SINTERING KINETICS OF MgO STUDIED ON MAGNESITE
OF PROVENANCE FROM THE CHITA DEPOSIT
A. V. Gropyanov
and V. M. Gropyanov
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 4, pp. 31 – 35, April, 2001.
The potential use of a mathematical simulation method for accumulative recrystallization of magnesite of
provenance from the Chita deposit is considered. The densification rate in sintered MgO, that is, the rate at
which grain boundaries form at the expense of contracting intergranular pores, is shown to be much higher
than the rate at which the grain boundaries disappear during the accumulative crystallization. An equation is
derived that provides an adequate description of the kinetic features of MgO sintering. The numerical parame
ters of this are physically meaningful, which allows one to gain deeper insight into the sintering mechanism of
MgO and thus go beyond the limits of a purely phenomenological approach.
The present paper is concerned with the accumulative
crystallization involved in the direct “from-carbonate” syn-
thesis of a fully dense clinker from magnesite recovered at
the Chita deposit. A component analysis of the sample tested
gave the following results, wt.% (recalculated in terms of
, 51.20; SiO
, 0.21; Al
, 0.26; CaO, 1.58;
Cylindrical pellets with a diameter of 25 mm and a
height of 25 – 30 mm pressed from powders of different de
gree of grinding were used in the experiments; the pellets
were calcined in a vacuum furnace at different heating rates
and different final temperatures. The relative porosity Z =
of the material as a function of temperature for
the CaO – MgO system is shown in Fig. 1 (here P
and P are
the pore volume fractions of intact and calcined specimens
measured at two heating rates. Individual curves in
Fig. 1a, b, and c illustrate the process of densification in
MgO as a function of temperature at different heating rates
(curve slopes). Considered as a whole, these curves convey
the essence of how the densification of MgO proceeds from
the initial grain size (the initial average size of powder parti
As is seen in Fig. 1a, the densification in MgO with an
initial grain size of 59.5 mm has its onset at about 1900 K and
the maximum densification rate falls into the range of
2000 – 2150 K. Starting from 2170 K, the sintering slows
down sharply, and under the temperature conditions of the
experiment, this process fails to proceed to completion
(Z ® 0). This behavior is typical of the two heating rates
used, however with the distinction that here (as in all situa
tions) the higher the heating rate, the lower the value of Z at
the same temperature.
At an initial grain size of 55.0 mm, MgO starts densifying
at 1900 K, attaining a maximum densification rate in the
range of 1950 – 2100 K. Here the sintering slows down at
T > 2100 K.
The course of sintering in MgO with an initial grain size
of 7.0 mm is shown in Fig. 1c. Here the onset of intense sin
tering occurs at 1830 K, and the process is completed
(Z ® 0) at 2100 – 2150 K.
Thus, a trend is clearly observed — with a decrease in
the initial grain size of the sintered powder and a decrease in
the heating rate, the sintering process becomes more intense,
and the sintering temperature tends to decrease.
As an example, a photomicrograph of the fracture sur
face of a periclase specimen (of provenance from the Chita
magnesite deposit) sintered at 2000 K is shown in Fig. 2.
To ensure the objectivity of estimating kinetic parame
ters, the available experimental data were processed using
four alternative types of kinetic equation (1) – (4) .
Refractories and Industrial Ceramics Vol. 42, Nos.3–4, 2001
1083-4877/01/0304-0162$25.00 © 2001 Plenum Publishing Corporation
St. Petersburg Institute for Refractory Materials Joint-Stock Co.,
St. Petersburg, Russia.