Combustion behavior of aluminized metal iodate composites. Part 1: Decomposition mechanism of metal iodates

Metal iodates are candidates of high temperature biocidal oxidizing agents owing to their high iodine and oxygen content. Here we explore the high temperature decomposition mechanism of alkali and alkaline metal iodates (LiIO3, NaIO3, KIO3, Mg(IO3)2, and Ca(IO3)2). Temperature-jump/time-of-flight mass spectrometry (T-Jump/ TOFMS) measurements reveal that while all of these iodates release O2, only Mg(IO3)2, Ca(IO3)2, and LiIO3 release significant amount of I2 and there is minimal I2 release from NaIO3 and KIO3. Thermogravimetricdifferential scanning calorimetry (TGA-DSC) measurement and X-ray diffraction (XRD) analysis of temperature dependent condensed phase species demonstrates the presence of two different decomposition pathways of metal iodates. LiIO3, Mg(IO3)2, and Ca(IO3)2, follow a two-step decomposition pathway: (1) Decomposition from metal iodate (MIO3, M=Mg, Ca, and Li) into metal orthoperiodate (Mx(IO6)y) accompanied by I2 and O2 release, and (2) decomposition from metal orthoperiodate to metal oxide (MO) accompanied by I2 and O2 release. NaIO3 and KIO3 follow a one-step decomposition pathway, where they decompose into NaI and KI, respectively, simultaneously releasing O2. Decomposition temperatures are estimated from thermodynamic data and compared between different decomposition pathways to predict which pathway is more favorable during decomposition. These estimations predict the decomposition pathway of the investigated metal iodates as they are largely consistent with the experimental results. This study unveils a simple strategy for predicting whether a metal iodate is a promising biocidal agent by assessing its feasibility of I2 release.