Dielectric Properties of Wollastonite and Pseudo-wollastonite

HAYASHI Kunio, FUKUI Masao, UEI Isao

doi:10.2109/jcersj1950.89.1028_165

It was suggested by Jackson that higher firing temperature would destroy the dielectric properties of wollastonite ceramics by the conversion of wollastonite (β-type) into pseudowollastonite (α-type). To confirm the possible causes of the destruction of the dielectric properties of wollastonite ceramics, the dielectric constant (ε) and dissipation factor (tanδ) of β-wollastonite obtained on two different methods (that is, a powder dispersion method and measurements using hot pressed bodies) were compared with those of α-wollastonite.<br>It was found that the β-wollastonite powder obtained on firing the glass with CaO⋅SiO₂ composition at 1000°C for 2 hours has good dielectric properties (ε=6.5, tanδ=4.2×10^-4) and the α-wollastonite powder obtained on firing the same glass at 1400°C for 2 hours also has similar properties (ε=8.6, tanδ=5.0×10^-4). ε and tanδ of the β-wollastonite bodies fabricated by hot pressing the glass powders with composition of CaO⋅SiO₂ added 1wt% of Al₂O₃ were found to be 7.4 and 3.9×10^-4, and those of the α-wollastonite bodies fabricated by hot pressing the α-wollastonite powders to be 8.4 and 4.4×10^-4, respectively. From the results of these measurements, no difference in the dielectric properties between β- and α-wollastonite was recognized.<br>It was supposed through the observation by optical microscope that the destruction in the dielectric properties of wollastonite ceramics fired at high temperatures was due to the microcracks produced in the glass matrix of sintered bodies by the difference of thermal expansion coefficient between α-wollastonite crystals and the glass matrix during cooling.

Dielectric Properties of Wollastonite and Pseudo-wollastonite

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