Soft metal as the second phase to enhance the mechanical and tribological properties of Si 3 N 4 ceramics was a focus of current research. Limited by the doping method and the low melting point of the metal, there were often phenomena such as nonuniform distribution and melting overflow of the second phase, which seriously deteriorated the properties of Si 3 N 4 . In this study, Cu-containing Si 3 N 4 was prepared by in-situ method using copper citrate as the second phase additive. The highly dispersed second phase helped Si 3 N 4 achieve significant improvements in fracture toughness and tribological properties. The phase composition, microstructure, hardness, fracture toughness, and tribological properties of Cu-containing Si 3 N 4 were investigated. XRD results indicated that the reinforcement phase was in the form of Cu 3 Si. When the Cu 3 Si phase content was 3 wt%, the fracture toughness of Cu-containing Si 3 N 4 could be increased by 27.1 % compared to the Si 3 N 4 . When the Cu 3 Si phase content reached 12 wt%, the wear rate at room temperature was reduced by 59 % compared to the substrate. The toughing mechanism could be summarized as the crack bridging and deflection of the Cu 3 Si phase. The anti-wear mechanism could be concluded as the reduction of micro-cracks in the friction film with the participation of Cu 3 Si phase, thus reducing the loss in the friction process.
Fanchao Zeng,Yongxia Zhu,Baofang Jin,Yongjun Ji,Lei Shi,Guangwen Xu,Dongxing Fu,Ziyi Zhong,Fabing Su
Multi-component promoters may efficiently improve the catalytic performance of the primary Cu-based catalysts in the Rochow-Müller reaction, but this approach is not well explored, and the roles of the promoters are not very clear. Herein, we report the ZrO 2 -supported CuO catalyst (CuO/ZrO 2 ) modified with a co-promoter of ZnO, Sn, and CuP prepared by a simple dry ball-milling method. The co-promoter could significantly increase the amount of surface adsorbed oxygen and improve the reducing ability of catalysts, facilitating the formation of the active Cu 3 Si phase and further advancing dimethyldichlorosilane ((CH 3 ) 2 SiCl 2 , M2) selectivity and Si conversion in the Rochow-Müller reaction. Compared to the state-of-the-art commercial catalyst, these CuO/ZrO 2 catalysts with the co-promoters all showed enhanced catalytic activity. Especially, the CuO/ZrO 2 catalyst with the co-existence of ZnO, Sn, and CuP promoters achieved the highest M2 selectivity and Si conversion, attributed to its most abundant surface adsorption oxygen and the strongest reducibility. This work opens up a new avenue to improve the catalytic activity of Cu-based catalysts for the Rochow-Müller reaction.
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