silicon for the chemical and solar industry XIII

from a similar work performed by Jo [22]. The silicon matrix absorbs part of the

stress caused by this dilatation. This material is universally known for its very low

ductility. However, it seems it has enough to absorb this stress. If the ductility of

silicon had not been high enough, cracks would have widely branched all over the

surface with high speed. The transformation has partially occurred in the untreated

sample during its solidification in the industrial mould. Annealing can enhance the

formation of LT-FeSi

and the precipitation of silicon. Cracks will be larger and more

common in an annealed sample. Figure 8 shows cracks in intermetallics from the

annealed sample. A comparison with the untreated sample can be referred to Figure 4.

Figure 8

Cracks due to FeSi

phase transformation in a particle of the annealed sample

4.4 Phase characterization

Figure 9 reports the relative phase content predicted by SiStruc

compared to the

amount measured with ImageJ

in the three samples. CaAl

is present in lower

amounts, since it is the last Ca-containing phase which solidifies. Ca would have

already reacted to form Al

CaFe

. FeSi

has a similar relative percentage between

the untreated sample and SiStruc

. Fe will rather form FeSi

or TiFeSi

in the

annealed sample, since the Ca content is reduced by the oxidative refining effect. Ti is

affected only by segregation, therefore TiFeSi

will be relatively more present in the

annealed sample. Al

increases relevantly, but its relative percentage is still

very low. In the end, the similarity between the sample treated at 600°C and the

untreated sample shows that at this temperature no changes in phase composition are

happening.

Figure 9

: Comparison between SiStruc

calculation and image analysis