D. Sreekanth

X-Ray Peak Profile Analysis of Nanostructured Hydroxyapatite and Fluorapatite

389  Abstract—In present study, X-ray peak profile analysis (XPPA) by modified Williamson-Hall (W-H) models, namely W-H-isotropic strain model (W-H-ISM), W-H-anisotropic strain model (W-H-ASM) and W-H-energy density model (W-H-EDM), was employed to estimate the microstructural parameters such as, crystallite size, lattice strain, lattice deformation stress and deformation energy density from the powder diffraction data obtained for the microwave synthesized hydroxyapatite (HA) and fluorapatite (FA) nanoparticles prepared under identical processing conditions of mixing and aging. The as-prepared powder particles were also characterized by transmission electron microscopy (TEM) method. The average crystallite size values estimated for HA and FA by XPPA were correlated to their respective transmission electron microscopy (TEM) analysis results. In addition, the estimated values of HA and FA were correlated to their in-vitro dissolution characteristics studied by ethylenediamine tetra-acetic acid (EDTA) titrimetric method. It is found that the average crystallite size estimated by W-H models is in good agreement with TEM results. The controlled in-vitro dissolution behavior of FA was found to be resulted out of its higher crystallite size, lower lattice strain and lower dislocation density compared to that of HA.

Plasma Electrolytic Oxidation and Characterization of Spark Plasma Sintered Magnesium/Hydroxyapatite Composites

Magnesium (Mg)/hydroxyapatite (HA) (10 wt.% and 20 wt.%) composites were prepared by using pure Mg and as synthesized HA powders using the spark plasma sintering (SPS) method. The objective of the present study is to improve the corrosion resistance of spark plasma sintered Mg/HA composites and to ensure that the degradation time of these composites match with that of bone remodeling. Mg and HA powders were ball milled for 2 h and spark plasma sintered at a temperature of 475 °C and pressure of 40 MPa in vacuum. The sintered compacts were further treated by plasma electrolytic oxidation (PEO) in order to improve the corrosion resistance. The structural, microstructural and morphological studies were done using X-ray diffraction, optical microscopy and scanning electron microscopy, respectively. The corrosion resistance of as-sintered and PEO treated Mg/HA composites was studied by potentiodynamic polarization test in a 7.4 pH simulated body fluid (SBF) environment. The corrosion test results of as-sintered composites showed that the corrosion resistance decreases with the increase in percentage of HA in the composite. However, the PEO treated Mg/HA composites have shown delayed onset of degradation. Therefore, it can be hypothesized that the PEO treated Mg/HA composites would serve as bioactive and biodegradable orthopedic implant materials with low corrosion rates.

The Role of Electrolyte Additives on the Corrosion Behavior of Ceramic Coatings Formed on ZM21 Magnesium Alloy by Plasma Electrolytic Oxidation

The present study emphasizes the effect of addition of sodium citrate (C6H5Na3O7.2H2O) and sodium tungstate (Na2WO4.2H2O) to a silicate based electrolyte system on the corrosion behavior of PEO treated ZM21 magnesium alloy. The phase composition of the as-developed coating was evaluated by X-ray diffraction (XRD) analysis, while its surface morphology, thickness and elemental distribution were observed using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Potentiodynamic polarization tests were done in 3.5 wt% NaCl solution to analyze the corrosion behavior of the ceramic coatings in simulated marine environment. The results of XRD showed that the phase composition of all coatings comprised of Mg2SiO4 and MgO irrespective of the additive used. In addition to Mg, Si and O, the presence of W, C in EDS spectrum indicated that these elements were incorporated into the coating from the electrolyte system containing tungstate and citrate. The corrosion test results revealed that the PEO coatings obtained in tungstate containing electrolyte solution showed higher corrosion resistance than those formed in citrate containing electrolyte solution.

Role of Electric Pulse Duty and Frequency on Properties of Micro-Arc Oxidized Titania Films Developed on Ti-6Al-4V

The present work is mainly focussed on studying the effect of electric pulse frequency and duty cycle on the structural, morphological and corrosion characteristics of micro arc oxidation (MAO) films developed for a fixed oxidation time of 2.5 min on Ti-6Al-4V biomedical implant material. For this purpose, the titania films are decisively developed under four different conditions arising from two levels of pulse duty cycle (10% and 75%) and frequencies (500 Hz and 1500 Hz). A phosphate based electrolyte system is employed for developing the titania films. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results demonstrated that though all the titania films are developed for the same oxidation time of 2.5 min, the rate of anatase to rutile phase transformation, the crystallite growth, the size and distribution of surface pores and film thickness of the titania film are strongly influenced by the electric pulse frequency and duty cycle. The potentiodynamic polarization (PDP) tests conducted under simulated body fluid (SBF) conditions (37 °C and 7.4 pH) showed that all the titania films could significantly improve the corrosion resistance of Ti-6Al-4V compared to that of the untreated alloy. Of all the titania films developed for the same oxidation time of 2.5 min, the one treated with 1500 Hz frequency and 75% duty cycle exhibited better corrosion resistance than those of the other films and the untreated Ti-6Al-4V implant material.

Effect of Micro Arc Oxidation Treatment Time on In-Vitro Corrosion Characteristics of Titania Films on Cp Ti.

 Abstract—The present work is aimed at the optimisation of treatment time for the development of an oxide film on commercially pure titanium (Cp Ti) implant material by micro arc oxidation (MAO) process, to improve its corrosion resistance under 7.4 pH simulated body fluid physiological conditions. The MAO treatments were conducted for 4, 8 and 12 min in constant current mode by a DC power supply unit with an aqueous electrolyte solution comprising 15 g/l of tri-sodium ortho phosphate (Na3PO4.12H2O). The phase composition of the fabricated films was analyzed by X-ray diffraction (XRD) technique. The morphology and thickness of the films were determined by scanning electron microscopy (SEM) and the corrosion characteristics were assessed by potentiodynamic polarization technique. The XRD results demonstrated that the oxide films mainly consisted of anatase phase. While the average size of isolated surface pores was in the range of 0.5 to 5 µm, the thickness of the film varied from 24 to 55 µm. A significant improvement in the corrosion resistance was observed for the MAO treated Cp Ti implant material compared to that of the untreated. The surface pore features, the thickness of the film and the corrosion characteristics of the developed films were correlated with the MAO treatment time. Of the three different MAO treatment times employed in the present study, 8 min treatment time was established to be an optimized one for developing oxide films on Cp Ti to provide an optimal surface porosity and to minimise corrosion rate under physiological conditions.