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MÖSSBAUER STUDY OF CRYSTALLITE FORMATION IN BASALT GLASS CERAMICS
P. Auric, J. Chappert, A. Bandyopadyay, J. Zarzycki
To cite this version:
P. Auric, J. Chappert, A. Bandyopadyay, J. Zarzycki. MÖSSBAUER STUDY OF CRYSTALLITE
FORMATION IN BASALT GLASS CERAMICS. Journal de Physique Colloques, 1980, 41 (C1),
pp.C1-277-C1-278. �10.1051/jphyscol:1980197�. �jpa-00219790�
JOURNAL DE PHYSIQUE Colloque C1, suppl&nent au n " 1 , Tome 41, janvier 1980, page C1-277
M~SSBAUER STlJDY OF CRYSTAU-ITE FORMATION I N BASALT GLASS CERAMICS
+ +
P.Auric, J. Chappert, A.K. Bandyopadyay and J. Zarzycki
Centre drEtudes NucZ&aires, D.R. F./Luboratoire d'lnteractions Hyperfinies, GrenobZe, France.
+
Laboratoire des Vemes, C. N. R.S., MontpeZZier, France.Missbauer spectroscopy has been used i n con- junction with other techniques f o r studying the c r y s t a l l i z a t i o n of Basalt Glass (50wt % Si02, 14wt % A1203, 13wt % Fe203, l O w t % CaO) as a function of heat treatment. F i r s t t h i s glass was melted twice a t 1500° C f o r 16 hours and subse- quently annealed a t 5i50 C . As such i t will be used a s a r e f e r e y e ("blank g l a s s " ) . The c r y s t a l - 1 ization stud jes 'were then carried out on samples heat-treated a t 600, 650, 700, 800, 900' C f o r 8 hours respectively.
X-ray d i f f r a c t i o n and transmission electron microscopic measurements did not allow t o detect the presence of any c r y s t a l l i n e phase in the blank glass and i n the sample heat-treated a t 600° C , while c r y s t a l l i t e s of magnetite and of some other minor phases such a s pyroxene were observed i n the other samples. The s i z e of t h e magnetit:
c l u s t e r s was estimated t o range between 40 A and
0
70 A. The lower the heat-treatment temperature, the smaller a r e the magnetite p a r t i c l e s .
Missbauer spectra were recorded a t various temperatures between helium and room temperatures on the same samples. Magnetic f i e l d s up t o 50 koe were applied a t 4.2 K. For each Missbauer spectrum, the contributions of two iron species have been separated.
-
Rebut% and d i 6 ~ ~ 6 b i 0 ~-
Some typical spectra, carried out a t room temperature a r e shown i n Fig. 1. Each spectrum, except f o r the 800 and 900 g l a s s , consists of two superimposed doublets. The l e s s intense one ( = 20 % ),
~ e ~ + , has Missbauer parameters r a t h e r similar t o t h a t of orthopyroxene [ I ] . The other one ( = 80 %) has been assigned t o magnetite i n a superparamagnetic s t a t e 121. Such an assignment was confirmed by experiments i n the presence of an external f i e l d . The 800 and 900 glass consist of the same two doublet spectra a sbefore, superimposed t o a d i f f u s e s i x l i n e magne- t i c spectrumcomi ng from magnetite be1 ow t h e blocking temperature.
-5.08 0 5.08
VELOCITY m m l s
Fig. 1.
-
Room temperature M6ssbauer spectra of blank glass and samples heat-treated a t 700 and 900' C for 8 hours. Solid lines are least squares f i t s .Miissbauer spectra performed a t 4 K a r e repre- sented i n Fig. 2. We find the same three contribu- tions : magnetite on each s i d e of the blocking temperature and ~ e ' + ions (20 %).
The superparamagneti c behaviour i s typical of small magnetic p a r t i c l e s
.
In several s t u d i e s 13-4-51 of such grains, i t has been reported t h a t t h e magnetic hyperfine s p l i t t i n g i s systematicallyArticle published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980197
C1-278 JOURNAL DE PHYSIQUE
smaller than t h a t found i n l a r g e r ones. Our expe- riments on the 800 and 900 a l a s s e s a t room tempe- r a t u r e confirm t h i s observation ; f o r example the 1 a r g e s t hyperf i ne f i e l d s ( ~ e ~ + tetrahedral s i t e s ) were estimated t o be 410 and 450 kOe f o r these two glasses respectively while i n the bulk magnetite Mc Nab
fi
[6] found 486 kOe. Accordi'ng t o the model of Morup and Topsoe [4], the hyperfine f i e l d f o r a p a r t i c l e of volume V , a t a temperatu- r e T i s written :Hhf ( V , I ) = Hhf [I-kT/KVI
f o r kT/KV << 1. Here kT i s the thermal energy and K i s r e l a t e d t o t h e anisotropy constant. I t should be noted t h a t i f T = OK, Hhf i s ipdependent of the p a r t i c l e s i z e , i n agreement with our measurements a t 4 K (Hhf = 510 kOe f o r a l l samples except f o r the blank one). Using the average dia- meters D of the p a r t i c l e s obtained by X-ray
0 0
d i f f r a c t i o n (D800 glass6= 64 A , DgOO glass = 70 A), we can c a l c u l a t e K = 10 erg. cm-3. From the ma- gnetic part of the blank glass spectrum a t 4 K , the hyperfine f i e l d i s estimated t o be roughly 430 kOe.This value gives an average s i z e of the
0
order of 12 A f o r the magnetite p a r t i c l e s of the blank g l a s s , below t h e blocking temperature.
The blocking temperature depends on the par- t i c l e s i z e . The s n a l l e r the p a r t i c l e s
,
the lower the blocking temperature. A t 4 K , t h e percentages of magnetite p a r t i c l e s which a r e above the bloc- king temperature a r e approximately 70 %, 0 % and 15 % f o r the blank, 700 and 900 glasses respecti- vely. We can explain t h i s evolution by taking i n t o account t h e mobility of the ions i n the glass during the thermal treatment. When the temperature of the sample i s 600-650' C , the iron ions can move and form microcrystals of magnetite whose s i z e i s increasing with temperature. A t 700' C , we can assume t h a t a l l the iron ions belong t o small c r y s t a l s ( = 55i).
Other ions such as ca2+,~ a + s t a r t moving only when T =.750° C. Then, they could a c t a s a solvent f o r the surface iron ions. As a consequence, a few iron cations may be isolated again and behave as superparamagnetic p a r t i c l e s
.
The main f e a t u r e of the MGssbauer spectra carried out a t 4 K , with an external magnetic f i e l d of 50 kOe applied p a r a l l e l t o the y-direction i s
the appearance of the l i n e s 2 and 5 of the 650 and 700 glass magnetic spectra. These l i n e s are normal- l y extinguished i n a longi tudinsl configuration when the y-ray direction i s parallel t o the iron magnetic moment. In the 900 g l a s s , we can hardly d e t e c t them i n the background. The appearance of these l i n e s has been explained by Haneda and Morrish [5] by assuming a non-collinear spin con- figuration of the surface cations i n small p a r t i - c l e s
.
The smaller the p a r t i c l e s,
the g r e a t e r t h e proportion of surface cations. Since the average microcrystal s i z e i s increasing from the 650 t othe 900 g l a s s , the proportion of surface cations i s so weak i n the 900 glass t h a t they a r e not detected i n the MGssbauer spectrum.
584
. .
.
>;n ' " BLANK GLASS
L
-5.145 0 5 3 4 5
VELOCITY rn m l s
Fig. 2.
-
Mossbauer spectra o f basalt glasses performed a t 4 K. Solid lihes are least squares f i t s .Redehencen
C11 BANC!IOFT, G . M . , BURNS, R.G. and STONE, A.J., Geochim. Cosmochim. Acta
32
(1968) 547.121 NEEL, L . , C. R. Acad. Sci. Paris
229
(1949) 664 131 MORUP, S., TOPSOE, H. and LIPKA, J . ,J . de Physique
2
(1976) C6-287.141 MORUP, S. and TOPSOE, H . , Appl. Phys. _11 (1976) 73.
[51 HANEDA, K. and MORRISH, A . H . , Phys. Letters
fi
(1977) 259.161 Mc.NAB, T . K . , FOX, R.A. and BOYLE, J.F., J: of Appl, Phys.
