑特性研究EI

通过对国产树脂进行改性处理 ,辅以高效增容剂和成核剂 ,制得综合性能优异的聚甲醛 /聚氨酯共混合金。再以此为基体制得高自润滑性和高抗磨性的聚甲醛共混合金复合材料。通过对增韧剂的选择与配比 ,以及不同的加工工艺条件 ,较好地解决了界面相容 ,组织分散等难题 ;考察了不同润滑剂 (有机硅油、石墨、聚四氟乙烯和二硫化钼等润滑材料 )对整体复合材料抗磨减摩特性的影响。结果表明 ,含有 10 % (质量 ) ,聚氨酯的聚四氟乙烯和硅油的改性聚甲醛 。     

Korrosionsverhalten binärer Magnesium‐Zink‐Legierungen in salzhaltigen Medien

Aluminum is a prevalent alloying element to improve the corrosion resistance of magnesium alloys. Recent investigations found out that alloying small amounts of zinc can decrease the corrosion rate of binary magnesium‐zinc alloys. Based on these results low‐alloyed MgZn‐alloys have been analyzed in gravimetric and electrochemical measurements using varied chloride containing media. It was detected that small amounts of zinc have positive effects on the corrosion behavior; in low as well as high concentrated sodium chloride solutions. The overall tendencies of the results from the gravimetric and electrochemical investigations can be correlated. This was underlined using micro‐tomography analyses.     

Enhancement in ethanol sensing response by surface activation of ZnO with SnO2

A surface functionalized gas sensing material convincingly giving enhanced response to ethanol is demonstrated by SnO₂ activated ZnO. Zinc oxide was synthesized by a chemical route, deposited on an alumina substrate and activated by tin dioxide obtained by on-site oxidation of tin chloride. The XRD study of samples confirmed wurtzite hexagonal structure of zinc oxide and FESEM investigation revealed that surface of activated ZnO microrods was covered by nanoparticles of tin dioxide. Sensing response of sensing elements activated with different concentrations of tin chloride solution has been investigated. It was found that response to ethanol vapor significantly enhanced (eight times) by surface activation with tin dioxide, which optimized at a concentration of 3 wt.%.     

陶瓷涂层加注管接头密封性能研究

球锥面密封结构是航空航天及化学工业中普遍采用的密封结构,对其密封性能研究及改进具有一定的工程应用价值。球锥面加注管接头的主要材料是1Cr18Ni9Ti,当重复使用时,接触表面极易发生磨损,影响密封特性。针对上述问题,采用涂层表面处理技术,提高表面抗磨损性能和密封性能。借助ANSYS有限元软件,模拟分析了接触表面的应力分布情况。陶瓷涂层弹性模量越大,接触应力越大,密封性越好,但粘结强度较低。当涂层与基体弹性模量相接近时,粘结强度较好。因此对4种陶瓷涂层进行等离子喷涂并进行密封及磨损试验研究。结果表明:TiN涂层加注管接头黏着磨损及磨粒磨损现象有较大改善,重复使用效果最好。     

Tensile mechanical properties of polyacetal after one and six months' immersion in Ringer's solution

The engineering polymer polyacetal (also known as polyoxymethylene) has a long history of clinical use including in the femoral component of the Freeman all-polymer knee replacement. The polymer is a promising material for novel applications including the femoral component of hip resurfacing prostheses. However, no work following the effect on mechanical properties of extended immersion in the physiological environment has been reported. Samples of five grades of polyacetal were obtained and tested on an MTS Bionix 858 at 37 degrees C in physiological saline. Three groups of specimens were tested: "as received"; immersed in Ringer's solution at 37 degrees C for one month; immersed in Ringer's solution at 37 degrees C for six months'. While there were negligible reductions in the ultimate tensile strengths, the Young's moduli of all polymer grades showed significant reductions (p < 0.01) of up to 19.5% following one months' immersion. There were negligible changes in ultimate tensile strength and stiffness between one and six months' immersion, however some polymers showed a small, but significant (p < 0.05) increase in stiffness. The percentage elongation and true stress for plastic instability showed negligible changes following immersion for one and six months'. These results encourage the use of polyacetal in load-bearing orthopaedic applications.     

Influence of precursor source on sol–gel deposited ZnO thin films properties

Zinc oxide thin films were deposited by sol gel technique on glass substrates using different precursors (zinc acetate, zinc nitrate and zinc chloride). In the present work we investigate the precursor nature influence on structural, morphological, optical, electrical properties and photocatalytic activity of ZnO thin films. For this purpose we have used X-rays diffraction (XRD), atomic force microscopy (AFM), UV–visible spectroscopy and Hall effect measurements for films characterization. The obtained results indicated that ZnO films properties are strongly influenced by the nature of the used precursor as reactant. Films photocatalytic activity was evaluated by the photo-degradation of methylene blue (MB) dissolved in aqueous solution under UV-A light. The obtained results indicated that ZnO thin films prepared from zinc acetate are more efficient than those prepared from zinc nitrate and zinc chloride.     

Simple solution phase synthesis of 3-D assembly of ZnO nanoneedles and its efficient field emission

Three dimensional (3-D) assemblies of ZnO nanoneedles have been synthesized on silicon substrate by a unique chemical process. Each nanoneedle in the assemblies was hexagonal faceted having [001] growth direction and tip diameter approximately 20 nm. The growth of 3-D assemblies was governed by the initial nuclei formation, followed by their aggregation and subsequently nanoneedle formation from each nucleus. Room temperature photoluminescence (PL) spectrum of the assemblies showed two prominent peaks, one narrow peak in the ultraviolet region (385 nm) and another broad peak in the visible region (440 nm-600 nm). The 3-D assemblies of ZnO nanoneedles showed very good field emission property with turn-on voltages 390 V, 530 V and 680 V for the anode-emitter distances of 100 microm, 200 microm and 300 microm respectively. The turn-on voltages showed a linear relationship with the anode-emitter distance. Field enhancement factor (beta) for the nanostructure was calculated to be 2873. The high beta value and the low turn-on field are attributed to the sharp needle like structure and their interesting three dimensional assemblies.     

Crystal growth, structure and characterizations of a new semiorganic nonlinear optical material—β-Alanine zinc chloride

The title compound, β-alanine zinc chloride—a new semiorganic nonlinear optical crystal was grown by slow evaporation technique. Single crystals of β-alanine zinc chloride have been subjected to X-ray diffraction analysis to determine the crystal structure. The powder X-ray diffractogram of the crystal has also been recorded. The amount of carbon, nitrogen and hydrogen in the crystals was also estimated. Fourier Transform Infrared and Raman spectral measurements have been carried out on the grown crystals in order to identify the functional groups. The presence of hydrogen and carbon in the β-alanine zinc chloride was confirmed by using proton and carbon nuclear magnetic resonance spectral analyses. The percentage of zinc in the crystal was determined by atomic absorption spectroscopy. Optical behavior such as ultraviolet-vis-near infrared transmittance spectrum and second harmonic generation has been investigated. The mechanical strength and thermal behavior of the grown crystal have been analyzed.     

Effect of zinc phosphate chemical conversion coating on corrosion behaviour of mild steel in alkaline medium: protection of rebars in reinforced concrete

We outline the ability of zinc phosphate coatings, obtained by chemical conversion, to protect mild steel rebars against localized corrosion, generated by chloride ions in alkaline media. The corrosion resistance of coated steel, in comparison with uncoated rebars and coated and uncoated steel rebars embedded in mortar, were evaluated by open-circuit potential, potentiodynamic polarization, cronoamperometry and electrochemical impedance spectroscopy. The coated surfaces were characterized by x-ray diffraction and scanning electron microscopy. First, coated mild steel rebars were studied in an alkaline solution with and without chloride simulating a concrete pore solution. The results showed that the slow dissolution of the coating generates hydroxyapatite Ca₁₀(PO₄)₆(OH)₂. After a long immersion, the coating became dense and provided an effective corrosion resistance compared with the mild steel rebar. Secondly, the coated and uncoated steel rebars embedded in mortar and immersed in chloride solution showed no corrosion or deterioration of the coated steel. Corrosion rate is considerably lowered by this phosphate coating.