Citation: Gerlich, M.; Trzci´ nski, W.; Hara, M. Some Aspects of the Burning Process of Antimony and Potassium Manganate(VII) Compositions. Materials 2022, 15, 4736. https://doi.org/10.3390/ ma15144736 Academic Editor: Antonio Gil Bravo Received: 21 June 2022 Accepted: 3 July 2022 Published: 6 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). materials Article Some Aspects of the Burning Process of Antimony and Potassium Manganate(VII) Compositions Marcin Gerlich 1,2, * , Waldemar Trzci´ nski 1 and Marcin Hara 1 1 Faculty of New Technologies and Chemistry, Military University of Technology, Kaliskiego 2, 00-908 Warsaw, Poland; waldemar.trzcinski@wat.edu.pl (W.T.); marcin.hara@wat.edu.pl (M.H.) 2 NITROERG S.A., Alfred Nobel Square 1, 43-150 Bieru ´ n, Poland * Correspondence: marcin.gerlich@wat.edu.pl Abstract: Antimony and potassium manganate(VII) compositions are widely used in time delay ele- ments of detonators. Despite the existing literature on such systems, there is no complete information on the burning process of Sb/KMnO 4 compositions in closed systems. There are also no data on the heat of their combustion in conditions of increased pressure without the access of oxygen from the air and on the composition of solid combustion products. These issues are the subject of the presented work. Keywords: delay composition; burn rate; gasless combustion 1. Introduction Sb/KMnO 4 compositions have been the subject of many studies. Due to the widespread use of this composition as a time-delay composition, there are reports in the literature on the reaction mechanism of the thermal decomposition of potassium permanganate with subsequent antimony oxidation [1] and the burning rate of this system [2–4]. Based on the results of the thermal analysis presented in the literature, the combustion products should be expected to contain compounds derived from the thermal decomposi- tion of potassium manganate(VII) and the products of antimony oxidation by the released oxygen. The occurrence of secondary reactions between the products of KMnO 4 decomposi- tion and the oxidation products of Sb is not confirmed. However, this possibility should not be rejected. In Ref. [1], on the basis of the DTA and TG curves, the two-stage decomposition of KMnO 4 was confirmed and the reactions reported in the literature for the first stage of the thermal decomposition of KMnO 4 at approx. 290 ◦ C and, for the second stage, at 620 ◦ C were quoted. The solid products of KMnO 4 decomposition can be: K 2 MnO 4 ,K 3 MnO 4 and solid solutions of K 2 O and MnO 2 . According to the authors of Ref. [1], Sb 2 O 3 and Sb 2 O 4 are the most likely products of antimony oxidation during thermal analysis conducted in the air atmosphere. The first one occurs between 300 and 500 ◦ C, the second one at 600 ◦ C. Two dominant peaks are visible on the DTA curve for the Sb/KMnO 4 composition (with 60 wt% antimony content) heated in the air atmosphere [1]. The first one is the exothermic decomposition of KMnO 4 , which takes place at a temperature of about 300 ◦ C. Another sharp exotherm (ignition of the composition), occurring at a temperature of about 500 ◦ C, comes from the oxidation of Sb with oxygen from the air (as evidenced by the rapid increase in the mass of the sample in the TG curve). An important observation of the authors of Ref. [1] is the finding of a wide, exothermic peak on the DTA curve without changing the mass of the sample above the temperature of 500 ◦ C during the test with inert gas (nitrogen). This fact is the basis for a hypothesis that, in such conditions, secondary reactions can take place in the system. On the basis of the area under the DTA curve, the total heat of the reaction for the tested composition in the air atmosphere was determined at ΔH = 2.11 kJ g −1 . The total thermal effect of the reaction in a nitrogen atmosphere was not determined in Ref. [1]. Materials 2022, 15, 4736. https://doi.org/10.3390/ma15144736 https://www.mdpi.com/journal/materials