Download or read book Mechanisms Governing the Growth Reactivity and Stability of Iron Sulfides written by Francis William Herbert and published by . This book was released on 2015 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: The kinetics of electrochemical processes in ionic materials are fundamentally governed by dynamic events at the atomic scale, including point defect formation and migration, and molecular interactions at the surface. A corrosion system comprising an iron sulfide film (passive layer) formed on iron or steel in contact with an hydrogen sulfide (H2S)- rich fluid can thus, in principle, be modeled by a series of unit reaction steps that control the rate of degradation under given thermodynamic conditions. This overarching thesis goal necessitates a concerted experimental and computational approach to determine the relevant kinetic parameters such as activation barriers Ea and rate constants v0 for the homogeneous and heterogeneous reactions of interest. These fundamental values can be obtained experimentally via temperature-dependent measurements on pure, model iron sulfide samples. This thesis therefore consists of three case studies on the stable Fe-S phases pyrrhotite (Fe1-xS) and pyrite (FeS2) to identify the elementary corrosion mechanisms and their kinetic parameters. Pyrrhotite is of interest because the off-stoichiometry of this phase leads to relatively rapid bulk processes such as diffusion; pyrite has a comparitively inert bulk but this work showed that it has a chemically labile surface. The first study focuses on two basic, rate-controlling steps in the growth of pyrrhotite: cation diffusion and sulfur exchange at the surface. First, iron self-diffusivity *DFe is determined across the temperature range 170-400 °C through magnetokinetic studies of the diffusion-driven "[lambda]" magnetic transformation, as well as direct tracer diffusion measurements in Fe1-xS crystals using secondary ion mass spectrometry (SIMS). This range encompasses the sponteneous magnetic and structural order-disorder temperature TN = 315 °C in pyrrhotite. The effect of spontaneous magnetization below TN is to increase the Fe vacancy migration energy by a combined 40% increasing Ea for diffusion from 0.83 eV in paramagnetic Fe1-xS to ~1.20 eV in the fully magnetized state. An extrapolation of the Arrhenius law from the paramagnetic regime would therefore overestimate actual diffusivities by up to 102 times at 150 °C. Second, the surface exchange of sulfur from H2S into the solid state in Fe1-xS is measured using electrical conductivity relaxation, yielding Ea = 1.1 eV for sulfur incorporation into pyrrhotite. With their similar thermal dependence, there is no clear temperature crossover from cation diffusion- to surface exchange-limiting regimes, or vice versa. Instead, surface exchange is expected to constrain pyrrhotite growth for films under ~100 [mu]m thickness, beyond which diffusion becomes the rate limiting mechanism, independent of external driving factors such as temperature. The second study explores the role of surface electronic states on the electrochemical reactivity of pyrite. Charge transfer between a solid surface and an adsorbate such as H2S requires the mutual availability of filled/empty electronic states at the same energy level. The semiconducting FeS2(100) surface is predicted to have intrinsic surface states (SS's) from Fe and S dangling bonds, as well as extrinsic SS's related to delocalized defects at the surface, both of which would affect charge transfer characteristics. A novel, broadly-applicable methodology is developed in this thesis to quantify the energy and density of these SS's, based on experimental scanning tunneling microscopy / spectroscopy (STM/STS) in conjunction with first principles tunneling current modeling. As a result, a decreased surface band gap Eg of 0.4 eV, compared to 0.95 eV in bulk pyrite, is measured. The findings highlight the need to differentiate between bulk and surface electronic structure when assessing heterogeneous reactivity, and have implications for the use of FeS2 in potential technological applications, for example as a photovoltaic adsorber. Finally, the dynamics of point defect formation and clustering on FeS2(100) under high-temperature, reducing conditions are investigated to understand the stability of the surface under extreme conditions. Synchrotron x-ray photoelectron spectroscopy (XPS) is used to measure a formation energy [delta]Hf for sulfur vacancies in the topmost atomic layer of 0.1 eV up to approximately 240 °C. Above this temperature, however, point defects are shown to condense into surface pits as measured by scnaning tunneling microscopy (STM). The combined, experimental XPS and STM results are replicated with high precision by a kinetic Monte Carlo (kMC) simulation, developed by Aravind Krishnamoorthy towards his doctoral thesis, of surface degradation on realistic length-and timescales of 10-10 - 10-7 m and up to several hours, respectively. The findings have implications for the initiation of surface breakdown via pitting in ionic passive films, as well as providing a broader understanding of the non-stoichiometry of the pyrite surface. The common thread is a focus on events at the atomic and electronic scale, with an emphasis on point defects. The results thereby facilitate a bottom-up approach to modeling electrochemical processes such as corrosion in Fe-S phases, in which the unit steps are cast into probabilistic simulation tools. While the three studies here comprise only a partial examination of the atomic-scale events regulating the behavior of Fe-S passive layers, this approach makes inroads towards more accurate component lifetime prediction and the design of robust materials for aggressive environments. Moreover, the fundamental surface and bulk physical chemistry of iron sulfides explored in this work has implications beyond corrosion to other uses of these materials, including potential magnetic devices (Fe1-xS) and earth-abundant photovoltaic and photoelectrochemical adsorbers (FeS2).
Download or read book Monthly Catalog of United States Government Publications written by and published by . This book was released on 1971 with total page 1388 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Modeling of Reactions Governing Metal Composition and Experimental Studies of Carbon Pickup for the Cupola Melting Furnace written by Veena Sahajwalla and published by . This book was released on 1992 with total page 412 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Monthly Catalog of United States Government Publications Cumulative Index written by United States. Superintendent of Documents and published by . This book was released on 1976 with total page 1466 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Tire Engineering written by Brendan Rodgers and published by CRC Press. This book was released on 2020-09-27 with total page 303 pages. Available in PDF, EPUB and Kindle. Book excerpt: The modern tire is the most complex, composite product in mass production. Yet given its complexity and required performance, there is little information in the public domain regarding its development. This book provides an introduction to tire design, construction, and manufacturing in the context of materials technologies used today, along with future trends and disrupting technologies. Focuses on design and construction Discusses the relationship between materials and performance Reviews tire uniformity as a key differentiator among manufacturers Evaluates design and construction features versus performance Written for engineers in the polymer, industrial, chemical, mechanical, and automotive industries, this book offers a comprehensive view of tire design, including materials selection, construction, manufacturing, quality control, and future trends.
Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1976-04 with total page 912 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Chemical Vapor Deposition 1960 1980 written by Donald T. Hawkins and published by Springer. This book was released on 1981-11-30 with total page 762 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1973 with total page 1064 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book STAR written by and published by . This book was released on 1966 with total page 1230 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book ORD Publications Summary written by United States. Environmental Protection Agency. Office of Research and Development and published by . This book was released on 1975 with total page 502 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Nanomaterials Chemistry written by C. N. R. Rao and published by John Wiley & Sons. This book was released on 2007-09-24 with total page 420 pages. Available in PDF, EPUB and Kindle. Book excerpt: With this handbook, the distinguished team of editors has combined the expertise of leading nanomaterials scientists to provide the latest overview of this field. They cover the whole spectrum of nanomaterials, ranging from theory, synthesis, properties, characterization to application, including such new developments as quantum dots, nanoparticles, nanoporous materials, nanowires, nanotubes, and nanostructured polymers. The result is recommended reading for everybody working in nanoscience: Newcomers to the field can acquaint themselves with this exciting subject, while specialists will find answers to all their questions as well as helpful suggestions for further research.
Download or read book Energy Research Abstracts written by and published by . This book was released on 1990 with total page 852 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Electrochemical Materials Science written by John Bockris and published by Springer Science & Business Media. This book was released on 2013-06-29 with total page 579 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is now time for a comprehensive treatise to look at the whole field of electrochemistry. The present treatise was conceived in 1974, and the earliest invitations to authors for contributions were made in 1975. The completion of the early been delayed by various factors. volumes has There has been no attempt to make each article emphasize the most recent situation at the expense of an overall statement of the modern view. This treatise is not a collection of articles from Recent Advances in Electrochemistry or Modern Aspects of Electrochemistry. It is an attempt at making a mature statement about the present position in the vast area of what is best looked at as a new interdisciplinary field. Texas A & M University J. O'M. Bockris University of Ottawa B. E. Conway Case Western Reserve University Ernest Yeager Texas A & M University Ralph E. White Preface to Volume 4 The science of degradation of materials involves a vast area of science and technology, the economic importance of which rivals that of any other clearly defined area affecting the standard of life. The basis of the corrosion process is the electrochemical charge-transfer reaction, and the center of the subject of the degradation of materials is electrochemical material science.
Download or read book U S Government Research Reports written by and published by . This book was released on 1964 with total page 1416 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Sulfidic Sediments and Sedimentary Rocks written by David Rickard and published by Newnes. This book was released on 2012-12-31 with total page 813 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book deals with sedimentary sulfides which are the most abundant authigenic minerals in sediments. Special emphasis is given to the biogeochemistry that plays such a central role in the formation of sedimentary sulfides. It will be of interest to scientists in a number of disciplines, including geology, microbiology, chemistry and environmental science. The sulfur system is important to environmental scientists considering the present and future effects of pollution and anoxia. The development of the sulfur system – particularly the characteristics of ocean anoxia over the last 200 Ma – is useful in predicting the future fate of the Earth surface system as well as in understanding the past. The biochemistry and microbiology of the sulfur system are key to understanding microbial ecology and the evolution of life. First monograph on sedimentary sulfides, covering the ancient and modern sedimentary sulfide systems Comprehensive, integrating chemistry, microbiology, geology and environmental science All key references are included and discussed
Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2710 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Technical Abstract Bulletin written by and published by . This book was released on 1967 with total page 866 pages. Available in PDF, EPUB and Kindle. Book excerpt:
