Metal dusting is a kind of catastrophic corrosion phenomenon that can be observed in several of petrochemical processes. It occurs on iron-, nickel- and cobalt-base metals in carbonaceous atmospheres at high temperature when gaseous carbon activity is higher than one. The process is particularly rapid for ferritic alloys The aim of this project was to compare the dusting kinetics of pure iron and a 2.25Cr-1Mo alloy steel under CO-H2-H2O atmosphere at 650??C. Polished (3??m) samples of iron and the steel were exposed to flowing CO-H2-H2O gas atmospheres at 650??C, when the gases were supersaturated with respect to graphite. The partial pressure of CO was varied between 0.25 and 0.9 atm, and the carbon activity was varied from 2.35 to 16, in order to obtain a series of experimental conditions. In most experiments, pO2 was less than 7.37E-24 atm, and no iron oxide could form. However, Cr2O3 would always have been stable. When exposed to these gases, both iron and steel developed a surface scale of Fe3C which was buried beneath a deposit of carbon, containing iron-rich nanoparticles (the dust). Examination by Scanning Electron Microscopy allowed the observation of fine and coarse carbon nanotubes, and also spiral filaments. However, the morphology of the graphitic carbon was not sensitive to pCO and aC. Moreover, the carbon deposit was gas permeable, allowing continuing gas access to the underlying metal. At a fixed=4.5, the carburizing rate clearly increased with CO content from 0.25 to 0.68 atm. However, increasing the CO content to higher value led to decreased rates, indicating that carburizing rate reaches a maximum value at pCO=0.68 atm. When pCO was fixed at 0.25 atm and 0.68 atm, and carbon activity was varied. The induction period was extended by the formation of protective oxide layers at low values of carbon activity (aC= 2.35 and 2.55) where pO2 exceed the iron oxide formation value. For other reaction conditions, the carbon uptake rate for iron and steel did not increase with aC. The present work showed that the carbon deposition rates were not proportional to pCO or pCOpH2. Instead, the rate was affected by the partial pressure of all three reaction gases, and the carbon uptake rate for both materials could be expressed at r=k1pCOpH2+k2pCO2+k3pH22 and the rate constant k3 has a negative value, corresponding to coke gasification. From XRD analyses, it was found that cementite was the only iron-containing phase in the dusting product. The cementite particles acted as catalysts for carbon deposition from the gas. The same deposition process at the surface of the cementite layer led to its disintegration, thereby producing the particles. This disintegration process was faster on the steel than on pure iron. Consequently, the rates of both metal wastage and coke accumulation were faster for the steel. It is concluded that chromium and molybdenum do not stabilize the carbide but accelerate its disintegration process. It is suggested that Cr2O3 fine particles in the cementite layers provide more nucleation sites in the cementite layer on steel, explaining its more rapid dusting kinetics. However, appropriate methods of proving this assumption, such as TEM and FIB, are required.

No description available.

No description available.

Metal dusting is a kind of catastrophic corrosion phenomenon that can be observed in several of petrochemical processes. It occurs on iron-, nickel- and cobalt-base metals in carbonaceous atmospheres at high temperature when gaseous carbon activity is higher than one. The process is particularly rapid for ferritic alloys The aim of this project was to compare the dusting kinetics of pure iron and a 2.25Cr-1Mo alloy steel under CO-H2-H2O atmosphere at 650??C. Polished (3??m) samples of iron and the steel were exposed to flowing CO-H2-H2O gas atmospheres at 650??C, when the gases were supersaturated with respect to graphite. The partial pressure of CO was varied between 0.25 and 0.9 atm, and the carbon activity was varied from 2.35 to 16, in order to obtain a series of experimental conditions. In most experiments, pO2 was less than 7.37E-24 atm, and no iron oxide could form. However, Cr2O3 would always have been stable. When exposed to these gases, both iron and steel developed a surface scale of Fe3C which was buried beneath a deposit of carbon, containing iron-rich nanoparticles (the dust). Examination by Scanning Electron Microscopy allowed the observation of fine and coarse carbon nanotubes, and also spiral filaments. However, the morphology of the graphitic carbon was not sensitive to pCO and aC. Moreover, the carbon deposit was gas permeable, allowing continuing gas access to the underlying metal. At a fixed=4.5, the carburizing rate clearly increased with CO content from 0.25 to 0.68 atm. However, increasing the CO content to higher value led to decreased rates, indicating that carburizing rate reaches a maximum value at pCO=0.68 atm. When pCO was fixed at 0.25 atm and 0.68 atm, and carbon activity was varied. The induction period was extended by the formation of protective oxide layers at low values of carbon activity (aC= 2.35 and 2.55) where pO2 exceed the iron oxide formation value. For other reaction conditions, the carbon uptake rate for iron and steel did not increase with aC. The present work showed that the carbon deposition rates were not proportional to pCO or pCOpH2. Instead, the rate was affected by the partial pressure of all three reaction gases, and the carbon uptake rate for both materials could be expressed at r=k1pCOpH2+k2pCO2+k3pH22 and the rate constant k3 has a negative value, corresponding to coke gasification. From XRD analyses, it was found that cementite was the only iron-containing phase in the dusting product. The cementite particles acted as catalysts for carbon deposition from the gas. The same deposition process at the surface of the cementite layer led to its disintegration, thereby producing the particles. This disintegration process was faster on the steel than on pure iron. Consequently, the rates of both metal wastage and coke accumulation were faster for the steel. It is concluded that chromium and molybdenum do not stabilize the carbide but accelerate its disintegration process. It is suggested that Cr2O3 fine particles in the cementite layers provide more nucleation sites in the cementite layer on steel, explaining its more rapid dusting kinetics. However, appropriate methods of proving this assumption, such as TEM and FIB, are required.

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

As an alternative to the present toxic chromate-based coating system now in use, the Mg-rich primer technology has been designed to protect Al alloys (in particular Al 2024 T3) and developed in analogy to Zn-rich primers for steel substrate. As an expansion of this concept, metal-rich primer systems based on Mg alloy particles as pigments were studied. Five different Mg alloy pigments, AM60, AZ91B, LNR91, AM503 and AZG, were characterized by using the same epoxy-polyamide polymer as binder, a same dispersion additive and the same solvent. Different Mg alloy-rich primers were formulated by varying the Mg alloy particles and their pigment volume concentrations (PVC). The electrochemical performance of each Mg alloy-rich primer after the cyclic exposure in Prohesion chamber was investigated by electrochemical impedance Spectroscopy (EIS). The results indicated that all the Mg alloy-rich primers could provide cathodic protection for AA 2024 T3 substrates. However, the Mg alloys as pigments in metal-rich primers seemed to exhibit the different anti-corrosion protection performances, such as the barrier properties, due to the different properties of these pigments. In these investigations, multiple samples of each system were studied and statistical methods were used in analyzing the EIS data. From these results, the recommendation for improved EIS data analysis was made. CPVC studies were carried out on the Mg alloy-rich primers by using three Mg alloy pigments, AM60, AZ91B and LNR91. A modified model for predicting CPVC is proposed, and the results showed much better agreement between the CPVC values obtained from the experimental and mathematical methods. Using the data from the AM60 alloy pigment system, an estimate of experimental coarseness was done on a coating system, the first time such an estimate has been performed. By combining various surface analysis techniques, such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and confocal Raman microscopy, the oxidation products formed after exposure were identified. It was found that variation of Al content in Mg alloy could significantly affect the pH of the microenvironment in the primer films and result in the formation of various oxidation products. / Air Force Office of Scientific Research (Grant No. 49620-02-1-0398)

As an alternative to the present toxic chromate-based coating system now in use, the Mg-rich primer technology has been designed to protect A1 alloys (in particular A1 2024 T3) and developed in analogy to Zn-rich primers for steel substrate. As an expansion of this concept, metal-rich primer systems based on Mg alloy particles as pigments were studied. Five different Mg alloy pigments. AM60, A719B, LNR91, AM503 and AZG, were characterized by using the same epoxy-polyamide polymer as binder, a same dispersion additive and the same solvent. Different Mg alloy-rich primers were formulated by varying the Mg alloy particles and their pigment volume concentrations (PVC). The electrochemical performance of each Mg alloy-rich primer alter the cyclic exposure in Prohesion chamber was investigated by electrochemical impedance Spectroscopy (EIS). The results indicated that all the Mg alloy-rich primers could provide cathodic protection for AA 2024 T3 substrates. However, the Mg alloys as pigments in metal-rich primers seemed to exhibit the different anti-corrosion protection performances, such as the barrier properties, due to the different properties of these pigments. In these investigations, multiple samples of each system were studied and statistical methods were used in analyzing the EIS data. From these results. the recommendation for improved EIS data analysis was made. CPVC studies were carried out on the Mg alloy-rich primers by using three Mg alloy pigments, AM60, A2918 and LNR91. A modified model for predicting CPVC is proposed, and the results showed much better agreement between the CPVC values obtained from the experimental and mathematical methods. Using the data from the AM60 alloy pigment system, an estimate of experimental coarseness was done on a coating system, the first time such an estimate has been performed. By combining various surface analysis techniques, such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and confocal Raman microscopy, the oxidation products formed alter exposure were identified. It was found that variation of A1 content in Mg alloy could significantly affect the pH of the microenvironment in the primer films and result in the formation of various oxidation products. / Air Force Office of Scientific Research (AFOSR) (Grant No. 49620-02-1-0398)

Tests were made at the Lubrication Laboratory at Virginia Polytechnic Institute to determine the mechanism of corrosion of Cadmium-Silver-Copper bearing metals, and if possible to develop a procedure to quantitatively rate oils and inhibitors with respect to corrosion. Two pieces of testing apparatus were employed - a jet-type oil bath and a glass apparatus. It was found that corrosion of the cadmium base bearing metals took place in the jet-type oil bath with jet velocities equal to 1.51 feet per second at temperatures of 300 and 325° F with Esso Motor Oil, No. 3. Corrosion did not take place at temperatures of 300 and 325° F in the jet-type oil bath when the jet velocities were decreased to 0.67 feet per second. Tests on the glass apparatus indicated that the corrosion was not electrolytic, that the presence of air (oxygen) at the oil-bearing interface was necessary for corrosion to proceed, and that the scrubbing action of the oil past the bearing face only partially influences the rate of corrosion. The jet-type apparatus is believed to be quantitative in its results if the surface condition of the bearing specimens and the velocity of the issuing oil jets are accurately controlled. Viscosity of the oil prior to and after the test was measured. No consistent trend of viscosity was noted, but a tendency for the viscosity of the oil to be directly proportional to the total weight of metal lost by corrosion was pointed out. / M.S.

No description available.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 160-164).