Ni-P Deposition Research Articles

Comparison of Hardness by Electrolytic and Electroless Deposition of Nickel on Aluminium

Abstract The work deals with the hardness characteristic of substrates coated with nickel through two primary methods: electrolytic deposition and electroless Ni-P deposition. The optimised process parameters for both the process was determined by varying a particular parameter keeping the rest constant in order to obtain minimum crystallite size of Ni. The size of the crystallite were determined using Scherrer’s equation. The optimized combination of process parameter for electrolytic deposition is: 270gm/lt of Nickel Sulfate, 60gm/lt Nickel Chloride, 35gm/lt Boric Acid, current density of 90mA/cm2 bath temperature of 55°C. The optimized combination of process parameter for electroless Ni-P deposition: 34gm/lt Nickel Sulfate, 23 gm/lt Sodium Hypophosphite, 46 gm/lt of Lactic acid, 42 gm/lt of Sodium Citrate, pH 5.0 and bath temperature 85°C. The optimised deposition rate 22μm/hr. Micro-hardness (Vickers) tests were conducted on the coated samples with a 50 gf load. The cause for difference in hardness was due to buildup of residual stress during deposition of Nickel on the substrate(aluminium). The orientation and surface texture of the materials are determined.

Improvement in the corrosion and wear properties of monel 400 alloy by electroless Ni-P deposition in seawater

Monel 400 alloy has been generally applied to marine equipment because of their outstanding corrosion resistance. However, poor abrasive resistance limits its service life. Herein, by depositing electroless Ni–P on Monel 400 alloy, the abrasive resistance after corrosion and wear tests and cathodic protection tests improved by 5 and 21 times, respectively. In addition, due to the inhibiting effect of the corrosion products of nickel and phosphorus, the corrosion resistance of the deposition is better. Ni–P deposition at 500 °C is more beneficial for improving the corrosion resistance and abrasive resistance of the alloy. More interestingly, the synergy between corrosion and wear of the alloy changes from inhibiting to promoting effects after Ni–P deposition.

Mechanical and Tribological Behavior of Nitrided AISI/SAE 4340 Steel Coated with NiP and AlCrN

In this study, novel surface engineering strategies to improve the wear performance of AISI 4340 were investigated. The strategies were as follows: (i) NiP deposition on a previously nitrided steel substrate, followed by NiP interdiffusion heat treatment at either 400 °C or 610 °C (referred to as duplex treatment); (ii) the deposition of AlCrN PVD coating on NiP layers on a previously nitrided steel substrate (referred to as triplex treatment). Prior to the deposition of AlCrN, the NiP was subjected to the interdiffusion heat treatment at either 400 °C or 610 °C. These strategies were compared with the performance of the AlCrN coating directly applied on nitrided steel. To characterize the microstructural features of each layer, X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) analysis were conducted. We also carried out mechanical and tribological behavior assessments. The tribological tests were carried out using a ball-on-disc tribometer under a constant load of 20 N and a tangential speed of 25 cm/s; cemented carbide spheres with a diameter of 6 mm were the counterpart body. The friction coefficient was continuously monitored throughout the tests. The results reveal that the wear mechanism for the AlCrN coating is predominantly oxidative. The most wear-resistant surface architecture was the one comprising AlCrN over the NiP layer subjected to interdiffusion heat treatment at either 400 °C or 610 °C.

One-Step PRC Surface Pretreatment for Plating Onto Al Alloys

Faraday will describe our recent work on the development of a one-step electrochemical surface preparation process to prepare aluminum alloys for direct electrodeposition. Coating on aluminum commonly requires extensive surface pretreatment processes prior to deposition, owing to aluminum’s reactive nature and affinity for oxygen, leading to the formation of an oxide film that negatively affects coating adhesion to the substrate. Therefore, preparing the surface is critical to remove any oils or dirt attached to the surface and to remove the native oxide film to increase coating adhesion. Conventionally these issues are addressed by a continuous sequence of twelve (12) pretreatment process steps to prepare the surface for deposition. Such an extensive number of processing steps requires significant capital investment for a new vendor, increases the probability of errors during the process, is time consuming (lower industrial throughput that ties up equipment), and requires large volumes of hazardous chemicals (Hydrofluoric Acid) that are environmentally unfavorable and introduce cost and safety concerns. Therefore, alternative techniques that do not require such extensive pretreatment processing with similar or better performance to conventional methods are desired.Faraday has recently developed a simple environmentally benign pretreatment process utilizing our pulse reverse electrofinishing approach that can dramatically reduce the number of procedures and complexities required to prepare the surface for the direct deposition onto Al alloys. A specific application of interest that requires low-cost, simple fabrication technology for the deposition of wear, erosion, corrosion fatigue resistant coatings onto Al is Neutrino Focusing Horns. Neutrino Focusing Horns, required for research on particle accelerators and storage rings, are commonly made of aluminum. These horns must withstand repetitive thermal and magnetic loadings over millions of pulses in a radiation and corrosive environment and the thickness of the inner conductor is minimized to reduce absorption and scattering of secondary particles in the conductor material. Therefore, protection of the focusing horns from erosion, corrosion and fatigue is of critical importance to assure long time reliability. The most successful coating thus far has been an electroless nickel coating with conventional 12 step pretreatment method. The application of this coating, however, is challenging due to the large size of the horn (4 m x 1 m x 1 m), and industrialization is challenging due to the low part volumes, high capitalization and large number of process steps.This presentation will focus pulse/pulse reverse surface preparation processes being developed by Faraday Technology. It will explore surface pretreatment procedures to simultaneously prepare various Al surfaces such as Al 6061, Al 4043, Al 1100, and Al 5086 and subsequent direct deposition of ZnNi, NiP, or Ni coatings. These coating have since been characterized and compared to baseline electroless NiP coatings for their functional properties. The results of these characterization studies will be discussed in detail.

Self-Activating Metal-Polymer Composites for the Selective Electroless Metallization of 3D Printed Parts

Nowadays, polymer based additive manufacturing (AM) is widely recognized as a powerful technology for the fabrication of complex three-dimensional objects of virtually any shape in a time, material, and cost effective way. Thanks to their characteristic advantages over conventional manufacturing strategies, AM technologies are the subject of relevant research efforts. In particular, great attention is placed on developing novel 3D printable materials characterized by improved properties and, among all, by novel functionalities, such as magnetic [1] and conductive properties [2]. In order to do this, the most common strategy relies on doping polymeric matrices with nanoparticles, obtaining thus functional 3D printable polymeric composites.Metal containing composites, in particular, can be exploited for their magnetic properties or for their mechanical behavior but also for their potential capability to trigger electroless deposition. It is well-known that electroless plating requires the presence of a catalytic surface, which can be constituted by the metallic particles embedded in the 3D printed composite. In this way, the need to activate the surface of non-conductive polymeric 3D printed parts can be avoided [3]. In addition, metallization can be carried out selectively by fabricating parts in a multi-material printing process [4] with both metal loaded and non-loaded materials. Since only the layers that contain the particles can metallize, conductive regions can be alternated with insulating zones to create metallic functional patterns on the surface of printed parts. This approach can enable the 3D printing of selectively self-metallizing parts, with possible applicability in the production of flexible and highly tridimensional electronic circuits, radiofrequency devices, microelectromechanical systems or microfluidic setups.The present work focuses on the development of a stereolithography (SLA) printable composite based on an acrylate resin loaded with nickel microparticles and its application as self-catalytic material for electroless metallization. This approach, unprecedented for SLA resins, eliminates the need of noble metal activation of the surface. Moreover, the usage of Ni is of great interest also due to the other properties that it can potentially impart to the printed parts: improved mechanical properties, high thermal conductivity, magnetizability. The SLA printability of the metal-loaded resin is assessed and the morphological properties of the 3D printed composites are investigated. Subsequently, the functional properties of the composites are determined, placing a particular emphasis on their capability to trigger NiP and Cu electroless deposition. Finally, the possibility to selectively metallize only specific areas is successfully demonstrated by metallizing a Ni-loaded pattern printed on a Ni-free base.[1] Huber et al.; Appl. Phys. Lett. 109, 162401 (2016)[2] Postiglione et al.; Compos. Part A Appl. Sci. Manuf. 76, 110-114 (2015)[3] Bernasconi et al.; J. Electrochem. Soc. 164, B3059–B3066 (2017)[4] Choi et al.; J. Mater. Process. Technol. 211, 318–328 (2011)

Facile Electroless Plating Method to Fabricate a Nickel-Phosphorus-Modified Copper Current Collector for a Lean Lithium-Metal Anode.

The compatibility of current collectors with reactive Li is key to inducing stable Li cycling and prolonged cycle life of lean Li-metal batteries. Herein, a thin and uniform layer of Ni-P complex was built on the surface of a Cu current collector (NiP@Cu) via an efficient, controllable, and cost-effective electroless plating method. The thickness, morphology, composition, and roughness of the Ni-P deposition were successfully regulated. Lithiophilicity of the current collector was greatly improved by Ni-P deposition, which effectively reduced the Li nucleation overpotential and suppressed the Li dendrite growth. In addition, NiP@Cu promoted an inorganic LiF/Li3P-rich solid electrolyte interphase to facilitate interfacial charge transfer and eliminate excessive side reactions between Li and the electrolyte. As a result, the Coulombic efficiency of half-cells remained above 98.5% for more than 400 cycles at 0.5 mA/cm2 and 98.2% for more than 250 cycles at 1 mA/cm2. Full cells with NiP@Cu also showed superior performance compared to those with bare Cu. This work proposes a promising surface modification method to develop a stable, dendrite-free, and cost-effective anode current collector for high-energy-density lean Li-metal batteries.

New Insight into Adherence of Ni-P Electroless Deposited Coatings on AA6061 Alloy through Al2O3 Ceramic

The adhesion quality of Ni-P coatings on aluminum is important for mechanical and anticorrosion properties. In this study, the adhesion of Ni-P coatings on nanoporous Al2O3 ceramic (NAC) was evaluated by impact testing. NAC was fabricated on AA6061 alloy by anodizing in sulfuric acid. The deposition of Ni-P coating was carried out on NAC with and without zincate pretreatment. It was found that zincate activation of Al2O3 accelerates the formation of Ni-P coating. A cross-sectional analysis using energy-dispersive X-ray spectroscopy showed that the mechanical properties and impact resistance of the Ni-P coating are strongly related to the chemical composition in the vicinity of its interface with Al2O3. The course of the formation process of Ni-P coating and its mechanisms are also very important. Although the formation of Ni-P coating was slower without zincate treatment, its stronger adhesion to NAC led to superior impact resistance compared to zincate-treated Al2O3. Improved durability of items with Ni-P coatings can benefit many applications.

Metallization on Sapphire and Low-Temperature Joining with Metal Substrates.

To meet the packaging requirements of sapphire in special electronic components, there is an urgent need for a joining process that can realize a good connection between sapphire and dissimilar metals at a low temperature. In this work, the surface of a sapphire substrate was successfully catalytically activated and metallized by an electroless nickel plating process. Moreover, the solderability and interconnection of metallized sapphire with Sn-based solders were evaluated and investigated at 250 °C, and the wetting angle of the Sn-based solders on sapphire on sapphire without and with metallization was 125° and 51°, respectively. The interfacial microscopic morphology and element distribution in the Cu/Sn-Ag solder/sapphire solder joints were analyzed. It was found that the middle solder layer has diffused during the reflow process, inferring good adhesion between sapphire and Cu substrate with the aid of the Ni-P deposition. Thus, a sapphire welding method with a simple process suitable for practical applications is demonstrated.

Investigations on Surface Behavior of Electro-Less Nickel Phosphorus Coatings with Nano Additives on Magnesium Alloy Used In Automotive Applications

To enhance the damage and corrosion behaviour for alloys, the coating is found because of the maximum fitted technique. Mg-based alloys have a good range of business application. These alloys show a high specific strength but bad attire and corrosion resistance. A standard coating of Cu, Ni & Zn etc. provides a physical barrier against the wear and tear rate and corrosion attack of magnesium substrate. In the recent study, plating Ni-P was thru going on AZ91 composite by immersing samples into Nickel sulphate bath in the existence of surfactants. The study of the mechanism of Ni-P deposits was studied utilizing SEM. Ni-P coating was coated consistently within the existence of surfactants. Result of surfactant and Result of Nano-additives ZnO, Al2O3 and SiO with various quantities were examined. 0.5 g/l Nano Al2O3 additive-enhanced the deposition of Ni-P on AZ91 magnesium composite and hereafter the similar consequences are detected just in case of SiO accumulation. Effect of ZnO was also noticed. So is extremely clear that Ni-P coating is extremely effective to scale back the corrosion and rise the wear and tear behaviour if it's used together with Nano additive and therefore the surfactants.

Study of the effect of pulse plating parameters on the electrodeposition of NiP and NiP/SiC coatings and their microhardness values

ABSTRACT This study is focused on finding optimised conditions for electrodeposition of NiP and NiP/SiC coatings, which enhance the coatings' microhardness. Both the effect of particles and the effect of heat treatment at 400°C for 1 h on the microhardness of the coating were studied. The effects of pulse electrodeposition parameters including duty cycle, frequency, and peak current density on the composition of NiP and NiP/SiC composite coatings were examined, and the results were compared with those from direct current plating. Pulse plating increased the current efficiency of NiP deposition while decreasing the phosphorus content of these coatings in comparison to direct plating, resulting in higher microhardness values. It was also shown that wt.%P in NiP coating depends not only on peak current density but also on bath charge of pulse plating. Pulse plating parameters (duty cycle and frequency) and the low incorporation of SiC particles did not affect microstructure or the microhardness of the coatings, while heat treatment was the main factor that increased microhardness.

Hydrogen in Electrolessly Deposited Ni/Au and Ni/Pd/Au Films

For the surface finishing of copper layer on printed circuit boards, autocatalytic electroless deposition of nickel-phosphorus alloy and immersion deposition of gold (ENIG, Ni-P/Au) or autocatalytic electroless deposition of Ni-P, palladium and immersion deposition of Au (ENEPIG, Ni-P/Pd/Au) are widely used. The Ni-P/Pd/Au surface finish is suitable not only for lead-free soldering but also for wire bonding [1]. For soldering, it was reported that hydrogen plasma improved bonding behavior and realized a flux-free process [2]. Electrochemically deposited metal films include hydrogen atoms. The hydrogen adsorbed in metal films causes various phenomena such as atomic diffusion, alloying, crystal growth, void formation. We have been investigating the atomistic state and behavior of hydrogen in electrodeposited metals by thermal desorption spectroscopy [3, 4]. In this study we measured changes in hydrogen amounts in the Ni-P/Au and Ni-P/Pd/Au surface finishes [5]. We used two different electroless Pd baths using formic acid (Ni-P/Pd/Au) and sodium phosphinate (Ni-P/Pd-P/Au) as reducing agents. The Ni-P films contained large amounts of diffusible hydrogen that desorbs at room temperature. During autocatalytic electroless deposition of Pd and Pd-P on Ni-P films, the greater part of the hydrogen in the Ni-P films desorbed. Although no hydrogen evolution accompanied immersion Au deposition, the hydrogen amounts in Ni-P/Au, Ni-P/Pd/Au, and Ni-P/Pd-P/Au films were much greater than in films without a Au layer. Moreover, at room temperature, they remained almost unchanged for one month after deposition, indicating that the thin Au layer (< 0.1 μm) prevents hydrogen desorption from the metal films. The high hydrogen concentration in Ni-P/Au films improved solder wettability.[1] Y. Oda, M. Kiso, S. Kurosaka, A. Okada, K. Kitajima, and S. Hashimoto, Proc. Internal. Microelectronic and Packaging Soc., IMAPS (2008).[2] T. Hagihara, T. Takeuchi, and Y. Ohno, Proc. 10th Electronics Packaging Technology Conf. (IEEE), 595 (2008).[3] N. Fukumuro, S. Kojima, M. Fujino, Y. Mizuta, T. Maruo, S. Yae, and Y. Fukai, J. Alloy. Comp., 645, S404 (2015).[4] N. Fukumuro, K. Tohda, and S. Yae, this symposium.[5] Y. Oda, Y. Sagara, N. Fukumuro, and S. Yae, J. Surf. Finish. Soc. Jpn., 70, 163 (2019).

Metallization of PET textile utilizing supercritical CO2 catalyzation

Metallization of polyethylene terephthalate (PET) textiles was realized by conducting the catalyzation step in supercritical CO2 and using an organometallic compound, palladium bis-hexafluoracetylacetonate (Pd(hfa)2, as source of the palladium catalyst for the later Ni-P deposition step. Electrical resistance of the Ni-P/PET was evaluated before and after adhesion and high temperature incubation tests to reveal durability of the Ni-P/PET. Electrical resistances of the Ni-P/PET prepared at 343 K did not vary much after two cycles of the tape adhesion test when the deposition time was longer than 1.0 h. The Ni-P/PET metallized at 343 K for 2.0 h retained a low electrical resistance at 0.038 Ω after the high temperature incubation test at 414 K. The supercritical CO2 catalyzation was confirmed to be an effective method to metallize PET textile.

Improving Surface Properties of Inconel 600 Alloy by Electroless Ni-P Deposition

The use of electroless Ni-P plating (EN) coating has attracted a surprising interest in the most recent years. Many useful characteristics of the electroless-plating method have created many benefits in different industries such as oil, gas, electronic, automotive, aerospace, and chemical. Some of the highlighted properties of such a method are superior corrosion resistance, superior mechanical properties, and uniform thickness of the coating as well as good surface finish properties, good adhesion characteristics, and a wide range of thickness. In this paper, electroless plating has been applied in a (Ni-P) bath at two different times of 2 and 3 hr respectively. After the plating, a heat treatment at 400 °C for an hour under vacuum 10-4 torr has been done. The prepared samples were characterized by energy dispersive spectroscopy, X-ray diffraction, and scanning electron microscopy (SEM). In addition, micro-hardness and corrosion rate following Tafel extrapolation in two acidic solutions (1M HCl and 1M H2SO4) were also determined. Vickers hardness values for specimens, coated by Ni -P at 2 and 3 hr have increased by 47 % and 32 % respectively. X-ray diffraction analysis for the coated surfaces showed two phases of Ni3P and NiP, presented before and after heat treatment. The SEM images of the cross sectional coated specimens revealed that the thickness of the coating is 68.43 and 92.71 µm for 2 and 3 hr coating time, respectively. Tafel analysis showed that the coated specimens had a lower corrosion current density compared to that for the bare specimens. The corrosion current density for the coated specimens in 1M H2SO4 increased by 57 % with 2 hr and 69 % at 3 hr coating time. While, the corrosion current density for the coated specimens in 1M HCl increased by 37 % and 83 % at 2 and 3 hr coating time respectively.

Ni-P nanostructures on flexible paper for morphology effect of nonenzymatic electrocatalysis for urea

This study accounts the controllable design over the structure and morphology of Ni-P nanomaterials directly growing on cellulose paper, and its excellent non-enzymatic electrocatalytic performance to urea. The Ni-P papers were prepared by simple solution soaking and electroless bathing. And the simple experimental steps and mild experimental conditions make it possible for large-scale industrial production, and potential for practical applications. In addition, tuning the pH and concentration of the electroless bath, the Ni-P nanomaterials with different morphologies of nanoflower, nanosheet, nanowire microsphere and microsphere were obtained. The Ni-P nanomaterials impart conductivity to cellulose paper while being potently sensitive to urea owing to its high catalytic activity. Cellulose paper has a large specific area and open macroporous framework which hadn't been damaged during the process of electroless bathing, providing much more activated sites for Ni-P deposition. And the prepared Ni-P papers, as composite materials of cellulose papers loading Ni-P nanomaterials, have high electrocatalytic properties to urea. Comparing the electrochemical behaviors of the four Ni-P paper electrodes with different morphologies, the Ni-P nanoflower paper electrode showed the best electrochemical performance with highest sensitivity of 683.46 μA mM−1 cm−2 in the low concentration range (0–1 mM) and 1140 μA mM−1 cm−2 in the high concentration range (1–11 mM), lowest detection limit of 12 μM, shortest response time of 3 s, which may owes to the highest surface area of the Ni-P nanoflower structure. It also has a good stability in room environment remaining 97% after 35 days of storage. Moreover, the electrocatalytic activities of the four Ni-P paper electrodes are ranked as follows: nanoflower > nanosheet > nanowire microsphere > microsphere. What's more, the long-term stability and repeatability, good selectivity of the flexible Ni-P paper make it successfully applied to swimming pool water quality monitoring.

Porous Nickel-Phosphorous Electrode Synthesized By Fast-Simple Electrodeposition Process for Efficient Overall Water Splitting

Water electrolysis is an electrolysis reaction of water, and it is a technology that can produce a large amount of hydrogen environmentally friendly. The purposes of water electrolysis are responding to current hydrogen demand and storing electric energy produced from renewable energy such as solar or wind power to solve their intermittency. Water electrolysis reaction is divided into two half reactions; hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The theoretical equilibrium potential of the water electrolysis is 1.23 V, but the electrolysis reaction of the actual water requires much higher voltage due to the slow kinetics of oxygen and hydrogen reaction. Therefore, in order to increase hydrogen production efficiency, it is necessary to develop a catalyst having high activity and low cost for OER and HER. At present, transition metal based materials such as iron (Fe), cobalt (Co), and nickel (Ni) are mainly studied as high efficiency and low cost catalysts for oxygen and hydrogen evolution reactions for alkaline water electrolysis. Those transition metals are being studied in the form of various compounds such as oxide, carbide, nitride and phosphide. Among various type of compounds, transition metal phosphides (TMP) have drawn much attention for use in the alkaline water electrolysis system. These TMP catalysts have relatively good catalytic activity and stability for both OER and HER, and have high electrical conductivity compared to oxide based catalyst. In addition, TMP catalysts can be synthesized using non-toxic precursors as compared to nitride and carbide based catalysts. However, since most of TMP catalysts requires several hours to days for synthesis process, including high temperature heat treatment processes, the efficiency problem has not been solved. In this study, we have developed a method for producing nickel-phosphorus electrodes for high efficiency oxygen and hydrogen evolution reaction by fast-simple electrodeposition method. The synthesis procedure of the Ni-P electrodes ends in a few seconds at room temperature. High cathodic current density was applied to promote the generation of hydrogen bubbles and the deposition of Ni-P, thereby obtaining a highly porous structure. Hydrogen bubbles played an important role in forming the porous Ni–P layer by acting as self-dynamic templates. The surface area of highly porous Ni-P (HP Ni-P) was 50 times larger than that of the flat Ni electrode. The HP Ni-P exhibits remarkable electro-catalytic activity and stability towards the HER and OER in alkaline solutions. For the HER, overpotential at 10 mA/cm2 was 180 mV, which is slightly higher than that of Pt/C, but HP Ni-P required a lower overpotential than that of Pt/C at the high current region. For the OER, HP Ni-P shows higher catalytic activity than IrO2 at the entire current region; overpotential at 10mA/cm2 was 287 mV. The durability of HP Ni-P was also superior to the precious metal-based catalysts (Pt/C, IrO2) and Ni electrode in the long-term chronopotentiometry test. This result is ascribed to increase in surface area by hydrogen bubble generation and electronic structure change of Ni. Electronic structure change may lead to change in adsorption energy of intermediate adsorbates such as H*, OH*, O* and OOH*, which are participated in the steps of HER and OER, and can promote the kinetics of reactions in alkaline media. Figure 1

Effect of Heat Treatment of AZ91 Magnesium Alloy on the Electroless Ni-P Deposition

Magnesium alloys are excellent choice for automobile, aerospace, and computer components owing to their light weight, unique physical and mechanical properties. However, poor corrosion resistance has restricted their applications in aggressive environments. The surface coating is one of the viable options to reduce the susceptibility of magnesium alloys to corrosion. The present study focuses on the effect of heat treatment of AZ91 magnesium alloy, for different durations at 400 °C, prior to electroless Ni-P deposition on corrosion resistance. The microstructure and elemental analysis of the heat-treated specimens are performed using SEM and EDS techniques respectively. It is observed that the duration of heat treatment has a significant effect on the surface morphology and microstructure of the alloy. The precipitates in the cast alloy (enriched with Mg and Al) fragmented and the transformed into a new Al and Zn rich phase, after 12 h heat treatment. The dissolution of precipitates, however, observed on heating further to 24 h and exhibited relatively a lesser corrosion current density. The dense electroless Ni-P deposition is formed on the alloy heat treated for 24 h. The corrosion behavior of the single Ni-P layer on the heat treated (for 12 h) and untreated alloy show a marked deterioration, as investigated by the anodic polarization and electrochemical impedance spectroscopy (EIS) techniques. Relatively a better corrosion performance is seen for the double-layer Ni-P deposition. The duplex layer coatings on the as cast and heat treated for 24 h at 400 °C substrates showed an improved corrosion resistance compared to that on the 12 h heat treated substrate.

Electroless deposition of Ni-P on a silicon surface

The present article concerns the metallization of silicon substrates by deposition of the nickelphosphorus alloy produced by an autocatalytic chemical process. The deposition electrolyte is composed of a metal salt, a reducing agent (sodium hypophosphite), a complexing agent (sodium citrate) and a buffer (ammonium acetate). The deposition could only be carried out after activation of the silicon by fixing catalytic species on its surface. The immersion of the silicon samples in palladium chloride made it possible to produce relatively thick and regular Ni-P coatings. The immersion time was optimized. The activation of Si was characterized by XPS and the Ni-P coating by XPS and SEM. The electrochemical study did not show any real mechanism changes compared to the Ni-P deposition on a conductive surface.

Study of the formation of alkaline electroless Ni-P coating on magnesium and AZ31B magnesium alloy

In this work, alkaline electroless Ni-P coatings were directly formed on commercial purity magnesium and AZ31B magnesium alloy substrates using a process that avoided the use of Cr(VI) compounds. The study focused on two aspects of coating formation: (i) the effect of the substrate roughness on the kinetics of the electroless Ni-P deposition process on magnesium; (ii) the morphological and chemical evolution of the coating on both magnesium and the AZ31B alloy. For these purposes, gravimetric measurements, scanning electron microscopy (SEM), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and open-circuit potential (OCP) measurements were employed. It is shown that a relatively rough substrate promotes the rapid formation of the Ni-P coating on the substrate surface in comparison with smoother substrates. Furthermore, the presence of fluoride ions derived from the NH4HF2 reagent in the electroless Ni-P plating bath leads to formation of MgF2 a few seconds after immersion in the bath. Subsequently, crystals of NaMgF3, with a cubic morphology, are developed, which later become embedded in the Ni-P matrix. The presence of fluorine species passivates the substrate during coating formation and hence restricts the decomposition of the electroless Ni-P plating bath, which can occur due to release of Mg2+ ions. Finally, according to gravimetric measurements, SEM and XRD, the plating process is initially faster on magnesium than on the alloy.

An electrode-separated piezoelectric immunosensor array with signal enhancement based on enzyme catalytic deposition of palladium nanoparticles and electroless deposition nickel-phosphorus

A differential piezoelectric immunosensor array was reported with signal enhancement based on the biometallization of palladium nanoparticles (Pd NPs) and successive electroless deposition Ni-P layer. In this strategy, the primary antibody probes were immobilized on the aminated quartz surface in an electrode-separated piezoelectric sensor (ESPS). After bounding with the corresponding antigen and alkaline phosphatase (ALP) conjugated second antibody, the ALP in the sandwich-type immunocomplex can catalyze the substrate of p-aminophenyl phosphate to generate p-aminophenol, which reduces Pd(II) in solution to Pd NPs onto the quartz surface. A successive signal amplification was performed by Pd NPs- promoted catalytic electroless deposition of Ni-P layer. A differential measurement mode was employed to eliminate the influence of non-mass effects, including the changes in conductivity, viscosity, density and temperature of the solution, as well as the baselines draft of piezoelectric sensors. The responses of the differential ESPS in fundamental frequency, third and fifth overtones were compared. The proposed method was applied to the determination of human IgG with a detection limit of 1pg/mL. Compared with biometallization of Pd NPs, the sensitivity is enhanced further by three orders of magnitude due to high activation energy in Ni-P deposition reaction and low baseline draft in differential measurement mode.

A Supercritical CO2 Promoted Electroless Ni-P Plating on Silk and Their Fundamental Characteristics Investigations

This study demonstrated a promising method to integrate flexible silk textiles and conductive Ni-P metal coatings for the increasing interest in wearable devices. Electroless plating with supercritical carbon dioxide (sc-CO2) was utilized to combine the two distinct materials together conformally. Ni-P was chosen for its electrical conductivity and high corrosion resistance while silk was chosen as the substrate for its flexibility. Sc-CO2 was used as a promoter in the catalyzation to enhance the compatibility between the Ni-P with the silk. This technique allows simplification of the electroless plating by excluding the pretreatments while the substrate remains undamaged after the catalyzation step. In addition, the sc-CO2 leads to an environmental friendly process by cutting down the usage of corrosive chemicals in the catalyzation step. This study therefore demonstrates a series of palladium (II) acetylacetonate catalyzation followed by Ni-P deposition on the silk. The lowest electrical resistance at 1.02 Ω was achieved at 4 min of the Ni-P plating time. Corrosion resistance of the Ni-P/silk in a solution simulating the human sweat was evaluated. Reliability of the Ni-P/silk composite material was revealed by comparing the electrical resistances and corrosion resistances before and after an adhesive test.