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All sourcesNASA NTRSDOE OSTI
NASA NTRS2026

Thermochemical Stability of Ca2Yb8(SiO4)6O2 Apatite in Presence of Molten Calcium-Magnesium-Aluminosilicate (CMAS)

Thermochemical stability of ytterbium silicon oxyapatite Ca 2 Yb 8 (SiO 4 ) 6 O 2 (CYbS) in the presence of molten calcium-magnesium aluminosilicate (CMAS) has been investigated at elevated temperatures for consideration as a thermal and environmental barrier coating (T/EBC) material. CYbS apatite powder was synthesized from the constituent oxides via a solid-state reaction method. Hot-pressed apatite substrates were exposed to molten CMAS at 1200, 1300, and 1400 °C for 1, 10, and 50 h. Development of phases in the interaction region of the heat-treated specimens was monitored using scanning electron microscopy, transmission electron microscopy, high-angle annular dark-field imaging, selected area electron diffraction, and energy dispersive x-ray spectroscopy. Monoclinic cyclosilicate Ca 3 Yb 2 (Si 3 O 9 ) 2 formed from interaction of CYbS apatite with CaO in the CMAS melt at the apatite-CMAS reaction front and continued to nucleate and grow within the residual CMAS in diffusion couples annealed for 1 to 50 h at 1200 °C as well as in those heat treated at 1300 °C for 1 h. Residual CMAS was depleted of Ca when cyclosilicate was present. Dendritic wollastonite (CaSiO3) was observed within the residual CMAS in couples annealed at 1200 and 1300 °C. Ingress of molten CMAS, because of its exponential decrease in viscosity, occurred through open pores and along the grain boundaries of the apatite substrates without any detectable chemical reaction at 1300 and 1400 °C. Results of this study indicate that Ca 2 Yb 8 (SiO 4 ) 6 O 2 apatite has the potential to mitigate the CMAS corrosion up to about 1200 °C but not at higher temperatures.

Narottam P Bansal↗
NASA NTRS2019

Electron Beam Damage in Apatite: Limitations for SKα Measurements of S6+/∑S

In magmatic systems, the availabil- ity of excess oxygen that can react with multivalent elements such as Fe and S to change their charge (oxi- dation of Fe2+ to Fe3+ or reduction of S6+ to S2-) is characterized by a parameter called the oxygen fugacity (ƒO2). The ƒO2 controls the availability of these ions and consequently the minerals—and the chemistry of those minerals—that crystallize from a melt. Mineral mode and chemistry control how magmas evolve, and given that ƒO2 varies by many orders of magnitude on different planets [2], understanding the ƒO2 of a mag- ma is critical to relating observations about a magma to the body on which it forms. The mineral apatite was long thought to only incor- porate S6+ in a coupled substitution for P5+, but recently natural apatites with S2- were identified in lunar mare basalts that crystallized at low ƒO2 [3]. This suggests that apatite can be used as a monitor of ƒO2 assuming that one can 1) measure S6+/∑S (S6+ over total sulfur), and 2) determine some partitioning relationship be- tween apatite and melt for S6+ and S2-. The most common method for measuring S6+/∑S is X-ray Absorption Near-Edge Spectroscopy (XANES), but given the limited access to synchrotron facilities, it is wise to explore the potential of other methods for measuring S6+/∑S. One such possible method relies upon the shift in energy of the sulfur K-α peak on the electron microprobe. However, apatite is subject to well-documented beam damage [4, 5], so it is neces- sary to evaluate under what conditions can reliable S6+ ethod.

de Chizelle, J. Kuhn↗
NASA NTRSDate not supplied

The oxidation state of sulfur in lunar apatites in meteorites versus Apollo rocks

Sulfur can be present in apatite mineral grains as S6+ [1], S2- [2], or a mixture of the two [3, 4]. The proportion of S6+ to S2- present in the apatite is thought to be predominantly controlled by the prevailing oxygen fugacity (fO2) conditions during crystallization (along with temperature, pressure, and major element composition; [2-4]). Measurements of apatites and proximal residual glass in the lunar basalts 12039 and 10044 by X-ray absorption near-edge structure (XANES) spectroscopy show that sulfur occurs as S2- in both the mesostasis glass and apatite when measurements are performed far from cracks or pits in the thin section [2], consistent with other mineralogical indications of low fO2 (∆IW-1) during petrogenesis. However, analyses of apatite grains in both samples that were acquired near cracks or pits in the thin section sometimes revealed minor but nonnegligible spectral evidence for the presence of S6+ (e.g., S6+/ΣS > 0.03; [2]). This evidence was interpreted as either primary S2- altered to S6+ in the thin section, or S6+ of secondary origin, deposited in the fractures of the samples [2, 5]. It is unknown whether this alteration is lunar or terrestrial in origin, with implications for lunar petrogenesis if lunar [e.g., 5], or sample handling and curation if terrestrial [e.g., 6]. Note: Extended abstract on document.

M. Brounce↗
DOE OSTI2023

Thermodynamic characterization of synthetic lead-arsenate apatites with different halogen substitutions

Abstract Thermodynamic parameters have been measured for synthetic analogs of the mimetite-group minerals Pb5(AsO4)3X (X = OH, Cl, Br, I) belonging to the apatite supergroup. Phases precipitated from aqueous solutions under ambient conditions with well characterized structures and compositions were studied. For each phase, dissolution enthalpy was experimentally determined by oxide melt drop solution calorimetry in a molten solvent of sodium molybdate (3Na2O·4MoO3) at 976 K. The enthalpy of formation from the elements ΔHf,elo was calculated using thermochemical cycles and was −3030.6 ± 11.5, −3026.6 ± 15.8, −2967.6 ± 25.0, and −2993.1 ± 12.2 kJ/mol for Pb5.00(AsO4)3.00OH0.86(CO3)0.07, Pb5.00(AsO4)3.00Cl0.80(CO3)0.10, Pb5.00(AsO4)3.00Br0.80(CO3)0.10, and Pb5.00(AsO4)3.00I0.45OH0.35(CO3)0.10, respectively. These ΔHf,elo values exhibit typical trends for apatites: they increased (were less negative) with the increasing molar mass and ionic radius of X and decreased with the electronegativity and ionization energy of X. The compilation and comparison of data for Ca-, Pb-, P-, and As-apatites revealed correlations indicating that thermodynamic enthalpic stability is largely influenced by chemical factors (e.g., differences in electronegativities of the elements, ionization energy, or ionic characteristics of the bonds) and to a lesser extent by physical and geometric parameters in the crystal structure related to the mass and size of the X anion. Using the correlations, it was possible to estimate the value of hitherto unknown ΔHf,elo for Pb5(AsO4)3F, −3144.3 ± 66.5 kJ/mol. The observed relationships apply to the entire apatite supergroup and can be used to predict the values of ΔHf,elo for phases that have not been studied experimentally. The new data on environmentally significant phases will contribute to the modeling of mineral-water interactions, particularly for potential use in the remediation of soils and wastes contaminated with Pb and As and in the immobilization of radioactive waste containing I-129.

Geochemistry & Geophysics↗
NASA NTRS2021

Thermal Expansion Coefficients of Ca2Y8(SiO4)6O2 and Ca2Yb8(SiO4)6O2 Apatite-type Silicates

High temperature X-ray diffraction (XRD) scans of Y2Si2O7 and Yb2Si2O7 reactions with calcium-magnesium-aluminosilicates (CMAS) were utilized to determine thermal expansion coefficients (CTEs) of Ca2Y8(SiO4)6O2 and Ca2Yb8(SiO4)6O2 apatite materials. In order to validate these measurements, the CTEs of Y2Si2O7, Yb2Si2O7 and SiO2 were also determined from the same scans. The directional CTEs for γ-Y2Si2O7 were determined to be αa=5.84×10-6/K, αb=6.81×10-6/K and αc=0.81×10-6/K, and β-Yb2Si2O7 was determined to have values of αa=6.89×10-6/K, αb=4.81×10-6/K and αc=2.78×10-6/K. The average CTEs of γ-Y2Si2O7 and β-Yb2Si2O7 were determined to be 4.5×10-6/K and 4.7×10-6/K, respectively, which agreed with previous analyses. Ca2Y8(SiO4)6O2 exhibited directional CTEs of αa=9.36×10-6/K and αc=7.95×10-6/K (averaged between two sets of data), whereas Ca2Yb8(SiO4)6O2 had values that were very similar (αa=9.63×10-6/K, αc=7.45×10-6/K). Both results for the Ca2RE8(SiO4)6O2 apatites correlated well with the limited data on apatite-type silicates available in literature.

rare earth↗
DOE OSTI2020

Structural Assessment of Fluorine, Chlorine, Bromine, Iodine, and Hydroxide Substitutions in Lead Arsenate Apatites (Mimetites)–Pb 5 (AsO 4 ) 3 X

Five lead-arsenate apatites (mimetites)-Pb 5 (AsO 4 ) 3 X—where X denotes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and hydroxide (OH)—were synthesized via precipitation from aqueous solutions. The crystal structures were determined through Rietveld refinement of powder synchrotron X-ray data. All the compounds crystallized in the hexagonal class symmetry (space group P6 3 /m). The Rietveld refinement indicated that mimetite-Cl, -Br, -I, and -OH had an anion deficiency at position X. Substitution of halogens in a mimetite structure brought about systematic changes in unit-cell parameters, interatomic distances, and metaprism twist angles φ, proportional to the substituted halogen’s ionic radius. Mimetite-OH did not follow the linear correlations determined within the series. Twist angle φ, a useful device for monitoring changes in apatite topology, ranged from 20.34° for mimetite-F to 11.42° for mimetite-I. The geometric method has been proposed for determining the diameter of hexagonal channels hosting halogens in apatites. A comparison of the results with halogenated pyromorphites showed similar systematic trends: the substitutions in mimetites have comparable effect on the interatomic distances as in their phosphorous analogues.

58 GEOSCIENCES↗
DOE OSTI2021

X-ray diffraction and in situ pressurization of dentine apatite reveals nanocrystal modulus stiffening upon carbonate removal

Bone-like materials comprise carbonated-hydroxyapatite nanocrystals (c-Ap) embedding a fibrillar collagen matrix. The mineral particles stiffen the nanocomposite by tight attachment to the protein fibrils creating a high strength and toughness material. The nanometer dimensions of c-Ap crystals make it very challenging to measure their mechanical properties. Mineral in bony tissues such as dentine contains 2~6 wt.% carbonate with possibly different elastic properties as compared with crystalline hydroxyapatite. Here we determine strain in biogenic apatite nanocrystals by directly measuring atomic deformation in pig dentine before and after removing carbonate. Transmission electron microscopy revealed the platy 3D morphology while atom probe tomography revealed carbon inside the calcium rich domains. High-energy X-ray diffraction in combination with in situ hydrostatic pressurization quantified reversible c-Ap deformations. Additionally, crystal strains differed between annealed and ashed (decarbonated) samples, following 1 or 10 h heating at 250 °C or 550 °C respectively. Measured bulk moduli (K) and a-/c-lattice deformation ratios (η) were used to generate synthetic K syn and ηsyn identifying the most likely elastic constants C 33 and C 13 for c-Ap. These were then used to calculate the nanoparticle elastic moduli. For ashed samples, we find an average E 11 =107 GPa and E 33 =128 GPa corresponding to ~5% and ~17% stiffening of the a-/c-axes of the nanocrystals as compared with the biogenic nanocrystals in annealed samples. Ashed samples exhibit ~10% lower Poisson's ratios as compared with the 0.25~0.36 range of carbonated apatite. Carbonate in c-Ap may therefore serve for tuning local deformability within bony tissues.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Exploration of a Combined LIBS and LA-ICP-MS Approach for Apatite Characterisation

A combined laser‐induced breakdown spectroscopy (LIBS) and laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) method is demonstrated for comprehensive apatite analysis. These measurements provide elemental imaging that can be used as a screening technique for chemical selection of grains for subsequent analysis (e.g., U‐Pb geochronology) or can be used to understand elemental distributions within a single grain that would have direct textural‐chemical implications (e.g., zoning patterns). Adding LIBS as a simultaneous measurement, to LA‐ICP‐MS U‐Pb geochronology, allowed for the direct determination of F (H and O show promise for future applications) in addition to major and trace elements of interest. Here, the quantitative measurements were validated against a series of apatites with known values and used to characterise a wide range of samples. Fluorine detection limits were determined to be as low as 70 μg g ‐1 F (broadband CMOS detector) and 4.2 μg g ‐1 F (ICCD detector). U‐Pb age dating was simultaneously collected by LA‐ICP‐MS with the quantitative elemental data from LIBS, providing a comprehensive method for geochronology.

Apatite↗
NASA NTRS2018

Chlorine Isotopic Compositions of Apatite in Apollo 14 Rocks: Evidence for Widespread Vapor-Phase Metasomatism on the Lunar Nearside ~4 Billion Years Ago

Compared to most other planetary materials in the Solar System, some lunar rocks display high delta (sup 37) Cl signatures. Loss of Cl in a H<<Cl environment has been invoked to explain the heavy signatures observed in lunar samples, either during volcanic eruptions onto the lunar surface or during large scale degassing of the lunar magma ocean. To explore the conditions under which Cl isotope fractionation occurred in lunar basaltic melts, five Apollo 14 crystalline samples were selected (14053,19, 14072,13, 14073,9, 14310,171 along with basaltic clast 14321,1482) for in situ analysis of Cl isotopes using secondary ion mass spectrometry. Cl isotopes were measured within the mineral apatite, with delta (sup 37) Cl values ranging from +14.6 ± 1.6 per mille to +40.0 ± 2.9 per mille. These values expand the range previously reported for apatite in lunar rocks, and include some of the heaviest Cl isotope compositions measured in lunar samples to date. The data here do not display a trend between increasing rare earth elements contents and delta (sup 37) Cl values, reported in previous studies. Other processes that can explain the wide inter- and intra-sample variability of delta (sup 37) Cl values are explored. Magmatic degassing is suggested to have potentially played a role in fractionating Cl isotope in these samples. Degassing alone, however, could not create the wide variability in isotopic signatures. Our favored hypothesis, to explain small scale heterogeneity, is late-stage interaction with a volatile-rich gas phase, originating from devolatilization of lunar surface regolith rocks ~4 billion years ago. This period coincides with vapor-induced metasomastism recorded in other lunar samples collected at the Apollo 16 and 17 landing sites, pointing to the possibility of widespread volatile-induced metasomatism on the lunar nearside at that time, potentially attributed to the Imbrium formation event.

apatit↗
DOE OSTI2023

Metallization and spin fluctuations in Cu-doped lead apatite

An electronic structure and magnetic properties analysis of the recently proposed Cu-doped lead apatite is performed. Here, we show that electronic structures of differently Cu-substituted structures are characterized by localized molecular Cu-O bands at or near the Fermi level. The Cu substitutions can happen at both Pb1 and Pb2 sites, leading to metallic and semiconducting systems differently. The electronic systems in these bands are highly unstable magnetically and form clusters of rigidly ferromagnetically coupled magnetic moments on Cu and neighboring oxygen atoms with a total moment of about 1µ B . The ground state of uniformly Cu-doped lead apatite appears to be magnetic and semiconducting. The nonuniform distribution of two Cu atoms at the nearest Pb2 sites leads to an antiferromagnetic semiconducting state with formation energy close to uniformly distributed Cu configurations. The inclusion of quantum spin fluctuations confirms the stability of magnetic Cu-O clusters. Our calculations revealed the absence of the long-range magnetic order between uniformly distributed Cu-O clusters, creating the spin glass type of system.

36 MATERIALS SCIENCE↗
NASA NTRS1985

An apatite-rich, ferroan, mafic lithology from lunar meteorite ALHA81005

Antarctic meteorite Allan Hills A81005 is a polymict, anorthositic regolith breccia of lunar origin. Most lithic clasts in the meteorite 81005 are similar to those from other lunar rocks. However, some, such as 'hyperferroan' anorthosites, have not been reported before the discovery of 81005. On the basis of the composition of some granulitic polymict breccia clasts, it appears possible that other new lithologies are present. In the present paper, a description is provided of an unusual, apatite-rich, ferroan, mafic lithology, and its origin is discussed. Three clasts which appeared to contain two minerals were separated as samples ,32 ,28 and ,27. It is found in a study that the clast in ,32 and ,28 is an apatite-rich ferroan anorthositic troctolite which is probably pristine. This rock is unique among lunar samples. On the basis of an evaluation of the significance of the results of the study, it is concluded that complex processes were apparently involved in the evolution of the primitive lunar crust.

Goodrich, C. A.↗
NASA NTRS1994

Partial melting of apatite-bearing charnockite, granulite, and diorite: Melt compositions, restite mineralogy, and petrologic implications

Melting experiments (P = 6.9 kbar, T = 850-950 deg C, NNO is less than fO2 is less than HM) were done on mafic to felsic charnockites, a dioritic gneiss, and a felsic garnet granulite, all common rock types in the Grenville basement of eastern North America. A graphite-bearing granulite gneiss did not melt. Water (H2O(+) = 0.60 to 2.0 wt %) is bound in low-grade, retrograde metamorphic minerals and is consumed during the earliest stages of melting. Most melts are water-undersaturated. Melt compositions range from metaluminous, silicic granodiorite (diorite starting composition) to peraluminous or weakly metaluminous granites (all others). In general, liquids become more feldspathic, less silicic, and less peraluminous and are enriched in FeO, MgO, and TiO2 with increasing temperature. Residual feldspar mineralogy controls the CaO, K2O, and Na2O contents of the partial melts and the behavior of these elements can be used, particularly if the degree of source melting can be ascertained, to infer some aspects of the feldspar mineralogy of the source. K-feldspar, a common restite phase in the charnockite and granulite (but not the diorite) should control the behavior of Ba and, possibly, Eu in these systems and yield signatures of these elements that can distinguish source regions and, in some cases, bulk versus melt assimilation. Apatite, a common restite phase, is enriched in rare earth elements (REE), especially middle REE. Retention of apatite in the restite will result in steep, light REE-enriched patterns for melts derived from the diorite and charnockites.

Beard, James S.↗
NASA NTRS2018

Tracing the Evolution of Hydrogen in the Martian Crust Through Laboratory Studies of Apatite

Introduction: Northwest Africa (NWA) 7034 and its pairings represent a regolith breccia of basaltic bulk composition, the finegrained matrix of which bears a strong resemblance to the major and trace element composition estimated for the ancient southern highlands crust on Mars. Therefore, NWA 7034 may represent a key sample for constraining the composition of the Martian crust, particularly the ancient highlands. Here we seek to constrain the hydrogen isotopic composition of the Martian crust using apatite [Ca5 (PO4)3(Cl,F,OH)]. Apatites across all lithologic domains in NWA 7034 have been affected by a Pb-loss event at ~1.5 Ga before present and so they are unlikely to have retained magmatic volatile composition and are more likely to have equilibrated with fluids within the Martian crust that may or may not have exchanged with the Martian atmosphere.

Barnes, Jessica↗
NASA NTRS2020

Apatites in Gale Crater

ChemCam is an active remote sensing instrument suite that has operated successfully on MSL since landing Aug. 6th, 2012. It uses laser pulses to remove dust and to analyze rocks up to 7 m away. Laser-induced breakdown spectroscopy (LIBS) obtains emission spectra of materials ablated from the samples in electronically excited states. The intensities of the emission lines scale with the abundances of the related element. ChemCam is sensitive to most major rock-forming elements as well as to a set of minor and trace elements such as F, Cl, Li, P, Sr, Ba, and Rb. The measured chemical composition can then be used to infer the mineralogical composition of the ablated material. Here, we report a summary of inferred apatite detections along the MSL traverse at Gale Crater. We present the geologic settings of these findings and derive some interpretations about the formation conditions of apatite in time and space.

Forni, O.↗
NASA NTRSDate not supplied

The Oxidation State of Sulfur in Martian Apatite- Implications for Redox of Surficial Processes

Meteorites from Mars record fO2 values of ∆IW = -1 to +6.5 [1, 2]. This relatively large range in fO2 has been attributed to igneous processes like differentiation and assimilation, or sometimes to alteration [2, 3], modifying the range inherited from the Martian mantle, which is thought to be closer to the values recorded by lunar basalts (~∆IW -1 [e.g., 1]). Trace element compositions reveal that those Martian meteorites that are light Rare Earth Elements (LREE) enriched record higher fO2 values than those that are LREE-depleted [2]. Sulfur (S) has been used to track redox and alteration processes on Mars because it can be present in multiple redox states varying from S2- in magmatic sulfides to S6+ in sedimentary sulfate deposits and alteration products like jarosite [4, 5]. Apatite (Ca5(PO4)3(F,Cl,OH)) is found in many of the Martian meteorites as a late stage crystallizing mineral. It can incorporate both S^(2-) [6] or S^(6+) [7] or mixtures of both [7, 8] in its crystal structure, and it has been hypothesized that the relative proportions of S^(2-) and S^(6+) in apatite will depend on the prevailing fO2 in which it formed (along with P, T, and major element composition). Note: Extended abstract on document.

P. Chowdhury↗
NASA NTRS2024

Mechanisms of Apatite Formation in Reactions of Yb 2-2x Gd 2x Si 2 O 7 with CMAS

Bulk β-Yb 1.9 Gd 0.1 Si 2 O 7 , β-Yb 1.6 Gd 0.4 Si 2 O 7 , and γ-Yb 1.4 Gd 0.6 Si 2 O 7 , along with baseline γ-Y 2 Si 2 O 7 and β-Yb 2 Si 2 O 7 were investigated in contact with a molten silicate to determine mechanisms of thermochemical degradation. A model 30.67CaO-8.25MgO-12.81AlO 1.5- 48.27SiO 2 silicate composition was deposited on the surfaces of the samples at a loading of ~2 mg/cm 2 . Reactions with the molten silicate resulted in the formation of a silicate apatite layer, which has been shown to reduce further molten silicate infiltration. Additions of gadolinium up to 30 mol% to Yb 2 Si 2 O 7 reduced infiltration up to ~60% compared to baseline Yb 2 Si 2 O 7 , but additional exposure time at temperature resulted in loss of the apatite layer. The results herein indicate that doping with gadolinium disilicate may not be beneficial in the long term degradation of disilicate-based EBCs by molten silicates.

Jamesa L. Stokes↗
DOE OSTI2024

Electron–Phonon Coupling in Copper-Substituted Lead Phosphate Apatite

Recent reports of room-temperature, ambient pressure superconductivity in copper-substituted lead phosphate apatite, commonly referred to as LK99, have prompted numerous theoretical and experimental studies into its properties. As the electron–phonon interaction is a common mechanism for superconductivity, the electron–phonon coupling strength is an important quantity to compute for LK99. In this work, we compare the electron–phonon coupling strength among the proposed compositions of LK99. The results of our study are in alignment with the conclusion that LK99 is a candidate for low-temperature, not room-temperature, superconductivity if electron–phonon interaction is to serve as the mechanism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Annealing of ion tracks in apatite under pressure characterized in situ by small angle x-ray scattering

Fission track thermochronology is routinely used to investigate the thermal history of sedimentary basins, as well as tectonic uplift and denudation rates. While the effect of temperature on fission track annealing has been studied extensively to calibrate the application of the technique, the effect of pressure during annealing is generally considered to be negligible. However, a previous study suggested elevated pressure results in a significantly different annealing behaviour that was previously unknown. Here, we present a method to study track annealing in situ under high pressure by using synchrotron- based small angle x-ray scattering (SAXS). To simulate fission tracks in a controlled environment, ion tracks were created in apatite from Durango, Mexico using 2 GeV Au or Bi ions provided by an ion accelerator facility. Samples were annealed at 250°C at approximately 1 GPa pressure using diamond anvil cells (DAcs) with heating capabilities. Additional in situ annealing experiments at ambient pressure and temperatures between 320 and 390°C were performed for comparison. At elevated pressure a significantly accelerated annealing rate of the tracks was observed compared with annealing at ambient pressure. However, when extrapolated to geologically relevant temperatures and pressures, the effects become very small. The measurement methodology presented provides a new avenue to study materials behaviour in extreme environments.

58 GEOSCIENCES↗