Pressureless low temperature sintering of nanocrystalline zirconia ceramics via dry powder processing

Abstract

Pressureless sintering approaches provide a simple avenue to manufacture dense ceramic parts with minimal processing equipment, but current pressureless sintering techniques have yet to demonstrate capabilities of producing dense ceramics while maintaining sub‐50 nm grain sizes. Nanocrystalline yttria stablized zirconia ceramics were process from 4 mol% yttria stablized zirconia (4YSZ) nanopowders with a crystallite size of 7.5 nm using dry cold isostatic pressing (CIP) where powders are dried immediately prior to green compact formation and CIP vacuum bagging. It is shown that CIP pressures >75 000 psi (517 MPa) effectively remove pores larger than 100 nm and that pressureless sintering occurs at reduced temperatures for green densities ≥50%. Though the sintering kinetics are shown to be similar to other zirconia nanopowder sintering studies, the small initial crystallize size and reduced sintering temperature allowed densities as high as 97.2%, while retaining a ceramic grain size at or below 40 nm. Produced nanocrystalline 4YSZ ceramics with a grain size of 30.3 nm and a density of 96.3% had Vicker's hardnesses as high as 14.2 GPa and Vicker's indentation fracture resistance of 3.43 MPa·m, demonstrating that simple processing approaches can be refined to fabricate nanocrystalline ceramics while maintaining high hardness and indentation fracture resistance.

Temperature Excursions Due to the Reaction Heat Produced by Atomic Layer Deposition on Nanostructured Substrates

“…The precursor to 4YSZ is a yttrium-zirconium hydroxide [8 mol % Y­(OH) 3 Zr­(OH) 4 , abbreviated 8YSZ-OH]. A nanoparticle powder was synthesized from this precursor using a reverse-strike co-precipitation method. , A 0.25 M solution was generated by mixing 19.01 g of ZrO­(NO 3 ) 2 ·6H 2 O (Sigma-Aldrich, technical grade) and 1.87 g of Y­(NO 3 ) 3 ·6H 2 O (Alfa Aeser, 99.9%) in 244 mL of deionized H 2 O with vigorous stirring overnight. The solution was divided with one aliquot transferred to a separatory funnel and added dropwise at approximately 1 drop per second to 345 mL of a 5 M NH 4 OH solution in deionized H 2 O while stirring.…”

Yttria- Stabilized Tetragonal Zirconia with Superior Mechanical Properties Prepared Using Gel Casting Technology and a Two-Stage Sintering Process

“…The ceramic forming methods can be classi ed into dry [11][12][13] and wet forming processes [14][15][16][17]. The wet forming processes, such as slip casting [14] and gel casting [15][16][17] have been used to prepare complex-shaped ceramics.…”