Y-TZP reinforced with reduced graphene oxide

Abstract

Purpose/aim: To develop a processing method for yttrium stabilized zirconia pollycrystal (YTZP) reinforced with reduced graphene oxide (rGO) and to verify the effect of rGO concentration on hardness and fracture toughness of the material. Materials and methods: The composite production included several steps: (a) synthesis of Y-TZP powder by coprecipitation route, (b) synthesis of graphene oxide from chemical exfoliation of graphite (modified Hummer’s method) followed by reduction with ascorbic acid, (c) sonication of reduced graphene oxide in Y-TZP suspension followed by drying (d) uniaxial pressing in metal device with diameter of 5mm and (e) sintering in a conventional tubular furnace (Argon/4%hydrogen atmosphere) or spark plasma sintering (SPS). The concentration of rGO in Y-TZP was fixed between 0.01 and 2.0 wt%. Sintered samples were characterized by X-ray diffraction, scanning electron microscopy, density measurements, and Vickers method for hardness and fracture toughness determination (indentation fracture). Data were analyzed by ANOVA and Tukey’s test with global significance level of 5%. Results: Results (Table 1) showed that the procedure stablished for dispersion of rGO in the Y-TZP resulted in good physical homogeneity of rGO and Y-TZP. Regarding the sintering procedure, it was observed that conventional sintering in a controlled atmosphere was not effective for ceramic densification due to microcrack formation at the ceramic surface. For conventional sintering, the hardness obtained for the rGO concentration of 2% was significantly lower than those obtained for all other concentrations, however, for this processing method, fracture toughness was not affected by rGO concentration. For SPS, both fracture toughness and hardness were affected by rGO concentration, with the lowest hardness mean value measured for the concentration of 0.05% and the lowest fracture toughness value measured for specimens with addition of 0.01% of rGO. Conclusions: The production of the composite Y-TZP/rGO was proved possible, and sintering via spark plasma resulted in higher mechanical properties of the composite material compared to conventional sintering. rGO concentration affected the hardness of the composite for both processing methods (conventional and SPS), however fracture toughness was only affected by rGO concentration for specimens processed via SPS.