In
an effort to protect metal substrates from extreme heat, polymer–clay
multilayer thin films are studied as expendable thermal barrier coatings.
Nanocomposite films with a thickness ranging from 2 to 35 μm
were deposited on steel plates and exposed to the flame from a butane
torch. The 35 μm coating, composed of 14 deposited bilayers
of tris(hydroxymethyl)aminomethane (THAM)-buffered polyethylenimine
(PEI) and vermiculite clay (VMT), decreased the maximum temperature
observed on the back side of a 0.32 cm thick steel plate by over 100
°C when heated with a butane torch. Upon exposure to high temperature,
the polymer and amine salt undergo pyrolysis and intumesce, subsequently
forming a char and blowing gas. The char encases the nanoclay platelets,
and a ceramic bubble is formed. The macro-scale bubble, in tandem
with the nanocomposite coating properties, increases resistance to
heat transfer into the underlying metal substrate. This heat shielding
behavior occurs through radiative effects and low aggregate through-plane
conductivity resulting from multilayer nanodomains and intumesced
porosity (i.e., conduction through the gas as the film expands to
form a ceramic bubble). These relatively thin and lightweight films
could be used to protect important metal parts (in automobiles, aircraft,
etc.) from fire-related damage or other types of transient high-temperature
situations.
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