Prakt. Met. Sonderband 38 (2006) 233 
e internal stainless steel. During the experiments of internal oxidation the electrical resistance was 
particles measured by a four-probe method with a bi-directional current of 100mA with a resolution 
3d on the of 10 uQ and accuracy of + 35uQ. In addition, the temperature changes were measured at 
je size of the central part of the sample with a Ni-NiCr thermocouple with an outer diameter of 1 mm 
ent on the and accuracy + 1.5 °C. 
needed to 
| therefore 
Ot easy to 
on of dilute 
aminations 
ad in the 
3 (99.99%) 
d cast bar 
e bar was 
> annealed 
periments 
ed in the 
{Fig." 1a) 
(two-stage 
“of internal 
> following iy 
he desired 
| oxidation Fig. 1: Laboratory device (a) and measurement cell (b) for in-situ electrical resistance 
vas cooled measurements 
3d on the 
pe, Nikon 
(Olympus 3. RESULTS AND DISCUSSION 
insisted of 
suspension The process of internal oxidation of Ag-Sn (2 at.% Sn) alloy starts with dissolution of 
ology, size oxygen into the surface layer of the alloy. Dissolved oxygen diffuses inward through the 
omposition metal matrix and reacts at the advancing reaction front with a less-noble solute element - 
EOL 840A Sn. After the solubility product is exceeded and the critical supersaturation for 
homogenous precipitation is attained fine oxide particles SnO, precipitate from the solid 
s by in-situ solution. The micrographs in figures 2a to 2d show the microstructure of the partially and 
e samples totally internally oxidized wire of silver — tin alloy. Internal oxidation was performed at 
u electrical 800°C and for different periods of times. The microstructures of samples consist of two 
ic cylinder different zones: (i) the darker internally oxidized zone and (ii) the brighter unoxidized solid 
The outer solution. The oxidation front is clearly visible as the sharp border between these two zones 
d the inner (Fig. 2a). The thickness of 10 zone increases with time and the wire with diameter of 0.5 
he sample. mm was completely internally oxidized after approximately 45 minutes. The chemical 
The high- composition of the precipitated particles was confirmed by the EDX chemical mapping 
ained with (Fig. 3). It can be seen that the oxide particles consist of tin and oxygen atoms forming 
e resistant probably the SnO; oxides 
a 
0