Electroless Coating Research Articles

Studies on Electroless Coatings at IIT Roorkee - A Brief Review

Since the introduction of Electroless (EL) coating in 1946 by Brenner and Riddle, the process has been the subject of steady growth. It is one of the most elegant methods available for the production of alloy coatings on surface. The technique involves the autocatalytic reduction, at the substrate/solution interface, of cations by EL bath released from suitable chemical reducing agents. EL coating technique is simple one, as can be manifested just by controlling pH and temperature of the coating bath. Such coatings are reported to provide excellent physical and mechanical properties. The electroless coatings are being studied at Indian Institute of Technology Roorkee since 1985. The structural and morphological behavior of Ni-P coatings for different phosphorous contents has been extensively studied. Sub-micron size coating islands and their transformations have been deduced. The metallography studies using hot stage within TEM to follow the phase transformations occurring at various temperatures have been studied for Ni-B EL coatings. The realization of mechanical bonding along with chemical bonding between EL coating and the substrate has been explained by coated copper on ceramic powder. As a forward step towards composite coatings, Ni-P-C, Ni-P-Al2O3, Ni-P-ZrO2has been developed by EL co-deposition technique. Ag-graphite coatings produced by EL technique exhibits nearly five times higher wear resistance and nearly two times better corrosion resistance apart from a good electrical conductor. The tribological behavior of electroless Ni-P-X and Ni-P coatings on steel and aluminium substrates in different conditions i.e., as coated, heat treated at various temperatures at different extents of time with different normal loads, have been studied in terms of dry sliding friction and wear against counter face of case hardened steel. In Ni-P-X nanocoating (X= ZrO2-Al2O3-Al3Zr), X has been producedin-situand are of nanosize particles. Such coating could be done on carbon fibre of 7µ diameter uniformly. Ni-P-ferrite nanocoatings with thickness less than nearly 1mm thick, is exhibiting good absorption of microwave in the range of 12-18 GHz which can be exploited for radar applications. Micro-thickness coatings are paying ways to nanocoatings. Nanocoatings are the coatings in which either the thickness of the coating is in nanolevel or second phase that dispersed in the coat matrix is of nanosize. To further explore the field of EL nanocomposite coatings, now days, a work on EL Ni-P-ZnO, TiO2, Al2O3, ZrO2and Ni-B-ZrO2for its mechanical properties has been carried out.

Recent Studies on Coating of some Magnesium Alloys; Anodizing, Electroless Coating and Hot Press Cladding

In the present study, coating of some magnesium alloys including AZ31 and AZ91 were studied using different techniques namely anodizing, electroless and hot press cladding. AZ91 alloy was coated using anodizing process using three types of environmental friendly electrolytes; the first based on sodium silicate, the second based on sodium hydroxide-boric acid-borax and the third on sodium silicate-potassium hydroxide-sodium carbonate-sodium tetra borate. Characterization of the anodizing layer was achieved by determination of surface morphology, microstructure, phase analysis, coat thickness, adhesion and corrosion resistance. It was found that the anodic film thickness increases with increasing the current density, anodizing voltage and deposition time until the deposition stops due to the formation of a thick anodic film. The range of the anodic film thickness is 28 42 µm.Optimization of the anodizing conditions - current density and deposition time was determined for each electrolyte. A corrosion efficiency ranging from 94% to 97% was reached; the highest value corresponding to the third electrolyte. Another study is the electroless Ni plating technique with zinc pre-treatment applied on several magnesium alloys and the effect of pre-treatment and post heat treatment on the coat characteristics. The surface morphology, surface roughness, thickness of the layer, EDX analysis, adhesion, hardness and corrosion resistance are covered in this part. The electroless layer thickness is about 6 µm. The results showed good bond quality of the coat maintaining good corrosion behaviour of electroless Ni-P based on potentiodynamic polarization tests in chloride solution where it was improved after heat treatment process. On the other hand, AZ31 was covered by a commercial pure aluminum sheet by hot pressing. The influence of the applied pressure, holding time and temperature on the bond characteristics was studied. The experimental investigation has revealed a good bond quality due to the effective mutual diffusion of Mg and Al. The phase analysis resulted in the formation of two equilibrium phases namely; Mg17Al12and Mg2Al3. The corrosion resistance of AZ31 is enhanced as a results of this process by 98.6%. Further points will be covered.Keywords: Magnesium alloys; Coating; Anodizing; Electroless; Hot press cladding; environmental friendly electrolytes; corrosion

Effects of Plating Bath Composition and Operating Condition on Properties of Electroless Coating for High Strength Aluminum Alloy

The table of L9 (34) of orthogonal design was adopted in the experiment. The optimal formulation and process conditions of electroless nickel plating on high strength aluminum alloy were determined. The influences of bath composition and operating conditions on the hardness and deposition rate were analyzed and discussed. The experimental results show that the optimal plating formulation were obtained, which were consisted of nickel sulfate hexahydrate(25g/L), sodium hypophosphite(20g/L) and sodium acetate(15g/L). The operating conditions are as follows: 80~85°C, pH value 5.0. The coating structure is more homogenous and compact, and the coating has good brightness. Meanwhile, the hardness is up to 376.8HV, and the deposition rate is 17.2μm/h. The order of effects on hardness is pH value, sodium acetate, sodium hypophosphite and nickel sulfate concentration in turn. The hardness of coating decreased after heat treatment on low temperature. When the temperature exceed 200°C, the hardness increased with temperature rising and reached the peak value at 400°C(565.3HV).

The Microstructure of Ni Layer on Single-Walled Carbon Nanotubes Prepared by an Electroless Coating Process

The single-walled carbon nanotubes (SWNTs, diameter: 2~3 nm), which were obtained in the suspension of purification solution, with Ni-P coating layers were obtained by an electroless deposition process. The SWNTs before and after coating were characterized by transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). An Ni-P layer on individual nanotube with thickness of 20 nm can be obtained after the deposition process. The X-ray diffraction (XRD) and selected area electron diffraction (SAED) analysis of Ni-P SWNTs before and after heat treatment show that the heat treatment caused the transformation of the amorphous Ni-P layer to the nanocrystalline Ni-P (crystalline Ni andNi3P intermetallic compound) layer. The XRD pattern of SWNTs with Ni-P layers after heat treatment revealed that the crystal structures of Ni in plating layer contained: hexagonal close-packed (hcp) structure and face-centered cubic (fcc) structure. The lattice parameters of Ni (fcc) andNi3P are larger than the bulk's, indicting that the lattice expansion has taken place. However, the lattice parameter of Ni (hcp) has no difference from the bulk's.

The High Thickness Ni Layer on Single-Walled Carbon Nanotubes Prepared by an Electroless Coating Process

The Single-walled carbon nanotubes were coated with Ni-P layers by an electroless plating technique. A Ni-P layers are thick and smooth and on individual nanotube with thickness of 20 nm can be obtained after the deposition process. The Single-walled carbon nanotubes were obtained in the suspension of purification solution. The samples have been characterized by X-ray diffraction, selected area electron diffraction, transmission electron microscopy and energy dispersive spectrometry.The coating layers after heat-treatment convert the amorphous Ni-P coated layers into the nanocrystalline Ni-P layers.

Influence of pH value on microstructure and thermal stability of Ni–P electroless coating prepared in acidic condition

Three kinds of Ni–P electroless coatings were prepared in nickel sulphate solution at different pH values of 4.5, 5.5 and 6.5 with the purpose of ascertaining the influence of pH value on microstructure, internal stress statue and thermal stability of the coatings. Laser curvature (LC) method was used to measure the residual stress level in the coatings. Scanning electronic microscopy (SEM) and transmission electronic microscopy with energy dispersive spectrum (TEM/EDS) were used to examine the surface morphology and internal phase structure of the coatings, respectively. Differential scanning calorimeter (DSC) was used to analyze the phase transformation and thermal stability of the coatings at high temperature. Results showed the Ni–P coating prepared at pH 5.5 with nano-crystal mixed in amorphous structure had the worst thermal stability. The relatively higher stability of Ni–P coatings prepared at pH 4.5 and 6.5 was ascribed to the lower tensile stress level and much finer grain size, respectively. Besides, inverse Hall–Petch effect of annealing strengthening might also contribute to the integrity of Ni–P coating prepared at pH 6.5.

Study on Bio-Limited Forming Technology Based on the Nano-Composite Electroless Coating

The nano-composite electroless coating was introduced into bio-limited forming technology for the first time, and the feasibility of the nano-composite electroless coating on microorganism was verified. The composite coated microorganism was analyzed by using optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The results showed that stirring method would make significant effect on the content of nano-particles in the composite coating. And compared with mechanical stirring, the magnetical stirring makes the content of Fe in the composite coating increase almost twice. The co-deposition mechanism of the composite coating was also discussed.

Study on Bio-Limited Forming Technology Based on the Nano-Composite Electroless Coating

Study on Bio-Limited Forming Technology Based on the Nano-Composite Electroless Coating

Electroless Coating Process of Carbon Nano Fibers by Copper Metal

A study of the different stages of the electroless deposition of copper on carbon nano fibers activated firstly by a chemical treatment of the carbon nano fiber and secondly by a two-step method has been performed from both a chemical and a morphological point of view. The combination of XPS measurements and scanning electron microscopy imaging has allowed optimizing the 2 different stage conditions. On a first hand, the different oxide concentration and treatment time of the carbon nano fibers and on a second hand the different conditions of the sensibilisation (Sn bath), activation (Pd bath) and coating (Cu bath) have ben studied. The control of the homogeneity and thickness of copper thin films on carbon nano fiber can be obtained and further more sintered in order to obtain fully dense materials.

Wear behavior of Ni–P and Ni–P–Al 2O 3 electroless coatings

In this research, hardness and wear resistance of two types of electroless coating have been investigated including Ni–P and Ni–P–Al 2O 3 coatings. These coatings were applied on AISI 1045 steel discs by electroless deposition process and then they were heat treated at 200, 400 and 600 °C for 1 h. Wear resistance of deposits was measured by the pin on disc method and wear surfaces and debris were studied by scanning electron microscopy (SEM). Also, microstructural changes were evaluated by X-ray diffraction (XRD) analysis. The results showed that the existence of alumina particles in Ni–P coating matrix led to an increase in the hardness and wear resistance of the deposits. It was also found that heat treated coatings at about 400 °C have the maximum hardness and wear resistance.

Studies on Electroless Coatings

Since the introduction of Electroless (EL) coating in 1946 by Brenner and Riddle, the process has been the subject of steady growth. It is one of the most elegant methods available for the production of protective coatings on surface. The technique involves the autocatalytic reduction, at the substrate/solution interface, of cations released from suitable chemical reducing agents with in the EL bath. EL coating technique is simple one, as can be manifested just by controlling pH and temperature of the coating bath. Such coatings are reported to provide excellent physical and mechanical properties. The nickel, silver and copper based alloy and composite EL coatings are being studied at Indian Institute of Technology Roorkee since 1985 and this paper deals with the gist of the same. The structural behavior of Ni-P coatings for different phosphorus contents has been extensively studied. Transmission electron microscopy (TEM) and magnetic movement studies have been used as tools for structural and kinetic studies, respectively. Submicron size coating islands and their transformations have been deduced. The metallography studies using hot stage within TEM to follow the phase transformations occurring at various temperatures have been studied for Ni-B, EL coatings. As a forward step towards composite coatings, Ni-P-C, Ni-P-Al2O3, Ni-P-ZrO2 etc. have been developed by co-deposition techniques. Ag-graphite composite coatings produced by EL technique exhibits ~5 times higher wear resistance and ~ 2 times better corrosion resistance apart from being a good electrical conductor. The tribological behavior of EL Ni-P-X and Ni-P coatings on steel and aluminium substrates in different conditions i.e., as-coated, heat treated at various temperatures at different extents of time with different normal loads, have been studied in terms of dry sliding friction and wear against counter face of case hardened steel. In Ni-P-X nanocoatings (X= ZrO2-Al2O3-Al3Zr), X has been produced in-situ and are composed of nano-sized particles. Such coating could be produced uniformly on carbon fibre of 7µ diameter. Ni-P and Cu are also coated successfully on graphite/ oxide powders of ~ 120µ sizes. Micro-thickness coatings are paving ways to nanocoatings. These are the coatings in which either the thickness of the coating is in nano level or the second phase, that dispersed in the coating matrix is of nano-size. Ni-P-Ferrite nano coatings with thickness less than ~0.1mm thick, is found to exhibit about 20db of absorption of microwave in the rage of 12-18 GHz which can be exploited for radar applications. Here the nano-sized ferrite particles are co-deposited along with the Ni-P EL coatings.

Application of Electroless Coating for Processing and Joining of Advanced Materials

Application of Electroless Coating for Processing and Joining of Advanced Materials

Characterization of carbon fabric coated with Ni-P and Ni-P-ZrO2-Al2O3 by electroless technique

Ni-P and Ni-P-ZrO2-Al2O3 (Ni-P-X) composite coatings on carbon fiber woven fabric have been attempted by electroless (EL) coating technique. For producing Ni-P EL coating, a sodium hypophosphite is used as reducing agent in alkaline bath whereas for producing composite coating, in the same bath, the co-precipitation of Al2O3 along with ZrO2 by a chemical reaction has been used. The bath used was maintained at pH value of 9 ± 0.25 and a temperature of 90 ± 2°C for all the coatings under investigation. The morphology of coatings has been studied under SEM and the phases have been identified by XRD and TEM. The phases like microcrystalline nickel, amorphous nickel, Ni5P4 and Ni12P5 have been identified to be present. The grain size of these phases has been seen to be in the range of 5–10 nm. The tensile strength of as-coated and heat treated samples of both the types of coatings have been compared with that of uncoated fabric. The UTS values of uncoated carbon fabric used has been found to 3.7 N/mm2 whereas that for heat treated after coating the fabric samples with Ni-P and Ni-P-ZrO2-Al2O3 EL coatings have been observed to be 11.1 and 12.4 N/mm2 respectively.

Electroless Coating of Non-Conducting Surfaces and Particles with Metallic Titanium in Molten Salts

Electroless Coating of Non-Conducting Surfaces and Particles with Metallic Titanium in Molten Salts

Magnetic moment studies on nickel coated titanium powders

Titanium aluminide intermetallics are gaining greater importance due to their low density, high melting temperature, good high temperature properties and oxidation resistance. Their brittle behaviour at low temperatures has resulted in several investigations aimed at improving their ductility. This can be improved either by suitably alloying or by microstructure control [1–5] and in some cases by both. In general, microstructural refinements developed through processing lead to improvements in both strength and ductility [6]. Thus, processing techniques that increase the range of attainable microstructures are fundamental to the development of new engineered materials. These alloys cannot be produced by the traditional metallurgical processes, because of the restricted range of the atomic percentage of the alloying elements. Conventional powder metallurgical (P=M) techniques can be used for preparing these alloys, with an additional step involving coating on the elemental powders. There are several coating methods available like vapour phase deposition techniques, spray deposition, electroplating, and electroless coating. Each of these has its advantages and disadvantages. Vapour phase deposition methods can be used for coating towbased fibres such as carbon fibres [7]. Electroplating methods can also be used for carbon fibres, for which the substrate should be a conducting material. Coating a powder with a particular element is easier by the electroless coating method because it gives a uniform coating on the substrate. The electroless plating process is an intermediate step in the fabrication of ceramic–metal and metal– metal composites, because it gives a uniform adherent metal coating on substrates. Electroless nickel can be applied to metallic surfaces as well as non-metallic materials to provide a coating of uniform thickness with excellent chemical and physical properties [8]. The production of the titanium aluminide intermetallic alloy from mixtures of the elemental powders may not produce a chemically homogeneous product under normal P=M processes. With pre-alloyed powders, the problem of heterogeneity can be largely eliminated, but it is not cost-effective. Electroless coatings on metal powders enable the coated powder to exhibit a high level of homogeneity during P=M preparation. The aim of this work was to investigate the feasibility of obtaining a satisfactory electroless nickel coating on Ti elemental powders and to analyse this coating with the help of magnetic properties. Measurement of magnetic moment is a novel idea to confirm the presence of nickel on the titanium elemental powders. The presence of nickel coating on titanium powders was further confirmed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies. Elemental powders of commercially pure titanium (,75 im) were used for the coating of nickel. The composition of the chemical deposition bath used for the coating of nickel on titanium powder is given in Table I. The proportion of elemental powders added to the coating bath was 70 g to 1 l. A pH of 8–9 was maintained by adding ammonia solution to the bath. With slow stirring, using a magnetic stirrer, all of the particles were allowed to come into contact with the solution. A temperature of 88 8C was maintained throughout the experiment. The coating time was varied (20, 30 and 40 min.) to increase the amount of nickel coated on the elemental powders. The coated powders were rinsed in distilled water, filtered out and dried under infrared (IR) light. Chemical analysis for the presence of nickel was done using dimethyl glyoxime dissolved in methanol. A purple precipitate confirmed the presence of nickel. The presence of coating was analysed with the help of SEM. The presence of nickel as a coating on the elemental powders was confirmed by EDS analysis. Figs 1 and 2 show the SEM micrographs of the uncoated and coated titanium powders. Fig. 3 shows the EDS analysis of nickel-coated titanium powders. Figs 2 and 3 establish the presence of nickel as a coating on the substrate. The magnetic moment test was conducted on the coated particles to confirm the increase in the coating thickness with time. The coating material and the substrate are ferromagnetic and paramagnetic, respectively. From the theory of magnetism, the magnetic moment increases directly with the increase in susceptibility of the material. This concept is used here to determine the increase in coating thickness. Fig. 4 shows magnetic moment plotted against magnetic field for different coating durations. The magnetic moment slowly increases

Electroless Coating Techniques in Electronics

Electroless deposited coatings are coming into prominence chiefly due to ease of their fabrication, unique magnetic and electronic properties as well as low costs. The present paper surveys the fun...

Electroless Coating of Ni Thin Layer on Diamond Fine Particles by Means of Photo-Catalytic Pd-Nucleation

Photo-catalytic deposition of fine Pd particles on diamond particles and subsequent electroless coating with Ni were studied, Fine Pd particles could be deposited by photo-irradiation in spite of the smaller energy of incident light (<3.9eV) than Eg of diamond (5.47eV). They have higher activity for the electroless coating of Ni than those deposited by means of the usual 2-liquid type sensitizing method. The resulting Ni layer was uniform and adhered closely to diamond particles. For good distribution and adherence of the Pd deposits, surface pre-treatment was very effective. Ethanol and i-propanol were suitable as a reducing agent for dense deposition, and the reaction temperature of 35°C was best. The density of the Pd particles seems to be determined by reduction of Pd2+ ion with an intermediate alcohol radical rather than by that with the photo-excited electron.