| Abstract Scope |
Boron nitride (BN) polycrystalline ceramics with high density were prepared without any other sintering additives. Boron nitride powders were modified by the high-energy ball-milling, making crystalline transition from hexagonal to turbostratic style partly and improve the sintering activity greatly. The dielectric properties, such as permittivity and loss tangent, are measured from very low frequency to very high frequency in details. Especially, the dielectric properties in microwave frequency range (1-18 GHz) were measured from room temperature up to 800 Celsius degree by and the stripline resonantor method and high Q resonance cavity method, and gain many important dielectric data in high temperature. The permittivity is about 4.3 and the dielectric loss is about 10-4 to 10-3 order of magnitude in the microwave frequency range from 7GHz to 18GHz and under 800 degree. The properties with Bending strength, fracture toughness and ablation were also measured for application, and prove very well. |