Synthesis by AACVD and Characterization of YSZ-Cr2O3 Nanocomposite Particles for their Potential Application in Reinforcing Structures

In nanomaterials science, nanostructured particles have attracted particular interest due to their novel properties and potential applications in various fields. These properties derive from their shape, size and internal structure. The use of nanostructured particles as fillers in metallic matrices has made it possible to produce lighter and stronger materials capable of replacing traditional materials. One of the properties of the particles is their mechanical properties; the hardness and mechanical strength of crystalline materials increase with decreasing size and vary according to their structure. At the nanometer scale, the atomic structure of nanocrystals is modified, becoming more resistant and acquiring mechanical properties superior to those of macro materials. A reinforcing material can be in the form of fibers, sheets or particles. Reinforcing the matrix with much smaller particles, in the nano-sized range, is one of the critical factors in producing high-performance composites, which yields improved mechanical properties, also when talking about nanocomposites, the hardness is increased due to its nanometric scale and its high surface area/volume ratio [1–2]. Yttria-stabilized zirconia (YSZ) is a ceramic with exceptional properties such as high hardness, high dielectric constant, chemical inertness, and high ionic conductivity at elevated temperatures. Chromium oxide, (Cr2O3), is known for its high hardness and melting temperature, good resistance to wear and high oxidation temperature. The objective of this work is to develop a nanocomposite material with these two metal oxides as reinforcement material due to its high hardness and low cost. Aerosol-assisted chemical vapor deposition (AACVD) was chosen for the growth of YSZ-Cr2O3 nanocomposite particles. The application of a physicochemical method in which the particles are synthesized in a single step is potentially advantageous. By adjusting the process parameters, we can easily control the particle size, crystallinity, chemical homogeneity and stoichiometry. The precursor solution was prepared using chromium (III) acetylacetonate, zirconium (IV) acetylacetonate and yttrium (III) acetate hydrate in a stoichiometric ratio of 40:45:15 respectively in 130 mL of methanol and a final molar concentration of 0.1 mol dm-1, the furnace was set at 723 K and an airflow of 250 mL/min was used as carrier gas. The synthesized particles were analyzed by SEM and are shown in Fig. 1a, it presents a spherical, solid and smooth morphology, the average size obtained by measuring 134 particles resulted in 349±74 nm. EDS analysis was performed on different particles and the elements of interest were found in the desired ratio, yttrium with respect to zirconium was obtained in a ratio greater than 30%, which is ideal to obtain the cubic phase, which has a high hardness [3]. Only chromium was obtained to a lesser extent, about 10% with respect to zirconium and yttrium, but this is good because, in a composite material, the reinforcing material must be in small amounts. In order to know the crystalline phases of the material, the analysis was made by GIXRD, Fig. 1b shows the diffraction spectrum, a lot of noise is observed, which indicates that the material is very amorphous and has little crystallinity, only some characteristic peaks are observed, at the 2θ angles of 30°, 50° and 60°, which belong to the YSZ and two of the characteristic peaks overlap with Cr2O3 at 50° and 60°. In order to obtain a higher crystallinity, it was decided to subject the material to a heat treatment at a temperature of 700°C for two hours, based on previous studies [4].The synthesized and heat-treated particles were analyzed by SEM and are shown in Fig. 2a, it presents a spherical, solid and rough morphology, the average size obtained is very similar without heat treatment and the elements of interest were found in the desired proportion, resulting in the same as in the analysis without heat treatment. In order to know the crystalline phases of the material, the analysis was carried out by GIXRD. Fig. 2b shows the diffraction spectrum, the crystallinity of the material is appreciated, existing peaks at angles 2θ angles of 30°, 34.8°, 50°, 59.4°, 62.3° and 73. 4° belonging to PDF 00–030–1468 of the cubic YSZ phase and also peaks at 24.3°, 33.7°, 36.3°, 41.4°, 50.1°, 54.8°, 58.45°, 63.5° and 73.4° belonging to PDF 00–085–0869 of the Cr2O3 phase. With less noise in the GIXRD analysis and the presence of a greater number of characteristic peaks, we can conclude that there is a greater crystallinity in the material with the heat treatment, also as seen in the TEM micrograph shown in Fig. 1c, it is observed as a smooth particle, where the crystallites are not appreciated, while in the micrograph shown in Fig. 2c, a particle with crystallites is observed throughout the particle. a) SEM micrograph of the spherical particles b) Crystalline phases obtained by GIXRD c) TEM micrograph of a spherical particle. a) SEM micrograph of the spherical particles with heat treatment b) Crystalline phases obtained by GIXRD c) TEM micrograph of a spherical particle with heat treatment.