Evaluation of different coating systems by electrochemical methods

Corrosion protection of organic coated steel is determined by free corrosion potential measurements and impedance spectroscopy. The results are classified by means of very basic considerations and evaluation figures are developed. These electrochemical data are correlated with the extent of the corrosion for each coating system. The evaluation figures are used for ranking coating systems and this ranking is correlated with the ranking with reference to the results of standardized and exposure tests.     

Effect of deposition conditions on the properties and annealing behavior of cold-sprayed copper

The deposition of copper by cold gas dynamic spraying has attracted much interest in recent years due to the capability to deposit low-porosity oxide-free coatings. However, it is generally found that as-deposited copper has a signicantly greater hardness, and potentially lower ductility, than bulk material. In this article, copper was deposited by cold spraying using helium as the driving gas at both 298 and 523 K. Evidence is presented indicating that the material sprayed at the lower temperature exhibits a lower dislocation density throughout the grain structure than the material sprayed at the higher temperature. The low stacking fault energy of copper restricts recovery during annealing, and thus microstructural changes during annealing only proceed once recrystallization begins. The material sprayed at low temperature (with the low dislocation density) exhibited recrystallization at annealing temperatures as low as 373 K with a corresponding reduction in hardness. However, the copper sprayed with helium at 523 K was resistant to annealing at temperatures up to 473 K where the dislocations in the structure prevented recrystallization. However, at higher temperatures, recrystallization did proceed (with corresponding reductions in hardness). The fracture behavior of the copper that was cold sprayed with helium at 523 K, both in the as-sprayed condition and following annealing, was measured and explained in terms of the annealing mechanisms proposed. The original version of this paper was published in the CD ROM Thermal Spray Connects: Explore Its Surfacing Potential, International Thermal Spray Conference, sponsored by DVS, ASM International, and HW International Institute of Welding, Basel, Switzerland, May 2–4, 2005, DVS-Verlag GmbH, Düsseldorf, Germany.     

Improved corrosion protection of aluminum alloys by electrodeposited silanes

Organofunctional silanes recently have emerged as outstanding, environmentally friendly corrosion protectors for metal substrates, compared with conventional chromate treatments. A simple immersion technique is typically used to coat the metal surface with silane films. However, the thickness and uniformity of the films are uncontrolled in this process. This paper proposes a new deposition technique for the silane films on the metal surface, i.e., by electrodeposition. Hydrolyzed silanes are water-soluble, ionized molecules, so they can be deposited on metals by electrodeposition. Various combinations of silane mixtures were tested at different voltages, pH values, bath concentrations, and exposure times on panels of alloy aluminum and mirror-polished ferro-plate. The surface structure was characterized by scanning electron microscopy (SEM) and ellipsometry. The resistance of the film to corrosion was investigated by direct current (DC) polarization and electrochemical impedance spectroscopy (EIS) techniques. Electrodeposition results in a more organized and uniform film with fewer pores, compared with immersed or dipped films. This paper was presented at the 2nd International Surface Engineering Congress sponsored by ASM International, on September 15–17, 2003, in Indianapolis, Indiana, and appears on pp. 320–26 of the Proceedings.     

Combinatorial materials research applied to the development of new surface coatings: II. Process capability analysis of the coating formulation workflow

A combinatorial process has been developed for the high throughput production and evaluation of surface coatings. The workflow designed for the production of arrays of liquid coatings involves the robotic transfer of aliquots of solutions of raw materials to an array of glass vials and mixing of the coatings using an unconventional magnetic stirring process. An investigation of the capability of the workflow to accurately and repeatedly prepare coating arrays was conducted as a function of solution viscosity and aliquot size. In addition, mixing capability was evaluated as a function of solution viscosity, total solution volume, and mechanism of stirring. Overall, the results of the study indicated that adequate accuracy and repeatability of the coating preparation process can be achieved as long as raw material solutions are designed such that viscosity is below about 250 cP and aliquot sizes are above about 75 μl. With regard to mixing capability, total solution volume was found to have a profound affect as did the stirring mechanism.     

Thermal Shock Failure in Thick Epoxy Coatings

In this paper we describe an apparatus for reproducibly measuring thermal shock resistance of thick polymer layers bonded to metals. The thermal shock behavior is discussed in terms of epoxy samples bonded to an aluminum substrate. It was found that both high resin toughness and low resin thermal expansion coefficient improved thermal shock resistance of thick coatings, but only a sample containing 60wt. % glass beads did not develop a failure crack. Effects of sample thickness, temperature gradient, and resin composition on thermal shock behavior are discussed.     

家电卷材涂料用HDI改性聚酯树脂的研制

以己二异氰酸酯（HDI）改性聚酯树脂与氨基树脂配制成家电用卷材涂料。阐述了氨酯键对涂膜性能的贡献。探讨了HDI用量对涂膜性能的影响。     

单组分聚脲材料在寒冷地区某大坝溢流面防护中的应用

水利水电工程泄洪建筑物表面经常遭受高速含沙水流或携带推移质的冲刷,经过一段时间的运行,往往会出现不同程度的磨损及气蚀破坏,采用性能优越的水工混凝土抗冲耐磨材料修复和防护尤为重要。本文通过单组分聚脲材料性能试验揭示了材料的特点,介绍了其在新疆某大坝溢流面防护中的应用情况,其处理技术对类似工程具有良好的借鉴意义。     

Thermodynamic Analysis of Chemical Vapor Deposition of BN + AIN Composite Coatings

Thermodynamic calculations were performed using a modified solgasmix-pv computer program in order to study the feasibility of codepositing boron nitride (BN) plus aluminum nitride (AIN) by chemical vapor deposition. Reactants considered were AICl₃, BCl₃ or B₂H₆, NH₃, and H₂. Deposition diagrams were generated for the BCl₃-AICl₃-NH₃ system over a range of processing conditions such as temperature, total system pressure, and reagent concentrations. Codeposition of BN + AIN was predicted by the calculations for temperatures in the range of 900 to 1700 K and pressures of 10.13 to 101.3 kPa. The predicted deposition efficiency at equilibrium was much higher for BN than for AlN at most reagent compositions. The AlN deposition efficiency increased with decreasing temperature and decreasing BCl₃ content, with increasing NH₃ content, or with the addition of H₂. Aluminum chlorides were found to be the dominant gaseous species.     

Studies of microhardness and mar resistance using a scanning probe microscope

Scanning probe microscopy (SPM) is in a period of rapid development. It shows great promise for characterizing coating surfaces. This paper describes modification of an SPM so that it can be used to mar the surfaces of coatings under controlled conditions and to characterize the mars. Mar resistance of coatings is analyzed in terms of a ‘three response, two mechanism model.' The three responses (fracture, elastic, and plastic) can be measured quantitatively using the SPM. Of the three responses, only two (fracture and plastic deformation) are marring mechanisms – elastic deformations recover instantaneously. In some cases mars resulting from plastic deformation may recover slowly with time or with immersion in water; this phenomenon is attributed to viscoelastic creep. Microhardness is also measured with the modified SPM. Some thermoset coatings appear to be substantially harder near their surfaces than in the mass of material, and such materials may respond quite differently to stress applied at different levels near the surface. This finding has important implications for all coating properties that are strongly influenced by the surface. A quantity called ‘micro mar resistance' is defined. It may be useful for comparing different coatings under specified conditions of marring. However, there can be no single quantity that expresses ‘mar resistance' of a coating under all conditions.     

涂料剖析

简要分析了不同涂料体系分析程序,说明了每种涂料剖析体系中应该注意的事项。