In pack aluminizing process:
1) NH4Cl (s) = NH3 (g) + HCl(g)
According to the following reaction is it more likely to react with Al solid powder(S,powder) or Al powder with surface liquid(L,powder)?
Which one participate in the reaction with gaseous chloride acid?
The Al with surface melt or the Al without surface melt?
2) n Al(Powder, S) + m HCl(g) = k AlxCly (g) + p H2 (g)
3) q Al(Powder, L) + f HCl(g) = l AlxCly (g) + r H2 (g)
Al(Powder, L) means Aluminum powder has a melt surface exited from the oxide shell.
Pack aluminizing process reactions:
NH4Cl=HCl + NH3
2Al+ 6HCl = 2AlCl3+ 3H2
Al + AlCl3 = 2AlCln + (3-n)Cl2
2AlCln + substrate = aluminized compound+ AlCl3
n is less than 3
Now AlCln is more stable thermodynamically than AlCl3 as the temperature increases above 800oC which is directly react with the substrate this reaction then produce AlCl3 which in turn react with aluminum again to form an AlCln.. this means that the AlCl3 is the activator element for the aluminizing process reactions as the rate determining steps for coating thickness built up.
Best regards.
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