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Study of formation and properties of the vitreous oxyfluoride system based on GeO2, PbF2 and ZnF2
Journal of Non-Crystalline Solids 112 (1989) 151-155 North-Holland, Amsterdam
151
Section 3. Glass formation and phase transformation STUDY OF F O R M A T I O N AND P R O P E R T I E S O F T H E V I T R E O U S O X Y F L U O R I D E S Y S T E M B A S E D O N GeO2, PbF 2 A N D ZnF 2 H E Shuping Department of Optical Fiber and Optical Cable, Wuhan Science Institute of Post and Telecommunications, Wuhan, PR China
XU Chao and G A N Fuxi Wuhan University of Technology, Wuhan, PR China
The vitreous region of the oxyfluoride system based on germanium dioxide, lead fluoride and zinc fluoride is obtained by using platinum crucibles. The physical properties such as the transition temperature, crystallization temperature, refractive index, density, thermal expansion coefficient and elastic modulus are measured. A description to the change rules of the physical properties of this system is given in detail. The glasses have a good transparency in the mid-infrared region. Their chemical durability is much better than that of fluoride glasses.
1. Introduction
Fluoride glasses are important because of their good transparency in the infrared region [1-6]. Their greatest shortcoming is their weak glass-forming ability and poor chemical durability. In order to improve glass formation, one of the effective ways is to incorporate oxides that have a strong glass-forming ability [7-8]. In recent years, more and more research has been performed on oxyfluoride glasses. Many oxyfluoride glasses such as fluorosilicate [9], fluorophosphate [9] and fluoroborate glasses [10] have special optical properties which means that they play an important role in optical glasses. However, the fluorogermanate glasses, whose transparency in the mid-infrared region is very good, have not been studied. As is well known, lead fluoride is a good glass modifier in fluoride glasses. Zinc fluoride is a weak glass former. The binary system ZnF2-PbF 2 was investigated by Demortain et al. [11]. In his work, a glass sample with a thickness of 10-20 ~m was obtained at a cooling rate of 10 6 K / s by pouring the melts between two rolling wheels. The sample has an IR absorption edge above 15 ~tm. Glass formation is expected to be significantly 0022-3093/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
improved by incorporating germanium dioxide. It is the purpose of this study to investigate the glass formation and physical properties of the ternary G e O 2 - P b F 2 - Z n F 2. This system is of interest theoretically in the research for new infrared materials.
2. Vitreous region and sample fabrication
Reagent grade PbF z and ZnF 2 were used as raw materials and GeO 2 was obtained by the hydrolysis of GeC14. Batches of 5-10 g were melted at 1000-1150°C for 10 min in platinum crucibles. Then the melts were poured onto a cooled copper plate. Whether one composition was a glass or not was examined by eye or microscope. A nitrogen atmosphere was used to prevent the fluorides from oxiding in the melting process. The vitreous region of this system is shown in fig. 1. Three series of formulas were selected in the vitreous region: (1) (70 - x)GeO2(20 + x)PbF210ZnF2, (2) (70 - y)GeOz30PbF2yZnF2, (3) 6 0 G E O 2 ( 4 0 - z ) P b F 2 z Z n F 2 (x, y, z = 0, 5, 10, 15, 20). Batches of 40 g were melted at (1070 _+ 30) o C for
152
He Shuping et aL / Vitreous oxyfluoride system based on Ge02, PbF2 and Z n F2
3. Measurement of glass properties
801:L20 ,0/o o
/(o o/\o,+ 20/
PbF2
90
"
80
~
70
"
\-1~ 60
50
40
30
20
10
ZnF2
Fig. 1. The vitreous region of the ternary G e O 2 - P b F 2 - Z n F 2 system, o , clear glass; zx, partially devitrified glass; O, imperfect melt; × , fully devitrified glass.
(40 + 5) min. A high-purity aluminum oxide ball was used to stir the melt. Bulk samples with a thickness of more than 20 mm were formed by pouring the melt into a preheated copper mould. The glass compositions and conditions of fabrication are all listed in table 1.
The glass transition temperature (T~) and crystallization temperature (T~) were determined from differential thermal analysis curves. The density was measured using the Archimedes principles. The thermal expansion coefficient was measured with a differential quartz dilatometer. The refractive index was measured by the oil immersion method and Young's elastic modulus was measured using a digital dynamic technique. The transparency in the mid-infrared region was measured by a 60SXB Fourier IR spectrometer. The samples were 4 mm thick with two parallel surfaces polished. The result is shown in fig. 2.
4. Results and discussion
4.1. The glass forming properties GeO2-PbFe-ZnF2
of
Figure 1 shows that the vitreous region is inclined to the GeO 2 side, which indicates that germanium dioxide plays the role of glass former when its content is high. When the content of
Table 1 Compositions and conditions of fabrication of glass samples Series
Samples
Percentage by molar
Melting temperature
Annealing temperature
GeO 2
PbF 2
ZnF 2
(oc)
(oc)
I
A1 B1 C1 D1 E1
70 65 60 55 50
20 25 30 35 40
10 10 10 10 10
1100 1100 1070 1060 1050
415 400 380 360 340
II
A2 B2 C2 D2 E2
70 65 60 55 50
30 30 30 30 30
0 5 10 15 20
1100 1100 1070 1100 1100
380 380 380 390 390
III
A3 B3 C3 D3 E3
60 60 60 60 60
40 35 30 25 20
0 5 10 15 20
1100 1100 1070 1100 1100
370 380 380 400 400
153
He Shuping et aL / Vitreous oxyfluoride system based on Ge02, PbF2 and ZnF2
i00,
,
,
,
~
,
1
""
0
I
8(
, 2--O--Ge--F 1
g 60 4
i 4o
\
I
3900
3400 240 24100 19100 Wavenumber (cm-I )
0 2-
+
I
1400
Fig. 2. The IR transmission spectra of samples A1 and El; the sample is about 4 mm thick.
germanium dioxide is lower than 20 wt.% (about 37 mol%), glasses can also be obtained by rapidly cooling the melts. In this region, it is not sufficient that GeO 2 is the only glass former, both PbF 2 and ZnF 2 participate in the formation of glass. Fluorine and oxygen ions have closely similar ionic radii and field strength. When fluorides are added to germanium dioxide glass, oxygen ions can be replaced by fluorine ions. This is shown as follows:
F The network of (GeO4) tetrahedra is destroyed to a certain extent, but, because of the strong polarization of lead ions and zinc ions, they can enter the network. Thus the broken chains are linked up and the strength of the network is reinforced. Although the content of germanium dioxide is very low, vitreous glass samples can be obtained.
4.2. Curves that have equal physical properties In the above experiments, we have measured various physical properties for each series of glass samples. Based on these results, we can estimate the changes of the physical properties for any glass sample in the vitreous region. Figures 3 and 4 show the curves that have equal glass transition temperature and equal density respectively. Accordingly, we can obtain the similar curves for other physical properties.
I O Ge0 2
2--O--Ge--O--
+ 2F-
I O
o
I I Z
O
> 2--O--Ge--F
?4
+ 0 2-
#o
I
O
I
y
I
X°
O
I
2--O--Ge--F
+ 2F-
PbF 2
90
80
70
60
5'0
/~0
30
20
10
ZnF2
I
O
1
Fig. 3. The curves that have equal glass transition temperature; O, experimental points.
154
He Shuping et al. / Vitreous oxyfluoride system based on Ge02, PbF2 and ZnF2
Ge02
glass c o m p o s i t i o n is s u b j e c t to c e r t a i n rules. F o r o x y f l u o r i d e glasses, the r a t i o o f F - / O 2 - i o n s will h a v e a n i m p o r t a n t e f f e c t o n the p h y s i c a l p r o p e r ties. In t h e G e O 2 - P b F 2 - Z n F 2 system, as the G e O 2 content decreases, fluorine atoms gradually subs t i t u t e for o x y g e n a t o m s a n d the s t r u c t u r a l s t r e n g t h o f glass n e t w o r k s d r o p s , w h i c h results in i m p o r t a n t c h a n g e s o f t h e p h y s i c a l p r o p e r t i e s s u c h as the glass t r a n s i t i o n t e m p e r a t u r e , c r y s t a l l i z a t i o n temperature, thermal expansion coefficient and elastic m o d u l u s . T a b l e 2 s h o w s the p h y s i c a l p r o p erties of e a c h series o f glass s a m p l e s . W h e n the r a t i o o f F - / O ~- i n c r e a s e s for the first series o f glasses w h i c h h a v e e q u a l Z n F 2 c o n tent, Tg a n d Tc d r o p , the t h e r m a l e x p a n s i o n c o e f f i c i e n t i n c r e a s e s a n d Y o u n g ' s elastic m o d u l u s E d e c r e a s e s . F o r the s e c o n d series o f glass s a m p l e s , b o t h the F - / O 2 - r a t i o a n d the Z n 2÷ c o n t e n t i n c r e a s e . B e c a u s e Z n 2÷ c a n l i n k up the b r o k e n n e t w o r k s to s o m e e x t e n t , the p h y s i c a l p r o p e r t i e s h a v e d i f f e r e n t c h a n g e s f r o m t h a t o f the first series o f glasses. F o r the t h i r d series o f glasses, the G e O 2 c o n t e n t is c o n s t a n t , the l i n k i n g r o l e o f Z n 2÷ f o r the b r o k e n n e t w o r k s was well e x p r e s s e d . A s t h e
lO PbF2
90
80
70
60
~;
4'o 3;
20
1o
z~2
Fig. 4. The curves that have equal glass density; the dotted line is inferred from experiment.
4. 3. T h e trends in p h y s i c a l properties
F o r b o t h o x i d e a n d f l u o r i d e glasses, the relat i o n s h i p b e t w e e n t h e p h y s i c a l p r o p e r t i e s a n d the
Table 2 Data of physical properties of glasses Sample
Trans. temp. T~ ( o C)
Cryst. temp. Tc ( ° C)
Thermal expansion coeff. ( x 10 - 6)
Density d (g/cm 3)
Refractive index n l~
Elastic modulus E (kg/mm 2)
Infrared absorpt. edge (cm 1)
A1 B1 C1 D1 E1
466 a) 450 430 408 381
630 a) 615 606 564 529
5.16 b) 5.24 6.33 7.08 8.00
5.23 b) 5.57 5.87 6.08 6.29
1.79 c) 1.84 1.87 1.89
6801 c) 6569 6582 6396 6230
1644 a)
A2 B2 C2 D2 E2
443 446 430
569 543 606
7.96 7.73 6.33 6.13 6.04
5.60 5.76 5.87 6.10 6.20
1.87 1.87 1.88 1.87
6701 6582
1585 1624 1506
A3 B3 C3 D3 E3
412 428 430 452 455
539 581 606 615 599
8.76 6.23 6.33 5.66 5.58
6.15 5.95 5.87 5.65 5.49
1.92 1.86 1.87
6416 6514 6582 6843 6763
~) Errors depend on measuring instrument, less than 1%. b) The largest deviation to average value is not more than 0.1%. c) Errors depend on measuring system and operating process, less than 5%.
1.84
1624 1467
He Shuping et al. / Vitreous oxyfluoride system based on GeO2, PbF2 and ZnF,
Z n 2 + / p b 2+ ratio increases, the glass transition temperature increases, the thermal expansion coefficient decreases and the elastic modulus increases. This shows that the network structure of this series of samples is strengthened. The density and the refractive index of the glasses are mainly affected by the lead content because the lead ion has a large molar weight and a high polarizability. It can be seen from table 2 and fig. 4 that both the density and the refractive index increase as the lead fluoride content increases. 4.4. I R t r a n s p a r e n c y
The IR absorption of glasses is dependent on the group vibration of the molecules, atoms and ions in glass networks. In the G e O 2 - P b F 2 - Z n F 2 system, the vibration of the G e - O bond primarily determines the IR absorption edge of the glass. Because of the incorporation of a lot of fluorine ions and heavy metal ions, the vibration of the G e - O bond is weakened. Table 2 shows that the I R absorption edge of these glasses is above 5.5 /~m and it will move towards longer wavelengths as the F - / O 2- ratio increases. 4.5.
155
5. Conclusions (1) There is a large vitreous region in the ternary oxyfluoride system based on GeO 2, PbF 2 and ZnF2, in which the GeO 2 content is from 35 to 100 mol%, PbF z is from 0 to 65 mol% and ZnF 2 is from 0 to 25 mol%. (2) The glass transition temperatures range from 380 o C to 450 o C, the crystallization temperatures are from 5 3 0 ° C to 700°C, the refractive indices from 1.75 to 1.95, the densities from 5.2 to 6.5 g / c m 3 and the thermal expansion coefficients from 5 × 10 -6 ° C - I to 10 × 10 -6 ° C - 1 . Young's elastic modulus is about 6500 k g / m m 2. (3) The I R absorption edge of these glasses is about 6.5 #m. Their chemical durability is superior to that of fluoride glasses. (4) The physical properties of these oxyfluoride glasses are affected by both the F - / O 2- ratio and the Pb 2+ content. When the F - / O 2- ratio is increased, the glass networks are depolymerized, which results in a decrease of the glass formation temperature, elastic modulus and an increase of the thermal expansion coefficient and I R absorption edge. When the lead content is increased, the refractive index and the density of this glass rapidly increased.
Chemical durability
Bulk samples whose two parallel surfaces were carefully polished were cleaned with alcohol. To test the moisture resistance of the glasses, we placed them into a container in which the temperature and humidity are constant. After different times of maintaining these samples at (75 _ 5 ) ° C and (85 _+ 5)% humidity, the glass surface was examined by a 10 × 10 microscope. This shows that, after 40 h, the glass surface has no change, but after 60 h, there are some spots on the surface of the samples.
References [1] B. Bendow, Proc. SPIE 320 (1982) 15. [2] M.G. Drexhage, O.H. E1-Bayoumi and C.T. Moynihan, Proc. SPIE 320 (1982) 27. [3] M. Poulain and M. Matachi, Sol. St. Chem. 3 (1982) 461. [4] M. Poulain, J. Non-Cryst. Solids 56 (1983) 1. [5] J. Lucas, J. Non-Cryst. Solids 80 (1986) 83. [6] M. Poulain, Mat. Res. Bull. 15 (1980) 735. [7] Hu Hefang, J. Chinese Silicates 13 (1985) 402. [8] Zhang Keli, J. Special Glasses (Chin.) 3 (1986) 42. [9] Gan Fuxi, Optical Glasses (Science Press, Beijing, 1982). [10] Cheng Jijian, J. Chinese Silicates 11 (1983) 55. [11] G. Demortain, Mat. Lett. 2 (4B) (1984) 320.
151
Section 3. Glass formation and phase transformation STUDY OF F O R M A T I O N AND P R O P E R T I E S O F T H E V I T R E O U S O X Y F L U O R I D E S Y S T E M B A S E D O N GeO2, PbF 2 A N D ZnF 2 H E Shuping Department of Optical Fiber and Optical Cable, Wuhan Science Institute of Post and Telecommunications, Wuhan, PR China
XU Chao and G A N Fuxi Wuhan University of Technology, Wuhan, PR China
The vitreous region of the oxyfluoride system based on germanium dioxide, lead fluoride and zinc fluoride is obtained by using platinum crucibles. The physical properties such as the transition temperature, crystallization temperature, refractive index, density, thermal expansion coefficient and elastic modulus are measured. A description to the change rules of the physical properties of this system is given in detail. The glasses have a good transparency in the mid-infrared region. Their chemical durability is much better than that of fluoride glasses.
1. Introduction
Fluoride glasses are important because of their good transparency in the infrared region [1-6]. Their greatest shortcoming is their weak glass-forming ability and poor chemical durability. In order to improve glass formation, one of the effective ways is to incorporate oxides that have a strong glass-forming ability [7-8]. In recent years, more and more research has been performed on oxyfluoride glasses. Many oxyfluoride glasses such as fluorosilicate [9], fluorophosphate [9] and fluoroborate glasses [10] have special optical properties which means that they play an important role in optical glasses. However, the fluorogermanate glasses, whose transparency in the mid-infrared region is very good, have not been studied. As is well known, lead fluoride is a good glass modifier in fluoride glasses. Zinc fluoride is a weak glass former. The binary system ZnF2-PbF 2 was investigated by Demortain et al. [11]. In his work, a glass sample with a thickness of 10-20 ~m was obtained at a cooling rate of 10 6 K / s by pouring the melts between two rolling wheels. The sample has an IR absorption edge above 15 ~tm. Glass formation is expected to be significantly 0022-3093/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
improved by incorporating germanium dioxide. It is the purpose of this study to investigate the glass formation and physical properties of the ternary G e O 2 - P b F 2 - Z n F 2. This system is of interest theoretically in the research for new infrared materials.
2. Vitreous region and sample fabrication
Reagent grade PbF z and ZnF 2 were used as raw materials and GeO 2 was obtained by the hydrolysis of GeC14. Batches of 5-10 g were melted at 1000-1150°C for 10 min in platinum crucibles. Then the melts were poured onto a cooled copper plate. Whether one composition was a glass or not was examined by eye or microscope. A nitrogen atmosphere was used to prevent the fluorides from oxiding in the melting process. The vitreous region of this system is shown in fig. 1. Three series of formulas were selected in the vitreous region: (1) (70 - x)GeO2(20 + x)PbF210ZnF2, (2) (70 - y)GeOz30PbF2yZnF2, (3) 6 0 G E O 2 ( 4 0 - z ) P b F 2 z Z n F 2 (x, y, z = 0, 5, 10, 15, 20). Batches of 40 g were melted at (1070 _+ 30) o C for
152
He Shuping et aL / Vitreous oxyfluoride system based on Ge02, PbF2 and Z n F2
3. Measurement of glass properties
801:L20 ,0/o o
/(o o/\o,+ 20/
PbF2
90
"
80
~
70
"
\-1~ 60
50
40
30
20
10
ZnF2
Fig. 1. The vitreous region of the ternary G e O 2 - P b F 2 - Z n F 2 system, o , clear glass; zx, partially devitrified glass; O, imperfect melt; × , fully devitrified glass.
(40 + 5) min. A high-purity aluminum oxide ball was used to stir the melt. Bulk samples with a thickness of more than 20 mm were formed by pouring the melt into a preheated copper mould. The glass compositions and conditions of fabrication are all listed in table 1.
The glass transition temperature (T~) and crystallization temperature (T~) were determined from differential thermal analysis curves. The density was measured using the Archimedes principles. The thermal expansion coefficient was measured with a differential quartz dilatometer. The refractive index was measured by the oil immersion method and Young's elastic modulus was measured using a digital dynamic technique. The transparency in the mid-infrared region was measured by a 60SXB Fourier IR spectrometer. The samples were 4 mm thick with two parallel surfaces polished. The result is shown in fig. 2.
4. Results and discussion
4.1. The glass forming properties GeO2-PbFe-ZnF2
of
Figure 1 shows that the vitreous region is inclined to the GeO 2 side, which indicates that germanium dioxide plays the role of glass former when its content is high. When the content of
Table 1 Compositions and conditions of fabrication of glass samples Series
Samples
Percentage by molar
Melting temperature
Annealing temperature
GeO 2
PbF 2
ZnF 2
(oc)
(oc)
I
A1 B1 C1 D1 E1
70 65 60 55 50
20 25 30 35 40
10 10 10 10 10
1100 1100 1070 1060 1050
415 400 380 360 340
II
A2 B2 C2 D2 E2
70 65 60 55 50
30 30 30 30 30
0 5 10 15 20
1100 1100 1070 1100 1100
380 380 380 390 390
III
A3 B3 C3 D3 E3
60 60 60 60 60
40 35 30 25 20
0 5 10 15 20
1100 1100 1070 1100 1100
370 380 380 400 400
153
He Shuping et aL / Vitreous oxyfluoride system based on Ge02, PbF2 and ZnF2
i00,
,
,
,
~
,
1
""
0
I
8(
, 2--O--Ge--F 1
g 60 4
i 4o
\
I
3900
3400 240 24100 19100 Wavenumber (cm-I )
0 2-
+
I
1400
Fig. 2. The IR transmission spectra of samples A1 and El; the sample is about 4 mm thick.
germanium dioxide is lower than 20 wt.% (about 37 mol%), glasses can also be obtained by rapidly cooling the melts. In this region, it is not sufficient that GeO 2 is the only glass former, both PbF 2 and ZnF 2 participate in the formation of glass. Fluorine and oxygen ions have closely similar ionic radii and field strength. When fluorides are added to germanium dioxide glass, oxygen ions can be replaced by fluorine ions. This is shown as follows:
F The network of (GeO4) tetrahedra is destroyed to a certain extent, but, because of the strong polarization of lead ions and zinc ions, they can enter the network. Thus the broken chains are linked up and the strength of the network is reinforced. Although the content of germanium dioxide is very low, vitreous glass samples can be obtained.
4.2. Curves that have equal physical properties In the above experiments, we have measured various physical properties for each series of glass samples. Based on these results, we can estimate the changes of the physical properties for any glass sample in the vitreous region. Figures 3 and 4 show the curves that have equal glass transition temperature and equal density respectively. Accordingly, we can obtain the similar curves for other physical properties.
I O Ge0 2
2--O--Ge--O--
+ 2F-
I O
o
I I Z
O
> 2--O--Ge--F
?4
+ 0 2-
#o
I
O
I
y
I
X°
O
I
2--O--Ge--F
+ 2F-
PbF 2
90
80
70
60
5'0
/~0
30
20
10
ZnF2
I
O
1
Fig. 3. The curves that have equal glass transition temperature; O, experimental points.
154
He Shuping et al. / Vitreous oxyfluoride system based on Ge02, PbF2 and ZnF2
Ge02
glass c o m p o s i t i o n is s u b j e c t to c e r t a i n rules. F o r o x y f l u o r i d e glasses, the r a t i o o f F - / O 2 - i o n s will h a v e a n i m p o r t a n t e f f e c t o n the p h y s i c a l p r o p e r ties. In t h e G e O 2 - P b F 2 - Z n F 2 system, as the G e O 2 content decreases, fluorine atoms gradually subs t i t u t e for o x y g e n a t o m s a n d the s t r u c t u r a l s t r e n g t h o f glass n e t w o r k s d r o p s , w h i c h results in i m p o r t a n t c h a n g e s o f t h e p h y s i c a l p r o p e r t i e s s u c h as the glass t r a n s i t i o n t e m p e r a t u r e , c r y s t a l l i z a t i o n temperature, thermal expansion coefficient and elastic m o d u l u s . T a b l e 2 s h o w s the p h y s i c a l p r o p erties of e a c h series o f glass s a m p l e s . W h e n the r a t i o o f F - / O ~- i n c r e a s e s for the first series o f glasses w h i c h h a v e e q u a l Z n F 2 c o n tent, Tg a n d Tc d r o p , the t h e r m a l e x p a n s i o n c o e f f i c i e n t i n c r e a s e s a n d Y o u n g ' s elastic m o d u l u s E d e c r e a s e s . F o r the s e c o n d series o f glass s a m p l e s , b o t h the F - / O 2 - r a t i o a n d the Z n 2÷ c o n t e n t i n c r e a s e . B e c a u s e Z n 2÷ c a n l i n k up the b r o k e n n e t w o r k s to s o m e e x t e n t , the p h y s i c a l p r o p e r t i e s h a v e d i f f e r e n t c h a n g e s f r o m t h a t o f the first series o f glasses. F o r the t h i r d series o f glasses, the G e O 2 c o n t e n t is c o n s t a n t , the l i n k i n g r o l e o f Z n 2÷ f o r the b r o k e n n e t w o r k s was well e x p r e s s e d . A s t h e
lO PbF2
90
80
70
60
~;
4'o 3;
20
1o
z~2
Fig. 4. The curves that have equal glass density; the dotted line is inferred from experiment.
4. 3. T h e trends in p h y s i c a l properties
F o r b o t h o x i d e a n d f l u o r i d e glasses, the relat i o n s h i p b e t w e e n t h e p h y s i c a l p r o p e r t i e s a n d the
Table 2 Data of physical properties of glasses Sample
Trans. temp. T~ ( o C)
Cryst. temp. Tc ( ° C)
Thermal expansion coeff. ( x 10 - 6)
Density d (g/cm 3)
Refractive index n l~
Elastic modulus E (kg/mm 2)
Infrared absorpt. edge (cm 1)
A1 B1 C1 D1 E1
466 a) 450 430 408 381
630 a) 615 606 564 529
5.16 b) 5.24 6.33 7.08 8.00
5.23 b) 5.57 5.87 6.08 6.29
1.79 c) 1.84 1.87 1.89
6801 c) 6569 6582 6396 6230
1644 a)
A2 B2 C2 D2 E2
443 446 430
569 543 606
7.96 7.73 6.33 6.13 6.04
5.60 5.76 5.87 6.10 6.20
1.87 1.87 1.88 1.87
6701 6582
1585 1624 1506
A3 B3 C3 D3 E3
412 428 430 452 455
539 581 606 615 599
8.76 6.23 6.33 5.66 5.58
6.15 5.95 5.87 5.65 5.49
1.92 1.86 1.87
6416 6514 6582 6843 6763
~) Errors depend on measuring instrument, less than 1%. b) The largest deviation to average value is not more than 0.1%. c) Errors depend on measuring system and operating process, less than 5%.
1.84
1624 1467
He Shuping et al. / Vitreous oxyfluoride system based on GeO2, PbF2 and ZnF,
Z n 2 + / p b 2+ ratio increases, the glass transition temperature increases, the thermal expansion coefficient decreases and the elastic modulus increases. This shows that the network structure of this series of samples is strengthened. The density and the refractive index of the glasses are mainly affected by the lead content because the lead ion has a large molar weight and a high polarizability. It can be seen from table 2 and fig. 4 that both the density and the refractive index increase as the lead fluoride content increases. 4.4. I R t r a n s p a r e n c y
The IR absorption of glasses is dependent on the group vibration of the molecules, atoms and ions in glass networks. In the G e O 2 - P b F 2 - Z n F 2 system, the vibration of the G e - O bond primarily determines the IR absorption edge of the glass. Because of the incorporation of a lot of fluorine ions and heavy metal ions, the vibration of the G e - O bond is weakened. Table 2 shows that the I R absorption edge of these glasses is above 5.5 /~m and it will move towards longer wavelengths as the F - / O 2- ratio increases. 4.5.
155
5. Conclusions (1) There is a large vitreous region in the ternary oxyfluoride system based on GeO 2, PbF 2 and ZnF2, in which the GeO 2 content is from 35 to 100 mol%, PbF z is from 0 to 65 mol% and ZnF 2 is from 0 to 25 mol%. (2) The glass transition temperatures range from 380 o C to 450 o C, the crystallization temperatures are from 5 3 0 ° C to 700°C, the refractive indices from 1.75 to 1.95, the densities from 5.2 to 6.5 g / c m 3 and the thermal expansion coefficients from 5 × 10 -6 ° C - I to 10 × 10 -6 ° C - 1 . Young's elastic modulus is about 6500 k g / m m 2. (3) The I R absorption edge of these glasses is about 6.5 #m. Their chemical durability is superior to that of fluoride glasses. (4) The physical properties of these oxyfluoride glasses are affected by both the F - / O 2- ratio and the Pb 2+ content. When the F - / O 2- ratio is increased, the glass networks are depolymerized, which results in a decrease of the glass formation temperature, elastic modulus and an increase of the thermal expansion coefficient and I R absorption edge. When the lead content is increased, the refractive index and the density of this glass rapidly increased.
Chemical durability
Bulk samples whose two parallel surfaces were carefully polished were cleaned with alcohol. To test the moisture resistance of the glasses, we placed them into a container in which the temperature and humidity are constant. After different times of maintaining these samples at (75 _ 5 ) ° C and (85 _+ 5)% humidity, the glass surface was examined by a 10 × 10 microscope. This shows that, after 40 h, the glass surface has no change, but after 60 h, there are some spots on the surface of the samples.
References [1] B. Bendow, Proc. SPIE 320 (1982) 15. [2] M.G. Drexhage, O.H. E1-Bayoumi and C.T. Moynihan, Proc. SPIE 320 (1982) 27. [3] M. Poulain and M. Matachi, Sol. St. Chem. 3 (1982) 461. [4] M. Poulain, J. Non-Cryst. Solids 56 (1983) 1. [5] J. Lucas, J. Non-Cryst. Solids 80 (1986) 83. [6] M. Poulain, Mat. Res. Bull. 15 (1980) 735. [7] Hu Hefang, J. Chinese Silicates 13 (1985) 402. [8] Zhang Keli, J. Special Glasses (Chin.) 3 (1986) 42. [9] Gan Fuxi, Optical Glasses (Science Press, Beijing, 1982). [10] Cheng Jijian, J. Chinese Silicates 11 (1983) 55. [11] G. Demortain, Mat. Lett. 2 (4B) (1984) 320.