Densification and dielectric properties of SrO–Al2O3–B2O3 ceramic bodies

Abstract

The influence of SrO (0·0-5·0 wt%) on partial substitution of alpha alumina (corundum) in ceramic composition (95 Al 2 O 3 -5B 2 O 3 ) have been studied by co-precipitated process and their phase composition, microstructure, microchemistry and microwave dielectric properties were studied. Phase composition was revealed by XRD, while microstructure and microchemistry were investigated by electron-probe microanalysis (EPMA). The dielectric properties by means of dielectric constant (ε r ), quality factor ( Q× f ) and temperature coefficient of resonant frequency (τ f ) were measured in the microwave frequency region using a network analyser by the resonance method. The addition of B 2 O 3 and SrO significantly reduced the sintering temperature of alumina ceramic bodies to 1600 • C with optimum density (∼ 4 g/cm 3 ) as compared with pure alumina powders recycled from Al dross (3·55 g/cm 3 sintered at 1700 • C).The sintered ceramic bodies show different ranges for the dielectric properties. Dielectric constant exists between 24 and 29, quality factor ( Q × f ) is ranging between 15,236 and 22,020 GHz with a slight increase than those recorded with commercial alumina (10,000 -20,000 GHz) and temperature coefficient of resonant frequency (τ f ) in the -69 to -83 ppm/ • C range. The addition of SrO up to 5 wt% leads to a maximum (ε r ) value (29) due to relatively higher ionic polarizability of Sr 2+ than that of the Al 3+ and B 3+ ions. On the other hand, changing chemical and phase composition with the formation of platelets of Sr-hexaluminate phase (SrAl 12 O 19 ) results in maximizing value of ( Q × f ) up to 22,020 GHz at ≈ 8 GHz and large negative charge of (τ f ) to -83 ppm/ • C.

Microwave dielectric properties of SnO‐SnF2‐P2O5 glass and its composite with alumina for ULTCC applications

“…There is an increased demand for new materials with attractive dielectric properties in the areas of wireless communication, satellite communication, electronic memory devices, and so on. 1,2 Low-temperature cofired ceramic technology (LTCC) is a well-established multilayer technology having numerous applications. 3 At present, extensive research is being carried out to develop new materials having sintering temperature less than 700°C.…”