DEFORMATION OF UNFIRED REFRACTORIES BASED
ON PHOSPHATE BINDERS
. 7. DEFORMATION OF COMPOSITES
BASED ON SILICON NITRIDE
V. S. Bakunov
and U. Sh. Shayakhmetov
Translated from Novye Ogneupory, No. 9, pp. 49 – 52, September 2007.
Original article submitted November 11, 2006.
Results are presented for a study of the deformation of phosphate composites based on Si
it possible to predict the behavior of these materials in service.
A study of the effect of deformation of phosphate com
posites based on Si
has been carried out in order
to predict the behavior of materials in service [10, 21]. At the
same time very essential data have been obtained for analyz-
ing and summarizing the results from the point of view of es-
tablishing scientific bases for composite technology and de-
termining their compositions. Results have been provided for
a study of deformation kinetics during heating and creep un-
der the action of mechanical loads for materials of two com-
positions, i.e. based on Si
as a binder (com-
position 1) and AKhFS (composition 2). Here the effect has
been considered for oxidation of silicon nitride on struc-
ture-sensitive properties. Specimens for testing made of
formed mixes with S:L = 3:1 were prepared by compaction
under a pressure of 50 MPa and subjected to preliminary heat
treatment at 300°C.
Both composites during heating air oxidized at 900°C.
Taking account of this feature creep strain was evaluated in
the range 700 – 900°C with a load from 0.1 to 1.2 MPa. The
nature of creep strain for composites up to 900°C and with a
load of 0.2 MPa (Fig. 33) is practically the same, and for 6 h
strain it did not exceed 0.01% for composite 1 and 0.02% for
composite 2; with a load of 0.4 MPa this increased to 0.05
and 0.07%, and with 0.6 MPa it increased to 0.12 and 0.14%
An increase in temperature to 950°C (Fig. 34) leads to an
increase in creep strain for specimens up to 0.04% (composi
tion 1) and 0.03% (composition 2) with a load of 0.2 MPa, to
1.04 and 0.92% with a load of 0.4 MPa, and to 2.25 and
1.80% with a load of 0.6 MPa. Specimens of composition 2
deform less than specimens of composition 1, in contrast to
deformation at 900°C that is connected with presence in the
composition of readily-melting silicon phosphates. An in-
crease in temperature to 1000°C causes specimen failure of
composition 1 under a load of 1.2 MPa in 30 min and under a
load of 0.6 MPa in 50 min. The creep activation energy for
these compositions appeared to equal 135 and 163 kJ/mole
respectively, that is less by a factor of 4.0 – 4.5 than values
for hot-pressed and sintered silicon nitride. Characteristics of
composites before and after creep testing under a load of
0.2 MPa and experimental values of parameters S, n and Q
found by the empirical creep equation
are provided in Tables 6 and 7 respectively.
Refractories and Industrial Ceramics Vol. 48, No. 4, 2007
1083-4877/07/4804-0294 © 2007 Springer Science+Business Media, Inc.
Completion. Started in Nos.1–6(2007).
Joint Institute of High Temperatures, Russian Academy of Sci
ences, GUP BashNIIstroi, Russia.
Fig. 33. Creep strain curves for compositions 1 (1, 3, and 5 ) and 2
(2, 4, and 6 ) at 900°C with a load, MPa: 1 and 2, 0,2; 3 and 4, 0,4; 5
and 6, 0,6.