THE STATE AND PROSPECTS OF MOLDING
BASED ON AQUEOUS SLIP OF INORGANIC MATERIALS
E. I. Suzdal’tsev
and D. V. Kharitonov
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 12, pp.4–7,December, 2002.
Methods for accelerating molding of large-sized thick-walled (d
= 16 – 20 mm) articles based on aqueous
slip of inorganic materials (namely, quartz glass and lithium-aluminosilicate glass) are analyzed. The most
promising is the method of electrophoretic molding of ceramics that shows good results in molding articles
from quartz glass slip. The possibility of applying this method to ceramics based on lithium-aluminosilicate
glass is yet to be investigated. The choice of material and design for the electrodes is another subject for inves
tigation, since the authors have encountered the problem of articles sticking to the electrode surfaces.
Casting products based on aqueous slip in porous,
mainly gypsum mold is the principal and the oldest method
for molding large-sized pieces. This method is based on the
capacity of porous bodies to absorb part of the water from
the slip owing to the capillary effect and diffusion processes.
In spite of the obvious advantages, this method has cer-
tain drawbacks, of which the main is the time-consuming
molding process (for instance, molding of a quartz ceramic
article d = 20 mm lasts 10 – 20 h and that of a glass-ceramic
piece based on lithium-aluminosilicate glass lasts 35 – 40 h),
moreover, the wall thickness formation in the upper part of
the article is half as slow as in the lower part, which gene
rates defects in molded pieces and causes waste. Thus, the
problem of increasing the rate of thickness formation and de
creasing the gradient of the rate of formation of the wall
height is topical and needs investigation.
One of the main factors determining the casting rate is
the degree of stabilization of suspension. Figure 1 shows the
kinetics of mass increment for quartz glass slip obtained with
various degrees of stabilization.
The casting rate to a large extent is determined as well by
the dispersion of the solid phase in suspension . Thus,
Fig. 2 shows examples of casting from high-density coarse-
and finely dispersed quartz glass suspensions. The time of
formation of a cast sample from the finely disperse slip
(curve 4 ) is 2.5 times longer than from the coarsely disperse
slip (curve 1 ); moreover, the porosity of samples cast from
the finely disperse slip is significantly higher, which is pro-
bably due to the poorer packing of finely disperse particles .
Another parameter affecting the casting rate is the mold
material, which is responsible for several factors characteriz-
ing the mold (porosity, capillary system, moisture capacity).
As an example, Fig. 3 shows the dependence of the mass in-
crement rate for the same initial suspension cast into differ-
ent molds .
The sample thickness increment can be accelerated as
well by increasing the pressure differential on the mold
walls, i.e., inside the mold pores and in the slip bordering
with the mold . The differential can be increased either by
Refractories and Industrial Ceramics Vol. 43, Nos. 11 – 12, 2002
1083-4877/02/1112-0367$27.00 © 2002 Plenum Publishing Corporation
Tekhnologiya State Research Center of the Russian Federation,
Obninsk, Kaluga Region, Russia.
Sample thickness, mm
Setting time, min
Fig. 1. Kinetics of mass increment for quartz glass slip obtained in
one stage with varying stabilization time: 1 ) initial slip, non-stabi
lized; 2 ) stabilization for 48 h; 3 ) stabilization for 96 h.