Investigation of nanoprecipitates within meteoritic metals as tracers of early Solar System processes Investigation of nanoprecipitates within meteoritic metals as tracers of early Solar System processes Goals: Here is proposed a TEM- and micro-PIXE-based study of nanoprecipitate structures, compositions, and distributions within iron meteorites and iron-rich meteorites. The preliminary studies show that nanoprecipitates are the hosts for many of the trace elements in the meteorites, and revealing their distribution is important for understanding the formation and evolution of early Solar System materials. This study will also be extended to metals in bencubbinites (CB chondrites), which are primitive, metal-rich breccias closely related to CR and CH chondrites. The disparate origins and thermal histories of the metal from iron meteorites and bencubbinites will provide valuable information on nanoprecipitate formation and composition. Introduction: Trace elements in iron meteorites are used to model crystallization processes that occured within asteroidal cores and to help elucidate the formation and thermal history of metal during nebular and planetary differentiation processes. While trace elements are determined by a number of analytical techniques such as SIMS and laser ablation ICPMS, these methods provide little data on the trace-element hosts. Studies of steels and alloys reveal that minor and trace elements often concentrate in nanoprecipitates, and there has been extensive study of their formation. Their chemistry, morphology, and distribution provides key information on a samples thermal history. Further, the role of trace elements in alloy formation, solidification, and physical properties is well documented. In contrast, there are virtually no studies of non-metal and PGE-rich nanoprecipitates in iron meteorites. Preliminary work: I initiated a preliminary TEM-EDS-EELS study and found abundant nanoprecipitates of unusual compositions in a range of irons and a stony-iron meteorite: Odessa (IAB-MG), Butler (ungrouped), Gibeon (IVA), Canyon Diablo (IAB-MG), Deep Springs (ungrouped), Brenham (PMG-an), Henbury (IIIAB), and Gressk (IIAB). Nanoprecipitates were extracted by cutting a fresh surface followed by etching with either HNO3/methanol or liquid bromine. This surface was then coated with a thin layer of C, which was subsequently floated off the meteorite by placing the sample back in the etchant. The adhering nanoprecipitates were then studied by TEM-EDS-EELS. A wide range of nanoparticles was discovered, e.g., Pd bearing alloys, PGE nuggets, Ge- and Ga- rich Ni phosphides, Cr-Mo nitrides, and Cr sulfides with PGEs. Composite nanoprecipitates were also found in Canyon Diablo and Odessa, including Cr-Mo nitrides with adhering caps of Pd-Sn or Fe-Ni-P particles. These composite nanoprecipitates provide information on precipitation sequence. Proposed research: Nanoparticles will be extracted and characterized by TEM and electron-beam techniques. Given the challenges of quantifying heavy elements by EDS and EELS, I will also use the micro-PIXE at ASU for their elemental characterization. The goal is to provide information on the nanoscale phase petrology of metal systems, which has an important bearing on trace element behavior and in some cases, larger scale structural characteristics of metal-rich meteorites. Programmatic considerations: The proposed study is designed to make significant advances in our understanding of the solid-state histories of meteorites, their formation, and accretion. By addressing problems related to processes that occurred in the early Solar System, we will provide fundamental new insights into the origin of our Solar System and its solid bodies. As such the proposed research encompasses the scope of the Emerging Worlds program designed to ... answer the fundamental science question of how the Solar System formed and evolved ... and ... conduct scientific invenstigations related to understanding the formation and early evolution of our Solar System.
|Effective start/end date||1/23/17 → 1/22/23|
- NASA: Goddard Space Flight Center: $300,000.00
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