Microstructure stability of fine-grained silicon carbide ceramics during annealing

Lee, Young-Il; Kim, Young‐Wook; Mitomo, Mamoru

doi:10.1023/b:jmsc.0000030713.40220.07

Cited by 30 publications

(21 citation statements)

References 23 publications

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“…3a) the primary crystalline phase is a-SiC and the secondary phase consists of yttrium aluminum garnet (YAG) oxides and magnesia spinel (MS), but small quantities of mutually miscible phases could exist. Analysis of SiC for the content of polytypes showed the presence of a large quantity of 6H-SiC before and after sintering (Table 4); this is confirmed by many studies where a-SiC and b-SiC powders were sintered with oxide additives [13,14].…”

Section: Resultssupporting

confidence: 67%

Mechanism of Liquid-Phase Sintering of Silicon Carbide and Nitride with Oxide Activating Additives

Перевислов

2013

Glass Ceram

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The mechanism of sintering and the particulars of structure formation in liquid-phase-sintered silicon carbide and sintered silicon nitride were studied. The formation of the structure core (SiC or Si 3 Ni 4 grains) -boundary layer (SiC oxide or SiAlON) -intergrain phase (oxides) was recorded.Owing to their high strength and hardness, good stability against oxidation and resistance to thermal shock as well possibilities for retaining mechanical properties at high temperatures silicon carbide based ceramic materials are widely used as construction materials in many areas of technology. Silicon carbide belongs to a class of compounds with strong covalent bonds, which impedes mass transfer during sintering without the use of special additives. Ordinarily, dense SiC-ceramic is obtained by means of liquid-phase sintering with oxide additives. The most promising ones are Al 2 O 3 , Y 2 O 3 and MgO, which promote the formation of melt and sintering by the liquid-phase method during heat-treatment [1].A model of the formation of SiC-grain structure consisting of nuclei with a boundary layer on their surface is presented in [2]. The presence of the elements Y, Al and O in the boundary layer of silicon carbide grains was determined by metallographic methods. A detailed study of the mechanism of dissolution -recrystallization during liquid-phase sintering of silicon carbide with a sintering additive consisting of yttrium aluminum garnet is presented in [2,3].A similar model of the structure nucleus -boundary layer -intergrain phase is characteristic for many ceramic systems, which Si 3 N 4 /SiAlON, BaTiO 3 -based solid alloys and carbonitrides with Co-and Ni-binder are [4,5].The formation of an amorphous boundary phase on silicon nitride grains was discovered during sintering of the composition Si 3 N 4 -MgO [6,7]. The model developed for sintering of silicon nitride with oxide additives [8,9] showed the formation of an amorphous film of the order of 1 -2 nm thick on silicon nitride grains; this is a result of attractive (Van der Waals) forces acting between grains and repulsive (capillary) forces at the boundary of a grain and the oxide additive. Subsequently, it was shown that a SiAlON boundary layer forms on Si 3 N 4 nuclei during sintering of Si 3 N 4 with the addition of aluminum-nitrate garnet 3Y 2 O 3 × 5Al 2 O 3 [10,11].The present work is devoted to a more detailed study of the mechanism of liquid-phase sintering of the carbide LPSSiC and silicon nitride SSN with oxide sintering additives in the system Al 2 O 3 -Y 2 O 3 -MgO. MATERIALS AND METHODSThe following powders were used: SiC (Volzhsk Abrasives Plant, Volzhsk), comminuted in a jet mill to particle size d 0.5 = 0.85 mm; Si 3 N 4 , LS-12 grade (Berlin, Germany), obtained by furnace sintering, average particle diameter d 0.5 = 0.75 mm (Table 1). The oxides Al 2 O 3 , Y 2 O 3 and MgO were used as sintering additives; they were added in a strictly eutectic ratio in accordance with the phase diagram of the ternary system MgO-Y 2 O 3 -Al 2 O 3 along the garnet-spin...

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Section: Resultssupporting

confidence: 67%

Mechanism of Liquid-Phase Sintering of Silicon Carbide and Nitride with Oxide Activating Additives

Перевислов

2013

Glass Ceram

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“…However, the sintered densities of these specimens were somewhat lower than those of the specimens fabricated from submicron powders. 17 It has been reported that the powder characteristics have a large influence on the sintering behavior of SiC ceramics. 12 ,18 With solid-state sintering, the presence of free carbon is beneficial, because it reacts with the SiO 2 present on the surface of the SiC particles.…”

Section: Resultsmentioning

confidence: 99%

Sinterability of Nano-Sized Silicon Carbide Powders

Kim

Lee

Mitomo

2006

J. Ceram. Soc. Japan

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The sinterability of three kinds of commercially available nano-sized SiC powders and a treated nano-sized SiC powder was investigated using Al 2 O 3 -Y 2 O 3 -CaO as a sintering additive. The commercially available, as-received nano-sized SiC powders were difficult to sinter to a relative density of 95! by conventional hot pressing. The effects of the free carbon and SiO 2 impurities in the starting powders on the sinterability of the nano-sized SiC powders were identical to those on the submicron SiC powders. However, both the extremely high free carbon content and low green density of the commercially available nano-sized SiC powders were responsible for their poor sinterability. The reduction of the free carbon content by oxidation and the control of the SiO 2 content by acid treatment were beneficial for enhancing the sinterability of the nano-sized SiC powder during liquid-phase sintering.

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“…without fibers, to discern the appropriate hot-pressing conditions. According to previous studies [14,15], Al 2 O 3 -Y 2 O 3 -CaO (AYC) can be used as an additive to sinter monolithic SiC at temperatures as low as 1750 o C. Furthermore, AYC can be crystallized easily without subsequent heat treatment after sintering [16]. For the composite fabrication, the densification process slowed after including fiber in the matrix, as indicated in Fig.…”

Section: Resultsmentioning

confidence: 99%

Process for dense 2D SiC fiber-SiC matrix composites

et al. 2007

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A new process using SiC fiber fabrics and SiC tapes to produce dense 2D SiC fiber-SiC (SiC/SiC) composites is demonstrated. The strategy for fabricating the SiC/SiC composites involves: (i) alternately stacking the SiC fiber fabrics and SiC tapes at room temperature, (ii) pyrolyzing of the stacked composites, and (iii) hot-pressing the pyrolyzed composites. By controlling the hot-pressing temperature, it is possible to obtain dense 2D SiC/SiC composites with relative densities of > 98 %. The 2D SiC/SiC composites show no degradation of the SiC fibers and a higher mechanical strength.

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Microstructure stability of fine-grained silicon carbide ceramics during annealing

Cited by 30 publications

References 23 publications

Mechanism of Liquid-Phase Sintering of Silicon Carbide and Nitride with Oxide Activating Additives

Mechanism of Liquid-Phase Sintering of Silicon Carbide and Nitride with Oxide Activating Additives

Sinterability of Nano-Sized Silicon Carbide Powders

Process for dense 2D SiC fiber-SiC matrix composites

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