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Evolution of microstructure in a glass of the system Na2OB2O3GeO2SiO2
Journal of Non-Crystalline Solids 49 (1982) 157-163 North-Holland Publishing Company
EVOLUTION OF MICROSTRUCTURE
157
IN A GLASS OF THE
SYSTEM Na20-B203-GeO2-SiO 2 F. G A U T H I E R
a n d J. G O M B E R T
Thomson CSF Laboratoire Fibres Optiques, Domaine de Corbeville, 91401 Orsay, France
The microstructure of a glass that possesses sub-liquidus immiscibility in the system Na20B203-GeO2-SiO 2 has been studied by scanning and transmission electron microscopy. Below 640°C the mechanism of phase separation is a spinodal decomposition and above 640°C nucleation and growth occur. In the early stages of phase separation the formation of the mean pore radius depends upon the type of mechanism involved. For nucleation and growth this variation is always a linear relation with the cube root of time whereas for spinodal decomposition only a cube root dependence of the time appears after a period of time, the higher the temperature, the shorter that time.
1. Introduction T h e q u a t e r n a r y systems N a 2 0 - B 2 O a - G e O 2 - S i O 2 d i s p l a y sub-liquidus immiscibility a n d some of the glasses u n d e r g o p h a s e s e p a r a t i o n [1]. The microstructure f o r m a t i o n of the two phases d e p e n d s u p o n the heat t r e a t m e n t (time, temperature). T h e p r e s e n t p a p e r reviews the m i c r o s t r u c t u r e f o r m a t i o n for a glass of the N a 2 0 - B 2 0 3 - G e O 2 - S i O 2 system that u n d e r g o e s phase separation. T h e p o r o u s structure was o b s e r v e d b y t r a n s m i s s i o n electron m i c r o s c o p y ( T E M ) a n d scann i n g electron m i c r o s c o p y (SEM). T h e average p o r e r a d i u s was c a l c u l a t e d from the m i c r o g r a p h s a n d c o m p a r e d with m e r c u r y p o r o s i t y m e a s u r e m e n t s .
2. P r o c e d u r e A base glass o f m o l a r c o m p o s i t i o n SiO 2 = 54%, G e O 2 - 10%, B203 = 28%, N a 2 0 - - - - 8 % was m e l t e d at 1250°C, stirred a n d fined for 20 h in a p l a t i n u m crucible. R o d s of 5 m m o u t s i d e d i a m e t e r were d r a w n a b o v e the coexistence t e m p e r a t u r e a n d q u e n c h e d in air. Pieces of these rods were cut, h e a t - t r e a t e d in a ± 0 . 5 ° C t e m p e r a t u r e c o n t r o l l e d furnace, etched for 20 s in a 10% h y d r o c h l o ric acid solution, a n d then rinsed in p u r e water a n d alcohol. A J E M 6C a n d a H i t a c h i S 700 were used for T E M a n d S E M respectively. C a r b o n - p l a t i n u m replicas were p r e p a r e d for the T E M o b s e r v a t i o n s whereas a surface m e t a l l i z a t i o n of the s a m p l e was necessary for the S E M studies. T h e ionic p h a s e of the h e a t - t r e a t e d s a m p l e was c o m p l e t e l y leached out for the 0022-3093/82/0000-0000/$02.75
© 1982 N o r t h - H o l l a n d
F. Gauthier, J. Gornbert / Evolution of microstructure
158
measurement of the average pore radius with a Micrometrics 9200 model mercury porosimeter. The micrographs were the basis for the determination of the mean pore radius (r). In the spinodal region, below 640°C, pores were considered as cylinders with a small radius in comparison with their length. In the nucleation and growth region pores were considered as spheres [2,3]. The Fullmann derivation [4] was applied to calculate the mean pore radius. For the nucleation and growth domain, the number N v of particles per unit volume was calculated. The surface area of the pores per unit volume [3] was derived from the following equation: S = 4 frr2Nv .
3. Results and discussion
The localization of the glass composition and the immiscibility region are represented in the tetrahedron of compositions (fig. 1) [6]. The coexistence temperature of the glass studied was found to be (703 ± 3)°C by the clearopalescence method and to be (701 ± 2 ) ° C by DSC measurements with a Dupont 1090 thermal analysis system (fig. 2). The glass was heat-treated at 560, 575, 580, 600, 620, 640 and 660°C for various periods of time, ranging from 15 min to about 40 h. Some micrographs are displayed in fig. 3. The mean pore radius calculated from the micrographs are listed in table 1. The pore surface area and the number of particles per unit volume are given in table 2. The measurement for a glass heat-treated at 575°C for 3 h gave a mean pore radius of 31 ,A which is also in good agreement with
Si02 i
.sc, ,C,TY Re ,o ,. SOO,UM BOROS,L,CATE
COMPOS,T,O. P.AN
COMPOSITION PLAN s,o,o,,O,o -¢
/-
', ; ~ "
~ ~
~,,,~ ~.~ ~
COMPOSm0N
NozO
/-~
..... L ~
_ -~
,
IMMISCIBILITYREGION .N T.E S,O, =,,°,'o
COMPOSITION P'AN
','t
--~ ,, ~
BzO)
Fig. |. R e , o n of immiscibility and studied glass composhion ( , ) in the tetrahedron of compositions.
F. Gauthier, J. Gombert / Evolution of microstructure
159
0SC
11 0 E
-I! ...i
-2
Tcoex: 701°C" ~ I
I 500
~o0
I 600
I 700
TEMPERATURE (oC) Fig. 2. Determination of the coexistence temperature by DSC analysis.
the SEM value. Fig. 4 shows the variation of the cumulative surface area versus pore diameter. The mean radii were plotted versus time on a logarithmic scale (fig. 5).
3.1. Spinodal decomposition For short periods of time and for temperatures under 640°C the increase of the mean pore radius is slow. After a certain time, the higher the temperature
Table 1 Mean pore radius versus time and temperature measured using TEM and SEM micrographs Time
Temperature (°C)
(h) 560 0,25 0,5 1 3 5 7 9 13 17 23 31 41
575
36
a
40 a
44 51 60
83 a
a Measured by SEM.
580
38 43 42 51 60 79 74 88 97
600
40 55-53 a 62 70 75 93 105 120 143 157
620
83 122 138 150-157 a 167 216 235 255 286 324
640
660
180 220 258 358 404 460 480 545
235 280 340 470 530 594
160
F. Gauthier, d. Gombert
560°C 23h
/
Evolution of rnicrostructure
600°C 311
I 620"C 31h
•
600°C 31 h
A
~C0.5h
A
~
3h
°
C
g
5750C 41h
h
. . . .
600"C 3h
i .......
620°C
7h
Fig. 3. TEM ( a - b - c - d - e - f ) and SEM (g-h-i) micrographs. Magnification A = 104; B = 2 × 104; C - 5 X 104; D = 105; E = 2 × I 0 5
the shorter the time, the mean pore radius increases with the cube root of time. This phenomenon, a result of the early stages of spinodal decomposition, is better visualized on a radius versus t I/3 plot (fig. 6). For long periods of time this linear dependence between the cube root of time and the mean radius
161
F. Gauthier, J. Gombert / Evolution of microstructure CUMULATIVE SURFACE AREA (R2/G) VS. PORE DIAMETER 100 ~
0.833
0%
20%
I
I
0,657
•
0.514
•
0.402
•
=
148.2580
40% I
0.315 O. 193
•
0.151
•
0,118
•
80%
I
I
TOTAL PORE VOLUME
0.2283 CC/G
TOTAL PORE AREA
148.2580 SQ-M/G
MEDIAN PORE DIAMETER (AREA)
0.247
60%
=
0.0055 MICROMETERS
MEDIAN PORE DIAMETER (VOLUME) =
0.0060 MICROMETERS
AVERAGE PORE DIA~ETER (4 V/A) -
0.0062 MICROMETERS
100% I
0.0926 0.0725
•
0.0567
•
0.0444
•
0.0347 0.0272
•
0.0213
•
0,0167
•
0.0130
•
0,0102 0.00799
•
0.00626 0.00490
0.00383 0.00300
Fig. 4. Variation of the cumulative surface area versus pore diameter.
c~
| W
i
I
I
I
i
I i I~
l T IME
I
I
I
I
I I 1110
I
I
I
I
Hours
Fig. 5. Mean pore radius versus time, logarithmic scales: A , TEM, [i], SEM; O, porosimetry.
F. Gauthier, J. Gombert / Evolution of microstructure
162
Table 2 N u m b e r of pores per unit volume and surface area of the pores per unit volume in the case of the nucleation and growth mechanism. Temperature
Time 0.25
Nv 640 ( × 10t4/cm 3) 660 S 640 (m2/cm 3) 660
0.50
143.3 60.6 58.3 42.0
76. I 37.1 46.6 36.6
I
3
5
7
49.4 19.4 41.3 20.3
17.7 7.3 28.5 16.9
12.2 4.8 25.0 15.5
8.6 3.5 22.9
9
13
7.3
4.9
21.1
18.3
value can be attributed [5] to a coarsening phenomenon (increase in pore diameter and a decrease in surface area of the phase boundaries).
3.2. Nucleation and growth At temperatures higher than or equal to 640°C the mean sphere radius values show a linear dependence on the cube root of the ageing time. Note that for extrapolation at t = 0 there appears to be a finite mean size "pore" radius of about 40 ,~. In that case, as shown by the early stage micrographs fig. (3e, f), the mechanism of phase separation is identified as nucleation and growth. According to Uhlmann and Kolbeck [5] this behavior also corresponds to a
1 TIME
2 (Houri)
3
}~
Fig. 6. Mean pore radius versus cube root of time.
F. Gauthier, J. Gombert / Evolution of microstructure
163
coarsening process: increase in the size and decrease in the n u m b e r of particles. The volume variation of the precipitated phase depends u p o n an energy barrier. The apparent activation energy has been found to be 70 k c a l / m o l which is a reasonable value for that kind of volume diffusion.
4. Conclusion The immiscibility of the chosen glass in the system N a 20-B203-GeO2 - S i O 2 follows a spinodal decomposition behavior at temperatures lower than 640°C, and a nucleation and growth behavior at temperatures of 640°C or higher. The formation of the mean pore radius depends u p o n the cube root of time in the nucleation and growth region. In the spinodal decomposition region, the mean pore radius follows a cube root dependence against the time, only after some time yield, the higher the temperature of heat-treatment, the shorter that yield. The authors wish to express their thanks to Mr. R. Ansel and Mr. C. Relandeau for their valuable collaboration in tracking the SEM and T E M pictures.
References [I] A. de Panafieu, Y. Nemaud, C. Baylac, M. Turpin, M. Faure and F. Gauthier, Phys. Chem. Glasses 21 (1980) 22. [2] I.M. Lifshitz and V.V. Sloyozov, J. Phys. Chem. Sol. 19 (1961) 35. [3] R.A. Mc. Currie and R.W. Douglas, Phys. Chem. Glasses 8 (1967) 132. [4] R.L. Fullmann, J. Metals (March, 1953) 447. [5] D.R. Uhlmann and A.G. Kolbeck, Phys. Chem. Glasses 17 (1976) 146. [6] J. Gombert, Propri6t6s physico-chimiques des verres de Borosilicates de Sodium dopes ~t l'oxyde de Germanium, Universit+ d'ORSAY, 23 novembre 1979. Th6se de 3~me Cycle.
EVOLUTION OF MICROSTRUCTURE
157
IN A GLASS OF THE
SYSTEM Na20-B203-GeO2-SiO 2 F. G A U T H I E R
a n d J. G O M B E R T
Thomson CSF Laboratoire Fibres Optiques, Domaine de Corbeville, 91401 Orsay, France
The microstructure of a glass that possesses sub-liquidus immiscibility in the system Na20B203-GeO2-SiO 2 has been studied by scanning and transmission electron microscopy. Below 640°C the mechanism of phase separation is a spinodal decomposition and above 640°C nucleation and growth occur. In the early stages of phase separation the formation of the mean pore radius depends upon the type of mechanism involved. For nucleation and growth this variation is always a linear relation with the cube root of time whereas for spinodal decomposition only a cube root dependence of the time appears after a period of time, the higher the temperature, the shorter that time.
1. Introduction T h e q u a t e r n a r y systems N a 2 0 - B 2 O a - G e O 2 - S i O 2 d i s p l a y sub-liquidus immiscibility a n d some of the glasses u n d e r g o p h a s e s e p a r a t i o n [1]. The microstructure f o r m a t i o n of the two phases d e p e n d s u p o n the heat t r e a t m e n t (time, temperature). T h e p r e s e n t p a p e r reviews the m i c r o s t r u c t u r e f o r m a t i o n for a glass of the N a 2 0 - B 2 0 3 - G e O 2 - S i O 2 system that u n d e r g o e s phase separation. T h e p o r o u s structure was o b s e r v e d b y t r a n s m i s s i o n electron m i c r o s c o p y ( T E M ) a n d scann i n g electron m i c r o s c o p y (SEM). T h e average p o r e r a d i u s was c a l c u l a t e d from the m i c r o g r a p h s a n d c o m p a r e d with m e r c u r y p o r o s i t y m e a s u r e m e n t s .
2. P r o c e d u r e A base glass o f m o l a r c o m p o s i t i o n SiO 2 = 54%, G e O 2 - 10%, B203 = 28%, N a 2 0 - - - - 8 % was m e l t e d at 1250°C, stirred a n d fined for 20 h in a p l a t i n u m crucible. R o d s of 5 m m o u t s i d e d i a m e t e r were d r a w n a b o v e the coexistence t e m p e r a t u r e a n d q u e n c h e d in air. Pieces of these rods were cut, h e a t - t r e a t e d in a ± 0 . 5 ° C t e m p e r a t u r e c o n t r o l l e d furnace, etched for 20 s in a 10% h y d r o c h l o ric acid solution, a n d then rinsed in p u r e water a n d alcohol. A J E M 6C a n d a H i t a c h i S 700 were used for T E M a n d S E M respectively. C a r b o n - p l a t i n u m replicas were p r e p a r e d for the T E M o b s e r v a t i o n s whereas a surface m e t a l l i z a t i o n of the s a m p l e was necessary for the S E M studies. T h e ionic p h a s e of the h e a t - t r e a t e d s a m p l e was c o m p l e t e l y leached out for the 0022-3093/82/0000-0000/$02.75
© 1982 N o r t h - H o l l a n d
F. Gauthier, J. Gornbert / Evolution of microstructure
158
measurement of the average pore radius with a Micrometrics 9200 model mercury porosimeter. The micrographs were the basis for the determination of the mean pore radius (r). In the spinodal region, below 640°C, pores were considered as cylinders with a small radius in comparison with their length. In the nucleation and growth region pores were considered as spheres [2,3]. The Fullmann derivation [4] was applied to calculate the mean pore radius. For the nucleation and growth domain, the number N v of particles per unit volume was calculated. The surface area of the pores per unit volume [3] was derived from the following equation: S = 4 frr2Nv .
3. Results and discussion
The localization of the glass composition and the immiscibility region are represented in the tetrahedron of compositions (fig. 1) [6]. The coexistence temperature of the glass studied was found to be (703 ± 3)°C by the clearopalescence method and to be (701 ± 2 ) ° C by DSC measurements with a Dupont 1090 thermal analysis system (fig. 2). The glass was heat-treated at 560, 575, 580, 600, 620, 640 and 660°C for various periods of time, ranging from 15 min to about 40 h. Some micrographs are displayed in fig. 3. The mean pore radius calculated from the micrographs are listed in table 1. The pore surface area and the number of particles per unit volume are given in table 2. The measurement for a glass heat-treated at 575°C for 3 h gave a mean pore radius of 31 ,A which is also in good agreement with
Si02 i
.sc, ,C,TY Re ,o ,. SOO,UM BOROS,L,CATE
COMPOS,T,O. P.AN
COMPOSITION PLAN s,o,o,,O,o -¢
/-
', ; ~ "
~ ~
~,,,~ ~.~ ~
COMPOSm0N
NozO
/-~
..... L ~
_ -~
,
IMMISCIBILITYREGION .N T.E S,O, =,,°,'o
COMPOSITION P'AN
','t
--~ ,, ~
BzO)
Fig. |. R e , o n of immiscibility and studied glass composhion ( , ) in the tetrahedron of compositions.
F. Gauthier, J. Gombert / Evolution of microstructure
159
0SC
11 0 E
-I! ...i
-2
Tcoex: 701°C" ~ I
I 500
~o0
I 600
I 700
TEMPERATURE (oC) Fig. 2. Determination of the coexistence temperature by DSC analysis.
the SEM value. Fig. 4 shows the variation of the cumulative surface area versus pore diameter. The mean radii were plotted versus time on a logarithmic scale (fig. 5).
3.1. Spinodal decomposition For short periods of time and for temperatures under 640°C the increase of the mean pore radius is slow. After a certain time, the higher the temperature
Table 1 Mean pore radius versus time and temperature measured using TEM and SEM micrographs Time
Temperature (°C)
(h) 560 0,25 0,5 1 3 5 7 9 13 17 23 31 41
575
36
a
40 a
44 51 60
83 a
a Measured by SEM.
580
38 43 42 51 60 79 74 88 97
600
40 55-53 a 62 70 75 93 105 120 143 157
620
83 122 138 150-157 a 167 216 235 255 286 324
640
660
180 220 258 358 404 460 480 545
235 280 340 470 530 594
160
F. Gauthier, d. Gombert
560°C 23h
/
Evolution of rnicrostructure
600°C 311
I 620"C 31h
•
600°C 31 h
A
~C0.5h
A
~
3h
°
C
g
5750C 41h
h
. . . .
600"C 3h
i .......
620°C
7h
Fig. 3. TEM ( a - b - c - d - e - f ) and SEM (g-h-i) micrographs. Magnification A = 104; B = 2 × 104; C - 5 X 104; D = 105; E = 2 × I 0 5
the shorter the time, the mean pore radius increases with the cube root of time. This phenomenon, a result of the early stages of spinodal decomposition, is better visualized on a radius versus t I/3 plot (fig. 6). For long periods of time this linear dependence between the cube root of time and the mean radius
161
F. Gauthier, J. Gombert / Evolution of microstructure CUMULATIVE SURFACE AREA (R2/G) VS. PORE DIAMETER 100 ~
0.833
0%
20%
I
I
0,657
•
0.514
•
0.402
•
=
148.2580
40% I
0.315 O. 193
•
0.151
•
0,118
•
80%
I
I
TOTAL PORE VOLUME
0.2283 CC/G
TOTAL PORE AREA
148.2580 SQ-M/G
MEDIAN PORE DIAMETER (AREA)
0.247
60%
=
0.0055 MICROMETERS
MEDIAN PORE DIAMETER (VOLUME) =
0.0060 MICROMETERS
AVERAGE PORE DIA~ETER (4 V/A) -
0.0062 MICROMETERS
100% I
0.0926 0.0725
•
0.0567
•
0.0444
•
0.0347 0.0272
•
0.0213
•
0,0167
•
0.0130
•
0,0102 0.00799
•
0.00626 0.00490
0.00383 0.00300
Fig. 4. Variation of the cumulative surface area versus pore diameter.
c~
| W
i
I
I
I
i
I i I~
l T IME
I
I
I
I
I I 1110
I
I
I
I
Hours
Fig. 5. Mean pore radius versus time, logarithmic scales: A , TEM, [i], SEM; O, porosimetry.
F. Gauthier, J. Gombert / Evolution of microstructure
162
Table 2 N u m b e r of pores per unit volume and surface area of the pores per unit volume in the case of the nucleation and growth mechanism. Temperature
Time 0.25
Nv 640 ( × 10t4/cm 3) 660 S 640 (m2/cm 3) 660
0.50
143.3 60.6 58.3 42.0
76. I 37.1 46.6 36.6
I
3
5
7
49.4 19.4 41.3 20.3
17.7 7.3 28.5 16.9
12.2 4.8 25.0 15.5
8.6 3.5 22.9
9
13
7.3
4.9
21.1
18.3
value can be attributed [5] to a coarsening phenomenon (increase in pore diameter and a decrease in surface area of the phase boundaries).
3.2. Nucleation and growth At temperatures higher than or equal to 640°C the mean sphere radius values show a linear dependence on the cube root of the ageing time. Note that for extrapolation at t = 0 there appears to be a finite mean size "pore" radius of about 40 ,~. In that case, as shown by the early stage micrographs fig. (3e, f), the mechanism of phase separation is identified as nucleation and growth. According to Uhlmann and Kolbeck [5] this behavior also corresponds to a
1 TIME
2 (Houri)
3
}~
Fig. 6. Mean pore radius versus cube root of time.
F. Gauthier, J. Gombert / Evolution of microstructure
163
coarsening process: increase in the size and decrease in the n u m b e r of particles. The volume variation of the precipitated phase depends u p o n an energy barrier. The apparent activation energy has been found to be 70 k c a l / m o l which is a reasonable value for that kind of volume diffusion.
4. Conclusion The immiscibility of the chosen glass in the system N a 20-B203-GeO2 - S i O 2 follows a spinodal decomposition behavior at temperatures lower than 640°C, and a nucleation and growth behavior at temperatures of 640°C or higher. The formation of the mean pore radius depends u p o n the cube root of time in the nucleation and growth region. In the spinodal decomposition region, the mean pore radius follows a cube root dependence against the time, only after some time yield, the higher the temperature of heat-treatment, the shorter that yield. The authors wish to express their thanks to Mr. R. Ansel and Mr. C. Relandeau for their valuable collaboration in tracking the SEM and T E M pictures.
References [I] A. de Panafieu, Y. Nemaud, C. Baylac, M. Turpin, M. Faure and F. Gauthier, Phys. Chem. Glasses 21 (1980) 22. [2] I.M. Lifshitz and V.V. Sloyozov, J. Phys. Chem. Sol. 19 (1961) 35. [3] R.A. Mc. Currie and R.W. Douglas, Phys. Chem. Glasses 8 (1967) 132. [4] R.L. Fullmann, J. Metals (March, 1953) 447. [5] D.R. Uhlmann and A.G. Kolbeck, Phys. Chem. Glasses 17 (1976) 146. [6] J. Gombert, Propri6t6s physico-chimiques des verres de Borosilicates de Sodium dopes ~t l'oxyde de Germanium, Universit+ d'ORSAY, 23 novembre 1979. Th6se de 3~me Cycle.