The copper concentration is more than 3% at the surface and decreases
until 70 μm depth unlike the sodium which increases, their
sum is rather stable. We suggest that the Nps can be formed along
the penetration depth and because Tin is present in the ten first
micrometers, we can estimate a maximal average fill factor fav=
0.03 for l=10 μm. Fig. 6 shows a similar behaviour for silver.
The silver concentration is about 1% at the surface and decreases
until 8 μm depth unlike the sodium which increases and their sum
is rather stable as in the copper exchange case: