FABRICATION OF HIGH-DENSITY QUARTZ CERAMICS:
RESEARCH AND PRACTICAL ASPECTS.
PART 5. A STUDY OF THE SINTERING OF MODIFIED QUARTZ CERAMICS
E. I. Suzdal’tsev
Translated from Novye Ogneupory, No. 1, pp. 42 – 52, January, 2006.
Original article submitted August 10, 2005.
Results of a study on the sintering and crystallization of modified quartz ceramics are reported. The addition
of boron nitride dopant at a concentration of 0.5 – 1.0 wt.% makes it possible to obtain a vacuum-dense quartz
ceramics with a minor amount of crystallization in the sintering temperature range of 1250 – 1270°C.
To study the sintering of quartz ceramics, both pure
(undoped) and modified with additives (dopants) BN, Si
, and Cr
, specimens have been prepared from sus-
pensions (as described in Part 4 of this communication series
“Fabrication of high-density quartz ceramics: research and
The process of sintering of materials was characterized
by following the changes in porosity and shrinkage of the
tests specimens. The sintering of pure and modified ceramics
was carried out using an electric furnace with heating silite
rods in air and in vacuum. However, the original specimens
prepared from modified materials differed markedly in po
rosity, which posed problems with comparing quantitatively
their sintering behavior. In this case, the efficiency of
sintering additives is better evaluated in terms of relative po
rosity (the fraction of “sintered” pores in the material):
P = I – P
where P is the fraction of sintered pores; P
is the open po
rosity of fired specimens; and P
is the porosity of semi-fi
nished specimens (green preforms).
The linear shrinkage and volume shrinkage in sintered
specimens were determined using the expressions below:
are the coefficients of linear and volume
shrinkage, %; L
are the initial and final size
and volume of the specimen.
The phase composition of the fired specimens was deter-
mined by x-ray phase analysis using a DRON-2 diffrac-
tometer; the chemical analysis was carried out as recom-
mended by factory standards. The structure of the materials
was studied using metallographic, scanning and electron mi-
croscopes. The degree of cristobalitization was also evalu-
ated using the coefficient of linear thermal expansion
The maximum permissible temperature was taken to be
the firing temperature at which the intensity of cristobalite
lines in the x-ray diffraction patterns was vanishingly small.
The ceramic indices (apparent density and open porosity)
were determined in conformance with State Standard GOST
2409–95. Occasionally (as needed), the true porosity of the
was determined using the formula
where g is the apparent density, g/cm
; d is the true density
of the material for each particular composition, g/cm
where a is the amount of an additive, g; d
are the den
sity of SiO
, as-received and with a dopant introduced, re
Refractories and Industrial Ceramics Vol. 47, No. 1, 2006
1083-4877/06/4701-0036 © 2006 Springer Science+Business Media, Inc.
Tekhnologiya Research and Production Enterprise, Obninsk,
Kaluga Region, Russia.
See Novye Ogneupory, No. 11, 19 – 24 (2005).