SCIENTIFIC RESEARCH AND DEVELOPMENT
MICROSTRUCTURE OF REFRACTORIES
WITH PARTICIPATION OF LANTHANUM CHROMITE
A. P. Shevchik
and S. A. Suvorov
Translated from Novye Ogneupory, No. 7, pp. 27 – 33, July 2009.
Original article submitted April 20, 2009.
Questions are considered concerning the microstructure of electrode refractories based on lanthanum chro
mite. On the example of a refractory composition of lanthanum chromite — yttrium oxide the formation of
stochastic phase-mosaic structure and its evolution during high-temperature exposure is demonstrated. The
main features of crystal phase and porosity transformation of refractory composite constituents are revealed.
Keywords: lanthanum chromite, refractory composite, microstructure, microstructure evolution.
Multiphase refractory composites based on lanthanum
chromite are used as high-temperature electrical conducting
materials in oxidizing gas atmospheres [1, 2]. In  the pos-
sibility is demonstrated of multiphase refractory materials
based on lanthanum chromite in heating modules for opera-
tion in an air atmosphere. These heating modules have a se-
ries of advantages over analogs within which as the electrical
conducting resistive material there is use, for example, of sil-
icon carbide, molybdenum disilicide, and single-phase mate-
rials based on lanthanum chromite. Heating modules fitted
with resistive elements of multiphase materials based on lan
thanum chromite, have an operating capacity up to 1750°C.
In publication  preparation is demonstrated for resistance
materials based on lanthanum chromite for resistance heating
elements with high heat liberation from the surface. for this
extrusion was used to prepare a U-shaped structure for resis
tive objects made of lanthanum chromite. This molding
method for electric heaters is promising fro creating heaters
with a single current lead.
The resistance properties of multiphase materials based
on lanthanum chromite govern not only the electrical con
ductivity of lanthanum chromite, but also distribution within
the volume of the refractory of dielectric and electrically
conducting components [3, 4]. A mechanism was presented
in  for lanthanum chromite electrical conductivity. The
leading role was demonstrated in electrical conductivity of
polarons that primarily diffuse over grain boundaries. In this
connection material electrical conductivity is affected con
siderably by grain surface development, and also the stability
of the surface chemical composition. In  surface phenom-
ena were considered in electrically conducting multiphase
material based on lanthanum chromite. In particular, the
x-ray electron spectrum was analyzed for the surface of
grains in a two-phase resistive composite of lanthanum chro-
mite – yttrium oxide. Analysis of the spectrum made it possi-
ble to identify a different valent state of chromium in the lan-
thanum chromite structure, responsible for the appearance of
electrical conducting properties of the material.
The aim of this work is to study the microstructure of re
fractory composites based on lanthanum chromite and its
evolution during high-temperature exposure in an air atmo
sphere. The microstructure of refractory composites was
studied in polished sections in reflected light.
Analysis of the microstructure of refractory composites
(1 – X )La
, where X is 5 – 40 wt.%,
x = 0.00, 0.04 (Table 1), showed that the linear size of lantha
num chromite crystallites is independent of the presence of
CaO found within the limits from 3.3 to 7.8 mm, Y
2.8 to 3.4 mm, and pores from 2.8 – 4.8 mm. With an increase
content in a composite there is successively a reduc
tion in lanthanum chromite crystallite size, that is accompa
nied by an increase in surface contact of lanthanum chromite
crystals with Y
crystals, since the linear size of Y
crystals is almost unchanged. This should have a favorable
effect on the stability of the electrophysical properties of a
refractory composite since the separation surface of the dif
ferent phases is subject to a lesser degree of recrystallization
Refractories and Industrial Ceramics Vol. 50, No. 4, 2009
1083-4877/09/5004-0266 © 2009 Springer Science+Business Media, Inc.
St. Petersburg State Technological University (Technical Univer
sity), St. Petersburg, Russia.