Crystallization and microstructure of metastable water quenched nanostructured 8 mol% yttria-stabilized zirconia using the solution precursor plasma spray method

A t′ tetragonally structured metastable 8 mol% yttria-stabilized zirconia (8 mol% YSZ) nanomaterial was synthesized by means of solution thermal plasma spray with water quenching of reacted species. Synthesis of the 8 mol% YSZ powder involved vaporization of a liquid precursor injected into a plasma jet where individual droplets, depending on their trajectory within the plasma, experienced varied thermal histories. Thus, not all the material produced underwent a complete gel → glass → nanocrystalline transformation sequence. Consequently, the collected powder contained a proportion of gel and glass (amorphous) state material. Additionally, the powder contained nano-scale and small micron-scale rapidly solidified 8 mol% YSZ particles. Following thermal treatment, the gel and the amorphous content transformed to produce (i) densely packed nanograin and (ii) chain-like nanograin aggregates. The nanograin aggregates are suggestive of a strong, yet short-range intergranular attraction, as predicted in computer simulation studies presented in the literature. Interestingly, this mixed morphology powder, after compaction and heat treatment at 1400 °C for 2 h, transformed into 98 % dense material with a homogeneous 200–500 nm grain size. For generating 8 mol% YSZ, the solution precursor plasma spray method offers a high synthesis rate using a low-cost precursor to produce powder that can be consolidated into morphologically homogeneous bulk nanomaterial.