镀层Cu含量对Ni-P-Cu镀层性能及电化学行为的影响

通过调整镀液中Cu离子浓度和添加剂成分,得到了具有不同Cu含量的Ni-Cu-P三元镀层。使用SEM、XRD、DSC、电化学测试等设备和手段研究了镀层性能,总结了Cu含量对Ni-Cu-P镀层性能的影响。结果表明,Cu含量越高的镀层具有越小的沉积颗粒和越致密的镀层结构。Cu元素的加入会降低镀层中P的含量,增加镀层的有序度。极化曲线测试表明,由于镀层结构和化学组成的改变,Cu含量较高的镀层具有更低的孔隙率,更高的耐蚀性。交流阻抗测试证实了该结果,并表明随Cu含量增大,三元镀层的腐蚀行为随之变化。     

Ni-P/纳米SiC复合镀层的电化学行为及耐蚀性能

为了深入研究纳米SiC对Ni-P电镀层在NaCl溶液中的电化学行为的影响,电沉积制备了Ni-P/纳米SiC复合镀层。采用扫描电子显微镜(SEM)观察了镀层的微观形貌,利用动电位极化曲线和交流阻抗技术研究了Ni-P/纳米SiC复合镀层在3.5%NaCl溶液中的电化学行为。结果表明:经过24 h浸泡,非晶Ni-P镀层和Ni-P/SiC2复合镀层在3.5%NaCl溶液中具有较高的电荷转移电阻,表现较好的耐蚀性;Ni-P/SiC20复合镀层在NaCl溶液中随着浸泡时间的延长,Nyquist谱半圆弧减小,因而镀层耐蚀性较差。     

超声波化学镀Ni-P镀层的性能研究

为寻求新的能量输入方式、在降低施镀温度的前提下改善化学镀层的耐蚀性能,将超声波技术引入化学镀工艺制备了Ni-P化学镀层,利用孔隙率测试方法、扫描电子显微镜、X射线衍射仪、动电位极化曲线及交流阻抗等手段,分析了镀层的孔隙率、组织结构和形貌以及镀层的耐腐蚀性能,并将超声波化学镀层与常规化学镀层进行了性能比较.结果表明,超声波技术的应用能有效地降低化学镀层的孔隙率,提高镀层的耐腐蚀性能.     

前处理对不锈钢表面化学镀Ni-P镀层结合力影响的研究

为了在不锈钢表面获得结合力合格的化学镀Ni-P镀层,研究了化学活化、化学活化 闪镀镍、阳极活化 闪镀镍3种前处理工艺对不锈钢上化学镀Ni-P层结合力的影响.采用淬冷法和划痕试验2种镀层结合力测试方法,对化学镀Ni-P层与不锈钢基体之间的结合力进行了评价.结果表明,采用化学活化 闪镀镍和阳极活化 闪镀镍的前处理工艺,Ni-P镀层与不锈钢基体之间的结合强度合格,而采用化学活化前处理的试样,Ni-P镀层与不锈钢基体之间结合强度不合格,原因在于经化学活化后,在不锈钢表面形成了一层黑灰色的腐蚀产物.在168 h的NaCl溶液中腐蚀失重试验表明,不锈钢失重1.2 mg,而化学镀Ni-P镀层未发现失重,说明化学镀Ni-P镀层耐腐蚀失重性能较不锈钢为好.     

化学镀镍磷层孔隙率的电化学评价

钢铁基体上的化学镀镍磷层属于阴极保护镀层,其孔隙率测定非常重要.为此,对化学镀镍磷层孔隙率电化学测定方法进行了探索.通过研究钢铁和化学镀镍磷层在不同介质中电化学行为的区别,选择了5%H2SO4作为测试介质,并研究了该介质中不同孔隙率镀镍磷层的电化学行为.结果表明:随镀层孔隙率的减少,镀层的自腐蚀电位逐渐从铁的自腐蚀电位向纯镍磷镀层的自腐蚀电位变化.而应用常规的孔隙率检测方法只能检测较大的孔隙.电化学方法与贴滤纸法孔隙率测试结果是一致的,说明该方法可行.     

化学镀非晶态Ni-P镀层盐雾腐蚀行为

为了改善铝合金的耐腐蚀能力,利用化学镀在5052铝合金表面制备了非晶态Ni-P镀层,通过SEM、EDS和XRD等手段对Ni-P镀层盐雾腐蚀前后表面-界面形貌、化学元素和物相组成进行了表征,分析了非晶态Ni-P镀层盐雾腐蚀失效机理.研究表明:化学镀Ni-P镀层为非晶态,由直径10～50!m的颗粒组成,颗粒分布比较均匀,界面结合状态良好;Ni-P镀层为高P镀层,其物相以单质Ni和Ni-P相为主;盐雾腐蚀后镀层表面整体耐蚀性强,表面原始缺陷是导致界面局部出现腐蚀坑和镀层脱落的主要原因.     

化学镀Ni-P镀层的生长机理研究

通过扫描电镜（SEM）等手段对化学镀Ni-P镀层断面形貌和表面形貌观察分析,研究了化学镀Ni—P镀层在不同配位剂（柠檬酸钠）浓度下的生长情况。结果表明,镀层在低配位剂浓度镀液中生长速度最快,镀层由层状组织组成;在中等配位剂浓度的镀液中镀层生长速度居中,镀层由较厚的层状组织组成;在高配位剂浓度的镀液中镀层生长速度最慢,由柱状组织组成。     

碳纤维表面预处理及化学镀Ni-P工艺对镀层性能的影响

过去,对碳纤维表面预处理、化学镀Ni-P工艺条件影响镀层性能影响的综合报道不多。为此,先对碳纤维表面预处理,再化学镀Ni-P。分析了粗化和活化对碳纤维表面形貌的影响,探讨了镀液温度、pH值、次磷酸钠还原剂和柠檬酸钠配位剂浓度,添加糖精、十二烷基硫酸钠对碳纤维表面化学镀Ni-P沉积速率的影响。采用扫描电镜(SEM)和能谱仪(EDS)观测了Ni-P镀层的表面、截面形貌,测试了不同工艺条件对Ni-P镀层与碳纤维的结合力。结果表明:粗化使碳纤维表面积增大,有助于提高其与镀层的结合力,AgNO3活化后碳纤维表面附着了较多的催化晶核;随着镀液温度、pH值和柠檬酸钠浓度的增加,化学镀Ni-P的沉积速率均呈先增大后减小的趋势;随着次磷酸钠浓度的增加,化学镀Ni-P的沉积速率先增大后相对稳定;加入糖精后的Ni-P镀层平整、光滑,完全覆盖碳纤维表面,与碳纤维结合良好。     

电镀Zn-Ni和化学镀Ni-P交替镀层的抗腐蚀性能

为了提高铸钢基体的耐腐蚀、耐磨性能，通过在铸钢基体上沉积化学镀Ni-P和电镀趾Ni的交替镀层的方法获得了一系列多层镀层。考察了多层镀层的外观和在5％NaCl中的抗腐蚀性能。研究表明，化学镀Ni-P在电镀趾Ni层上的沉积以及在铸钢基体上沉积Zn-Ni与Ni-P的交替镀层是可行的；所有交替镀层的耐腐蚀性优于相同厚度的Ni-P化学镀层；亚层厚度为1μm和2μm的交替镀层比相同厚度的Zn-Ni单层镀层的耐腐蚀性更为可靠；镀层厚度相同且Ni-P亚层的厚度超过0．5μm时，交替镀层的耐腐蚀性随着层数和Zn-Ni亚层厚度的增加而增加，这主要是多层效应的结果；在长达1a的浸泡腐蚀试验期同，所有镀层的外观都是令人满意的，都没有出现鼓泡和剥裂现象。     

Ni—W-P／Pr2O3化学镀层的电化学行为

采用极化曲线技术研究化学镀层的电化学性能,受到测量信号的干扰,且不能研究其中各子过程及其动力学的特征.以化学镀方法制备了Ni-W-Pr2O3镀层和Ni-W-P镀层,利用交流阻抗技术,研究了基体、Ni-W-P和Ni-W-P/Pr2O3合金镀层在3.5%NaCl水溶液中的腐蚀电化学行为,得出了电位时效图、交流阻抗谱图,并利用拟合程序EQUIVCRT对阻抗试验数据进行了拟合.结果表明:Ni-W-P/Pr2O3镀层电阻随着时间的延长呈现出不断增长的趋势,钝化膜在不断生成;镀层电阻在6.0h后迅速增大,镀层有自封闭现象,稀土失去电子,使镀层更加致密;Ni-W-P/Pr2O3镀层比Ni-W-P镀层具有更优异的耐蚀性能.     

Electrochemical investigation and characterization of thin-film porosity

In thin-film applications it is necessary to control film properties such as homogeneity and porosity to obtain high-quality coatings. Electrochemistry can be a very helpful tool since it can provide information about processes taking place at the interface between substrate and coating. Different thin carbon-based coatings were deposited via physical vapour deposition methods and vapour phase polymerization on pure iron substrates: fullerene films, which were modified by an ion bombardment and thin films of poly(p-xylylene), which is a very good insulating polymer. The film porosity and stability of the film/substrate system against aqueous corrosion were investigated and compared using cyclic voltammetry. The dependence of porosity and film stability on various deposition process parameters such as film thickness and plasma conditions was measured via the dissolution current density and the open circuit potential shift of the substrate material. It could be shown that the two measurements, current density I_crit. and open circuit potential E_ocp. can provide useful complementary information about film porosity that can lead to a better understanding of the coatings properties and the deposition process as well.     

Preparation and characterization of Ni-Cu-P/CNTs quaternary electroless composite coating

Ni-Cu-P/carbon nanotubes (CNTs) quaternary composite coatings were successfully obtained on low carbon steel matrix by electroless plating. The effects of CNTs concentration in the bath on the microstructure of the composite coatings, CNTs content in the composite coatings and the hardness of composite coatings before and after heat treatment at 400 °C have been studied. In addition, the corrosion resistance of Ni-Cu-P/CNTs composite coatings was evaluated by anodic polarization curves in 3.5 wt.% NaCl solution at room temperature. It was noted that the CNTs concentration remarkably influenced the surface morphology of the coatings. With increasing CNTs concentration, both the CNTs content in the composite coatings and the hardness of composite coatings increased at first and then decreased. And the composite coatings after heat treatment provided higher hardness than the as-deposited coatings. The corrosion resistance of Ni-Cu-P/CNTs composite coatings is excellent compared with that of Ni-Cu-P coatings.     

Synthesis and characterization of nanocrystalline silver coating of fly ash cenosphere particles by electroless process

Electroless nanocrystalline Ag coating of fly ash cenosphere particles utilizing a Sn-Pd catalyst system is demonstrated in this article. The deposition of pure metallic nanocrystalline Ag on the fly ash cenosphere particle surface is confirmed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) analysis. Under the described conditions of electroless coating, average nanocrystalline Ag-coating thickness is observed to be approximately 220 nm, using a focused ion beam technique, which is less than that observed by transmission electron microscopy (TEM) (260-360 nm). TEM observation further reveals that the Ag-coating is made up of 50 nm Ag nanocrystallites, which is comparable with the size of approximately 37 nm obtained from the XRD data. The mechanism of the electroless Ag-coating process is discussed. Ag-coated fly ash particles find applications in manufacturing conducting polymers for electromagnetic interference shielding applications.     

Nickel coating on peptide nanotubes by electroless plating

A cyclic tri-β-peptide, cyclo(4-(4-pyridyl)-β-homoalanine)₃, was synthesized. The cyclic peptide was crystallized into μm-sized rods. Electron diffraction analysis revealed that the rod was composed of peptide nanotubes, which were formed by molecular stacking of the cyclic peptides, with nanotube alignment along the long axis of the rod. Ni coating of the rod crystals was carried out by electroless plating. The pyridyl groups at the side chains of the cyclic peptides were used for immobilization of Pd(II) ions on the surface as catalyst for the reduction reaction. The rod crystals were coated with Ni layers, but the electronic conductivity of the Ni-coated rods was found to be low probably due to the grain boundaries between Ni nanocrystals on the μm-sized rod surface.     

Characterization of phase transformation behaviour and microstructural development of electroless Ni-B coating

Phase transformation behaviour of amorphous electroless Ni-B coating with a targeted composition of Ni-6 wt% B is characterized in conjunction with microstructural development and hardness. Microscopic observations of the as-deposited coating display a novel microstructure which is already phase separated at multiple length scales. Spherical colonies of ∼5 μm consist of 2-3 μm nodular regions which are surrounded by ∼2-3 μm region that contains fine bands ranging from 10 to 70 nm in width. The appearance of three crystalline phases in this binary system at different stages of heat treatment and the concomitant variation in hardness are shown to arise from nanoscale fluctuations in the as-deposited boron content from 4 to 8 wt%. High temperature annealing reveals continuous crystallization up to 430 °C, overlapping with the domain of B loss due to diffusion into the substrate. The implications of such a microstructure for optimal heat treatment procedures are discussed.     

Improved electroless process of copper coating ceramics. 1. Some parameters of coating glass substrates

The shortcomings of the available electroless processes, such as scarcity of information on the controlling parameters, bath instability, poor film adhesivity and film contamination are reported. The process described in this paper differs from the conventional process not only in the raw materials used but also in the operational details. The criteria of choice of such materials are discussed. Further, the parameters affecting the quality of electroless copper films are defined and some of them,viz., concentration of bath ingredients and the number of sensitisation-activation treatments needed, are optimised for coating on glass substrates. It has been found that the bath decomposition, a hazard peculiar to an electroless bath can be avoided by maintaining the bath pH below 10.86. The substrate should undergo three sensitisation-activation treatments to receive complete coating. The adhesivity of copper film on glass substrate achieved by this improved process is more than 21.6 kg/cm² as compared to 7 kg/cm³, which is the adhesivity of evaporated copper film on the same substrate.     

Electrochemical deposition and evaluation of electrically conductive polymer coating on biodegradable magnesium implants for neural applications

In an attempt to develop biodegradable, mechanically strong, biocompatible, and conductive nerve guidance conduits, pure magnesium (Mg) was used as the biodegradable substrate material to provide strength while the conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) was used as a conductive coating material to control Mg degradation and improve cytocompatibility of Mg substrates. This study explored a series of electrochemical deposition conditions to produce a uniform, consistent PEDOT coating on large three-dimensional Mg samples. A concentration of 1 M 3,4-ethylenedioxythiophene in ionic liquid was sufficient for coating Mg samples with a size of 5 × 5 × 0.25 mm. Both cyclic voltammetry (CV) and chronoamperometry coating methods produced adequate coverage and uniform PEDOT coating. Low-cost stainless steel and copper electrodes can be used to deposit PEDOT coatings as effectively as platinum and silver/silver chloride electrodes. Five cycles of CV with the potential ranging from ?0.5 to 2.0 V for 200 s per cycle were used to produce consistent coatings for further evaluation. Scanning electron micrographs showed the micro-porous structure of PEDOT coatings. Energy dispersive X-ray spectroscopy showed the peaks of sulfur, carbon, and oxygen, indicating sufficient PEDOT coating. Adhesion strength of the coating was measured using the tape test following the ASTM-D 3359 standard. The adhesion strength of PEDOT coating was within the classifications of 3B to 4B. Tafel tests of the PEDOT coated Mg showed a corrosion current (I_CORR) of 6.14 × 10^?5 A as compared with I_CORR of 9.08 × 10^?4 A for non-coated Mg. The calculated corrosion rate for the PEDOT coated Mg was 2.64 mm/year, much slower than 38.98 mm/year for the non-coated Mg.     

Synthesis and characterization of electroless Ni-P coated graphite particles

Electroless alkaline bath is used to coat Ni-P graphite particles of average size, 150 μm. Amorphous nickel and graphite phases are observed in X-ray diffraction of the coated particles. The crystallite size from diffraction peaks is found to be 9·56 nm. The microstructural studies are carried out with field emission scanning electron microscope (SEM) on the uncoated and coated graphite particles. Uncoated particles showed irregular and fractured surfaces while the surface of coated particles revealed the presence of Ni-P globules. Sizes of Ni-P globules are observed to be in the range 175–250 nm. The presence of Ni and P are confirmed by the energy dispersive spectrometer results. The effect of coating bath composition is studied and an increasing trend in deposition is observed up to 50 gl⁻¹ of stabilizer as well as up to 20 gl⁻¹ of the reducing agent, however, the trend reverses afterwards. The phenomena of nucleation and growth of the Ni-P layer over the graphite surface have been demonstrated through SEM studies and a model has been proposed to demonstrate the growth mechanism of Ni-P globules.     

Shell porosity in spray fluidized bed coating with suspensions

An experimental study regarding spray fluidized bed coating with aqueous suspensions is presented. The dependency of coating shell morphology on drying parameters, atomization pressure and composition of suspension is investigated. The results are compared to existing work regarding spray fluidized bed coating with aqueous solutions of crystalline material. Contrary to coating with solutions, coating shell smoothness and porosity does not depend on drying conditions. Nevertheless, atomizing pressure and mass fraction of solids in suspension have large influence on coating shell morphology. High atomization pressures, leading to small droplets, result in smooth coating surfaces and low shell porosities. A similar trend is observed for a low mass fraction of solids in the suspension.