2.2 Effect of pore structure on abrasion resistance
2.2.1 Effect of open and closed state of the pores on abrasion resistance
The correlations between the AC total porosity ratio, open porosity ratio and abrasion resistance are shown in Figure 9 and Figure 10. Except for C-x, the abrasion resistance shows a negative correlation with the total porosity ratio and open porosity ratio, and the linear fitting results of R2 were 0.7267 and 0.6371, respectively. The higher R2 of the former implies all pores, regardless of closed pore or open pore, have significant effect on AC abrasion resistance. The relatively weak correlations indicate that there may be other indexes that affect AC abrasion resistance, such as surface roughness, ash content, etc.
The abrasion occurs at the AC particles surface contacting each other. The shear stress generated due to the relative motion, which causes the AC particles surface layer to peel off. So, only the pores near the AC particles surface can have a great impact on the AC abrasion. After the outermost layer is peeled off, the closed pore inside will eventually be exposed to the surface to become open pore, and then affect the AC abrasion resistance. Therefore, the initial opening and closing state of the pore does not significantly affects the abrasion resistance.
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FIGURE 9 Correlation between total porosity and abrasive strength
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FIGURE 10 Correlation between open porosity and abrasive strength
2.2.2 Effect of pore size distribution on abrasion resistance
Except for C-x, the correlations between abrasion resistance and the pore volume of 0-2 nm, 2-500 nm, above 500 nm of 12 ACs are shown in Figure11- Figure 13. The fitting results show that the abrasion resistance is more closely related to the pore volume of 0-2 nm than that of 2-500 nm, and there is no obvious correlation with the pore volume above 500 nm. Therefore, the small pore is the main destroying reason for the abrasion resistance. When the pore volume is constant, the more the small pores, the more damage to the abrasion resistance.
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FIGURE 11 Correlation between 0-2 nm pore volume and abrasive strength
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FIGURE 12 Correlation between 2-500 nm pore volume and abrasive strength
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FIGURE 13 Correlation between above 500 nm pore volume and abrasive strength
Unlike the compressive strength, the abrasion only takes place in AC surface, and the abrasion resistance is the ability of the AC surface to resist shear stress damage. The stronger the bonding force between the AC surface particles, the higher the abrasion resistance. The micro-convex model of the abrasion resistance believes that the micro-convex with different height is densely distributed on the material surface. When the external material contacted with the micro-convex and moved relatively.[21] The micro-convex will become the stress point of the material surface. Under the cutting action of the external material, the stressed point fractures and forms abrasion debris[15]. The pores divide the AC surface into numerous stress points. As shown in Figure 14, when the pore volume is constant, the smaller the pore size, the larger the pore number, and the smaller the stress point is divided, which in turn leads it is worn more easily. Therefore, the smaller pore will be a major factor in destroying the AC abrasion resistance.