Vol. 12
No. 5
J. CENT. SOUTH UNIV. T E C H N O L .
Oct. 2005
Article ID: 1005 - 9784(2005)05 - 0521 - 05
Forming regularity and relation between composition and property of B2Oa-BaO-ZnO glass ® LU An-xian()~i~,~r), LI X u e ( ~ N ) , LIN Na()[~ ~}l]~) (School of Materials Science and Engineering, Central South University, Changsha 410083, China) Abstract: B 2 0 s - B a O - Z n O g l a s s w a s p r e p a r e d by u s i n g conventional m e l t q u e n c h i n g technology. T h e f o r m i n g r e g u larity a n d t h e r e l a t i o n s h i p b e t w e e n t h e c o m p o s i t i o n a n d t h e p r o p e r t y of ]32 O~ - B a O - Z n O g l a s s were investigated. T h e r e s u l t s s h o w t h a t t h e c o m p o s i t i o n r a n g e for f o r m i n g B203 - BaO - Z n O g l a s s is v e r y wide, b u t t h e c o n t e n t of B203 h a s a limit w i t h i n mole fraction of 2 5 ~ - 7 5 ° / o o . W h e n t h e c o n t e n t of B203 is over t h e limit, t h e m e l t will be divided into t w o p h a s e s w i t h different c o m p o s i t i o n s and s t r u c t u r e s , w h e r e a s too low c o n t e n t of Bz 03 will r e s u l t in t h e crystallization of t h e m e l t d u r i n g t h e cooling process. T h e t h e r m a l e x p a n s i o n coefficient, t h e t r a n s i t i o n t e m p e r a t u r e and t h e resistivity of the glass at room temperature are (5 - 10) X 10 -6 °C i , 480 - 620 °C and ( 1 . 5 - 3 . 0 ) X 101° fl • m , respectively.
Key words: B 2 O a - B a O - Z n O g l a s s ; g l a s s f o r m i n g r a n g e ; t h e r m a l e x p a n s i o n coefficient; t r a n s i t i o n t e m p e r a t u r e ; resistivity
CLC number: TQ171
1
INTRODUCTION
Color plasma display panel (PDP) is a kind of eligible apparatus for large area, hang-on-wall high definition televisions, computer monitors and various display panels for civilian and military application E1-3J. Compared with other flat display panels, the market perspective for PDP is rapidly growing because of their advantages such as thin thickness, low density, large area and large visual angle E4'5~. The glass substrates and the display electrodes in PDP are the main parts and play a very important role in high performance PDP E6?. In order to protect the electrodes, it is necessary to cover a dielectric layer on the electrodes of the front substrate glass in PDP. Generally, the glasses used as the dielectric materials in PDP almost contain heavymetal Pb 2+ ions, which cause serious pollution of environmentEr-9~. As a result, these glasses must be replaced by Pb-free glasses E1°-143. B2O3-BaO-ZnO glass with lower melting temperature possesses suitable thermal and electrical properties E15~matching PDP substrate glass and is used as a candidate of Ph-free dielectronic layer c~6~. In this paper, the forming regularity and the relation among composition, structure and property of BeO3-BaO-ZnO glass were investigated. 2
Document code: A
form glass in Bz Oa-BaO-ZnO ternary system, first, the B2 03-BaO binary system glass was investigated by conventional melt quenching technology. Then, ZnO was gradually added into the B2O3-BaO binary system to obtain the three-composition glass forming district. Table 1 lists the chemical compositions of the prepared samples from B2O3-BaO-ZnO trinary system. Table 1 Chemical compositions of samples in B2Os-BaO-ZnO trinary system (mole fraction, %) Sample No.
B2 03
BaO
ZnO
A-1
65
15
20
A 2
60
20
20
A-3
50
30
20
A-4
40
40
20
A-5
30
50
20
Sample No.
B20a
BaO
ZnO
B-I
50
45
5
B2
50
40
10
B-3
50
30
20
B-4
50
20
30
B-5
50
I0
40
EXPERIMENTAL 2.2
2.1
O
Glass forming range of Bz 03-BaO-ZnO ternary system In order to determine the composition range to
Measurement of property The density (p) of the glass was measured using Archimedes method. The transition temperature (tg) of glass was determined from DTA curve
Receiveddate: 2004 - 10 - 02; Accepted date: 2004 - 12 - 24 Correspondence:LU An xian, PhD, Professor; Tel: +86-731-8830351 ; E-mail: axlu@mail, csu. edu. cn
• 522 •
and thermal expansion coefficient curve. T h e thermal expansion coefficient(a) of the samples with the dimensions of 5 mm X 5 mm X 20 mm was measured on TAS100 thermal mechanical analyzer at a heating rate of 10 °C/min from room temperature to 300 °C. T h e resistivity of the glass sample with dimensions of 10 mm X 10 mm X 10 mm was measured on NF2511A insulated resistance apparatus.
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2005
move in the melt, which results in the crystallization of the melt during cooling process. B203
/5
RESULTS AND DISCUSSION
3. 1 Glass forming district of B203-BaO-ZnO ternary glasses T h e glass forming district of BzO3 - BaO ZnO ternary system is shown in Fig 1. It can be observed from Fig. 1 that no glass can be made in the BaO - Z n O binary system. In the binary Bz 03 BaO system, glass can be obtained when the mole fraction of B203 changes from 35% to 7 5 G . H o w ever, if the mole fraction of BaO approaches to 70% or that of B203 is lower than 3 5 % , the free oxygen ions from BaO melt increase, which makes glass network structure damage and results in the crystallization of the binary system melt during cooling process. Compared with Bz03 - BaO system, Bz 03 - ZnO binary system has a narrow composition range for forming glass, that is the mole fraction of B203 from 40% to 55%. A.s for B2Oa B a O - ZnO ternary system there are many factors that affect its glass forming, such as discontinuousness of network structure, accumulation, polarization, coordination n u m b e r , electric field strength and relative kinetics factors. It can be seen from Fig. 1 that BzOa - BaO - ZnO trinary system has a wider composition range for forming glass with lower content of ZnO but higher content of BaO. T h e possible reason is that Zn 2+ has small ion radius and stronger electric field strength, which increases the crystallization trend of the melt and weakens the glass forming ability of BzOa BaO - ZnO. When the mole fraction of B2Oa is higher than 7 5 % , the guantity of [-BO3] in the melt increases and forms partially bigger aggregate groups of [-BOa]. Ba 2+ and Zn 2+ ions in the melt connect to the intensive part of negative oxygen ions on the aggregate groups of [-BOa-] and form the nucleus of micro-crystals. These nuclei grow up and separate from the rich BzOa phase because of gravity effect during cooling process of the B20a - BaO - ZnO melt. When the mole fraction of Bz Oa is lower than 35G ,the connection degree of I-BOa] is low and Ba 2+, Zn 2+ and O 2- ions are easy to
Vol. 12
3
0
~
7
0
0 ~ 5 0
°g
%XXXG4-o
Z A°
aoY\/K/VVVWVV no 10
20
30
40
50
60
70
80
90
Mole fraction/%
Fig. 1
Forming range of BzO3-BaO-ZnO
ternary glass o--Transparency; zx Translucency; o--Opacity
3.2
Relation between composition and thermal expansion coefficient T h e thermal expansion coefficient ( a ) of 2 0 Z n O - x B 2 0 3 - ( 8 0 - x ) B a O glass continually decreases with the increase of the molar ratio of Bz Oa to ZnO ( n ( B z 0 3 ) / n ( Z n O ) ) (see Fig. 2). This change is attributed to the change of glass structure. T h e connection degree and the strength of glass network play an important role in the thermal expansion coefficient. T h e increase of n (Bz 03 )/n (ZnO) means the decrease of ZnO and the increase of BzOa. The connection degree of network structure of the glass becomes higher because of the increase of [-BOa ] and the partial transition from [-BOa] to [-BO~1, therefore the thermal expansion coefficient continually decreases with the increase of the content of Bx03. On the other hand, if the content of B203 is kept constant, the thermal expansion coefficient continually increases with the increase of the content of BaO (see Fig. 3). T h e possible reason is that the breaking network action of BaO is more obvious than the repairing network action of ZnO. 3. 3
Relation between composition and transition temperature Lower et al E173 reported the transition temperatures (tg) of M O - B 2 0 3 ( M = M g , Ca, Sr, Ba) glass. In Fig. 4, the transition temperature of 20ZnO - xBz 03 - (80 -- x ) BaO glass is compared with that of B203 - BaO. T h e transition tempera-
LI Xue, et al: Forming regularity and relation between composition and property of B203-BaO-ZnO glass
tetrahedral. T h e two dimensional layered structure of pure B2Oa changes into the three dimensional network structure of B203-BaO with the participation of [-BO4] units into the glass network. Such a three dimensional cross-linking of structural net-
11 10 ~.
9
,~
8
---
7
i
work gives the glass higher transition temperature. When n(MO)/n(Bz03) is about 0 . 5 , the transition temperature is about 608 °C . Following this,
4
L
I
1.4
I
t.8
2.2
I
i
2.6
30
3.4
n(B203)/n(ZnO) Fig. 2
• 523 °
Relation between n(Bz 03)/n(ZnO) and a of Bz O3-BaO-ZnO glass
transition temperature begins to decrease with the increase of n(MO)/n(B203), which is attributed to the appearance of a great deal of non-bridging oxygen in the structure network. This change is similar to that of the thermal expansion coefficient of the glass. At the same time, it can also be observed from Fig. 4 that the lowering trend of transition temperature in the binary system is more obvious than that of ternary system. Figs. 5 and 6 show the effect of n(BaO)/n(ZnO) and n(B203)/n(ZnO) on transition temperature, respectively.
i
580
e~
5;
oE
I
I
I
I
2
4
6
8
10
n(BaO)/n(ZnO) Fig. 3
540
e~
o 500
Relation between n(BaO)/n(ZnO) and a of Bz O3-BaO-ZnO glass
460 0
I
I
I
I
2
4
6
8
10
n(BaO)/n(ZnO) 600
Fig. 5
Effect of n(BaO)/n(ZnO) on tg of B2 O3-BaO-ZnO glass
e~
560 580
O
520
E
o~
560
e~
E
480 0.3
0.'6
0'.9
1)2
115
118
2'.1
214
n(MO)/n(B203) Fig. 4
Relation between tg and n(MO)/n(Bz 03 ) l--B202 -BaO binary glass; 2--B202 - BaO - ZnO ternary glass
540
e. O e,
520
5° 14
;.2
216
3.4
n(BEOa)/n(ZnO) Fig. 6
ture of pure B203 glass is only 260 °C. H o w e v e r , when BaO is introduced into pure Bz03 glass, the transition temperature will increase. This is because more W + ions exist in the form of FBO4]
118
Effect of n(B203)/n(ZnO) on tg of Bz 03-BaO-ZnO glass
According to Figs. 5 and 6, when the content is constant, the transition temperature of
of B203
• 524 •
Journal CSUT
the glass changes a little with the increase of n(BaO)/n(ZnO). H o w e v e r , the transition temperature of the glass increases rapidly with the increase of n (B2 O3 ) / n (ZnO), which suggests that Bz O3 plays a more important role in transition temperature than BaO and ZnO. 3.4
Relation between composition and resistivity Fig. 7 shows the influence of mole fraction of
Bz03 on the resistivity of the glass w h e n the content of ZnO is kept constant. When the mole fraction of BzO3 changes from 30°/oo to 4 0 % , a number of F BO3 ] triangles are aggregated into [-B306 ] units and some [-BO4 ] tetrahedrons are formed.
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Fig. 8. It can be observed that the density of the glass increases with the increase of BaO content when Bz 03 content is kept constant. T h e main reason is that Ba 2+ ions are much heavier in mass than Zn 2+ ions and W + ions. It is also possible that Ba 2+ ions with bigger ion radius can offer more free oxygen ions, damage the network structure of glass and increase the volume of the glass in each unit mass, therefore, the density of the glass decreases with the decrease of B20a content or the increase of BaO content, when the ZnO content is kept constant. 5.0
H o w e v e r , the coordination of Zn 2+ almost does not change. T h e r e f o r e , it can be supposed that the decrease of resistivity is due to the suppressed effect from Ba 2+ ions. Filling in the network intervals of the glass structure, Ba 2+ ions with bigger radius can counteract the movement of Zn 2+ ions, which
~ 4.0 "~ 3.5 3.0 2.5
causes the decrease of the resistivity of the glass. This means that Ba 2+ ions play a more obvious role
1'0
2;
3'0 4'0 x(BaO)/%
5})
6'0
Fig. 8 Effect of mole fraction of BaO on 50Bz 03-xZnO- ( 5 0 - - x) BaO glass
in the resistivity. When the mole fraction of BzOa increases from 40% to 5 0 % , some Zn 2+ ions participate in the network with the decrease of [-BO~ ] units and the increase of [BO4] units, which re-
4
sults in the decrease of mobile Zn 2+ ions, so the resistivity increases obviously. This suggests that Zn 2+ ions play an important role in the resistivity. When the mole fraction of BzO3 is increased from 5 0 ~ to 6 0 % , the resistivity begins to decrease again. T h e reason is that the connecting degree of the network structure in the glass becomes more perfect with the increase of Bz02 and the decrease of BaO content.
1) The B203-BaO-ZnO glass has a vey wide composition range for forming glass, but the mole fraction of B203 is limited within 35°//00 - 75 %. When the mole fraction of B203 is higher than 7 5 ~ , the nuclei will grow up and be separated
5
4 2 1
3'0
3;
4'0
4;
5'0
5;
6;
65
X(B203)/?/o Fig. 7
Effect of mole fraction of B203 on
of 2 0 Z n O - x B 2 0 3 - ( 8 0 - - x ) B a O glass 3.5
from the rich B203 phase because of the gravity effect during the cooling process of the melt in B203-BaO-ZnO ternary system. When the mole fraction of Bz03 is lower than 35 % , Ba 2+ , Zn 2+ and 0 2 . ions are easy to move in the melt, which results in the crystallization of the melt during cooling process. 2) In 20ZnO-xBzO3-(80--x)BaO ,the thermal expansion coefficient decreases with the increase of
6 •
CONCLUSIONS
Relation between composition and density The effect of BaO content on density of 5 0 B 2 O s - x Z n O - ( 5 0 - - x ) B a O glass is shown in
B203 content. When the content of BzO3 is kept constant, the thermal expansion coefficient increases with the increases of the content of BaO. The thermal expansion coefficient of the glass is about (5 - 10) X 10 .6 °C 1 ; the transition temperature is 4 8 0 - 620 °C and the resistivity at room temperature is (1.5 - 3.0) X 101° 12 • m. REFERENCES
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(Edited by CHEN Wei-ping)
