Transparent nanocrystalline spinel by room temperature high-pressure compaction

Wollmershauser, James A.; Feigelson, Boris N.; Qadri, S. B.; Villalobos, Guillermo; Hunt, Michael; Imam, M. Ashraf; Sanghera, Jasbinder S.

doi:10.1016/j.scriptamat.2013.05.014

Cited by 21 publications

(8 citation statements)

References 16 publications

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“…15 Two K-type thermocouples were inserted through both high-pressure cell assembly lids. The high-pressure experiments were performed in a pressless multianvil split-sphere apparatus 22,53 equipped with an 8−6-type multianvil system. After a 25 min pressurization to 2 GPa, samples were sintered at various temperatures from 640 to 850 °C for 15 min.…”

Section: Methodsmentioning

confidence: 99%

Below the Hall–Petch Limit in Nanocrystalline Ceramics

et al. 2018

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Reducing the grain size of metals and ceramics can significantly increase strength and hardness, a phenomenon described by the Hall-Petch relationship. The many studies on the Hall-Petch relationship in metals reveal that when the grain size is reduced to tens of nanometers, this relationship breaks down. However, experimental data for nanocrystalline ceramics are scarce, and the existence of a breakdown is controversial. Here we show the Hall-Petch breakdown in nanocrystalline ceramics by performing indentation studies on fully dense nanocrystalline ceramics fabricated with grain sizes ranging from 3.6 to 37.5 nm. A maximum hardness occurs at a grain size of 18.4 nm, and a negative (or inverse) Hall-Petch relationship reduces the hardness as the grain size is decreased to around 5 nm. At the smallest grain sizes, the hardness plateaus and becomes insensitive to grain size change. Strain rate studies show that the primary mechanism behind the breakdown, negative, and plateau behavior is not diffusion-based. We find that a decrease in density and an increase in dissipative energy below the breakdown correlate with increasing grain boundary volume fraction as the grain size is reduced. The behavior below the breakdown is consistent with structural changes, such as increasing triple-junction volume fraction. Grain- and indent-size-dependent fracture behavior further supports local structural changes that corroborate current theories of nanocrack formation at triple junctions. The synergistic grain size dependencies of hardness, elasticity, energy dissipation, and nanostructure of nanocrystalline ceramics point to an opportunity to use the grain size to tune the strength and dissipative properties.

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Section: Methodsmentioning

confidence: 99%

Below the Hall–Petch Limit in Nanocrystalline Ceramics

et al. 2018

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“…In spite of this, a recent paper of Wollmershauser et al . [ 45 ] showed that the hardness of magnesium aluminate spinel, used as a model hard ceramic material, rigorously followed the Hall-Petch relationship down to grain sizes of 28 nm.…”

Section: Why Nanostructured Ceramics?mentioning

confidence: 99%

Structural Ceramic Nanocomposites: A Review of Properties and Powders’ Synthesis Methods

Palmero

2015

Nanomaterials

242

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Ceramic nanocomposites are attracting growing interest, thanks to new processing methods enabling these materials to go from the research laboratory scale to the commercial level. Today, many different types of nanocomposite structures are proposed in the literature; however, to fully exploit their exceptional properties, a deep understanding of the materials’ behavior across length scales is necessary. In fact, knowing how the nanoscale structure influences the bulk properties enables the design of increasingly performing composite materials. A further key point is the ability of tailoring the desired nanostructured features in the sintered composites, a challenging issue requiring a careful control of all stages of manufacturing, from powder synthesis to sintering. This review is divided into four parts. In the first, classification and general issues of nanostructured ceramics are reported. The second provides basic structure–property relations, highlighting the grain-size dependence of the materials properties. The third describes the role of nanocrystalline second-phases on the mechanical properties of ordinary grain sized ceramics. Finally, the fourth part revises the mainly used synthesis routes to produce nanocomposite ceramic powders, underlining when possible the critical role of the synthesis method on the control of microstructure and properties of the sintered ceramics.

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“…21,22 A nanocrystalline grain structure in tetragonal zirconia ceramics potentially provides the opportunity to design the optical esthetics (ie degree of opacity) to match natural teeth without additional dopants. 9 More importantly, the nanostructure stabilizes the tetragonal phase 2 reducing the risk of low-temperature degradation known to increase surface roughness and decrease strength. 23 Tetragonal | 61 DRAZIN et Al. zirconia ceramics also have utility as thermal barrier coatings because of the combination of low thermal conductivity and superior mechanical properties.…”

Section: Introductionmentioning

confidence: 99%

“…Fully dense nanocrystalline ceramics with grain sizes below 50 nm represent a group of materials where their "intrinsic" physical properties can be greatly modified by the nanostructure. 1 The nanostructure has been shown to play a role in the phase stability, 2 electrical 3,4 and thermal transport, 5,6 optical transmission, [7][8][9][10] and mechanical properties. [11][12][13][14][15][16] Yttria stabilized zirconia (YSZ) ceramics are used in myriad applications spanning thermal barrier coatings [17][18][19] to dental materials 20 and stand to benefit greatly from a designed nanostructure that allows tuning of the thermal, optical, and mechanical properties.…”

Section: Introductionmentioning

confidence: 99%

“…Tetragonal yttria stabilized zirconia ceramics have widespread application in the dental field where shaped ceramics are used as crowns . A nanocrystalline grain structure in tetragonal zirconia ceramics potentially provides the opportunity to design the optical esthetics (ie degree of opacity) to match natural teeth without additional dopants . More importantly, the nanostructure stabilizes the tetragonal phase reducing the risk of low‐temperature degradation known to increase surface roughness and decrease strength .…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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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.

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Transparent nanocrystalline spinel by room temperature high-pressure compaction

Cited by 21 publications

References 16 publications

Below the Hall–Petch Limit in Nanocrystalline Ceramics

Below the Hall–Petch Limit in Nanocrystalline Ceramics

Structural Ceramic Nanocomposites: A Review of Properties and Powders’ Synthesis Methods

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

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