Corrosion Behavior of Spherical Chromium Carbide Reinforced NiCrBSi Hardmetal Coatings in Sulphuric Acid Solution

In the present work, four groups of spherical chromium carbide reinforced NiCrBSi hardmetal coatings were prepared on AISI 4145 steel by plasma transferred arc (PTA) technique. The corrosion behavior of the four as-received hardmetal coatings in 0.5 mol/L H2SO4 solution was investigated by polarization curve and electrochemical impedance spectroscopy (EIS). The results revealed that more Cr-rich carbides (Cr3C2, Cr7C3 and M23(C, B)6) are formed in the chromium carbide reinforced coatings, while for the NiCrBSi hardmetal coating only Cr7C3 carbide was detected by XRD. The polarization results show that the chromium carbide reinforced NiCrBSi hardmetal coatings have positive corrosion potential and lower corrosion current, providing a better protective effect to the substrate metal. The combined effects of Cr-rich carbide ceramic phases and a more stable passive film of Cr2O3 greatly improved the corrosion resistances of the chromium carbide reinforced NiCrBSi hardmetal coatings. The coating with the highest spherical chromium carbide addition has more pores because of the thermal stress due to the difference of thermal expansion coefficient between the NiCrBSi bonding phase and chromium carbide reinforced phase. The negative effects of the pores weaken the corrosion resistance, and the coating with the 30% chromium carbide content shows the best corrosion resistance. For NiCrBSi hardmetal coatings with higher reinforced chromium carbide content, the repeatability of the corrosion current obtained by polarization fitting is not as good as that of coatings with lower chromium carbide content. The repeatability of polarization results becomes worse when the specimens keep in a more stable passive state.

The effect of Fe3+ ions on the electrochemical behaviour of ocean manganese nodule reduction leaching in sulphuric acid solution

The effect of Fe3+ ions on the ocean manganese nodule reductive leaching in imitated sulphuric acid solutions was investigated.

Corrosion inhibition of ethanol extract of Moringa oleifera leaves on aluminium in 1m sulphuric acid solution

The aim of this research is to use the wet loss method to determine how well Moringa oleifera in H2SO4 inhibits aluminum corrosion. Weight loss was measured before and after corrosion on aluminum coupons with a thickness of 0.15cm, a width of 3cm, and a length of 4cm, all of which were 98 percent pure. Increases in inhibitor concentrations improve inhibition effectiveness, which ranges from 35.29 % to 47.06 % to 64.71 percent to a maximum of 82.35 %, but decreases as temperature and immersion time rise. The inhibition efficiency of the formulation consisting of 1M H2SO4 medium and 0.4g/L inhibition is 82.35 %. This means that the inhibitor is well-adsorbed on the surface of the aluminum metal, resulting in a significant reduction in corrosion rate. As a result, further research into corrosion inhibition should be done with this type of plant. The Langmuir adsorption isotherm (where Gads(kj/mol) is found to be -13.694 and Kads is 13.53) was followed in the adsorption of inhibitor molecules on Aluminum sheet surface. The absorption peaks corresponding to the functional groups – C=O, -C=N, C-OH, and C=C were found in the infrared spectrograph of the leaf extracts. These functional groups may have interacted with the aluminum sheet's surface, preventing oxidation. Organic compounds in the leaf extracts, such as alkaloids, saponins, tannins, and phenolics, were thought to be the source of these functional classes. Green extracts of M. oleifera are recommended for use as corrosion inhibitors against other inorganic compounds. It has a higher inhibitory performance, is readily available, biodegradable, less expensive, and environmentally friendly.

Heap Leaching of Greek Low-Grade Nickel Oxide Ores by Dilute Sulphuric Acid at a Pilot-Plant Scale

The present paper gives the thus far unpublished results of a pilot-scale heap leaching test of a Greek low-grade nickel oxide ore, aiming at verifying, at a large scale, the amenability of Greek laterites to heap leaching by the HELLAS (Heap Leaching LAteriteS) process, developed at the National Technical University of Athens for the first time worldwide and patented by some of the authors as early as in 1991. The test was conducted at the site of Aghios Ioannis mine of G.M.M.S.A. LARCO in 2006–2008 and was financed and supervised by the Institute of Geology and Mineral Exploration (I.G.M.E). The ore sample, 800 t, was from the “Triada” deposit of LARCO, in Euboea, and contained 0.73% nickel, 0.06% cobalt, 35.6% iron and 15% silicon. The ore was ground to −18 mm and the leaching agent was 2N (100 g/L) sulphuric acid solution. The nickel and cobalt recoveries obtained at the time of termination but not completion of the test, after four leaching cycles and 114 days of irrigation, were 60 and 36%, respectively. The corresponding nickel and cobalt concentrations in the produced leach liquor were 3.4 and 0.17 g/L, respectively. The value of the ratio Fe/Ni in the leach liquor was 10/1, much lower than the value 45/1 in the ore, thus showing the selectivity of the leaching of nickel over iron in the Greek ores by the above method. The consumption of sulphuric acid was 66 kg H2SO4/kg Ni recovered. The preliminary feasibility study, that followed the test, confirmed the economic viability of the integrated HELLAS process for the low-grade nickel oxide ores of Greece.

Deterioration of concrete sewers

The corrosion and maintenance of concrete sewers have always been an area of social as well as financial priority. The corrosion of the concrete sewer system is related to biodegradation of concrete which led to formation of sulphuric acid. The sulphuric acid so produced affects the life span of structure by causing expansion which eventually led to collapse of structure as a whole. The damage is further amplified in case of splashing of waste waters in the sewer network as compared to stagnant waters. In order to access the degree of damage an experimental program was carried out. This paper presents the results of degradation depth of concrete subjected to stagnant and flowing condition of sulphuric acid solution (H2SO4) made with different the water-cement ratio and concentration of sulphuric acid. For this purpose, concrete cubes with various water-cement ratios were made. These cubes were exposed to sulphuric acid solution of pH 1,2,3 and 4. The results revealed that surrounding conditions play one the important role in deciding the erosion depth in addition to water cement ratio. From the experiment it was also affirmed that erosion depth depends on the concentration of the acidic solution.

Henna Leaves Extract as Green Corrosion Inhibitor for 304 Stainless Steel in Sulphuric Acid Solution

The corrosion inhibition of 304 stainless steel in 1.0 M H2SO4 has been investigated in the presence of Henna leaves (Lawsonia Inermis) extract using weight loss measurement and Scanning Electron Microscope (SEM) analysis. The study indicates that the corrosion inhibition efficiency increases with the increase in concentration of Henna leaves extract and decreases with increase in temperature. SEM analysis indicated the changes in metal surface morphology in the presence of inhibitor. The result obtained indicated that Henna leaves extract act as an efficient green corrosion inhibitor for 304 Stainless Steel.