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常壓燒結한 SiC-ZrB₂ 電導性 複合體의 特性에 미치는 In Situ YAG의 影響
辛龍德(Yong-Deok Shin),朱陣榮(Jin-Young Ju),高台憲(Tae-Hun Ko),李政勳(Jung-Hoon Lee) 대한전기학회 2008 전기학회논문지 Vol.57 No.11
The effect of content of Al₂O₃+Y₂O₃ sintering additives on the densification behavior, mechanical and electrical properties of the pressureless-sintered SiC-ZrB₂ electroconductive ceramic composites was investigated. The SiC-ZrB₂ electroconductive ceramic composites were pressurless-sintered for 2 hours at 1,700[℃] temperatures with an addition of Al₂O₃+Y₂O₃(6 : 4 mixture of Al₂O₃ and Y₂O₃) as a sintering aid in the range of 8 ~ 20[wt%]. Phase analysis of SiC-ZrB₂ composites by XRD revealed mostly of α-SiC(6H), ZrB₂ and In Situ YAG(A1?Y₃O₁₂). The relative density, flexural strength, Young's modulus and vicker's hardness showed the highest value of 89.02[%], 81.58[㎫], 31.44[㎬] and l.34[㎬] for SiC-ZrB₂ composites added with 16[wt%] Al₂O₃+Y₂O₃ additives at room temperature respectively. Abnormal grain growth takes place during phase transformation from β-SiC into α-SiC was correlated with In Situ YAG phase by reaction between Al₂O₃ and Y₂O₃ additive during sintering. The electrical resistivity showed the lowest value of 3.14×10?²Ωㆍ㎝ for SiC-ZrB₂ composite added with 16[wt%] Al₂O₃+Y₂O₃ additives at 700[℃]. The electrical resistivity of the SiC-TiB₂ and SiC-ZrB₂ composite was all negative temperature coefficient resistance (NTCR) in the temperature ranges from room temperature to 700[℃]. Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites.
常壓燒結한 SiC-ZrB₂ 傳導性 複合體의 微細構造와 特性에 미치는 Annealing 溫度의 影響
辛龍德(Yong Deok Shin),朱陳榮(Jin Young Ju) 대한전기학회 2006 전기학회논문지C Vol.55 No.9
The effect of pressureless-sintered temperature on the densification behavior, mechanical and electrical properties of the SiC-ZrB₂ electroconductive ceramic composites was investigated. The SiC-ZrB₂ electroconductive ceramic composites were pressureless-sintered for 2 hours at temperatures in the range of 1,750~1,900[℃], with an addition of 12[wt%] of Al₂O₃+Y₂O₃(6:4 mixture of Al₂O₃ and Y₂O₃) as a sintering aid. The relative density and mechanical properties are increased markedly at temperatures in the range of 1,850~1,900[℃]. The relative density, flexural strength, vicker's hardness and fracture toughness showed the highest value of 81.1[%], 230[㎫], 9.88[㎬] and 6.05[㎫ㆍm½] for SiC-ZrB₂ composites of 1,900[℃] sintering temperature at room temperature respectively. The electrical resistivity was measured by the Pauw method in the temperature ranges from 25[℃] to 700[℃]. The electrical resistivity showed the value of 1.36×10?⁴, 3.83×10?⁴, 3.51×10?⁴ and 3.2×10?⁴[Ωㆍ㎝] for SZ1750, SZ1800, SZ1850 and SZ1900 respectively at room temperature. The electrical resistivity of the composites was all PTCR(Positive Temperature Coefficient Resistivity). The resistance temperature coefficient showed the value of 4.194×10?³, 3.740×10?³, 2.993×10?³, 3.472×10?³/[℃] for SZ1750, SZ1800, SZ1850 and SZ1900 respectively in the temperature ranges from 25[℃] to 700[℃]. It is assumed that because polycrystallines, such as recrystallized SiC-ZrB₂ electroconductive ceramic composites, contain of porosity and In Situ YAG(Al?Y₃O₁₂) crystal grain boundaries, their electrical conduction mechanism are complicated. In addition, because the condition of such grain boundaries due to Al₂O₃+Y₂O₃ additives widely varies with sintering temperature, electrical resistivity of the SiC-ZrB₂ electroconductive ceramic composites with sintering temperature also varies with sintering condition. It is convinced that β-SiC based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.
무가압 어닐드한 SiC-TiB₂ 전도성 복합체의 특성에 미치는 In Situ YAG의 영향
辛龍德(Yong-Deok Shin),朱陳榮(Jin-Young Ju),高台憲(Tae-Hun Ko) 대한전기학회 2008 전기학회논문지 Vol.57 No.5
The composites were fabricated 61[vol.%] β-SiC and 39[vol.%] TiB₂ powders with the liquid forming additives of 8, 12, 16[wt%] Al₂O₃+Y₂O₃ as a sintering aid by pressureless annealing at 1650[℃] for 4 hours. The present study investigated the influence of the content of Al₂O₃+Y₂O₃ sintering additives on the microstructure, mechanical and electrical properties of the pressureless annealed SiC-TiB₂ electroconductive ceramic composites. Reactions between SiC and transition metal TiB₂ were not observed in the microstructure and the phase analysis of the pressureless annealed SiC-TiB₂ electroconductive ceramic composites. Phase analysis of SiC-TiB₂ composites by XRD revealed mostly of α -SiC(6H), β-SiC(3C), TiB₂, and In Situ YAG(Al?Y₃O₁₂). The relative density of SiC-TiB₂ composites was lowered due to gaseous products of the result of reaction between SiC and Al₂O₃+ Y₂O₃. There is another reason which pressureless annealed temperature 1650[℃] is lower 300-450[℃] than applied pressure sintering temperature 1950-2100[℃]. The relative density, the flexural strength, the Young's modulus and the Vicker's hardness showed the highest value of 82.29[%], 189.5[Mpa], 54.60[Gpa] and 2.84[Gpa] for SiC-TiB₂ composites added with 16[wt%] Al₂O₃+Y₂O₃ additives at room temperature. Abnormal grain growth takes place during phase transformation from β-SiC into α-SiC was correlated with In Situ YAG phase by reaction between Al₂O₃ and Y₂O₃ additive during sintering. The electrical resistivity showed the lowest value of 0.0117[Ω. ㎝] for 16[wt%] Al₂O₃+Y₂O₃ additives at 25[℃]. The electrical resistivity was all negative temperature coefficient resistance (NTCR) in the temperature ranges from 25℃ to 700[℃]. The resistance temperature coefficient of composite showed the lowest value of -2.3×10?³[℃]?¹ for 16[wt%] additives in the temperature ranges from 25[℃] to 100[℃].