Study on mechanism underlying the acceleration of pitting corrosion of B30 copper-nickel alloy by sulfate-reducing bacteria in seawater.

In this paper, the relationship between the pitting corrosion formation of B30 copper-nickel (CuNi) alloy and the metabolism of sulfate-reducing bacteria (SRB) was investigated. Combined with the influence of temperature during the actual operation of the cooling systems, the evolution law of the alloy passivation film was analyzed, and the mechanism of SRB promoting the accelerated development of B30 CuNi alloy pitting corrosion was revealed. The results show that SRB significantly promoted the pitting formation and development of B30 CuNi alloy. The maximum pitting depth was 3.9 µm in the sterile system and 15.3 µm with SRB, which was 3.9 times higher than that of sterile system. The loose porous Cu2S film formed by SRB metabolites and copper matrix was easily penetrated by corrosive anions, which promoted copper dissolution and led to pit nucleation. The sulfide adsorbed on the surface prevented or delayed the passivation of B30 CuNi alloy by blocking the adsorption site of O atom, and the corrosion nuclei continued to grow. The non-uniformity caused by the film peeling accelerated the longitudinal development of pitting corrosion, and the expansion and coalescence of adjacent pits caused the transverse development of pitting corrosion. Temperature had a certain influence on the SRB and the formation of B30 CuNi alloy passivation film. The passivation film was formed rapidly at 50 °C with poor quality and the passivation property of Cu2O film was weakened. With the increase of temperature, the pitting potential of sterile system negative shifted from 0.447 to 0.360 V (vs. SCE), while SRB system from 0.340 to 0.198 V (vs. SCE), and the pitting resistance decreased. The passivation film with defects and the Cu2S reduced the barrier efficiency of the film and accelerated the pitting corrosion of B30 CuNi alloy.

Mechanism underlying the acceleration of pitting corrosion of B30 copper-nickel alloy by Pseudomonas aeruginosa.

Despite its excellent corrosion resistance, B30 copper-nickel alloy is prone to pitting, particularly when exposed to microorganisms. The mechanism underlying the acceleration of pitting in this alloy is not fully understood. In this study, the acceleration of pitting corrosion in B30 copper-nickel alloy caused by a marine microorganism named Pseudomonas aeruginosa (P. aeruginosa) was investigated using surface analysis and electrochemical techniques. P. aeruginosa significantly accelerated the pitting in B30 copper-nickel alloy, with a maximum pitting depth of 1.9 times that of the abiotic control and a significant increase in pitting density. This can be attributed to extracellular electron transfer and copper-ammonia complex production by P. aeruginosa, accelerating the breakdown of the passivation film.

Electrochemical Evaluation of Stress Corrosion Cracking Susceptibility of Ti-6Al-3Nb-2Zr-1Mo Alloy Welded Joint in Simulated Deep-Sea Environment.

Titanium alloys have high specific strength and excellent corrosion resistance and have been applied in deep-sea engineering fields. However, stress corrosion cracking may become one of the biggest threats to the service safety of a high-strength titanium alloy, as well as its weldment. In this work, stress corrosion cracking of a gas-tungsten-arc-welded Ti-6Al-3Nb-2Zr-1Mo (Ti6321) alloy influenced by the applied potentials in simulated deep-sea and shallow-sea environments was investigated by combining slow strain rate testing with electrochemical measurements. The results showed that the service environment and applied potential have a substantial effect on the stress corrosion cracking behavior of the Ti6321 welded joint. The Ti6321 welded joint exhibited higher stress corrosion susceptibility in a simulated deep-sea environment and at a strong polarization level owing to the diminishing protection of the passive film under passivation inhibition and the enhancement of the hydrogen effect. The fracture of a Ti6321 welded joint in the weld material could be attributed to the softening effect of the thick secondary α within the coarse-grained martensite. The electrochemical evaluation model of stress corrosion cracking susceptibility of a Ti6321 welded joint in a simulated marine environment was established by adding the criterion in the passivation region based on the literature model, and four potential regions corresponding to different stress corrosion cracking mechanisms were classified and discussed. Our study provides useful guidance for the deep-sea engineering applications of Ti6321 alloys and a rapid assessment method of stress corrosion risk.

Antioxidant activities of the polysaccharides of Chuanminshen violaceum.

The water-soluble polysaccharides were extracted and purified from the root of Chuanminshen violaceum (CVPS). The antioxidant activities of the CVPS were evaluated both with in vitro and in vivo experiments. The results of the in vitro antioxidant assay suggested that the CVPS scavenged DPPH, hydroxyl, and superoxide anion radicals. The oral administration of three different doses of CVPS administered over a period of 6 weeks to D-galactose induced aging mice models, enhanced the activities of T-SOD, Mn-SOD, Cu, Zn-SOD, and CAT, and markedly decreased the content of MDA. Therefore, significant up-regulation of mRNA expression levels of Cu, Zn-SOD, Mn-SOD, CAT, glutathione peroxidase 1 (GPx), thioredoxin 1 (Trx1), and thioredoxin 2 (Trx1) occurred. Finally, the results demonstrated that the CVPS are a novel potential resource for natural antioxidants and anti-aging drugs.