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The effects of B2O3 and P2O5 on the crystallization behavior and
dielectric properties of sol-
gel prepared stoichiometric cordierite and anorthite were
studied. From the results, it was
found that both B2O3 and P2O5 in the cordierite would promote
the formation of α- cordierite. And the addition
of P2O5 could also cause the densification of cordierite.
However, these additions had little influences on the dielectric
constant and loss tangent of stoichiometric cordierite.
Contrastingly, only the additions of B2O3 to the stoichiometric
anorthite promoted the formation of the triclinic phase.
Addition of P2O5 did not affect the crystallization of
anorthite. Both bulk densities and the dielectric constants of
sintered anorthite decreased with the increase of B2O3 and P2
O5. In addition, gel-
derived cordierite glass powder with composition of
MgO/Al2O3/SiO2=25/22/53 were prepared and mixed with gel-derived
stoichiometric anorthite glass powder with
various weight percentages and sintered to form cordierite-
anorthite composites. Composites of the same compositions were
also prepared by sol-gel of Ca-Mg-Al-Si four components
system. In these composites, it was found that cordierite
could promote the formation of the triclinic phase of anorthite
and anorthite could enhance the formation of α-cordierite
regardless of the preparation method. SEM and EDS analyses
showed that spherical anorthite were surrounded by cordierite in
the anorthite-rich samples. The wetting between anorthite and
cordierite appeared to be good. This would result in good
sinterability in the cordierite-anorthite system. The samples
prepared by sol-gel process howshow better relationships
between properties and compositions than those by powder mixing
process. The densities of the cordierite-anorthite glass
ceramics prepared by sol-gel process were between 2.2 and 2.7 g/
cm3, and the dielectric constants (5.4∼7.0) lineally increased
with the weight percentage of the anorthite. When cordierite-
anorthite glass ceramics contained 20 to 60wt% of
anorthite, the samples showed low thermal expansion
coefficients:4.0∼4.5×10-6/℃ at 100℃, and 2.5∼4.0×10-6/℃
at 200℃.
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