The uptake of silver from a molten silver chloride bath by an aluminosilicate glass is highly sensitive to the presence of sodium in the salt bath under both equilibrium and nonequilibrium conditions. The delta-n resulting from the silver dopant is reduced by nearly an order of magnitude by the addition of just 5-mol % sodium chloride to the melt. The addition of zinc chloride or lead chloride can be used to maintain high delta-n values in the presence of sodium in the melt.
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Silver Activity Coefficients in AgCl/NaCl Melts as a Function of Silver Concentration at 502°C
Silver mole fraction (Xag)
Measured silver activity coefficient
Calculated silver activity coefficient
1.000
1.000
1.000
0.995
1.012
1.000
0.950
1.093
1.002
0.880
1.239
1.009
Note: The middle column contains values calculated from the experimental data in Ref. 10. The rightmost column contains values calculated from regular solution theory using the net interaction energy given in Ref. 9.
Table II
Comparison of Reported K and n Values for Several Glass Types and the Chloride and Nitrate Binary Melts
Reference 12 gives the equilibrium constant to within a factor of the Ag/Na mobility ratio in Vycor.
Table III
Characteristics of the Bausch & Lomb Aluminosilicate Glass with an Exchange for Silver
Oxide
Wt. %
SiO2
67.0
Al2O3
7.4
Na2O
25.6
Transition temperature
507°C
Base index
1.501 ±0.001 at sodium d line
Abbe number
57.7
Maximum predicted delta-n
0.149
Table IV
Results of Atomic Absorption Analysis on Equilibrium Interdiffusions
Mol % NaCl in starting bath
XAgglass
XNaglass
0.5
0.109
0.207
5
0.058
0.223
12
0.017
0.178
K = 2.4 × 10−3 (Glass prefers Na)
n = 1.8 (Glass is nonideal)
Table V
Surface Concentrations of Nonequilibrium Interdiffusions as Measured by Energy Dispersive X-Ray Spectroscopy
Mol % NaCl in starting bath
XNamelt
XAgglass
XNaglass
0
0.005
0.032
0.131
0.5
0.008
0.027
0.136
5
0.050
0.007
0.157
12
0.120
0.004
0.159
K = 1.5 × 10−3 (Glass prefers Na)
n = 1.8 (Glass is nonideal)
Table VI
Comparison of Various Interdiffusions Using ZnCl2 and PbCl2 Solvents to Pure AgCl Melts
Sample
Temp (°C)
Melt composition
Stirred
Delta-n
Diff depth (mm)
1
515
400-g AgCl
60 rpm
0.080
3.3
2
520
46-g AgCl
None
0.086
3.1
58-g ZnCl2
3
515
70-g AgCl
None
0.035
2.9
4
520
18-g AgCl
None
0.059
2.8
82-g ZnCl2
5
513
54-g AgCl
None
0.061
4.7
70-g PbCl2
Tables (6)
Table I
Silver Activity Coefficients in AgCl/NaCl Melts as a Function of Silver Concentration at 502°C
Silver mole fraction (Xag)
Measured silver activity coefficient
Calculated silver activity coefficient
1.000
1.000
1.000
0.995
1.012
1.000
0.950
1.093
1.002
0.880
1.239
1.009
Note: The middle column contains values calculated from the experimental data in Ref. 10. The rightmost column contains values calculated from regular solution theory using the net interaction energy given in Ref. 9.
Table II
Comparison of Reported K and n Values for Several Glass Types and the Chloride and Nitrate Binary Melts
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