A nonscattering coating for a cylinder

A thin coating with an extended reaction (see Acoust. Phys. 53, 535 (2007)) is used to reduce the reflection and scattering of waves from an infinite cylinder. The coating is shown to be more efficient compared to conventional coatings.     

Development and evaluation of electroless Ag-PTFE composite coatings with anti-microbial and anti-corrosion properties

Electroless Ag-polytetrafluoroethylene (PTFE) composite coatings were prepared on stainless steel sheets. The existence and distribution of PTFE in the coatings were analysed with an energy dispersive X-ray microanalysis (EDX). The contact angle values and surface energies of the Ag-PTFE coatings, silver coating, stainless steel, titanium and E. coli Rosetta were measured. The experimental results showed that stainless steel surfaces coated with Ag-PTFE reduced E. coli attachment by 94-98%, compared with silver coating, stainless steel or titanium surfaces. The anti-bacterial mechanism of the Ag-PTFE composite coatings was explained with the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The anticorrosion properties of the Ag-PTFE composite coatings in 0.9% NaCl solution were studied. The results showed that the corrosion resistance of the Ag-PTFE composite coatings was superior to that of stainless steel 316L.     

Multi-layered electroless Ni–P coatings on powder-sintered Nd–Fe–B permanent magnet

This paper has shown a successful protective coating scheme for powder-sintered Nd–Fe–B permanent magnet using multi-layered electroless nickel (EN) deposition. A low-phosphorus nickel layer is plated with an alkaline EN solution first, followed by a high-phosphorus nickel layer plated with an acidic solution. An additional topcoat by medium-phosphorus nickel on the high-phosphorus coating is also explored. It is shown that the high-phosphorus nickel layer coated in acidic solution provides the best corrosion protection because of its dense amorphous structure. The medium phosphorus topcoat is also dense and is able to provide reasonable corrosion resistance. The low-phosphorus layer itself does not have enough corrosion resistance; its main role is to provide an intermediate coating on the powder-sintered magnet. X-ray diffraction measurement shows that the low-phosphorus coating consists of nano-crystallines, and the high- and the medium-phosphorus coatings are dominated by amorphous structure. Microscopic observation and scratch test on these composite coatings demonstrate good adhesion between the magnet and the coatings. Remanence and coercivity of the plated magnet decrease with the applied coatings, but measured values are still very attractive for practical applications among known hard magnets.     

Improvement in the properties of plasma-sprayed metallic, alloy and ceramic coatings using dry-ice blasting

Dry-ice blasting, as an environmental-friendly method, was introduced into atmospheric plasma spraying for improving properties of metallic, alloy and ceramic coatings. The deposited coatings were then compared with coatings plasma-sprayed using conventional air cooling in terms of microstructure, temperature, oxidation, porosity, residual stress and adhesion. It was found that a denser steel or CoNiCrAlY alloy coating with a lower content of oxide can be achieved with the application of dry-ice blasting during the plasma spraying. In addition, the adhesive strength of Al₂O₃ coating deposited with dry-ice blasting exceeded 60 MPa, which was nearly increased by 30% compared with that of the coating deposited with conventional air cooling. The improvement in properties of plasma-sprayed metallic, alloy and ceramic coatings caused by dry-ice blasting was attributed to the decrease of annulus-ringed disk like splats, the better cooling efficiency of dry-ice pellets and even the mechanical effect of dry-ice impact.     

Pulsed laser deposition of thin-film coatings using an antidroplet shield

The formation of thin-film coatings of molybdenum diselenide is studied during the deposition of a laser-induced material flux using a shield that is placed on the path of the expansion of this flux in order to trap the droplet fraction. To increase the efficiency of atomic scattering into the shadow zone (behind the shield), deposition is carried out in an inert gas (argon). As the argon pressure increases to 2 Pa, low-density coatings with a developed surface relief form in the shadow zone. When a negative bias voltage is applied to a substrate, the quality of the coating increases substantially. Numerical experiments based on the combination of two computer models that describe physical processes on the atomic level using Monte Carlo methods are performed to reveal the factors that affect the thickness, chemical composition, and structure of the MoSe _x coatings deposited in the shadow zone. The results of calculating the dynamics of the laser-induced atomic flux in a chamber with a shield are used to simulate the coating growth. The deposition of a scattered atomic flux under conditions of surface bombardment by incident particles is shown to substantially increase the coating density and to smooth away the surface relief.     

Influence of TaCl5 partial pressure on texture structure of TaC coating deposited by chemical vapor deposition

TaC was deposited on graphite substrate with different TaCl₅ partial pressure at 800 °C and 1200 °C by chemical vapor deposition. Microstructures and texture structures of the prepared coatings were researched with X-ray diffraction and scanning electronic microscopy. When the coating deposition process is controlled by surface reaction kinetics (800 °C), TaCl₅ partial pressure had little influence on the microstructure and texture structure of the coating. When the coating formation process is controlled by diffusion kinetics (1200 °C), the microstructure, texture structure of the prepared TaC grains vary greatly with TaCl₅ partial pressure. In the diffusion controlled process, the increasing of TaCl₅ partial pressure will result in the changing of gas supersaturation, and then the occurrence of secondary nucleation, which is the main reason for the changing of coating morphology and texture structure. With the help of competitive growth in (1 0 0) and (1 1 1) directions, the formation mechanism of the different texture coatings are discussed in detail. In addition, a diffusion model of deposition species around step-edge-corner was also proposed to explain the growth mechanism of the texture coatings.     

Double-ceramic-layer thermal barrier coatings based on La2(Zr0.7Ce0.3)2O7/La2Ce2O7 deposited by electron beam-physical vapor deposition

Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La₂(Zr_0.7Ce_0.3)₂O₇ (LZ7C3) and La₂Ce₂O₇ (LC) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, interdiffusion, surface and cross-sectional morphologies, cyclic oxidation behavior of DCL coating were studied. Energy dispersive spectroscopy and X-ray diffraction analyses indicate that both LZ7C3 and LC coatings are effectively fabricated by a single LZ7C3 ingot with properly controlling the deposition energy. The chemical compatibility of LC coating and thermally grown oxide (TGO) layer is unstable. LaAlO₃ is formed due to the chemical reaction between LC and Al₂O₃ which is the main composition of TGO layer. Additionally, the thermal cycling behavior of DCL coating is influenced by the interdiffusion of Zr and Ce between LZ7C3 and LC coatings. The failure of DCL coating is a result of the sintering of LZ7C3 coating surface, the chemical incompatibility of LC coating and TGO layer and the abnormal oxidation of bond coat. Since no single material that has been studied so far satisfies all the requirements for high temperature applications, DCL coating is an important development direction of TBCs.     

Multifunctional high-temperature D5 MAI and M1 MAI coatings

Theoretical and practical aspects of creating reliable protective coatings of the heat-stressed structural components of hypersonic aircrafts for operating in high-enthalpy oxygen-containing gas flows are discussed. The main mechanisms of disintegration of coating under these conditions were identified and criteria for estimating their contributions. The danger of oxidation the material protected by the coating is largely associated with the formation of open pores and cracks in the coating. A new physicochemical model of a heterophase coating was proposed, which was used to create a number of materials for manufacturing layered coatings for applying onto high-melting alloys and C/C, C/SiC, and Si/SiC composite materials. These coatings are capable of effectively protecting for gas corrosion and erosion within the temperature range covered, 300–2100 K. When exposed to high temperature, the microcomposite material applied is capable of self-organizing into a multilayer multifunctional coating with a low catalytic activity, K _w ～ 3 m/s, and a rather high emissivity, ? ≈ 0.7–0.8. The coating is is a multilayer nanostructure with a thickness of individual layers of 10–1000 nm. The coating is capable of fast self-healing of micro- and macrodefects. The coating were tested when applied onto niobium-based alloys and carbon materials under conditions imitating the reentry of a space vehicle into the dense atmosphere.     

Effect of potassium fluoride in electrolytic solution on the structure and properties of microarc oxidation coatings on magnesium alloy

Oxide coatings were produced on AM60B magnesium alloy substrate making use of microarc oxidation (MAO) technique. The effect of KF addition in the Na₂SiO₃-KOH electrolytic solution on the microarc oxidation process and the structure, composition, and properties of the oxide coatings was investigated. It was found that the addition of KF into the Na₂SiO₃-KOH electrolytic solution caused increase in the electrolyte conductivity and decrease in the work voltage and final voltage in the MAO process. Subsequently, the pore diameter and surface roughness of the microarc oxidation coating were decreased by the addition of KF, while the coating compactness was increased. At the same time, the phase compositions of the coatings also varied after the addition of KF in the electrolytic solution, owing to the participation of KF in the reaction and its incorporation into the oxide coating. Moreover, the coating formed in the electrolytic solution with KF had a higher surface hardness and better wear-resistance than that formed in the solution without KF, which was attributed to the changes in the spark discharge characteristics and the compositions and structures of the oxide coatings after the addition of KF.     

A new approach to optimizing pigmented coatings considering both thermal and aesthetic effects

Pigmented coatings with high reflectivity against solar irradiation can be used to control unwanted thermal heating that occurs as materials absorb sunlight such as heat in buildings that increases cooling loads. However, these surfaces produce glare that is unpleasant to the eye, and the coatings themselves can damage the appearance of the coated object. We introduce a new optimization method that embraces both thermal and aesthetic requirements. Our proposed coatings maximize the reflectivity of the near infrared (NIR) region to reduce thermal heating, while for aesthetic appeal they also minimize the visible (VIS) reflected energy received by human eyes, especially at wavelengths where eye sensitivity is high. The optimization parameter is defined as the ratio of the total reflected energy in the NIR region to that in the VIS region weighted by human eye sensitivity. Titanium dioxide is used as the pigment, and databases of its radiative properties are constructed using the Mie theory. To compute reflectivity, nongray radiative heat transfer in an anisotropic scattering monosized pigmented layer, with independent scattering, including direct and diffuse solar irradiations, is analyzed using radiation element method by ray emission model (REM²). Colors are calculated and optimization parameter is evaluated by using spectral reflectivity. Finally, the optimum values of particle size, volume fraction of pigment, and coating thickness are obtained.     

X-ray photoelectron spectroscopy study of the passive films formed on thermally sprayed and wrought Inconel 625

There is a well known performance gap in corrosion resistance between thermally sprayed corrosion resistant coatings and the equivalent bulk materials. Interconnected porosity has an important and well known effect, however there are additional relevant microstructural effects. Previous work has shown that a compositional difference exists between the regions of resolidified and non-melted material that exist in the as-sprayed coatings. The resolidified regions are depleted in oxide forming elements due to formation of oxides during coating deposition. Formation of galvanic cells between these different regions is believed to decrease the corrosion resistance of the coating. In order to increase understanding of the details of this effect, this work uses X-ray photoelectron spectroscopy (XPS) to study the passive films formed on thermally sprayed coatings (HVOF) and bulk Inconel 625, a commercially available corrosion resistant Ni-Cr-Mo-Nb alloy. Passive films produced by potentiodynamic scanning to 400 mV in 0.5 M sulphuric acid were compared with air-formed films. The poorer corrosion performance of the thermally sprayed coatings was attributed to Ni(OH)₂, which forms a loose, non-adherent and therefore non-protective film. The good corrosion resistance of wrought Inconel 625 is due to formation of Cr, Mo and Nb oxides.     

Semiclassical description of reactions at energies near the Coulomb barrier

The modified semiclassical approximation of Coulomb matrix elements is extended to include effects of distorting nuclear potentials in the scattering wave functions. The applicability and efficiency of the proposed semiclassical method are discussed. The advantages of this approximation are shown for a typical heavy-ion transfer reaction.     

斜角入射沉积法制备渐变折射率薄膜的折射率分析

斜角入射沉积法是一种制备薄膜的新颖方法,它可以用来制备渐变折射率薄膜.本文首先探讨了膜料的沉积入射角为α,薄膜柱状生长倾斜角为β时的薄膜的填充系数;之后利用drude理论,分析研究了斜角入射沉积法制备渐变折射率薄膜的折射率与薄膜的入射角和生长方向的关系. 关键词： 斜角入射沉积 渐变折射率 填充系数     

Formation of titania composite coatings on carbon steel by plasma electrolytic oxidation

Titania composite coatings were prepared on carbon steel by plasma electrolytic oxidation in silicate electrolyte and aluminate electrolyte with titania powers doping in the electrolytes. The microstructure of the coatings was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The properties of the coatings including bond strength, thickness, thermal shock resistance and corrosion resistance varying with the quantities of titania powers in the electrolytes were studied. Investigation results revealed that the coating obtained in silicate electrolyte was composed of anatase-TiO₂, rutile-TiO₂ crystal phases and some Fe, Si, P elements; coating obtained in aluminate electrolyte consisted of anatase-TiO₂, Al₂TiO₅ and some Fe, P elements. Coatings obtained in two types of electrolytes show porous and rough surface. With increasing the concentration of titania powers in the electrolytes, the coating surface first became more compact and less porous and then became more porous and coarse. The bond strength and thickness were not strongly affected by concentration of titania powers in electrolytes. The valves were 23 MPa and for 66 μm for coatings obtained in aluminate electrolyte, and 21 MPa and 35 μm for coatings obtained in silicate electrolyte. Coatings obtained in silicate electrolyte showed a little better thermal shock resistance than those obtained in aluminate electrolyte and the best coatings were obtained with middle concentration of titania powers in the electrolytes. All coated samples showed better corrosion resistance than the substrate in 3.5 wt% NaCl solution. The best coatings were also obtained with middle concentration of titania powers doping in both electrolytes whose corrosion current density was decreased by 2 orders of magnitude compared with the substrate.     

Optimization and design of pigments for heat-insulating coatings

This paper reports that heat insulating property of infrared reflective coatings is obtained through the use of pigments which diffuse near-infrared thermal radiation.Suitable structure and size distribution of pigments would attain maximum diffuse infrared radiation and reduce the pigment volume concentration required.The optimum structure and size range of pigments for reflective infrared coatings are studied by using Kubelka-Munk theory,Mie model and independent scattering approximation.Taking titania particle as the pigment embedded in an inorganic coating,the computational results show that core-shell particles present excellent scattering ability,more so than solid and hollow spherical particles.The optimum radius range of core-shell particles is around 0.3 ～ 1.6 μm.Furthermore,the influence of shell thickness on optical parameters of the coating is also obvious and the optimal thickness of shell is 100-300 nm.     

Microstructural inhomogeneity in plasma-sprayed hydroxyapatite coatings and effect of post-heat treatment

The microstructural inhomogeneity in the plasma-sprayed hydroxyapatite (HA) coatings was characterized by using electron probe microanalyser (EPMA). A simple and artful method was developed to detect the interface characteristics. All the samples for observation were ground and polished along the direction parallel to the coating surfaces. The BSE images directly and clearly showed the inhomogeneity in the as-sprayed coatings with the amorphous regions being bright gray and crystalline regions being dark gray. X-ray diffractometer (XRD) patterns indicated that after immersion in deionized water for 20 days, bone-like apatite and α-Ca₂P₂O₇ precipitated on the polished surfaces of the as-sprayed HA coatings. The post-heat treatment could eliminate the microstructural inhomogeneity in the coatings. Only β-Ca₂P₂O₇ precipitated on the surfaces of the heat-treated HA coatings. The immersed samples were re-polished till tiny substrate was bared to investigate the effect of immersion on interface. It was shown that the immersion decreased the cohesive strength of the as-sprayed coatings. There were more and broader cracks in the splats that came into contact with the substrate and amorphous phase increased toward the coating-substrate interface. Post-heat treatment was proved to reduce the peeling off of coating during re-polishing operation. It was proposed that the distributions of amorphous phase and cracks in as-sprayed coatings are detrimental to coating properties and should be modified through improving the plasma spraying processing.     

Protective sol-gel coating on silicate phosphor used in light emitting diodes

In this study, an orange-red silicate phosphor that is used in light emitting diodes (LEDs) was coated with a SiO₂ blocking layer via a sol-gel reaction of tetra-ethyl ortho-silicate (TEOS) to investigate its reliability as an encapsulant. A sol-gel coating protects the phosphor surface from moisture and reactive materials and improves the reliability of the phosphor. The efficacy of the phosphor coating following an 85 °C and 85 relative humidity (Rh)% test decreased by 7%, whereas an uncoated phosphor coating decreased by 35%. A SiO₂ sol-gel coating decreases the luminous efficiency by a small amount with each coating.     

彩色发光涂料的光学测量

彩色发光涂料是一种高光效、长余辉的光致发光材料。当对其进行光学测量时,为避免因激发光被探测器接收而对测量结果产生的影响,提出在实验中如何设定特殊的装置,从而保障对发光涂料的光学特性进行有效的测量。根据光度学理论中有关照度和发光亮度的关系,通过实验对三种不同的彩色发光涂料在同样光照条件下的亮度测量,同一种发光涂料在不同颜色光照下的发光亮度比较,以及在彩色发光涂料的亮度衰减情况给出了测量的结果。     

HfO2/SiO2多层高反膜激光预处理技术

采用不同的光斑移动距离,对电子束蒸发制备的HfO2/SiO2多层高反膜进行了单步及多步预处理。结果表明:为了使薄膜不产生损伤,预处理最高能量密度最好不超过薄膜零几率损伤阈值的90%; 相同预处理效率下进行的单步预处理对提高光学薄膜抗激光损伤阈值的效果比多步预处理好;对HfO2/SiO2高反膜进行98.4%能量覆盖的两步预处理后薄膜损伤阈值提高81%;控制薄膜的缺陷源,初始物质应采用金属Hf。     

Characteristic and biocompatibility of the TiO2-based coatings containing amorphous calcium phosphate before and after heat treatment

TiO₂-based coating containing amorphous calcium phosphate (CaP) was prepared on titanium alloy by microarc oxidation (MAO). The increase in the EDTA-2Na concentration was unfavorable for the crystallization of TiO₂. After heat treatment, the amorphous CaP was crystallized. The thickness of the MAO coatings did not change when heat-treated at 400, 600 and 700 °C; while it increased slightly after heat treatment at 800 °C due to the crystallization of amorphous CaP and growth of TiO₂. No apparent discontinuity between the coatings and substrates was observed at various heat-treatment temperatures, indicating the MAO coatings with good interfacial bonding to the substrate. The heat treatment did not alter the chemical composition of the MAO coating and the chemical states of Ti, Ca and P elements. However, it increased the roughness (Ra) of the MAO coating and improved the wetting ability of the MAO coating. In this work, preliminary investigation of the MG63 cell proliferation on the surface of the MAO and heat-treated MAO coatings was conducted. The MAO coating surface with about Ra = 220 nm may be suitable for the MG63 cell adhesion and proliferation. The increased roughness of the heat-treated MAO coatings may result in a decrease in the ability for cell adhesion and proliferation.