ELABORATION PROCESS OF REFRACTORY MATERIALS BY REACTIVE PROJECTION OF OXIDE, PEROXIDE AND METALS

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ELABORATION PROCESS OF REFRACTORY MATERIALS BY REACTIVE PROJECTION OF

OXIDE, PEROXIDE AND METALS

M. Pilatti, J. Cransveld, G. Raymond, E. Plumat, P. Duvigneaud

To cite this version:

M. Pilatti, J. Cransveld, G. Raymond, E. Plumat, P. Duvigneaud. ELABORATION PROCESS OF REFRACTORY MATERIALS BY REACTIVE PROJECTION OF OXIDE, PEROXIDE AND MET- ALS. Journal de Physique Colloques, 1986, 47 (C1), pp.C1-159-C1-163. �10.1051/jphyscol:1986123�.

�jpa-00225551�

ELABORATION PROCESS OF REFRACTORY MATERIALS BY REACTIVE PROJECTION OF OXIDE, PEROXIDE AND METALS

M. PILATTI, J. CRANSVELD, G. RAYMOND, E. PLUMAT* and P.H. DUVIGNEAUD*

TSIROFOVR,

'Université Libre de Bruxelles, 50, Avenue F. Roosevelt, B-1050 Bruxelles, Belgium

Résumé - Un montage a été élaboré pour pulvériser avec précision des com- posés d'oxydes réfractaires, peroxydes ou métaux, avec une granulométrie contrôlée. Le produit réfractaire est obtenu par fusion et recrystallisa- tion sur un substrat préchauffé. Des compositions des systèmes Ca-Al203 et Ca0-Al203-Zr02 ont été synthétisées. Elles ont été analysées par dif- fraction des rayons X et MEB. Des matériaux denses et bien crystallisés ont été déposés. Ce procédé peut être u t i l i s é avec succès pour réparer des fours en fonctionnement à 1500°C.

Abstract - A device has been set up for spraying with accuracy a compound having a controlled grain size of refractory oxide, peroxide and metals.

The refractory material is obtained by melting and recristallisation on a preheated substrate. Composition in the CaC.Al203 system and in the CaO-Al2Q3-Zr02 system have been synthesized. They have been analysed by X-ray diffraction and SEM. Dense and well cristallized materials have been deposited. This process can be successfully applied for the repair of a furnace in operation at 1500°C.

I. INTRODUCTION.

A technical process has been applied for repairing furnaces in operation at high tem- perature. Some experimental results have been analized in previous paper /1//2/. The first applications have been devoted to the system Al203-Ca0. Those results have been completed to an other area of the diagram. Different compounds of alumina powder, aluminum powder and calcium peroxide have been projected in a furnace at more or less 1500°C.

A first industrial device has been constructed with the needed control system.

The composition and structure of the deposited materials has been determined.

II. EXPERIMENTAL.

2.1. Projection equipment.

The first device has been realised in order to project a mixed compound of very fine powder of refractory oxide aluminium powder and calcium peroxide. The average size of the powder is - 1 vm. The equipment includes : the mixer, the projec- tion device, a furnace.

The main equipment (fig. 1 and 2) is assembled on a car : the mixed powder is intro- duced in a distributing container. The flow is defined with a dosing screw operated

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986123

cl-160 JOURNAL DE PHYSIQUE

a t a v a r i a b l e speed. The powder discharged i n a low pressure a i r chamber i s t r a n s - p o r t e d pneumatically w i t h d r y and o i l f r e e a i r . The f l o w i s r e g u l a t e d w i t h accurate pressure c o n t r o l . The powder i s sprayed i n t h e furnace w i t h w a t e r - j a c k e t t gun.

The system i s c o n t r o l l e d w i t h e l e c t r o v a l v e s , pressure gauge and t h e r m o s t a t i c regu- l a t i o n f o r i n s u r i n g a constant f l o w and complete s a f e t y . The device i s a b l e t o p r o j e c t 15 t o 50 Kg/h.

2.2. Raw M a t e r i a l s .

I n a f i r s t stage, compositions i n t h e A1203-Ca0 system where synthesized. The raw m a t e r i a l s were : A1 powder, Alp03 powder and Ca0p IXPER.

The f i r s t t e s t s w e r e performed u s i n g Ca02 IXPER 60C c o n t a i n i n g 60 wt % Ca02. The remainder c o n s i s t s o f CaO + CaC03. F u r t h e r attempts were performed w i t h CaOp IXPER 75 C c o n t a i n i n g 75 % CaOp.

T y p i c a l m i x t u r e compositions were :

- 50 % A1203 ( i n weight)

- 50 % A1 + CaOp where CaOp i s t h e t r u e peroxide c o n t e n t

- The Al/CaOp r a t i o was 0.25.

I n t h e case o f IXPER 60 C, the f i n a l t h e o r e t i c a l A1203 c o n t e n t was 58 % whereas i n t h e case o f IXPER 75 C, t h e f i n a l A1203 content was 65 %.

FEEDING MIXER

WATER JACKETED GUN

Figure 1 : Process drawing.

I n a second stage, compositions i n t h e system A1203-Ca0-Zr02 were synthesized. The Zr02 powder was s u p p l i e d by HVH. The mean g r a i n s i z e was 5 um.

Two m i x t u r e s were i n v e s t i q a t e d , u s i n q o n l y Ca02 IXPER 75 C as a CaO precurseur. - - The t h e o r e t i c a l compositi6ns were :

1)CaO : 3 0 % 2)CaO : 2 0 %

These m i x t u r e s were p r o j e c t e d o n t o a w a l l o f r e f r a c t o r y b r i c k s placed i n a furnace

t r e a t e d a t 1500°C. The a i r flow ranged between 20 and 40 l / h o u r ; t h e powder f l o w

ranged between 20 and 40 Kg/hour.

Figure 3 : C-A deposit

The phase composition and microstructure was investigated by X-Ray d i f f r a c t i o n and scanning electron microscopy on samples prepared from IXPER 60 and IXPER 75 C . In the case of IXPER 60 C , specimens have been sampled on upper and lower p a r t s of the refractory wall. The upper samples consist of mixtures of CaA1204 (CA) and Ca12A114033 (C2A7) phases whereas the lowest samples mainly consist of r e c r y s t a l l i -

zed C12A7. As shown by the binary A1203-Ca0 phase diagram, the enrichment i n lime

i n the lowest part a r i s e s from the occurence of the e u t e c t i c between C12A7 and CA a t

1360°C. As t h i s mixture has a A1203 content of 58 %, more than the half of t h i s i s

melted a t 1500°C so t h a t a liquid phase of composition close t o C12A7 flows down and

recrystal l i ses during the cooling process. 131

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I n t h e case o f IXPER 75 C, no CpA7 i s l o n g e r detected by XRD. The o n l y phases are CA and CAZ. I n f a c t t h e AI203 c o n t e n t (65 %) l i e s i n t h e e q u i l i b r i u m f i e l d o f s o l i d s CA + CA2, t h e s o l i d u s o f which i s a t 160Z°C.

This observation o f completemelting ~f t h i s m i x t u r e d u r i n g t h e p r o j e c t i o n means t h a t the exothermi c r e a c t i o n leads t o temperatures we1 l above 1600°C. T y p i c a l mi c r o s t r u c - t u r e s by S.E.M. o f b o t h compositions are shown i n f i g . 4 a and 4 b.

The two compositions i n v e s t i g a t e d i n the A1203-Ca0-Zr02 system m e l t as w e l l as t h e A1203-Ca0 b i n a r y compositions. However, d u r i n g t h e c o o l i n g process, some cracks are observed.

The XRD examination o f t h e m i x t u r e c o n t a i n i n g 30 % CaO shows CaZrOg, CA and CA2 pha- ses w h i l e t h e m i x t u r e c o n t a i n i n g 20 % CaO shows cubic ZrOz, CaZr03 and CA2. By

S.E.M. t h e z i r c o n i a phases occur as c l e a r , equiaxed g r a i n s of 1 5 pm diameter i n a m a t r i x o f calcium aluminates ( f i g . 5a and 5 b ) .

The A1203/CaO + AI203 r a t i o s i n b o t h m i x t u r e s a r e r e s p e c t i v e l y 54 % and 67 %. As t h e z i r c o n i a r e a c t s o n l y w i t h c a l c i a and forms no e u t e c t i c w i t h t h i s o x i d e below 2200°C, i t i s b e l i e v e d t h a t two stages are i n v o l v e d i n t h e compounds formation :

1- Aluminate formation from l i q u i d phase as described above f o r t h e b i n a r y system

Al203-CaO .

2- Reaction o f aluminate w i t h z i r c o n i a y i e l d i n g : i- ZrCa03 from CA + l i q u i d alumina- t e i n t h e m i x t u r e c o n t a i n i n g 30 % CaO ; ii- Zr02 (cubic) s a t u r a t e d w i t h CaO from s o l i d r e a c t i o n w i t h CA + CA2 i n t h e m i x t u r e c o n t a i n i n g 20 % CaO. 141

F i g u r e 4. a. S.E.M. photograpn o f a b. S.E.M. photograpo o f a p o r i s h e d p o l i s h e d c r o s s - s e c t i o n showing t h e CA cross-section snow-rng t h e c r y s t a l - and i n t e r s t i t i a l C12A7 phases. l i s a t i o n of CA and CA2 ( d a r k ) .

No m o n o c l i n i c Zr02 phase was detected i n b o t h m i x t u r e s so t h a t t h e crack formation d u r i n g the c o o l i n g process a r e n o t assumed t o a r i s e from t h e Zr02 q u a d r a t i c

ZrO2 monoclinic t r a n s f o r m a t i o n b u t r a t h e r t o d i f f e r e n t thermal expansion c o e f f i c i e n t s of z i r c o n i a - r i c h phases ( a > 10.10-6/"~)and aluminate phases ( a < 10.10-6/"~).

I V - CONCLUSIONS.

This new process has been a p p l i e d successfuly a t an i n d u s t r i a l p i l o t scale.

Dense and w e l l c r i s t a l l i z e d m a t e r i a l s have been deposited, s i m u l a t i n g t h e r e f r a c t o -

r y r e p a i r i n a furnace i n o p e r a t i o n a t 1500°C.

ACKNOWLEDGEMENTS

This project has been f i n a n c i a l l y sponsorec by the Region Wallonne and has been developped by the Association Monmentanee Eurofour-Tsira.

The refractory materials have been analized a t the Universitg Libre de Bruxelles -

Chimie I n d u s t r i e l l e e t Chimie des Solides.

REFERENCES.

/ l / Plumat, E., Duvigneaud, P.H., Naessens, F.- Science of Ceramics 11, 185 (1981).

/2/ Plumat, E.- S i l i c a t e s I n d u s t r i e l s , 46, 2, 35-42 (1981).

/3/ System A1203-Ca0. Fig. 231-233 - Phase diagram f o r Ceramists - The American Ceramic Society Inc (1964).

/4/ System Zr02-CaO - Phase diagram f o r Ceramists (Fig. 242-243) -The American

Ceramic Society Inc (1964).