Electroless nickel

Abstract: Since the inception of electroless coating by Brenner & Riddell in 1946, it has been the subject of research interest and, in the past two decades, emphasis has shifted to the studies of its properties and applications. The co-deposition of paniculate matter or substance within the growing film has led to a new generation of electroless composite coatings, many of which possess excellent wear and corrosion resistance. This valuable process can coat not only electrically conductive materials including graphite but also fabrics, insulators like plastics, rubber etc. The low coating rates with these can provide better reflectivity of plated surfaces and many more applications. Coatings can be tailored for desired properties by selecting the composition of the coating alloy/composite/metallic to suit specific requirements. The market for these coatings is expanding fast as the potential applications are on the rise. In the present article, an attempt has been made to review different electroless alloy/composite coatings with respect to bath types and their composition, properties and applications. Different characterisation studies have been conducted on various electroless nickel-based coatings with emphasis on wear and corrosion properties.

Abstract: Electroless nickel-plating on AZ91D magnesium alloy has been investigated to understand the effect of substrate microstructure and plating parameters. The initial stage of the deposition was investigated using scanning electron microscopy (SEM) and energy dispersive X-ray analysis on substrates plated for a very short interval of time. The early stage of growth was strongly influenced by the substrate microstructure. Plating was initiated on b-phase grains probably due to the galvanic coupling of b and eutectic a-phase. Once the b-phase was covered with the coating, it then spread onto eutectic a and primary a-phase. The coating produced with the optimised bath showed 7 wt.% phosphorus with a hardness of approximately 600–700 VHN. The optimum ligand to metal ion ratio was found to be 1:1.5, while the safe domain for thiourea (TU) was in the range of 0.5–1 mgyl. Fluoride was found to be an essential component of the bath to plate AZ91D alloy with an optimum value of 7.5 gyl. The presence of 0.25–0.5 mgyl mercapto-benzo-thiosole (MBT) found to accelerate the plating process. 2003 Elsevier B.V. All rights reserved.

Abstract: There is disclosed a process for electroless plating of a conductive metal layer onto the surface of a non-conductive substrate, in which the substrate surface is prepared for receiving a coating of activator using conventional methods, and the coating of activator is applied by contacting the substrate surface with a stabilized sensitizing solution comprising ions of at least one Group VIII and IB transition metal, preferably palladium chloride, stannous ions in a molar concentration in excess of that of the transition metal ions, an acid, and a buffering salt; followed by contacting the sensitized substrate surface with a noble metal activating solution to catalyze the substrate surface for subsequent electroless plating. The sensitized and activated substrate is then contacted with an aqueous dry film photoresist, which is then imaged and developed to form a predetermined electrical circuit pattern, using conventional methods. The cleaned and imaged substrate is then immersed in an acidic electroless nickel metal depositing solution, for a time, at a concentration, and at a temperature sufficient to prepare the substrate for subsequent pattern electroplating, said acidic electroless metal depositing solution comprising ions of nickel, a complexing agent, a reducing agent capable of reducing said metal ions to a metallic state in an acidic medium, provided that said reducing agent does not include formaldehyde or a formaldehyde generating composition, one or more stabilizers, and water.