Tribology of electroless nickel coatings – A review

The electrochemical capacitor (EC), also called as supercapacitor, is an energy storage device possessing a unlimited life-cycle and high power density known to store energy in the double-layer or through supercapacitance as a result of an applied potential. Fundamental values in relation to the major chemical and physical qualities of electrode materials are explained in the following review, with carbon-made electrodes, specially activated carbon highlighted in regards to their improvement of the typical power and energy densities of ECs. Supercapacitive materials, remarkably transition metal oxides are revealed by the potential to further develop EC performance through synergistic effects and asymmetric design. Recently, several chemically deposited metal oxide thin film electrodes as well as ruthenium oxide, manganese oxide, cobalt oxide, nickel oxide, iron oxide, ferrites etc., have been evaluated in supercapacitors. This review presents supercapacitor performance data of metal oxide thin film electrodes on activated carbon offered by electroless plating as a suitable, fast and economical technique. The supercapacitors demonstrated the specific capacitance (Sc) principles, which are relatively comparable with bulk electrode values; therefore, it is likely that metal oxide films will continue to play a major role in supercapacitor technology and are expected to significantly develop the capabilities of these devices in the near future.

The development supercapacitor from activated carbon by electroless plating—A review

Flexible and wearable electronics is one major technology after smartphones. It shows remarkable application potential in displays and informatics, robotics, sports, energy harvesting and storage, and medicine. As an indispensable part and the cornerstone of these devices, soft metal electrodes (SMEs) are of great significance. Compared with conventional physical processes such as vacuum thermal deposition and sputtering, chemical approaches for preparing SMEs show significant advantages in terms of scalability, low-cost, and compatibility with the soft materials and substrates used for the devices. This review article provides a detailed overview on how to chemically fabricate SMEs, including the material preparation, fabrication technologies, methods to characterize their key properties, and representative studies on different wearable applications.

Chemical formation of soft metal electrodes for flexible and wearable electronics

Electroless nickel–boron baths reduced with sodium borohydride can be stabilized with various agents such as thallium nitrate or lead tungstate with no fundamental modification of deposition rates and stability. To improve the mechanical properties of electroless nickel–boron deposits, various heat treatments are applied. At low temperatures, no fundamental changes in the deposit structure are observed, only an improvement of adhesion on aluminium substrate. The values of the Knoop microhardness obtained on these heat-treated deposits are near 600 hk 100 . At higher temperatures, structural changes take place and the nickel–boron deposits crystallize. The microhardness rises until 1050 hk 50 for heat treatments at 350 °C for 4 h. A diffusion layer between the electroless nickel deposit and the aluminium substrate appears at high heat treatment temperatures. The results of scratch tests show that the Ni–B deposits, with or without heat treatments, have good tribological properties under external solicitations. They are hard, wear and abrasion resistant, and also have good adhesion to the aluminium substrate.

Heat treatments for electroless nickel–boron plating on aluminium alloys

The effect of borohydride, thallium acetate, ethylenediamine and sodium hydroxide concentrations, and the coating bath temperature on both the coating rate and boron content of the electroless Ni–B films was investigated systematically. The Ni–B coating rate increased with the increase in thallium acetate and sodium hydroxide concentrations, but it was not very sensitive to the borohydride concentration. Below 90 g L − 1 ethylenediamine concentration the coating efficiency was significantly low and above this value as the ethylenediamine concentration increased the coating rate decreased slightly. Below 85 °C the coating rate was very low and above this temperature it was insensitive to the bath temperature. The boron content of Ni–B film increased with the increase in the borohydride concentration and the bath temperature, and decreased with the increase in thallium acetate and ethylenediamine concentrations. Up to 50 g L − 1 sodium hydroxide concentration, the boron content of the film increased and above this concentration it was insensitive to the sodium hydroxide concentration. As the boron content of Ni–B film increased, both the corrosion resistance and microhardness of Ni–B film increased. Heat treatment brought significant improvement in the microhardness but the corrosion resistance of Ni–B film was observed to decrease due to the disappearance of the amorphous characteristics of the as-deposited Ni–B film and the formation of the Ni–B compound phases.

Effect of coating bath composition on the properties of electroless nickel–boron films

Light alloys are more and more widely used, notably in aeronautics and the car industry. To improve their superficial properties, they can be covered with a hard and wear resistant protective layer. In this article, we examine the possibility of depositing a thick autocatalytic electroless Ni–B plating on aluminium alloys. We propose an alkaline bath containing sodium borohydride as the reducing agent. The deposition rate is held constant by a regular replenishment of the Ni–B bath allowing a rate of about 25 μm/h. The Knoop microhardness of the Ni–B deposits after the bath reaches about 750 hk100. Appropriate heat treatment can increase the deposit microhardness up to more than 1000 hk100 but must be applied with regard to the substrate properties. The study of these heat treatments will be published in a further paper.

Autocatalytic electroless nickel-boron plating on light alloys

Light alloys are more and more widely used notably in aeronautics and the car industry. To improve their superficial properties, they can be covered with a hard and wear resistant protective layer. In this article, we examine the possibility of plating a thick autocatalytic electroless Ni-B deposit on aluminium alloys. We propose an alkaline bath containing sodium borohydride as the reducing agent. The deposition rate is held constant by a regular replenishment of the Ni-B bath allowing a rate of about 25 μm/h. The Knoop microhardness of the Ni-B deposits after the bath reaches about 750 hk 1 0 0 . An appropriate heat treatment can increase the deposit microhardness up to more than 1000 hk 1 0 0 but must be applied in regard to the substrate properties. The study of these heat treatments will be published in a further paper.

The present work aims at evaluating the corrosion performance of a cerium immersion treatment on zinc electroplated. For comparison, zinc coatings pretreated with a commercial chromate treatment were also examined. The corrosion behaviour of pretreated zinc surfaces under immersion in sodium chloride was investigated by potentiodynamic polarization to evaluate the effect of cerium on the oxygen reduction reaction. The influence of immersion time, temperature of cerium solutions, stirring influence, cerium concentrations, cerium salt, pH of the solution and oxidation state of cerium are also investigated. Scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) were used to characterize the sample surfaces after treatments. In order to compare the corrosion performance of cerium pretreated samples, an accelerated test in a humid chamber was carried out. The results indicate that the cerium film formed on the zinc surfaces markedly suppressed the cathodic process. The accelerated corrosion test shows that white rust formation is delayed although the protection given by this treatment is less efficient than with commercial chromate treatments.

J.-P. Petitjean

Papers

Autocatalytic electroless nickel-boron plating on light alloys

Autocatalytic electroless nickel-boron plating on light alloys

Cerium treatments for temporary protection of electroplated steel

The Trivalent Chromium Pretreatment Applied to Aluminium 1050