An investigation has been conducted on the corrosion inhibition of mild steel by molybdate, nitrite and zinc ions in aqueous chloride media containing cupric ions. Molybdate inhibits mild steel corrosion in near neutral and alkaline (pH 6 and above) chloride media and accelerates corrosion in acidic media (below pH 6) both in the presence and absence of cupric ions. Nitrite inhibits mild steel corrosion in chloride media at pH 4.5 and above, but accelerates corrosion below pH 4.5 both in the presence and absence of cupric ions. Molybdate and nitrite act as a synergistic corrosion inhibitor in chloride media with or without cupric ions at pH 4.5 and above. In the acidic region between pH 3 and 4.5, the combination can decrease corrosion with a low concentration of molybdate and high concentration of nitrite. These concentrations depend on the relative amounts of molybdate and nitrite present in the system. Zinc ions inhibit mild steel corrosion only in acidic chloride media. Based on the experimental results, mechanisms of action of molybdate, nitrite and zinc ions on mild steel corrosion in aqueous chloride media with or without cupric ions have been proposed.Keywords: Molybdate; Nitrite; Mild steel; Corrosion rate; Synergistic corrosion inhibitor.© 2009 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.DOI: 10.3329/jsr.v1i1.1053
The variation of discharge capacity during charge-discharge cycling of a PbO, electrode, prepared by pressing PbO, powder onto a smooth lead disc, in sulfuric acid and acidic ammonium sulfate solutions of various concentrations was investigated by the potentiodynamic technique. The discharge capacity was found to increase with cycle number in 0.05-4.3 rnol dm-3 H2S04; this was explained in terms of the increase in porosity of the electrode with cycling. The rate of increase was highest in a 1 rnol dmM3 solution. The presence of ammonium sulfate decreased the discharge capacity at all concentrations of sulfuric acid except for the 1 rnol dm-3 solution where it caused a small increase in capacity. The morphology of the electrode was studied by scanning electron microscopy and the results are correlated with the discharge capacity.These results indicated that a solution of composition 0.5 rnol dm-3 ammonium sulfate and 1 .O rnol dm-3 sulfuric acid will produce a greater utilization of positive plate active material (PbO,) during discharge. This result, taken together with the results of earlier studies on lead in acidic sulfate electrolytes, points to the possibility of a Pb/H,SO,, (NH,),SO,/PbO, battery for electricvehicle propulsion.
Optimum PO 4 -P level in surface and ground water is essential for maintaining good health and environment. In this study, the PO 4 -P level was measured for 148 different water samples collected from ponds, supply tape and tube-well of 8 different areas of Rajshahi City Corporation. All the sites of surface water bodies crossed the United States Environmental Protection Agency (USEPA) criterion of 0.01-0.03 mg L -1 PO 4 -P to be free from eutrophication. Among the samples, 4.2% were within the range (0.025-0.1 mg L -1 ) of onset of eutrophication while 95.8% crossed the hyper-eutrophication level (> 0.10 mg L -1 ). However, most of the ground (83.1%) and tap (92.7%) water were excellent in quality for drinking with respect to PO 4 -P level (<1 mg L -1 ). Only 15.3% of ground water and 7.3% of tap water were good quality and a negligible amount (1.6%) of ground water was fair quality.
An investigation was conducted on the anodisation of commercial grade aluminium in aqueous sodium sulphate and sodium oxalate solutions. The parameters investigated were anodisation potential and electrolyte composition. Degree of anodisation was evaluated by visual observation of the anodised surface, analyses of current-concentration graphs at constant potential and current-potential characteristics, and measurement of corrosion rate of the anodised surface. Anodisation potential played an important role on the degree of anodisation. The optimum potential was 400 mV and 800 mV wrt saturated Ag/AgCl (SSE) reference electrode for sodium sulphate and sodium oxalate solutions respectively. Below and above the optimum potential poor anodisation was due to insufficient production of Al 3+ to form anodic film and surface breakdown respectively. Anodisation increased with the increase of oxalate concentration. Sulphate concentration was less effective on the degree of anodisation. Between the two electrolytes sodium oxalate was more suitable than sodium sulphate for aluminium anodisation.
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