Tribological properties of a synthetic mica-organic intercalation compound used as a solid lubricant

Abstract

Solid lubricants have long been widely used to enhance lubricity and to achieve a longer die life in the field of tribological applications. Molybdenum disulfide (MoS2) is the most desirable solid lubricant because of its low friction coefficient, good anti-seizure ability stemming from easy cleavage and excellent adhesion to the metal surface. Although MoS2 performs well, it has a disadvantage in that its black appearance significantly stains the working environment. Therefore, non-black solid lubricants are strongly desired. Herein, we investigated the properties of a clay-organic intercalation compound as a solid lubricant. It is well known that some types of layered clay minerals have a cation exchange capacity and are capable of being intercalated with an organic cation between the silicate layers. This reaction is based on the ion exchange of exchangeable inorganic ions (Na+, K+, etc.) in the layered clay minerals. In this study, we examined the properties of synthetic mica, whose silicate layers were intercalated with a cationic organic compound (dioctadecyl dimethyl ammonium chloride). We evaluated the lubrication performance of the mica using a newly devised upsetting-ironing type tribometer. X-ray diffraction (XRD) results show that the distance between the silicate layers of the intercalated synthetic mica increased to 36.6Å from 12.6Å for a non-intercalated one. Owing to the increase in the interlayer distance, the lubrication coating containing the synthetic mica-organic intercalation compound showed a much improved lubrication performance than that of the non-intercalated one. These findings indicate that the lubricity of the clay minerals is highly dependent on the friction between the different silicate layers, and that the cationic organic compound incorporated into the interlayers can improve the lubricity. This result means that the clay-organic intercalation compound is a promising solid lubricant as an alternative to MoS2.