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To balance mechanical strength, friction stability, and low wear, a novel wear-resistant component system: modified sepiolite-complex ceramic powder, was employed in copper-based composite materials, leading to the successful preparation of samples with outstanding mechanical and frictional performance. The material exhibits high friction stability, low wear, and the simultaneous occurrence of a high friction coefficient, which may be caused by uniquely composed dual friction film. The external layer of the friction film consists of Cu 2 O, Fe 2 O 3 , and CaO metal-films, while the internal layer consists of B 2 O 3 film, graphite, and sepiolite. Additionally, modified sepiolite (composed of sepiolite, CaCO 3 and enstatite) plays a dual role in wear resistance and high-temperature lubrication. Furthermore, the Gradient Boosting Decision Tree (Gbdt) model was found to provide more meaningful guidance for predicting friction coefficients. [ABSTRACT FROM AUTHOR]

An imbalance of osteoblasts (OBs) and osteoclasts (OCs) in a chronic inflammatory microenvironment is an important pathological factor leading to osteoporosis. Eicosapentaenoic acid (EPA) has been shown to suppress inflammation in macrophages and adipocytes. However, the effect of EPA on OBs and OCs has yet to be fully elucidated. We explored the roles of EPA in the differentiation of OBs and OCs, as well as the coupling between OBs and OCs in an inflammatory microenvironment. The effects of EPA on estrogen deficiency-induced osteoporosis were also evaluated. Mouse bone marrow mesenchymal stem cells (mBMSCs) and mouse bone marrow-derived macrophages (mBMMs) were used for in vitro OBs and OCs differentiation. TNF-α was used to create an inflammatory microenvironment. We examined the effects of EPA on osteoblastogenesis in the absence or presence of TNF-α and collect OBs' culture medium as the conditioned medium (CM). Then we examined the effects of EPA and CM on RANKL-induced osteoclastogenesis. The in vivo effects of EPA were determined using an ovariectomized (OVX) mouse model treated with EPA or vehicle. High-dose EPA was shown to promote osteoblastogenesis in an inflammatory environment in vitro , as well as upregulate expression of OBs-specific proteins and genes. ARS and ALP staining also showed that high-dose EPA-treated groups restored mBMSCs' impaired osteogenic capacity caused by TNFa. Mechanistically, EPA suppressed the NF-κB pathway activated by TNF-α in mBMSCs and rescued TNF-α-mediated inhibition of osteoblastogenesis. EPA was also shown to inhibit expression of RANKL and decrease the RANKL/OPG ratio in OBs in an inflammatory environment. CM from TNF-α-stimulated OBs promoted osteoclastogenesis of mBMMs; EPA-treated CM prevented this. In the OVX mouse model, EPA supplementation prevented bone loss in an estrogen deficiency-induced inflammatory environment. EPA was demonstrated for the first time to restore mBMSCs' impaired osteogenic capacity caused by TNFa-induced inflammation and rescue the OBs/OCs balance via regulation of RANKL and OPG expression in OBs. EPA showed a remarkable ability to prevent bone loss in OVX mice, suggesting a potential application of EPA in postmenopausal osteoporosis. [ABSTRACT FROM AUTHOR]

To alleviate the issues of matrix softening and excessive wear faced by copper-based composites matched with C/C–SiC disc during high-speed braking, the research was conducted to investigate the impact of composite ceramic (TiC–B 4 C, TB) powder on copper matrix composites prepared through conventional powder metallurgy method. TiC–B 4 C powder was produced using the high-energy ball milling method, and a suitable milling time (48 h) was established to obtain the maximum disorder degree. The results revealed that TB2 (6% TB) had the highest densification and the best mechanical and thermal performance, as compared to other composites. However, there were differences in tribological properties, with TB4 (10% TB) achieving the maximum friction coefficient, while TB2 (6% TB) exhibited more stable friction performance. As the TB powder content increased, larger tribo-films were formed on the worn surface. However, the influence of TB powder content (less than 10% TB) on friction performance was mainly due to mechanical strength and structural tightness, rather than the formation of tribo-films. The friction layer consisted of three parts: the top nanostructure layer composed of nanoparticles (C, Cu, Fe, B, O, and Ti), the middle tribo-film composed of graphite and B 2 O 3 , and the lower elastic deformation zone. [ABSTRACT FROM AUTHOR]

High-speed rail brake pads mainly face the lack of stability of tribological performance under high temperature. An effective approach that is often employed is to reinforce copper-based powder metallurgy (PM) with single ceramic particle to obtain superior properties. In this paper, preparation of the dual ceramic particles (B 4 C–TiC) reinforced copper-based PM by powder metallurgy route, and paired as friction discs using the self-made carbon-ceramic composite. Influence of synergistic strengthening effect of B 4 C and TiC on tribological behavior and wear mechanisms were investigated. The result reveals that the more content of TiC (less 5%) in B 4 C–TiC, the greater the performance improvement, especially when the ratio of TiC/B 4 C is 5:3, the copper-based PM obtains exceptional mechanical and thermal performance, but different tribological behavior at different braking speed. The main factor affecting the tribological behavior at middle-speed (4500 rpm) is TiC, while is B 4 C at high-speed (6000 rpm) due to the generation of B 2 O 3 tribo-film. With the ratio of TiC/B 4 C increases, the generation of B 2 O 3 tribo-film goes through a change of first increased to the maximum, and then disappeared. While wear mechanism of copper-based PM goes through the transitional stage from abrasive wear to slight oxidative wear, severe oxidative wear, abrasive wear and adhesive wear, respectively. [ABSTRACT FROM AUTHOR]

To enhance the bonding capability of composite ceramic powder and subsequently improve the friction stability of copper-based composite materials, B 4 C-SiC ceramic powder modified at different temperatures was used. The results indicate that elevating the modification temperature of ceramic powder promotes faster growth of particles and enhances inter-particle bonding. The mechanical properties of the copper-based composite material are significantly improved, particularly at 1400 °C, owing to the filling of pores and the particle reinforcement effect of ceramic. Meanwhile, the friction coefficient and wear exhibit a gradual increase, mainly caused by the formation of microasperities from larger ceramic particles and sepiolite, leading to changes in the friction-film and friction mechanism. The primary wear mechanism shifts from abrasive wear (1200 °C-1300 °C-1400 °C) to oxidative wear (1500 °C). [ABSTRACT FROM AUTHOR]

Changing precipitation patterns and global warming have greatly changed winter snow cover, which can affect litter decomposition process by altering soil microenvironment or microbial biomass and activity. However, it remains unknown how and to what extent snow cover affects litter decomposition during winter and over longer periods of time. Here, we conducted a meta-analysis to synthesize litter decomposition studies under different levels of snow cover. Overall, deepened snow significantly enhanced litter decomposition rate and mass loss by 17% and 3%, respectively. Deepened snow enhanced litter carbon loss by 7% but did not impact the loss of litter nitrogen or phosphorus. Deepened snow increased soil temperature, decreased the frequency of freeze-thaw cycles, and stimulated microbial biomass carbon and bacterial biomass during winter, but had no effect on these parameters in summer. The promoting effect of deepened snow cover on litter decomposition in winter is mainly due to its positive effect on microbial decomposition by increasing soil temperature and reducing freeze-thaw cycles exceeded its negative effect on physical fragmentation of litter by reducing freeze-thaw cycles. Our findings indicate that the changes in winter snow cover under global change scenarios can greatly impact winter litter decomposition and the associated carbon cycling, which should be taken into consideration when assessing the global carbon budget in modeling. • Deepened snow cover accelerated litter decomposition by 17%. • Deepened snow enhanced carbon loss but had no effect on the loss of nitrogen or phosphorus. • The stimulation of deepened snow on litter decomposition mainly occurred in winter. • The elevated microbial decomposition under deepened snow accelerated winter litter decomposition. [ABSTRACT FROM AUTHOR]

By incorporating the dual ceramic elements TiB 2 /B 4 C, we investigated their impact on the mechanical properties, thermal properties, and friction performance of copper-based powder metallurgy materials, and elucidated the friction wear mechanism. Additionally, machine learning algorithms were employed to predict the friction coefficient and stability coefficient. The conclusions are as follows:With the increase in the TiB 2 /B 4 C ratio, the trend of mechanical properties initially increases and then decreases, with the optimum ratio being 5:3 for TiB 2 and B 4 C, exhibiting superior mechanical properties. Moreover, B 4 C enhances the thermal conductivity of copper-based friction materials more effectively than TiB 2. In terms of overall friction performance, the ratio of TiB 2 to B 4 C at 5:3 yields better frictional properties. The primary components of the friction surface friction film are CuO, Cu 2 O, Fe 2 O 3 , and B 2 O 3 , transitioning from a ceramic film to a metallic film as the TiB 2 /B 4 C ratio increases. The friction wear mechanism shifts from abrasive wear to severe fatigue wear as the TiB 2 /B 4 C ratio increases, accompanied by oxidative wear. Furthermore, an AdaBoost algorithm model was developed to effectively predict the friction coefficient and stability coefficient, with accuracies of 0.9993 and 0.8739, respectively. [ABSTRACT FROM AUTHOR]