Thesis (Ph. D.)--University of Michigan, 1928.

Thesis--Ph. D., University of Hong Kong, 1977.

The dissolution rates of niobium and zirconium cylinders in liquid steel have been measured in a 'dynamic way', with the help of a data acquisition and process control facility. Two distinct periods were identified; the steel shell period and the free dissolution period. / Lower bath superheats allowed a reaction to take place at the steel shell/niobium interface while higher superheats didn't; the intermetallic compounds Fe$ sb 2$Nb and Fe$ sb 2$Nb$ sb 3$ were identified as the reaction products. Niobium dissolved relatively slowly in liquid steel and its dissolution speed was increased under dynamic conditions (i.e., inductively stirred baths). / In the case of zirconium, an exothermic reaction occurred at the steel shell/zirconium interface and the intermetallics Fe$ sb 2$Zr and FeZr$ sb 2$ were identified as the reaction products. This reaction was triggered at 1220 K by the formation of a liquid Fe-Zr (76 at% Zr) eutectic. For the experimental conditions under which this study was performed, the hydrodynamic conditions of the steel baths did not seem to influence the dissolution rates of zirconium. / A simplified mathematical model was used in order to simulate the coupled heat and mass transfer phenomena which take place during the two periods.

No description available.

No description available.

The kinetics of dissolution of titanium and vanadium in liquid steel has been studied. Two periods were distinguished: the steel shell period and the free dissolution period. / In the case of titanium, it is shown that the customary frozen shell of steel encases the cylinder following its initial immersion. Premature internal dissolution then begins as a result of liquid eutectic of Fe(,0.3) Ti(,0.7) composition forming at the inner steel shell boundary. This phenomenon triggers an exothermic dissolution and erosion of the inner steel shell. The net result is considerable shortened shell melting times. During the free dissolution period, the temperature of the titanium dissolving at the interface increases and the dissolution process becomes self-accelerating. / During the steel shell period with pure vanadium and ferrovanadium alloys, no reaction was observed between the steel shell and vanadium. For low grade ferrovanadium alloys, the dissolution proceeds via a heat transfer mechanism. On the other hand, for high grades, ferrovanadium mass transfer mechanisms dominate. / A simplified mathematical model of the process has been developed to describe the coupled heat and mass transfer phenomena involved in the various systems studied.

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 (M.S.)--Worcester Polytechnic Institute. / Keywords: rust formation; AISI 8620 steel; gas carburizing. Includes bibliographical references (leaves 39-40).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 65-68). Also available via the Internet.