WET PROCESSES FOR THE PREPARATION OF ISOMETRIC FERRITE PIGMENTS WITH SPINEL STRUCTURE AND DEFINED FINENESS

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WET PROCESSES FOR THE PREPARATION OF ISOMETRIC FERRITE PIGMENTS WITH SPINEL

STRUCTURE AND DEFINED FINENESS

H. Hibst

To cite this version:

H. Hibst. WET PROCESSES FOR THE PREPARATION OF ISOMETRIC FERRITE PIGMENTS

WITH SPINEL STRUCTURE AND DEFINED FINENESS. Journal de Physique Colloques, 1985,

46 (C6), pp.C6-55-C6-58. �10.1051/jphyscol:1985609�. �jpa-00224847�

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JOURNAL DE PHYSIQUE

Colloque C6, supplkrnent a u n09, Tome 46, septernbre 1985 page C6-55

WET PROCESSES FOR THE PREPARATION OF ISOMETRIC F E R R I T E PIGMENTS WITH S P I N E L STRUCTURE AND DEFINED FINENESS

H. H i b s t

BASF AktiengeseZZschaft, AmmoniakZaboratorium, 0-6700 Ludwigshafen, F.R.G.

Resume

-

Au moyen d ' u n procede humide de n e u t r a l i s a t i o n e t d ' o x y d a t i o n combinees, on p a r v i e n t

Z

r e g l e r l a & p a r t i t i o n g r a n u l o m 6 t r i q u e des

f e r r i t e s

a

s t r u c t u r e s p i n e l l e a f i n d ' o b t e n i r une d i s t r i b u t i o n granulome- t r i q u e e t r o i t e

a

l ' i n t e r i e u r d ' u n e l a r g e gamme (10

-

100 m2/g de s u r f a c e s p e c i f i q u e e q u i v a l e n t e )

.

Le procede a u t o r i s e l a p r e p a r a t i o n de pigments magnetiques y-CoxFe3-x04 5-0

sx

d'une f i n e s s e s u f f i s a n t e , i s o t r o p e s , m u l t i a x i a u x e t d ' u n e h a u t e c b e r c i v i t@ a i n s i que de y-ZnxFe3-x04,5-0

,sx

t r G s f i n s p o u r l e s encres magnetiques c o l o r e e s ( I m p r i m e r i e e t Toners).

A b s t r a c t

-

A wet n e u t r a l i z a t i o n / o x i d a t i o n process a l l o w s f e r r i t e s w i t h s p i n e l s t r u c t u r e t o be ~ r o d u c e d i n a wide range o f d e f i n e d , h i g h degrees o f fineness (10

-

100 m / g ) and a narrow p a r t i c l e s i z e d i s t r i b u t i o n . F i n e l y d i v i d e d , i s o m e t r i c , h i g h l y c o e r c i v e and m u l t i a x i a l

b-CoxFe3-x04.5-0.5x magnetic pigments and v e r y f i n e 1 y d i v i d e d , h i g h l y magnetic r-ZnxFe3-x04.5-0,5x f o r c o l o u r e d magnetic p r i n t i n g i n k s and t o n e r s can t h u s be obtained.

1. I n t r o d u c t i o n

Barium f e r r i t e p l a t e l e t s ( 1 ) and i s o m e t r i c f e r r i t e powders w i t h s p i n e l s t r u c t u r e and h i g h m u l t i a x i a l m a g n e t o c r y s t a l l i n e a n i s o t r o p y a t t r a c t i n t e r e s t f o r new h i g h - d e n s i t y magnetic s t o r a g e t e c h n o l o g i e s . I s o m e t r i c f e r r i t e s a r e c u r r e n t l y b e i n g t r i e d o u t i n magnetic i s o t r o p i c s t o r a g e media f o r a l o n g i t u d i n a l / v e r t i c a l r e c o r d i n g mode ( 2 ) . Thesepigments a r e a l s o i m p o r t a n t f o r magnetic l i q u i d s , magnetic p r i n t i n g i n k s , and t o n e r s . Wet chemical syntheses ( 3 ) a r e r e q u i r e d f o r t h e p r o d u c t i o n o f v e r y f i n e l y d i v i d e d and l a r g e l y u n s i n t e r e d i r o n o x i d e

pigments. To o b t a i n a narrow p a r t i c l e s i z e d i s t r i b u t i o n and a homogeneous d i s t r i b u t i o n o f s u b s t i t u t e d i o n s i n t h e l a t t i c e , t h o s e wet methods seem t o o f f e r t h e most prospects, which proceed s o l e l y from s o l u t i o n s o f metal s a l t s (and a i r ) w i t h o u t t h e a d d i t i o n o f any s o l i d s .

2. O x i d a t i o n process

I n t h e o x i d a t i o n process (4,5) f e r r i t e powders a r e o b t a i n e d f r o m aqueous

d i s p e r s i o n s o f M(I1)- and F e ( I 1 ) - h y d r o x i d s (M = Co, Zn, ...) ( r e a c t i o n I ) by a i r o x i d a t i o n ( r e a c t i o n 11) a t T

>

50 "C ( 0 4 x 1 ) :

I ) x ~ 2 '

+

(3-X) ~ e + ~6 OH- +

-

3 (MxFe3-x)l/3(0H)2)

These powders can be f u r t h e r o x i d i z e d t o p o t a c t i c a l l y w i t h a d d i t i o n a l a i r a t T = 300 "C, r e t a i n i n g t h e i r c r y s t a l h a b i t and s t r u c t u r e i n a m e t a s t a b l e s t a t e ( 6 ) :

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985609

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C6-56 JOURNAL DE PHYSIQUE

A l t h o u g h d e c r e a s i n g F e ( I 1 ) - c o n t e n t due t o o x i d a t i o n ( r e a c t i o n 111) reduces u n i - a x i a l a n i s o t r o p y and l e a d s t o i n c r e a s i n g +-values (mr = Mr/MS) ( f i g . l ) , t h e c o e r c i v i t y Hc and mr f o r $'-Fez03 a r e t o o l o w f o r i s o t r o p i c magnetic r e c o r d i n g . By s u b s t i t u t i n g C O ~ + , t h e m a g n e t o c r y s t a l l i n e a n i s o t r o p y and H~ can be

s u b s t a n t i a l l y increased. I n t h e c u b i c p a r t i c l e s , t h i s l e a d s t o a t r i a x i a l p r e f e r r e d d i r e c t i o n of magnetism i n ( 7 a ) w i t h a maximum mr v a l u e o f 0.83 ( 8 ) . O n l y t h e f i n e l y d i v i d e d d'-C0~Fe3-~04.5-0.5~ produced i n t h e n e u t r a l pH range has h i g h Hc and mr ( f i g . 2). As t h e Co c o n t e n t x r i s e s , c o e r c i v i t y i n c r e a s e s t o 120 kA/m a t f i r s t and t h e n f a l l s a t x > 0.6 ( f i g . 3 ) .

Flg. I - Fe30, (a1 (oxldatlon method: FeCI2 t NaM + a l r .

r

-

⁹⁰^r.^a⁼^const.)^am^Y-Fe2O3⁽⁰¹ ^{Fig. 2}

^-

Coo.z5Fe2,7504 ( x ) (oxIdation method:

CK12 + FeCIZ + Nalw + a i r . 1 = 90 -C.

pH

-

^canst.)^and 7-C00,25Fe2.750,.375 (01

The p a r t i c l e s i z e o f t h e f e r r i t e s depends on r e a c t i o n parameters such as pH, T, and c a t i o n c o n c e n t r a t i o n ( 5 ) . The a t t a i n a b l e f i n e n e s s i s r e s t r i c t e d t o s p e c i f i c BET s u r f a c e areas o f S N ~ L 12 m2/g ( f i g . 1,2). I n t h e c u b i c c r y s t a l h a b i t observed, t h i s corresponds t o a p a r t i c l e d i a m e t e r

0

o f 0.15 ,um and a p a r t i c l e volume V o f 8

.

10-4 hm3. However V = 2

.

^10-4,um3 ^{( 0}⁼0.1 pm; S N ~ = 20 m2/g) i s necessary f o r low-noi se m a g n e t i c pigments.

3. N e u t r a l i z a t i o n process

I n t h e n e u t r a l i z a t i o n process (9,lO) aqueous d i s p e r s i o n s of M(I1)-, F e ( I 1 ) - and F e ( I I 1 ) - h y d r o x i d e s w i t h a m o l a r c o n c e n t r a t i o n o f A = [ ~ e 3 7 / [ ~ 2 +

+

F e 2 V = 2 ( r e a c t i o n I V ) a r e heated a t T,50 "C w i t h e x c l u s i o n o f a i r ( r e a c t i o n V):

I V ) X ~ 2 ' + ( l - x ) Fez+ + 2 Fe3+ + 8 OH-

-

3 (MxFe3-x)l/3(0~)8/3~

'-01

¹⁴⁰¹ ^mr

0.04

&-

0.64

'MI &

o.., .1l

.

0-2' 40

:! fd

Fig. 3 - ^CqFe3-i0, ^{( 4}(oxIdation r t h o d : C d l Z + FeC12 +

*om + alp. pH r 7.5. 1

-

PO -C) and ~ - C ~ f q , 0 4 ~ 5 . 0 . 5 x (01

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The f e r r i t e powders o b t a i n e d a r e e x t r e m e l y f i n e l y d i v i d e d ( 0 = 60

-

²⁰⁰A (114;

S N ~ > I 0 0 m z l g ) . Thus t h e volume o f t h e s e u l t r a f i n e p a r t i c l e s (V

<

2

.

^10-6 ^m⁾

i s c o n s i d e r a b l y l e s s t h a n t h e c r i t i c a l v a l u e o f 2

.

1 0 - 5 ~ m 3 fo r r - F e 2 0 3 (2), and t h e i r superparamagnetic c h a r a c t e r i s t i c i s n o t u s e f u l f o r magnetic s t o r a g e . 4. N e u t r a l i z a t i o n / o x i d a t i o n process

The new wet chemical method ( 1 3 ) s t a r t s w i t h aqueous d i s p e r s i o n s o f M(I1)-, F e ( I 1 ) - and F e ( I I 1 ) - h y d r o x i d s , which c o n t a i n i n c o n t r a s t t o t h e n e u t r a l i z a t i o n process an excess o f F e ( I 1 ) and a m o l a r c o n c e n t r a t i o n r a t i o A =

~ e 3 ~ / ~ 2 + + ~ e 2 3

<

2 ( r e a c t i o n V I ) . I n t h e f i r s t stage, t h i s i n i t i a l

p r e c i p i t a t e i s heated t o T

>

50 "C w i t h a h i g h n u c l e a t i o n r a t e under e x c l u s i o n o f a i r ( r e a c t i o n V I I ) . A f t e r w a r d s , t h e m i x t u r e i s o x i d i z e d by p a s s i n g a i r t h r o u g h i t , w i t h t h e r e s u l t s t h a t t h e MxE3-x04 n u c l e i grow homogeneously ( r e a c t i o n V I I I ) : V I ) x ~ 2 +

+

(1-x+y) Fez+

+

( 2 - y ) Fe3+

+

( 8 - y ) OH-

-

( M ~ F e 3 - x ) l / 3 ( o ~ ) ( 8 - y ) / 3

1

y = 2 o r A = f l e 3 2 7 / D 2 + + ~ e 2 Y = ( 2 - y ) / ( l + y ) = 0 r e p r e s e n t s t h e r e a c t i o n c o n d i t i o n s o f t h e o x i d a t i o n process, y = 0 o r A = 2 t h o s e o f t h e n e u t r a l i z a t i o n process.

As A i n t h e o r i g i n a l p r e c i p i t a t e r i s e s , t h e pigment p a r t i c l e s become i n c r e a s i n g l y f i n e r ( f i g . 4

-

6 ) . The d e f i n e d degree o f f i n e n e s s t h a t can t h u s be achieved over a v e r y wide range l i e s between t h a t f o r t h e o x i d a t i o n process ( < 10 m2/g), and t h a t f o r t h e n e u t r a l i z a t i o n process ( > l o 0 m2/g). F o r small v a l u e s o f A = 0.05 an s i g n i f i c a n t i n c r e a s e i n Hc and mr can be observed ( f i g s . 4,5). As i s r e v e a l e d by e x a m i n a t i o n under t h e e l e c t r o n microscope, t h i s can be a s c r i b e d t o a narrower p a r t i c l e s i z e d i s t r i b u t i o n . The new process p e r m i t s t h e p r o d u c t i o n o f a d e q u a t e l y f i n e l y d i v i d e d r-CoxFe3-x04.5-0.5x w i t h h i g h c r y s t a l 1 in e m u l t i a x i a l a n i s o t r o p y and c o e r c i v i t y ( f i g . 5 ) . The temperature-dependence o f Hc i n c r e a s e s as usual w i t h mr and has a v a l u e o f 8 (kA./m)/lO "C a t room t e m p e r a t u r e f o r mr = 0.8. I t can be decreased, p o s s i b l y t o g e t h e r w i t h t h e m a g n e t o s t r i c t i o n a s s o c i a t e d w i t h t h e h i g h c r y s t a l a n i s o t r o p y , b y s u b s t i t u t i n g o t h e r elements. Good p r o s p e c t s a l s o appear t o be h e l d o u t by a p a r t i a l change-over f r o m volume t o s u r f a c e doping.

2

5'

c . .

2 2 u

", = A

26

<

24.

22. 901 a

18. 7010.91 I : 16. 6010.01 14 5010.71 I : 12 4oIo.sl

I :

70 30lo.sJ

I ,

8 2 0 ~ 0 . 4 1 A

0 0.05 0.1 0.15 0.2

0 01 , ^A

0 0.5 1.0 1.5 2

F I ~ . 5 - CO ~, ~~F( X I (cmblned neutrallzatlonl ~~ .~ ~~, r i g . 4 - r y 4 ( x ) (canblned neutralfzatlon-oxtdatlm method: oridatlon r t h a d : c d 1 2 + FeCIZ + r&13 + IbOH + a i r . reel + F ~ C I + Ham + a l r . T = 90 'C. pH = 7.51 and I = 80 -C. pH = 7.51 and r-Coo~19FeZ.8104.405 (0) Y-F<o~ ((a) :A = ( 2 - y ) f ( l t y l = Z F ~ ~ + ~ / C F ~ ~ + J I ₍₁

-

(2-y)l(l+y) = C F ~ ~ ' J / C C O ~ ' + f e 2 + ~ 1

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JOURNAL DE PHYSIQUE

The f i n e n e s s o f ZnXFe3-,O4 depends s t r o n g l y on t h e z i n c c o n t e n t x as w e l l as on t h e r e l a t i o n s s h i p d e s c r i b e d w i t h A. With i n c r e a s i n g SN t h e pigments a r e more s i n t e r e d d u r i n g o x i d a t i o n t o r-ZnxFe3-x04.5-0.5x a t 360 " C ( f i g . 6 ) . As x i n c r e a s e s , t h e c o l o u r o f t h e s e pigments changes from brown t o y e l l o w , and t h e s u i t a b i l i t y f o r t o p p i n g i s improved. I f t h e z i n c c o n t e n t i s l o w ( x < 0.5), an i n c r e a s e i n magnetic s a t u r a t i o n above t h e l e v e l o f undoped b+-Fe203 ( 7 b ) i s observed ( f i g . 7 ) . Consequently, f i n e l y d i v i d e d zinc-doped r - F e 2 0 3 i s more s u i t a b l e f o r t h e p r o d u c t i o n o f c o l o u r e d magnetic p r i n t i n g i n k s and t o n e r s .

Flg. 7 - Zn,F~-xo, 1x1 and 2n,Fq-,O C.5- ( 0 ) ( p ~ p s ~ a t l o n I n flg. 6)

I w i s h t o t h a n k Dr. H. Jakusch and Dr. U. Kullmann f o r magnetic measurements and Dr. W. Steck f o r d i s c u s s i o n s .

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2

(1982) 263; Angew. Chem. I n t . Ed. Engl.

1

(1982) 270

2. J.U. Lemke, IEEE Trans. Magn.

15

(1979) 1561; J. ~ p p l

.

~ h y s . 53 (1982) 2561 3. W. Steck, I n t . Seminar Magn. Lnf. Techn., Gregynog 1984 ( u n p u n i s h e d ) 4. R. B r i l l , K. Schoenemann, I G $ ? r b e n i n d u s t r i e AG, DP 712 457 (1935)

5 . T. Takada, M. Kiyama, F e r r i t e s Proc. I n t . Conf., Kyoto 1970 ( p u b l . 1971)

6. W. F e i t k n e c h t , Pure Appl

.

^Chem.

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( 1 9 6 4 ) 423

7. J. S n i t , H.P.J. Wijn, F e r r i t e , P h i l i p s Techn. B i b l . , 1962; ( a ) pp. 191-193;

( b ) pp. 172-176

8. E.P. Wohlfarth, J. Phys. Radiuq 20 (1959) 295 9. W.C. Elmore, phys. Rev.

54,

( 1 9 3 8 F 3 0 9

10. W.J. Schuele, V.D. Deetscr'eek, J. Appl. Phys. Suppl

. ²

(1961) 235 S 11. R.E. Vanderberghe e t a1

.,

^J. dagn. Magn. Mat.

15-18

(1980) 1117 12. E. K i j s t e r i n " p a r t i c u l a t e r e c o r d i n g media", ed. C.D. Mee ( i n p r i n t ) 13. H. H i b s t , BASF AG ( p a t e n t a p p l i c a t i o n f i l e d )