T.S.N. Sankara Narayanan

Electroless Ni–P composite coatings

This review outlines the development of electroless Ni–P composite coatings. It highlights the method of formation, mechanism of particle incorporation, factors influencing particle incorporation, effect of particle incorporation on the structure, hardness, friction, wear and abrasion resistance, corrosion resistance, high temperature oxidation resistance of electroless Ni–P composite coatings as well as their applications. The improvement in surface properties offered by such composite coatings will have a significant impact on numerous industrial applications and in the future they will secure a more prominent place in the surface engineering of metals and alloys.

Thermal properties of siliconized epoxy interpenetrating coatings

This work involves the development of a novel siliconized epoxy interpenetrating coating system using epoxy resin as base, hydroxyl-terminated polydimethylsiloxane (HTPDMS) as modifier, γ-aminopropyltriethoxysilane (γ-APS) as crosslinking agent and dibutyltindilaurate (DBTDL) as catalyst. Polyamidoamine and aromatic polyamine adduct were used as curing agents for the above coating systems. The thermal behaviour, glass transition temperature (Tg) and morphological characteristics of unmodified epoxy and siliconized epoxy coating systems cured by polyamidoamine (B) and aromatic polyamine adduct (D) were studied using thermogravimetric analysis, differential scanning calorimetry and scanning electron microscopy, respectively, and the results are discussed. From the study, it is observed that the thermal stability of epoxy coating systems is enhanced when siloxane is incorporated to them. There is a slight decrease in the glass transition temperature observed for silicone-modified epoxy coatings and SEM analyses reveal that siliconized epoxy coating systems show heterogeneous morphology.

Electroless Ni–Co–P ternary alloy deposits: preparation and characteristics

The formation of electroless Ni–Co–B ternary alloy deposits was studied using varying bath parameters and operating conditions. Variation in metallic ratio of the bath enables the formation of electroless Ni–Co–B deposits with varying contents of nickel, cobalt and boron. The Ni–Co–B deposits were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM) to assess the phase constituents, phase transition behaviour, thermal behaviour Curie transition and magnetic properties, respectively. The study reveals that electroless Ni–Co–B alloy deposits are amorphous in the as-deposited condition. DSC traces indicate two exothermic peaks, corresponding to the separation of nickel phase from the amorphous matrix and formation of Co3B phase. TGA studies exhibit Curie transition peaks corresponding to nickel and Co3B. VSM studies show that the saturation magnetic moment increases with increase in the cobalt content of the film and with increase in annealing temperature.

Polarization and impedance studies on zinc phosphate coating developed using galvanic coupling

Galvanic coupling technique is capable of producing coatings of desired thickness. Good quality coatings can be produced at low temperature. Galvanic coupling of mild steel (MS) with the other cathode materials such as titanium (Ti), copper (Cu), brass (BR), nickel (Ni), and stainless steel (SS) accelerates iron dissolution, enables quicker consumption of free phosphoric acid and facilitates an earlier attainment of point of incipient precipitation, resulting in a higher amount of coating formation. In the present investigation, potentiodynamic polarization and electrochemical impedance spectra on MS substrates phosphated using galvanic coupling are studied. This study reveals that MS substrates phosphated under galvanically coupled condition possess better corrosion resistance than the substrates phosphated under uncoupled condition.

Tailoring the composition of fluoride conversion coatings to achieve better corrosion protection of magnesium for biomedical applications

The methodology of deposition of fluoride conversion coatings is modified with the use of galvanic coupling, agitation of the electrolyte solution, and addition of K2CO3, which helps to provide a better understanding of the mechanism and new avenues to tailor the composition of the coating. A very good correlation exists between the F/O ratio of the coatings prepared under varying experimental conditions and their icorr, |Z| and phase angle maximum; the higher the F/O ratio, the better the corrosion protective ability of the coatings in Hanks balanced salt solution. The corrosion behaviour of the coatings of the present study suggests that fluoride conversion coatings show much promise for their use for biomedical applications, as long as their uniformity is improved and the composition is tailored to enrich the MgF2 phase, encompassing a higher F/O ratio.

Acceleration of the phosphating process—the utility of galvanic coupling

The principle of galvanic corrosion is utilized to accelerate the rate of iron dissolution and rate of phosphating coating formation.

Electroless Ni-B-Si3N4 Composite Coating: Deposition and Evaluation of Its Characteristic Properties

Deposition of electroless (EL) Ni-B-Si3N4 composite coating and its characteristic properties are addressed.Hydrogen evolution limits the level of incorporation of Si3N4 particles in the EL Ni-B matrix to 2 wt%. Incorporation Si3N4 particles increased the surface roughness of the matrix but did not influence its structure. The microhardness of EL Ni-B-Si3N4 composite coating in its as-plated condition is 632 ± 17 HV0.1. Heat treatment at 350 and 450°C for 1 h increased its hardness. Adhesive wear is the predominant wear mechanism of EL Ni-B-Si3N4 composite coating. Its corrosion protective ability did not differ much with its plain counterpart.

A simple strategy to modify the porous structure of plasma electrolytic oxidation coatings on magnesium

A simple strategy to modify the porous structure of the oxide coating formed on Mg by plasma electrolytic oxidation (PEO) is addressed. Post-treatment of PEO coated Mg using 3 M NaOH at 60 °C for 1 h modifies its porous structure, helps to seal the smaller pores and decrease the size of the medium and bigger sized pores, increases the surface roughness but provides a better homogeneity of the surface, changes its chemical nature, improves its corrosion resistance in Hanks balanced salt solution, facilitates apatite growth in simulated body fluids and promotes cell viability and growth in cell culture media.

Studies on acceleration of the low temperature zinc phosphating processes

SUMMARY The present work aims to discuss the effective means of accelerating the low temperature zinc phosphating processes by employing two methodologies and to evaluate the possible implications of adopting such methodologies in decreasing the processing time. The first one utilizes the galvanic corrosion principle whereas the second one involves the addition of a powerful oxidizing agent, namely, iodine pentoxide to the bath. It is suggested that both methods would impart a higher rate of metal dissolution, which would be helpful in accelerating the rate of deposition. Phosphate coatings were produced on mild steel substrates using a zinc phosphating bath capable of operating at low temperature (27°C). under both uncoupled and galvanically coupled conditions (with stainless steel or copper substrate) and with and without the addition of iodine pentoxide. The study revealed an enhanced dissolution of mild steel when it is galvanically coupled to more noble metals and also when the bath is modified with iodine pentoxide. It is concluded that the processing time of the low temperature zinc phosphating processes can be considerably decreased by adopting either the galvanic coupling methodology or the addition of iodine pentoxide.

Surface modification of magnesium and its alloys for biomedical applications: Opportunities and challenges

Description based on online resource; title from PDF title page (ebrary, viewed January 22, 2015). ; Electronic reproduction. Palo Alto, Calif. : ebrary, 2015. Available via World Wide Web. Access may be limited to ebrary affiliated libraries. ; Electroni