SYNTHESIS OF MULLITE FROM TOPAZ, REFRACTORY CLAY,
AND CLAY-TOPAZ COMPOSITIONS
T. V. Vakalova,
V. M. Pogrebenkov,
A. V. Ivanchenkov,
and O. A. Konovalova
Translated from Novye Ogneupory, No. 7, July, 2004, pp. 41 – 48.
Original article submitted May 28, 2004.
Results of a study of the phase formation in topaz-containing rocks and clay-topaz compositions are reported.
The percentage of topaz in its mixtures with refractory clay is shown to be an important factor controlling the
formation of crystalline phases.
Recent studies have shown that topaz rocks are promis
ing materials for use in the technology of aluminosilicate ce-
ramics. The end product of topaz decomposition is mullite;
therefore it was thought of interest to study in greater detail
the physicochemical processes involved in thermal degrada-
tion of topaz and other components of topaz rocks — in par-
ticular, quartz, and to see in what a manner topaz-based addi-
tives may affect the formation of mullite from kaolinite (al-
lowing for the eventual occurrence of fluorine species in to-
Quartz-topaz rocks from the Kopna deposit (Kemerov-
skaya Oblast’, Russia) were used in the study: rocks labeled
T1 – T3 were higher in quartz (77, 73.4, and 65.7% quartz,
respectively); rock T4 was higher in topaz (55%), and topaz
concentrate (TC) was highest in topaz (70%); here topaz was
a finely dispersed, flotation-beneficated material (<0.088
mm). Relevant characteristics are given in Table 1. One will
note that the topaz concentrate was rather high in ferrugine
ous admixtures (2.35% Fe
), which imparted a yellow-
brown color to it.
Preliminarily, the raw topaz materials were ground to a
particle size not in excess of 0.088 mm. Green preforms were
molded by semidry pressing under a load of 25 MPa and
sintered at 850 to 1350°C holding for 1 h at maximum tem-
An x-ray phase analysis (DRON-3M diffractometer, Cu
radiation) was used to follow the decomposition of topaz
rocks and formation of new phases. Identification features
for the evolution of phase composition were x-ray lines
0.540 and 0.338 nm for mullite, 0.405 nm for cristoballite,
0.334 nm for residual (unreacted) quartz, and 0.348 nm for
The formation of mullite during thermal dissociation of
topaz is controlled by the quartz component of a quartz-topaz
rock. Quartz present in the rock as a major component acts to
activate the formation of mullite (mullitization). In all
quartz-topaz rocks containing quartz at high concentrations
(77% in T1 to 65.7% in T3), mullite was observed to appear
Refractories and Industrial Ceramics Vol. 45, No. 5, 2004
1083-4877/04/4505-0355 © 2004 Springer Science + Business Media, Inc.
Tomsk Polytechnical University, Tomsk; Nizhnii Tagil Iron-and-
Steel Works (NTMK) Joint-Stock Co., Nizhnii Tagil, Russia.
TABLE 1. Chemical Composition of Raw Materials (wt.%)
Species, label SiO
CaO MgO R
T1 82.94 9.85 0.79 0.35 0.70 0.10 — 5.27
T2 80.97 11.05 0.37 0.15 0.60 1.14 — 6.04
T3 75.94 15.29 0.79 0.41 0.20 0.70 — 7.49
Topaz rock T4 59.65 26.14 0.35 0.11 0.10 1.31 — 12.34
Topaz concentrate TC 40.98 34.12 2.36 0.86 1.14 1.20 — 19.08
Clay (Troshkovskoe deposit) 49.63 35.43 2.52 0.73 0.95 1.30 0.52 8.93*
* Calcined at 1000°C, otherwise — at 1350°C.