Processing of high performance silicon carbide

2012

Four types of commercially available SiC powders were hot-pressed with 1 wt % Dy 2 O 3 AlN additives in a 3:2 molar ratio. Three submicron-sized SiC powders could be densified so as to have a relative density higher than 98%, whereas a micron-sized SiC powder showed limited densification up to 93.5%. SiC ceramics fabricated from ¢-SiC powders exhibited electrical resistivities (³10 ¹1 ³·cm) that were lower than those from ¡-SiC powders (³10 1 ³·cm). The lower electrical resistivity of the SiC ceramics fabricated from ¢-SiC powders could be attributed to a higher carrier density and enhanced charge mobility when compared to the SiC ceramics from ¡-SiC powders.©2012 The Ceramic Society of Japan. All rights reserved.Key-words : SiC, Sintering, Electrical resistivity [Received January 5, 2012; Accepted February 28, 2012] Silicon carbide (SiC) is considered to be a suitable material for various structural applications such as mechanical seals, bearings, cylinder liners, armor plates, and mirror materials for astronomical telescopes due to its superior properties of high hardness, high temperature strength, and excellent resistance to wear and corrosion.1)6) In addition, SiC ceramics with or without a small amount of additives have attracted considerable attention for use in semiconductor processing, nuclear fusion reactors, and high temperature thermomechanical applications because of their excellent chemical and thermal stability and good mechanical properties.7)11) In the mid 1970s, Lange 12) first reported on the successful densification of SiC by liquid-phase sintering with the addition of Al 2 O 3 as a sintering additive. Since this innovative work, interest in liquid-phase sintered (LPS)-SiC has grown continuously because such materials exhibit better mechanical properties than solid-state sintered SiC ceramics.2),6),13)17) Methods for the successful densification of SiC ceramics with a smaller amount of sintering additives via liquid-phase sintering include (1) the use of colloidal processing for the homogeneous distribution of sintering additives 18),19) and (2) the addition of in situsynthesized nano-sized SiC into submicron-sized SiC powders. 20) In this study, the sinterability of four different commercially available SiC powders was investigated with the addition of 1 wt % AlNDy 2 O 3 additives by hot pressing. The effect of the SiC powder characteristics on the electrical resistivity of the hot-pressed SiC ceramics was also investigated. The AlNDy 2 O 3 additive system was selected because of the success of previous research on the densification of SiC with AlN-rare earth oxide systems 4),11) and the good chemical stability of Dy 2 O 3 at high temperatures in the presence of SiC. 21)Four types of commercially available SiC powders were used as starting materials; their characteristics are shown in Table 1. The crystalline phase of powders A1 and A2 is ¡-SiC, while that of B1 and B2 is ¢-SiC. 22) The mixtures were dried, sieved (60 mesh), pressed uniaxially, and heat-treated at 200°C for 2 h in air so ...

mentioning

confidence: 99%

Influence of powder characteristics on the electrical resistivity of SiC ceramics

Lim

2012

“…Liden et al 16) sintered SiC ceramics with 3 wt % additives (2 wt % Al 2 O 3 and 1 wt % Y 2 O 3 ) by collidal processing. Hirata et al 17) also sintered SiC ceramics with 2.86 wt % additives (1.44 wt % Al 2 O 3 and 1.42 wt % Y 2 O 3 ) by collidal processing. Kumar et al 6) sintered SiC ceramics with 3 wt % RE 2 O 3 AlN additives (RE = Sc, Lu, Y).…”

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confidence: 99%

Effect of in situ-synthesized nano-size SiC addition on density and electrical resistivity of liquid-phase sintered silicon carbide ceramics

Lim

et al. 2011

Submicron-size SiC ceramics were sintered to densities >97% of the theoretical density by adding 5 wt % in situ-synthesized nano-size SiC and 2 wt % AlNRE 2 O 3 (RE = Y, Er). The SiC ceramics showed very low electrical resistivity in an order of 10 ¹4 ³·m. This low electrical resistivity was attributed to the smaller amount (2 wt %) of sintering additives addition and their microstructural characteristics, i.e., growth of nitrogn-doped SiC grains and the confinment of non-conducting Y-and Er-containing phases in the junction areas.©2011 The Ceramic Society of Japan. All rights reserved.Key-words : SiC, Sintering, Electrical resistivity [Received June 15, 2011; Accepted September 20, 2011] Silicon carbide (SiC) ceramics with a small amount of additives or without additives have attracted considerable attention for use in semiconductor processing, nuclear fusion reactors, and high temperature thermomechanical applications because of their excellent chemical and thermal stability and good mechanical properties.1)8) In the early 1980 s, Omori and Takei 9) reported an innovative approach to fully densify SiC at temperatures as low as 1850°C via liquid-phase sintering by adding rare earth oxides to the starting powder. Since this innovative work, interest in liquidphase sintered (LPS)-SiC has grown continuously, becausae LPSSiC ceramics show better mechanical properties than solid-state sintered SiC ceramics. sintered SiC ceramics with 3 wt % RE 2 O 3 AlN additives (RE = Sc, Lu, Y). SiC ceramics sintered with a smaller amount of additives would be more beneficial for applications in semiconductor processing and nuclear fusion reactors because of their better chemical and thermal stability.In this study, the sinterability of SiC ceramics with 2 wt % additives (RE 2 O 3 AlN, RE = Y, Er) was investigated with or without 5 wt % in-situ-synthesized nano-size SiC addition. The electrical resistivity of the resulting SiC ceramics was also investigated.For SiC with 2 wt % additives, submicron ¢-SiC (Ultrafine, Betarundum, Ibiden Co. Ltd.), polysiloxane (1036 kg/m 3 , GE Toshiba Silicones Co., Ltd., Tokyo, Japan), phenol resin (1090 kg/m 3 , Kangnam Chemical Co. Ltd., Incheon, Korea), Y 2 O 3 (99.9%, Kojundo Chemical Lab Co. Ltd., Sakado, Japan), Er 2 O 3 (99.9%, Kojundo Chemical Lab Co. Ltd., Sakado, Japan) and AlN (grade B, H. C. Starck, Berlin, Germany) were mixed at the weight ratio shown in Table 1 by ball milling using SiC balls and a polypropylene jar for 24 h in ethanol. The AlN:RE 2 O 3 molar ratio was 3:2. The mixtures were dried, sieved (60 mesh), pressed uniaxially and heat-treated at 200°C for 2 h in air to cross-link the polysiloxane in the mixture. The compact was heat-treated at 1450°C for 1 h and hot-pressed at 2050°C for 6 h under 40 MPa in an atmospheric pressure of nitrogen.The relative densities of the hot-pressed specimens were determined using the Archimedes method. The theoretical densities of each specimen were calculated according to the rule

“…Therefore, sintering additives, such as metals, oxides, and non-oxides, are usually added to densify SiC ceramics. 1)3) Among the compositions investigated as sintering additives, Al 2 O 3 Y 2 O 3 CaO (AYC) was found to be most effective in the development of an in situ-toughened microstructure at low temperatures 4) as well as the crystallization of the grain boundary phases. 5) In addition, the SiC ceramics sintered with AYC additives showed crack healing ability after heat-treatment at 1100°C for 1 h in air.…”

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confidence: 99%

Processing of porous silicon carbide with toughened strut microstructure

Eom

Narisawa

2010

Porous SiC ceramics were fabricated by the carbothermal reduction of polysiloxane-derived SiOC containing hollow microspheres followed by sintering. The effect of the Al 2 O 3 Y 2 O 3 CaO (AYC) content on the microstructure and flexural strength of the porous SiC ceramics were investigated. The growth of large platelet ¡-SiC grains increased with increasing additive content due to enhanced grain growth and the ¢ ¼ ¡ phase transformation of SiC. In situ toughened microstructures consisting of large platelet grains and fine equiaxed grains were obtained when 10 or 20 wt% AYC was added. The porosity generally decreased with increasing the additive content, whereas the flexural strength increased. The typical flexural strength of the porous SiC ceramics sintered with 10 wt% AYC was 61 MPa at a porosity of 44%.