3.2.3. Effect ofHNO3 on coating formation
3.2.3.1. Surface morphology of steam treated surface using aqueous
HNO3 solution. Fig. 6(a) and (c), shows the typical surface morphology of Peraluman 706TM surface after 10 min steam treatment
with steam generated from an aqueous solution of HNO3 having
pH 3.0 and pH 2.0. In general, steam generated from HNO3 solution
formed a needle like structure, however the cell size of the needle
like structure was denser at high pH conditions (lower concentrations) as shown in Fig. 6(b) and (d). The EDS analysis revealed the
presence of N at the intermetallic particles, although no nitrogen
signal was observed from the oxide layer over the matrix.