Densification and dielectric properties of SrO-Al sub(2)O sub(3)&#x20 13; B sub(2)O sub(3) ceramic bodies

The influence of SrO (0.0-5.0 wt%) on partial substitution of alpha alumina (corundum) in ceramic composition (95 Al sub(2)O sub(3)-5B sub(2)O sub(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 ( epsilon sub(r)), quality factor (Q f) and temperature coefficient of resonant frequency ( tau sub(f)) were measured in the microwave frequency region using a network analyser by the resonance method. The addition of B sub(2)O sub(3) and SrO significantly reduced the sintering temperature of alumina ceramic bodies to 1600 degree C with optimum density ( 4g/cm super(3)) as compared with pure alumina powders recycled from Al dross (3.55g/cm super(3) sintered at 1700 degree 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 ( tau sub(f)) in the -69 to -83 ppm/ degree C range. The addition of SrO up to 5wt% leads to a maximum ( epsilon sub(r)) value (29) due to relatively higher ionic polarizability of Sr super(2+) than that of the Al super(3+) and B super(3+) ions. On the other hand, changing chemical and phase composition with the formation of platelets of Sr-hexaluminate phase (SrAl sub(12)O sub(19)) results in maximizing value of (Q f) up to 22,020 GHz at approximately 8 GHz and large negative charge of ( tau sub(f)) to -83 ppm/ degree C.