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An Electron Microscope Investigation of Eight Ataxite and One Mesosiderite Meteorites

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Lehigh University Lehigh Preserve Theses and Dissertations 1-1-1981 An electron microscope investigation of eight ataxite and one mesosiderite meteorites. Paul M. Novotny Follow this and additional works at: http://preserve.lehigh.edu/etd Part of the Materials Science and Engineering Commons Recommended Citation Novotny, Paul M., "An electron microscope investigation of eight ataxite and one mesosiderite meteorites." (1981). Theses and Dissertations. Paper 1944. This Thesis is brought to you for free and open access by Lehigh Preserve. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Lehigh Preserve. For more information, please contact [email protected]. AN ELECTRON MICROSCOPE INVESTIGATION OF EIGHT ATAXITE AND ONE MESOSIDERITE METEORITES by Paul M. Novotny A Thesis Presented to the Graduate Committee of Lehigh University in Candidacy for the Degree of Master of Science in Metallurgy and Materials Engineering Lehigh University 1981 ProQuest Number: EP76217 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest EP76217 Published by ProQuest LLC (2015). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 CERTIFICATE OF APPROVAL This thesis is accepted in partial fulfillment of the requirements for the degree of Master of Science. (date) (Drofessor in Charge) (Department Chairman) ii TABLE OF CONTENTS Page CERTIFICATE OF APPROVAL ii TABLE OF CONTENTS iii LIST OF TABLES v LIST OF FIGURES vi ABSTRACT 1 INTRODUCTION 3 BACKGROUND Classification of Meteorites 5 Metallic Phases in Meteorites 7 Estherville 14 Ataxites 16 Analytical Electron Microscopy 17 Cooling Rates 24 Fe-Ni Phase Diagram 27 EXPERIMENTAL PROCEDURES Light and Scanning Electron Optical Sample Preparation 29 TEM/STEM Sample Preparation 30 STEM Procedure 31 K-Factor Determination 34 RESULTS Estherville 37 Microstructure - Light and SEM 37 iii Microchemistry 38 Microprobe Analysis 38 STEM Analysis 38 TEM Results 39 Microstructure 39 Diffraction 40 Ataxites 41 Light and SEM Microstructure Examination 41 TEM Results 44 Microchemistry 4 7 K_ ... Results 49 Te-Ni DISCUSSIONS Interfall Measurements 52 X-ray Analysis 56 Estherville 58 Ataxites 67 a Decomposition 72 SUMMARY 75 REFERENCES 161 APPENDIX 167 VITA 169 iv LIST OF TABLES Page Table 1 Comparison of Structural and Chemical 80 Classes Table 2 Ataxites Investigated in This Study 81 FIGURE TITLES Pa PP Figure 1 Log-log plot of gallium vs. nickel. The 82 chemical groupings of the iron meteorites are shown. Figure 2 Log-log plot of germanium vs. nickel. Note 82 the similar groupings" as in Figure 1. Figure 3 Fe-Ni and Fe-Ni(P) Phase Diagrams. 83 Figure k Austcnite start and martensite start 83 temperatures for the Fe-Ni binary system. Figure 5 M-shaped composition profile across a kamacite- 84 taenite-plessite-taenite-kamacite region. Figure 6 Schematic composition profiles of plessite 85 a+ formation. a) y •+ a+y b) Y "* <*2 "* Y Figure 7 Light photomicrograph of the cloudy zone in 86 a taenite lamellae in Estherville. Figure 8 TEM bright field photomicrograph of the cloudy 86 zone in Carlton. Figure 9 Schematic ray diagram of a TEM/STEM. 87 Figure 10 Rapid method for determining the cooling rates 88 of iron meteorites. Figure 11 Light photomicrograph of taenite (T) finger 88 in kamacite (K) matrix. 2% Nital etch. vi Figure 12 Light photomicrograph of cloudy zone (C.Z.) 89 with its rim of cleartaenite (C.T.). 22 Nital etch. Figure 13 Microprobe trace (black dots) across area 89 to be made into TEM/STEM disc. Polarized light reveals ordered taenite as regions of light and dark contrast within the clear taenite. Unetched. Polarized light. Figure 14 SEK photomicrograph of taenite finger. Note 90 veinlikc network within the cloudy zone. 27. Nital etch. Figure 15 SEM photomicrograph of cloudy zone in 90 Estherville. A vein of taenite is seen as well as the expected honeycomb structure. The kamacite appears as the etched out phase. 2% Nital etch. Figure 16 SEM photomicrograph of Estherville cloudy 91 zone near clear taenite. 2% Nital etch. Figure 17 SEM photomicrograph of Estherville cloudy 91 zone. Taenite crystallites can be seen starting to coalesce at several locations. 2% Nital etch. Figure 18 SEM photomicrograph of taenite finger in 92 cloudy zone. Note how some taenite vii crystallites appear to have coalesced or grown together. 22 Nital etch. Figure 19 SEM photomicrograph showing region of 92 Estherville sample that was spark machined into 3 mm rod, 2% Nital. Figure 20 Composition profile obtained from the micro- 93 probe trace across the taenite shown in Figure 13. Figure 21 Composition profile obtained from SEM 94 trace across the Widmanstatten a/clear taenite interface in Estherville. Figure 22 Composition profile obtained from STEM 95 trace across the clear taenite/cloudy zone interface. Figure 23 Composition profile obtained from STEM 96 trace across a single y crystallite bordered by martensite within the cloudy zone. Figure 24 TEM bright field image of cloudy zone in 97 Estherville (T=taenite). Figure 25 TEM bright field image of cloudy zone. Note 97 the fine structure within the bec phase. Figure 2C TEM bright field image of cloudy zone showing 98 the fine structure within the bec phase. viii Figure 27 TEM bright field of the cloudy zone. The 98 lath-like fine structure of the bec phase is clearly evident. Figure 28 [100] zone axis diffraction pattern from 99 clear taenite. Note the superlattice spots indicating ordering. Figure 29 [100] zone axis diffraction pattern from 99 clear taenite. Note Che superlattice spots. Figure 30 [100 ] zone axis diffraction pattern from 100 clear taenite. Note the superlattice spots. Figure 31 a) [l00] zone axis microdiffraction pattern 101 from clear taenite. Note the superlattice spots. b) Indexed 1100] pattern with all superlattice spots. Figure 32 f122 ] clear taenite zone axis diffraction 102 pattern with superlattice spots. Figure 33 Bright field (a) and centered dark field (b) 103 from ordered spot in diffraction pattern shown in Figure 33c. Note small particles of ordered taenite in 33b. 33d shows the indexed diff- raction pattern. ix Figure 34 Microdiffraction pattern from a single 105 Y crystallite in the cloudy zone. The pattern is a [100] zone axis with [001] superlattice spots. Figure 35 Microdiffraction pattern from a single 105 Y crystallite in the cloudy zone. [l00] zone axis with [001] superlattice spots. Figure 36 Bright field (a) centered dark field 106 from Y spot (b) and centered dark field from superlattice spot (c) from diffraction pattern (d) of cloudy zone. Note particulate nature of both Y and ordered Y in the cloudy zone. Figure 37 Bright field (a) centered dark field from 108 Y spot (b) and centered dark field from superlattice spot (c) from diffraction pattern (d) of the cloudy zone. Note par- ticulate nature of both Y and ordered Y. A V Figure 38 Microdiffraction patterns from two adjacent 110 Y crystallites in the cloudy zone. [100] zone axis patterns. Note the superlattice spots. Figure 39 a) Microdiffraction pattern from clear 111 adjacent to the cloudy zone, b) Microdiffraction pattern from y crystallite within the cloudy zone. Figure 40 a) Selected area diffraction pattern of 112 the cloudy zone. b) Indexed pattern showing Nishyama-Wassterman orientation. Figure 41 Light photomicrograph of Arltunga. 2% 113 Nital etch. Figure 42 SEM photomicrograph of Arltunga. Note 113 Widmanstatten a grains with taenite rims. 2% Nital etch. Figure A3 SEM photomicrograph of Arltunga. Note 114 internal structure of the taenite rims. 2Z Nital etch. Figure 44 SEM photomicrograph of Arltunga. Internal 114 structure within the taenite is very evident. 22 Nital etch. Figure 45 Light photomicrograph of Nordheiin. Large 115 Widmanstatten a platelets can be seen in center of picture. 27, Nital etch. Figure 46 SEM photomicrograph of Nordheim. Ribbon-like 115 taenite rims are clearly seen surrounding the kamacite. 2% Nital etch. Figure 47 SEM photomicrograph of Nordheim. Multigranular 116 kamacite is seen to be surrounded by taenite. xi 27. Nital etch. Figure 48 SEM photomicrograph of Nordheim. No internal 116 structure is seen within the taenite. 2% Nital etch. Figure 49 Light photomicrograph of Guffey showing 117 Widmanstatten a -♦• a+y type plessite. 27. Nital. Figure 50 SEM photomicrograph of Guffey. Note 117 multigranular kamacite structure with taenite rims. 2% Nital etch. Figure 51 SEM photomicrograph of Guffey. Fine 118 structure within taenite can be seen. 2% Nital. Figure 52 SEM photomicrograph of Guffey. Fine 118 structure within taenite is clearly seen. 2% Nital. Figure 53 Light photomicrograph of Tawallah Valley. H9 Widmanstatten a platelets are shown in a matrix of fine plessite. 2% Nital etch. Figure 54 SEM photomicrograph of Tawallah Valley. 119 Fine plessite from decomposed martensite is present between a platelets. 27. Nital etch. Figure 55 SEM photomicrograph of Tawallah Valley. Fine 120 ■0 plessite structure is evident. 27, Nital etch, xii Figure 56 SEM photomicrograph of Tawallah Valley. 120 Left side of picture shows the part of the Y rim surrounding an a platelet. Note the various size y rods in the plessite. 21 Nital. Figure 57 Light photomicrograph of Hoba. A kamacite 121 platelet surrounded by its taenite rim is shown in the matrix of plessite. 2% Nital etch. Figure 58 SEM photomicrograph of fine plessite structure 121 in Hoba.
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  • The Formation of the Widmanstätten Structure in Meteorites

    The Formation of the Widmanstätten Structure in Meteorites

    Meteoritics & Planetary Science 40, Nr 2, 239–253 (2005) Abstract available online at http://meteoritics.org The formation of the Widmanstätten structure in meteorites J. YANG* and J. I. GOLDSTEIN Department of Mechanical and Industrial Engineering, College of Engineering, University of Massachusetts, Amherst, Massachusetts 01003, USA *Corresponding author. E-mail: [email protected] (Received 16 October 2003; revision accepted 13 November 2004) Abstract–We have evaluated various mechanisms proposed for the formation of the Widmanstätten 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 Widmanstätten 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 Widmanstätten 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 Widmanstätten pattern, is not applicable to the metal in meteorites. The formation of the Widmanstätten 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 Widmanstätten 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.