Mechanism of High Temperature Corrosion by Model Naphthenic Acids
Naphthenic acid (NAP) corrosion is one of the major concerns for corrosion engineers in refineries, particularly with the increasing acidity in “opportunity crudes”. However, complex compositions of NAP in crude oil make it difficult to evaluate accurately their corrosive behavior. In the present study, several model acids, including 4-phenylbutyric acid, 1-naphthoic acid, and 4-cyclohexyl pentanoic acid, have been tested in lab scale experiments previous applied to real crude fractions. Pretreatment/challenge protocol tests the corrosive behavior of the model acids under temperature and velocity ranges close to those encountered in refineries. This work demonstrates that the pretreatment of carbon steel and 9Cralloy with model acids yields iron oxide scales with different morphology and chemical composition as determined by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). It is postulated that the formation of the iron oxide scale resulted from the decomposition of iron naphthenate on the surface at high temperatures.
Nearly stoichiometric iron monoxide formed as a metastable intermediate in a two-stage disproportionation of quenched wüstite. Thermodynamic and kinetic aspects
Quenched metastable wustites are shown to undergo a two-stage disproportionation reaction on heating. A mixture of nearly stoichiometric iron monoxide and magnetite is formed during the first stage, which takes place at ≈ 470 K. The resulting nearly stoichiometric Fe1−yO remains metastable up to ≈ 530 K. Above this temperature the stable two-phase mixture of iron and magnetite is slowly formed. The thermodynamic and kinetic aspects of this two-stage disproportionation reaction have been studied in a step-wise heated adiabatic calorimeter. The decomposition behaviour is rationalized in a Gibbs energy of formation representation of stable and metastable phases in the iron-oxygen system. The antiferromagnetic to paramagnetic order-disorder transition which takes place in Fe1−yO at ≈ 196 K is found to be greatly influenced by the oxygen content; it becomes much more cooperative as the exact 1:1 stoichiometry is approached.
High‐Pressure Synthesis of the Stoichiometric Compound FeO
A stoichiometric compound, Fe1.000O, was synthesized at high pressures above 36 kbar at 770°C by a reaction between Fe0.950O and metallic iron. The cell dimension of Fe1.000O was determined to be 4.323±0.001 A at atmosphere pressure.