Browsing by Author "S.M.A. Hosseini"

Now showing 1 - 4 of 4

Active-passive behaviour of titanium and titanium alloy (VT-9) in sulphuric acid solution
(1993) S.M.A. Hosseini; V.B. Singh
Corrosion behaviour of titanium and VT-9 has been studied in sulphuric acid solution in the whole range of concentration at 30 °C. Effect of temperature on the corrosion behaviour has also been investigated. Titanium and its alloy (VT-9) showed active-passive behaviour. A large range of potential for passivity was observed in all the concentrations at different temperatures. Critical current density for passivation (icr) increased with increasing temperature while it increased with concentration up to 11 M; thereafter it decreased. In general, Ti and VT-9 exhibited similar corrosion behaviour, however passivation current density (ip) and critical current density (icr) differed to some extent. The passivation current density is higher in case of VT-9 than Ti while icr is lower under similar conditions. The stability of the film formed on the surface of the titanium and VT-9, examined under different experimental conditions, reveals the formation of protective uniform passive film on the metal and alloy. © 1993.
An investigation on dissolution and passivation behaviour of Ti-6Al-4V in sulphuric acid
(1998) V.B. Singh; S.M.A. Hosseini
Potentiostatic technique has been employed to investigate the polarization behaviour of a titanium alloy (Ti-6Al-4V) in a wide concentration range (1-17 M) of sulphuric acid, at 30°C and 40°C. Effect of temperature variation of the experimental solution has been studied in selected concentrations (5M and 9M) of the acid. The cathodic current density increased in accordance with increasing acid concentration, temperature and applied potential. Anodic polarization studies showed active-passive transition and broad passivity range of potential available for the stability of alloy. The critical current density and passivity current density (ic and ip) increased with an increase in the concentration and temperature of the solution. However, these values decreased in solution above 11M sulphuric acid. The passivated specimen revealed formation of uniform and stable anodic film during longer exposure time. Apparent activation energy, obtained from Arrhenius plots, corresponding to critical current densities is of order for the chemical reaction. Impedance measurements indicate that the passive film has the characteristics of valve metal in respect of capacitance and formation potential, and consists of two types of grains on the surface.
Corrosion behaviour of Ti-6Al-4V in phosphoric acid
(Kluwer Academic Publishers, 1994) V.B. Singh; S.M.A. Hosseini
Ti-6A1-4V shows distinct active-passive behaviour in phosphoric acid over a wide concentration range. The cathodic polarization curves are similar over a wide range of acid concentration and temperatures. The alloy undergoes active dissolution and turns passive in the negative potential region followed by a wide range of passivity at all acid concentrations at different temperatures. Increasing acid concentration up to 11 M results in an increase in critical current density (icr). The passive current density (ip) increases up to an acid concentration of 9 M while at 13 M icr and ip decrease appreciably. A significant increase in both icr and ip occurs with increase in solution temperature. The passive specimen remained stable for a long time when exposed to phosphoric acid under open circuit conditions. © 1994 Chapman & Hall.
The electrochemical and corrosion behaviour of titanium and its alloy (VT-9) in phosphoric acid
(1993) V.B. Singh; S.M.A. Hosseini
Using potentiostatic techniques, cathodic and anodic polarization behaviour of titanium and its alloy (VT-9) have been investigated in different concentrations of H3PO4 solution at 30°C. Selected compositions of the acid were taken to study the effect of temperature on the metal and its alloy. They showed active/passive behaviour and a large passivity range of potential in different acid concentrations at different temperatures. The critical current density for passivity of the specimens was found to increase with increasing acid concentration and temperature, but it decreased in 13 M phosphoric acid. The polarization curves for Ti and VT-9 are alike in nature and the difference lies in the critical current density and passive current density which are higher for the alloy. SEM micrographs show the formation of a uniform passive surface on the metal and alloy which remained stable under exposed condition for a long duration. © 1993.