Study of the parameters in microwave dissolution methods using a magnetic stirring device in the microwave unit. Application to dissolution of high-carbon ferrochromium

Abstract

Microwave sample preparation methods have come a long way since the earliest experiments with domestic microwave ovens. This study concerned the decomposition of ferrochromium samples containing a high proportion of insoluble carbides by means of a focused microwave digestion system. The experimental results showed that samples were completely decomposed in HNO₃–HF mixed acids. Optimization of the microwave dissolution programmes involved the study of acid mixture volume, the control of pressure and temperature inside a reference vessel, power control and the influence of magnetic stirring during the dissolution processes. Chromium was determined potentiometrically in each of the intermediate digests obtained during optimization of the procedure, for demonstration of the successive recoveries of this element. The selected dissolution 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 stirring) and 5 min at 250 W/15 min at 400 W/5 min at 500 W (with stirring) and showed excellent reproducibility with a slightly improved RSD when magnetic stirring was used. The accuracy was determined using three high-carbon ferrochromium reference materials: ECRM 585-1 from the Bureau of Analysed Samples, BAM 530-1 from the Bundesanstalt für Materialprüfung and BCS 204-4 from British Chemical Standards. The results were compared with those obtained using a classical dissolution procedure. The microwave solutions could also be used for the simultaneous determination of major and minor elements in FeCr samples by spectroscopic techniques.