S.K. Seshadri

Bio: S.K. Seshadri is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Corrosion & Coating. The author has an hindex of 22, co-authored 53 publications receiving 1999 citations.

Calcium phosphate-based coatings on titanium and its alloys

Abstract: Use of titanium as biomaterial is possible because of its very favorable biocompatibility with living tissue. Titanium implants having calcium phosphate coatings on their surface show good fixation to the bone. This review covers briefly the requirements of typical biomaterials and narrowly focuses on the works on titanium. Calcium phosphate ceramics for use in implants are introduced and various methods of producing calcium phosphate coating on titanium substrates are elaborated. Advantages and disadvantages of each type of coating from the view point of process simplicity, cost-effectiveness, stability of the coatings, coating integration with the bone, cell behavior, and so forth are highlighted. Taking into account all these factors, the efficient method(s) of producing these coatings are indicated finally.

Thermal oxidation of Ti6Al4V alloy: Microstructural and electrochemical characterization

Abstract: Thermal oxidation (TO) of Ti6Al4V alloy was performed at 500, 650 and 800 °C for 8, 16, 24 and 48 h in air. The morphological features, structural characteristics, microhardness and corrosion resistance in Ringer's solution of TO Ti6Al4V alloy were evaluated and compared with those of the untreated one. The surface morphological features reveal that the oxide film formed on Ti6Al4V alloy is adherent to the substrate at 500 and 650 °C irrespective of the oxidation time whereas it spalls off when the alloy is oxidized at 800 °C for more than 8 h. X-ray diffraction (XRD) measurement reveals the presence of Ti(O) and α-Ti phases on alloy oxidized at 500 and 650 °C, with Ti(O) as the dominant phase at 650 °C whereas the alloy oxidized at 800 °C exhibits only the rutile phase. Almost a threefold increase in hardness is observed for the alloy oxidized at 650 °C for 48 h when compared to that of the untreated one. Thermally oxidized Ti6Al4V alloy offers excellent corrosion resistance in Ringer's solution when compared to that of the untreated alloy.

Friction and wear behavior of electroless Ni–P and Ni–W–P alloy coatings

Abstract: Electroless nickel (EN) plating has received attention as a hard coating for industrial applications due to its high hardness, uniform thickness as well as excellent corrosion and wear resistance. The electroless Ni–P deposit is a supersaturated alloy in as-deposited state, and can be strengthened by precipitation of nickel phosphide crystallites with suitable heat treatments. However, the hardness of Ni–P films degrades with excessive annealing due to grain coarsening. An alternative to Ni–P coatings is the ternary alloy coating with the addition of a third element to the binary Ni–P system. The ternary Ni–M–P alloy, where M is typically a transition metal such as W, Co, Mn, Re and Mo has superior properties compared to the binary Ni–P alloy, and therefore, could extend its range of applications. The present paper discusses the synthesis and tribological behavior of Ni–P and Ni–W–P deposits. Deposition is done from an acidic electroless bath. Deposits with varying tungsten content were synthesized. Chemical analysis shows that tungsten incorporation reduces the phosphorus content in the deposit. Phosphorus content varied from 5 to 12 wt.% depending upon the tungsten incorporation in the deposit which in turn varied between 2 and 14 wt.%. Coatings with high tungsten content exhibit very good wear resistance compared to binary Ni–P as well as low tungsten ternary alloy deposits.

A novel route for synthesis of nanocrystalline hydroxyapatite from eggshell waste

Abstract: The eggshell waste has been value engineered to a nanocrystalline hydroxyapatite (HA) by microwave processing. To highlight the advantages of eggshell as calcium precursor in the synthesis of HA (OHA), synthetic calcium hydroxide was also used to form HA (SHA) following similar procedure and were compared with a commercially available pure HA (CHA). All the HAs were characterized by X-ray powder diffraction (XRD) method, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and specific surface area measurements. Nanocrystalline nature of OHA is revealed through characteristic broad peaks in XRD patterns, platelets of length 33-50 nm and width 8-14 nm in TEM micrograph and size calculations from specific surface area measurements. FT-IR spectra showed characteristic bands of HA and additionally peaks of carbonate ions. The cell parameter calculations suggest the formation of carbonated HA of B-type. The OHA exhibits superior sinterability in terms of hardness and density than both SHA and CHA may be due to larger surface area of its spherulite structure. The in vitro dissolution study shows longer stability in phosphate buffer and cell culture test using osteoblast cells establishes biocompatibility of OHA.

Structure and phase transformation behaviour of electroless Ni-P composite coatings

Abstract: This paper addresses the structural characteristics and phase transformation behaviour of plain electroless Nix2013;P coating and electroless Nix2013;Px2013;Si3N4, Nix2013;Px2013;CeO2 and Nix2013;Px2013;TiO2 composite coatings. The X-ray diffraction patterns of electroless Nix2013;Px2013;Si3N4, Nix2013;Px2013;CeO2 and Nix2013;Px2013;TiO2 composite coatings are very similar to that of plain electroless Nix2013;P coating, both in as plated and heattreated conditions. Selected area electron diffraction (SAED) patterns obtained on the Nix2013;P matrix of Nix2013;Px2013;Si3N4, Nix2013;Px2013;CeO2 and13; Nix2013;Px2013;TiO2 composite coatings exhibit diffuse ring patterns resembling the one obtained for plain electroless Nix2013;P coating. Phase transformation behaviour studied by differential scanning calorimetry (DSC) indicates that the variation in crystallization temperature and the energy evolved during crystallization of plain electroless Nix2013;P coating and electroless Nix2013;Px2013;Si3N4, Nix2013;Px2013;CeO2 and Nix2013;Px2013;TiO2 composite coatings is not significant. The study concludes that incorporation of Si 3N4, CeO2 and TiO2 particles in the Nix2013;P matrix does not have any influence on the structure and phase transformation behaviour of electroless Nix2013;P coatings.

Palladium-Based Electrocatalysts for Alcohol Oxidation in Half Cells and in Direct Alcohol Fuel Cells

Abstract: Direct alcohol fuel cells (DAFCs) are attracting increasing interest as power sources for portable applications due to some unquestionable advantages over analogous devices fed with hydrogen.1 Alcohols, such as methanol, ethanol, ethylene glycol, and glycerol, exhibit high volumetric energy density, and their storage and transport are much easier as compared to hydrogen. On the other hand, the oxidation kinetics of any alcohol are much slower and still H2-fueled polymer electrolyte fuel cells (PEMFCs) exhibit superior electrical performance as compared to DAFCs with comparable electroactive surface areas.2,3 Increasing research efforts are therefore being carried out to design and develop more efficient anode electrocatalysts for DAFCs.

Synthesis methods for nanosized hydroxyapatite with diverse structures.

Abstract: Hydroxyapatite (HAp) is the major mineral constituent of vertebrate bones and teeth. It has been well documented that HAp nanoparticles can significantly increase the biocompatibility and bioactivity of man-made biomaterials. Over the past decade, HAp nanoparticles have therefore increasingly been in demand, and extensive efforts have been devoted to develop many synthetic routes, involving both scientifically and economically new features. Several investigations have also been made to determine how critical properties of HAp can be effectively controlled by varying the processing parameters. With such a wide variety of methods for the preparation of HAp nanoparticles, choosing a specific procedure to synthesize a well-defined powder can be laborious; accordingly, in the present review, we have summarized all the available information on the preparation methodologies of HAp, and highlighted the inherent advantages and disadvantages involved in each method. This article is focused on nanosized HAp, although recent articles on microsized particles, especially those assembled from nanoparticles and/or nanocrystals, have also been reviewed for comparison. We have also provided several scientific figures and discussed a number of critical issues and challenges which require further research and development.

Bioceramics of calcium orthophosphates

Abstract: A strong interest in use of ceramics for biomedical applications appeared in the late 1960's. Used initially as alternatives to metals in order to increase a biocompatibility of implants, bioceramics have become a diverse class of biomaterials, presently including three basic types: relatively bioinert ceramics, bioactive (or surface reactive) and bioresorbable ones. Furthermore, any type of bioceramics could be porous to provide tissue ingrowth. This review is devoted to bioceramics prepared from calcium orthophosphates, which belong to the categories of bioresorbable and bioactive compounds. During the past 30-40 years, there have been a number of major advances in this field. Namely, after the initial work on development of bioceramics that was tolerated in the physiological environment, emphasis was shifted towards the use of bioceramics that interacted with bones by forming a direct chemical bond. By the structural and compositional control, it became possible to choose whether the bioceramics of calcium orthophosphates was biologically stable once incorporated within the skeletal structure or whether it was resorbed over time. At the turn of the millennium, a new concept of calcium orthophosphate bioceramics, which is able to regenerate bone tissues, has been developed. Current biomedical applications of calcium orthophosphate bioceramics include replacements for hips, knees, teeth, tendons and ligaments, as well as repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jawbone, spinal fusion and bone fillers after tumor surgery. Potential future applications of calcium orthophosphate bioceramics will include drug-delivery systems, as well as they will become effective carriers of growth factors, bioactive peptides and/or various types of cells for tissue engineering purposes.

Current Perspectives Calcium Phosphate Nanocoatings and Nanocomposite Coatings in Dentistry

Abstract: The purpose of coatings on implants is to achieve some or all of the improvements in biocompatibility, bioactivity, and increased protection from the release of harmful or unnecessary metal ions. During the last decade, there has been substantially increased interest in nanomaterials in biomedical science and dentistry. Nanocomposites can be described as a combination of two or more nanomaterials. By this approach, it is possible to manipulate mechanical properties, such as strength and modulus of the composites, to become closer to those of natural bone. This is feasible with the help of secondary substitution phases. Currently, the most common composite materials used for clinical applications are those selected from a handful of available and well-characterized biocompatible ceramics and natural and synthetic polymers. This approach is currently being explored in the development of a new generation of nanocomposite coatings with a wider range of oral and dental applications to promote osseointegration. The aim of this review is to give a brief introduction into the new advances in calcium phosphate nanocoatings and their composites, with a range of materials such as bioglass, carbon nanotubes, silica, ceramic oxide, and other nanoparticles being investigated or used in dentistry.

Alkaline direct alcohol fuel cells

Abstract: The faster kinetics of the alcohol oxidation and oxygen reduction reactions in alkaline direct alcohol fuel cells (ADAFCs), opening up the possibility of using less expensive metal catalysts, as silver, nickel and palladium, makes the alkaline direct alcohol fuel cell a potentially low cost technology compared to acid direct alcohol fuel cell technology, which employs platinum catalysts. A boost in the research regarding alkaline fuel cells, fuelled with hydrogen or alcohols, was due to the development of alkaline anion-exchange membranes, which allows the overcoming of the problem of the progressive carbonation of the alkaline electrolyte. This paper presents an overview of catalysts and membranes for ADAFCs, and of testing of ADAFCs, fuelled with methanol, ethanol and ethylene glycol, formed by these materials.