256 results on '"Joseph I. Goldstein"'
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2. The Milton pallasite and South Byron Trio irons: Evidence for oxidation and core crystallization
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Richard D. Ash, Timothy J. McCoy, Joseph I. Goldstein, K. Nagashima, Catherine M. Corrigan, V. S. Reynolds, William F. McDonough, J. Yang, and Connor D. Hilton
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010504 meteorology & atmospheric sciences ,Chemistry ,Geochemistry ,Pallasite ,Plessite ,010502 geochemistry & geophysics ,01 natural sciences ,Parent body ,Kamacite ,Schreibersite ,Meteorite ,Geochemistry and Petrology ,Chondrite ,Tetrataenite ,0105 earth and related environmental sciences - Abstract
The link between the Milton pallasite and the South Byron Trio irons is examined through metallography and metallogaphic cooling rates; major, minor, and trace element compositions of metal; inclusion mineralogy and mineral compositions; and oxygen isotopic compositions. The metallic hosts of these Ni-rich meteorites (18.2–20.3 wt% Ni) are dominated by plessite with spindles of kamacite and schreibersite. The presence of ∼50 nm wide tetrataenite and absence of high-Ni particles in the cloudy zone in Milton suggest cooling of ∼2000 K/Myr or >10,000 K/Myr. Compositionally, the metallic host in all four meteorites exhibits modest (1–2 orders of magnitude compared to CI chondrites) depletions of volatile elements relative to refractory elements, and marked depletions in the redox sensitive elements W, Mo, Fe, and P. Oxygen isotopic compositions (Δ17O) are, within uncertainty, the same for the Milton and the South Byron Trio and for IVB irons. Similarities in metallography, metal composition, inclusion mineralogy, and oxygen (Δ17O), molybdenum and ruthenium isotopic composition suggest that the Milton pallasite and South Byron Trio irons could have originated on a common parent body as chemically distinct melt, or on separate parent bodies that experience similar cosmochemical and geochemical processes. The Milton pallasite and South Byron Trio irons share a number of properties with IVB irons, including metallography, enrichment in highly siderophile elements and nickel, inclusion mineralogy and oxygen isotopic composition, suggesting they formed in a similar nebular region through common processes, although Milton and the South Byron Trio did not experience the dramatic volatile loss of the IVB irons. Depletions in W, Mo, Fe, and P relative to elements of similar volatility likely result from oxidation, either in the nebula prior to accretion or on the parent body during melting. Oxidation of ∼73 wt% Fe is indicated, with a correspondingly FeO-rich mantle and smaller core. If Milton and the South Byron Trio sample a common core, Milton formed near the surface of the core after stripping of the silicate shell and may have experienced rapid solidification and contamination by an impactor. The molten core, from which the South Byron Trio irons crystallized, solidified from the outside in. more...
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- 2019
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3. Ion microprobe analyses of carbon in Fe–Ni metal in iron meteorites and mesosiderites
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Gary R. Huss, Joseph I. Goldstein, and Edward Scott
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010504 meteorology & atmospheric sciences ,Chemistry ,Metallurgy ,chemistry.chemical_element ,Plessite ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Taenite ,Kamacite ,Nickel ,Meteorite ,Geochemistry and Petrology ,engineering ,Graphite ,Tetrataenite ,0105 earth and related environmental sciences ,Haxonite - Abstract
Carbon concentrations in kamacite, taenite, and plessite (kamacite-taenite intergrowths) were measured in 18 iron meteorites and 2 mesosiderites using the Cameca ims 1280 ion microprobe at the University of Hawai‘i with a 5–7 μm beam and a detection limit of Grains of taenite and fine-grained plessite in carbon-rich meteorites, which all have normal M-shaped nickel profiles due to slow cooling, have diverse carbon contents and zoning profiles. This is because taenite decomposed by diverse mechanisms over a range of temperatures, when nickel could only diffuse over sub-μm distances. Carbon diffusion through taenite to growing carbides was rapid at the upper end of this temperature range, but was very limited at the lower end of the temperature range. In mesosiderites, carbon increases from 12 ppm in tetrataenite to 40–115 ppm in cloudy taenite as nickel decreases from 50% to 35%. Low carbon levels in tetrataenite may reflect ordering of iron and nickel; higher carbon in cloudy taenite is attributed to metastable bcc phase, possibly martensite, with ∼300 ppm carbon intergrown with tetrataenite. Pearlitic plessite, which only forms in carbon-rich irons, contains much less carbon than martensitic plessite: 10–20 ppm and 300–500, respectively, in IAB irons. Pearlitic plessite consists of μm-scale intergrowths of low-nickel kamacite and tetrataenite, which formed during cooling from ∼450 to 300 °C when haxonite was forming. Martensitic plessite decomposed to tetrataenite and metastable high-nickel kamacite at temperatures below 300 °C, which depended on nickel content. Carbon accumulated in untransformed taenite when haxonite growth ceased, producing M-shaped carbon profiles. Bulk carbon concentrations inferred from our ion probe data are 3–4 ppm in IVA, IVB, and Tishomingo, which has IVB-like depletions of moderately volatile siderophiles. Published bulk carbon contents of IVA and IVB irons are >10 times higher suggesting contamination problems. Our ion probe analyses and observations of carbide and graphite show that bulk carbon decreases with decreasing germanium and other moderately volatile elements from group IAB, through IIAB and IIIAB, to group IVA and IVB. These trends may have been inherited from fractionated chondritic precursors, or may have been produced by impacts that caused volatile loss, separation of mantle from core material, and relatively rapid cooling of irons poor in volatiles and carbon. more...
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- 2017
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4. Scanning Electron Microscopy and X-Ray Microanalysis
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Joseph I. Goldstein, Dale E. Newbury, Joseph R. Michael, Nicholas W.M. Ritchie, John Henry J. Scott, David C. Joy, Joseph I. Goldstein, Dale E. Newbury, Joseph R. Michael, Nicholas W.M. Ritchie, John Henry J. Scott, and David C. Joy more...
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- X-ray microanalysis, Scanning electron microscopy
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This thoroughly revised and updated Fourth Edition of a time-honored text provides the reader with a comprehensive introduction to the field of scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS) for elemental microanalysis, electron backscatter diffraction analysis (EBSD) for micro-crystallography, and focused ion beams. Students and academic researchers will find the text to be an authoritative and scholarly resource, while SEM operators and a diversity of practitioners — engineers, technicians, physical and biological scientists, clinicians, and technical managers — will find that every chapter has been overhauled to meet the more practical needs of the technologist and working professional. In a break with the past, this Fourth Edition de-emphasizes the design and physical operating basis of the instrumentation, including the electron sources, lenses, detectors, etc. In the modern SEM, many of the low level instrument parameters are now controlled and optimized by the microscope's software, and user access is restricted. Although the software control system provides efficient and reproducible microscopy and microanalysis, the user must understand the parameter space wherein choices are made to achieve effective and meaningful microscopy, microanalysis, and micro-crystallography. Therefore, special emphasis is placed on beam energy, beam current, electron detector characteristics and controls, and ancillary techniques such as energy dispersive x-ray spectrometry (EDS) and electron backscatter diffraction (EBSD).With 13 years between the publication of the third and fourth editions, new coverage reflects the many improvements in the instrument and analysis techniques. The SEM has evolved into a powerful and versatile characterization platform in which morphology, elemental composition, and crystal structure can be evaluated simultaneously. Extension of the SEM into a'dual beam'platform incorporating bothelectron and ion columns allows precision modification of the specimen by focused ion beam milling. New coverage in the Fourth Edition includes the increasing use of field emission guns and SEM instruments with high resolution capabilities, variable pressure SEM operation, theory, and measurement of x-rays with high throughput silicon drift detector (SDD-EDS) x-ray spectrometers. In addition to powerful vendor- supplied software to support data collection and processing, the microscopist can access advanced capabilities available in free, open source software platforms, including the National Institutes of Health (NIH) ImageJ-Fiji for image processing and the National Institute of Standards and Technology (NIST) DTSA II for quantitative EDS x-ray microanalysis and spectral simulation, both of which are extensively used in this work. However, the user has a responsibility to bring intellect, curiosity, and a proper skepticism to information on a computer screen and to the entire measurement process. This book helps you to achieve this goal.Realigns the text with the needs of a diverse audience from researchers and graduate students to SEM operators and technical managersEmphasizes practical, hands-on operation of the microscope, particularly user selection of the critical operating parameters to achieve meaningful resultsProvides step-by-step overviews of SEM, EDS, and EBSD and checklists of critical issues for SEM imaging, EDS x-ray microanalysis, and EBSD crystallographic measurementsMakes extensive use of open source software: NIH ImageJ-FIJI for image processing and NIST DTSA II for quantitative EDS x-ray microanalysis and EDS spectral simulation.Includes case studies to illustrate practical problem solvingCovers Helium ion scanning microscopyOrganized into relatively self-contained modules – no need to'read it all'to understand a topicIncludesan more...
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- 2017
5. Scanning Electron Microscopy and X-Ray Microanalysis
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Joseph I. Goldstein, Dale E. Newbury, Joseph R. Michael, Nicholas W.M. Ritchie, John Henry J. Scott, and David C. Joy
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- 2018
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6. High Resolution Imaging
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John Henry J. Scott, David C. Joy, Dale E. Newbury, Joseph R. Michael, Nicholas W. M. Ritchie, and Joseph I. Goldstein
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010302 applied physics ,Beam diameter ,Materials science ,business.industry ,Resolution (electron density) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Secondary electrons ,Optics ,Feature (computer vision) ,Electron optics ,0103 physical sciences ,0210 nano-technology ,business ,Visibility ,Image resolution ,Beam (structure) - Abstract
“High resolution SEM imaging” refers to the capability of discerning fine-scale spatial features of a specimen. Such features may be free-standing objects or structures embedded in a matrix. The definition of “fine-scale” depends on the application, which may involve sub-nanometer features in the most extreme cases. The most important factor determining the limit of spatial resolution is the footprint of the incident beam as it enters the specimen. Depending on the level of performance of the electron optics, the limiting beam diameter can be as small as 1 nm or even finer. However, the ultimate resolution performance is likely to be substantially poorer than the beam footprint and will be determined by one or more of several additional factors: (1) delocalization of the imaging signal, which consists of secondary electrons and/or backscattered electrons, due to the physics of the beam electron specimen interactions; (2) constraints imposed on the beam size needed to satisfy the Threshold Equation to establish the visibility for the contrast produced by the features of interest; (3) mechanical stability of the SEM; (4) mechanical stability of the specimen mounting; (5) the vacuum environment and specimen cleanliness necessary to avoid contamination of the specimen; (6) degradation of the specimen due to radiation damage; and (7) stray electromagnetic fields in the SEM environment. Recognizing these factors and minimizing or eliminating their impact is critical to achieving optimum high resolution imaging performance. Because achieving satisfactory high resolution SEM often involves operating at the performance limit of the instrument as well as the technique, the experience may vary from one specimen type to another, with different limiting factors manifesting themselves in different situations. Most importantly, because of the limitations on feature visibility imposed by the Threshold Current/Contrast Equation, for a given choice of operating conditions, there will always be a level of feature contrast below which specimen features will not be visible. Thus, there is always a possible “now you see it, now you don’t” experience lurking when we seek to operate at the limit of the SEM performance envelope. more...
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- 2017
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7. Quantitative Analysis: From k-ratio to Composition
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Joseph I. Goldstein, David C. Joy, Joseph R. Michael, John Henry J. Scott, Nicholas W. M. Ritchie, and Dale E. Newbury
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Physics ,Wavelength ,Spectrometer ,Analytical chemistry ,Composition (combinatorics) ,Quantitative analysis (chemistry) ,Energy (signal processing) ,Intensity (heat transfer) ,Line (formation) - Abstract
A k-ratio is the ratio of a pair of characteristic X-ray line intensities, I, measured under similar experimental conditions for the unknown (unk) and standard (std): $$ k={I}_{unk}/{I}_{std} $$ The measured intensities can be associated with a single characteristic X-ray line (as is typically the case for wavelength spectrometers) or associated with a family of characteristic X-ray lines (as is typically the case for energy dispersive spectrometers.) The numerator of the k-ratio is typically the intensity measured from an unknown sample and the denominator is typically the intensity measured from a standard material—a material of known composition. more...
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- 2017
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8. Backscattered Electrons
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Joseph I. Goldstein, Dale E. Newbury, Joseph R. Michael, Nicholas W. M. Ritchie, John Henry J. Scott, and David C. Joy
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- 2017
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9. Low Beam Energy X-Ray Microanalysis
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Joseph R. Michael, Joseph I. Goldstein, John Henry J. Scott, Nicholas W. M. Ritchie, Dale E. Newbury, and David C. Joy
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Physics ,Astrophysics::High Energy Astrophysical Phenomena ,Excited state ,Ionization ,Atomic physics ,Beam energy ,Energy (signal processing) ,Intensity (heat transfer) ,Beam (structure) ,Excitation ,Exponential function - Abstract
The incident beam energy, E0, is the parameter that determines which characteristic X-rays can be excited: the beam energy must exceed the critical excitation energy, Ec, for an atomic shell to initiate ionization and subsequent emission of characteristic X-rays. This dependence is parameterized with the “overvoltage” U0, defined as $$ {U}_0={E}_0/{E}_c $$ U0 must exceed unity for X-ray emission. The intensity, Ich, of characteristic X-ray generation follows an exponential relation: $$ {I}_{ch}={i}_Ba{\left({U}_0-1\right)}^n $$ where iB is the beam current, a and n are constants, with 1.5 ≤ n ≤ 2. more...
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- 2017
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10. Energy Dispersive X-ray Spectrometry: Physical Principles and User-Selected Parameters
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Joseph I. Goldstein, David C. Joy, Joseph R. Michael, John Henry J. Scott, Nicholas W. M. Ritchie, and Dale E. Newbury
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Materials science ,Binding energy ,Charge carrier ,Electron hole ,Atomic physics ,Ionization energy ,Photon energy ,Kinetic energy ,Valence electron ,Semiconductor detector - Abstract
As illustrated in Fig. 16.1, the physical basis of energy dispersive X-ray spectrometry (EDS) with a semiconductor detector begins with photoelectric absorption of an X-ray photon in the active volume of the semiconductor (Si). The entire energy of the photon is transferred to a bound inner shell atomic electron, which is ejected with kinetic energy equal to the photon energy minus the shell ionization energy (binding energy), 1.838 keV for the Si K-shell and 0.098 keV for the Si L-shell. The ejected photoelectron undergoes inelastic scattering within the Si crystal. One of the consequences of the energy loss is the promotion of bound outer shell valence electrons to the conduction band of the semiconductor, leaving behind positively charged “holes” in the valence band. In the conduction band, the free electrons can move in response to a potential applied between the entrance surface electrode and the back surface electrode across the thickness of the Si crystal, while the positive holes in the conduction band drift in the opposite direction, resulting in the collection of electrons at the anode on the back surface of the EDS detector. This charge generation process requires approximately 3.6 eV per electron hole pair, so that the number of charge carriers is proportional to the original photon energy, Ep: $$ n={E}_p/3.6\ eV $$ For a Mn K-L3 photon with an energy of 5.895 keV, approximately 1638 electron–hole pairs are created, comprising a charge of 2.6 × 10−16 coulombs. Because the detector can respond to any photon energy from a threshold of approximately 50 eV to 30 keV or more, the process has been named “energy dispersive,” although in the spectrometry sense there is no actual dispersion such as occurs in a diffraction element spectrometer. more...
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- 2017
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11. Image Formation
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Joseph I. Goldstein, Dale E. Newbury, Joseph R. Michael, Nicholas W. M. Ritchie, John Henry J. Scott, and David C. Joy
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- 2017
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12. Compositional Mapping
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Joseph I. Goldstein, Dale E. Newbury, Joseph R. Michael, Nicholas W. M. Ritchie, John Henry J. Scott, and David C. Joy
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- 2017
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13. SEM Case Studies
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John Henry J. Scott, David C. Joy, Dale E. Newbury, Joseph R. Michael, Nicholas W. M. Ritchie, and Joseph I. Goldstein
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Crystal ,Optical axis ,Surface (mathematics) ,Software ,business.industry ,Computer graphics (images) ,Stereo pair ,Microscopist ,business ,Anaglyph 3D ,Geology - Abstract
When studying the topographic features of a specimen, the microscopist has several useful software tools available. Qualitative stereomicroscopy provides a composite view from two images of the same area, prepared with different tilts relative to the optic axis, that gives a visual sensation of the specimen topography, as shown for a fractured galena crystal using the anaglyph method in Fig. 15.1 (software: Anaglyph Maker). The “3D Viewer” plugin in ImageJ-Fiji can take the same members of the stereo pair and render the three-dimensional surface, as shown in Fig. 15.2, which can then be rotated to “view” the surface from different orientations (Fig. 15.3). more...
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- 2017
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14. SEM Image Interpretation
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Dale E. Newbury, Nicholas W. M. Ritchie, Joseph R. Michael, John Henry J. Scott, David C. Joy, and Joseph I. Goldstein
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Physics ,Specimen characteristics ,Image (category theory) ,Electron ,Atomic physics ,Secondary electrons ,Interpretation (model theory) - Abstract
Information in SEM images about specimen properties is conveyed when contrast in the backscattered and/or secondary electron signals is created by differences in the interaction of the beam electrons between a specimen feature and its surroundings. The resulting differences in the backscattered and secondary electron signals (S) convey information about specimen properties through a variety of contrast mechanisms. Contrast (Ctr) is defined as $$ {C}_{\mathrm{tr}}=\left({S}_{\mathrm{max}}-{S}_{\mathrm{min}}\right)/{S}_{\mathrm{max}} $$ where is Smax is the larger of the signals. By this definition, 0 ≤ Ctr ≤ 1. more...
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- 2017
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15. Trace Analysis by SEM/EDS
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Joseph I. Goldstein, John Henry J. Scott, Nicholas W. M. Ritchie, Joseph R. Michael, David C. Joy, and Dale E. Newbury
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Materials science ,Analytical chemistry ,Mass concentration (chemistry) ,Trace analysis - Abstract
«Trace analysis” refers to the measurement of constituents presents at low fractional levels. For SEM/EDS the following arbitrary but practical definitions have been chosen to designate various constituent classes according to these mass concentration (C) ranges more...
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- 2017
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16. Qualitative Elemental Analysis by Energy Dispersive X-Ray Spectrometry
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Dale E. Newbury, David C. Joy, John Henry J. Scott, Joseph R. Michael, Nicholas W. M. Ritchie, and Joseph I. Goldstein
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Range (particle radiation) ,Materials science ,Photon ,chemistry ,Elemental analysis ,Calibration ,Linearity ,chemistry.chemical_element ,Atomic physics ,Photon energy ,Copper ,Energy (signal processing) - Abstract
Before attempting automatic or manual peak identification, it is critical that the EDS system be properly calibrated to ensure that accurate energy values are measured for the characteristic X-ray peaks. Follow the vendor’s recommended procedure to rigorously establish the calibration. The calibration procedure typically involves measuring a known material such as copper that provides characteristic X-ray peaks at low photon energy (e.g., Cu L3-M5 at 0.928 keV) and at high photon energy (Cu K-L3 at 8.040 keV). Alternatively, a composite aluminum-copper target (e.g., a copper penny partially wrapped in aluminum foil and continuously scanned so as to excite both Al and Cu) can be used to provide the Al K-L3 (1.487 keV) as the low energy peak and Cu K-L3 for the high energy peak. After calibration, peaks occurring within this energy range (e.g., Ti K-L3 at 4.508 keV and Fe K-L3 at 6.400 keV) should be measured to confirm linearity. A well-calibrated EDS should produce measured photon energies within ±2.5 eV of the ideal value. Low photon energy peaks below 1 keV photon energy should also be measured, for example, O K (e.g., from MgO) and C K. For some EDS systems, non-linearity may be encountered in the low photon energy range. Figure 18.1 shows an EDS spectrum for CaCO3 in which the O K peak at 0.523 keV is found at the correct energy, but the C K peak at 0.282 keV shows a significant deviation below the correct energy due to non-linear response in this range. more...
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- 2017
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17. Variable Pressure Scanning Electron Microscopy (VPSEM)
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Nicholas W. M. Ritchie, Joseph I. Goldstein, John Henry J. Scott, Dale E. Newbury, David C. Joy, and Joseph R. Michael
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Materials science ,Scanning electron microscope ,Torr ,Variable pressure ,Analytical chemistry ,Sample chamber - Abstract
The conventional SEM must operate with a pressure in the sample chamber below ~10−4 Pa (~10−6 torr), a condition determined by the need to satisfy four key instrumental operating conditions
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- 2017
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18. X-Ray Microanalysis Case Studies
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John Henry J. Scott, Joseph R. Michael, Dale E. Newbury, David C. Joy, Joseph I. Goldstein, and Nicholas W. M. Ritchie
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Materials science ,Chemical engineering ,fungi ,Alloy ,technology, industry, and agriculture ,engineering ,Substrate (chemistry) ,engineering.material ,X ray microanalysis ,Characterization (materials science) - Abstract
Background: As part of a study into the in-service failure of the bearing surface of a large water pump, characterization was requested of the hard-facing alloy, which was observed to have separated from the stainless steel substrate, causing the failure. more...
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- 2017
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19. Cathodoluminescence
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Joseph I. Goldstein, Dale E. Newbury, Joseph R. Michael, Nicholas W. M. Ritchie, John Henry J. Scott, and David C. Joy
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- 2017
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20. Ion Beam Microscopy
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Joseph I. Goldstein, Dale E. Newbury, Joseph R. Michael, John Henry J. Scott, David C. Joy, and Nicholas W. M. Ritchie
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Materials science ,Microscope ,Ion beam ,business.industry ,Scanning electron microscope ,Scanning confocal electron microscopy ,Focused ion beam ,law.invention ,Ion beam deposition ,Optics ,law ,Microscopy ,Electron microscope ,business - Abstract
Electron beams have made possible the development of the versatile, high performance electron microscopes described in the earlier chapters of this book. Techniques for the generation and application of electron beams are now well documented and understood, and a wide variety of images and data can be produced using readily available instruments. While the scanning electron microscope (SEM) is the most widely used tool for high performance imaging and microanalysis, it is not the only option and may not even always be the best instrument to choose to solve a particular problem. In this chapter we will discuss how, by replacing the beam of electrons with a beam of ions, it is possible to produce a high performance microscope which resembles an SEM in many respects and shares some of its capabilities but which also offers additional and important modes of operation. more...
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- 2017
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21. Electron Beam—Specimen Interactions: Interaction Volume
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Joseph I. Goldstein, Joseph R. Michael, David C. Joy, John Henry J. Scott, Nicholas W. M. Ritchie, and Dale E. Newbury
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Range (particle radiation) ,Materials science ,Optics ,business.industry ,Atom ,Ultra-high vacuum ,Cathode ray ,Physics::Accelerator Physics ,Electron ,Residual ,business ,Beam (structure) ,Electron gun - Abstract
By selecting the operating parameters of the SEM electron gun, lenses, and apertures, the microscopist controls the characteristics of the focused beam that reaches the specimen surface: energy (typically selected in the range 0.1–30 keV), diameter (0.5 nm to 1 μm or larger), beam current (1 pA to 1 μA), and convergence angle (semi-cone angle 0.001–0.05 rad). In a conventional high vacuum SEM (typically with the column and specimen chamber pressures reduced below 10−3 Pa), the residual atom density is so low that the beam electrons are statistically unlikely to encounter any atoms of the residual gas along the flight path from the electron source to the specimen, a distance of approximately 25 cm. more...
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- 2017
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22. Characterizing Crystalline Materials in the SEM
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Dale E. Newbury, John Henry J. Scott, David C. Joy, Joseph I. Goldstein, Joseph R. Michael, and Nicholas W. M. Ritchie
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Diffraction ,Crystal ,Materials science ,Crystal structure ,Electron ,Microstructure ,Molecular physics ,Charged particle ,Electron backscatter diffraction ,Amorphous solid - Abstract
While amorphous substances such as glass are encountered both in natural and artificial materials, most inorganic materials are found to be crystalline on some scale, ranging from sub-nanometer to centimeter or larger. A crystal consists of a regular arrangement of atoms, the so-called «unit cell,» which is repeated in a two- or three-dimensional pattern. In the previous discussion of electron beam–specimen interactions, the crystal structure of the target was not considered as a variable in the electron range equation or in the Monte Carlo electron trajectory simulation. To a first order, the crystal structure does not have a strong effect on the electron–specimen interactions. However, through the phenomenon of channeling of charged particles through the crystal lattice, crystal orientation can cause small perturbations in the total electron backscattering coefficient that can be utilized to image crystallographic microstructure through the mechanism designated «electron channeling contrast,» also referred to as «orientation contrast» (Newbury et al. 1986). The characteristics of a crystal (e.g., interplanar angles and spacings) and its relative orientation can be determined through diffraction of the high-energy backscattered electrons (BSE) to form «electron backscatter diffraction patterns (EBSD). more...
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- 2017
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23. ImageJ and Fiji
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Dale E. Newbury, David C. Joy, John Henry J. Scott, Joseph R. Michael, Joseph I. Goldstein, and Nicholas W. M. Ritchie
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Focus (computing) ,Microscope ,Computer science ,business.industry ,Interface (computing) ,USB ,law.invention ,Software ,law ,Computer graphics (images) ,Microscopist ,Instrumentation (computer programming) ,business ,Graphical user interface - Abstract
Software is an essential tool for the scanning electron microscopist and X-ray microanalyst (SEMXM). In the past, software was an important optional means of augmenting the electron microscope and X-ray spectrometer, permitting powerful additional analysis and enabling new characterization methods that were not possible with bare instrumentation. Today, however, it is simply not possible to function as an SEMXM practitioner without using at least a minimal amount of software. A graphical user interface (GUI) is an integral part of how the operator controls the hardware on most modern microscopes, and in some cases it is the only interface. Even many seemingly analog controls such as focus knobs, magnification knobs, or stigmators are actually digital interfaces mounted on hand-panel controllers that connect to the microscope control computer via a USB interface. more...
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- 2017
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24. DTSA-II EDS Software
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David C. Joy, Dale E. Newbury, Joseph I. Goldstein, John Henry J. Scott, Joseph R. Michael, and Nicholas W. M. Ritchie
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Software ,Ms excel ,Computer science ,Vendor ,business.industry ,Nothing ,Reading (process) ,media_common.quotation_subject ,Subject (documents) ,Software engineering ,business ,Subject matter ,media_common - Abstract
Reading about a new subject is good but there is nothing like doing to reinforce understanding. With this in mind, the authors of this textbook have designed a number of practical exercises that reinforce the book’s subject matter. Some of these exercises can be performed with software you have available to you—either instrument vendor software or a spreadsheet like MS Excel or LibreOffice/OpenOffice Calc. Other exercises require functionality which may not be present in all instrument vendor’s software. Regardless, it is much easier to explain an exercise when everyone is working with the same tools. more...
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- 2017
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25. Focused Ion Beam Applications in the SEM Laboratory
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Nicholas W. M. Ritchie, David C. Joy, Joseph R. Michael, John Henry J. Scott, Joseph I. Goldstein, and Dale E. Newbury
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Materials science ,Ion beam ,business.industry ,Optoelectronics ,Sample preparation ,Plasma ,Large range ,business ,Focused ion beam ,Secondary electrons ,Ion source ,Ion - Abstract
The use of focused ion beams (FIB) in the field of electron microscopy for the preparation of site specific samples and for imaging has become very common. Site specific sample preparation of cross-section samples is probably the most common use of the focused ion beam tools, although there are uses for imaging with secondary electrons produced by the ion beam. These tools are generally referred to as FIB tools, but this name covers a large range of actual tools. There are single beam FIB tools which consist of the FIB column on a chamber and also the FIB/SEM platforms that include both a FIB column for sample preparation and an SEM column for observing the sample during preparation and for analyzing the sample post-preparation using all of the imaging modalities and analytical tools available on a standard SEM column. A vast majority of the FIB tools presently in use are equipped with liquid metal ion sources (LMIS) and the most common ion species used is Ga. Recent developments have produced plasma sources for high current ion beams. The gas field ion source (GFIS) is discussed in module 31 on helium ion microscopy in this book. more...
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- 2017
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26. Quantitative Analysis: The SEM/EDS Elemental Microanalysis k-ratio Procedure for Bulk Specimens, Step-by-Step
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John Henry J. Scott, Joseph R. Michael, Joseph I. Goldstein, Dale E. Newbury, Nicholas W. M. Ritchie, and David C. Joy
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Materials science ,Analytical chemistry ,Microanalysis - Abstract
This module discusses the procedure used to perform a rigorous quantitative elemental microanalysis by SEM/EDS following the k-ratio/matrix correction protocol using the NIST DTSA-II software engine for bulk specimens. Bulk specimens have dimensions that are sufficiently large to contain the full range of the direct electron-excited X-ray production (typically 0.5–10 μm) as well as the range of secondary X-ray fluorescence induced by the propagation of the characteristic and continuum X-rays (typically 10–100 μm). more...
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27. X-Rays
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Joseph I. Goldstein, Dale E. Newbury, Joseph R. Michael, Nicholas W. M. Ritchie, John Henry J. Scott, and David C. Joy
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- 2017
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28. SEM Imaging Checklist
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David C. Joy, Joseph R. Michael, Dale E. Newbury, John Henry J. Scott, Nicholas W. M. Ritchie, and Joseph I. Goldstein
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Outgassing ,Materials science ,Optics ,Ground ,business.industry ,Airlock ,Magnification ,Electron ,Adhesive ,business ,Stub (electronics) ,Shrinkage - Abstract
A conducting or semiconducting specimen must maintain good contact with electrical ground to dissipate the injected beam current. Without such an electrical path, even a highly conducting specimen such as a metal will show charging artifacts, in the extreme case acting as an electron mirror and reflecting the beam off the specimen. A typical strategy is to use an adhesive such as double-sided conducting tape to both grip the specimen to a support, for example, a stub or a planchet, as well as to make the necessary electrical path connection. Note that some adhesives may only be suitable for low magnification (scanned field dimensions greater than 100 × 100 μm, nominally less than 1,000× magnification) and intermediate magnification (scanned field dimensions between 100 μm x 100 μm, nominally less than 1,000X magnification and 10 μm × 10 μm, nominally less than 10,000× magnification) due to dimensional changes which may occur as the adhesive outgases in the SEM leading to image instability such as drift. Good practice is to adequately outgas the mounted specimen in the SEM airlock or a separate vacuum system to minimize contamination in the SEM as well as to minimize further dimensional shrinkage. Note that some adhesive media are also subject to dimensional change due to electron radiation damage during imaging, which can also lead to image drift. more...
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- 2017
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29. Energy Dispersive X-Ray Microanalysis Checklist
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John Henry J. Scott, Dale E. Newbury, Joseph R. Michael, David C. Joy, Joseph I. Goldstein, and Nicholas W. M. Ritchie
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Materials science ,Analytical chemistry ,Checklist ,Energy (signal processing) ,X ray microanalysis - Published
- 2017
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30. Secondary Electrons
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Joseph I. Goldstein, Dale E. Newbury, Joseph R. Michael, Nicholas W. M. Ritchie, John Henry J. Scott, and David C. Joy
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- 2017
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31. Image Defects
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Joseph I. Goldstein, Dale E. Newbury, Joseph R. Michael, Nicholas W. M. Ritchie, John Henry J. Scott, and David C. Joy
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- 2017
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32. Low Beam Energy SEM
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Joseph I. Goldstein, Nicholas W. M. Ritchie, Joseph R. Michael, Dale E. Newbury, John Henry J. Scott, and David C. Joy
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Physics ,Range (particle radiation) ,Incident beam ,Electron ,Atomic number ,Atomic physics ,Beam energy ,Atomic mass ,Energy (signal processing) - Abstract
The incident beam energy is one of the most useful parameters over which the microscopist has control because it determines the lateral and depth sampling of the specimen properties by the critical imaging signals. The Kanaya–Okayama electron range varies strongly with the incident beam energy: $$ {R}_{K-O}(nm)=\left(27.6\ A/{Z}^{0.89}\rho \right){E_0}^{1.67} $$ where A is the atomic weight (g/mol), Z is the atomic number, ρ is the density (g/cm3), and E0 (keV) is the incident beam energy, which is shown graphically in Fig. 11.1a–c. more...
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- 2017
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33. Analysis of Specimens with Special Geometry: Irregular Bulk Objects and Particles
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Nicholas W. M. Ritchie, David C. Joy, Joseph I. Goldstein, Joseph R. Michael, John Henry J. Scott, and Dale E. Newbury
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Materials science ,Basis (linear algebra) ,Astrophysics::High Energy Astrophysical Phenomena ,Geometry ,Microanalysis ,Special geometry - Abstract
There are two “zero-th level” assumptions that underpin the basis for quantitative electron-excited X-ray microanalysis
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- 2017
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34. Attempting Electron-Excited X-Ray Microanalysis in the Variable Pressure Scanning Electron Microscope (VPSEM)
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Joseph R. Michael, John Henry J. Scott, Joseph I. Goldstein, Dale E. Newbury, David C. Joy, and Nicholas W. M. Ritchie
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Materials science ,Scanning electron microscope ,Excited state ,Variable pressure ,Composite number ,Electron ,Atomic physics ,Microanalysis ,Electron scattering ,Beam (structure) - Abstract
While X-ray analysis can be performed in the Variable Pressure Scanning Electron Microscope (VPSEM), it is not possible to perform uncompromised electron-excited X-ray microanalysis. The measured EDS spectrum is inevitably degraded by the effects of electron scattering with the atoms of the environmental gas in the specimen chamber before the beam reaches the specimen. The spectrum is always a composite of X-rays generated by the unscattered electrons that remain in the focused beam and strike the intended target mixed with X-rays generated by the gas-scattered electrons that land elsewhere, micrometers to millimeters from the microscopic target of interest. more...
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- 2017
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35. The Visibility of Features in SEM Images
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Joseph R. Michael, Joseph I. Goldstein, Nicholas W. M. Ritchie, Dale E. Newbury, John Henry J. Scott, and David C. Joy
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Physics ,Signal processing ,Noise (signal processing) ,business.industry ,media_common.quotation_subject ,Signal ,Secondary electrons ,Optics ,Digital image processing ,Contrast (vision) ,Imaging Signal ,Visibility ,business ,media_common - Abstract
The detection in SEM images of specimen features such as compositional differences, topography (shape, inclination, edges, etc.), and physical differences (crystal orientation, magnetic fields, electrical fields, etc.), depends on satisfying two criteria: (1) establishing the minimum conditions necessary to ensure that the contrast created by the beam–specimen interaction responding to differences in specimen features is statistically significant in the imaging signal (backscattered electrons [BSE], secondary electrons [SE], or a combination) compared to the inevitable random signal fluctuations (noise); and (2) applying appropriate signal processing and digital image processing to render the contrast information that exists in the signal visible to the observer viewing the final image display. more...
- Published
- 2017
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36. Determining cooling rates of iron and stony-iron meteorites from measurements of Ni and Co at kamacite–taenite interfaces
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Joseph I. Goldstein, J. Yang, and Edward Scott
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Kamacite ,chemistry.chemical_compound ,Meteorite ,Geochemistry and Petrology ,Chemistry ,Metallurgy ,Analytical chemistry ,Electron microprobe ,Tetrataenite ,Taenite ,Mantle (geology) ,Silicate ,Phase diagram - Abstract
Analyses and modeling of Ni zoning in taenite in differentiated meteorites provide metallographic cooling rates at ∼500 °C that are inconsistent with conventional formation models. Group IVA iron meteorites have very diverse cooling rates of 100–6600 °C/Myr indicating that they cooled inside a large metallic body with little or no silicate mantle (Yang et al., 2007). Wasson and Hoppe (2012) have questioned these diverse cooling rates on the basis of their ion probe measurements of Ni/Co ratios at the kamacite–taenite interface in two group IVA and in two group IIIAB iron meteorites. To investigate their claims and to assess methods for determining relative cooling rates from kamacite–taenite interface compositions, we have analyzed 38 meteorites—13 IVA, 14 IIIAB irons, 4 IAB complex irons, 6 pallasites and a mesosiderite—using the electron probe microanalyzer (EPMA). Ni concentrations in taenite (Niγ) and kamacite (Niα) at kamacite–taenite interfaces are well correlated with metallographic cooling rates: Niγ values increase from 30 to 52 wt.% while Niα decreases from 7 to 4 wt.% as cooling rates decrease. EPMA measurements of Niγ, Niα, and Niα/Niγ, can therefore be used to provide order-of-magnitude estimates of relative cooling rates. Concentrations of Co in kamacite and taenite at their interface (Coα, Coγ) are controlled by bulk Ni and Co composition, as well as cooling rate. The ratios Coα/Coγ and (Co/Ni)α/(Co/Ni)γ are correlated with cooling rate, but because of significant scatter, these parameters should not be used to estimate cooling rates. Our analyses of 13 group IVA irons provide robust support for diverse cooling rates that decrease with increasing bulk Ni, consistent with measurements of cloudy zone size and tetrataenite width. Apparent equilibration temperatures, which are inferred from Niγ values and the Fe–Ni–P phase diagram and Ni diffusion rates in taenite, show that cooling rates of IVA irons vary by a factor of ≈100, in excellent agreement with the metallographic cooling rates. Similar calculations using Niγ/Niα and Coα/Coγ ratios and phase diagram data give factors that are an order of magnitude lower but have larger uncertainties. Thus we strongly disagree with the conclusion of Wasson and Hoppe (2012) that interface concentrations of Ni and Co are in any way in conflict with the cooling rates of Yang et al. (2008). Our measurements confirm that the IVA irons could not have cooled in an asteroidal core surrounded by a silicate mantle, and also that main-group pallasites cooled slower than IIIAB irons and did not cool at the boundary between the mantle and core from which the IIIAB irons originated. Our data provide additional evidence that mesosiderites, which formed by impact mixing of Fe–Ni melt and crustal rocks, cooled at uniquely slow rates. more...
- Published
- 2014
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37. De Magnete et Meteorite: Cosmically Motivated Materials
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Frederick E. Pinkerton, N. Bordeaux, Laura H. Lewis, Joseph I. Goldstein, A. Mubarok, Eric Poirier, Ralph Skomski, and Katayun Barmak
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Magnetization ,Materials science ,Ferromagnetism ,Meteorite ,Condensed matter physics ,Magnet ,Context (language use) ,Coercivity ,Tetrataenite ,Temperature coefficient ,Electronic, Optical and Magnetic Materials - Abstract
Meteorites, likely the oldest source of magnetic material known to mankind, are attracting renewed interest in the science and engineering community. Worldwide focus is on tetrataenite, a uniaxial ferromagnetic compound with the tetragonal L1 0 crystal structure comprised of nominally equiatomic Fe-Ni that is found naturally in meteorites subjected to extraordinarily slow cooling rates, as low as 0.3 K per million years. Here, the favorable permanent magnetic properties of bulk tetrataenite derived from the meteorite NWA 6259 are quantified. The measured magnetization approaches that of Nd-Fe-B (1.42 T) and is coupled with substantial anisotropy (1.0-1.3 MJ/m 3) that implies the prospect for realization of technologically useful coercivity. A highly robust temperature dependence of the technical magnetic properties at an elevated temperature (20-200 °C) is confirmed, with a measured temperature coefficient of coercivity of -0.005%/K, over one hundred times smaller than that of Nd-Fe-B in the same temperature range. These results quantify the extrinsic magnetic behavior of chemically ordered tetrataenite and are technologically and industrially significant in the current context of global supply chain limitations of rare-earth metals required for present-day high-performance permanent magnets that enable operation of a myriad of advanced devices and machines. more...
- Published
- 2014
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38. Thermal and collisional history of Tishomingo iron meteorite: More evidence for early disruption of differentiated planetesimals
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Ingo Leya, Paul G. Kotula, J. Yang, Joseph I. Goldstein, Edward Scott, Joseph R. Michael, and Ansgar Grimberg
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Kamacite ,Meteorite ,Geochemistry and Petrology ,Martensite ,Metallurgy ,Iron meteorite ,Geology ,Troilite ,Taenite ,Parent body ,Electron backscatter diffraction - Abstract
Tishomingo is a chemically and structurally unique iron with 32.5 wt.% Ni that contains 20% residual taenite and 80% martensite plates, which formed on cooling to between −75 and −200 °C, probably the lowest temperature recorded by any meteorite. Our studies using transmission (TEM) and scanning electron microscopy (SEM), X-ray microanalysis (AEM) and electron backscatter diffraction (EBSD) show that martensite plates in Tishomingo formed in a single crystal of taenite and decomposed during reheating forming 10–100 nm taenite particles with ∼50 wt.% Ni, kamacite with ∼4 wt.%Ni, along with martensite or taenite with 32 wt.% Ni. EBSD data and experimental constraints show that Tishomingo was reheated to 320–400 °C for about a year transforming some martensite to kamacite and to taenite particles and some martensite directly to taenite without composition change. Fizzy-textured intergrowths of troilite, kamacite with 2.7 wt.% Ni and 2.6 wt.% Co, and taenite with 56 wt.% Ni and 0.15 wt.% Co formed by localized shock melting. A single impact probably melted the sub-mm sulfides, formed stishovite, and reheated and decomposed the martensite plates. Tishomingo and its near-twin Willow Grove, which has 28 wt.% Ni, differ from IAB-related irons like Santa Catharina and San Cristobal that contain 25–36 wt.% Ni, as they are highly depleted in moderately volatile siderophiles and enriched in Ir and other refractory elements. Tishomingo and Willow Grove therefore resemble IVB irons but are chemically distinct. The absence of cloudy taenite in these two irons shows that they cooled through 250 °C abnormally fast at >0.01 °C/yr. Thus this grouplet, like the IVA and IVB irons, suffered an early impact that disrupted their parent body when it was still hot. Our noble gas data show that Tishomingo was excavated from its parent body about 100 to 200 Myr ago and exposed to cosmic rays as a meteoroid with a radius of ∼50–85 cm. more...
- Published
- 2014
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39. Intrinsic Properties of Fe-Substituted $L1_{0}$ Magnets
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Joseph I. Goldstein, Arti Kashyap, Jeffrey E. Shield, M. J. Lucis, S. Constantinides, Priyanka Manchanda, Laura H. Lewis, Pankaj Kumar, David J. Sellmyer, A. Mubarok, Katayun Barmak, and Ralph Skomski more...
- Subjects
Magnetization ,Magnetic anisotropy ,Materials science ,Magnetic moment ,Ferromagnetism ,Condensed matter physics ,Magnet ,Antiferromagnetism ,Density functional theory ,Electrical and Electronic Engineering ,Anisotropy ,Electronic, Optical and Magnetic Materials - Abstract
First-principle supercell calculations are used to determine how 3d elemental additions, especially Fe additions, modify the magnetization, exchange and anisotropy of L10-ordered ferromagnets. Calculations are performed using the VASP code and partially involve configurational averaging over site disorder. Three isostructural systems are investigated: Fe-Co-Pt, Mn-Al-Fe, and transition metal-doped Fe-Ni. In all three systems the iron strongly influences the magnetic properties of these compounds, but the specific effect depends on the host. In CoPt(Fe) iron enhances the magnetization, with subtle changes in the magnetic moments that depend on the distribution of the Fe and Co atoms. The addition of Fe to MnAl is detrimental to the magnetization, because it creates antiferromagnetic exchange interactions, but it enhances the magnetic anisotropy. The replacement of 50% of Mn by Fe in MnFeAl2 enhances the anisotropy from 1.77 to 2.5 MJ/m3. Further, the substitution of light 3d elements such as Ti, V, Cr into L10-ordered FeNi is shown to substantially reduce the magnetization. more...
- Published
- 2013
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40. Group IVA irons: New constraints on the crystallization and cooling history of an asteroidal core with a complex history
- Author
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Paul G. Kotula, Joseph I. Goldstein, J. R. Michael, J. Yang, Nancy L. Chabot, Douglas Rumble, Richard J. Walker, Catherine M. Corrigan, Richard D. Ash, William F. McDonough, and Timothy J. McCoy
- Subjects
Fractional crystallization (geology) ,Analytical chemistry ,Mineralogy ,Plessite ,Isotope dilution ,Silicate ,Parent body ,Kamacite ,chemistry.chemical_compound ,chemistry ,Meteorite ,Geochemistry and Petrology ,Chondrite ,sense organs ,Geology - Abstract
We report analyses of 14 group IVA iron meteorites, and the ungrouped but possibly related, Elephant Moraine (EET) 83230, for siderophile elements by laser ablation ICP-MS and isotope dilution. EET was also analyzed for oxygen isotopic composition and metallographic structure, and Fuzzy Creek, currently the IVA with the highest Ni concentration, was analyzed for metallographic structure. Highly siderophile elements (HSE) Re, Os and Ir concentrations vary by nearly three orders of magnitude over the entire range of IVA irons, while Ru, Pt and Pd vary by less than factors of five. Chondrite normalized abundances of HSE form nested patterns consistent with progressive crystal–liquid fractionation. Attempts to collectively model the HSE abundances resulting from fractional crystallization achieved best results for 3 wt.% S, compared to 0.5 or 9 wt.% S. Consistent with prior studies, concentrations of HSE and other refractory siderophile elements estimated for the bulk IVA core and its parent body are in generally chondritic proportions. Projected abundances of Pd and Au, relative to more refractory HSE, are slightly elevated and modestly differ from L/LL chondrites, which some have linked with group IVA, based on oxygen isotope similarities. Abundance trends for the moderately volatile and siderophile element Ga cannot be adequately modeled for any S concentration, the cause of which remains enigmatic. Further, concentrations of some moderately volatile and siderophile elements indicate marked, progressive depletions in the IVA system. However, if the IVA core began crystallization with � 3 wt.% S, depletions of more volatile elements cannot be explained as a result of prior volatilization/condensation processes. The initial IVA core had an approximately chondritic Ni/Co ratio, but a fractionated Fe/Ni ratio of � 10, indicates an Fedepleted core. This composition is most easily accounted for by assuming that the surrounding silicate shell was enriched in iron, consistent with an oxidized parent body. The depletions in Ga may reflect decreased siderophilic behavior in a relatively oxidized body, and more favorable partitioning into the silicate portion of the parent body. Phosphate inclusions in EET show D 17 O values within the range measured for silicates in IVA iron meteorites. EET has a typical ataxitic microstructure with precipitates of kamacite within a matrix of plessite. Chemical and isotopic evidence for a genetic relation between EET and group IVA is strong, but the high Ni content and the newly determined, rapid cooling rate of this meteorite show that it should continue to be classified as ungrouped. Previously reported metallographic cooling rates for IVA iron meteorites have been interpreted to indicate an inwardly crystallizing, � 150 km radius metallic body with little more...
- Published
- 2011
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41. Thermal and impact histories of reheated group IVA, IVB, and ungrouped iron meteorites and their parent asteroids
- Author
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J. Yang, Joseph R. Michael, Tuan D. Pham, Paul G. Kotula, Edward Scott, Timothy J. McCoy, and Joseph I. Goldstein
- Subjects
Kamacite ,Geophysics ,Recrystallization (geology) ,Meteorite ,Space and Planetary Science ,Martensite ,Metallurgy ,Mineralogy ,Plessite ,Taenite ,Troilite ,Geology ,Electron backscatter diffraction - Abstract
The microstructures of six reheated iron meteoritesotwo IVA irons, Maria Elena (1935), Fuzzy Creek; one IVB iron, Ternera; and three ungrouped irons, Hammond, Babb's Mill (Blake's Iron), and Babb's Mill (Troost's Iron)owere characterized using scanning and transmission electron microscopy, electron-probe microanalysis, and electron backscatter diffraction techniques to determine their thermal and shock history and that of their parent asteroids. Maria Elena and Hammond were heated below approximately 700-750 � C, so that kamacite was recrystallized and taenite was exsolved in kamacite and was spheroidized in plessite. Both meteorites retained a record of the original WidmanstItten pattern. The other four, which show no trace of their original microstructure, were heated above 600-700 � C and recrystallized to form 10-20 lm wide homogeneous taenite grains. On cooling, kamacite formed on taenite grain boundaries with their close-packed planes aligned. Formation of homogeneous 20 lm wide taenite grains with diverse orientations would have required as long as approximately 800 yr at 600 � C or approximately 1 h at 1300 � C. All six irons contain approximately 5-10 lm wide taenite grains with internal microprecipitates of kamacite and nanometer-scale M-shaped Ni profiles that reach approximately 40% Ni indicating cooling over 100-10,000 yr. Un-decomposed high-Ni martensite (a2) in taeniteothe first occurrence in ironsoappears to be a characteristic of strongly reheated irons. From our studies and published work, we identified four progressive stages of shock and reheating in IVA irons using these criteria: cloudy taenite, M-shaped Ni profiles in taenite, Neumann twin lamellae, martensite, shock-hatched kamacite, recrystallization, microprecipitates of taenite, and shock- melted troilite. Maria Elena and Fuzzy Creek represent stages 3 and 4, respectively. Although not all reheated irons contain evidence for shock, it was probably the main cause of reheating. Cooling over years rather than hours precludes shock during the impacts that exposed the irons to cosmic rays. If the reheated irons that we studied are representative, the IVA irons may have been shocked soon after they cooled below 200 � C at 4.5 Gyr in an impact that created a rubblepile asteroid with fragments from diverse depths. The primary cooling rates of the IVA irons and the proposed early history are remarkably consistent with the Pb-Pb ages of troilite inclusions in two IVA irons including the oldest known differentiated meteorite (Blichert-Toft et al. 2010). more...
- Published
- 2011
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42. Thermal history and origin of the IVB iron meteorites and their parent body
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Edward Scott, Joseph R. Michael, J. Yang, Paul G. Kotula, and Joseph I. Goldstein
- Subjects
Fractional crystallization (geology) ,Analytical chemistry ,Mineralogy ,Taenite ,Silicate ,Mantle (geology) ,Parent body ,Kamacite ,chemistry.chemical_compound ,chemistry ,Meteorite ,Geochemistry and Petrology ,Tetrataenite ,Geology - Abstract
We have determined metallographic cooling rates of 9 IVB irons by measuring Ni gradients 3 lm or less in length at kamacite–taenite boundaries with the analytical transmission electron microscope and by comparing these Ni gradients with those derived by modeling kamacite growth. Cooling rates at 600–400 C vary from 475 K/Myr at the low-Ni end of group IVB to 5000 K/Myr at the high-Ni end. Sizes of high-Ni particles in the cloudy zone microstructure in taenite and the widths of the tetrataenite rims, which both increase with decreasing cooling rate, are inversely correlated with the bulk Ni concentrations of the IVB irons confirming the correlation between cooling rate and bulk Ni. Since samples of a core that cooled inside a thermally insulating silicate mantle should have uniform cooling rates, the IVB core must have cooled through 500 C without a silicate mantle. The correlation between cooling rate and bulk Ni suggests that the core crystallized concentrically outwards. Our thermal and fractional crystallization models suggest that in this case the radius of the core was 65 ± 15 km when it cooled without a mantle. The mantle was probably removed when the IVB body was torn apart in a glancing impact with a larger body. Clean separation of the mantle from the solid core during this impact could have been aided by a thin layer of residual metallic melt at the core-mantle boundary. Thus the IVB irons may have crystallized in a well-mantled core that was 70 ± 15 km in radius while it was inside a body of radius 140 ± 30 km. more...
- Published
- 2010
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43. Main-group pallasites: Thermal history, relationship to IIIAB irons, and origin
- Author
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Edward Scott, J. Yang, and Joseph I. Goldstein
- Subjects
Kamacite ,Olivine ,Meteorite ,Geochemistry and Petrology ,engineering ,Pallasite ,Mineralogy ,engineering.material ,Tetrataenite ,Achondrite ,Geology ,Taenite ,Mantle (geology) - Abstract
We have determined metallographic cooling rates below 975 K for eight main group (MG) pallasites from Ni profiles across taenite lamellae of known crystallographic orientation in metallic regions with Widmanstatten patterns. Comparison with profiles generated by modeling kamacite growth gave cooling rates ranging from 2.5 to 18 K/Myr. Relative cooling rates were also inferred from the sizes of cloudy zone particles in 28 MG pallasites (86-170 nm) and tetrataenite bandwidths in 20 MG pallasites (1050-2170 nm), as these parameters are positively correlated with each other and negatively correlated with the metallographic cooling rates. These three different techniques show that MG pallasites cooled below 975 K at significantly diverse rates. Since samples from the core-mantle boundary should have indistinguishable cooling rates, MG pallasites could not have cooled at this location. Group IIIAB irons, which were previously thought to be core samples from the MG pallasite body, have faster cooling rates (� 50-350 K/Myr) and smaller cloudy zone particle sizes and tetrataenite bandwidths. This shows that IIIAB irons cooled faster than MG pallasites and could not plausibly be from the same body. The absence of related iron meteorites and achondrites and our thermal constraints suggest that MG pallasites cooled at diverse depths in a pallasitic body consisting of well-mixed olivine and metallic Fe-Ni. Such a body may have formed during an impact on a differentiated asteroid or protoplanet that mixed olivine mantle fragments with residual Ir-poor molten metal from the out- ermost part of a core that chemically resembled the IIIAB core and was � 80% fractionally crystallized. Separation of the solid core and most of the associated mantle may have resulted from a grazing hit-and-run impact with a larger protoplanet or asteroid. Thermal calculations suggest that the radius of the pallasitic body was 400 km but the likely presence of a regolith would reduce this estimate considerably. 2010 Elsevier Ltd. All rights reserved. more...
- Published
- 2010
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44. Iron meteorites: Crystallization, thermal history, parent bodies, and origin
- Author
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Joseph I. Goldstein, Nancy L. Chabot, and Edward Scott
- Subjects
Kamacite ,Geophysics ,Fractional crystallization (geology) ,Meteorite ,Geochemistry and Petrology ,Chondrite ,Geochemistry ,Widmanstätten pattern ,Formation and evolution of the Solar System ,Protoplanet ,Iron meteorite ,Geology - Abstract
We review the crystallization of the iron meteorite chemical groups, the thermal history of the irons as revealed by the metallographic cooling rates, the ages of the iron meteorites and their relationships with other meteorite types, and the formation of the iron meteorite parent bodies. Within most iron meteorite groups, chemical trends are broadly consistent with fractional crystallization, implying that each group formed from a single molten metallic pool or core. However, these pools or cores differed considerably in their S concentrations, which affect partition coefficients and crystallization conditions significantly. The silicate-bearing iron meteorite groups, IAB and IIE, have textures and poorly defined elemental trends suggesting that impacts mixed molten metal and silicates and that neither group formed from a single isolated metallic melt. Advances in the understanding of the generation of the Widmanstatten pattern, and especially the importance of P during the nucleation and growth of kamacite, have led to improved measurements of the cooling rates of iron meteorites. Typical cooling rates from fractionally crystallized iron meteorite groups at 500–7001C are about 100–10,0001C/Myr, with total cooling times of 10 Myr or less. The measured cooling rates vary from 60 to 3001C/Myr for the IIIAB group and 100–66001C/Myr for the IVA group. The wide range of cooling rates for IVA irons and their inverse correlation with bulk Ni concentration show that they crystallized and cooled not in a mantled core but in a large metallic body of radius 150750 km with scarcely any silicate insulation. This body may have formed in a grazing protoplanetary impact. The fractionally crystallized groups, according to Hf–W isotopic systematics, are derived originally from bodies that accreted and melted to form cores early in the history of the solar system, o1 Myr after CAI formation. The ungrouped irons likely come from at least 50 distinct parent bodies that formed in analogous ways to the fractionally crystallized groups. Contrary to traditional views about their origin, iron meteorites may have been derived originally from bodies as large as 1000 km or more in size. Most iron meteorites come directly or indirectly from bodies that accreted before the chondrites, possibly at 1–2 AU rather than in the asteroid belt. Many of these bodies may have been disrupted by impacts soon after they formed and their fragments were scattered into the asteroid belt by protoplanets. r 2009 Elsevier GmbH. All rights reserved. more...
- Published
- 2009
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45. Thermal histories of IVA iron meteorites from transmission electron microscopy of the cloudy zone microstructure
- Author
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Edward Scott, Joseph R. Michael, J. Yang, Paul G. Kotula, and Joseph I. Goldstein
- Subjects
Materials science ,Metallurgy ,Analytical chemistry ,Microstructure ,Silicate ,Taenite ,Kamacite ,chemistry.chemical_compound ,Geophysics ,chemistry ,Space and Planetary Science ,Transmission electron microscopy ,Grain boundary ,Particle size ,Tetrataenite - Abstract
We have measured the size of the high-Ni particles in the cloudy zone and the width of the outer taenite rim in eight low shocked and eight moderately to heavily shocked IVA irons using a transmission electron microscope (TEM). Thin sections for TEM analysis were produced by a focused ion beam instrument. Use of the TEM allowed us to avoid potential artifacts which may be introduced during specimen preparation for SEM analysis of high Ni particles more...
- Published
- 2009
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46. Metallographic cooling rates and origin of IVA iron meteorites
- Author
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J. Yang, Joseph I. Goldstein, and Edward Scott
- Subjects
chemistry.chemical_compound ,Cooling rate ,Fractional crystallization (geology) ,chemistry ,Meteorite ,Geochemistry and Petrology ,Thermal ,Metallurgy ,Cooling rates ,Radius ,Thermal model ,Silicate ,Geology - Abstract
We have determined the metallographic cooling rates for 13 IVA irons using the most recent and most accurate metallographic cooling rate model. Group IVA irons have cooling rates that vary from 6600 C/Myr at the low-Ni end of the group to 100 C/Myr at the high-Ni end of the group. This large cooling rate range is totally incompatible with cooling in a mantled core which should have a uniform cooling rate. Thermal and fractional crystallization models have been used to describe the cooling and solidification of the IVA asteroid. The thermal model indicates that a metallic body of 150 ± 50 km in radius with less than 1 km of silicate on the outside of the body has a range of cooling rates that match the metallographic cooling rates in more...
- Published
- 2008
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47. Olivine zoning and retrograde olivine-orthopyroxene-metal equilibration in H5 and H6 chondrites
- Author
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Joseph I. Goldstein, M. I. Petaev, and R. J. Reisener
- Subjects
Olivine ,Analytical chemistry ,Mineralogy ,Plessite ,Electron microprobe ,engineering.material ,Silicate ,Taenite ,Kamacite ,chemistry.chemical_compound ,Geophysics ,chemistry ,Space and Planetary Science ,Chondrite ,engineering ,Supercooling ,Geology - Abstract
Electron microprobe studies of several H5 and H6 chondrites reveal that olivine crystals exhibit systematic Fe-Mg zoning near olivine-metal interfaces. Olivine Fa concentrations decrease by up to 2 mol% toward zoned taenite + kamacite particles (formed after relatively small amounts of taenite undercooling) and increase by up to 2 mol% toward zoneless plessite particles (formed after ~200 °C of taenite undercooling). The olivine zoning can be understood in terms of localized olivine-orthopyroxene-metal reactions during cooling from the peak metamorphic temperature. The silicate-metal reactions were influenced by solid-state metal phase transformations, and the two types of olivine zoning profiles resulted from variable amounts of taenite undercooling at temperatures more...
- Published
- 2006
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48. Metallographic cooling rates of the IIIAB iron meteorites
- Author
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Joseph I. Goldstein and J. Yang
- Subjects
Fractional crystallization (geology) ,Meteorite ,Geochemistry and Petrology ,Phase (matter) ,Metallurgy ,Nucleation ,Mineralogy ,Atmospheric temperature range ,Widmanstätten pattern ,Iron meteorite ,Taenite ,Geology - Abstract
An improved computer simulation program has been developed and used to re-measure the metallographic cooling rates of the IIIAB irons, the largest iron meteorite chemical group. The formation of this chemical group is attributed to fractional crystallization of a single molten metallic core during solidification. Group IIIAB irons cooling rates vary by a factor of 6 from 56 to 338 °C/My. The cooling rate variation for each meteorite is much smaller than in previous studies and the uncertainty in the measured cooling rate for each meteorite is greatly reduced. The lack of correction for the orientation of the kamacite–taenite interface in the cooling rate measurement of a given meteorite in previous studies not only leads to large cooling rate variations but also to inaccurate and low cooling rates. The cooling rate variation with Ni content in the IIIAB chemical group measured in this study is attributable, in part, to the variation in nucleation temperature of the Widmanstatten pattern with Ni content and nucleation mechanism. However, the factor of 6 variation in cooling rate of the IIIAB irons is hard to explain unless the IIIAB asteroidal core was exposed or partially exposed in the temperature range in which the Widmanstatten pattern formed. Measurements of the size of the island phase in the cloudy zone of the taenite phase and Re–Os data from the IIIAB irons and the pallasites make it hard to reconcile the idea that pallasites are located at the boundary of the IIIAB asteroid core. more...
- Published
- 2006
- Full Text
- View/download PDF
49. The formation of plessite in meteoritic metal
- Author
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Joseph I. Goldstein and Joseph R. Michael
- Subjects
Kamacite ,Crystallography ,Geophysics ,Materials science ,Space and Planetary Science ,Phase (matter) ,Martensite ,Plessite ,Tetrataenite ,Single crystal ,Taenite ,Electron backscatter diffraction - Abstract
Plessite is a mixture of body-centered cubic (bcc) kamacite (α), face-centered cubic (fcc) taenite (γ), and/or ordered FeNi-tetrataenite (γ") phases and is observed in the metal of iron, stony- iron, and chondritic meteorites. The formation of plessite was studied by measuring the orientation of the bcc and fcc phases over large regions of plessite using electron backscatter diffraction (EBSD) analysis in five ataxites, the Carlton IAB-IIICD iron, and zoneless plessite metal in the Kernouve H6 chondrite. The EBSD results show that there are a number of different orientations of the bcc kamacite phase in the plessite microstructure. These orientations reflect the reaction path γ (fcc) → α2 (bcc) in which the α2 phase forms during cooling below the martensite start temperature, Ms, on the close- packed planes of the parent fcc phase according to one or more of the established orientation relationships (Kurdjumov-Sachs, Nishiyama-Wasserman, and Greninger-Troiano) for the fcc to bcc transformation. The EBSD results also show that the orientation of the taenite and/or tetrataenite regions at the interfaces of prior α2 (martensite) laths, is the same as that of the single crystal parent taenite γ phase of the meteorite. Therefore, the parent taenite γ was retained at the interfaces of martensite laths during cooling after the formation of martensite. The formation of plessite is described by the reaction γ → α2 + γ → α + γ. This reaction is inconsistent with the decomposition of martensite laths to form γ phase as described by the reaction γ → α2 → α + γ, which is the classical mechanism proposed by previous investigators. The varying orientations of the fine exsolved taenite and/or tetrataenite within decomposed martensite laths, however, are a response to the decomposition of α2 (martensite) laths at low temperature and are formed by the reaction α2 → α + γ. more...
- Published
- 2006
- Full Text
- View/download PDF
50. The formation of the Widmanstätten structure in meteorites
- Author
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J. Yang and Joseph I. Goldstein
- Subjects
Kamacite ,Crystallography ,Phase boundary ,Geophysics ,Meteorite ,Space and Planetary Science ,Chemistry ,Chondrite ,Plessite ,Widmanstätten pattern ,Iron meteorite ,Phase diagram - Abstract
We have evaluated various mechanisms proposed for the formation of the Widmanstatten pattern in iron meteorites and propose a new mechanism for low P meteoritic metal. These mechanisms can also be used to explain how the metallic microstructures developed in chondrites and stony-iron meteorites. The Widmanstatten pattern in high P iron meteorites forms when meteorites enter the three- phase field α + γ + Ph via cooling from the γ + Ph field. The Widmanstatten pattern in low P iron meteorites forms either at a temperature below the (α + γ)/(α + γ + Ph) boundary or by the decomposition of martensite below the martensite start temperature. The reaction γ → α + γ, which is normally assumed to control the formation of the Widmanstatten pattern, is not applicable to the metal in meteorites. The formation of the Widmanstatten pattern in the vast majority of low P iron meteorites (which belong to chemical groups IAB-IIICD, IIIAB, and IVA) is controlled by mechanisms involving the formation of martensite α2. We propose that the Widmanstatten structure in these meteorites forms by the reaction γ → α2 + γ → α + γ, in which α2 decomposes to the equilibrium α and γ phases during the cooling process. To determine the cooling rate of an individual iron meteorite, the appropriate formation mechanism for the Widmanstatten pattern must first be established. Depending on the Ni and P content of the meteorite, the kamacite nucleation temperature can be determined from either the (γ + Ph)/(α + γ + Ph) boundary, the (α + γ)/(α + γ + Ph) boundary, or the Ms temperature. With the introduction of these three mechanisms and the specific phase boundaries and the temperatures where transformations occur, it is no longer necessary to invoke arbitrary amounts of under-cooling in the calculation of the cooling rate. We conclude that martensite decomposition via the reactions γ → α2 → α + γ and γ → α2 + γ → α + γ are responsible for the formation of plessite in irons and the metal phases of mesosiderites, chondrites, and pallasites. The hexahedrites (low P members of chemical group IIAB) formed by the massive transformation through the reaction γ → αm → α at relatively high temperature in the two- phase α + γ region of the Fe-Ni-P phase diagram near the α/(α + γ) phase boundary. more...
- Published
- 2005
- Full Text
- View/download PDF
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