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

Abstract

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

Electrical resistivity of silicon carbide ceramics sintered with 1 wt% aluminum nitride and rare earth oxide

“…46 Recently, SiC ceramics sintered with 2 wt% AlN-RE 2 O 3 (RE = Y, Er) showed an electrical resistivity of 7.2-8.1 × 10 −4 m at room temperature, 23 which was comparable to those of the specimens in the present study, with the exception of SLu. The SiC with 2 wt% AlN-Er 2 O 3 additive showed an electrical resistivity of 8.1 × 10 −4 m at room temperature, 23 whereas the electrical resistivity of the SEr specimen, which contained 1wt% AlN-Er 2 O 3 , was 5.9 × 10 −4 m at room temperature. These results suggest that a decrease in the additive content is beneficial in decreasing the electrical resistivity of SiC ceramics.…”

“…The enhanced densification in the specimens containing 5 wt% nano-sized SiC can be understood in terms of (1) the enhanced driving force of the powder compacts for densification due to the high surface area of nano-sized SiC and (2) the increased packing density of the specimens due to the addition of nano-sized to submicron-sized SiC. 23 The enhanced densification or almost complete densification at lower temperatures was observed when nano-sized SiC [26][27][28][29][30] or mechanically alloyed nano-sized SiC powders 20 were used as the starting material. Therefore, the addition of in situ-synthesized nano-sized SiC is beneficial for the densification of submicron-sized SiC with a small amount (1 wt%) of additives.…”

“…Hirata et al 22 sintered SiC ceramics with 2.14-2.40 wt% Al 2 O 3 -Y 2 O 3 additives by colloidal processing. Lim et al 23 was able to densify SiC ceramics with 2 wt% AlN-RE 2 O 3 (RE = Y, Er) by adding 5 wt% in situ-synthesized nano-sized SiC. 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.…”

Influence of Y2O3 addition on electrical properties of β-SiC ceramics sintered in nitrogen atmosphere

“…Polysiloxane and phenol resin were added to enhance densification of the samples by synthesizing nano-sized SiC particles. 24,25 The Y 2 O 3 content in the mixture of the raw materials was 3.1 wt% (3.1Y), 6.3 wt% (6.3Y), and 12.6 wt% (12.6Y). A baseline material without Y 2 O 3 was also fabricated (0Y).…”

High temperature strength of silicon carbide sintered with 1 wt.% aluminum nitride and lutetium oxide

“…Hirata et al 27 sintered SiC ceramics with 2.14-2.40 wt.% Al 2 O 3 -Y 2 O 3 additives by colloidal processing. Lim et al 28 In the present study, a SiC ceramic with 1 wt.% AlN-Lu 2 O 3 was fabricated by hot-pressing. Its grain boundary structure was characterized using HRTEM, and the high-temperature strength of the ceramic was investigated up to 1600 • C. The relative density of the hot-pressed specimen was determined using the Archimedes method.…”