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On the thermodynamics of aluminum cladding oxidation: water as the catalyst for spontaneous combustion
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Abstract(s)
A recent article (Casey et al. in J Failure Anal
Prev 22:1252–1259, 2022) finds a thermodynamic explanation for the catastrophic effect of water as an
extinguisher in aluminum-clad tower block fires (Entropy
22: 14, 2020) to be ‘‘unsubstantiated hypotheses’’ and
‘‘suppositions unsupported by data’’. The article by Casey
et al., however, is misleading because it is based upon a
false premise that it is the hydrolysis of solid aluminum
panels that produce hydrogen (H2), which was not detected
in their experiments. The combustion of aluminum (Al) to
alumina (Al2O3) reaction is highly exothermic to the extent
that it can be explosive, but the reaction is inhibited, for all
temperatures of solid and liquid Al, below the melting
point of alumina (2250 C), by the formation of a thin
nanometre skin of alumina that prevents combustion. In
tower block infernos of Al-plastic cladding materials, there
cannot be production of detectable hydrogen gas, as
wrongly assumed by Casey et al., who only investigate the
laboratory hydrolysis reaction of solid aluminum in cladding samples, and not the combustion conditions at
temperatures exceeding 1500 C. Here we show that H2 is
an intermediate in the Al-combustion mechanism of cladding fires, and that water (H2O) is the catalyst. This is one
of two possible reaction mechanisms that enable combustion by circumventing direct oxidation of Al. For cladding
with adjacent plastic insulation material, water provides an
alternative mechanism via methane and the carbide Al4C3
as intermediates, also with H2O as the catalyst.
Description
Keywords
Aluminum cladding Aluminum fire Water catalysis Oxidation looping
Pedagogical Context
Citation
Publisher
Springer