A NEW GENERATION OF DEFLOCCULANTS AND MICROSILICA
USED TO MODIFY THE PROPERTIES OF A CONVENTIONAL
REFRACTORY CASTABLE BASED ON A CHAMOTTE FILLER
and R. Stonis
Translated from Novye Ogneupory, No. 5, pp. 44 – 48, May, 2006.
Original article submitted February 3, 2006.
An efficient deflocculant for a conventional refractory castable based on a chamotte filler is proposed. A parti
cle distribution analysis is given for a dry castable mix containing microsilica, and the physicomechanical
properties of the conventional refractory castable modified with microsilica and Castament FS40 polycarbo
xylate deflocculant are studied.
At present, medium and low-cement heat-resistant cas-
tables, along with the conventional ones, have found applica-
tion in the manufacture of refractory linings for heat-pow-
ered units. The preparation of high-grade medium and low-
cement castables requires careful control of the mixing re-
gime, amount and quality of water added, temperature, and
other processing conditions . Because of the difficulty in
preparing castables relatively low in cement, preference has
been given to conventional refractory castables which, al-
though not free from shortcomings, are still less sensitive to
variations in processing parameters. The strength of a con
ventional castable fired at 800 – 1000°C showed a 50 – 70%
decrease in comparison with the hardening strength; thermal
stability and other properties (firing shrinkage) also failed to
meet standard norms for the service of lining in heat-pow
ered units. Despite this, the wide range of conventional
castables offered by many leading manufactures may need
further study and improvement.
Measures have been proposed that were aimed at im
proving the properties of refractory castables: the use of effi
cient deflocculants and combinations thereof; optimum
granulometric composition of the dry mixture; the use of var
ious dispersing and ultra-dispersing aids. In recent years, a
new generation of deflocculants — Castament polycarbo
xylate esters — has gained acceptance owing to their signifi
cant dispersing effect . The conventional deflocculants
operate on the principle of electrostatic dispersing. The new
deflocculants are controlled by a double effect: (i) electro
static and spatial repulsion of cement particles and (ii) dis-
persing of cement particles. The new deflocculant was
mainly tested using refractory castable based on high-alu-
mina cements (Al
about 70%) and dense fillers of bauxi-
te, andalusite, and tabular alumina [3 – 5]. Still, data on this
deflocculant in composites with alumina cement (Al
about 40%) and porous chamotte fillers are sadly lacking.
Ultradisperse microsilica, widely used in advanced refrac-
tory castables, has been tried to improve the properties of the
conventional heat-resistant castable .
Our goal was to study the effect produced by the
Castament FS40 polycarboxylate deflocculant and micro
silica (taken in dosed amounts) on the properties of a con
ventional refractory castable high in alumina cement (25%)
and containing a chamotte filler with the view of further im
proving their physicomechanical characteristics.
Gorkal-40 alumina cement (Al
³ 40%) and ultradis
perse microsilica (92.5% SiO
, 1.5% carbon; 2.0% K
O; specific surface 15,000 m
/kg) were used; both
materials were available from Poland. The chamotte fillers
(0 – 10 mm) with an open porosity of 17.8 and bulk density
of 1150 kg/m
were prepared from crushed ShA-grade
chamotte brick (Al
£ 40%). The disperse chamotte with a
specific surface of 400 m
/kg and bulk density of 1100 kg/m
was prepared using a laboratory mill. Four formulations have
been considered (see Table 1).
Test specimens shaped as a cube with an edge of 70 mm
were prepared. Water content in the castable mix (controlled
by the ASTM C 860–91 method ) was varied to provide
Refractories and Industrial Ceramics Vol. 47, No. 3, 2006
1083-4877/06/4703-0178 © 2006 Springer Science+Business Media, Inc.
Gediminas Institute for Thermal Insulation, Vilnius, Lithuania.