Friction between α-Al2O3(0001) surfaces and the effects of surface hydroxylation

Slip Mechanisms of Hydroxylated α-Al2O3 (0001)/(0001) Interfaces: A First-Principles Molecular Dynamics Study

“…A friction coefficient was not obtained for the HP phase of partial-OH, since the data could not be fit accurately to a linear expression due to the variable number of bonds formed across the interface at different P . The friction coefficient of 0.039 for the full-OH system is identical with that reported in earlier force-field based MD simulations . No data are available for comparison of the friction coefficient for the LP phase, but it is within the range of coefficients reported for smooth (μ = 0.08) and rough (μ = 0.33 to 0.52) alumina surfaces sliding in air …”

“…This is consistent with recent force-field based MD simulations of hydroxylated (0001)/(0001) Al 2 O 3 interfaces, which show that partial hydroxylation leads to an increase in friction. 47,50 Fitting the data obtained in the present study to F ) F 0 + µL yields static friction coefficients of µ ) 0.039 and 0.280 for the full-OH and LP phases of the partial-OH system, respectively. A friction coefficient was not obtained for the HP phase of partial-OH, since the data could not be fit accurately to a linear expression due to the variable Smooth sliding behavior is exhibited by the full-OH system at all P and partial-OH at P ) 0, 2, and 4 GPa.…”

“…The first model, referred to as “full-OH”, was formed by cleaving bulk Al 2 O 3 (alumina) to yield two Al-terminated (0001) surfaces, and replacing all terminal Al 3+ ions with three protons. This model has been employed previously in force-field based MD simulations of friction and slip on hydroxylated (0001)/(0001) Al 2 O 3 interfaces. ,,, The optimized structure of this model is shown in Figure a. The second model explored will be designated “partial-OH”.…”

“…This model has been employed previously in force-field based MD simulations of friction and slip on hydroxylated (0001)/(0001) Al 2 O 3 interfaces. 21,47,49,50 The optimized structure of this model is shown in Figure 1a. The second model explored will be designated "partial-OH".…”

Smoothed particle hydrodynamics study of friction of the coarse-grained α-Al2O3/α-Al2O3 and α-Fe2O3/α-Fe2O3 contacts in behavior of the spring interfacial potential

“…8that at micron-scale the friction coefficient of the systems almost does not depend on both the sliding direction and the CG particle size, only a small reflection occurring in the CG systems of the α-Al2O3 oxide. The friction coefficient of reducing from 0.24 to 0.09 in the stable region ( observed for all the CG α-Al2O3 systems is in accordance with the experimentally unlubricated sliding friction coefficient of the alumina/alumina or sapphire/sapphire contact such as 0.07 for the smoothed contact[28], 0.08 ± 0.02 for the rough contact of  nm[29] and about from 0.15 to 0.19 for the rough contact of 20 a R  nm[30], or the MD simulation value of 0.12 for the pure α-Al2O3 (0001)/α-Al2O3(0001) contact held at 300 K[31]. The friction coefficient of the CG α-Fe2O3 systems in the stable region reduces from 0.21 to 0.09 being not agreeably with the steady value of 0.60[32] reported for the Fe2O3 ball/Fe2O3 flat pairs.…”