Fabrication and characterization of rod-like nano-hydroxyapatite on MAO coating supported on Mg-Zn-Ca alloy

The poor corrosion resistance of magnesium alloys is a dominant problem that limits their clinical application. In order to solve this challenge, micro-arc oxidation (MAO) was used to fabricate a porous coating on magnesium alloys and then electrochemical deposition (ED) was done to fabricate rod-like nano-hydroxyapatite (RNHA) on MAO coating. The cross-section morphology of the composite coatings and its corresponding energy dispersion spectroscopy (EDS) surficial scanning map of calcium revealed that HA rods were successfully deposited into the pores. The three dimensional morphology and scanning electron microscopy (SEM) image of the composite coatings showed that the distribution of the HA rods was dense and uniform. Atomic force microscope (AFM) observation of the composite coatings showed that the diameters of HA rods varied from 95 nm to 116 nm and the root mean square roughness (RMS) of the composite coatings was about 42 nm, which were favorable for cellular survival. The bonding strength between the HA film and MAO coating increased to 12.3 MPa, almost two times higher than that of the direct electrochemical deposition coating (6.3 MPa). Compared with that of the substrate, the corrosion potential of Mg-Zn-Ca alloy with composite coatings increased by 161 mV and its corrosion current density decreased from 3.36 × 10⁻⁴ A/cm² to 2.40 × 10⁻⁷ A/cm² which was due to the enhancement of bonding strength and the deposition of RNHA in the MAO pores. Immersion tests were carried out at 36.5 ± 0.5 °C in simulated body fluid (SBF). It was found that RNHA can induce the rapid precipitation of calcium orthophosphates in comparison with conventional HA coatings. Thus magnesium alloy coated with the composite coatings is a promising candidate as biodegradable bone implants.     

Electrocatalysis of oxygen reduction reaction on Nafion/platinum/gas diffusion layer electrode for PEM fuel cell

In this work a new membrane electrode based on Pt-coated Nafion membrane was fabricated. Chemical deposition process was used to coat platinum on Nafion 117 membrane and then Pt-coated Nafion membrane was hot pressed on gas diffusion layer (GDL) to make new membrane electrode. The electrochemical and chemical studies of the Pt-coated Nafions were investigated by electrochemical techniques, X-ray diffraction and scanning electron microscopy. The electrochemical results indicated that as the concentration of H₂PtCl₆ increased, the oxygen reduction reaction rate increased until the concentration was reached where the reduction reaction was limited by the problem of mass transport. The electrochemical results for oxygen reduction reaction showed that the new electrode which prepared by plating Nafion membrane with 0.06 M H₂PtCl₆ in electroless plating solution, has a higher performance than other electrodes. The XRD results showed that the average platinum particle size of the best sample was about 3 nm. The loading of platinum for this electrode was 0.153 mg cm⁻².     

Synthesis of titanium nitride thin films deposited by a new shielded arc ion plating

Thin films of titanium nitride (TiN) were deposited on stainless steel substrates by a modified deposition technique, double-layered shielded arc ion plating with vicarious circular holes (DL-SAIP). The results show that the TiN film with the distance of 10 mm between the double-layered shield plates had the least droplets. The deposition rate of the films prepared with the new technique was more homogeneous than that of all the other shielded arc ion plating. The film/substrate adhesion and microhardness values of the TiN films were higher than 40 N and 18 GPa, respectively. Thus such TiN thin films can be expected in applications.     

A corrosion resistant cerium oxide based coating on aluminum alloy 2024 prepared by brush plating

Cerium oxide based coatings were prepared on AA2024 Al alloy by brush plating. The characteristic of this technology is that hydrogen peroxide, which usually causes the plating solution to be unstable, is not necessary in the plating electrolyte. The coating showed laminated structures and good adhesive strength with the substrate. X-ray diffraction and X-ray photoelectron spectroscopy analysis showed that the coatings were composed of Ce(III) and Ce(IV) oxides. The brush plated coatings on Al alloys improved corrosion resistance. The influence of plating parameters on structure and corrosion resistance of the cerium oxide based coating was studied.     

Electroless Pd and Ag deposition kinetics of the composite Pd and Pd/Ag membranes synthesized from agitated plating baths

The atomic absorption spectroscopy (AAS) has been successfully utilized for the measurement of the Pd and Ag ion concentrations in the plating baths and to elucidate the effects of temperature, initial metal ion and reducing agent concentrations and agitation on the electroless plating kinetics of Pd and Ag metals. The initial metal ion concentrations for Pd and Ag were varied over a range of 8.2–24.5 mM and 3.1–12.5 mM, respectively. The plating reactions were conducted in a constant temperature electroless plating bath over a temperature range of 20–60 °C and an initial hydrazine concentration range of 1.8–5.4 mM. It was found that the electroless plating of both Pd and Ag were strongly affected by the external mass transfer in the absence of bath agitation. The external mass transfer limitations for both Pd and Ag deposition have been minimized at or above an agitation rate of 400 rpm, resulting in a maximum conversion of the plating reaction at 60 °C and dramatically shortened plating times with the added advantage of uniform deposition morphology. The derivation of the differential rate laws and the estimation of the reaction orders and the activation energies for the electroless Pd and Ag kinetics were conducted via non-linear regression analysis based on the method of initial rates. For a constant-volume batch reactor, the integrated rate law was solved to calculate the conversion and the reactant concentrations as a function of plating time. The model fits were in good agreement with the experimental data. Furthermore, the bath agitation and the plating conditions used in the kinetics study were adopted for the synthesis of 16–20 μm thick composite Pd/Ag membranes (10–12 wt% Ag) and a pure-Pd membrane with a hydrogen selective dense Pd layer as thin as 4.7 μm. While hydrogen permeance of the Pd/Ag membranes A and B at 450 °C were 28 and 32 m³/m²-h-atm^0.5, the H₂ permeance for the 4.7 μm thick pure-Pd membrane at 400 °C was as high as 63 m³/m²-h-atm^0.5_. The long-term permeance testing of all the membranes synthesized from agitated plating baths resulted in a relatively slow leak growth due primarily to the improved morphology obtained via the bath agitation and modified plating conditions.     

LY12CZ铝合金表面等离子浸没离子注入氮层的摩擦磨损性能研究

对LY12CZ(2024)铝合金进行了氮等离子体浸没离子注入(PIII)处理,分析比较了不同工艺参数下离子注入前后试样的化学组成、各元素的化学价态及其摩擦磨损性能.结果表明:铝合金表面改性层中形成了弥散强化的氮化铝(AlN)相;与基体相比,铝合金试样在不同条件下处理后的表面显微硬度均有所提高,最大增幅达1.4倍;铝合金的磨损质量损失减少了75%,摩擦系数显著降低,表面综合性能得到了显著改善.     

电刷镀镍纳米镀层的结构和磨损性能

应用电刷镀技术,以快速镍镀液制备了镍纳米镀层;用X射线衍射仪和原子力显微镜分析了经不同温度下热处理后的镍刷镀层的结构和晶粒尺寸,并测定了刷镀层的显微硬度和耐磨性能.结果表明:镀层的晶粒大小随热处理温度的升高先降低而后增大,经300 ℃热处理后的镍纳米镀层的晶粒尺寸小于30 nm;镍镀层在300 ℃左右热处理时表现出较明显的强化趋势,相应镀层的晶粒尺寸最小、硬度最大;而镀层的耐磨性随热处理温度的变化与镀层的硬度略有不同,经200 ℃热处理后的镍镀层的耐磨性能最好.     

搅拌速率对β-PbO_2-CeO_2-ZrO_2复合电极材料电化学性能的影响

为了提高三价铬镀铬工艺中阳极材料的性能,采用阳极氧化法制备了掺杂纳米颗粒的β-Pb O2-Ce O2-Zr O2复合电极材料。通过扫描电化学显微镜和析氧极化曲线的测量,考察了不同搅拌速率条件下制备的复合电极材料在硫酸盐体系三价铬镀液中的电催化活性,利用塔菲尔曲线考察了复合电极材料的耐蚀性,并辅以扫描电镜表征了电极材料的微观形貌。结果表明:当施镀搅拌速率为350 r·min-1时,所制备的复合电极材料具有结构致密、电催化活性高、耐蚀性强等特点。     

氮化钛微粉增强镍磷化学复合镀层的组织及其摩擦磨损性能研究

利用自蔓延高温合成法得到的氮化钛微粉制备了Ｎｉ－Ｐ－ＴｉＮ化学复合镀层，采用Ｘ射线衍射仪，扫描电子显微镜和电子探针分析了镀层的组织和结构，并在球－块摩擦磨损试验机上对镀层的摩擦学特性进行了研究，结果表明，ＴｉＮ微粉可使Ｎｉ－Ｐ化学镀层的组织明显细化，且能提高镀层的最佳时效硬化温度随着Ｎｉ－Ｐ－ＴｉＮ化学复合镀层中ＴｉＮ共析量的增摩擦系数逐渐降低并趋于稳定，耐磨性则存在的一个最佳ＴｉＮ含量；ＴｉＮ微     

以硼氢化钠为还原剂化学镀镍的电化学研究

采用线性电位扫描伏安法研究了以硼氢化钠为还原剂的化学镀镍体系, 考查了镀液组成及工艺条件对化学镀镍硼阴、阳极过程的影响, 结果表明: 乙酸镍和硼氢化钠含量的提高分别促进了Ni²⁺的还原反应和BH₄^-的氧化反应; 乙二胺、氢氧化钠以及添加剂硫脲、糖精钠对阴、阳极反应均有不同程度的抑制作用, 同时添加剂中的硫元素加速了镍的氧化; 升高温度有利于阴、阳极反应的进行.