Future Needs for Tribo-Corrosion Research and Testing

Tribo-corrosion is an emerging interdisciplinary subject that spans from basic research on the behavior of surfaces in mechanical contact in chemically active surroundings to the test methods needed to quantify its effects, and from the selection of materials for bio-implants to the minimization of surface degradation and wastage in advanced energy conversion systems. Such a diverse field brings with it many challenges in understanding, testing, standardization, and application to engineering practice. This paper summarizes a panel discussion and participant survey held at the Third International Symposium on Tribo-Corrosion in Atlanta, Georgia, USA, in April 2012. It reflects a sense of agreement on many of the key scientific challenges in the field and the fact that tribo-corrosion is still in its infancy in terms of broad industry recognition, education, and the ability of those who conduct tribo-corrosion research to connect their laboratory results and theories to applications. Some sub-fields, notably the bio-tribo-corrosion of medical implants, have witnessed active international research efforts, but the engineering community in many other important areas of technology may not yet be aware of the field despite numerous tribo-corrosion problems that may exist within their purview

Some thoughts on modelling abrasion-corrosion : wear by hard particles in corrosive environments

Wear by hard particles can involve abrasion or erosion and is one of the most severe forms of wear. When a corrosive environment is present, the material loss rate can be significantly increased due to interactions (synergy) between the mechanical and chemical/electrochemical actions. In developing strategies for mitigating such adverse synergistic effect, it is important to understand the complex effect of various parameters on material loss under given tribocorrosion conditions. In this paper, a model is presented for wear-corrosion synergy in abrasive wear by hard particles applicable to many conditions in both the marine renewable (abrasion by high concentrations of large sand particles on tidal turbines) and extractive metallurgy (abrasive wear in mineral extraction). The mechanical wear loss is modeled based on the grooving mechanism (micro-cutting/micro-ploughing). Wear-enhanced corrosion is calculated from the fresh surface areas generated by grooving and the corresponding transient corrosion current. The concept of “corrosion-degraded layer” on the worn surface is introduced to account for the corrosion-enhanced wear; within this corrosion-degraded layer, the material loss rate is higher under the same mechanical wear conditions than in the material that is unaffected by corrosion. Based on the model, the effect of wear conditions on synergy in hard particle wear-corrosion has been discussed. The relative thickness of the corrosion-degraded layer to the depth of hard particle penetration (grooving) in the mechanical wear is found to be an important parameter in determining the relative severity of synergy in different tribocorrosion systems. Good qualitative agreement has been observed between the predictions and published experimental results obtained from a range of abrasion-corrosion and erosion-corrosion lab testing

The effect of dissolved oxygen in slurry on erosion-corrosion of En30B steel

Synergistic effect between corrosion and wear has been widely recognized in many tribo-corrosion systems. In most wet application conditions, dissolved oxygen (DO) is a controlling factor to the dynamics of corrosion process and is therefore expected to have significant impact on the tribo-corrosion performance of materials. In this study, the effect of DO (0 - 24 ppm) on erosion-corrosion behaviour of En30B low alloy steel has been investigated using a slurry pot erosion-corrosion test apparatus in a slurry containing 35wt% silica sand and 3.5% NaCl solution at 30°C and 45°C. The synergistic effect and its contributing components, i.e., erosion-enhanced corrosion and corrosion-enhanced erosion, have been measured/analysed. The total erosion-corrosion loss and synergy of the En30B steel increases with DO in the slurry, initially rapidly at DO levels below ~5 ppm and then less rapidly at the higher DO levels. The synergistic effect is mainly due to corrosion-enhanced erosion with negligible contributions from erosion-enhanced corrosion. Temperature has a significant effect on the total erosion-corrosion loss. Total erosion-corrosion was 34% higher at 45°C (in still air) than at 30°C. Mechanisms for the observed phenomena have been discussed based on the concept of corrosion-accelerated micro-crack propagation

LBH589 Inhibits proliferation and metastasis of hepatocellular carcinoma via inhibition of gankyrin/stat3/akt pathway

Background: Gankyrin has shown to be overexpressed in human liver cancers and plays a complex role in hepatocarcinogenesis. Panobinostat (LBH589), a new hydroxamic acid-derived histone deacetylase inhibitor has shown promising anticancer effects recently. Here, we investigated the potential of LBH589 as a form of treatment for hepatocellular carcinoma (HCC). Methods: Gankyrin plasmid was transfected into HCC cells, and the cells were selected for more than 4 weeks by incubation with G418 for overexpression clones. The therapeutic effects of LBH589 were evaluated in vitro and in vivo. Cell proliferation, apoptosis, cell cycle, invasive potential, and epithelial-mesenchy-mal transition (EMT) were examined. Results: LBH589 significantly inhibited HCC growth and metastasis in vitro and in vivo. Western blotting analysis indicated that LBH589 could decrease the expression of gankyrin and subsequently reduced serine-phosphorylated Akt and tyrosine-phosphorylated STAT3 expression although the total Akt and STAT3 were unaffected. LBH589 inhibited metastasis in vitro via down-regulation of N-cadherin, vimentin, TWIST1, VEGF and up-regulation of E-cadherin. LBH589 also induced apoptosis and G1 phase arrest in HCC cell lines. Ectopic expression of gankyrin attenuated the effects of LBH589, which indicates that gankyrin might play an important role in LBH589 mediated anticancer effects. Lastly, in vivo study indicated that LBH589 inhibited tumor growth and metastasis, without discernable adverse effects comparing to control group, with abrogating gankyrin/STAT3/Akt pathway. Conclusions: Our results suggested that LBH589 could inhibit HCC growth and metastasis through down-regulating gankyrin/STAT3/Akt pathway. LBH589 may present itself as a novel therapeutic strategy for HCC

Electrical and magnetic properties of antiferromagnetic semiconductor MnSi2N4 monolayer

Two-dimensional antiferromagnetic semiconductors have triggered significant attention due to their unique physical properties and broad application. Based on first-principles calculations, a novel two-dimensional (2D) antiferromagnetic material MnSi2N4 monolayer is predicted. The calculation results show that the two-dimensional MnSi2N4 prefers an antiferromagnetic state with a small band gap of 0.26 eV. MnSi2N4 has strong antiferromagnetic coupling which can be effectively tuned under strain. Interestingly, the MnSi2N4 monolayer exhibits a half-metallic ferromagnetic properties under an external magnetic field, in which the spin-up electronic state displays a metallic property, while the spin-down electronic state exhibits a semiconducting characteristic. Therefore, 100% spin polarization can be achieved. Two-dimensional MnSi2N4 monolayer has potential application in the field of high-density information storage and spintronic devices

Nutlin-3 overcomes arsenic trioxide resistance and tumor metastasis mediated by mutant p53 in Hepatocellular Carcinoma

Background: Arsenic trioxide has been demonstrated as an effective anti-cancer drug against leukemia and solid tumors both in vitro and in vivo. However, recent phase II trials demonstrated that single agent arsenic trioxide was poorly effective against hepatocellular carcinoma (HCC), which might be due to drug resistance. Methods: Mutation detection of p53 gene in arsenic trioxide resistant HCC cell lines was performed. The therapeutic effects of arsenic trioxide and Nutlin-3 on HCC were evaluated both in vitro and in vivo. A series of experiments including MTT, apoptosis assays, co-Immunoprecipitation, siRNA transfection, lentiviral infection, cell migration, invasion, and epithelial-mesenchy-mal transition (EMT) assays were performed to investigate the underlying mechanisms. Results: The acquisition of p53 mutation contributed to arsenic trioxide resistance and enhanced metastatic potential of HCC cells. Mutant p53 (Mutp53) silence could re-sensitize HCC resistant cells to arsenic trioxide and inhibit the metastatic activities, while mutp53 overexpression showed the opposite effects. Neither arsenic trioxide nor Nutlin-3 could exhibit obvious effects against arsenic trioxide resistant HCC cells, while combination of them showed significant effects. Nutlin-3 can not only increase the intracellular arsenicals through inhibition of p-gp but also promote the p73 activation and mutp53 degradation mediated by arsenic trioxide. In vivo experiments indicated that Nutlin-3 can potentiate the antitumor activities of arsenic trioxide in an orthotopic hepatic tumor model and inhibit the metastasis to lung. Conclusions: Acquisitions of p53 mutations contributed to the resistance of HCC to arsenic trioxide. Nutlin-3 could overcome arsenic trioxide resistance and inhibit tumor metastasis through p73 activation and promoting mutant p53 degradation mediated by arsenic trioxide

Methodology development for investigation of slurry abrasion corrosion by integrating an electrochemical cell to a miller tester

Material losses in slurry handling systems constitute a significant fraction of cost in oil sands, mining, and mineral processing operations. It is thus important to better understand wear attack mechanisms and major factors affecting wear in such applications. In this work, a methodology and a testing system have been developed to study the abrasion–corrosion synergism during slurry abrasion based on a Miller test machine by incorporating a three-electrode electrochemical cell. The proposed methodology has then been validated experimentally using QT 100 steel. It has been shown that cathodic protection using such system setup is effective in suppressing the corrosion effect on the total material loss. In general, corrosion-induced enhancement on slurry abrasion loss rate increases with slurry corrosivity but inversely with sliding speed

Modelling sliding wear: from dry to wet environments

Corrosive species in various forms exist widely in the environment and can significantly affect wear behaviour of materials, usually accelerating wear. Under conditions where the environments are seemingly non-deleterious in terms of corrosivity, some species from the environment can still affect the tribological behaviour of materials. It is thus extremely important to recognise the roles of reactive species in affecting the tribological processes and to understand the processes of tribo-corrosion interactions. In this paper, the mechanisms of wear debris generation and the roles of reactive species in the generation of wear debris during sliding wear in gaseous or aqueous environments are discussed. The effect of environment on the development of wear-protective layers is described. Based on the proposed mechanisms, mathematical models for sliding wear in both dry and aqueous environments are outlined, and the validity of the models is assessed against experimental data in sliding conditions