Influence of the Silicon Carbide Particle Size on Dielectric Characteristics, Thermal Conductivity, and Microwave Absorption of Pressureless-Sintered AlN–(20–50)% SiC Composites

• Published in: Powder metallurgy and metal ceramics 2022-05, Vol.61 (1-2), p.50-59
• Main Authors: Chasnyk, V.I., Kaidash, O.M., Vovk, L.M., Fesenko, I.P.
• Format: Article
• Language: English
• Subjects: Absorbers; Absorptance; Absorptivity; Aluminum compounds; Analysis; Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Composite materials; Composites; Delay lines; Dielectric loss; Dielectric properties; Dielectrics; Electric waves; Electromagnetic radiation; Electromagnetic waves; Electromagnetism; Functional materials; Glass; Heat conductivity; Heat transfer; Materials Science; Measurement methods; Metallic Materials; Microwave absorption; Microwave attenuation; Natural Materials; Nitrides; Permittivity; Refractory and Ceramic Materials; Resonators; Silicon; Silicon carbide; Sintering; Thermal conductivity; Traveling wave tubes; Traveling waves; Voltage standing wave ratios; Wave attenuation
• ISSN: 1068-1302; 1573-9066
• DOI: 10.1007/s11106-022-00294-w

The application of ceramic dielectrics in various microwave electronic instruments and devices is determined by their properties such as dielectric constant, dielectric loss factor, thermal conductivity, and absorptance. Alumina nitride composites with dielectric losses (high dielectric loss tangent tgδ varying from 0.1 to 0.6 ) are promising functional materials, but there are few publications with detailed dielectric characteristics including thermal conductivity, which is especially important for devices with high output power. To determine the dielectric characteristics (ε′ and tgδ), the resonance measurement method with a cylindrical resonator was employed. The electromagnetic energy absorptance L (attenuation in a bulk absorber with respect to absorber length) was used to compare absorbers of different sizes. Microwave attenuation in the absorber ring located in a resonator of the delay line of the traveling-wave tube model was measured employing a P2-61 panoramic meter for voltage standing wave ratio and attenuation. Experimental values of the real and imaginary ε′′ parts of the complex dielectric constant in pressureless-sintered AlN–SiC composites with different contents and sizes of semiconducting silicon carbide particles are presented. When SiC increases from 20 to 50% in the AlN-based composite, ε′ becomes 1.7–2.1 times higher and ε′′ 5.4–6.8 times higher. The smaller the SiC particles, the greater the increase in ε′ and ε′′, silicon carbide content being the same. The relationship between the thermal conductivity and electromagnetic energy absorptance in the AlN–SiC composites was studied. The range of compromise values was found: they combine relatively high thermal conductivity, 45–55 W/(m · K), and significant absorptance, L = 2.8–3.5 dB/mm, corresponding to the highest silicon carbide content (40–50%) and microsized SiC particles (2.3–4.4 μm). A relationship was established between the imaginarabsorptance L(dB/mm) = 2.8 ɛ ′ ′ 2 , allowing the absorptance to be determined from known ε′′ at a frequency of 3.3 GHz.