Band 26, Heft 1

ABSTRACT The in vitro and in vivo research results show very low corrosion rate of Ti bioalloys. Among different sources of corrosion, the general and localized corrosion in vitro and fretting corrosion in vivo are the most expected degradation processes. Three possible mechanisms of dissolution of Ti biomaterials include: dissolution of titania layer, diffusion of elements through the oxide layer, electrochemical reaction in corrosive environment of the bare metal inside the damaged layer. The corrosion processes result in deterioration of human body by corrosion products followed by loosening of implant and possible serious diseases. The standard research techniques are inadequate as regards the assessment of long-term corrosion, localized corrosion of porous materials and dissolution of oxide layer. The further research is necessary to estimate the critical steps allowing for metals dissolution and optimization by physical modelisation and treatment by mathematical techniques, especially fuzzy logic and neural networks.

ABSTRACT Corrosion inhibition of mild steel (MS) in 1M hydrochloric acid (HCl) medium and 1M sulfuric acid (H 2 SO 4 ) medium by sulfadimidine (SDE) have been studied by weight loss method, electrochemical measurements, SEM and quantum chemical studies. The weight loss studies were conducted at different temperatures (30°C, 40°C, 50°C & 60°C) using various concentrations of SDE (0,25,50, 100, 150,200,250,300,400 & 500ppm) and at two time intervals (1h and2h). Inhibition efficiency was found to increase with increasing SDE concentration. It is found that SDE produces corrosion inhibition through adsorption obeying Temkin's adsorption isotherm. The ΔG ads values reveal the type of adsorption to be physisorption. The E a values for corrosion process determined using Arrhenius equation also support this. The recorded polarization data showed that the corrosion resistance was greatly enhanced in the presence of increasing SDE concentrations which was complimented by impedance measurements. SDE acts as anodic type of inhibitor. Surface examination using SEM revealed the protection efficiency of SDE which was complimented by quantum studies.

ABSTRACT An Y 2 O 3 -modified chromizing coating was produced by chromizing an as-electrodeposited Ni-Y 2 O 3 composite film using pack cementation method at 1100°C for 3hr. For comparison, chromizing was also performed in the same condition on an as-deposited Ni film without Y 2 O 3 particles. Oxidation at 900°C for 120hr showed that compared to the Y 2 O 3 -free chromizing coating, the Y 2 O 3 -modified chromizing coating exhibited a superior oxidation resistance. The effect of Y 2 O 3 on the chromization and oxidation of the chromizing coating is discussed in detail.

ABSTRACT The most important cathodic process of metal corrosion is oxygen reduction. This process, however, is a complicated multistep catalytic process. A well known catalytic oxygen activator is the acidic Fe 3+ /Fe 2+ redox system. In the case of rusting iron the Fe 2+ ion containing lepidocrocite is the catalytic activator of oxygen. There are many metal complexes capable of oxygen activation. They can help increasing metal corrosion rate.

ABSTRACT Various species of microbes present in marine environments are responsible for the corrosion of metals. The objectives of this work were to analyze both the growth of some marine microorganisms in the presence of Pb, and biocorrosion in a dynamic system. Carbon steel AISI 1020 coupons were inserted in a PVC (“loop”) system, with the goal of simulating natural conditions, and exposed to seawater, using lead concentrations of 25 to 50 ppm. For fifteen days, the planktonic and sessile populations—aerobic, anaerobic, and sulfate-reducing bacteria (SRB)—were quantified through the MPN technique. The corrosion rate was determined by the weight loss of the coupon. The coupons were also microscopically analyzed, and the percentage pit/cm 2 was determined using the GLOBAL Lab IMAGE Program. The resistance of the planktonic bacteria to the Pb was dependent upon the bacterial group. The SRB were more sensitive to the presence of lead, demonstrating mortality proportional to the metal concentration. After 15 days, a larger number of sessile bacteria was determined on the biofilm exposed to 25 ppm of Pb, and a reduction of the number of cells in 50 ppm, especially for the SRB. The corrosion rate of the coupons exposed to 25 ppm of Pb was elevated, much higher than that of those exposed to 50 ppm. The percentage pits/cm 2 was 5.64 and 2.66, respectively, for 25 and 50 ppm of lead. These results suggest that the rise in lead concentration inhibited the growth of SRB, and the corrosion was directly affected by the activity of the SRB.