STUDY OF THE PARAMETERS IN MICROWAVE DISSOLUTION METHODS USING A MAGNETIC STIRRING DEVICE IN THE MICROWAVE UNIT - APPLICATION TO DISSOLUTION OF HIGH-CARBON FERROCHROMIUM

Microwave sample preparation methods have come a long may since the ea rliest experiments with domestic microwave ovens. This study concerned the decomposition of ferrochromium samples containing a high proporti on of insoluble carbides by means of a focused microwave digestion sys tem. The experimental results showed that samples were completely deco mposed in HNO3-HF mixed acids, Optimization of the microwave dissoluti on programmes involved the study of acid mixture volume, the control o f pressure and temperature inside a reference vessel, power control an d the influence of magnetic stirring during the dissolution processes. Chromium was determined potentiometrically in each of the intermediat e digests obtained during optimization of the procedure, for demonstra tion of the successive recoveries of this element. The selected dissol ution procedure provided a recovery of 99-100% Cr under the following conditions: 5 min at 250 W/30 min at 400 W/15 min at 500 W (without st irring) and 5 min at 250 W/15 min at 400 W/5 min at 500 W (with stirri ng) and showed excellent reproducibility with a slightly improved RSD when magnetic stirring was used. The accuracy was determined using thr ee high-carbon ferrochromium reference materials: ECRM 585-1 from the Bureau of Analysed Samples, BAM 530-1 from the Bundesanstalt fur Mater ialprufung and BCS 204-4 from British Chemical Standards. The results were compared with those obtained using a classical dissolution proced ure. The microwave solutions could also be used for the simultaneous d etermination of major and minor elements in FeCr samples by spectrosco pic techniques.