Silicon nitride-BAS composites

A low cost-high performance silicon nitride-BAS composite can be fabricated via pressureless sintering. In this composite, the BAS glass-ceramic serves as an effective liquid-phase-sintering aid, to attain full densification and complete the a-(3 Si,iN4 phase transformation, and remains as a structural matrix that is reinforced by the silicon nitride whiskers, Si3N4 whiskers grow in random directions in a near completely crystallized matrix of hex-acelsian BAS. 

TABLE 4. Grain size distributions for the Si3N4-BAS composite from different ratio of starting silicon nitride powders with their indentation fracture toughness and flexural strength... 

Development of the S13N4-BAS composite combines excellent mechanical properties of silicon nitride with the excellent electrical properties of barium aluminosilicate (BAS). When totally isotropic and randomly reinforced, the electrical performance of composite is greatly enhanced. The dielectric constant of the composite at room temperature is 7.3 and increases linearly to 8.6 at 1400°C, at a constant 35 GHz . The values measured fall between those of hot pressed silicon nitride and BAS. A loss tangent value of 0.0003 has been measured at room temperature . 

---