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The Chemical Etching of Aluminium in Caustic Soda Solutions

1976; Taylor & Francis; Volume: 54; Issue: 1 Linguagem: Inglês

10.1080/00202967.1976.11870366

1745-9192

B. Chatterjee, R. W. Thomas,

Aluminum Alloy Microstructure Properties

SummaryThe chemistry of the caustic soda-aluminium reaction is briefly outlined. Dissolution rates of 99.5% purity aluminium and HE9 alloys are measured and the effects of concentration, temperature, water purity, dissolved aluminium, sodium gluconate, metal composition and ageing treatment noted. Arrhenius plots for various etchants are all linear and of the same slope and indicate a homogeneous chemical reaction under all conditions with an activation energy of 46 kJ /mole (11 kcal/mole). An electrochemical mechanism is proposed in which the iron containing constituent provides the cathodic sites and plays the major part in the dissolution process. The progress of etching is monitored by specular gloss measurements using the Gloss Head of DEF 1053, Method 11. By relating the drop in specular gloss to the weight of metal removed a measure of etch effectiveness for various etchants is obtained. Used baths are better for etching than new baths and dissolved zinc makes etching less effective. The response to etching of various variants of HE9 composition is studied. The TF condition is better for etching than the TB condition. The factors which determine the response will be discussed in a future paper.