The Effect of Addition of Nanoparticles, Especially ZrO2-Based, on Tribological Behavior of Lubricants

Abstract

The aim of the paper was to discuss different effects, such as, among others, agglomeration of selected nanoparticles, particularly those from zirconia, on the tribological behavior of lubricants. The explanation of the difference between the concepts of ‘aggregation’ and ‘agglomeration’ for ZrO2 nanoparticles is included. The factors that influence such an agglomeration are considered. Classification and thickeners of grease, the role of additives therein, and characteristics of the lithium grease with and without ZrO2 additive are discussed in the paper. The role of nanoparticles, including those from ZrO2 utilized as additives to lubricants, particularly to the lithium grease, is also discussed. The methods of preparation of ZrO2 nanoparticles are described in the paper. The agglomeration of ZrO2 nanoparticles and methods to prevent it and the lubrication mechanism of the lithium nanogrease and its tribological evaluation are also discussed. Sample preparation and a ball-on disc tester for investigating of spinning friction are described. The effect of ZrO2 nanoparticles agglomeration on the frictional properties of the lithium grease is shown. The addition of 1 wt.% ZrO2 nanoparticles to pure lithium grease can decrease the friction coefficient to 50%. On the other hand, the agglomeration of ZrO2 nanoparticles in the lithium grease can increase twice the friction coefficient relative to that for the pure grease.

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Tribological Performance Investigation of a Commercial Engine Oil Incorporating Reduced Graphene Oxide as Additive

“…Aggregation takes place whenever the Van der Waals forces between the nanomaterials are stronger than the repulsive ones [16] and the Brownian motion cannot overcome the attraction. When agglomeration occurs in the nanomaterials' dispersions, sedimentation is sped up, while friction performance is negatively affected [17,18]. Hence, long-term stability still remains challenging towards the formulation of highly efficient and reliable nanolubricants in order not to settle down after a long time of storage, ensuring negligible mechanical failure (wear) between worn surfaces [16,19].…”

Structure of nanoparticles in the ZrO2-Y2O3 system, as obtained under hydrothermal conditions

“…Due to the presence of several polymorphic modifications [1][2][3][4] zirconium dioxide is of interest as a model for studying the effect of the synthesis methods and parameters on the formation of nanocrystals with different structure [5][6][7][8][9][10][11][12][13][14][15]. Zirconium dioxide based nanomaterials with various structures, morphologies, and particle size parameters have a wide range of applications [16][17][18][19][20][21][22][23][24][25][26][27], which makes the above studies relevant from a practical point of view as well.…”