Electric current assisted sintering of ceramics – steps and pitfalls on the way to transparency

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F60461373%3A22310%2F18%3A43916754" target="_blank" >RIV/60461373:22310/18:43916754 - isvavai.cz</a>

Výsledek na webu

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DOI - Digital Object Identifier

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Jazyk výsledku

angličtina

Název v původním jazyce

Electric current assisted sintering of ceramics – steps and pitfalls on the way to transparency

Popis výsledku v původním jazyce

Electric current assisted sintering (ECAS), also called pulsed electric current sintering (PECS) or field assisted sintering technique (FAST), but more widely known under the popular – albeit less appropriate – name spark plasma sintering (SPS), has gained considerable attention from the scientific community during the last few decades, because it is a convenient method for the fast densification of otherwise hard-to-sinter ceramic powders, both oxide and non-oxide. While in the case of metal powders the densification is always affected by the flow of electric current through the sample itself (initially via the particle contact points and subsequently via the sinter necks), this is usually not the case for ceramic powders, at least not for temperatures below which ionic conductivity plays a significant role. Therefore, in contrast to metals, in ceramics it is essentially only the Joule heating of the mold (usually a graphite mold) and the ensuing high heating rate that distinguishes ECAS from other forms of (uniaxial) hot pressing. Thus, also the sintering mechanisms in ECAS are not too different from those of (uniaxial) hot pressing. Since ECAS is an extremely versatile method, allowing the simultaneous control of many process parameters and conditions, such as electric current levels and pulse rates, temperature schedules (including heating and cooling rates, dwell times and hold temperatures), pressure schedules (including pressure increase and decrease rates, dwell times and hold pressures) and atmospheres (usually vacuum or inert), the number of actual and potential applications of ECAS is steadily increasing and already now too large to be treated in a single review. Therefore, the present contribution focusses on recent ECAS achievements and progress in the special field of translucent and transparent ceramics. For the preparation of these materials appropriate grain size, extremely high density and the minimization (preferably absence) of second phase inclusions are critical factors. Following an outline describing the historical development of ECAS and related techniques, the principle of ECAS is briefly described, current opinions concerning sintering mechanisms are summarized, and the problem of carbon contamination is discussed in some detail. In this context the use of boron nitride as a protective coating and lithium fluoride as a sintering aid is mentioned. Fundamental optical properties are defined, an overview of microstructural factors affecting transmittance is given, and literature data (ECAS conditions and resulting optical properties) are compared for various oxide (and a few silicate, phosphate or non-oxide) ceramics that have so far been prepared in transparent or at least translucent form for wavelengths close to the visible or infrared range of the electromagnetic spectrum. The materials reviewed in this chapter include, among others, alumina, lutecia, magnesia, yttria, zirconia, titanates, zirconates, lutetium compounds, magnesium aluminate spinel (magnesia alumina spinel), yttrium aluminum garnet (YAG), hydroxyapatite, mullite, aluminum nitride, aluminum oxynitride, silicon aluminum oxynitride, calcium fluoride, magnesium fluoride, sphalerite, and yttria-magnesia nanocomposites.

Název v anglickém jazyce

Electric current assisted sintering of ceramics – steps and pitfalls on the way to transparency

Popis výsledku anglicky

Electric current assisted sintering (ECAS), also called pulsed electric current sintering (PECS) or field assisted sintering technique (FAST), but more widely known under the popular – albeit less appropriate – name spark plasma sintering (SPS), has gained considerable attention from the scientific community during the last few decades, because it is a convenient method for the fast densification of otherwise hard-to-sinter ceramic powders, both oxide and non-oxide. While in the case of metal powders the densification is always affected by the flow of electric current through the sample itself (initially via the particle contact points and subsequently via the sinter necks), this is usually not the case for ceramic powders, at least not for temperatures below which ionic conductivity plays a significant role. Therefore, in contrast to metals, in ceramics it is essentially only the Joule heating of the mold (usually a graphite mold) and the ensuing high heating rate that distinguishes ECAS from other forms of (uniaxial) hot pressing. Thus, also the sintering mechanisms in ECAS are not too different from those of (uniaxial) hot pressing. Since ECAS is an extremely versatile method, allowing the simultaneous control of many process parameters and conditions, such as electric current levels and pulse rates, temperature schedules (including heating and cooling rates, dwell times and hold temperatures), pressure schedules (including pressure increase and decrease rates, dwell times and hold pressures) and atmospheres (usually vacuum or inert), the number of actual and potential applications of ECAS is steadily increasing and already now too large to be treated in a single review. Therefore, the present contribution focusses on recent ECAS achievements and progress in the special field of translucent and transparent ceramics. For the preparation of these materials appropriate grain size, extremely high density and the minimization (preferably absence) of second phase inclusions are critical factors. Following an outline describing the historical development of ECAS and related techniques, the principle of ECAS is briefly described, current opinions concerning sintering mechanisms are summarized, and the problem of carbon contamination is discussed in some detail. In this context the use of boron nitride as a protective coating and lithium fluoride as a sintering aid is mentioned. Fundamental optical properties are defined, an overview of microstructural factors affecting transmittance is given, and literature data (ECAS conditions and resulting optical properties) are compared for various oxide (and a few silicate, phosphate or non-oxide) ceramics that have so far been prepared in transparent or at least translucent form for wavelengths close to the visible or infrared range of the electromagnetic spectrum. The materials reviewed in this chapter include, among others, alumina, lutecia, magnesia, yttria, zirconia, titanates, zirconates, lutetium compounds, magnesium aluminate spinel (magnesia alumina spinel), yttrium aluminum garnet (YAG), hydroxyapatite, mullite, aluminum nitride, aluminum oxynitride, silicon aluminum oxynitride, calcium fluoride, magnesium fluoride, sphalerite, and yttria-magnesia nanocomposites.

Druh

C - Kapitola v odborné knize

CEP obor

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OECD FORD obor

20504 - Ceramics

Projekt

<a href="/cs/project/GA18-17899S" target="_blank" >GA18-17899S: Částečně a plně slinutá keramika - příprava, mikrostruktura, vlastnosti, modelování a teorie slinování</a><br>

Návaznosti

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Rok uplatnění

2018

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Název knihy nebo sborníku

Polycrystalline Materials – Synthesis, Performance and Applications

ISBN

978-1-5361-3864-1

Počet stran výsledku

80

Strana od-do

99-178

Počet stran knihy

187

Název nakladatele

Nova Science Publishers, Inc.

Místo vydání

New York

Kód UT WoS kapitoly

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