Studies of the porosity in electroless nickel deposits on magnesium alloy

In the present paper, the porosity of the plating coating was evaluated by the combination of corrodkote and filter paper, the effects of the plating solution on the porosity were investigated, and the properties of the porous coatings were studied through scanning electron microscopy (SEM) and electrochemical potentiodynamic polarization. The results show that the eriothrome black T indicator used as an indicator of the coating porosity for coatings on magnesium alloy is more effective than magneson indicator and sodium alizarinesulfonate indicator. The porosity in electroless nickel deposits on magnesium alloy was well evaluated by the combination of corrodkote and filter paper. It is revealed that the pores exist on both grain surface and grain boundaries. An affecting trend of the plating bath parameters on the coating porosity was obtained.     

Porosity and effective mechanical properties of plasma-sprayed Ni-based alloy coatings

The aim of this paper was to address the relationship between the porosity and micro-mechanical properties of the Ni-based alloy coatings which were prepared by a novel plasma-spraying system. The porosity and the mechanical properties of the coatings varied through changing the spraying parameters. Experimental results showed that the measured data of porosity, Young’s modulus and micro-hardness of the coating exhibited high scattering and followed the Weibull distribution. From statistic trend, the micro-hardness and Young’s modulus of the coating decreased with increasing the porosity of the coating. Moreover, generally, with increasing the micro-hardness of the coating, Young’s modulus of the coating increased.     

Effect of spraying power on the microstructure and mechanical properties of supersonic plasma-sprayed Ni-based alloy coatings

The aim of this paper was to investigate the microstructure and mechanical properties of the supersonic plasma-sprayed Ni-Cr-B-Si-C coatings prepared at different spraying powers. The microstructure, phase composition, porosity, Young's modulus, micro-hardness, and residual stresses of the coatings were investigated and determined. The variations of the porosity, Young's modulus and micro-hardness of the coatings were evaluated by using statistical method. Results showed that the variations of porosity, Young's modulus and micro-hardness of the coatings followed the Weibull distributions. With increasing the porosity, the micro-hardness and Young's modulus of the coating decreased. The mean value of the Young's modulus of the coating calculated from Weibull plot was almost proportional to the square root of the micro-hardness of the coating. With increasing the power, Young's modulus of the coating increased, which, in turn, resulted in the increment of the residual stress at the coating surface.     

Porosity, mechanical properties, residual stresses of supersonic plasma-sprayed Ni-based alloy coatings prepared at different powder feed rates

The aim of this paper was to investigate the effect of powder feed rate (PFR) on the microstructure and mechanical properties of the supersonic plasma-sprayed Ni-Cr-B-Si-C coatings. The microstructure, porosity and mechanical properties of the coatings and the residual stresses at the coating surfaces were experimentally determined. Results showed that the variations of porosity, elastic moduli and micro-hardness of the coatings followed Weibull distribution. From the statistical trend, the porosity of the coating increased with increasing PFR. However, the elastic modulus and the micro-hardness of the coating decreased and reached local minima and then increased with increasing PFR. Elastic modulus could be generally considered to be an increasing function of micro-hardness. The mean value of the elastic modulus of the coating calculated from Weibull plot was almost proportional to the square root of the mean value of the micro-hardness of the coating. Moreover, with increasing PFR, the residual stress at the coating surface, which was mainly governed by the elastic modulus of the coating, decreased to a local minimum and then increased.     

Investigation of locally resonant absorption and factors affecting the absorption band of a phononic glass

We experimentally and theoretically investigated the mechanisms of acoustic absorption in phononic glass to optimize its properties. First, we experimentally studied its locally resonant absorption mechanism. From these results, we attributed its strong sound attenuation to its locally resonant units and its broadband absorption to its networked structure. These experiments also indicated that the porosity and thickness of the phononic glass must be tuned to achieve the best sound absorption at given frequencies. Then, using lumped-mass methods, we studied how the absorption bandgaps of the phononic glass were affected by various factors, including the porosity and the properties of the coating materials. These calculations gave optimal ranges for selecting the porosity, modulus of the coating material, and ratio of the compliant coating to the stiff matrix to achieve absorption bandgaps in the range of 6–30 kHz. This paper provides guidelines for designing phononic glasses with proper structures and component materials to work in specific frequency ranges.     

SiO_2光学增透膜的制备及光学性能

在碱催化体系中以正硅酸乙酯 (TEOS)为前驱体制得SiO2 溶胶 ,采用旋转镀膜法 (spin coating)制备SiO2 光学增透膜。研究了在不同制备条件下对膜层光学性质的影响 ,推算了膜层的折射率及厚度 ,并由此给出膜层孔隙率以及膜层的厚度与转速的关系     

Anodized aluminum oxide membranes of tunable porosity with platinum nanoscale-coating for photonic application

We fabricate anodized aluminum oxide (AAO) membranes with platinum (Pt) coating of various thickness ranging from 0 nm to 12 nm. We also demonstrate the tunability of membrane porosity, to add a degree of freedom in addition to the Pt coating, for optical modulation that can be used in photonic application. The reflectance measurement and its analysis are provided based on Fabry–Perot etalon optics that takes into account spectral dependence of optical absorption and loss in the AAO membrane. It is revealed that the frequency-dependent optical finesse (color purity) enhances nonlinearly with the Pt thickness, by the quantitative estimation, while the effective refractive index is substantially governed by the membrane porosity. These features can allow for the AAO membrane to be used as a dye-free color displaying film with efficient tunability of both displaying color and its color purity. In particular, the strong dependence of an effective refractive index on porosity is demonstrated such that the AAO membrane can have the effective refractive index down to about 1.2, making it a possible candidate for a single layer anti-reflection coating material deposited on optical components including low-index glass. We also fabricate, by facile dipping method, an AAO membrane whose pore size changes gradually along a direction on its surface. This intra-membrane modulation of porosity allows it to find application in an optical grating or band-pass filter whose transmission wavelength varies with position on the device surface.     

Special features of the grain structure of polycrystalline NaNbO<Subscript>3</Subscript> with 3-0 connection

Grain structure of porous sodium niobate ceramics (with 3-0 connection and variable porosity changing from 1.0 to 13.6%) fabricated under different conditions is investigated and the microstructure parameters are calculated for different degrees of porosity. It is demonstrated that with increasing degree of porosity, the character of the sodium niobate grain structure changes due to the formation and ordering of the pore -multilayered grain coating clusters, sharp increase in the total pore surface area, and its significant excess over the external sample surface area. These structural changes can influence significantly the integral electrophysical characteristics of the porous sodium niobate ceramics and determine a high degree of its piezoanisotropy.     

Numerical simulation of deformation and fracture of a material with a polysilazane-based coating

The paper studies the localization of plastic deformation and fracture in a material with a porous coating. A dynamic boundary value problem in the plane strain formulation is solved. The numerical simulation is performed by the finite difference method. The composite structure corresponds to the experimentally observed one and is specified explicitly in the calculation. A generation procedure of the initial finite-difference grid is developed to describe the coating structure with adjustable porosity and geometry of the substrate-coating interface. Constitutive equations for the steel substrate include an elastic-plastic model of an isotropically hardening material. The ceramic coating is described by a brittle fracture model on the basis of the Huber criterion which accounts for crack nucleation in triaxial tension zones. It is shown that the specific character of deformation and fracture of the studied composite results from the presence of local tensile regions in the vicinity of pores and along the coating-substrate interface, in both tension and compression of the coated material. The interrelation between inhomogeneous plastic flow in the steel substrate and crack propagation in the coating is studied.     

Microstructure, microhardness and dry friction behavior of cold-sprayed tin bronze coatings

In this paper, two types of tin bronze coatings (Cu-6 wt.% Sn and Cu-8 wt.% Sn) were prepared by cold spray process. The as-sprayed coatings were subjected to a vacuum heat treatment at 600 °C for 3 h. The coating microstructure, microhardness and tribological performance were characterized. The effects of the tin content and the vacuum heat treatment on the microstructure, microhardness and tribological behavior of the coatings were investigated. It is found that the as-sprayed CuSn6 (As6) and CuSn8 (As8) coatings exhibit practically an identical porosity. Meanwhile, As8 presents a higher microhardness than As6. In addition, the increase of the tin content in the powder feedstock leads to a lower wear rate. After a heat treatment, coating porosities are significantly reduced. However, the coating hardness is significantly decreased and the coating presents a much decreased wear resistance. For the as-sprayed coatings, such factors as ploughing and particle delamination could determine the sliding process. The heat treatment results in a distinct modification of the tribological behavior. For the annealed coatings, the adhesion, between the coating and the counterpart, could play a dominant role in the sliding process.     

Effect of laser melting on plasma-sprayed aluminum oxide coatings reinforced with carbon nanotubes

The effect of laser melting on the microstructure and mechanical properties of plasma-sprayed aluminum oxide composite coating reinforced with 4 wt% multi-walled carbon nanotubes (CNTs) is reported. Laser-melted layer consists of dense, coarse columnar microstructure which is significantly different from plasma-sprayed coating that consists of splats and porosity. CNTs retained their original cylindrical graphitic structure after undergoing laser irradiation. Three dimensional heat flow model has been developed to estimate temperature variation in the laser-melted composite layer. Laser-melted layers show an increase in the microhardness at the expanse of degradation of fracture toughness. Nanoindentation study indicates an increase in the elastic modulus and yield strength of the laser-melted layer which is attributed to dense microstructure with absence of weak-bonding splats and porosity.     

阴极移动对不规则零件镀镍层性能的影响

在电真空器件的制造过程中,不规则零件的镀镍是关键步骤之一。采用阴极移动技术在不规则零件表面沉积了镀镍层。利用X射线荧光仪、激光共聚扫描显微镜、弯曲阴极法研究了阴极移动对镀层沉积率、表面形貌、孔隙率和内应力等的影响。结果表明:当阴极移动速率在1.5m/min以上时,可以明显降低不规则零件的针孔现象,但无法完全消除:阴极移动不会影响不规则零件的电沉积速率,但会使镀层的结晶颗粒变大,导致零件表面粗糙度增大;阴极移动可以显著地降低镀层的孔隙率和镀层的内应力,但是与移动的速率关系不大。     

On the use of perforations to improve the sound absorption of porous materials

The concept of meso-perforations in appropriately chosen porous media can help enhance their sound absorption performance. The meso-perforated materials are also referred to as “double porosity materials” since they are made up of two interconnected networks of pores of different characteristic size. Several theoretical, numerical and experimental works have been accomplished on the subject by the authors. The purpose of this paper is to give a synthetic review of these works and establish practical design rules to develop optimized noise control solutions based on this concept. The paper presents two complementary models to deal with this kind of materials: an analytical model based on homogenization techniques and a numerical model relying on a finite element discretization of the domains. The limits of these models are discussed. The choice of the design parameters is then been investigated in order to provide practical design rules. This choice relies on a criterion which is evaluated from the knowledge of the resistivity, porosity and tortuosity of the micropous medium, and the calculation of a geometrical parameter defined from the chosen mesoscopic structure. Experimental and numerical results regarding the influence of the mesopore profile along the thickness performed in a appropriately chosen substrate microporous medium are presented. The agreement between the models and the experiments is satisfactory. Results show that significant enhancements of the absorption properties can be obtained over a selected frequency band by adjusting the mesopore profile. It is also shown that interesting absorbing properties can be obtained when coating a double porosity medium with an impervious screen.     

Composite ceramic-Ni60 coating fabricated via supersonic plasma spraying

Using the supersonic plasma spraying (SPS) technique, a composite ceramic-Ni60 coating was prepared on a 45# steel substrate. The particle morphology, coating morphology, and phase structure of the coating were analyzed via scanning electron microscopy and X-ray diffraction. Moreover, the tribological properties of the coating were determined via friction and wear experiments. The results revealed that: the crystal structure of the SPS-produced coating is composed of six phase-structure types, and the coating structure was dense with low porosity. During the wear test (rotation speed of ball: 300 rpm, load: 50 N), the friction coefficient decreased by 32.75%, and the coating underwent abrasive wear (wear mechanism).     

多孔薄层强化竖管外壁凝结换热的理论研究

1前言在壁上涂以极薄多孔层以强化凝结换热的问题很少研究过。目前，只有几位学者对恒壁温的短平壁进行了初步的研究［‘－‘l，而对坚圆管尚未见有人研究。为密切与实际应用相结合，我们对具有涂层的变壁温的长竖管进行了理论和实验研究，本文就理论问题进行了探讨。2理论模型及数值计算多孔薄层很薄，故凝液膜边界层被分成两层：内层（多孔薄层液膜层）和外层（纯液膜层）。系统简图如图1。坚管外壁上喷涂上一层导热率较高的多孔介质薄层。厚度为h，热导率为k。，孔隙率为。，渗透率为Kp，管长为L，壁温为几，蒸汽饱和温度为Ts，凝液膜…     

SEM and XRF spectroscopy methods for studying and controlling the surface morphology of metal-polymer films

The surface morphology and the degree of porosity of metal-polymer films deposited by the electrolytic method are studied using scanning electron microscopy (SEM) and X-ray fluorescence (XRF) spectroscopy. Mathematical processing is performed, and the structure of the sample surfaces is analyzed using images obtained in the mode of secondary-electron recording. The volume-packing coefficients for heterogeneous coatings are determined using the XRF analysis data. The dependence of the surface structure and volume-packing coefficient of copper in the film on the polymer type and the coating thickness is established.     

激光重熔对等离子喷涂ZrO_2-20%Y_2O_3热障涂层隔热性能的影响

采用大气等离子喷涂(APS)技术在铝基体表面制备氧化锆(ZrO2-20%Y2O3,质量分数)热障涂层,并用脉冲激光对其进行重熔处理,研究了激光重熔对涂层组织形貌、物相转变和隔热性能的影响。研究结果表明激光的比能量对涂层的成型及性能有重要影响,过高的比能量会使涂层表面粗糙度增加,涂层成型变差。在选用合适的低比能量激光重熔条件下,扫描电镜观察结果表明经激光重熔可消除喷涂态涂层的孔隙和层状结构。对粉末和重熔前后的涂层进行了X射线衍射分析,结果表明喷涂及重熔过程中都没有发生相变;隔热试验结果表明重熔后涂层的隔热温度有所下降。     

Low-loss deposition of solgel-derived silica films on tapered fibers

Films of porous silica are deposited on the uniform waists of tapered fibers in minutes by a modified solgel dip coating method, inducing less than 0.2 dB of loss. The coated tapers are an ideal platform for realizing all-fiber devices that exploit evanescent-field interactions with the deposited porous film. As an example we demonstrate structural long-period gratings in which a periodic index variation in the film arises from the porosity variation produced by spatially varying exposure of the waist to a scanned CO2 laser beam. The long period grating is insensitive to temperature up to 800 degrees C.     

Studies on adhesion characteristics and corrosion behaviour of vinyltriethoxysilane/epoxy coating protective system on aluminium

The corrosion stability of vinyltriethoxysilane/epoxy coating protective system on aluminium is strongly related to the strength of bonds forming at the metal/organic coating interface. This article is a study of adhesion, composition, electrochemical and transport properties of epoxy coatings electrodeposited on bare aluminium and aluminium pretreated by vinyltriethoxysilane (VTES) during exposure to 3% NaCl. The VTES film was deposited on aluminium surface from 2% vinyltriethoxysilane solution during 30 s. From the values of adhesion strength (pull-off test), time dependence of pore resistance and coating capacitance of epoxy coating (impedance measurements) and diffusion coefficient of water through epoxy coating (gravimetric liquid sorption measurements), the influence of VTES sublayer on the corrosion stability of the electrodeposited epoxy coating was shown.The work discusses the role of the VTES pretreatment in the enhanced adhesion and corrosion stability of epoxy cataphoretic coating. The electrochemical results showed that the aluminium pretreatment by VTES film improved barrier properties of epoxy coating (greater pore resistance and lower coating capacitance). The lower value of diffusion coefficient of water through epoxy coating indicates the lower porosity, while the smaller adhesion reduction points to better adhesion of epoxy coating on aluminium pretreated by VTES film. The composition of the deposited coatings investigated by XPS enabled the clarification of the bonding mechanism.     

Ultrasonic attenuation in plasma-sprayed coating materials

Measurements have been made of the attenuation in thin samples of plasma-sprayed molybdenum, nickel aluminide and aluminium coating materials in the frequency range 2.5 to 15 MHz. It has been found that attenuation is dependent on the structure of the coatings and in particular on porosity. Interference effects in such thin samples are shown to be unimportant because of their high attenuations. An analysis of ultrasonic attenuation through thin samples is presented.