REFRACTORIES CONTAINING FREE CaO — CANDIDATES
FOR INDUSTRIAL APPLICATIONS
A. V. Gropyanov
Translated from Novye Ogneupory, No. 4, pp. 32 – 37, April, 2002.
A brief survey of the state of the art of lime refractories is presented: availability of raw materials, physico
chemical and mechanical properties (refractoriness, apparent density, open porosity, compressive strength,
Young, shear, bulk moduli, Poisson’s ratio, strength intensity factors, thermal linear expansion coefficient), ef
fects due to grain composition, additives, and bonds are discussed, technologies for preparation of CaO-based
are considered, and prospects for large-scale application in industry are outlined.
Modern metallurgy of high-purity steels and alloys is
characterized by the involvement of refractory materials and
slags of enhanced basicity because this allows the use of
higher processing temperatures and facilitates the removal of
impurities by reducing them to a low-melting state. Corre-
spondingly, this requires that the fraction of basic refractories
in steel-melting and teeming units be increased. Magnesium
oxide-based refractories are currently gaining ever-increas-
ing acceptance in the field.
The bar charts in Fig. 1 compare patents for different ba-
sic refractory materials issued in decades of the past century
(data available from an IBM Intellectual Property Network
patent data base, U.S.). As can be seen, there is growing in
terest in CaO – MgO-based refractories. One will note the in
creased number of patents for periclase-carbon refractories.
However, at present the natural sources of naturally pure
raw materials for periclase refractories are in clear decline.
For this reason, one has to choose between alternatives: (i) to
use lower-grade raw materials (which will inevitably lead to
a deterioration of quality of the end refractory product be
cause of impurities); (ii) to use dressing technologies on a
larger scale, or (iii) to develop new technologies based on the
use of highly basic raw materials.
Reserves of naturally pure raw materials for production
of lime and lime-periclase refractories are practically inex
haustible in comparison to the limited stock of raw materials
for periclase refractories. Furthermore, many raw sources for
periclase refractories are not readily available (Table 1). This
makes the development of new technologies for lime and
lime-periclase refractories an urgent necessity, with the pri
ority given to lime-based refractories.
Calcium oxide in its refractory properties is virtually not
inferior to magnesium oxide (Fig. 2) and is distinctly supe-
rior in basicity. In particular, magnesium compounds exhibit
a certain degree of amphoterism, which places them closer to
beryllium and zinc compounds rather than to calcium, stron-
tium, and barium (Fig. 3).
Beryllium, strontium, and barium compounds are not
widely used in the refractory industry because of their rather
rare occurrence in nature.
For this reason, CaO in its capacity of a Vold and Lewis
base with respect to virtually all elements and compounds
Refractories and Industrial Ceramics Vol. 44, No. 6, 2003
1083-4877/03/4406-0373$25.00 © 2003 Plenum Publishing Corporation
St. Petersburg Institutes for Refractory Material Joint-Stock Co.,
St. Petersburg, Russia.
Number of patents
1970 – 1980 1980 – 1990 1990 – 2000
Fig. 1. Bar charts illustrating the intellectual property trend in the
field of basic refractories: 1 ) lime; 2 ) periclase; 3 ) periclase-car
bon; 4 ) dolomite.
Exceptions to the rule are metals of group Ia and their compounds
and compounds of the monovalent thallium, silver and other metals.