# Automatic Transmission Fluids in Electrified Transmissions: Compatibility with Elastomers
## 3 Results and Discussion
### Results of Complementary Tests  
The X-ray Diffraction (XRD) tests were used to look for changes in the crystalline structure of the materials. The level of crystallinity in a polymer reveals its long-range order and has an effect on its properties. The more crystalline a polymer is, the more regularly its chains are aligned. The density and hardness increase with the degree of crystallinity, which means that the calculation of the crystallinity of the polymers tested in this study was helpful in correlating and understanding the mechanical properties that were measured experimentally. Considerable amounts of an amorphous substance in a phase mixture shows up as what is referred to as the amorphous profile. Instead of the characteristic diffraction peaks originated by a crystalline compound, X-rays are scattered continuously over a broad 20 range. By defining the background intensity (separating the crystalline peaks from the amorphous profiles) and entering a constant background value, the HighScore software [28] calculates the crystallinity percentage automatically based on the following equation:  
\[\text{Crystallinity [\%]}=100\times\Sigma\text{I}_{\text{net.}}/(\Sigma\text{I}_{ \text{tot.}}-\Sigma\text{I}_{\text{const.bgr.}}) \tag{1}\]  
where I\({}_{\text{net. }}\) represents the peak intensity (crystalline part), I\({}_{\text{tot. }}\) is the total intensity, and I\({}_{\text{const.bgr. }}\) is the intensity of the defined background (amorphous profile). Figures 5-7 show the XRD spectra of the elastomers both in the fresh state and after 168 h of aging in each lubricant. The spectra of fresh and aged elastomers allow us to compare and identify possible changes in the structure of elastomers. Only the fresh and 168 h aged samples results are reported, as no influence of the aging time was found in the long term. Figures 5 and 6 show the same \(y\)-axis scale, while Figure 7 presents a larger \(y\)-axis scale due to the greater intensity of silicone peaks during the XRD analysis. Figure 5: XRD spectra expressed in arbitrary units (a.u.) for the FKM (fresh and after 168 h of aging). Figure 6: XRD spectra expressed in arbitrary units (a.u.) for the EPDM (fresh and after 168 h of aging). Figure 7: XRD spectra expressed in arbitrary units (a.u.) for the silicone (fresh and after 168 h of aging). In the EPDM fresh sample, calcium carbonate was identified as a crystalline additive. However, it was not possible in this case to calculate the percentage of crystallinity accurately, because the profile observed between 6 and 28 20 (Figure 6) did not allow separation of the amorphous area from the semi-crystalline area with a constant background methodology. Table 6 shows the crystallinity percentage of silicone, according to Equation (1) after aging in the different lubricants for 168 and 672 h, as well as that of a fresh sample. The analysis of the crystallinity percentage values showed that the measured changes in mechanical properties (hardness and tensile strength) are indeed explained by the significant changes in the crystallinity percentage. This decrease in crystallinity is well illustrated in the expanded window in Figure 7 and was reproduced in all of the crystalline phase peaks of the fresh silicone sample. Figure 7 had to be displayed with a different scale compared to Figures 5 and 6, as the crystallinity peaks are much sharper than in those cases, which is reflected in the crystallinity percentages of the respective fresh samples (65% for silicone, 21% for FKM, and unidentified for the EPDM). In addition, a qualitative analysis of the crystalline phases found silicon oxide (SiO\({}_{2}\)) additive. Figures 8-10 show the infrared absorbance spectra for samples of the elastomers: FKM, EPDM, and silicone, respectively. Results are shown for fresh material and after the aging process in different lubricants for 168 and 672 h. The FTIR tests were carried out to detect possible variations in the polymeric structure of the elastomers.