الفهرس 
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Abstract
This study investigated the effect of prophylactic and bleaching treatments
on the corrosion behavior of Ni-Cr alloy. Forty disc shaped samples of 1 cm diameter and 0.5 cm height were used
in this study. Half of them were subjected to different porcelain firing cycles (heat treated) before treatment with prophylactic or bleaching agents, and then all of them were subjected to corrosion test. The corrosion products were measured using A.A.S. Finally scanning electron microscopy (SEM) was
performed. The corrosion behavior of the investigated alloy (including pitting corrosion) was studied using potentiodynamic polarization technique in aerated 1 % NaCl solution with pH 7.
Typical scanning electron microscopy (SEM) obtained for the heat treated
and as received alloy samples has indicated the difference in the particle size and distribution.
The results showed that, open circuit potential (OCP) – time curves for a time
period of 3 – 4 hours of immersion for the treated and untreated group samples
with different prophylactic and bleaching agents indicated that the as received group samples treated with prophylactic and bleaching agents became passivated within this time period. The OCP - time curves representing the behavior of the heat treated group samples not treated with prophylactic or bleaching agents indicated pitting attack by Cl ions. The results also indicated that inspite of the passive state exhibited by the heat treated group samples treated with prophylactic or bleaching agents, the potentiodynamic polarization curves indicated pitting attack by Cl ions. The metastable pits associated with current transients were readily observable by scanning electron microscopy (SEM) after the run.The pronounced decrease in corrosion current density (Icorr) for group
samples treated with prophylactic agents, for both heat treated and as received group samples, suggested inhibiting effects of the compounds constituting the prophylactic agents, through adsorption of their molecules at the electrode surface together with O2 molecules. On the other hand, the as received group samples treated with prophylactic agents ( group samples no. 7&8 ) exhibit stable passivity under potentiodynamic polarization conditions, resisting pitting
attacks by Cl ions with considerable low values of passive current density. The SEM for both group samples after anodic polarization indicated no pits.