Figure 4: Improvement percent of breakdown voltage of different nanofluids at varying concentrations [6].
Longevity: Coefficient of friction and wear width/diameter The coefficient of friction has a significant role in determining the efficient operation and longevity of components of motor vehicles. The components near the engine are in an environment of intense motion, and thus must be suited to run in this condition. The goal of the addition of nanoparticles in greases is to decrease the coefficient of friction. In addition to this, the wear width/diameter indicates the physical damage oil or lubricant undergoes. Wear width/diameter is the measure of damage a surface undergoes. In tests such as ball-on-disk, the ball is rubbed against a rotating disk. The contact between the ball and disk is coated with a lubricant. The scar damage the ball sustains is then measured. From this test, smaller scars reveal a superior lubricity of the lubricant/grease. This is relevant for moving parts motion, thus reducing wear width and diameter is vital for efficiency and longevity of greases and lubricants.
Investigations on the tribological behaviour of SiO2 nanoparticles in SN-500 base oil found a decrease
in the coefficient of friction with the addition of nano-enhancing particles [7]. Tests were conducted at forces of 10, 30 and 50 N and at weight percent concentrations of 0.5% to 0.75%. As shown in Figure 5, SiO2
nanoparticles in SN-500 base fluid have lower
coefficient of friction than the pure SN-500 base oil. However, the coefficient of friction for SN-500 base oil at 10 N has large variations as time elapses, therefore conclusions at lower forces are difficult to make. In general, at higher forces and higher weight concentrations of nanoparticles, the coefficient of friction decreases.
Continued on page 18 LUBE MAGAZINE NO.186 APRIL 2025 17
Figure 5: Coefficient of friction of lubricants at varying forces (10, 20 ,30 N) (a) SN-500 (b) SiO2
[7].
A similar study investigated the friction coefficient as a function of time [8]. The paper experimented with mineral oil, synthetic oil, sunflower oil, and soybean oil with CuO and ZnO nanoparticles. The study conducted a ball-on-disk test with the nano-enhanced lubricant acting as the boundary between the ball and disk. Figure 6 depicts the friction coefficient of the varying oils as time elapsed. The base synthetic oil exhibited higher coefficients of friction compared to the nanosynthetic oil. Sunflower and soybean oil were found to have the opposite effect, with the CuO and ZnO increasing friction coefficient.
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