High-temperature friction performances of graphite blocks (GBs) and zinc phosphate impregnated graphite blocks (IGBs) were evaluated under various friction temperatures. The surface of IGB exhibited extremely lower average friction coefficient values, that was 0.007 at 400 °C and 0.008 at 450 °C, in comparison to that of GB (0.13 at 400 °C and 0.16 at 450 °C, respectively). The worn surface of IGB in the high-temperature friction test was smoother and more complete than that of GB. The wear under high temperature and load caused the transformation of zinc pyrophosphate to zinc metaphosphate and the formation of a continuous large-area boundary lubrication layer combined with graphite and metallic element on the wear surface. The superior tribology property of IGB could be attributed to the digestion of iron oxides by tribo-chemical reactions and passivation of the exposed dangling covalent bonds. Specifically, the layered structure generated on the IGB wear interface effectively decreased the adhesive forces and prevented the surface from serious damage.

    Abstract
    1 Introduction
    2 Experimental procedures
        2.1 Preparation of GBs and IGBs
        2.2 Friction tests
        2.3 Characterization
    3 Results and discussion
        3.1 The properties and microstructure of the GBs and IGBs
        3.2 Friction coefficient and characterization of GB and IGB
        3.3 Characterization of wear surface
    4 Conclusions
    Acknowledgements 
    References

• Yuxuan Xu(College of Materials Science and Engineering, Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Chuanjun Tu(College of Materials Science and Engineering, Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Yanli Liu(College of Materials Science and Engineering, Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Ping Liu(College of Materials Science and Engineering, Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Gang Chen(College of Materials Science and Engineering, Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Jiao Tan(College of Materials Science and Engineering, Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Wei Xiong(Key Laboratory for Special Sealing of Hunan Province)
• Yubo He(Key Laboratory for Special Sealing of Hunan Province)
• Shilin Liang(Harbin Electric Carbon Research Institute)
• Qingchun Ma(Harbin Electric Carbon Research Institute)