pH‐dependent lubrication mechanism of graphene oxide aqueous lubricants on the strip surface during cold rolling

Abstract

The tribological performance and lubrication mechanism of graphene oxide (GO) aqueous lubricants with different pH levels on the strip surfaces during cold rolling were investigated. And triethanolamine (TEA) was used to adjust the pH levels of GO lubricants. The morphology of GO and physical characterization of GO lubricants were carried out. Four‐ball tribological tests and cold rolling experiments were conducted to obtain the tribological behaviors of GO lubricants on the strip surfaces. To figure out the lubrication mechanism, the surfaces of the rolled strips using GO lubricants were analyzed utilizing a series of experiments. The increase in the pH value of lubricants changed the intrinsic structure of GO, resulting in better dispersibility and wettability. The change of physical characteristics significantly improved the antifriction and antiwear properties of lubricants, and the alkaline lubricant (pH 9.0) exhibited the best lubrication performance. A diameter–height ratio (λd) applied by a calculation method was proposed to approximatively ascertain the lubrication regime during the cold rolling. The λd and the surface quality of the rolled strips indicated that the lubrication regime was the boundary lubrication when using the alkaline lubricant. Moreover, GO particles in the alkaline lubricant could repair the strip surface by mending effect and form the physically adsorbed layers. The layers prevented direct contact between rolled surfaces, further amending the surface quality of the rolled strips.

Water lubrication of graphene oxide-based materials

“…The GO solution at pH=10 did not show any lubricant properties. However, Meng's research [50] found that alkaline GO suspension (pH=9) adjusted by triethanolamine behaved better lubrication performance on the strip surfaces during cold rolling. The COF, wear scar diameter, and the minimum rolling thicknesses of the rolled strips in GO aqueous suspension (pH=9) decreased by 28.6%, 21.6%, and 10.84%, respectively, and the last nonseizure load decreased by 20%, versus GO aqueous suspension with pH of 2.8.…”

A Comprehensive Review of Water-Based Nanolubricants

“…In the case of pH-dependent GO as water-based nanoadditives, two studies were reported by He et al [17] and Meng et al [76], which proposed two different preparation processes. A mechanical de-agglomeration method was used by He et al [17] to prepare GO suspension with 0.06 wt.% GO and 0.1 M NaOH in DW under high intensity ultrasonic agitation (400 W) for 10 min, resulting in good dispersion stability for a week.…”

“…The pH value was adjusted by NaOH and varied from 3.1 to 9.7, which had insignificant influence on agglomeration of GO sheets. In contrast, Meng et al [76] mixed triethanolamine (TEA) with 0.1 wt.% GO in DIW to adjust the pH value from acidic (pH 2.8) to alkaline (pH 9). They found that the lubricant with pH 9 was the most homogeneous with no precipitation for 50 days.…”

“…The effect of pH on the stability of water-based lubricants has been investigated by many researchers using NPs such as graphene oxide (GO). For instance, Meng et al [76] discovered that alkaline GO water-based lubricant (pH 9.0) presented the most effective lubricity, and an increase in lubricant pH value can modify the GO structure, improving the dispersibility of GO in water.…”

Enhanced lubrication performance of triethanolamine functionalized reduced graphene oxide on the cold‐rolled surface of strips

“…Cold rolling was one of the most important metal forming processes to obtain the required size, mechanical properties, and surface finish 1,2 . But the friction and wear caused great losses in materials and energy, which remained a challenge to be addressed at present 3,4 .…”