Focused-microwave-induced combustion: investigation of KClO3thermal 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.