Shaily M. Bhola

Microbial Corrosion in Linepipe Steel Under the Influence of a Sulfate-Reducing Consortium Isolated from an Oil Field

This work investigates microbiologically influenced corrosion of API 5L X52 linepipe steel by a sulfate-reducing bacteria (SRB) consortium. The SRB consortium used in this study was cultivated from a sour oil well in Louisiana, USA. 16S rRNA gene sequence analysis indicated that the mixed bacterial consortium contained three phylotypes: members of Proteobacteria (Desulfomicrobium sp.), Firmicutes (Clostridium sp.), and Bacteroidetes (Anaerophaga sp.). The biofilm and the pits that developed with time were characterized using field emission scanning electron microscopy (FE-SEM). In addition, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) and open circuit potential (OCP) were used to analyze the corrosion behavior. Through circuit modeling, EIS results were used to interpret the physicoelectric interactions between the electrode, biofilm and solution interfaces. The results confirmed that extensive localized corrosion activity of SRB is due to a formed biofilm in conjunction with a porous iron sulfide layer on the metal surface. X-ray diffraction (XRD) revealed semiconductive corrosion products predominantly composed of a mixture of siderite (FeCO3), iron sulfide (FexSy), and iron (III) oxide-hydroxide (FeOOH) constituents in the corrosion products for the system exposed to the SRB consortium.

Electrochemical Behavior of Titanium and Its Alloys as Dental Implants in Normal Saline

The electrochemical behavior of pure titanium and titanium alloys in a simulated body fluid (normal saline solution) has been tested, and the results have been reported. The significance of the results for dental use has been discussed. The tests also serve as a screening test for the best alloy system for more comprehensive long-term investigations.

Povidone–iodine as a corrosion inhibitor towards a low modulus beta Ti-45Nb implant alloy in a simulated body fluid

Povidone-iodine and various bactericidal agents used in dental procedures may affect the corrosion response of an implant/prosthesis in the oral environment. The effect of various concentrations of povidone–iodine (PI) on the corrosion behavior of a low modulus beta titanium alloy, Ti-45Nb, has been investigated in normal saline solution. The open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization measurements have been used to assess the electrochemical response of the alloy surface on PI addition so as to effectively predict the prosthetic treatment outcome. As the concentration of PI is increased, the corrosion rate decreases, suggested by decreased Rp values. Povidone–iodine acts as an anodic inhibitor by adsorbing on the anodic sites of the alloy. Addition of PI to a simulated body fluid such as normal saline leads to a decrease in corrosion rate of Ti-45Nb alloy.

Effect of Water on the Corrosion Behavior of Mild Carbon Steel in E10 blend

The effect of phase separation in E10 blend upon water addition on the corrosion behavior of mild carbon steel was investigated using electrochemical and morphological techniques. Increase in water addition resulted in increase in corrosion kinetics of steel exposed to water-ethanol phase. Both uniform and localized corrosion were observed on areas of the steel surface in this phase, with the extent of corrosion being the greatest near the interface of the two separating phases.

Effect of povidone-iodine addition on the corrosion behavior of cp-Ti in normal saline.

The effect of various concentrations of povidone–iodine (PI) on the corrosion behavior of a commercially pure titanium alloy (Ti-1) has been investigated in normal saline solution to simulate the povidone–iodine addition in an oral environment. The open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization measurements have been used to characterize the electrochemical phenomena occurring on the alloy surface. The open circuit potential values for Ti-1 in various concentrations of PI shift considerably towards noble direction as compared to pure normal saline. In the potentiodynamic polarization curve for Ti-1 in various solutions, the cathodic current density has increased for all concentrations of PI and the anodic current density has decreased. Only the 0.1% PI concentration is able to inhibit corrosion of Ti-1 in normal saline and the other higher concentrations studied, accelerate corrosion. The EIS data for Ti-1 in normal saline and in various concentrations of PI follows a one time constant circuit, suggesting the formation of a single passive film on Ti-1 which is not altered by the addition of PI to normal saline.

Cellular Response of Titanium and Its Alloys as Implants

The cellular response of osteocytes to commercially pure titanium (α) and its alloys (α + β and β) has been tested in a culture media, and the results have been supplemented by analyses from various techniques such as inductively coupled plasma atomic emission spectroscopic (ICP-AES) analysis, X-ray photoemission spectroscopy (XPS), scanning electron microscopy (SEM), metallography, and electrochemical measurements. These results have been correlated with respect to the presence of various alloying elements in these alloys to qualify them for human application. The newer β alloys have been examined for their potential use as implants. These results serve as a preliminary baseline to characterize the best alloy system for a comprehensive long-term investigation.

Structure and properties of solid state diffusion bonding of 17-4PH stainless steel and titanium

Abstract Solid state diffusion bonded joint between titanium and 17-4 precipitation hardening stainless steel was carried out in the temperature range of 800–1050°C in steps of 50°C for 30 min and also at 950°C for 30–180 min in steps of 30 min under a uniaxial pressure of 3·5 MPa in vacuum. Bonded samples were characterised using light microscopy, field emission scanning electron microscopy and X-ray diffraction technique. Up to 850°C for 30 min, FeTi phase was formed at the diffusion interface; however, α-Fe+λ, χ, Fe2Ti and FeTi phases and phase mixtures were formed above 850°C for 30 min and at 950°C for all bonding times. Maximum tensile strength of ∼326 MPa, shear strength of ∼254 MPa and impact toughness of ∼24 J were obtained for the diffusion couple processed at 1000°C for 30 min and 30–180 min time interval at 950°C, and maximum tensile strength ∼323 MPa, shear strength ∼243 MPa and impact toughness of ∼22 J were achieved when bonding was processed for 120 min. The residual stress of the bonded joints increases with the increase in bonding temperatures and times.

Electrochemical Study of Diffusion Bonded Joints between Micro-Duplex Stainless Steel and Ti6Al4V Alloy

In the present study, corrosion behavior of a diffusion bonded interface formed between micro-duplex stainless steel (MDSS) and a mixed titanium alloy (Ti6Al4V) formed at 900°C for 60 minutes under 4MPa uniaxial pressure in vacuum has been investigated in 1M HCl and 1 M NaOH solutions using various electrochemical measurements such as Equilibrium Potential (EP), Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PD). For comparison, corrosion behavior of base metal alloys, MDSS and Ti6Al4V have also been also characterized. Bonded interface has been characterized in light optical microscopy and scanning electron microscopy using back scattered electron. The layer wise σ phase and λ+FeTi phase mixture has been observed at the bond interface and the bond tensile strength and shear strength were ~556.4MPa and ~420.2MPa, respectively. The corrosion rates of the bonded joint are intermediate to the corrosion rates of MDSS and Ti6Al4V alloy.

STUDY OF CORROSION OF SUPER MARTENSITIC STAINLESS STEEL UNDER ALTERNATING CURRENT IN ARTIFICIAL SEAWATER WITH ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY

The assessment of corrosion requires the use of tools able to quantify the corrosion but often times also qualify it. Electrochemical Impedance Spectroscopy (EIS) is a laboratory tool that can provide both qualification and quantification of corrosion. EIS was successfully used to compare the thickness of the corrosion products formed during the application of different alternating current (AC) densities as well as to characterize pitting. When EIS is applied at the open circuit potential, the technique is nondestructive and predicts the corrosion behavior of the electrode. It can also be used at cathodic potentials while still being nondestructive, providing information about the electrode reaction kinetics, diffusion and electrical double layer.

ELECTROCHEMICAL IMPEDANCE ANALYSIS OF β‐TITANIUM ALLOYS AS IMPLANTS IN RINGERS LACTATE SOLUTION

Commercially pure titanium and two β‐titanium alloys, TNZT and TMZF, have been characterized using various electrochemical techniques for their corrosion behavior in Ringers lactate solution. The variation of corrosion potential and solution pH with time has been discussed. Electrochemical Impedance Spectroscopy has been used to fit the results into a circuit model. The stability of the oxides formed on the surface of these alloys has been correlated with impedance phase angles. Cyclic Potentiodynamic Polarization has been used to compute the corrosion parameters for the alloys. TMZF is found to be a better β‐alloy as compared to TNZT.