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Borosilicate glass–alumina composites with (1 − x ) Glass + x Al 2 O 3 ( x = 0, 5, 10, 25 vol.%) were prepared and the effect of Al 2 O 3 addition on the structural, electrical and thermal characteristics was investigated. XRD patterns revealed the presence of cristobalite (SiO 2 ) in sintered borosilicate glass and that the addition of Al 2 O 3 hinders cristobalite formation. This behavior is due to the diffusion of some Al 3+ ions from alumina to glass, which leads to changes in glass structure and composition as identified by SEM/EDS. Cristobalite was undetected in composites containing 10% Al 2 O 3 that attained the lowest thermal expansion coefficient value (∼4.6 × 10 −6 °C −1 ). Conductivity (dc and ac) increased with the amount of Al 3+ ions present in the glass structure as modifiers and formers. Dielectric constant values, in the range 5.0–7.2, increased with Al 2 O 3 addition and the values of loss tan δ (1.5–2.1 × 10 −2 ) indicate that these materials are good insulators. |
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