# Study on the Tribological Properties of F-T DS/ZnFe-LDH Composite Lubricating Material
## 3 Results and Discussion
### Structure Analysis and Surface Topography Analysis  
The SEM images of the three lubricating materials are seen in Figure 4. Figure 4a,d is FS, Figure 4b,e is ZnFe-LDH, Figure 4c,f is FS/ZnFe-LDH. As we can see from Figure 4, FS is an agglomeration composed of spherical carbon particles, but ZnFe-LDH and FS/ZnFe-LDH consist of nanoplates and particles. Compared with FS/ZnFe-LDH, ZnFe-LDH can be observed as more dispersed nanoplatelets, while FS/ZnFe-LDH is a stacked layered structure of nanoplatelets, with some particles and soot filling in between the nanoplatelets.  
Influence of the Three Lubricating Materials on the Anti-Friction Performance of 10\({}^{\#}\) Wo  
Figure 6a,c,e shows the friction coefficient (FC) variation with test time for the above three lubricating materials, respectively. Figure 6b,d,f shows the average friction coefficient (AFC) changes with the additional amount of the above three lubricating materials, respectively. As shown in Figure 6a,d, FS has a certain anti-friction effect. As the convergence of FS in base oil increases, the changing trend of FC appears to decrease and then increase. When the addition amount is 0.4 wt.%, the FC is the smallest but still fluctuates, and when the additional amount is increased to 0.5 wt.%, the FC rises sharply, and there is a big fluctuation. As a 10\({}^{\#}\) WO additive, FS itself is a kind of agglomerate of carbon microspheres, prone to agglomeration in 10\({}^{\#}\) WO. And when the added amount is large, the agglomeration of soot is more serious, making the anti-friction effect of FS ineffective, so the FC curve is unstable [31]. Figure 6a shows that when the FS content is 0.2 wt.%, the FC rises sharply after 1400 s. The reason for this is that FS has poor oil solubility and uneven dispersion in 10\({}^{\#}\) WO. Figure 6b,c, the FC change diagram and AFC change diagram of ZnFe-LDH, shows that the friction reduction effect of ZnFe-LDH is limited. When the addition amount of ZnFe-LDH was 0.1 wt.%, the FC was the lowest. After adding ZnFe-LDH to 10\({}^{\#}\) WO, it was found that the FC curves of all the added concentrations showed a sharp increase in FC after 1200 s. After the addition of ZnFe-LDH reached the minimum of 0.1 wt.%, the AFC continued to increase with the increase of the addition, but the highest AFC did not exceed the AFC of 10\({}^{\#}\) WO. Analysis of the reason for this phenomenon is that ZnFe-LDH, as a material mainly composed of nanosheet, the limited dispersibility in the base oil makes its anti-friction effect unsatisfactory. Furthermore, it shows that when ZnFe-LDH is used as an additive of 10\({}^{\#}\) WO, the added content should not be too high. From Figure 6e,f we see that compared with FS and ZnFe-LDH, the FC of each addition amount of FS/ZnFe-LDH is relatively lower, and the trend of AFC change is first to decrease and then increase. When the addition amount of FS/ZnFe-LDH was 0.2 wt.%, the AFC was the smallest, and the FC curve was relatively steadier without large fluctuations. The reason is that the unique \"sandwich layer\" structure of FS/ZnFe-LDH has played a role. Besides, FS/ZnFe-LDH added cetyltrimethylammonium bromide during the preparation process, and the surface was grafted with long carbon chains, which improved its oil solubility and dispersibility [32]. The AFC of 10\({}^{\#}\) WO is 0.114, and the minimum AFC of the three lubricating materials are 0.09, 0.084, and 0.072, respectively. Compared with 10\({}^{\#}\) WO, the minimum AFC of the three lubricating materials was reduced by 21.05%, 26.32%, and 36.84%, respectively. FS/ZnFe-LDH has the largest reduction in AFC, which proves that the lubrication performance of FS/ZnFe-LDH is the best among the above three lubricating materials.