Hydrothermally synthesized smectite as a thickener with favorable rheological and tribological properties over a wide temperature range

Abstract

Lubricating grease is essential for many applications. Although smectite grease is an important type of lubricating grease, its properties can be inconsistent due to variations in the properties of natural smectite. In this work, pure smectite was synthesized from an H2O/NH4F/Mg(CH3COO)2/Al(NO3)3/tetraethoxysilane/NaOH system by a one-step hydrothermal method. Compared with natural smectite, synthetic smectite has a larger cation exchange capacity (CEC), smaller particle size, and fluffier morphology. The pure smectite grease showed higher energy storage modulus and better thixotropy than natural smectite grease at the same thickener content. Synthetic smectite grease showed more stable tribological behavior, maintaining better anti-wear and anti-friction properties at different test temperatures. These improvements can be mainly ascribed to its fixed elemental composition, larger CEC, good rheological properties, and absence of impurities. Due to the convenient synthetic method and superior rheological and tribological performances, synthetic smectite as a grease thickener has promising potential for use in demanding advanced precision instruments, as well as pharmaceuticals, food, and other industrial fields.