• P K De

      Articles written in Bulletin of Materials Science

    • Corrosion behaviour of amorphous Ti48Cu52, Ti50Cu50 and Ti60Ni40 alloys investigated by potentiodynamic polarization method

      A Dhawan S Roychowdhury P K De S K Sharma

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      Potentiodynamic polarization studies were carried out on virgin specimens of amorphous alloys Ti48Cu52, Ti50Cu50 and Ti60Ni40 in 0.5 M HNO3, 0.5 M H2SO4 and 0.5 M NaOH aqueous media at room temperature. The value of the corrosion current density (𝐼corr) was maximum for Ti48Cu52 alloy in all the three aqueous media as compared to the remaining two alloys. The value of 𝐼corr for the alloy Ti48Cu52 was maximum (𝐼corr = 2.6 × 10-5 A/cm2) in 0.5 M H2SO4 and minimum (𝐼corr = 3.5 × 10-6 A/cm2) in 0.5 M NaOH aqueous solutions. In contrast, the alloy Ti60Ni40 exhibited the least corrosion current density in 0.5 M HNO3 (𝐼corr = 4.0 × 10-7 A/cm2) and in 0.5 M NaOH (𝐼corr = 5.5 × 10-7 A/cm2) aqueous media as compared to those for Ti–Cu alloys, while its value in 0.5 M H2SO4 was comparable to that for Ti50Cu50. It is suggested that the alloy Ti60Ni40 is more corrosion resistant than the alloys Ti48Cu52 and Ti50Cu50 in all the three aqueous media.

    • Role of dispersion conditions on grindability of yttria stabilized zirconia (YSZ) powders

      S Ramanathan K P Krishna Kumar P K De S Banerjee

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      A precursor for zirconia – 8 mole% yttria (YSZ–ZrO2–8 m% Y2O3) powder was prepared by coprecipitation and the calcination temperature was fixed as 900°C from TG–DTA and XRD studies. The calcined powder could be dry ground only to a mean particle size (𝐷50) of 6 𝜇m containing substantial amount of coarse agglomerates in the size range 10–100 𝜇m. The dispersion conditions for its wet grinding were evaluated through zeta-potential and viscosity studies. The zeta-potential variation with pH of the aqueous suspensions of the powder exhibited maximum numerical values at 3 and 11 pH, exhibiting the ideal pHs for dispersion stability through electrostatic columbic repulsion mechanism. Slurries of dry ground powders with solid concentration in the range 15–30 vol.% exhibited pseudo-plastic flow characteristics, indicating presence of flocculates. With progress of grinding, the increase in viscosity of the slurries became less significant with decreasing solid concentration. Even though the particle size of the ground slurries decreased with decreasing solid content, there was little change in it for slurries with solid content < 20 vol.%. Grinding conditions for formation of sinter-active powders of YSZ with sub-micron size (𝐷50\ ∼ 0.7 𝜇m free of agglomerates of size > 5 𝜇m) were established. Compacts from this powder could be sintered at 1400°C to translucent bodies with 99% theoretical density.

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