Table 2: Elements identified by SEM on the surface of sample 1 in three regions denoted as Spectrum 1, Spectrum 2, Spectrum 3 in Figure 3.

Element Weight% Atomic%

Spectrum 1 O K 25.48 54.41
Fe K 74.52 45.59

O K 28.20 56.27
Spectrum 2 Si K 4.73 5.38
Fe K 67.07 38.35

Spectrum 3 O K 55.08 68.28
Si K 44.92 31.72