Jin-Young Ju

The Development of an Electroconductive SiC-ZrB 2 Composite through Spark Plasma Sintering under Argon Atmosphere

The SiC-ZrB2 composites were fabricated by combining 30, 35, 40, 45 and 50 vol. % of zirconium diboride (ZrB2) powders with silicon carbide (SiC) matrix. The SiC-ZrB2 composites and the sintered compacts were produced through spark plasma sintering (SPS) under argon atmosphere, and its physical, electrical, and mechanical properties were examined. Also, the thermal image analysis of the SiC-ZrB2 composites was examined. Reactions between β-SiC and ZrB2 were not observed via x-ray diffraction (XRD) analysis. The apparent porosity of the SiC+30vol.%ZrB2, SiC+35vol.%ZrB2, SiC+40vol.%ZrB2, SiC+45vol.%ZrB2 and SiC+50vol.%ZrB2 composites were 7.2546, 0.8920, 0.6038, 1.0981, and 10.0108%, respectively. The XRD phase analysis of the sintered compacts demonstrated a high phase of SiC and ZrB2. Among the SiC+ZrB2 composites, the SiC+50vol. %ZrB2 composite had the lowest flexural strength, 290.54MPa, the other composites had more than 980MPa flexural strength except the SiC+30vol.%ZrB2 composite; the SiC+40vol.%ZrB2 composite had the highest flexural strength, 1011.34MPa, at room temperature. The electrical properties of the SiC-ZrB2 composites had positive temperature coefficient resistance (PTCR). The V-I characteristics of the SiC-ZrB2 composites had a linear shape in the temperature range from room to 500℃. The electrical resistivities of the SiC+30vol.%ZrB2, SiC+35vol.%ZrB2, SiC+40vol.%ZrB2 SiC+45vol.%ZrB2 and SiC+50vol.%ZrB2 composites were 4.573×10 -3 , 1.554×10 -3 , 9.365×10 -4 , 6.999×10 -4 , and 6.069×10 -4 Ω·cm, respectively, at room temperature, and their resistance temperature coefficients were 1.896×10 -3 , 3.064×10 -3 , 3.169×10 -3 , 3.097×10 -3 , and 3.418×10 -3 /℃ in the temperature range from room to 500℃, respectively. Therefore, it is considered that among the sintered compacts the SiC+35vol.%ZrB2, SiC+40vol.%ZrB2 and SiC+45vol.%ZrB2 composites containing the most outstanding mechanical properties as well as PTCR and V-I characteristics can be used as an energy friendly ceramic heater or ohmic-contact elec- trode material through SPS.

The Development of an Electroconductive SiC-ZrB 2 Ceramic Heater through Spark Plasma Sintering

The SiC-ZrB₂ composites were fabricated by combining 30, 35, 40 and 45vol.% of Zirconium Diboride (hereafter, ZrB₂) powders with Silicon Carbide (hereafter, SiC) matrix. The SiCZrB₂ composites, the sintered compacts, were produced through Spark Plasma Sintering (hereafter, SPS), and its physical, electrical, and mechanical properties were examined. Also, the thermal image analysis of the SiC-ZrB₂ composites was examined. Reactions between β-SiC and ZrB₂ were not observed via X-Ray Diffractometer (hereafter, XRD) analysis. The relative density of the SiC+30vol.%ZrB₂, SiC+35vol.%ZrB₂, SiC+40vol.%ZrB₂, and SiC+45vol.%ZrB₂ composites were 88.64%, 76.80%, 79.09% and 88.12%, respectively. The XRD phase analysis of the sintered compacts demonstrated high phase of SiC and ZrB₂ but low phase of ZrO₂. Among the SiC-ZrB₂ composites, the SiC+35vol.%ZrB₂ composite had the lowest flexural strength, 148.49㎫, and the SiC+40vol.%ZrB₂ composite had the highest flexural strength, 204.85㎫, at room temperature. The electrical resistivities of the SiC+30vol.%ZrB₂, SiC+35vol.%ZrB₂, SiC+40vol.%ZrB₂ and SiC+45vol.%ZrB₂ composites were 6.74×10?⁴, 4.56×10?³, 1.92×10?³, and 4.95×10?³Ωㆍ㎝ at room temperature, respectively. The electrical resistivities of the SiC+30vol.%ZrB₂, SiC+35vol.%ZrB₂ SiC+40vol.%ZrB₂ and SiC+45[vol.%]ZrB₂ composites had Positive Temperature Coefficient Resistance (hereafter, PTCR) in the temperature range from 25℃ to 500℃. The V-I characteristics of the SiC+40vol.%ZrB₂ composite had a linear shape. Therefore, it is considered that the SiC+40vol.%ZrB₂ composite containing the most outstanding mechanical properties, high resistance temperature coefficient and PTCR characteristics among the sintered compacts can be used as an energy friendly ceramic heater or electrode material through SPS.

A Study on Optimum Spark Plasma Sintering Conditions for Conductive SiC-ZrB2 Composites

Conductive SiC-ZrB2 composites were produced by subjecting a 40:60 (vol%) mixture of zirconium diboride (ZrB2) powder and β-silicon carbide (SiC) matrix to spark plasma sintering (SPS). Sintering was carried out for 5 min in an argon atmosphere at a uniaxial pressure and temperature of 50 MPa and 1500 °C, respectively. The composite sintered at a heating speed of 25 °C/min and an on/off pulse sequence of 12:2 was denoted as SZ12L. Composites SZ12H, SZ48H, and SZ10H were obtained by sintering at a heating speed of 100 °C/min and at on/off pulse sequences of 12:2, 48:8, and 10:9, respectively. The physical, electrical, and mechanical properties of the SiC-ZrB2 composites were examined and thermal image analysis of the composites was performed. The apparent porosities of SZ12L, SZ12H, SZ48H, and SZ10H were 13.35%, 0.60%, 12.28%, and 9.75%, respectively. At room temperature, SZ12L had the lowest flexural strength (286.90 MPa), whereas SZ12H had the highest flexural strength (1011.34 MPa). Between room temperature and 500 °C, the SiC-ZrB2 composites had a positive temperature coefficient of resistance (PTCR) and linear V-I characteristics. SZ12H had the lowest PTCR and highest electrical resistivity among all the composites. The optimum SPS conditions for the production of energy-friendly SiC-ZrB2 composites are as follows: 1) an argon atmosphere, 2) a constant pressure of 50 MPa throughout the sintering process, 3) an on/off pulse sequence of 12:2 (pulse duration: 2.78 ms), and 4) a final sintering temperature of 1500 °C at a speed of 100 °C/min and sintering for 5 min at 1500 °C.