Band 34, Heft 4

The corrosion behavior of nickel (Ni)-based alloys used for low-temperature aqueous or condensed systems is reviewed in detail in this paper. Commercially available pure Ni, nickel-copper (Ni-Cu), nickel-molybdenum (Ni-Mo), nickel-chromium-molybdenum (Ni-Cr-Mo), and nickel-chromium-iron (Ni-Cr-Fe) alloys as well as cast Ni-based alloys are addressed. It is shown that Ni-Cr-Mo alloys are multipurpose alloys that can be used in both reducing and oxidizing conditions. Special attention is given to a few Ni alloys, which not only extend the range of usefulness of existing alloys by overcoming their limitations but are also reliable and cost-effective and have opened new areas of applications.

To develop damage evolution models, the process of stress corrosion cracking has been distinguished into two stages of “incubation” and static fatigue. The dominative damage accumulation mechanism in the incubation stage is stress-enhanced corrosion, whereas, in the static fatigue stage, besides the corrosion-enhanced static fatigue mechanism, stress-enhanced corrosion might be nonnegligible too. Life curves with or without threshold behavior can be well explained by considering the contribution of corrosion damage accumulation in the static fatigue stage. It has been found that the incubation life is relatively small if the total life is long, but it will play an important role when total life is short, especially in cases with singular stress field. An equivalent stress has been proposed too to deal with stress corrosion under complicated stress states.

Specific chemical environments affect industrial objects. Portland cement composites (concrete and mortar) were impregnated with a special polymerized sulfur and technical soot as a filler (polymer sulfur composite). Sulfur and technical soot were applied as industrial waste. Portland cement composites were made of the same aggregate, cement, and water. The durability of the prepared cement composite samples was tested in 5% solution of HCl and 5% solution of H 2 SO 4 as a function of immersion time. The changes in mechanical strength and mass of the samples were periodically measured. Cement composites impregnated with sulfur composite exhibited limited mechanical strength and mass loss, while the physico-mechanical properties of the Portland cement concrete regressed rapidly. The loss in weight of ordinary concrete impregnated with sulfur composite, kept in aqueous solutions of acids, hydroxides, salts, and in water for a year was determined using 100×100×100 mm samples. The same samples were then used in compressive strength tests. The image analysis used for surface destruction monitoring, performed by scanning microscopy for the determination of damaged surface area and the original surface area before acid resistance testing, showed similar results. Based on the image analysis results, a model for predicting the degradation of mechanical strength during durability testing was established. The fact that the calculated and experimental strength values were not vastly different proved the validity of the proposed model. A brief summary of new products related to the special sulfur composite is given as follows: impregnation, repair, overlays, and precast polymer concrete will be presented. Sulfur composite as a polymer coating impregnation, which has received little attention in recent years, currently has some very interesting applications.

In this work, the corrosion-wear synergistic effect for nanocrystalline Fe(Al), 20 wt.% Al 2 O 3 /Fe(Al) composites with and without 4 wt.% Cr in artificial seawater (3.5% NaCl aqueous solution with 60 kg/m 3 quartz sand) was investigated. The results showed that the main damage behavior of Al 2 O 3 /Fe(Al) composites was a corrosive effect because of its poor corrosion resistance and high hardness, whereas for Fe(Al) material, the main damage mode was a chiseling action by solid particles, due to its relatively low hardness. With 4 wt.% Cr addition, the erosion weight loss at different erosion rates decreased by more than 30%. The Al 2 O 3 /Fe(Al) composites had good pure wear resistance, while poor corrosion resistance resulted in an increase in the interaction of corrosion and wear (about 70% of the total damage amount).

Methanol extract of Aloe vera leaves (AE) as a green inhibitor for controlling corrosion of low-alloy steel (mild steel) in 0.5 m HCl solution was studied using gravimetric analysis, potentiostatic polarization measurements, electrochemical impedance spectroscopy and quantum analysis. The results obtained revealed that AE has fairly good inhibiting properties against corrosion of mild steel in 0.5 m HCl solution, with efficiency >97%. Also, the inhibition was mixed type that follows the Langmuir adsorption isotherm. The value of ΔG reveals that AE inhibits the corrosion rate via physical type adsorption on the mild steel surface which is further supported by Dubinin-Radushkevich isotherm.