Focused-microwave-induced combustion: investigation of KClO3 thermal decomposition as O2 source

Abstract

Potassium chlorate is proposed here as a chemical source of O2 in focused-microwave-induced combustion. The thermal decomposition of this compound generates enough O2 to maintain the combustion and participate in gas phase reactions responsible for HNO3 regeneration. An animal feed concentrate is the reference material and test sample used. Important parameters such as HNO3 concentration in the absorbing solution, volumes of igniting and oxidizing agents added to the sample, and microwave total incidence time were evaluated using a multivariate approach. The method efficiency was evaluated by determining both the residual carbon content (RCC) in the digestates and the recoveries of Ca, Mg, Mn, P and Zn using inductively coupled plasma optical emission spectrometry. Recoveries in the 82.3–102% range were obtained for all elements studied using 5 mL of an absorbing solution with 5.0 mol L−1 of HNO3, and adding 110 μL of NH4NO3 6.0 mol L−1 plus 140 μL of KClO3 0.5 mol L−1 to the solid sample, in a 7 min digestion program. A RCC value of 20% and a final acid concentration of 0.19 mol L−1 were obtained in the combustion of 100 mg of sample under optimized conditions. These preliminary results show the capabilities of a simple, inexpensive method with potential for different applications in procedures taking no longer than a few minutes. It is compatible with commercially available focused-microwave systems and requires no instrumental modification for its implementation.