Impact of Copper Oxide Additions on the Microstructure, Physical, and Tribological Properties of Geopolymer Composites

This study investigates the influence of copper oxide (CuO) concentrations (0-50 wt.%) on the phase evolution, thermal stability, and tribological performance of metakaolin-based geopolymer composites after a 28-day curing period. Phase constitution, microstructure, tribological, and thermal behaviors were examined using XRD, SEM, hardness, wear, and DSC analyses. XRD analysis revealed that the incorporation of CuO into the geopolymer composite weakens quartz peaks and forms CuO phases, indicating a dominant amorphous aluminosilicate structure. The addition of CuO to the geopolymer composite was verified by FTIR analysis, which showed improved structural stability through spectrum shifts in the Si-O-Si, Al-O-Si, and Cu-O bands. DSC analysis revealed that adding CuO to the geopolymer composite reduces mass loss above 800 °C and suppresses the 720 °C crystallization peak, indicating enhanced thermal stability and formation of stable Cu-based phases. Tribological results showed that CuO addition reduced the wear rate from 0.00058 mm³/Nm for the geopolymer composite to 0.00025 mm³/Nm, while the coefficient of friction (COF) decreased from 0.39 to 0.29.