OPTIMIZED COMPOSITION OF THE SLIP FOR PREPARING
HIGH-POROSITY PERMEABLE QUARTZ CERAMICS
S. E. Porozova
Translated from Ogneupory i Tekhnicheskaya Keramika, Nos.7–8,pp.45–48,July – August, 2002.
The preparation of a high-porosity permeable ceramic by the duplication method using thixotropic slips is de
scribed. An aqueous solution of methylcellulose is used as the dispersion medium.
Quartz ceramics made of sintered amorphous silica or
glass waste at temperatures below the melting point are defi
cient, unlike most ceramic materials, in the crystalline phase
. The advantageous features of quartz ceramics come from
the dual nature of the surface of quartz glass containing both
silanol and siloxane groups, which imparts hydrophilic and
hydrophobic properties to it . Owing to the occurrence of
hydrophilic and hydrophobic sites, quartz ceramic is of po-
tential interest as a high-temperature heat- and corrosion-re-
sistant material , and also as support for catalysts, adsor-
bents, and various organic substrates. Quartz ceramic with an
open porosity of 75 – 90% (Fig. 1) prepared by duplication
of a polymeric matrix is best suited for that purpose .
A specific feature of high-porosity materials thermally
treated by the above method is the active effect due to the gas
phase associated with the sufficiently large surface and slen
der bridging links . Introduction of B
, BN , or
 is of little help in this particular case because of the
active diffusion of oxygen in the material in the stage prior to
the formation of silicate glasses. To prevent crystallization, it
has been recommended to add boron in the form of an amor
phous powder  at a concentration of 0.5 – 3.0% .
The method of polymeric-matrix duplication may be
considered a variety of the slip-casting method using an inac
tive mold. Here rheological characteristics of the slip and
their optimization are of utmost importance in determining
the strength and other properties of the final product .
Usually, aqueous suspensions, preliminarily subjected to
aging or the appropriate mechanical treatment, are used to
prepare quartz ceramics [1, 10]. The slips thus prepared are
not suitable for duplicating the cellular-network framework
of a polymeric matrix . Inorganic bonds likewise cannot
be used to prepare quartz glass-based slips because of the ex
ceptional sensitivity of quartz glass, in distinction from many
other materials, to even trace amounts of extraneous impuri
ties . A way towards solving the problem of anchoring the
layer of a ceramic powder on the dried surface of a polymer
impregnated with the precursor suspension may be the use of
the liquid phase of aqueous solutions of organic adhesives
, in particular, methylcellulose.
Our goal in this work was to prepare aqueous solutions
of methylcellulose for thixotropic slips and to use them for
preparation of a high-porosity permeable quartz ceramic by
the method of polymeric matrix duplication.
Aqueous solutions of methylcellulose 65 (TU 6-01-717–72
(MTs) Specifications) were used as the dispersion medium
for slips. The quartz glass waste was ground and mixed with
powdered amorphous boron using a porcelain mill with
uralite grinding bodies. The slips were prepared by homoge
nizing the component in a porcelain mortar and pestle and in
a “Sand” planetary mill equipped with a chalcedony pan and
chalcedony grinding bodies. The viscosity was measured
Refractories and Industrial Ceramics Vol. 43, Nos.7–8, 2002
1083-4877/02/0708-0269$27.00 © 2002 Plenum Publishing Corporation
Fig. 1. Overall view of a specimen of quartz ceramic with a poro
sity of 85%.
Research Center for Powder Materials Science, Perm, Russia.