1070-4272/01/7407-1076$25.00C2001 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 74, No. 7, 2001, pp. 1076 !1078. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 7,
2001, pp. 1048!1050.
Original Russian Text Copyright + 2001 by Gorbatova, Ban’kovskaya, Yuritsyn, Malygina.
AND INDUSTRIAL INORGANIC CHEMISTRY
Refractoriness and Phase Composition of ZrB
G. N. Gorbatova, I. B. Ban’kovskaya, N. S. Yuritsyn, and I. S. Malygina
Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, St. Petersburg, Russia
Received December 21, 2000; in final form, March 2001
Abstract-The influence of silicon concentration and of the mode and time of heat treatment in air on the
refractoriness and phase composition of ZrB
3Si materials was studied. Recommendations are given for
preparing refractory coatings on graphite in air using the given materials.
Coatings of ZrB
on a carbon material have been
obtained in argon at 1900oC .
In this work we studied the feasibility of using
3Si materials for obtaining refractory coatings on
graphite in air at lower temperature. We studied how
the silicon concentration and the mode and time of
heat treatment influence the refractoriness and phase
composition of the material.
Oxidation of ZrB
has been described in the litera-
ture . Up to 1000oC ZrB
is oxidized only slight-
ly, but at higher temperatures the oxidation accelerates
sharply. The primary components of the oxide film
are zirconium dioxide and hydrated boron(III) oxide,
which evaporates at high temperatures. A scale formed
on zirconium diboride shows no protective properties,
because, owing to porosity, it does not impede oxygen
diffusion into the sample. Zirconium diboride is used
as refractory material. It is incorporated in a number
of the composite alloys operating at high temperatures
in an oxidizing medium. Also, it is a coating com-
ponent. Thus, it is necessary to enhance its resistance
This is provided by addition of silicon-containing
compounds . Doping of the boride alloys with
silicon or metal silicides yielding volatile oxides
results in the formation of the oxide film that mainly
consists of borosilicate glass and reliably protects the
alloy from oxidation. According to the published data,
boride materials with addition of silicon-containing
compounds are prepared by hot pressing or sintering
of the appropriate mixtures in inert medium. In this
work, samples in the form of slip castings were used
without additional heat treatment. The samples were
dried to constant weight at room temperature.
The samples for studying refractoriness were heated
in an electric furnace with silicon carbide heaters in
air under the static conditions at 1400oC for 5, 15,
30, and 60 min. Three samples were heated for each
time. The heat resistance was judged from the weight
change (mg cm
) of the sample heated for the given
The open porosity of the samples was determined
by water absorption. The phase composition of the
surface after heating was studied on a DRON-2.0 dif-
radiation, Ni filter). The micro-
structure of the samples was studied on an MIM-8M
metallographic horizontal microscope. Zirconium
diboride (pure grade) and silicon (KR-1 grade) were
finely dispersed powders with particles no larger than
63 mm. The materials studied are presented in Table 1.
Each charge was mixed for 20 min. Then, slip cast-
ing was used for preparing the samples as castings.
The binder was a 2% solution of carboxymethyl cellu-
lose. The samples were 1.5 0 1.5 0 0.5 cm in size.
The samples were dried in air for 233 days.
We studied how the silicon concentration and the
mode and time of heat treatment affect the refractori-
ness and composition of the ZrB
3Si samples. The
obtained results are plotted in the figure and given
in Tables 1 and 2.
The figure shows the weight change of the samples
heated in air at 1400oC as a function of the heating
time. As seen, the silicon-containing samples are oxi-
dized less intensely than zirconium diboride. Heating
of the samples is accompanied by complex processes
including oxidation of the initial components with
atmospheric oxygen, interaction of the resulting com-
pounds with each other, formation of borosilicate
glass, volatilization of boron(III) oxide, and partial
evaporation of silicon from the sample surface. The
total contribution of all the occurring processes is re-
flected in the figure.