Papers by Author: E. Mohandas

Abstract: Hydroxyapatite (HAP) Ca₁₀(PO)₆(OH)₂ is widely used as a bioactive ceramics since it forms a chemical bonding to bone. The dominant requirement for the development of HAP coatings on metallic implants is the preparation of stoichiometric material with required chemical and phase composition (Ca/P molar ratio 1.67). In this work the preparation of HAP films by sol-gel method on alumina and its characterization are described. The coating was done using dip-coating method, starting from a colloidal suspension of hydroxyapatite. Compound formation of HAP is confirmed using GIXRD. By Energy Dispersive X-Ray spectroscopy (EDX) analysis Ca/P ratio of the HAP was found to be 1.657 which is very close to the stoichiometric value of 1.67. The FTIR spectra of the coatings were used to determine the presence of chemical species of the coatings. Surface Characterization has been carried out using SEM & AFM techniques. Wettability study has been carried out using OCA and it was found that hydrophobicity decreases with the increase in HAP thickness. Corrosion studies have been carried out using electrochemical analyzer (ECA) in Ringer solution and best corrosion resistance was observed for the thickest sample. The paper discusses the variations in surface morphology using SEM, AFM & EDX and its effect on biocompatibility.

Abstract: TaN-Cu nanocomposite thin films used as materials for thin-film resistors (TFR) were prepared by magnetron pulsed dc reactive sputtering. Structural and morphological properties of films deposited on (100) Si as a function of nitrogen flow rate and substrate temperature is investigated. With the introduction of N2 gas flow indicated with different phases of nanocrystalline h-Ta, Ta2N, TaN, Ta4N5 and Cu. XRD analysis of the films deposited with increasing substrate temperature at constant flow rate of nitrogen 10 sccm indicated that the nanocrystalline with bi-phasic (fcc-TaN and fcc-Cu). The microstructure of the films was investigated by scanning electron microscopy and high-resolution transmission electron microscopy.

Abstract: The effect of thermal ageing on the heat capacity and transformation behaviour of behaviour of 9Cr-1Mo-0.1C (wt.%) ferritic / martensitic steel has been studied using differential scanning calorimetry (DSC) in the temperature range 473 to 1273 K. It is found that a-ferrite + carbide ® g-austenite phase transformation temperature is only mildly sensitive to microstructural details; but the enthalpy change associated with this phase transformation and especially, the change in specific heat around the transformation regime are found to be dependent on the starting microstructure generated by thermal ageing treatment. Prolonged ageing for about 500 to 5000 hours in the temperature range 823 to 923 K contributed to a decrease in heat capacity, as compared to the normalised and tempered sample. The martensite microstructure is found to possess the lowest room temperature CP among different microstructures.