George,
Yes, the etch is nitric acid in ethanol, normally used at a
concentration of 2%. A very useful textbook, recently revised,
decsribes this.
The reference is G. Petzow, 1999: Metallographic etching, 2nd edition:
techniques for metallography, ceramography, plastography, (Materials
Park OH: ASM International), ISBN 0-87170-633-4.
Among other useful subjects this book coves hazards involved with
etchants. On p201 it states:
"Mixtures of alcohols with nitric acid can form different reaction
products (aldehydes, carbonic acids, explosive nitrogen compounds
etc.). The tendency to explode increases with decreasing molecular size
of the produced component. A nitric acid content of 5% should not be
exceeded with ethanol and 35% with methanol. Do not store these
mixtures."
It is conventional metallographic practice to store 1% and 2% nitric
acid in ethanol solutions: I certainly would not store a 5% solution
and there is no metallographic need for it.
Yours,
Peter
-------------------
Peter Northover
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