Zinc-steel polarity reversal. I. Effect of bicarbonate concentration and temperature

The open circuit potentials of 2 types of zinc and mild steel were followed with time in different NaHCO3 solutions [10-5-10-1 M] at different temperatures [25-80 degree]. No potential reversal of polarity was observed between zinc and mild steel at room temperature. At higher temperatures, passivation of zinc and mild steel would preferentially occur, and potential reversal was manifested, particularly for pure zinc. Impurities, even in minute amounts, enhanced the activation of zinc, as well as sodium hydroxide at adequate concentration even in presence of the bicarbonate. AES survey analysis of the electrode surface gave more insight on the corrosion products

Synthesis of some 4-substituted-pyrimidinylaminophenyl-6-aryl-1,2,5,6-tetrahydro-2-thioxopyrimidine derivatives as possible antimicrobial agents

A novel series of 4-substituted-pyrimidinylaminophenyl-6- aryl -1, 2, 5, 6-tetrahydro-2-thioxopyrimdines was synthesized. Treatment of 2- amino-4- chloro-6- methyl-pyrimidine [Ia] with p-aminoacetophenone afforded the corresponding key intermediate [II]. The latter was reacted with a number of aryl aldehydes to yield the chalcone analogues [III] which undergo cyclocondensation with thiourea to furnish the target compounds [IV]. Preliminary antimicrobial screening showed that some of these novel thioxopyrimidines posses moderate activity against certain gram positive bacteria

Some electrochemical behavior of low corrosion metals III- Tantalum in aqueous solutions

The oxide film growth on Ta in 0.1 M solutions of HCl, HNO3, H2SO4, H2CrO4 and their respective sodium salts was examined at low current densities. The kinetics of film formation was stated and the local current density at open circuit was calculated in the tested media. The variation of the open circuit potential of Ta with time was traced in buffer solutions covering the range from pH 1 to 13. The results showed that the possibility of the metal to be used as an indicator electrode and was tested for acid-base and precipitation potentiometric titration. The equivalent point obtained was satisfactory and in accordance with other standard recommended electrodes

Electrochemical studies on the anodic polarization of silver

The potentio-dynamic anodic polarization of silver exhibit different peaks at different potentials depending on the selectrolyte used. In neutral sulfate solutions the major process is the Ag2O formation, while in presence of NaNO3, as an oxidizing agent, a peak which may represent the AgO formation appears at a later more anodic potential. The two peaks can be found together depending on the ambient concentration of both Na2SO4 and NaNO3. The presence of Cl- ions, either as HCl or NaCl, causes the rise of current at approximate 0.1 V which increases with increase of Cl- concentration independent of pH. This study showed that the early stages of growth occur by two- dimensional surface process on the Ag electrode forming a porous lager of AgCl giving a chance for nucleation of three-dimensional phase. The presence of NaNO3 with chloride solutions causes the appearance of the peak representing AgO formation

simple preheating treatment of aluminium to improve its resistance to pitting corrosion

The pitting corrosion resistance of the aluminum alloy has been achieved by a simple preheating treatment. Different techniques were used: potentiodynamic polarization, weight loss, thermometric and examination of the surface by scanning microscope. The proposed procedure composed of two processes, the first one was to expose the surface of metal to heated distilled water at 100C for 60-120 min. The same effect was realized by exposure of the metal to superheated steam. The second procedure was the exposure of the aluminum to a hot solution of inhibitor for 5 minutes. The role of the first step was to modify the chemical composition and thickness of the protecting film on the metal surface. The film thickness was found to increase by time of treatment. Less hydrated aluminium hydroxide exhibited the best chemical resistance [Boehmite, Gibbsite]. The role of inhibitor in the second process was played by preventing hydration of the produced surface film which initiated the pitting corrosion. The nature of the last method was found dependent on the type of inhibitor used

Effect of metal cations on the corrosion behavior of Ti, Al, Cu-Ni and Al-Brass in chloride solutions

The effect of addition of Cu2+, Co2+, Cd2+ and Fe3+ cations to chloride solutions on the potentiodynamic polarization of Al, Ti, Cu- Ni [66-34] and Al-brass was investigated. The study was confirmed by the XPS examination. It was found that Fe3+ ions cause an increase of the corrosion current, i.e. corrosion rate for Al, Ti and Cu-Ni alloy and a decrease at low concentrations [10-5 - 10-4 mol dm-3] for Al-brass. Cu2+ and Co2+ cations increase the corrosion rate of the metals, while inhibition of alloys is manifested at low cations concentration. Cd+2 cations behave as an activator but show slight inhibition at low concentration for Al-brass. The results were interpreted on the basis of exchange reactions causing deposition of the metal cations on the surface of the electrode

Stress corrosion cracking of alpha-brass in solutions containing some sulphur species

Stress corrosion cracking [SCC] tests were carried out for alpha-brass in solutions of Na2SO3 and Na2S2O3 by using the constant slow strain rate technique. It was found that brass is susceptible to undergo SCC in Na2SO3 and Na2S2O3 solutions at the open-circuit as well as at the anodic polarization conditions. The susceptibility to SCC increases with increase of the solution concentration and with anodic polarization. The mode of cracking was intergranular in Na2O3 solutions and mixed to predominantly transgranular in Na2S2O3 solutions. The susceptibility of brass to SCC is greater in thiosulfate solutions as compared with sulfite solutions

Corrosion inhibition of 304 stainless steel in H3PO4 / Cl-Solutions by the anions of Cr, Mo, N, W, and B III Synergistic effect of anions

The beneficial action of the alloying elements Cr, Mo, W, N, B and Cu on the corrosion resistance of stainless steel has been attributed to the formation of protective passive surface film containing these elements. A study on the formation of such passive film with the help of oxyanions of the alloying elements has been undertaken. Chromate, molybdate, tungstate, nitrite and nitrate anions improve the corrosion resistance of 304 stainless steel in H3PO4/Cl- solution. NO-2/Cr2O72- and MoO42- are more effective in retarding the active corrosion, while the nitrogen species [NO2-, NO3-] are the most effective for pitting attack. The effect of binary and tertiary mixtures of these oxyanions has been examined. Some mixtures afford considerable protection for both active and pitting corrosion. In their presence, the corrosion resistance of the simple 304 steel may be compared with that of more expensive highly alloyed grades