Continued from page 15
end of the studied density concentrations of SiO2 nanoparticles in the grease. There is also a notable
difference in BDV between Midel-7131 and Karamay #25. The paper concluded that SiO2
nanoparticles
have superior performance in synthetic esters. Noting that synthetic esters mixed with SiO2
nanoparticles
performed significantly better than Karamay #25, it can be suggested that the type of grease/mixture can impact results such as AC breakdown voltage.
Figure 1: Influence of nanoparticles concentrations of colNF and sNF on AC breakdown voltage (kV) [4].
In another study, Xiangyu et al. studied TiO2 and SiO2
nanoparticles due to their good tribological properties that can be exploited in semi-insulation materials [2]. The study evaluated the BDV of nano-TiO2 nano-SiO2
and doped SnO2
particles in comparison to nanometer Sb (ATO). As seen in Figure 2, as weight
concentration of the nanoparticles increased, BDV of SiO2
and TiO2 increased significantly in comparison
to ATO. At the highest concentration recorded, nano-TiO2
therefore reveals that nano-SiO2
attained the greatest increase. This and TiO2
and other similar nanoparticles can possibly enhance BDV.
Figure 3: Average breakdown voltage (kV) of SiO2 and Karamay #25 at particle sizes 15 and 50 nm [5].
enhanced Midel-7131
Figure 2: AC breakdown voltage (kV) as a function of the weight concentration of additives [2].
A similar study by Fasehullah et al. [5] investigated the impact of insulative SiO2
nanoparticle strength on synthetic ester (Midel-7131) and mineral oil
(Karamay #25). As depicted in Figure 3, both SiO2 nanoparticles sizes of 15 and 50 nanometres show an increase in the BDV in the Midel-7131 and Karamay #25 enhanced greases. A trend seen from previous studies is that the average BDV decreased at the high
An additional paper used Midel-7131 as a base in order to analyse the AC breakdown voltage of Fe3
O4 ZrO2 , SiO2 and Al2 O3 , ZnO, enhanced synthetic esters [6].
Higher density concentrations of the nanoparticles in the enhanced synthetic ester led to a general increase in BDV and a subsequent decrease in BDV at the higher end of studied concentrations, as seen in Figure 4. This decrease at higher concentrations can be attributed to possible agglomeration of the nanoparticles in the ester which prohibits their electrical properties being imparted efficiently to the matrix.
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