Polymer brush coatings for combating marine biofouling

A variety of functional polymer brushes and coatings have been developed for combating marine biofouling and biocorrosion with much less environmental impact than traditional biocides. This review summarizes recent developments in marine antifouling polymer brushes and coatings that are tethered to material surfaces and do not actively release biocides. Polymer brush coatings have been designed to inhibit molecular fouling, microfouling and macrofouling through incorporation or inclusion of multiple functionalities. Hydrophilic polymers, such as poly(ethylene glycol), hydrogels, zwitterionic polymers and polysaccharides, resist attachment of marine organisms effectively due to extensive hydration. Fouling release polymer coatings, based on fluoropolymers and poly(dimethylsiloxane) elastomers, minimize adhesion between marine organisms and material surfaces, leading to easy removal of biofoulants. Polycationic coatings are effective in reducing marine biofouling partly because of their good bactericidal properties. Recent advances in controlled radical polymerization and click chemistry have also allowed better molecular design and engineering of multifunctional brush coatings for improved antifouling efficacies.     

High strain rate deformation and cracking of AA 2219 aluminium alloy welded propellant tank

Aluminium alloy AA 2219 (Al–6.6Cu–1Mn) is the candidate material for the fabrication of propellant storage tank of launch vehicle. Cold rolled sheets of 6.5 mm thickness are used to make the cylindrical shell, while sheets of 4.5 mm thickness are used for the construction of dome through petal forming technique. Petals, formed through cone rolling, treated to T87 temper condition are welded together by TIG welding to configure the dome. Such domes are joined to the cylindrical shell through a ring by TIG welding.The upper stage consists of two tanks, one oxidizer tank (liq. O₂) and other fuel tank (liq. H₂). After completing various developmental qualification tests, propellant flow rate test of one of the system was carried out. Almost all the liquid oxygen of the tank was removed and only a little quantity remained at the bottom. During one of the subsequent tests; when dry nitrogen gas was purged to evaporate the remaining liquid oxygen, the oxidizer tank dome catastrophically fractured with an audible sound. Fracture of oxidizer tank dome, placed at lower part of the system caused excessive deformation and subsequently it also caused fracture of fuel tank dome placed just over it.Detailed metallurgical investigations were carried out on the failed components and it was found that the tank failed under very high strain rate deformation. This paper brings out the details of the investigation carried out.     

Corrosion behaviour of sol–gel treated and painted AA2024 aluminium alloy

Design, development and scale-up of environmentally friendly coatings are very important in order to replace chromate based coatings for aluminium alloys. Barrier properties, paint adhesion and possibly self-healing ability are relevant aspects for replacement of chromate-based pre-treatments. Sol–gel materials are candidates for use in protective coating applications, as it is possible to form highly adherent and chemically inert oxide films on metal substrates.     

Effect of the polymerization conditions on the swelling of a copolymer of AA/AMPS/BA via experimental design

To study the effect of the polymerization conditions on swelling, a copolymer was synthesized from the monomers acrylamide (AA), 2‐acrylamido‐2‐methyl‐propanosulfonic acid (AMPS) and N,N‐methylenobisacrylamide (BA) as crosslinker by an inverse emulsion technique. The conditions were: concentration of organic solvent, s (an isoparaffinic hydrocarbon, commercially Isopar M), concentration of emulsifier, e (sorbitan trioleate, commercially Tween 85), and reaction temperature, T. These three variables (factors) were explored to achieve highest water absorbency, a 2³ factorial experimental design having been applied to find the main and two‐factor interaction effects of those variables on the swelling capacity. A predictive model including the factors for the swelling is proposed, allowing for the estimation of absorbency capacity in this type of copolymers. The results show that the optimum values of the variables given by the experimental design were s = 8.1, e = 1.0, and T = 49°C, with predicted swelling capacity of 1041 and experimental of 1014. The variables are relevant, with a preponderance of s, and the effect of the square of temperature is also significant. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

7050/Gr复合材料的制备及性能研究

采用热压和粉末包套挤压方法制备7050和7050/Gr材料,测试力学性能和内耗性能,利用金相显微镜和透射电镜观察材料组织。结果表明:通过热压制备的7050/Gr复合材料力学性能很低;粉末包套挤压制备的7050/Gr复合材料随Gr含量提高,7050/Gr的强度、弹性模量下降,伸长率也降低;热处理后复合材料的强度大幅度提高,T6态时强度最高,7050/4Gr、7050/5Gr的抗拉强度和伸长率分别为535 MPa、9.5%和526 MPa、3.5%;内耗测试结果表明,7050/5Gr复合材料的内耗比7050合金的内耗高,它们的内耗值均随测试频率降低和测试温度升高而增加,7050/5Gr复合材料的内耗属动滞后型的复相型阻尼合金的内耗机制。     

基于分区策略的蚂蚁算法

蚂蚁算法是一种解决组合优化问题的有效算法,该算法具有许多优良的性质,但是也存在一些缺点,如计算时间较长等。该文在基本蚂蚁算法的基础上,提出分区策略和信息素直接优化策略。分区策略加快了蚂蚁算法初期信息素的获得速度,信息素直接优化方法加速了蚂蚁算法后期收敛的速度。实验表明,这种改进有效提高了蚂蚁算法的搜索效率。     

锻造工艺参数对7050铝合金再结晶行为的影响

利用Gleeble-1500热模拟实验机对7050铝合金进行了等温压缩实验，与有限元仿真软件DEFORM3D模拟实验相结合，通过应力-应变与组织分析研究了7050铝合金在不同锻造工艺参数条件下的再结晶行为，结果表明，通过改变温度和应变速率能有效控制再结晶体积分数和晶粒尺寸。     

7050铝合金热压缩变形的流变应力本构方程

对7050铝合金在应变速率为0.01～10s-1、变形温度为250～450℃条件下的流变应力行为进行了实验研究.结果表明:7050铝合金热压缩变形中发生了明显的动态回复与动态再结晶,流变应力随应变速率的增加而增加,随温度的增加而降低;通过线性回归分析计算出7050材料的应变硬化指数n以及变形激活能Q,获得了7050铝合金高温条件下的流变应力本构方程.     

Role of Chloride Ion and Dissolved Oxygen in Electrochemical Corrosion of AA5083-H321 Aluminum-Magnesium Alloy in NaCl Solutions under Flow Conditions

Flow-induced corrosion consists electrochemical and mechanical components. The present paper has to assessed the role of chloride ion and dissolved oxygen in the electrochemical component of flow induced corrosion for AA5083-H321 aluminum-magnesium alloy which is extensively used in the construction of high-speed boats, submarines, hovercrafts, and desalination systems, in NaCl solutions. Electrochemical tests were carried out at flow velocities of 0, 2, 5, 7 and 10 m/s, in aerated and deaerated NaCl solutions with different sodium chloride concentrations. The results showed that the high rate of oxygen reduction under hydrodynamic conditions causes an increase in the density of pits on the surface. The increase of chloride ions concentration under flow conditions accelerates the rate of anodic reactions, but have no influence on the cathodic reactions. Thus, in the current work, it was found that under flow conditions, due to the elimination of corrosion products inside the pits, corrosion resistance of the alloy is increased.