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Abstract

The study presents the influence of increasing the amount of β-spodumene (LiAlSi2O6) as Li2O-content
flux on phase composition, microstructural evolution and physical properties of high alumina porcelain
material containing ~61% of Al2O3.
New porcelain compositions based on clays and high amount of calcined alumina were developed with
the introduction of Li2O in combination with K2O as flux. Sintering behaviour, phase composition,
microstructure and physical properties of new compositions were investigated in comparison with reference
composition containing K2O and Na2O as flux. Li2O was added in the amount of 1.0, 1.2 and 1.6 wt.% via
calcined commercial spodumene concentrate. Conventional ceramic processing routes comprising wet
milling and extrusion technique were used to prepare the test samples, which were fired in the laboratory
furnace at seven selected temperatures in temperature range 950 1350 °C and in the industrial gas kiln at
1315 °C.
Li2O-bearing compositions reach higher degree of densification at lower temperature in comparison to
reference composition. The influence on densification is greater with the amount of Li2O increasing.
During heat treatment the phase composition of bodies is influenced by the amount of Li2O added. It is
evident, that the diminishing of quartz at the presence of Li2O in temperature range 1150 to 1250 °C is due
to quartz reaction with -spodumene forming lithium aluminium silicates. The first reaction product is
LiAlSi3O8. The reaction at higher temperature leads to the formation of LixAlxSi1-xO2, when the amount of
Li2O is 1.6 wt.%. In the process of quartz reaction with lithium compounds lithium aluminium silicates
with higher amount of SiO2 are formed. The presence of lithium minerals, which are characteristic by low
thermal expansion, contributes to the lower CTE of bodies containing Li2O.
Homogeneous microstructure, high bulk density and absence of quartz contribute to improved flexural
strength of compositions with 1.0 and 1.2 wt. % of Li2O fired at 1300 °C. When fired at higher temperature
all compositions containing Li2O attain noticeably lower flexural strength mainly due to bloating
phenomena, which increases with the increasing amount of Li2O as obvious from bulk density decrement.
The increasing amount of Li2O greatly affects the deformation during firing in industrial gas kiln, which
considerably increases with the increasing amount of Li2O. Under the existent firing schedule in industrial
kiln the most favourable mechanical and thermal characteristics in view of industrial perspective are
attained by composition with 1.0 wt. % Li2O.
Our investigations of Li2O as the main flux constituent in high alumina porcelain bodies show that Li2O
is a strong fluxing agent contributing to the attainment of high mechanical strength and good thermal shock
resistance, which strongly depends on its amount and firing conditions. Generally, it lowers the firing
temperature. New body formulations suitable for the industrial application were developed.