Page 39 - PCMI Journal July 2018

David Allen | Emeritus Professor | Cranfield University | UK Photochemical Machining of Aerospace Materials
5/31/18
Aluminium is not the easiest material to etch
• Despite the “good” PCMI ‘etchability rating’, I have found that aluminium is not a “favourite” material to etch in many commercial etching companies in UK, Europe and USA as it requires special etchant formulations that render them only applicable to aluminium.
• The PCM industry is obviously attracted to “universal” etchants that can be applied to many different materials to reduce costs.
Aluminium etchants
• Aluminium is soluble in dilute mineral acids and alkali metal hydroxides and therefore termed amphoteric. The usual PCM etchants comprise either
• Mineral acids (e.g. based on HCl) or
• Sodium hydroxide (NaOH) or
• Ferric chloride (FeCl3)
• Many formulations of aluminium etchants have been found in the literature and patents databases relating to the fabrication of aerospace components by chemical milling and in printing plate manufacture.
• I have a Bendix publication from 1974 that lists more than 80 etchant formulations evaluated for performance to improve resolution.
Issue 131 July 2018 PCMI Journal 38
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