We are trying to etch DP600 using LePera etchant. As soon as we add Sodium metabisulfite to Picral, the picric acid crystallizes as powder at the bottom. Even after stirring for long it does not goes back into solution. We etched despite all this and then picric acid crystallized on specimen surface. Can someone tell what we could be doing wrong? Thanks…
LePera's reagent is to be obtained by adding 1 wt % aq. solution of sodium metabisulfite (Na2S2O5) to a solution of 4 wt % picric acid (C6H2(NO2)3OH) in ethyl alcohol, in a 1:1 vol. ratio. Cf.: F. S. Le Pera, "Improved etching technique to emphasize martensite and bainite in high-strength dual-phase steel", Journal of Metals, 32(3), March 1980, pp. 3-39.
The etchant is a mixture of two pristine solutions . Volumes of 30 ml of reagent 1
and 30ml of reagent 2 are poured into two different beakers. "Just before the etching
is started, the solutions are mixed in a small crystallizing vessel"
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