The Experts below are selected from a list of 2076 Experts worldwide ranked by ideXlab platform

J. I. Goldstein - One of the best experts on this subject based on the ideXlab platform.

  • ordinary chondrite metallography part 1 fe ni taenite cooling experiments
    Meteoritics & Planetary Science, 2003
    Co-Authors: R J Reisener, J. I. Goldstein
    Abstract:

    Cooling rate experiments were performed on P-free Fe-Ni alloys that are compositionally similar to ordinary chondrite metal to study the taenite → taenite + Kamacite reaction. The role of taenite grain boundaries and the effect of adding Co and S to Fe-Ni alloys were investigated. In P-free alloys, Kamacite nucleates at taenite/taenite grain boundaries, taenite triple junctions, and taenite grain corners. Grain boundary diffusion enables growth of Kamacite grain boundary precipitates into one of the parent taenite grains. Likely, grain boundary nucleation and grain boundary diffusion are the applicable mechanisms for the development of the microstructure of much of the metal in ordinary chondrites. No intragranular (matrix) Kamacite precipitates are observed in P-free Fe-Ni alloys. The absence of intragranular Kamacite indicates that P-free, monocrystalline taenite particles will transform to martensite upon cooling. This transformation process could explain the metallography of zoneless plessite particles observed in H and L chondrites. In P-bearing Fe-Ni alloys and iron meteorites, Kamacite precipitates can nucleate both on taenite grain boundaries and intragranularly as Widmanstatten Kamacite plates. Therefore, P-free chondritic metal and P-bearing iron meteorite/ pallasite metal are controlled by different chemical systems and different types of taenite transformation processes.

  • Ordinary chondrite metallography: Part 2. Formation of zoned and unzoned metal particles in relatively unshocked H, L, and LL chondrites
    Meteoritics & Planetary Science, 2003
    Co-Authors: R J Reisener, J. I. Goldstein
    Abstract:

    We studied the metallography of Fe-Ni metal particles in 17 relatively unshocked ordinary chondrites and interpreted their microstructures using the results of P-free, Fe-Ni alloy cooling experiments (described in Reisener and Goldstein 2003). Two types of Fe-Ni metal particles were observed in the chondrites: zoned taenite + Kamacite particles and zoneless plessite particles, which lack systematic Ni zoning and consist of tetrataenite in a Kamacite matrix. Both types of metal particles formed during metamorphism in a parent body from homogeneous, P-poor taenite grains. The phase transformations during cooling from peak metamorphic temperatures were controlled by the presence or absence of grain boundaries in the taenite particles. Polycrystalline taenite particles transformed to zoned taenite + Kamacite particles by Kamacite nucleation at taenite/taenite grain boundaries during cooling. Monocrystalline taenite particles transformed to zoneless plessite particles by martensite formation and subsequent martensite decomposition to tetrataenite and Kamacite during the same cooling process. The varying proportions of zoned taenite + Kamacite particles and zoneless plessite particles in types 46 ordinary chondrites can be attributed to the conversion of polycrystalline taenite to monocrystalline taenite during metamorphism. Type 4 chondrites have no zoneless plessite particles because metamorphism was not intense enough to form monocrystalline taenite particles. Type 6 chondrites have larger and more abundant zoneless plessite particles than type 5 chondrites because intense metamorphism in type 6 chondrites generated more monocrystalline taenite particles. The distribution of zoneless plessite particles in ordinary chondrites is entirely consistent with our understanding of Fe-Ni alloy phase transformations during cooling. The distribution cannot be explained by hot accretion-autometamorphism, post-metamorphic brecciation, or shock processing.

  • the metallographic cooling rate method revised application to iron meteorites and mesosiderites
    Meteoritics & Planetary Science, 2001
    Co-Authors: W D Hopfe, J. I. Goldstein
    Abstract:

    A major revision of the current Saikumar and Goldstein (1988) cooling rate computer model for Kamacite growth is presented. This revision incorporates a better fit to the ala + y phase boundary and to the yla + y phase boundary particularly below the monotectoid temperature of 400 "C. A reevaluation of the latest diffusivities for the Fe-Ni system as a function of Ni and P content and temperature is made, particularly for Kamacite diffusivity below the paramagnetic to ferromagnetic transition. The revised simulation model is applied to several iron meteorites and several mesosiderites. For the mesosiderites we obtain a cooling rate of 0.2 "ClMa, about lox higher than the most recent measured cooling rates. The cooling rate curves Erom the current model do not accurately predict the central nickel content of taenite halfwidths smaller than -10 pm. This result calls into question the use of conventional Kamacite growth models to explain the microstructure of the mesosiderites. Kamacite regions in mesosiderites may have formed by the same process as decomposed duplex plessite in iron meteorites.

  • The microstructure and formation of duplex and black plessite in iron meteorites
    Geochimica et Cosmochimica Acta, 1993
    Co-Authors: J. Zhang, David J. Williams, J. I. Goldstein
    Abstract:

    The plessite microstructure in the taenite region of the Widmanstatten pattern of two iron meteorites (Grant and Carlton) was studied using high spatial resolution analytical electron microscopy. The microstructure of the plessite varies because the martensite transformation and subsequent decom position during cooling of the meteorite occurs over a wide temperature range and a broad taenite Ni composition range. The plessite has a progressively finer two-phase structure as the taenite Ni content increases. Duplex plessite is observed optically at Ni contents below '— 13 to 14 wt% and is formed by martensite decomposition at martensite lath boundaries to a micro-structure of tetrataenite (FeNi) pre cipitates in a Kamacite (a) matrix. These precipitates have a relatively large size (typically >200 nm wide), and have a habit plane of { 11 l}f which is parallel to the { 1 l0}. The precipitates also have a Ni composition of '—50 wt%, and are in equilibrium with the matrix phase, Kamacite, of '--'4 wt% Ni. The growth of tetrataenite in low Ni duplex plessite is controlled by volume diffusion and the Ni content of the tetrataenite and Kamacite is consistent with that of the Widmanstatten pattern a/'y interface ('—50 wt% Ni tetrataenite/'—'4 wt% Ni Kamacite). Black plessite is observed optically at Ni contents above 13 to 14 wt% Ni. The black plessite contains tetrataenite which forms by martensite decomposition at martensite lath boundaries and also within the original plate or lath martensite below '--'400°C. The FeNi precipitates within the original martensite are very thin plates or fine needles (typically 10 to 20 nm wide). The plates or needles have a habit plane of {l 1 I}r. which is parallel to the {l I0}, have a Ni composition of '—'57 to 60 wt% Ni, and are surrounded by a matrix phase, Kamacite, of '--'10 wt% Ni. The growth of the tetrataenite (FeNi) within the martensite and the presence of a high Ni content in tetrataenite and matrix Kamacite are a result of partial interface control at temperatures below '--'400°C.

Sylvain Pont - One of the best experts on this subject based on the ideXlab platform.

  • minor and trace element concentrations in adjacent Kamacite and taenite in the krymka chondrite
    Meteoritics & Planetary Science, 2016
    Co-Authors: Neda Meftah, Smail Mostefaoui, E H Guedda, Albert Jambon, Sylvain Pont
    Abstract:

    We report in situ NanoSIMS siderophile minor and trace element abundances in individual Fe-Ni metal grains in the unequilibrated chondrite Krymka (LL3.2). Associated Kamacite and taenite of 10 metal grains in four chondrules and one matrix metal were analyzed for elemental concentrations of Fe, Ni, Co, Cu, Rh, Ir and Pt. The results show large elemental variations among the metal grains. However, complementary and correlative variations exist between adjacent Kamacite-taenite. This is consistent with the unequilibrated character of the chondrite and corroborates an attainment of chemical equilibrium between the metal phases. The calculated equilibrium temperature is 446 ± 9 °C. This is concordant with the range given by Kimura et al. (2008) for the Krymka post-accretion thermal metamorphism. Based on Ni diffusivity in taenite, a slow cooling rate is estimated of the Krymka parent body that does not exceed ~1K/Myr, which is consistent with cooling rates inferred by other workers for unequilibrated ordinary chondrites. Elemental ionic radii might have played a role in controlling elemental partitioning between Kamacite and taenite. The bulk compositions of the Krymka metal grains have non-solar (mostly subsolar) element/Ni ratios suggesting the Fe-Ni grains could have formed from distinct precursors of non-solar compositions or had their compositions modified subsequent to chondrule formation events.

  • Minor and trace element concentrations in adjacent Kamacite and taenite in the Krymka chondrite
    Meteoritics and Planetary Science, 2016
    Co-Authors: Neda Meftah, Smail Mostefaoui, E H Guedda, Albert Jambon, Sylvain Pont
    Abstract:

    We report in situ NanoSIMS siderophile minor and trace element abundances in individual Fe-Ni metal grains in the unequilibrated chondrite Krymka (LL3.2). Associated Kamacite and taenite of 10 metal grains in four chondrules and one matrix metal were analyzed for elemental concentrations of Fe, Ni, Co, Cu, Rh, Ir and Pt. The results show large elemental variations among the metal grains. However, complementary and correlative variations exist between adjacent Kamacite-taenite. This is consistent with the unequilibrated character of the chondrite and corroborates an attainment of chemical equilibrium between the metal phases. The calculated equilibrium temperature is 446 ± 9 °C. This is concordant with the range given by Kimura et al. (2008) for the Krymka post-accretion thermal metamorphism. Based on Ni diffusivity in taenite, a slow cooling rate is estimated of the Krymka parent body that does not exceed ~1K/Myr, which is consistent with cooling rates inferred by other workers for unequilibrated ordinary chondrites. Elemental ionic radii might have played a role in controlling elemental partitioning between Kamacite and taenite. The bulk compositions of the Krymka metal grains have non-solar (mostly subsolar) element/Ni ratios suggesting the Fe-Ni grains could have formed from distinct precursors of non-solar compositions or had their compositions modified subsequent to chondrule formation events.

Neda Meftah - One of the best experts on this subject based on the ideXlab platform.

  • minor and trace element concentrations in adjacent Kamacite and taenite in the krymka chondrite
    Meteoritics & Planetary Science, 2016
    Co-Authors: Neda Meftah, Smail Mostefaoui, E H Guedda, Albert Jambon, Sylvain Pont
    Abstract:

    We report in situ NanoSIMS siderophile minor and trace element abundances in individual Fe-Ni metal grains in the unequilibrated chondrite Krymka (LL3.2). Associated Kamacite and taenite of 10 metal grains in four chondrules and one matrix metal were analyzed for elemental concentrations of Fe, Ni, Co, Cu, Rh, Ir and Pt. The results show large elemental variations among the metal grains. However, complementary and correlative variations exist between adjacent Kamacite-taenite. This is consistent with the unequilibrated character of the chondrite and corroborates an attainment of chemical equilibrium between the metal phases. The calculated equilibrium temperature is 446 ± 9 °C. This is concordant with the range given by Kimura et al. (2008) for the Krymka post-accretion thermal metamorphism. Based on Ni diffusivity in taenite, a slow cooling rate is estimated of the Krymka parent body that does not exceed ~1K/Myr, which is consistent with cooling rates inferred by other workers for unequilibrated ordinary chondrites. Elemental ionic radii might have played a role in controlling elemental partitioning between Kamacite and taenite. The bulk compositions of the Krymka metal grains have non-solar (mostly subsolar) element/Ni ratios suggesting the Fe-Ni grains could have formed from distinct precursors of non-solar compositions or had their compositions modified subsequent to chondrule formation events.

  • Minor and trace element concentrations in adjacent Kamacite and taenite in the Krymka chondrite
    Meteoritics and Planetary Science, 2016
    Co-Authors: Neda Meftah, Smail Mostefaoui, E H Guedda, Albert Jambon, Sylvain Pont
    Abstract:

    We report in situ NanoSIMS siderophile minor and trace element abundances in individual Fe-Ni metal grains in the unequilibrated chondrite Krymka (LL3.2). Associated Kamacite and taenite of 10 metal grains in four chondrules and one matrix metal were analyzed for elemental concentrations of Fe, Ni, Co, Cu, Rh, Ir and Pt. The results show large elemental variations among the metal grains. However, complementary and correlative variations exist between adjacent Kamacite-taenite. This is consistent with the unequilibrated character of the chondrite and corroborates an attainment of chemical equilibrium between the metal phases. The calculated equilibrium temperature is 446 ± 9 °C. This is concordant with the range given by Kimura et al. (2008) for the Krymka post-accretion thermal metamorphism. Based on Ni diffusivity in taenite, a slow cooling rate is estimated of the Krymka parent body that does not exceed ~1K/Myr, which is consistent with cooling rates inferred by other workers for unequilibrated ordinary chondrites. Elemental ionic radii might have played a role in controlling elemental partitioning between Kamacite and taenite. The bulk compositions of the Krymka metal grains have non-solar (mostly subsolar) element/Ni ratios suggesting the Fe-Ni grains could have formed from distinct precursors of non-solar compositions or had their compositions modified subsequent to chondrule formation events.

H.j. Axon - One of the best experts on this subject based on the ideXlab platform.

  • A metallographic study of the Angra dos Reis (iron) meteorite
    2015
    Co-Authors: H.j. Axon, C. V. Waine
    Abstract:

    SUMMARY. The Angra dos Reis (iron) has been studied metallogl"aphically and an attempt has been made to discuss the circumstances under which the following elements of structure formed: clear etching and frosty etching Kamacite, decorated Neumann lines, giant rhabdites, plate rbabdites, rhabdite clusters, microrhabdites, cohenite, and remelted troilite. The remelted troilite is taken to indicate a shock event. However, since there are no metallographically visible indications of shock in the Kamacite and since the back reflection X-ray diffraction pattern shows only very faint Debye-Scherrer arcs superimposed on a pattern of sharp spots, it is concluded that the shock event ook place at a temperature that allowed shock effects to anneal out of the Kamacite almost completely. A sub-microscopic precipitate in the metallic matrix is observable with the electron microscope and may represent the final precipitation of phosphide from shocked Kamacite. TnE Angra dos Reis (iron) is recorded by Hey (I966) as a nickel-poor ataxite. The main mass is in the Vatican collection and Salpeter 0957) has recorded it as a hexa-hedrite under the name Pseudo-Angra dos Reis. Our own examination indicates a hexahedrite structure. Salpeter reports that a complete individual of 6175 g and clearly showing flight markings was part of a collection, which was sent from Brazi

  • Copyright the Mineralogical Society
    2015
    Co-Authors: H.j. Axon, J. Kinder, C. W. Haworth, J. W. Horsfield
    Abstract:

    have provided the source of chromium and the Kamacite may have provided the source of nitrogen for this product

  • A metallographic and microprobe study of the metal phases in the Weekeroo Station meteorite
    2015
    Co-Authors: H.j. Axon, P. L. Smith
    Abstract:

    SUMMARY. The Kamacite contains a general precipitation of micrometre-sized particles of exsolved taenite. Larger particles are found decorating Neumann lines and at Kamacite grain boundaries. The coexisting Kamacite and taenite appear to have nickel contents of 6"4 % and about 53 %, which are consistent with a temperature ofabout 330-60 ~ on the binary iron-nickel equilibrium diagram. WEEKEROO STATION is reported by Hey (1966) as a brecciated coarsest octahedrite of true band width 2"55 mm and with silicate inclusions. The macrostructure has been figured by Nininger 095o) and Wasserburg and Burnett (1969) show a new photo-graph of the same section. Nickel contents of 6"89, 7"5 I, and 7.25 have been reporte

  • A metallographic and microprobe study of the Brenham pallasite
    2015
    Co-Authors: H.j. Axon, E. D. Yardley
    Abstract:

    SUMMARY. A metallographic study has been made of the macroscopic and microscopic features of the Brenham pallasite. The microprobe has been used to investigate the condition of Kamacite inter-faces with second Kamacite grains, olivine, schreibersite, troilite, and taenite and of taenite interfaces with olivine. The results indicate that grain-boundary migration of nickel may be important in these structures. THE structure of the metallic phase in the Brenham pallasite has recently been reported by Massalski and Park (1964) who conclude that the conditions of cooling in the later stages of the formation of the Kamacite taenite structure were similar to, but probably rather more rapid than, the conditions that applied at the similar stage in the formation of octahedrites. Goldstein and Short (I967), however, have proposed that the metal in Brenham shows a particularly slow cooling rate. Wahl (1965) has discussed the general question of pallasite structures and has proposed that they formed in low-gravitation environments at the centres of parent bodies. The present study was conducted on a slice measuring lO•215 7 cm obtained as specimen ~o'I84 from Ward's Natural Science Foundation. The specimen was sectioned fo

  • A metallographic and microprobe examination of a metallic nodule from the Bondoc Peninsula mcteorite
    2015
    Co-Authors: H.j. Axon, M. J. Naslr
    Abstract:

    THE Bondoc Peninsula meteorite appears to be unstable and is disintegrating as the result of terrestrial corrosion. The meteorite is complex with occasional 1 to 3 cm dia. 'Nodules ' of 'iron-class ' material, fig. I, within which are numerous non-metallic inclusions. These range in size from o'5-I-5 mm and vary in shape from the extremes of angular to globular, shown in figs. 2 and 3. The metallic groundmass of fig. I is a polycrystalline array of Kamacite grains that are equant in shape and about 3 to 4 mm dia. The boundaries between these Kamacite grains are heavily invaded by corrosion product. The films of cracked schreibersite and strips of cornpositionally zoned taenite that are present at the Kamacite boundaries each contribute about a % by volume and their average Ni contents are about 45 wt % and 4o wt ~ respectively. When these figures are combined with the average 6-2 wt % Ni, o.75 wt % Co, and o.o2 wt % P of the Kamacite the resulting bulk composition of the metal is-- ~ 7"5 wt % Ni,-- ~ o'7 Wt~o Co, N o'3 wt % P. Nital etching reveals partially annealed Neumann bands in the Kamacite, indicat-ing a late stage reheating below about 5oo ~ Hbwever, the M profile method of Wood (1967) when applied to the zoned taenite yields a cooling rate of o. I-o- 5 ~ before this reheating event

David N. Seidman - One of the best experts on this subject based on the ideXlab platform.