Characterization of porous silicon nitride/silicon oxynitride composite ceramics produced by sol infiltration

Abstract

a b s t r a c tPorous silicon nitride/silicon oxynitride composite ceramics were fabricated by silica sol infiltration of aqueous gelcasting prefabricated Si 3 N 4 green compact. Silica was introduced by infiltration to increase the green density of specimens, so suitable properties with low shrinkage of ceramics were achieved during sintering at low temperature. Si 2 N 2 O was formed through reaction between Si 3 N 4 and silica sol at a temperature above 1550 • C. Si 3 N 4 /Si 2 N 2 O composite ceramics with a low linear shrinkage of 1.3-5.7%, a superior strength of 95-180 MPa and a moderate dielectric constant of 4.0-5.0 (at 21-39 GHz) were obtained by varying infiltration cycle and sintering temperature.

Fabrication and properties of porous boron nitride/silicon oxynitride ceramic composites via gas pressure sintering

“…Si 2 N 2 O grains exhibited typical elongated lath-like morphology [1]. Generally, the densification process was facilitated by increasing the amount of sintering additive [19,20]. However, in the present research, the density reached its maximum when Li 2 O increased from 5.0 mol% to 7.5 mol%.…”

“…Since porous ceramics were reported to have better thermal shock resistance [15,[18][19][20], porous BN/Si 2 N 2 O ceramic composites may exhibit a better resistance than the dense bodies. Therefore, the critical temperature difference (ΔT) of the porous BN/Si 2 N 2 O composites was expected to be increased to 1200°C or higher.…”

“…All specimens exhibit both low dielectric constant (ε b 4.49) and loss tangent (tanδ b 0.0056), which is acceptable for radome application. Generally, the dielectric constant of materials increases while loss tangent increases with the improvement of relative density, respectively [20].…”

“…Generally, porous ceramics have better thermal shock resistance and are easier to be machined into complex shapes than the dense ceramics [18][19][20]. Although BN/Si 2 N 2 O is a proper electro-magnetic wave penetrating material, little work has been done on preparation of porous BN/Si 2 N 2 O ceramics.…”

Mechanical and Dielectric Properties of Two Types of Si3N4 Fibers Annealed at Elevated Temperatures

“…The relationships between the imaginary part and conductivity of two Si 3 N 4 fibers corresponded reasonably with Equation (6). It is known that the dielectric constant and dielectric loss decrease as the porosity increases [39]. This was caused by the SiN x O y decomposition following annealing at 800 °C.…”