3.3.1. SEM Analysis

Figure 3 shows the morphological aspect of the Arboblend V2 Nature material coated with Metco ™ 143 (ZrO<sup>2</sup> 18TiO<sup>2</sup> 10Y2O3). A uniform coating of the biopolymer mass is observed. The coating consists of spherical component particles having a dimensions

variation between 1 and 27 µm. The particles retain their spherical shape due to the very rapid cooling on contact with the base matrix. They do not flatten in the form of splats as is conventional in the case of coatings on metal substrate [46]. The fact that the basic matrix contains various particles in shape and size, in large quantities and evenly distributed, leads to an increase in mechanical properties. *Polymers* **2021**, *13*, x FOR PEER REVIEW 11 of 22

**Figure 3.** SEM analysis of the P3–143–9 passes samples: Zirconium dioxide (bearing balls)—orange arrow; Titanium dioxide—blue arrow; Yttrium oxide—green arrow. **Figure 3.** SEM analysis of the P3–143–9 passes samples: Zirconium dioxide (bearing balls)—orange arrow; Titanium dioxide—blue arrow; Yttrium oxide—green arrow.

Figure 4 shows the polymer matrix containing particles from the coating formed by chromium oxide. Some of these particles are heterogeneously distributed, and another Yttrium oxide (green arrow, Figure 3) shows a porous spherical morphology in the form of a sintered agglomerate.

part is embedded in the polymeric structure. Their size varies from 18 µm to 30 µm, and they have rectangular shapes specific to chromium oxide. The spherical microparticles can be attributed to the presence of Fe2O3 and SiO2, which are released in small quantities in the structure of the Amdry 6420 powder, maximum 0.4% and 0.45%, respectively. Compared to the P3–143–9 passes sample, the material incorporated a smaller amount of powder appearance, which represents the lower capacity of the coating and embedding chromium oxide in the polymeric structure. Figure 4 shows the polymer matrix containing particles from the coating formed by chromium oxide. Some of these particles are heterogeneously distributed, and another part is embedded in the polymeric structure. Their size varies from 18 µm to 30 µm, and they have rectangular shapes specific to chromium oxide. The spherical microparticles can be attributed to the presence of Fe2O<sup>3</sup> and SiO2, which are released in small quantities in the structure of the Amdry 6420 powder, maximum 0.4% and 0.45%, respectively. Compared to the P3–143–9 passes sample, the material incorporated a smaller amount of powder appearance, which represents the lower capacity of the coating and embedding chromium oxide in the polymeric structure.

The coating of chromium oxide, silicon oxide and titanium oxide (Cr2O3-xSiO2-yTiO2, Figure 5) highlights a relatively uneven distribution of microparticles, similar to the situation presented in Figure 4. The particles are of different shapes with mostly polyhedral appearance (TiO2—green arrow) but there are also spherical (SiO2—blue arrow) and rectangular (Cr2O3—orange arrow) structures, their dimensions varying between 1 and 63 µm. The particles are embedded in the polymer mass. Both Figures 4 and 5 show chromium oxide, and this compound does not have a better adhesion compared to the sample coated with P3–143–9 passes (Figure 3), which does not contain chromium oxide.

The coating of chromium oxide, silicon oxide and titanium oxide (Cr2O3-xSiO2-yTiO2, Figure 5) highlights a relatively uneven distribution of microparticles, similar to the situation presented in Figure 4. The particles are of different shapes with mostly polyhedral

ide—blue arrow; Yttrium oxide—green arrow.

mium oxide in the polymeric structure.

500× 2000× **Figure 3.** SEM analysis of the P3–143–9 passes samples: Zirconium dioxide (bearing balls)—orange arrow; Titanium diox-

> Figure 4 shows the polymer matrix containing particles from the coating formed by chromium oxide. Some of these particles are heterogeneously distributed, and another part is embedded in the polymeric structure. Their size varies from 18 µm to 30 µm, and they have rectangular shapes specific to chromium oxide. The spherical microparticles can be attributed to the presence of Fe2O3 and SiO2, which are released in small quantities in the structure of the Amdry 6420 powder, maximum 0.4% and 0.45%, respectively. Compared to the P3–143–9 passes sample, the material incorporated a smaller amount of powder appearance, which represents the lower capacity of the coating and embedding chro-

**Figure 4.** SEM analysis of the P6–6420–9 passes samples. **Figure 4.** SEM analysis of the P6–6420–9 passes samples. chromium oxide, and this compound does not have a better adhesion compared to the sample coated with P3–143–9 passes (Figure 3), which does not contain chromium oxide.

500× 2000×

**Figure 5.** SEM analysis of the P9–136–9 passes samples. **Figure 5.** SEM analysis of the P9–136–9 passes samples.
