Solutions in the system HF-HNO3-C3H6O3 (lactic acid) can be used as etching reagents for ferrites and garnets and possibly for oxides in general. All specimens are polished before etching by hand grinding on a No. 400 grit with subsequent grinding in appropriate steps through No. 4/0 emery paper. for the final polishing step, a water slurry of Linde A is used on either a hand honeycomb wax lap or a rotating nylon cloth lap. Specimens suitable for etching are normally prepared within 1 hr. The etchant is agitated during all etching procedures. Experimental conditions which are satisfactory for etching a number of oxide compounds are listed in Table 1. The strength of a mixture of HF-HNO3-C3H6O3 is dependent on the concentration of the NO2^+ ion formed from the reaction of hydrofluoric acid with nitric acid. An increase in the reagent temperature or decrease in the lactic acid concentration will increase the NO2^+ content. Hence, the reactivity of the etching reagent is easily adjusted for a part
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