Page 45 - PCMI Journal July 2018
P. 45
David Allen | Emeritus Professor | Cranfield University | UK Photochemical Machining of Aerospace Materials
5/31/18
Ferric chloride etchants for aluminium (5)
There was a need to investigate other safer additives to dilute ferric chloride.
Lightwala has investigated:
• Orthophosphoric acid (H3PO4) • Polyphosphoric acid
• Nitric acid (HNO3)
• Hydrochloric acid (HCl)
All brought a marked improvement in etch rate. Etching for 10 min gave higher etch rates and smoother finish than etching for 5 min, thereby illustrating the protective effect of the passivating layer.
Regeneration of aluminium etchants
Etchant
Regeneration system
Ferric chloride
Chlorine gas
(lowering the cost by at least a factor > 2 according to Wible)
Sodium hydroxide
Secondary crystallisation of Al(OH)3 from NaAlO2 to release sodium hydroxide
Alkaline potassium ferricyanide
Electrolysis using a semi- permeable membrane to separate anode from cathode.
Ozonolysis.
Issue 131 July 2018 PCMI Journal 44
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