Application of Quaternary Acid Mixture to Microwave Digestion Effective for Various Kinds of Steel Samples

This paper suggests a procedure of an improved digestion method, which can be applied to a variety of steel samples, for preparing the sample solution to quantify alloyed elements and sulfur simultaneously in inductively coupled plasma atomic emission spectrometry. A conventional digestion method using a mixture of hydrochloric and nitric acid has a poor ability to decompose tool steel completely. Alternatively, a microwave digestion method, in which an acid mixture of hydrochloric acid, hydrofluoric acid, nitric acid, and phosphoric acid was prepared with 1:1:1:1 volume ratio, enabled various steel samples including tool steel and stainless steel to be fully decomposed. Due to no addition of sulfuric acid, the sulfur content in the samples could be determined. The suggested procedure was applicable to determine sulfur, vanadium, chromium, manganese, cobalt, nickel, molybdenum, and tungsten in a variety of steel alloys using the same dissolution procedure.