Flammability of sulfur powder - An extremely hazardous chemical

Zhe Zeng, Ibukun Oluwoye, Mohammednoor Altarawneh, Bogdan Z. Dlugogorski

Research output: Contribution to journalArticlepeer-review


This contribution investigates the propensity of low-temperature ignition of sulfur, a hazardous substance because of its facile flammability. We applied the coupled thermogravimetric analyser and differential scanning calorimeter (TGA-DSC), in conjunction with a vertically-entrained reactor, to study the ignition behaviour of sulfur powder. The thermogravimetric measurements capture the ignition temperature of sulfur powder that transforms itself to partly polymerised S8 phase (Sγ) prior to ignition, revealing a temperature as low as 480 K. Likewise, experiments performed in a vertically-entrained reactor, coupled with an online Fourier-transform infrared (FTIR) spectrometry confirm the ignition temperature of Sγ of between 473 K and 483 K, as well as the full conversion of S into SO2 at 503 K. The density-functional-theory calculations for the S + O2 reaction identify the formation of SO + O as the initiation step, with a shallow activation barrier of 24.6 kJ mol−1. Further oxidation of SO + O2 → SO2 + O proceeds slower with a relatively high activation barrier at 34.0 kJ mol−1, acting as the bottleneck step of oxidation of elementary S, in analogy to the DSC profile of Sγ ignition.

Original languageEnglish
Article number103088
Pages (from-to)1-7
Number of pages8
JournalFire Safety Journal
Early online date6 May 2020
Publication statusPublished - Mar 2021


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