TITLE:
Gaskets with Expandable Graphite Treated with Nitric, Sulphuric, Phosphoric Acids and Ferric Chloride
AUTHORS:
Heinrich Horacek
KEYWORDS:
Nanomaterials, Thermal Properties, Industrial Application, Exfoliated Graphite
JOURNAL NAME:
Open Access Library Journal,
Vol.2 No.4,
April
30,
2015
ABSTRACT:
The task was to find out the most appropriate expandable graphite
intercalation compound GIC for intumescent seals. The application in fire seals
required GICs, which exerted high expansion at low burning rates. Therefore
graphite was treated with nitric, sulphuric, phosphoric acids and ferric
chloride. Phosphoric acid with its flame retardant properties was the
favourite, but graphite treated with it, did not exfoliate, therefore
expandable graphite was post treated with phosphoric acid. Elemental analysis
and thermogravimetric measurements led to chemical formulas of GICs. Their
heats of exfoliation were determined by differential scanning calorimetry, by
the work done given by the product of increased specific volume and atmospheric
pressure, by the Arrhenius plot of
exfoliated specific volume dependent on temperature and were calculated in a
complete balance of weights and heats of formation. It turned out that
the sum of heats of intercalation and exfoliation corresponded with the heats
of decomposition and gasification of the intercalated compounds. When the heat
of intercalation was added to the lattice energy of graphite, the lattice
energy of GIC was obtained. Electron microscopy indicated that expansion did
not happen in monolayers but in nanoplatelets consisting of about 40 atomic
layers. The expandable GICs were incorporated into polyvinyl acetate strips and
applied as fire gaskets in gaps. In a fire test, the gap protected by the strip
comprising the GIC treated with sulphuric and phosphoric acid showed the best
performance, which corresponded with the highest observed expansion and with
the second highest temperature of maximum speed of combustion.