High-temperature creep of alumosilicate concretes on phosphate binder

Refractories and bldustrial Ceramics Ibl. 40, Nos. l l - 12, 1999

UDC 666.974.2.001.4

H I G H - T E M P E R A T U R E C R E E P O F A L U M O S I L I C A T E C O N C R E T E S

O N P H O S P H A T E B I N D E R

U. Sh. Shayakhmetov, 1 I. M. Valiev, t K. A. Vasin, ~ and R. S. Malikov ~

Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp. 21 - 24, November, 1999.

Results of h~gh-temperature creep tests of alumosllicate concretes on a phosphate binder that consists of a mixture of electrocorundum, technical alumina, and pyrophilllte are presented. The mixing liquid is H3PO 4 and an alumochromophosphate binder. The creep tests have been performed using an installation created by BashNIPIstrom State Enterprise, which makes it possible to test three specimens in one cycle simultaneously. The experimental data on the deformation of the concretes as a function of the pressing pressure, the treatment temperature, and the test conditions (the time, the temperature, and the load) are presented. The present work is the first attempt to study the endurance of materials on phosphate binders under the joint action of high pres- sures and loads.

INTRODUCTION

Materials on phosphate binders have been widely used recently for manufacturing high-temperature refractories [ 1 ]. The most popular are alumosilicate materials with from 60 to 90% A1203. They are used in various heating units under a wide range of mechanical and thermal loads. However, we can scarcely find published data on the deformation properties of alumosilicate materials on phosphate binders, in par- ticular, on the high-temperature creep, which is very impor- tant for evaluating the deformability of the materials before failure under the action of a static load and a constant temperature (close to the temperature of the beginning of delbr- mation under load).

The first attempt to study the creep of alumosilicate materials on phosphate binders was made by the Eastern Insti- tute of Refractories [2] in tests of alumosilicate concretes on various binders, i.e., an alumophosphate binder, liquid glass, and high-alumina cement. A comparison of the properties of these concretes has shown the preference of concretes on the alumophosphate binder where the constancy of the volume and the high-temperature creep is concerned.

The present paper concerns the results of tests of alumosilicate refractories on phosphate binders for high-temperature creep. The concretes have been fabricated from a mixture of electrocorundum with additives of finely dispersed powders of technical alumina and pyrophyllite. We analyze the dependence of their creep on such process parameters as

t BashNIPIstrom State Enterprise. Ufa, Russia: Kuganakskti Plant, Russia.

499

the pressing pressure and the temperature of prior heat treat-

ment. We also studied the effect of the kind of phosphate

binder and the test conditions (time, temperature, load) on

the deformation of the concretes.

CONCRETE COMPOSITIONS AND THE DEVICE FOR CREEP TESTS

The original materials for the concretes were normal

electrocorundum of fractions 8 0 0 - 1000 (No. 80) and 126 -

160 gm (No. 12), alumina of grade GK, pyrophyllite of the

Mozyr'-Ovruchskoe deposit, and a phosphate binder consist-

ing of 85% orthophosphoric acid (H3PO4) of analytical grade and an alumochromophosphate binder (AKhFS, TU

6-18-166-83). We studied four compositions, namely, elec-

trocorundum - alumina - H3PO 4 (composition 1 ), electrocorundum - alumina - AKhFS (composition 2 ), electrocorun-

d u m - pyrophyllite - H3PO 4 (composition 3 ). and electrocorundum - pyrophyllite-AKhFS (composition 4 ). Cylindrical specimens for the creep tests 36 mm in diameter and 50 nun

high were fabricated by pressing of semidry mixtures under

40 MPa. The content of the phosphate binder in the mixture

was I0 - 15 wt.%. The specimens were heat treated prelimi-

narily at 570, 670, and 1170 K. The creep tests were per-

formed by the method specified by GOST 25040-82 on a le-

ver installation in BashNIPlstrom State Enterprise which

made it possible to test three specimens at a time in one temperature regime. The block diagram and the appearance of the installation are presented in Figs. 1 and 2.

1083-4877/99/I 112-0499522.00 �9 2000 Kluwer Academic/Plenum Pubhshers

500 U. Sh. S h a y a k h m e t o v et al.

13

16

12 1l 10 ~,\ . : ~ ~

~ I ,2 ~

~. ~ ~'- ? 7_.-

i,' ;! ( o~ ,I - -

( ool

9

6 f

r

Fig. 1. Block diagram of the mstallation tbr testing concretes for creep resistance.

The installation consists of an electric furnace 1 with silicon carbide heaters 2 and has a heating space 3 for placing the tested specimens. The specimens are mounted on the lower silicon-carbide loading rods fastened in shells with cooling jackets 5 and inserted into the furnace through three openings in the bottom part of the lining. The specimens are loaded by loads 6 with the help of three lever systems with a hinge connection 7, and the load is transferred through the le- vers with the help of upper silicon-carbide loading rods 8. The rods 8 are inserted through the top openings in the furnace and fastened in shells 9 with cooling jackets used for avoiding the effect of the heat fluxes from the electric furnace on the lever and measuring systems. The deformation is measured by gauges of two types simultaneously, namely, clock indicators 10 and induction gauges I1 (12 are the measuring stocks). The lever systems 6 are fixed on three stands

Fig. 2. Appearance of the installation for creep tests of specimens of refractory concretes at _<1820 K.

4

3

~2

7

r o 6

I, ,/

�9 , * 5

�9 4

T T I , i i i

2 4 6 8 10 12 14

Time, h 16

Fig. 3. Creep curves of specimens of corundum concrete of compositions I (1 and 3 ) and 2 (2, 4 - 7) tested under the conditions presented in the table:

Curve l e s t t e m p e r a - Load , H e a t - t r e a t m e n t ture , K M P a t empera tu re , K

1 1670 0.2 1170

2 1670 0.2 1170

3 1770 1.0 1170 4 1770 1.0 1170

5 1770 2.0 1170 6 1770 1.5 570

7 1770 2.0 570

13. The installation is equipped with devices for detecting 14

and plotting 15 the deformation curves, a control device 16,

and a device for electronic control of the heating temperature 17.

RE SUL T S A N D T H E I R D I S C U S S I O N

The creep tests of alumosilicate concretes on phosphate binders were performed at 1670 and 1770 K (compositions ! and 2 ) and 1620 and 1720 K (compositions 3 and 4 ). The

choice has been made with allowance for the results of the

determination of the temperature of the beginning of deformation under a standard load of 0.2 MPa. For compositions 1

and 2 it was equal to about 1890 K, for compositions 3 and 4

it was 1610 and 1703 K. The creep curves of the phosphate corundum concrete of

compositions 1 and 2 are shown in Fig. 3. The deformations

in specimens heat treated at 1170 K and at 1670 K under a load of 0.2 MPa differ little and do not exceed 0.12% (curve 1,

composition 1 ) and 0.20% (curve 2, composition 2) after 14 h. When the test temperature increases to 1770 K and the load increases too, the deformation increases considerably. It

attains 0.82% (curve 3, composition 1 ) and 1.10% (curve 4,

composition 2 ) under a load of 1.0 MPa and increases to

2.5% (curve 5, composition 2 ) under a load of 2.0 MPa. The

High-Temperature Creep of Alumosilicate Concretes on Phosphate Binder 501

specimens with AKhFS deform somewhat more than those

with H3PO 4, which is caused by the greater strength of the structural skeleton in the compositions bonded by ortho-

phosphoric acid. The specimens of corundum concrete on a phosphate

binder heat treated at 570 K (for example, of composition 2 )

break rapidly by a brittle-plastic mechanism, i.e., in 30 min

at 1770 K and 1.5 MPa (curve 6) and in 50rain under 2.0 MPa (curve 7). This can be connected with the low

strength of the structural skeleton of the concrete that pre-

dominantly consists of aluminum phosphate and with thermal transformations that occur in the concrete under the action of the mechanical loads and temperatures.

The deformation of corundum-pyrophyllite concretes

with a phosphate binder (compositions 3 and 4) in 24-h

creep tests at 1620 and 1720 K is higher (Fig. 4) than that of

compositions 1 and 2, which is explainable by the presence

of fine disperse pyrophyllite that causes the appearance of a

great amount of liquid phase at the test temperature. The

prior treatment of concrete specimens of compositions 3 and 4 at 670 K causes brittle-plastic fracture in 2 . 0 -3 . 2 h at 1720 K and a lower load (0.6 MPa) than in the case of compositions 1 and 2 (curves 6 and 7 in Fig. 4); at the same time,

a prior treatment at 1170 K does not cause fracture in the

specimens (curves 1 - 5 ). Compositions 3 and 4 are charac-

terized by one more feature, namely, the concrete based on orthophosphoric acid (composition 3 ) deforms more than the

concretes based on AKhFS (curves 4 and 5, respectively).

This is explainable by the interaction between the onho-

phosphoric acid and the silica-bearing component of the concrete, i.e., pyrophyllite, with the formation of low-mehing silicophosphates [3] that have a liquid state at the test temperatures.

The creep of alumosilicate concretes of compositions 1 - 4 at 1670 K and 0.2 MPa during 140 h (Fig. 5) is equal to 0.29, 0.52, 2.6, and 2.23%, respectively. Analyzing the

curves, we see that the deformation rate of the concrete de- creases continuously with time. The highest deformation rate

is exhibited by compositions 3 and 4, which contain pyrophyllite. Compositions 1 and 2 bearing up to 90~ AI203 have a higher creep resistance.

CONCLUSIONS

The results of creep tests of alumosilicate concretes on a phosphate binder have shown that the technological parame-

ters have a considerable influence on the kinetics of thezr de-

formation at a high temperature. For example, a prior heat

treatment of specimens of all the tested compositions at 570 and 670 K causes rapid brittle-plastic fracture (in 2 .0 - 3.2 h), whereas a prior treatment of the specimens at 1170 K gives typical deformation curves after testing under the same load, temperature, and time conditions.

.= 5

d .--q 4

3

0 30

Time, h

5

, e 7 ~ 4 ~ 4

I f ~ t

[ l , / /

1 / I I ~ i / ,....-" ~ .~,_____.-.,--~---~,-----"

1~1/,/, m i i 1 i i

5 10 15 20 25

Fig. 4. Creep curves of specimens ofa corundum-pyrophyllite concrete of compositions 3 (4 and 7 ) and 4 ( 1 - 3.5 and 6 ) tested under the conditions presented in the table:

Test tempera- Load, Heat- t reatment C urve

ture, K MPa temperature . K

1 1620 0.2 1170 2 1620 0.6 1170

3 1620 1.0 1170

4 1720 0.2 1170

5 1720 0.2 1170 6 1720 0.6 670

7 1720 0.6 670

2 . ")

O

r -

4

f /

20 60 100 140

Time, h

Fig. 5, Dependence of the creep of specimens of corundum (1 and 2 ) and corundum-pyrophyllite concretes (3 and 4 ) on the time of their testing at 1670 K and 0.2 MPa.

For all the compositions the maximum deformation rate

is observed in the first 1 .5- 2.5 h (unsteady creep) and is

connected with the phase state of the binder. The composi-

tion with an additive of finely milled alumina has a lower de-

formation than that with finely dispersed pyrophyllite, i.e.,

the creep of the concretes depends on the content ofAleO 3 in

them. The stage of steady creep for corundum castables con-

502 U. Sh. Shayakhmetov et al.

taining up to 90% A1203 exceeds 140 h at 1670 K under the

action of a load of 0.2 MPa, which allows us to recommend

compositions 1 and 2 for long-term service in structural parts

of heating units. We can infer that the wide use of unfired refractory mate-

rials on phosphate binders in high-temperature engineering

requires additional research of not only the strength, elastic,

and structural properties but also the deformation properties,

including high-temperature creep.

REFERENCES

1. A. P. Petrov and I. L. Rachkovan, Metalphosphate-Based Mate- rials, Chemistry, Moscow (1976).

2. E S. Mamykin, V. D. Koshkarev, and A. K. Purgin. "Creep of refractory concretes with alumosilicate fillers on various binders." m: Proc. Eastern hist. o f Refi'actories (Mater. All-Union Conf. on Refi'actol 3' Concretes, 19 - 21 No~: 1968), Issue 10 [in Russian], Sverdlovsk (1970), pp. 135 - 142.

3. T. Y. Tien and F. A. Hummel, "System $102 P2Os," J. Am. Ceram. Soc., 45(9), 422 - 424 (1962).

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High-temperature creep of alumosilicate concretes on phosphate binder