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FORMATION AND SINTERING OF γ-Al2 O3 WITH MgO ADDITIONS FROM COPRECIPITATED
HYDRATES
J. Katanic-Popovic, M. Gasic, Lj. Kostic-Gvozdenovic
To cite this version:
J. Katanic-Popovic, M. Gasic, Lj. Kostic-Gvozdenovic. FORMATION AND SINTERING OF γ- Al2 O3 WITH MgO ADDITIONS FROM COPRECIPITATED HYDRATES. Journal de Physique Colloques, 1986, 47 (C1), pp.C1-31-C1-35. �10.1051/jphyscol:1986105�. �jpa-00225489�
J3URNAL DE PHYSIQUE
Colloque C1, suppl6ment au n02, Tome 47, fgvrier 1986 page cl-31
FORMATION AND SINTERING OF 7-Al,O, WITH MgO ADDITIONS FROM COPRECIPITATED HYDRATES
J. KATANIC-POPOVIC, M. GASIC and Lj. KOSTIC-GVOZDENOVIC"
" B o r i s K i d r i c h " I n s t i t u t e for N u c l e a r S c i e n c e , P.O.B. 5 2 2 , B e o g r a d , Y u g o s f a v i a
* ~ a c u l t y of T e c h n o l o g y and M e t a l l u r g y , K a r n e g i j e v a 4 , 11000 B e o g r a d , Y u g o s l a v i a
Resume - Oes poudres d'alumine-y avec un dopage homogene o n t e t e obtenues par c a l c i n a t i o n des c o p r e c i p i t e s AlOOH - Mg(OH)2 formant des s o l u t i o n s s o l i d e s . L ' i n f l u e n c e du dopage, pour des r a p p o r t s Mg/Al de 0.02 L3 0.06 sur l e f r i t t a g e a e t e analysee par mesure de l a densite, de l a p o r o s i t e , des r e t r a i t s l i n e a i r e s a i n s i que par determination de l a r e s i s t a n c e L3 l a t r a c t i o n .
A b s t r a c t - The gavma A1-0 powders w i t h homogeneous doppant d i s t r i b u t i o n were
obtained by c a l c i n a t i o n L o ? c o p r e c i p i t a t e s consisted o f AlOOH s o l i d s o l u t i o n s w i t h Mg(OH)2. The e f f e c t o f a d d i t i v e w i t h Mg/A1 i o n r a t i o 0.02-O.C6 on s i n t e - r i n g was analysed by d e n s i t y , p o r o s i t y , l i n e a r shrinkage and t e n s i l e s t r e n g t h determi nations.
I - INTRODUCTION
I n t h e previous papers /1,2/ i t was shown t h a t a d d i t i o n o f MgO i n the form o f magne- sium n i t r a t e promoted c o m p r e s s i b i l i t y and i n some e x t e n t t h e s i n t e r a b i l i t y o f commer- c i a l grade g i b b s i t e f o r p r o d u c t i o n c a t a l y s t supports. I t was demonstrated t h a t b r u c i t e and g i b b s i t e d i d n o t form s o l i d s o l u t i o n s d e s p i t e t h e i r s i m i l a r i t y i n s t r u c t u r e , w h i l e boehmi t e formed metastable s o l i d s o l u t i o n s w i t h b r u c i t e /3/. These s o l i d s o l u t i o n s can be formed as c o p r e c i p i t a t e s from m i x t u r e s o f aluminum and magnesium s a l t s w i t h a l k a l i /4,5/.
This paper deals w i t h t h e e f f e c t s o f doping agent Mg(OH)z, c o p r e c i p i t a t e d w i t h pseu- doboehmi t e on t h e f o r m a t i o n and s i n t e r i n g o f gamma A1 203.
I1 - EXPERIMENTAL PROCEDURE
M a t e r i a l was prepared by p r e c i p i t a t i o n method /4/ from 1,O M s o l u t i o n s o f aluminum and magnesium c h l o r i d e s w i t h 10% amonium hydroxide a t t h e constant temperature (65'~,) a d the pH value 9-10. A f t e r washing and d r y i n g p r e c i p i t a t e s were c a l c i n e d a t 500°c,
r:
2 i n o r d e r t o o b t a i n powders w i t h h i g h s p e c i f i c s u r f a c e areas (Table 1 ) . On t h e b a s i s o f the r e s u l t s obtained from thermal analyses (TGA and DTA) t h e temperature o f c a l c i - n a t i o n was chosen. The spectrochemical a n a l y s i s was used f o r MgO c o n t e n t determina- t i o n and n i t r o g e n a d s o r p t i o n areameter f o r s p e c i f i c surface area measurements. The p r e c i p i t a t e s and c a l c i n e d powders were wet ground i n alumina b a l l m i l l i n d i s t i l l e d water i n order t o deagl omerate p a r t i c l e s . The p r i s m a t i c samples ( f o r d i 1 atometri c examinations) were made by c o l d p r e s s i n g a t 100 MPa and a l s o c y l i n d r i c a l samples ( f o r d e n s i t y and s t r e n g t h ) a t 100 and 150 MPa. The compacts were s i n t e r e d a t 7 0 0 0 ~ , 2 ~ i n a i r ( h e a t i n g r a t e zOc/min). The s i n t e r i n g temperature was chosen on t h e b a s i s of t h e X-ray r e s u l t s . Gamma A1203 w i t h o u t a d d i t i v e was transformed t o t h e t a phase on t h e
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986105
(21-32 J O U R N A L DE PHYSIQUE
temperature h i g h e r than 7000C. The d e n s i t i e s o f pressed samples were determined by measuring dimensions and weights, t h e d e n s i t i e s o f s i n t e r e d samples by immersion i n xylene. The diametral compresion t e s t was used f o r measuring t h e t e n s i l e s t r e n g t h o f pressed and s i n t e r e d c y l i n d r i c a l samples 161.
TPJLE 1. THE CHAP,ACTEkISTICS OF CALCIEiEIj P0IIDEP.S AT 500°C
---
4. 244 i
5 , 0.06 190 I
I
6. SP! NEL 28.2 i 1 0
7 . 28
I11 - RESULTS AND DISCUSSION
The p r e c i p i t a t e products contained pseudoboehmi t e as p o o r l y c r y s t a l 1 iz e d phase. The decreasing o f I R absor t i o n peaks i n s p e c t r a presented i n Fig.1, a t frequency 1073 as w e l l as a t 3262 c i P f o r boehmite was evidented f o r c o p r e c i p i t a t e s . The sharp absorption peaks a t 3780 and 900 cm-? f o r b r u c i t e were missed i n c o p r e c i p i t a t e s I R spectra. These r e s u l t s and t h e broadening o f X-ray peaks w i t h i n c r e a s i n g o f Mg/A1 i o n r a t i o i n p r e c i p i t a t e s ( F i g .2a) p o i n t e d o u t t h a t probably metastable s o l i d s o l u t i o n s between pseudoboehmite and b r u c i t e were formed.
LOO0 3000 2000 1000
FREQUENCY I CIS' 1
PBhkr PSEUDOBOEHMITE
KATIC
PBI30 PB 020
PB150 PBOLO PBO2 006
OLE
0 01.
0.00
Fig.1. I n f r a r e d absorp- t i o n spectra o f pseudobo- ehmite, b r u c i t e and co- p r e c i p i t a t e s .
L 5 35 2 5 15 2e (a) 65 5 5 45 35 2 5 2e (b)
Ghk! = GAMMA A1203
Fig.2. X-ray d i f f r a c t o g r a m s o f pseudoboehmi t e and c o p r e c i p i t a t e s ( a ) and powders c a l c i n e d a t 5 0 0 ~ ~ ( b ) .
M g / A i I O N H A T I C
Very i n t e n s i v e w e i g h t l o s s i n t h e t e m p e r a t u r e range 200-400'~ (completed a b o u t 5 0 0 ~ ~ ) and t h e endothermic peaks f o r d e h y d r a t i o n and phase t r a n s f o r m a t i o n t o gamma A120 i n t h e temperature range 4 5 0 - 4 9 0 ' ~ were observed. From I R and X-ray d a t a ( F i g . 2 b ) i ? was concluded t h a t t h e c a l c i n e d powders c o n s i s t e d f r o m p o o r l y c r y s t a l l i z e d gamma o r e t a A1 O3 and s o l i d s o l u t i o n s w i t h magnesia.
I t cou?d be assumed t h a t Plg2+ i o n s occupated t h e c a t i o n vacancies i n t e t r a h e d r a l po- s i t i o n s i n gamma alumina s t r u c t u r e and formed t h e s o l i d s o l u t i o n s . The observed broadening o f X-ray peaks ( F i g . 2 b ) f o r t h e c o m p o s i t i o n w i t h 0.06 Mg/Al r a t i o would be a t t r i b u t e d t o t h e appearance o f l o w c r y s t a l l i z e d MgA1204 ( s p i n e l ) as w e l l as some inhomogenei t y i n l a t t i c e c o n s t a n t w i t h i n t h e c r y s t a l 1 i t e s .
M g I A l I O N R A T I O x -0.00 A -0.02 a -0-OL -0 0 6
-
' r n
.. .
LOO-
-
1 300 LOO 500 600 900 800
-
T E M P E R A T U R E I ? )
I
Fig.3. The r e l a t i o n between s p e c i f i c s u r f a c e area and t h e teniperature o f c a l c i n a t i o n f o r pseudoboehmite and c o p r e c i p i t a t e powders.
Very s i m i l a r r e l a t i o n between s p e c i f i c s u r f a c e a r e a and c a l c i n a t i o n t e m p e r a t u r e f o r t h e samples w i t h d i f f e r n t Mg/A1 i o n r a t i o c o u l d be seen i n t h e F i 5 . 3 . I t was n o t i - ced t h a t a d d i t i o n o f i4gqi i o n s had r e l a t i v e l y s m a l l i n f l u e n c e on t h e s p e c i f i c s u r - f a c e area up t o 0.04 Mg/A1 r a t i o . Some g r e a t e r decrease was r e g i s t e r e d f o r 0,06 Plg/Al r a t i o . T h i s c o u l d be caused by t h e presence o f mixed magnesia alumina s p i n e l , which had c o n s i d e r a b l y s m a l l e r s p e c i f i c s u r f a c e area ( T a b l e 1 ) .
I
'1:161 I C N @ & T I C ::z:o- a06 2.0
F i g . 4 . D i l a t o m e t r i c curves o f t h e samples ob- t a i n e d f r o m o x i d e s and h y d r o x i d e s .
C I - 3 4 JOURNAL DE PHYSIQUE
The sample obtained from oxide ( c a l c i n e d powder) w i t h o u t a d d i t i v e d i d n ' t s h r i n k du- r i n g s i n t e r i n g up t o 8 0 0 ~ ~ ( t h e d i l a t o m e t r i c curves i n the Fig.4). The r e l a t i v e li- near shrinkage o f samples obtained from oxides w i t h MgO a d d i t i o n s depended from Mg/Al r a t i o . These shrinkages were up t o 0,5% i n the temperature range t o 800'~. The s h r i n -
TABLE i. THE CHARACTERISTICS OF PPESSED AND SIF!TERED SAI!PLES OBTAIPIED l'll0r HYUROXIDE
kage o f samples o b t a i n e d from hydroxides i s very i n t e n s i v e u p t o 6 0 0 ' ~ and i t was caused by dehydration and phase transformation, and a l s o was i n f l u e n c e d by MgO ad- d i t i o n . The l i n e a r shrinkage f o r these samples i n the range 600-800'~ was about 1%.
ION RATIO NG/AL
0.00
TABLE 3. THE CHARACTERISTICS ,OF PRESSED AND SINTERED SAFPLES OBTAINED FROR OXIDE
The d e n s i t i e s and t e n s i l e s t r e n g t h o f pressed and s i n t e r e d samples (shown i n t h e Tables 2 and 3) depended on p r e s s i n g pressure b u t they were p r a c t i c a l l y independent' from MgO a d d i t i o n . P r e v i o u s l y observed e f f e c t /1,2/ o f MgO a d d i t i o n was n o t pronoun- ced i n t h e c o p r e c i p i t a t e d samples. The d e n s i t i e s and mean t e n s i l e s t r e n g t h s o f t h e s i n t e r e d samples obtained from hydroxides were some h i g h e r than those from oxides.
However, the h i g h value o f standard d e v i a t i o n s from mean values o f t e n s i l e s t r e n g t h measurements r a i s e d d i f f i c u l t i e s f o r i n t e r p r e t a t i o n o f r e s u l t s .
PRESSING PRESSURE (RPA)
100 150
I V . CONCLUSIONS
- Chemical p r e c i p i t a t i o n method was used t o prepare homogeneous doped pseudoboehmite w i t h b r u c i t e . Coprecipi t a t e d products were c o n s i s t e d o f metastable s o l i d s o l u t i o n s
DENSITY (BCH-~)
PRESSED
1.25 1.42
BEAN VALUE OF TENSILE STRENGTH
(NPA)
SINTERED
1,16 1.23
PRESSED
3.5 : 1.4 3.5 * 1.4
-.
SINTEREO
4,6 * 1,2 2.9 0.8
as p o o r l y c r y s t a l l i z e d g e l s .
- The c a l c i n e d powders were poor1 c r y s t a l l i z e d gamma o r e t a A120jas w e l l as s o l i d s o l u t i o n s w i t h magnesia. The M a t i o n a d d i t i o n caused t h e spec, IC s u r f a c e area decrease and i n t h e same t i m e t h e gamma A1 0 phase s t a b i l i t y improvement.
- The d e n s i t i e s and mean t e n s i l e s t r e n g t h s OF $he s i n t e r e d samples o b t a i n e d f r o m h y d r o x i d e s were h i h e r t h a n those f r o m o x i d e s .
- The a d d i t i o n o f Mgei i o n s up t o 0.06 Mg/Al r a t i o had r e l a t i v e l y small e f f e c t on 1 i near s h r i n k a g e d u r i n g s i n t e r i n g , on d e n s i t i e s and t e n s i l e s t r e n g t h s i n compari- son w i t h pure gamma A1203.
REFERENCES
/I/ KataniC-Popovie, J., GaSiC, M. and KiCeviC, D., i n " S i n t e r i n g - Theory and P r a c t i c e " , Mater. S c i . Monographs, 14 (1982) 153, D.Kolar, S.Pejovnik and M.M.Ri s t i e (Eds . ) E l s e v i e r S c i . P u b T Comp. Amsterdam, Oxford, New York.
/2/ KataniC-PopoviC, J. and GaSiC, M. Travaux d'ICSOBA 13 (1983) 369.
/3/ Mascolo, G., Marino, 0. and Pappalardo, W., Trans. =it. Ceram.Soc., 81
(1982) 75.
/4/ ratt ton, R.J., Amer.Ceram.Soc. V u l l . , 48 (1969) 759.
/5/ F e i t k n e c h t , W., H e l v . Chim.Acta., 25, (1942) 555.
/6/ Rudnick, A., Hunter, A.R. and H o l d G , F.C., Mater-Res. Standards, 3 (1963) 283.
