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NASA NTRSDate not supplied

Contamination, Transportation or Transmutation in LENR Material Analyses

LENR experiments using various loading and triggering mechanisms rely on a variety of elemental and isotopic assays to determine LENR effects. These assays include optical microscopy, Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis (SEM/EDX), X-Ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM). All of these methods observe the surface of a material. By dissolving or vaporizing the sample, Inductively Coupled Plasma Optical Element Spectroscopy (ICP-OES) can determine elemental composition (ppb) or with mass spectroscopy, isotopes (ICP/MS). One can use a focused ion beam (FIB) to cut open a sample and observe the “cut” with either SEM/EDX, or Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS). High Purity Gamma Ray Spectroscopy (HPGe) and alpha/ beta Liquid Scintillator spectroscopy can be used. We’ve employed these assay methods in our NASA GRC research under both the Advanced Energy Conversion and Lattice Confinement Fusion Projects. However, there are limitations associated with each of these methods ranging from handling contamination, instrumental limitations including sensitivity and field of view, and sample preparation.

Low Energy Nuclear Reactions↗
NASA NTRS2007

Multifunctional, High-Temperature Nanocomposites

In experiments conducted as part of a continuing effort to incorporate multifunctionality into advanced composite materials, blends of multi-walled carbon nanotubes and a resin denoted gPETI-330 h (wherein gPETI h is an abbreviation for gphenylethynyl-terminated imide h) were prepared, characterized, and fabricated into moldings. PETI-330 was selected as the matrix resin in these experiments because of its low melt viscosity (<10 poise at a temperature of 280 C), excellent melt stability (lifetime >2 hours at 280 C), and high temperature performance (>1,000 hours at 288 C). The multi-walled carbon nanotubes (MWCNTs), obtained from the University of Kentucky, were selected because of their electrical and thermal conductivity and their small diameters. The purpose of these experiments was to determine the combination of thermal, electrical, and mechanical properties achievable while still maintaining melt processability. The PETI-330/MWCNT mixtures were prepared at concentrations ranging from 3 to 25 weight-percent of MWCNTs by dry mixing of the constituents in a ball mill using zirconia beads. The resulting powders were characterized for degree of mixing and thermal and rheological properties. The neat resin was found to have melt viscosity between 5 and 10 poise. At 280 C and a fixed strain rate, the viscosity was found to increase with time. At this temperature, the phenylethynyl groups do not readily react and so no significant curing of the resin occurred. For MWCNT-filled samples, melt viscosity was reasonably steady at 280 C and was greater in samples containing greater proportions of MWCNTs. The melt viscosity for 20 weightpercent of MWCNTs was found to be .28,000 poise, which is lower than the initial estimated allowable maximum value of 60,000 poise for injection molding. Hence, MWCNT loadings of as much as 20 percent were deemed to be suitable compositions for scale-up. High-resolution scanning electron microscopy (HRSEM) showed the MWCNTs to be well dispersed in the polymer matrices, while high-resolution transmission electron microscopy shows splits in the walls of the MWCNTs but no catastrophic breakage of tubes. To further assess processing characteristics prior to scale-up, samples containing 10, 15, and 20 weight-percent of MWCNTs were processed through a laboratory melting extruder. HRSEM of the extruded fibers shows significant alignment of MWCNTs in the flow direction (see figure). For the samples containing 20 weight-percent of MWCNTs, difficulties were encountered during feeding, and the temperature of a rotor in the extruder rose to 245 C because of buildup of frictional heat; this indicates that materials of this type having MWCNT concentrations .20 weight- percent may not be melt-processable. On the basis of the results from the foregoing characterizations, samples containing 10, 15, and 20 weight-percent of MWCNTs were scaled up to masses of .300 g and used to make specimens having dimensions of 10.2 by 15.2 by 0.32 cm. These specimens were molded by (1) injecting the mixtures, at temperatures between 260 and 280 C, into a tool made of the low-thermal-expansion alloy InvarR and then (2) curing for 1 hour at 371 C. The tool was designed to impart shear during the injection process in an attempt to achieve some alignment of the MWCNTs in the flow direction.

Connell, John W.↗
NASA NTRS2009

Stardust Interstellar Preliminary Examination (ISPE)

In January 2006 the Stardust sample return capsule returned to Earth bearing the first solid samples from a primitive solar system body, C omet 81P/Wild2, and a collector dedicated to the capture and return o f contemporary interstellar dust. Both collectors were approximately 0.1m(exp 2) in area and were composed of aerogel tiles (85% of the co llecting area) and aluminum foils. The Stardust Interstellar Dust Col lector (SIDC) was exposed to the interstellar dust stream for a total exposure factor of 20 m(exp 2-) day during two periods before the co metary encounter. The Stardust Interstellar Preliminary Examination ( ISPE) is a three-year effort to characterize the collection using no ndestructive techniques. The ISPE consists of six interdependent proj ects: (1) Candidate identification through automated digital microsco py and a massively distributed, calibrated search (2) Candidate extr action and photodocumentation (3) Characterization of candidates thro ugh synchrotronbased FourierTranform Infrared Spectroscopy (FTIR), S canning XRay Fluoresence Microscopy (SXRF), and Scanning Transmission Xray Microscopy (STXM) (4) Search for and analysis of craters in f oils through FESEM scanning, Auger Spectroscopy and synchrotronbased Photoemission Electron Microscopy (PEEM) (5) Modeling of interstell ar dust transport in the solar system (6) Laboratory simulations of h ypervelocity dust impacts into the collecting media

Westphal, A. J.↗
NASA NTRS2024

Ternary Feldspar Within Felste Clasts From Apollo Impact Melt Breccia 72255

Granitic clasts with unique ternary feldspar compositions have been identified within samples of the layered impact melt breccia from Apollo 17 Station 2 Boulder 1 (72215, 72235, 72255 and 72275), and in a felsite clast from station 3 (73215). These “ternary” compositions seemingly plot within the miscibility gap of the albite-anorthite-orthoclase (Ab-An-Or) system. Feldspars with these compositions have not been identified in terrestrial samples, and equilibrium feldspar compositions from laboratory experiments indicate they would not be thermodynamically stable. Thus, the physiochemical processes involved in forming these unique ternary feldspars remain poorly understood. To better constrain the formation of ternary feldspar within lunar breccias, we have undertaken a coordinated scanning electron microscope (SEM)-based coupled electron backscatter diffraction (EBSD) and energy dispersive spectrometry (EDS), electron microprobe analyzer (EPMA) wavelength dispersive spectrometry, and transmission electron microscopy (TEM) study. The goals of this study are twofold: 1) confirm whether ternary feldspar is present as coherent, single-crystals or sub-microscopic intergrowths of normal compositions, and 2) better constrain the formation conditions of clasts containing ternary feldspar.

T. M. Erickson↗
NASA NTRS2005

Surface and Internal Structure of Pristine Presolar Silicon Carbide

Silicon carbide is the most well-studied type of presolar grain. Isotope measurements of thousands [1,2] and structural data from over 500 individual grains have been reported [3]. The isotope data indicate that approximately 98% originated in asymptotic giant branch stars and 2% in supernovae. Although tens of different polytypes of SiC are known to form synthetically, only two polytypes have been reported for presolar grains. Daulton et al. [3] found that for SiC grains isolated from Murchison by acid treatments, 79.4% are 3C cubic beta-SiC, 2.7% are 2H hexagonal alpha-SiC, 17.1% are intergrowths of and , and 0.9% are heavily disordered. They report that the occurrence of only the and polytypes is consistent with the observed range of condensation temperatures of circumstellar dust for carbon stars. Further constraint on the formation and subsequent alteration of the grains can be obtained from studies of the surfaces and interior structure of grains in pristine form, i.e., prepared without acid treatments [4,5]. The acid treatments remove surface coatings, produce etch pits around defect sites and could remove some subgrains. Surface oxides have been predicted by theoretical modeling as a survival mechanism for SiC grains exposed to the hot oxidizing solar nebula [6]. Scanning electron microscopy studies of pristine SiC shows some evidence for the existence of oxide and organic coatings [4]. We report herein on transmission electron microscopy studies of the surface and internal structure of two pristine SiC grains, including definitive evidence of an oxide rim on one grain, and the presence of internal TiC and AlN grains.

Stroud, Rhonda, M.↗
NASA NTRS1995

A new technique for ground simulation of hypervelocity debris

A series of hypervelocity damage experiments were preformed on spacecraft materials. These experiments employed a technique which accelerates micro flyer plates simulating space debris traveling at 3 to 8 km/sec. The apparatus used to propel the micro flyer plates was compact and fit well into a space environmental chamber equipped with instrumentation capable of analyzing the vapor ejected from the sample. Mechanical damage to the sample was also characterized using optical and scanning electron microscpopy. Data for this work was obtained from hypervelocity impacts on a polysulfone resin and a graphite polysulfone composite. Polysulfone was selected because it was flown on the Long Duration Exposure Facility (LDEF) which spent several years in low earth orbit (LEO). Chemistry of the vapor produced by the impact was analyzed with a time of flight mass spectrometer, (TOFMS). This represents the first time that ejected vapors from hypervelocity collisions were trapped and analyzed with a mass spectrometer. With this approach we are able to study changes in the vapor chemistry as a function of time after impact, obtain a velocity measurement of the vapor, and estimate a temperature of the surface at time of impact using dynamic gas equations. Samples of the vapor plume may be captured and examined by transmission electron microscopy. Studies were also conducted to determine mechanical damage to a graphite polysulfone composite and a polysulfone resin. Impact craters were examined under optical and scanning electron microscopes. The collision craters in the matrix were typical of those shown in conventional shock experiments. However, the hypervelocity collisions with the graphite polysulfone composite were remarkably different than those with the resin.

Roybal, R.↗
NASA NTRS1990

Growth and characterization of CdS crystals

A growth method for the physical vapor transport of compound semiconductors in closed ampoules is described. With the unique techniques applied in the heat treatment of the starting materials and the temperature profiles provided by the three-zone translational furnace, large crystals of CdS have been grown successfully by the method at lower temperatures than previously used. Both unseeded and seeded growth have been investigated. The CdS crystals were examined using optical and scanning electron microscopies (SEM) to study the microstructure and the dislocation etch-pits. The crystals were further characterized by infrared (IR) and ultraviolet (UV) transmission measurements.

Su, Ching-Hua↗
NASA NTRS1985

Corrosion behavior of surface films on boron-implanted high purity iron and stainless steels

Boron (dose, 2 x 10 to the 17th ions/sq cm) was implanted into high purity iron, AISI 316 austenitic stainless steel, and AISI 440C martensitic stainless steel, at 40 keV. The film structure of implanted samples was examined and characterized by contrast and diffraction analyses utilizing transmission electron microscopy. The effect of B(+) ion implantation on the corrosion behavior was studied using the potentiodynamic polarization technique. Tests were performed in deaerated 1 N H2SO4 and 0.1 M NaCl solutions. Scanning electron microscopy was used to examine the morphology of the corroded surfaces after testing.

Kim, H. J.↗
NASA NTRS2008

Transmission Electron Microscopy of Cometary Residues from Micron-Sized Craters in the Stardust Al-Foils

We report Transmission Electron Microscopy (TEM) investigations of micro-craters that originated from hypervelocity impacts of comet 81P/Wild 2 dust particles on the aluminium foil of the Stardust collector. The craters were selected by Scanning Electron Microscopy (SEM) and then prepared by Focused Ion Beam (FIB) milling techniques in order to provide electron transparent cross-sections for TEM studies. The crater residues contain both amorphous and crystalline materials in varying proportions and compositions. The amorphous component is interpreted as resulting from shock melting during the impact and the crystalline phases as relict minerals. The latter show evidence for shock metamorphism. Based on the residue morphology and the compositional variation, the impacting particles are inferred to have been dominated by mixtures of submicron olivine, pyroxene and Fe-sulfide grains, in agreement with prior results of relatively coarse-grained mineral assemblages in the aerogel collector.

Leroux, Hugues↗
NASA NTRS1975

Fretting of titanium at temperatures to 650 C in air

Fretting wear experiments were conducted on high-purity titanium at temperatures up to 650 C. Results indicate that up to about 500 C, the fretting wear increases with temperature. A further increase in the temperature up to 650 C results in decreasing fretting wear. This change in trend of fretting wear with temperature is shown to be associated with a change in oxidation rate. Additional experiments at 650 C showed a transmission from a low rate of fretting wear to a higher rate occurred after exposure to a number of fretting cycles; the number of cycles required to cause this transition was dependent on the normal load. Scanning electron microscopy studies revealed that this transition was marked by cracking and disruption of the surface oxide film. A model was proposed that coupled the oxidation rate kinetics of titanium at 650 C with the occurrence of wear at the surface of the oxide film.

Bill, R. C.↗
NASA NTRS1982

Irradiation effects in rapidly and conventionally solidified alloys. Phase stability in rapidly solidified N i-Nb under Ni ion irradiation

Two alloy compositions in the Ni-Nb system (Ni60Nb40 and Ni85Nb15) were produced by rapidly quenching from the melt with the piston anvil technique. The Ni60Nb40 was transformed to a metastable, partially crystalline state by heat treatment in a differential scanning calorimeter. The Ni85Nb15 was fully crystalline, with the majority of the grains composed of collections of primary dendrite arms. Both compositions were irradiated with 4 MeV Ni++ ions. The irradiation induced microstructures were examined by transmission electron microscopy and compared with thermally aged samples. The thermal evolution was arrested by ion irradiation in the temperature range studied, by inhibiting the nucleation of the NiNb phase. No irradiation induced voids were observed. It is found that the ion irradiation drives the microstructure along a different path than thermal evolution.

Source record↗
NASA NTRS1998

Control of seed development in Arabidopsis thaliana by atmospheric oxygen

Seed development is known to be inhibited completely when plants are grown in oxygen concentrations below 5.1 kPa, but apart from reports of decreased seed weight little is known about embryogenesis at subambient oxygen concentrations above this critical level. Arabidopsis thaliana (L.) Heynh. plants were grown full term under continuous light in premixed atmospheres with oxygen partial pressures of 2.5, 5.1, 10.1, 16.2 and 21.3 kPa O2, 0.035 kPa CO2 and the balance nitrogen. Seeds were harvested for germination tests and microscopy when siliques had yellowed. Seed germination was depressed in O2 treatments below 16.2 kPa, and seeds from plants grown in 2.5 kPa O2 did not germinate at all. Fewer than 25% of the seeds from plants grown in 5.1 kPa oxygen germinated and most of the seedlings appeared abnormal. Light and scanning electron microscopic observation of non-germinated seeds showed that these embryos had stopped growing at different developmental stages depending upon the prevailing oxygen level. Embryos stopped growing at the heart-shaped to linear cotyledon stage in 5.1 kPa O2, at around the curled cotyledon stage in 10.1 kPa O2, and at the premature stage in 16.2 kPa O2. Globular and heart-shaped embryos were observed in sectioned seeds from plants grown in 2.5 kPa O2. Tissue degeneration caused by cell autolysis and changes in cell structure were observed in cotyledons and radicles. Transmission electron microscopy of mature seeds showed that storage substances, such as protein bodies, were reduced in subambient oxygen treatments. The results demonstrate control of embryo development by oxygen in Arabidopsis.

NASA Discipline Plant Biology↗
NASA NTRS2026

Investigation of Bipropellant Plume-Induced Contamination Effects on Coverglass Materials

Contamination and degradation of external spacecraft materials by unburned and partially combusted species from bipropellant thruster plumes has long been observed as a key component of the induced space environment. Space shuttle flight experiments and returned flight hardware from the International Space Station (ISS) have both experienced microscopic impact features induced by high-velocity thruster plume droplets. Analytical results have shown that droplet impingement angle relative to a receiving surface plays a key role in the surface damage. Although impacts with normal impingement angles contribute more severely to surface degradation than highly oblique angles, surface effects at higher impingement angles should not be dismissed. Thruster plume-induced materials degradation is a complex phenomenon that depends on a variety of parameters, including but not limited to material type, system temperature and pressure, plume composition, and thruster firing specifications such as number of pulses, pulse duration, and sample distance from the thruster. For space applications, attaining the vacuum pressure and temperature conditions necessary for flight-like plume expansion and exposure conditions is not a trivial task. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt, DLR) is a facility uniquely capable of simulating such conditions. Test coupons were exposed to bipropellant thruster firings under high vacuum at the DLR facility. Percent area coverage (PAC) and droplet size distributions were evaluated for the uncoated and coated solar array coverglass materials over a range of impingement angles (0̊ to 75̊). A post-test imaging workflow was developed that aimed to quantify changes in sample surface morphology obtained from scanning electron microscopy (SEM) images using the Image Processing and Analysis in Java (ImageJ) tool; an opensource image processing software. The goal was to create a framework through which to evaluate the effect of bipropellant-induced PAC and droplet size distribution on solar array coverglass optical transmission losses. Understanding this relationship is important because optical transmission losses are known to lead to current reduction in solar power generation systems. In addition to the development of surface characterization workflows, valuable lessons learned as they pertain to future investigations and experiments will be discussed. The authors hope that sharing these lessons will facilitate more utilization of DLR’s unique capabilities as well as open the conversation for how best to address experimental characterization of flight-like plume expansion and its impacts on materials surface degradation effects.

Gateway↗
NASA NTRS1998

Electronic Properties of Carbon Nanotubes and Junctions

Metallic and semiconducting Single Wall Carbon Nanotubes (CNT) have recently been characterized using scanning tunneling microscopy (STM) and the manipulation of individual CNT has been demonstrated. These developments make the prospect of using CNT as molecular wires and possibly as electronic devices an even more interesting one. We have been modeling various electronic properties such as the density of states and the transmission coefficient of CNT wires and junctions. These studies involve first calculating the stability of junctions using molecular dynamics simulations and then calculating the electronic properties using a pi-electron tight binding Hamiltonian. We have developed the expertise to calculate the electronic properties of both finite-sized CNT and CNT systems with semi-infinite boundary conditions. In this poster, we will present an overview of some of our results. The electronic application of CNT that is most promising at this time is their use as molecular wires. The conductance can however be greatly reduced because of reflection due to defects and contacts. We have modeled the transmission through CNT in the presence of two types of defects: weak uniform disorder and strong isolated scatterers. We find that the conductance is affected in significantly different manners due to these defects Junctions of CNT have also been imaged using STM. This makes it essential to derive rules for the formation of junctions between tubes of different chirality, study their relative energies and electronic properties. We have generalized the rules for connecting two different CNT and have calculated the transmission and density of states through CNT junctions. Metallic and semiconducting CNT can be joined to form a stable junction and their current versus voltage characteristics are asymmetric. CNT are deformed by the application of external forces including interactions with a substrate or other CNT. In many experiments, these deformation are expected to occur naturally. We will present some preliminary results of our calculations of the modification of CNT electronic properties as a result of deformations.

Anantram, M. P.↗
NASA NTRS2006

Microstructural Study of Micron-Sized Craters Simulating Stardust Impacts in Aluminum 1100 Targets

Various microscopic techniques were used to characterize experimental micro- craters in aluminium foils to prepare for the comprehensive analysis of the cometary and interstellar particle impacts in aluminium foils to be returned by the Stardust mission. First, SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive X-ray Spectroscopy) were used to study the morphology of the impact craters and the bulk composition of the residues left by soda-lime glass impactors. A more detailed structural and compositional study of impactor remnants was then performed using TEM (Transmission Electron Microscopy), EDS, and electron diffraction methods. The TEM samples were prepared by Focused Ion Beam (FIB) methods. This technique proved to be especially valuable in studying impact crater residues and impact crater morphology. Finally, we also showed that InfraRed microscopy (IR) can be a quick and reliable tool for such investigations. The combination of all of these tools enables a complete microscopic characterization of the craters.

Leroux, Hugues↗
NASA NTRS1985

Some strategies for quantitative scanning Auger electron microscopy

The general applicability of power law forms of the background in electron spectra is pointed out and exploited for background removal from under Auger peaks. This form of B(E) is found to be extremely sensitive to instrumental alignment and to fault-free construction - an observation which can be used to set up analyser configurations in an accurate way. Also, differences between N(E) and B(E) can be used to derive a spectrometer transmission function T(E). The questions of information density in an energy-analysing spatially-resolving instrument are addressed after reliable instrumental characterization has been established. Strategies involving ratio histograms, showing the population distribution of the ratio of a pair of Auger peak heights, composition scatter diagrams and windowed imaging are discussed and illustrated.

Browning, R.↗
NASA NTRSDate not supplied

High Resolution Imaging and Analysis of Terrestrial Impact Glass: Amorphous Materials, Phyllosilicates and Everything in Between

Introduction: Impact cratering is one of the most ubiquitous geologic processes shaping the surface of all solid bodies in our solar system. Impacts are also a major source of clay minerals, poorly crystalline clay-like phases and amorphous (i.e., lacking long-range atomic order) materials on Earth and Mars. Phyllosilicates and amorphous materials have consistently formed a major component (~20-70 wt%) of every single drilled rock and soil sample in Gale Crater on Mars, as determined by the CheMin instrument on Curiosity. The origin of the amorphous component is speculative, but could be primary impact or volcanic-produced glass(es) deposited via aeolian or fluvial processes, secondary aqueous alteration products or chemical precipitates; it is likely to be a combination of all three possibilities. Efforts to determine the composition of these materials across the rover’s traverse through Gale Crater are ongoing. Naturally occurring amorphous phases are found in a variety of environments on Earth, and terrestrial analogue studies may help shed light on how they may have formed on Mars. Primary and altered impact glass are likely widespread on Mars and may have contributed to the amorphous component found throughout Gale Crater. In its pristine, unaltered state, impact glass (i.e., melt glass) is considered amorphous. However, truly unaltered glass is rarely preserved in crater fill impactites as it quickly alters in the post-impact environ-ment, commonly forming a mixture of hydrated aluminosilicate phases whose structures are not always discernable at the microscale (i.e., they may be amorphous or contain short-range order). These phases are part of an incredibly complex group of materials; differences in their composition and crystalline structure (or lack thereof) and genetic relationship to the more well-crystalline clay minerals are often only discernable at the nanoscale, beyond the resolution of traditional X-ray diffractometers (XRD) and scanning electron microscopes/microprobes (SEM/EPMA) alone. In this contribution, we summarize recent results from ongoing characterization of clay minerals, poorly crystalline clay-like phases, and amorphous materials preserved in altered terrestrial impact glass from the Chicxulub (~66 Ma) and Ries (~15 Ma) impact structures. This work has been performed using a combination of high-resolution transmission electron microscopy (HR-TEM), SEM, microprobe/EPMA, Raman spectroscopy and XRD.

Impact crater↗
NASA NTRS2013

Transmission Electron Microscopy of Itokawa Regolith Grains

Introduction: In a remarkable engineering achievement, the JAXA space agency successfully recovered the Hayabusa space-craft in June 2010, following a non-optimal encounter and sur-face sampling mission to asteroid 25143 Itokawa. These are the first direct samples ever obtained and returned from the surface of an asteroid. The Hayabusa samples thus present a special op-portunity to directly investigate the evolution of asteroidal sur-faces, from the development of the regolith to the study of the effects of space weathering. Here we report on our preliminary TEM measurements on two Itokawa samples. Methods: We were allocated particles RA-QD02-0125 and RA-QD02-0211. Both particles were embedded in low viscosity epoxy and thin sections were prepared using ultramicrotomy. High resolution images and electron diffraction data were ob-tained using a JEOL 2500SE 200 kV field-emission scanning-transmission electron microscope. Quantitative maps and anal-yses were obtained using a Thermo thin-window energy-dispersive x-ray (EDX) spectrometer. Results: Both particles are olivine-rich (Fo70) with μm-sized inclusions of FeS and have microstructurally complex rims. Par-ticle RA-QD02-0125 is rounded and has numerous sub-μm grains attached to its surface including FeS, albite, olivine, and rare melt droplets. Solar flare tracks have not been observed, but the particle is surrounded by a continuous ~50 nm thick, stuctur-ally disordered rim that is compositionally similar to the core of the grain. One of the surface adhering grains is pyrrhotite show-ing a S-depleted rim (~8-10 nm thick) with nanophase Fe metal grains (<5 nm) decorating the outermost surface. The pyrrhotite displays a complex superstructure in its core that is absent in the S-depleted rim. Particle RA-QD02-0211 contains solar flare particle tracks (~2x109 cm-2) and shows a structurally disordered rim ~100 nm thick. The track density corresponds to a surface exposure of ~103-104 years based on the track production rate of [1]. The dis-ordered rim is nanocrystalline with minor amorphous material between crystalline domains. Quantitative element maps show the outermost ~10 nm of the disordered rim is Si-rich. Discussion and Conclusions: Both particles record the ef-fects of space weathering processes on Itokawa. Noguchi et al. [2] proposed that the disordered rims they observed on Itokawa particles largely result from solar wind radiation damage and we arrive at a similar conclusion for the two particles we analyzed. The microstructure of the S-depleted layer on the pyrrhotite grain in RA-QD02-0125 is similar to that observed in troilite irradiated with ~1018 4 kV He+ [3, 4]. Prolonged irradiation has also been shown to disorder pyrrhotite such that the superstructure reflec-tions are lost [5].

Keller, Lindsay P.↗