Influence of pore structure inhomogeneities in green compacts on strength and reliability of Y-TZP

Galakchov, A.V.; Shevchenko, V.Ja.

doi:10.1016/0955-2219(90)90023-9

Cited by 8 publications

(3 citation statements)

References 4 publications

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“…A dry‐pressing process is commonly applied for the preparation of porous zirconia blocks. In this study, the common presence of intragranular and intergranular voids formed by packing of powder granules was confirmed, indicating that homogeneous packing cannot be easily achieved, although the 3Y‐TZP powders have been thermal spray granulated to improve the powder flowability and packing homogeneity. Once these voids formed, they are difficult to heal completely.…”

Section: Discussionmentioning

confidence: 75%

Effect of Multistep Processing Technique on the Formation of Micro‐defects and Residual Stresses in Zirconia Dental Restorations

Zhao

Zhang

Liu

et al. 2013

Journal of Prosthodontics

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Section: Discussionmentioning

confidence: 75%

Effect of Multistep Processing Technique on the Formation of Micro‐defects and Residual Stresses in Zirconia Dental Restorations

Zhao

Zhang

Liu

et al. 2013

Journal of Prosthodontics

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“…Inter-agglomerate compaction leads to rapid "filling" of low-coordinate inter-agglomerate pores and "shrinkage" of agglomerates in size. This shrinkage in the initial sintering stage often leads to growth of inter-agglomerate cavities [4,5]. Only as there is a reduction in the coordinate number of inter-agglomerate pores as a result of the absorption recrystallization of inter-agglomerate grains is there a start in their second stage of compaction by a normal mechanism.…”

Section: Agglomerates In Nanopowders and Ceramic Technology 349mentioning

confidence: 97%

Agglomerates in nanopowders and ceramic technology

Галахов

2009

Refract Ind Ceram

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Questions are considered connected with use in ceramic technology of ultrafine powder raw material with agglomerated particles. It is shown that presence of agglomerates in nanopowders unavoidably leads to formation in sintered material of structural defects in the form of residual porosity and microcracks. Data are provided for a quantitative dependence of pore structure characteristics for a powder compact on the content of agglomerated particles and the connection of pore structure characteristics with sintering kinetics and the properties of the sintered material obtained.One of the main tendencies in the development of contemporary ceramic material technology is the extensive use of powders with a submicron particle size. Use of powder with particles of this size makes it possible to intensify sintering considerably, to promote preparation of material with a fine grain structure and improved physicomechanical properties.Recently quite productive technology has been developed for preparing ultrafine powders, however, attempts to use them in mass production often does not lead to the expected effect. In spite of the predicted theory, compacts of submicron powders after sintering do not reach an acceptable density, they have coarse unsintered pores and other defects within them, thus worsening material properties [1, 2]. A powder system of nanoparticles should not be considered as a simple collection of individual particles. As a result of the high specific surface in these powder systems the finest individual particles are collected into well-formed, sometimes strongly sintered groups of particles, that have been given the name agglomerates. An example is shown in Fig. 1 of an electron microscope picture of agglomerates in submicron powders of transformation-strengthened structural ceramic of the composition ZrO 2 + 3 mol.% Y 2 O 3 . With an average size of individual particles of 0.036 mm the average size of agglomerates is 5.8 mm, i.e. it exceeds the size of individual particles by more than two orders of magnitude. The pore structure of a compact of agglomerated powder is extremely nonuniform. Apart from the finest pores between individual submicron powder particles (intra-agglomerate) they contain a significant number of coarse high-coordination 2 inter-agglomerate pores. These pores in size exceed the intra-agglomerate sizes by a factor of several tens or hundreds. Presence of two types of pores is confirmed by the nature of the distribution of pores in a compact. This distribution of the pore volume within a compact is shown in Fig. 2, compacted from ultrafine agglomerated ZrO 2 (Y 2 O 3 ) powder with an avFig. 1. Agglomerates in submicron powders of the composition ZrO 2 + 3 mol.% Y 2 O 3 : a) collection of agglomerates in powder at low magnification; b ) structure of an individual agglomerate. * The coordination number of a pore equals the number of particles surrounding it.

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“…These inhomogeneities can be envisioned as local porosity fluctuations caused by differences in particle packing. 8 -11 For compacts prepared from spray-dried powders, two possible illustrations dominate the literature: a qualitative description of inter-and intra-agglomerate pores 6,8,12 and a quantitative distinction among three levels (fine micropores, coarse micropores, and macropores). 13 Hierarchical structures with a multimodal pore-size distribution must be present, but a quantitative description of porosity evolution versus location during sintering has long been lacking.…”

mentioning

confidence: 99%

X‐ray Computed Tomography and Mercury Porosimetry for Evaluation of Density Evolution and Porosity Distribution

Lannutti

Klobes

et al. 2000

Journal of the American Ceramic Society

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X-ray computed tomography (CT) and mercury porosimetry were combined to connect density gradients and the distribution of open porosity in a sintered compact. CT clearly showed that open porosity follows the initial distribution of low-density zones. Mercury porosimetry detected three distinct levels of porosity. Microstructural examination correlated the porosity level with the coordination of (i) two to three or (ii) multiple grains around pores. This combination of techniques provides a novel tool for the study of pore and density-gradient evolution during sintering.

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Influence of pore structure inhomogeneities in green compacts on strength and reliability of Y-TZP

Cited by 8 publications

References 4 publications

Effect of Multistep Processing Technique on the Formation of Micro‐defects and Residual Stresses in Zirconia Dental Restorations

Effect of Multistep Processing Technique on the Formation of Micro‐defects and Residual Stresses in Zirconia Dental Restorations

Agglomerates in nanopowders and ceramic technology

X‐ray Computed Tomography and Mercury Porosimetry for Evaluation of Density Evolution and Porosity Distribution

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