DSC study of the deposition reactions of zinc pack coatings up to 550°C
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Zn pack coating formation takes place in three steps as differential scanning calorimetry shows. The initial step (at 193.9°C) is endothermic and involves the transformation of α-NH4Cl to β-NH4Cl and the NH4Cl decomposition to NH3 and HCl. During the second step (at 248.6°C), which is exothermic, Zn2+ salts are formed and most probably ZnCl2. Finally at 264.1°C (endothermic reaction) it seems that ZnCl2 is decomposed to form Zn that is deposited on the ferrous substrate. The as-cast Zn diffuses in the iron substrate forming the gamma and delta phase of the Fe–Zn phase diagram. Al2O3 is not involved in the above-mentioned mechanism and acts only as filler.
Keywordschemical vapor deposition DSC characterization metallic coatings pack cementation
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