“…Friction coefficients of that magnitude, obtained during those lubricating conditions, represent low energy loss together with zero environmental impact [2]. In this context, Ferreira [3] defined that µ < 0.01, obtained in steady state, could be called ultra-low friction coefficient (ULFC). Besides self-mated Si3N4, ULFC was also observed for self-mated SiC [4,5] and for unmated Al2O3-Si3N4 pair [2,3,[6][7][8], during water lubrication.…”