A TECHNOLOGY FOR ACCELERATED CALCINATION
OF LITHIUM ALUMINOSILICATE GLASS CERAMICS
E. I. Suzdal’tsev
and D. V. Kharitonov
Translated from Novye Ogneupory, No. 5, pp. 27 – 39, May, 2004.
The results of a study of the processes of sintering and crystallization of Li-aluminosilicate glass ceramics
have shown a route towards saving heat-treatment time (by a factor of 2.5 – 3.0) and power consumption with
out detriment to the major physicomechanical characteristics of the components produced.
Glass ceramics, in order to display the required physico
chemical properties (maximum amount of crystallization
centers for obtaining a fine-grained microstructure that
would ensure high mechanical strength, proper crystallinity,
and phase composition) are subjected to heat treatment .
The physicochemical properties of glass ceramics should
not be regarded as a function of a single particular parameter
(unlike as practiced, for example, in the production of quartz
ceramics [2 – 6]), considering that reaching a high level of
properties for a glass ceramic is possible only through strict
control over a range of heat treatment parameters such as
heating and cooling rates, nucleation temperature, and hold-
ing time at a specified temperature (nucleation or crystalliza
tion) [1, 7].
In recent years, a technology has been developed that al
lows fabrication of large-sized, complex-shaped components
from glass ceramics of b-spodumene composition (radio
transparent nose fairings for aircraft) including operations
typically used in ceramic technologies such as the grinding
of precursor lithium aluminosilicate glass, preparation of
aqueous slips, slip-casting molding, and heat treatment of
green preforms [8 – 11]. A specific feature of the newly de
veloped ceramic technology is that it requires the sintering of
green preforms molded from high-disperse precursor pow
der. The heat treatment of conventional glass ceramics is
now a well-established process (mostly controlled by the
phase composition of the precursor glass); by contrast, the
sintering of glass ceramic prepared by ceramic technology
remainsg a poorly controlled technique.
The potential use of ceramic technology for preparation
of glass ceramics from powdered Li-aluminosilicate glasses
has been discussed earlier in the literature [12 – 16]; how
ever, some progress in the manufacture of large-sized com
plex-shaped has been achieved in our recent works only
[8 – 11]. Further efforts in the field [17, 18] have led to the
development of a mathematical model which, in our opinion,
may provide a route towards an optimum heat-treatment re-
gime . Robustness of this model was borne out by exper-
imental studies: good agreement between experimental and
predicted data has been obtained, which undoubtedly lends
support to the usefulness of the model. Using the model
made it possible to reduce the amount of work concerned
with the optimization of heat treatment regimes. Still, the
model, despite its evident benefits, suffers from a grave
drawback — it prescribes much time for heat treatment
(60 – 70 h), which is counter to the major requirement of
saving processing time of technological process [1, 7, 18].
The failure to meet this requirement in a serial production
will result in the use of an increased amount of technological
equipment (burning kilns) and incur costs in energy and la
bor. Thus saving heat treatment time of glass ceramics of
b-spodumene composition is a challenging problem.
Currently, the following process parameters are typically
used in the production of glass ceramics based on Li-alumi
nosilicate glass :
Green preform drying at £ 250°C, h ..........1–2
Heating rate, K/h..................40–60
Nucleation temperature, °C ...............650
Holding time at 650°C, h..................5
Upper-limit crystallization temperature, °C ......1250
Holding time at 1250°C, h ...............4–6
Cooling regime ...............Furnace-cooled.
The process time measured from batch loading to un
loading was 60 – 70 h.
Therefore our goal in this study was to seek ways that
would allow one to save heat-treatment time in the produc
Refractories and Industrial Ceramics Vol. 45, No. 4, 2004
1083-4877/04/4504-0255 © 2004 Springer Science+Business Media, Inc.
Tekhnologiya Federal State Unitary Enterprise Research and Pro
duction Association, Obninsk, Kaluga Region, Russia.