ABSTRACT
To suppress the corrosion and erosion wear of dissolvable magnesium alloy ball seats in wellbores, Fe-based amorphous coatings were deposited on dissolvable Mg-RE alloy substrates, and their microstructure, corrosion behavior, and erosion wear behavior were studied. The thickness of Fe-based amorphous coatings on dissolvable Mg-RE alloy substrates can reach 1000 µm without any cracks, and their porosity and amorphous contents are 0.79% and 86.8%, respectively. Although chloride ions will damage the compactness and protective efficacy of passive films, Fe-based amorphous coatings still maintain low corrosion current density (3.31 µA/cm2) and high pitting potential (1 VSCE) in 20 wt% KCl solution. Due to their higher hardness, the erosion wear resistance of Fe-based amorphous coatings is about 4.16 times higher than that of dissolvable Mg-RE alloy substrates when the impact angle is 30°. Moreover, the erosion rates of Fe-based amorphous coatings exhibit a nonlinear relationship with the impact angle, and the erosion rate reaches the highest value when the impact angle is 60°. The erosion wear mechanisms of Fe-based AMCs vary with the impact angles, including cutting, delamination, splat fracture, and deformation wear. This work can provide effective guidance for the corrosion and wear protection of plugging tools made from dissolvable magnesium alloy.
ABSTRACT
Oxidative stress has currently been proposed as a risk factor associated with the development and proression of osteoporosis. In this study, we identify the effect of mangiferin (MAN) on apoptosis and differentiation of osteoblast-like MC3T3-E1 cells insulted by H2O2. We firstly found that MAN can promote cell proliferation of MC3T3-E1 cells in a time- and dose-dependent manner and stimulate the phosphorylation of ERK5. Cells were divided as five groups: control, H2O2 (100 µM, control), H2O2 + MAN (5 µM), H2O2 + MAN (10 µM), and H2O2 + MAN (20 µM). MAN can significantly decrease H2O2-induced apoptosis and elevated ROS level of MC3T3-E1 cells. The expressions of caspase-3, caspase-9 and Bax/Bcl-2 were increased with H2O2 treatment, and MAN can reverse these changes. In addition, Nrf2 and its downstream target effectors (HO1, NQO1) were dramatically attenuated in MC3T3-E cells treatment with H2O2, while MAN can significantly increase the expression of Nrf2, HO1 and NQO1. The expression of ERK5 was down regulated by RNA interference in MC3T3-E1 cells, and we found that MAN (20 µM) pretreatment didn't make remarkable decrease in cell apoptosis or expressions of apoptosis-related proteins in H2O2-insulted siRNA-ERK5 cells. This study indicated that MAN can protect osteoblast against oxidative damage by modulation of ERK5/Nrf2 signaling, which can be new agent for osteoporosis.