RESEARCH IN THE FIELD OF PREPARING MOLDED
AND UNMOLDED REFRACTORIES BASED ON HIGH-ALUMINA HCBS.
PART 7. SINTERING AND SECONDARY MULLITE FORMATION
OF MATERIALS BASED ON COMPOSITE COMPOSITION HCBS
DURING NONISOTHERMAL HEATING AND ISOTHERMAL FIRING
Yu. E. Pivinskii
and P. V. Dyakin
Translated from Novye Ogneupory, No. 10, pp. 42 – 51, October 2016.
Original article submitted December 7, 2015.
The effect of nonisothermal heating in a high-temperature dilatometer and isothermal heating in the range
900 – 1600°C on sintering and secondary mullite formation for specimens based on composite composition
HCBS, including with refractory clay additions, is studied. Maximum shrinkage values of 0.4 – 1.3% depend-
ing on composition are noted with nonisothermal heating up to 1200 – 1250°C or after isothermal firing at
1100 – 1200°C. Specimen growth index (up to 2.0 – 2.5%) after high-temperature firing depends on SiO
tent that indicates the volume of secondary mullite formed.
Keywords: bauxite, mullite, corundum, HCBS, VFQG, nonisothermal heating, isothermal heating, primary
and secondary mullite, shrinkage, growth, porosity.
Among binder systems there are many forms of high-alu-
mina ceramic concretes produced in OAO Dinur [1 – 3],
there is use of composite composition HCBS containing not
only high-alumina bauxite, but also very fine quartz glass
(VFQG) and certain refractory clay additives [3 – 8].
The main proportion of SiO
in original bauxite as a re
sult of high temperature firing to chamotte enters into reac
tion with Al
with formation of so-called primary mullite,
whose content is 10 – 15%. In addition, in order to improve
thermomechanical property indices and volume constancy of
refractories applied to high-alumina ceramic concrete tech
nology it is also necessary to form secondary mullite. Intro
duction into the composition of HCBS of both VFQG and
also refractory clay, having a relatively high SiO
(55 – 60% in calcined substance), will make it possible dur
ing firing or high-temperature service to accomplish second-
ary mullite formation, i.e., to resolve this problem.
The task is set in this work of detailed study of sintering
and secondary mullite formation in specimens made from
HCBS with different SiO
content, and a certain amount
within them of both VFQG and added refractory clay.
PRIMARY AND SECONDARY
In the technology in question for traditional ceramic and
refractory materials of mullite or high-alumina composition
the generally accepted terms are “primary mullite” and “sec
ondary mullite” [9 – 12]. In technology for the production of
mullite composition refractories kaolin raw material (with
addition of alumina), sillimanite group minerals, alumina hy
drates are used, and also in a number of cases direct synthesis
is accomplished for mullite from silicon and aluminum ox
ides. Physicochemical processes with use of the aforemen
tioned raw materials have specific features. In reactions of
argillaceous substance with alumina there is formation of pri
Refractories and Industrial Ceramics Vol. 57, No. 5, January, 2017
1083-4877/17/05705-0536 © 2017 Springer Science+Business Media New York
Parts 1 – 3 of the article were published in Novye Ogneupory
Nos. 8, 10, and 12 (2015), and parts 4 – 6 in Nos. 2, 4, and 6
OOO NVF Kerambet-Ogneupor, St. Petersburg, Russia.
FGBOU VPO St. Petersburg State Technological University
(Technical University), St. Petersburg, Russia.