Preparation And Tribological Behavior Research Of 2D Tungsten Disulfide Nano-Lubricating Material

In recent years,with the advancement of industrial technology,the demand for new solid lubrication increases as machine output,rotation speed,sliding speed,load increase and use in harsh environments such as high temperature and vacuum.As a solid lubricant,tungsten disulfide(WS2)nanosheets have significant characteristics in terms of physical properties.However,it is very difficult for two-dimensional(2D)nanomaterials used in the field of tribology,because of its high-cost,the complex process and poor dispersion stability.Hence,developing low-cost preparation process and designing novel nanostructures are necessary measures to broaden the field of nanomaterials lubrication.In this work,based on the top-down exfoliation technology,the size and thickness of WS2 are adjusted,and their tribological properties as lubricant additives were studied detailedly.The main points are as follows:(1)A facile and high-quality microwave-assisted ultrasonic exfoliation process for few-layer WS2 nanosheets is proposed.Ammonium carbonate((NH4)2CO3)was used as a expansion agent,the pre-impregnated bulk WS2 was subjected to microwave expansion,gases generated via the thermal decomposition of(NH4)2CO3 were used to initially peel the interlayers and subsequently WS2 nanosheets were obtained by the liquid phase sonication in dimethyl sulfoxide(DMSO).WS2 nanosheets with the average lateral size of?400 nm and thickness of?3 layers were exfoliated quickly,efficiently and cheaply.The tribological properties show that WS2 nanosheets can form a well-distributed deposited-film on the sliding surface and the anti-friction and anti-wear properties were significantly improved with only 1.0 wt.%of WS2 nanosheets was added into lubricant.(2)A hydrothermal-assisted grinding process for WS2 quantum dots was carried out.Phosphoric acid was used as thermal solvent,the strong coordination of phosphate radicals destroys the covalent bonds in WS2 nanosheets by a high temperature and pressure reaction and then ultrathin WS2 quantum dots were designed under wet-grinding of ethanol solution.The as-exfoliated WS2 quantum dots with thickness of?0.7 nm and lateral size of less than 10 nm,showing strong photoluminescence.The dispersions of the nanostructure in the lubricant keep relatively well stability,thus they can significantly reduce the friction coefficient,especially,when 1.0 wt.%of WS2 quantum dots were added into grease,the average friction coefficient and wear volume were decreased by 36.73%and 92.54%relative to grease,respectively.(3)The exfoliation process of WS2 nanosheets in this paper was optimized and the amplification tests were repetitively inspected.Based on the existing preparation methods and costs of WS2 nanosheets in the market,the cost was calculated for the as-exfoliated WS2 nanosheets according to the local social and economic conditions.We found that the cost of materials for WS2 nanosheets exfoliated by our process was 1.3 yuan/g.This was expected to become a new way to commercialize WS2 nanosheets through improvement and trial production at factory.