Alumina
thin films are deposited inside the channels of stainless
steel tubular reactors by atomic layer deposition (ALD) to deactivate
the metal surface for the purpose of coke suppression. The ALD equipment
is modified to incorporate the high-aspect-ratio metal tubes into
the flow path of the ALD system. Experimental parameters are adjusted
to ensure complete and uniform coverage of the internal surfaces of
the metal tubes. The thicknesses of the passivation layers are precisely
controlled by adjusting the number of ALD cycles. In coking experiments,
the passivated metal tubes are used as reactors for thermal cracking
of a hydrocarbon fuel composed of C12–C16 paraffins. The lifetime of the experimental system passivated by
ALD alumina films can be up to 5 times longer than that of the system
using bare metal tubes as the reactor. When the tested metal tube
samples are analyzed, it is discovered that the ALD alumina film remains
intact after the coking experiment, indicating that the metal-catalyzed
filament coke formation can be completely inhibited by the ALD alumina
passivation layer.
Pool
boiling of CaSO4 solution on prepared microscale and nanoscale
hydrophobic titania–fluoroalkylsilane (TiO2–FPS)
composite coatings on polished AISI304 stainless steel (SS) substrates
was carried out to evaluate the antifouling behavior of these surfaces.
Lower fouling resistance and looser, slender, and larger CaSO4 crystals on hydrophobic TiO2–FPS coatings
were observed compared to those on the TiO2 coatings and
SS surfaces. The colloidal interaction energies between crystalline
particles and coated surfaces were analyzed by using the extended
Dejaguin– Landau–Verwey–Overbeek (XDLVO) theories
to explore the possible mechanism of inhibition of fouling. The results
of the XDLVO analyses generally agree to the experimental observations.
The Lewis acid–base component contributes most of the total
XDLVO interaction energy. Low surface free energy and electron donor
component of heat transfer surface lead to a low fouling resistance
and a small initial deposition rate of CaSO4 fouling. On
the basis of the XDLVO evaluations, a key strategy to reduce the CaSO4 deposition rate on heat transfer surface is suggested.
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