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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Structural, electronic and thermodynamic properties of britholites Ca{sub 10−x}La{sub x}(PO{sub 4}){sub 6−x}(SiO{sub 4}){sub x}F{sub 2} (0 ≤ x ≤ 6): Experiment and theory

Highlights: • The structural and electronic properties of apatites with the general formula Ca{sub 10−x}La{sub x}(PO{sub 4}){sub 6−x}(SiO{sub 4}){sub x}F{sub 2} (0 ≤ x ≤ 6) have been investigated by means of the density functional theory. • The calculated enthalpy of formation of the compounds increased with the substitution degree. • The decrease in stability is probably due to the disorder induced in the Ca/LaO{sub 6}F polyhedron, following the substitution. - Abstract: The apatite-type compounds Ca{sub 10−x}La{sub x}(PO{sub 4}){sub 6−x}(SiO{sub 4}){sub x}F{sub 2} with 0 ≤ x ≤ 6 were prepared using a high temperature solid state reaction and were characterized by X-ray diffraction. The crystal structure, chemical bonding, electronic structure and formation energy of all relaxed structures were analyzed by density functional theory (DFT). The calculated results show that the predicted geometry can well reproduce the structural parameters. The incorporation of La{sup 3+} into the fluorapatite (FA) structure induced especially at the level of the S(2) sites a certain disorder which is responsible for the weakening in the stability with x. Excellent agreement were obtained between the calculated and experimental results. Moreover, the band structure indicates that despite the reduction of the band gap with x content all materials remain insulating.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Carbonated hydroxyapatite starting from calcite and different orthophosphates under moderate hydrothermal conditions: Synthesis and surface reactivity in simulated body fluid

Highlights: • Carbonated apatite (CAP) could be easily obtained from CaCO{sub 3} and orthophosphates. • Highest CaCO{sub 3} dissolution and apatitic carbonate content were obtained with H{sub 3}PO{sub 4}. • A-B-type CAP was formed. • The synthesized CAP was thermally stable up to 1000 °C. • This CAP showed high biomineralization activity before and after thermal treatment. - Abstract: The one-step synthesis of carbonated hydroxyapatite (CAP) using calcite and different orthophosphates was investigated in a closed batch reactor. Only orthophosphoric acid could lead to the complete decomposition of calcite particles, when the reaction temperature was set at 80 °C. On the other hand, the reaction time and the dilution of the initial calcite suspension had no significant influence on the formation of the solid products. CAP was formed as the main crystalline calcium phosphate with the carbonate content in the range of 4.2–4.6 wt.%. The thermal decarbonation of the synthesized CAP started at 750 °C but it was only significant at 1000 °C under air atmosphere. This thermal decarbonation was total at 1200 °C or above. All CAP samples and products following thermal treatments were found bioactive in the test using simulated body fluid (SBF) solution.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Lithium substitution in strontium chlorapatite studied by solid state NMR spectroscopy

Strontium Chlorapatites with various amounts of Li substitution (Sr{sub 10-x}Li{sub x}(PO{sub 4}){sub 6}Cl{sub 2-δ}) were prepared by solid state reaction method and characterized by powder XRD and solid state NMR spectroscopy. XRD reveals shortening of lattice parameters upon Li incorporation. The linewidth of {sup 31}P solid state Magic Angle Spinning NMR spectra decreases with increase in Li content within the apatite phase. This study confirms Li uptake within the apatite phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Lanthanum and neodymium solubility in simplified SiO{sub 2}-B{sub 2}O{sub 3}-Na{sub 2}O-Al{sub 2}O{sub 3}-CaO high level waste glass

Lanthanum and neodymium incorporation in simplified high level waste glasses has been investigated for SiO{sub 2}B{sub 2}O{sub 3}Na{sub 2}OAl{sub 2}O{sub 3}CaO compositions quenched from 1200 degrees C, for varying La /(La + Nd) (atomic) and increasing rare-earth oxides contents. In this system and beyond the solubility limit, rare-earths (RE) elements are reported to form apatite phases with the general formula Ca{sub 2}RE{sub 8}(SiO{sub 4}){sub 6}O{sub 2}. In the current study, speciation of these trivalent RE{sup 3+} cations in both amorphous network and crystal phases was determined from X-ray diffraction, scanning electron microscopy, optical absorption at 10 K, Raman spectroscopy, and electron probe microanalysis. It appeared that RE{sub 2}O{sub 3} solubility was higher for La -rich formulations than for Nd -rich ones and that an increase in the RE oxide content reduces the connectivity of the network building units through formation of non-bridging oxygens at the expense of the oxygen bridges. This depolymerization of the glass network did not affect neodymium environment which consisted in silicate tetrahedra. The composition of the apatite crystals was found to be affected by the La /(La + Nd) of the parent glass and deviation from the ideal composition (Ca{sub 2}RE{sub 8}(SiO{sub 4}){sub 6}O{sub 2}) occurred in the neodymium end of the system. It thus appears that both RE{sub 2}O{sub 3} solubility and crystal composition are strongly dependent on the type and crystal chemistry of the RE elements. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

Sulfur Species in Zinc-Rich Condylar Zones of a Rat Temporomandibular Joint

We performed synchrotron-based micro-X-ray absorption near-edge spectroscopy (µ-XANES) coupled with micro-X-ray fluorescence (µ-XRF) for the identification of elements that included biometal zinc (Zn) and nonmetal sulfur (S) (and its species) in the condylar zones of a rat temporomandibular joint (TMJ). Zone-specific spatial localization of biometal Zn and nonmetal S from a materials viewpoint when correlated with hypoxia inducible factor-1α (HIF-1α) (a surrogate for tissue oxygenation) can provide insights into Zn-specific redox pathways at the vulnerable subchondral interface. Histologic localization of Zn, HIF-1α, and sulfur-rich proteoglycans (PGs) were mapped using an optical microscope. The µ-XRF maps coupled with site-specific micro-X-ray diffraction (µ-XRD) patterns were used to underline Zn-incorporated biological apatite in the subchondral bone and the bone of a rat TMJ condyle. Results demonstrated an association between Zn, PG, and HIF-1α histologic maps with µ-XRF, µ-XANES, and µ-XRD data and provided insights into plausible biological S species in Zn-enriched zones of a rat TMJ condyle. Spatially localized Zn and S underscore their roles in cell and tissue functions in a zone-specific manner. Elemental Zn with organic and inorganic S species at the cartilage-bone interface and the biomineral phase of Zn-enriched biological apatite from subchondral bone to condylar bone were ascertained using µ-XRF-XANES and µ-XRF-XRD. The coupled µ-XRF-XANES in situ complemented with µ-XRF-XRD in situ and immunohistochemistry provided valuable biological insights into zone-specific biological pathways in rat TMJ condyles. Based on these data, we present a workflow to reliably map and correlate S species within Zn-enriched regions of cartilage, bone, and their interface. We suggest the use of this correlative and complementary microspectroscopic spatial information for zone-specific localization of biometal Zn and nonmetal S to gain insights into plausible microanatomy-specific oxidative stress in the TMJ.

apatites↗
DOE OSTI2025

Thermal Characterization and Exhumation of Northwest San Juan Basin Area, NM

The San Juan Basin (SJB), located in southwestern Colorado northwestern New Mexico, containing Paleozoic through middle Cenozoic strata, formed as a partitioned basin approximately 80 Ma in response to the Laramide orogeny. The SJB is a commercially mature, petroleum-producing basin, and currently being explored for CCUS and geothermal resources. Modern heat flow within the SJB is spatially variable with higher geothermal gradients in its northern and eastern portions. The temporal history of the basin thermal history is essential for understanding capacity for carbon storage and geothermal exploration. We present thermochronometric analyses of two surface and two subsurface samples to constrain spatial-temporal thermal evolution of the northwestern San Juan Basin. Apatite (U-Th)/He thermochronometric analyses were conducted on Cliff House and Kirtland Formation outcrops and subsurface samples of the Ojo Alamo and Pictured Cliffs Formations from a DOE funded, CCUS project pilot-well. In addition, vitrinite reflectance data and 1D basin modelling constrain possible time-temperature pathways of the samples in an area where no previous studies have constrained the uplift/exhumation of the Hogback Monocline using thermochronometry. Modeling suggests that elevated subsurface temperatures developed simultaneously with regional late Oligiocene volcanism in the San Juan Volcanic field and timing of maximum burial in the SJB. Late Miocene to Pliocene cooling/exhumation through the apatite (U-Th)/He partial retention zone support stratigraphic evidence of the Colorado Plateau uplift, possibly regional epeirogenic uplift driven by mantle processes.

02 PETROLEUM↗
DOE OSTI2016

Assessment of a Hydroxyapatite Permeable Reactive Barrier to Remediate Uranium at the Old Rifle Site, Colorado - 16193

We have performed an initial evaluation and testing program to assess the effectiveness of a hydroxyapatite (Ca{sub 10}(PO{sub 4}){sub 6}(OH){sub 2}) permeable reactive barrier and source area treatment to decrease uranium mobility at the Department of Energy (DOE) former Old Rifle uranium mill processing site in Rifle, western Colorado. Uranium ore was processed at the site from the 1940's to the 1970's. The mill facilities at the site as well as the uranium mill tailings previously stored there have all been removed. Groundwater in the alluvial aquifer beneath the site still contains elevated concentrations of uranium and is currently used for field tests to study uranium behavior in groundwater and investigate potential uranium remediation technologies. The technology investigated in this work is based on in situ formation of apatite in sediment to create a subsurface apatite PRB and also for source area treatment. The process is based on injecting a solution containing calcium citrate and sodium into the subsurface for constructing the PRB within the uranium plume. As the indigenous sediment micro-organisms biodegrade the injected citrate, the calcium is released and reacts with the phosphate to form hydroxyapatite (precipitate). This paper reports on proof-of-principle column tests with Old Rifle sediment and synthetic groundwater. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2013

Improved zircon fission-track annealing model based on reevaluation of annealing data

The thermal recovery (annealing) of mineral structure modified by the passage of fission fragments has long been studied by the etching technique. In minerals like apatite and zircon, the annealing kinetics are fairly well constrained from the hour to the million-year timescale and have been described by empirical and semi-empirical equations. On the other hand, laboratory experiments, in which ion beams interact with minerals and synthetic ceramics, have shown that there is a threshold temperature beyond which thermal recovery impedes ion-induced amorphization. In this work, it is assumed that this behavior can be extended to the annealing of fission tracks in minerals. It is proposed that there is a threshold temperature, T0, beyond which fission tracks are erased within a time t0, which is independent of the current state of lattice deformation. This implies that iso-annealing curves should converge to a fanning point in the Arrhenius pseudo-space (ln t vs. 1/T). Based on the proposed hypothesis, and laboratory and geological data, annealing equations are reevaluated. The geological timescale estimations of a model arising from this study are discussed through the calculation of partial annealing zone and closure temperature, and comparison with geological sample constraints found in literature. It is shown that the predictions given by this model are closer to field data on closure temperature and partial annealing zone than predictions given by previous models.

annealing↗
DOE OSTI2017

Controls on rare earth element distributions in ancient organic-rich sedimentary sequences: Role of post-depositional diagenesis of phosphorus phases

Here, the processes that dictate the formation and preservation of rare earth element (REE) signatures in ancient marine black shales are incompletely understood, thus potentially limiting the utility of the REEs as geochemical tracers. Here, we report on whole-rock REE analyses of six black shale formations from different ages and depositional settings, which fall within three general groupings: Group 1 is characterized by low whole-rock REE content (ΣREE) (< 250 μg/g) and middle- and heavy-REE-enriched patterns (Gd N /La N < 2, Yb N /La N < 2.5); Group 2 is characterized by low ΣREE (< 250 μg/g) but greater middle-REE-enriched patterns (Gd N /La N > 2, Yb N /La N < 3); and Group 3 is characterized by high ΣREE (> 250 μg/g) and moderately middle-REE-enriched patterns (Gd N /La N ~ 1.5–2.5, Yb N /La N ~ 1). Representative samples from these groups were selected from the Marcellus and Hushpuckney shales and subjected to a multi-step leaching procedure, to isolate four extractable P-phases (reducible, authigenic carbonate-associated, detrital apatite, organic). In Group 1 samples with low carbonate content (< 4% CaCO 3 ), REEs were hosted mainly in the organic (50% of ΣREE) and siliciclastic fractions (37%); whereas in samples with greater carbonate content (> 25% CaCO 3 ), REEs were hosted mainly in carbonate-associated phases (53%). In Group 2, REEs were hosted mainly in the carbonate-associated (64%) and organic fractions (30%), and in Group 3, REEs were hosted mainly in the carbonate-associated (60%), detrital apatite (23%), and siliciclastic fractions (16%). Authigenic phases include minerals such as carbonate fluorapatite and authigenic calcite that, if present, tend to dominate the whole-rock REE inventory. In the absence of carbonate, whole-rock REE content depends on the relative REE contributions of the organic and siliciclastic fractions.

58 GEOSCIENCES↗
DOE OSTI2021

Binding mechanism and binding free energy of amino acids and citrate to hydroxyapatite surfaces as a function of crystallographic facet, pH, and electrolytes

Hydroxyapatite (HAP) is the major mineral phase in bone and teeth. The interaction of individual amino acids and citrate ions with different crystallographic HAP surfaces has remained uncertain for decades, creating a knowledge gap to rationally design interactions with peptides, proteins, and drugs. In this contribution, we quantify the binding mechanisms and binding free energies of the 20 end-capped natural amino acids and citrate ions on the basal (001) and prismatic (010)/(020) planes of hydroxyapatite at pH values of 7 and 5 for the first time at the molecular scale. We utilized over 1500 steered molecular dynamics simulations with highly accurate potentials that reproduce surface and hydration energies of (hkl) hydroxyapatite surfaces at different pH values. Charged residues demonstrate a much higher affinity to HAP than charge-neutral species due to the formation of superficial ion pairs and ease of penetration into layers of water molecules on the mineral surface. Binding free energies range from 0 to -60 kJ/mol and were determined with ~10% uncertainty. The highest affinity was found for citrate, followed by Asp(-) and Glu(-), and followed after a gap by Arg(+), Lys(+), as well as by His(+) at pH 5. The (hkl)-specific area density of calcium ions, the protonation state of phosphate ions, and subsurface directional order of the ions in HAP lead to surface-specific binding patterns. Amino acids without ionic side groups exhibit weak binding, between -3 and 0 kJ/mol, due to difficulties to penetrate the first layer of water molecules on the apatite surfaces. We explain recognition processes that remained elusive in experiments, in prior simulations, discuss agreement with available data, and reconcile conflicting interpretations. In conclusion, the findings can serve as useful input for the design of peptides, proteins, and drug molecules for the modification of bone and teeth-related materials, as well as control of apatite mineralization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Environmental impact of ongoing sources of metal contamination on remediated sediments

One challenge to all remedial approaches for contaminated sediments is the continued influx of contaminants from uncontrolled sources following remediation. We investigated the effects of ongoing contamination in mesocosms employing sediments remediated by different types of active and passive caps and in-situ treatment. Our hypothesis was that the sequestering agents used in active caps and in situ treatment will bind elements (arsenic, chromium, cadmium, cobalt, copper, nickel, lead, selenium, and zinc) from ongoing sources thereby reducing their bioavailability and protecting underlying remediated sediments from recontamination. Most element concentrations in surface water remained significantly lower in mesocosms with apatite and mixed amendment caps than in mesocosms with passive caps (sand), uncapped sediment, and spike solution throughout the 2520 hour experiment. Element concentrations were significantly higher in Lumbriculus variegatus from untreated sediment than in Lumbriculus from most active caps. Moreover, Pearson correlations between element concentrations in Lumbriculus and metal concentrations in the top 2.5 cm of sediment or cap measured by diffusive gradient in thin films (DGT) sediment probes were generally strong (as high as 0.98) and significant (p<0.05) for almost all tested elements. Metal concentrations in both Lumbriculus and sediment/cap were lowest in apatite, mixed amendment, and activated carbon treatments. Finally, these findings show that some active caps can protect remediated sediments by reducing the bioavailable pool of metals/metalloids in ongoing sources of contamination.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Molecular Investigation of the Initial Nucleation of Calcium Phosphate on TiO 2 Substrate: The Effects of Surface Nanotopographies

Nucleation and biomineralization of apatite on titanium-based material surfaces is crucial to improve surface biocompatibility, osseointegration, and rapid bone ingrowth in biomedical applications such as joint replacements. Here, this work is designed to provide new insights on the molecular processes in the initial nucleation of calcium phosphate on TiO 2 surface by means of classical molecular dynamics (MD) simulations. Aggregation of calcium and phosphate ions in pure aqueous solution was studied, and the free energies during ion adsorption was investigated by the calculation of PMFs. The MD results suggest surface hydroxylation rate and nanotopographies of TiO 2 substrate contribute significantly to the initial nucleation of calcium phosphate. Our simulations suggest that surface hydroxyls on TiO 2 provide active sites for the aggregation of calcium phosphate. Both calcium ions and phosphate ions could bind to the hydroxylated TiO 2 surface directly or indirectly via the first water layer. Surface nanotopographies (e.g., grooves or ridges) seem to be able to restrict the diffusion of calcium ions and phosphate ions, hence offering more opportunities for adsorption by trapping ions inside channels. In conclusion, it can be inferred that apatite may be formed more favorably on porous or concave surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Using Biomimetic Polymers in Place of Noncollagenous Proteins to Achieve Functional Remineralization of Dentin Tissues

In calcified tissues such as bones and teeth, mineralization is regulated by an extracellular matrix, which includes non-collagenous proteins (NCP). This natural process has been adapted or mimicked to restore tissues following physical damage or demineralization by using polyanionic acids in place of NCPs, but the remineralized tissues fail to fully recover their mechanical properties. Here we show that pre-treatment with certain amphiphilic peptoids, a class of peptide-like polymers consisting of N-substituted glycines that have defined monomer sequences, enhances ordering and mineralization of collagen and induces functional remineralization of dentin lesions in vitro. In the vicinity of dentin tubules, the newly formed apatite nano-crystals are co-aligned with the c-axis parallel to the tubular periphery and recovery of tissue ultrastructure is accompanied by development of high mechanical strength. The observed effects are highly sequence-dependent with alternating polar and non-polar groups leading to positive outcomes while diblock sequences have no effect. The observations suggest aromatic groups interact with the collagen while the hydrophilic side chains bind the mineralizing constituents and highlight the potential of synthetic sequence-defined biomimetic polymers to serve as NCP mimics in tissue remineralization.

Chien, Yung-Ching↗
DOE OSTI2017

In situ examination of osteoblast biomineralization on sulfonated polystyrene-modified substrates using Fourier transform infrared microspectroscopy

Osteoporosis is a skeletal disorder that is characterized by the loss of bone mineral density (BMD) resulting in increased risk of fracture. However, it has been shown that BMD is not the only indicator of fracture risk, as the strength of bone depends on a number of factors, including bone mass, architecture and material properties. We present that physiological mineral deposition requires the formation of a properly developed extracellular matrix (ECM), which recruits calcium and phosphate ions into the synthesis of apatite crystals. Temporal and spatial compositional and structural changes of biological apatite greatly depend on the properties of the crystals initially formed. As such, Fourier-transform infrared microspectroscopy (FTIRM) is capable of examining adaptive remodeling by providing compositional information such as the level of mineralization and carbonate substitution, as well as quality and perfection of the mineral phase. The objective of this study was to evaluate the in vitro mineralization development of MC3T3-E1 murine calvarial preosteoblasts cultured on different substrata by comparing FTIRM measurements from two subclones (mineralizing subclone 4 and nonmineralizing subclone 24) maintained in culture for up to 21 days. The results showed that modulation of the substrate surface using a thin coating of sulfonated polystyrene (SPS) provided favorable conditions for the development of a mineralizable ECM and that the mineral formed by the osteoblasts was similar to that of fully mineralized bone tissue. Specifically, the mineralizing subclone produced significantly more mineral phosphate when cultured on SPS-coated substrates for 21 days, compared to the same culture on bare substrates. In contrast, the level of mineralization in nonmineralizing subclone was low on both SPS-coated and uncoated substrates. The mineralizing subclone also produced comparable amounts of collagen on both substrates; however, mineralization was significantly higher in the SPS culture. The nonmineralizing subclone produced comparable amounts of collagen on day 1 but much less on day 21. Collagen maturity ratio increased in the mineralizing subclone from day 1 to day 21, but remained unchanged in the nonmineralizing subclone. In conclusion, these results suggest that SPS-treatment of the substrate surface may alter collagen remodeling; however, other factors may also influence osteoblast mineralization in the long term.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Phosphorus Sorption to Aluminum‐based Water Treatment Residuals Reacted with Dairy Wastewater: 2. X‐Ray Absorption Spectroscopy

Phosphorus capture from wastewater can decrease water pollution and provide a P‐rich fertilizer alternative for use in agricultural production. This study was conducted to elucidate P retention mechanisms in Al‐based water treatment residuals (Al‐WTR) to gain insight regarding P sorption and the potential for P release from Al‐WTR after reaction with dairy wastewater. Synchrotron‐based microfocused X‐ray fluorescence (micro‐XRF) spectrometry, bulk P K ‐edge X‐ray absorption near edge structure spectroscopy (XANES), and P K ‐edge micro‐XANES spectroscopy were used to determine P distribution and speciation within the Al‐WTR materials. Bulk XANES analyses indicated a shift from ∼56 P atom % Ca‐associated P in the initial Al‐WTR to ∼32% P atom % Ca‐associated P after reaction with wastewater; Al‐associated P made up the remainder of the P species. According to XANES analyses, adsorption appeared to be the primary P retention mechanism in the Al‐WTR materials. However, micro‐XANES analyses depicted a more complicated picture of P retention mechanisms, with regions of primarily Al‐associated P, regions of primarily Ca‐associated P, regions of mixed Al‐ and Ca‐associated P, and distinct apatite‐ or octocalcium phosphate‐like P grains. Synchrotron micro‐XRF mapping further suggested that exposure of the aggregate exteriors to wastewater caused P to diffuse into the porous Al‐WTR aggregates. Organic P species were not explicitly identified via P K ‐edge XANES despite high organic matter content, suggesting that organic P may have been predominantly associated with mineral surfaces. Although diffusion and sorption to Al may decrease P bioavailability, Ca‐associated P may increase P bioavailability from Al‐WTR that is reused as a soil amendment. Core Ideas XAS provided unambiguous evidence of P associations with Al and Ca in water treatment residuals. Phosphorus adsorbed to Al and Ca surfaces in Al‐based water treatment residuals. Grains of apatite‐ or octocalcium phosphate‐like P were found in water treatment residuals. Phosphorus diffused into aggregates on reaction with P‐rich wastewater. Evidence from electron microscopy and XRD complemented these findings.

Massey, Michael S.↗
DOE OSTI2019

Mechanisms Responsible for Soil Phosphorus Availability Differences between Sprinkler and Furrow Irrigation

From a historical perspective, human‐induced soil erosion and resulting soil phosphorus (P) losses have likely occurred for thousands of years. In modern times, erosion risk and off‐site P transport can be decreased if producers convert from furrow to sprinkler irrigation, but conversion may alter nutrient dynamics. Our study goal was to determine soil P dynamics in furrow‐ (in place since the early 1900s) versus sprinkler‐irrigated (installed within the last decade) soils from four paired producer fields in Idaho. Furrow‐ and sprinkler‐irrigated soils (0–5 cm; Aridisols) contained on average 38 and 20 mg kg −1 of Olsen‐extractable P (i.e., plant‐available P), respectively; extractable P values over 40 mg kg −1 limit Idaho producers to P application based on crop uptake only. Soil samples were also analyzed using a modified Hedley extraction. Furrow‐irrigated soils contained greater inorganic P concentrations in the soluble+aluminum (Al)‐bound+iron (Fe)‐bound, occluded, and amorphous Fe‐bound pools. Phosphorus K ‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy was unable to detect Fe‐associated P but indicated greater amounts of apatite‐like or octacalcium phosphate‐like P in furrow‐irrigated producer soils, while sprinkler‐irrigated fields had lower amounts of apatite‐like P and greater proportions of P bound to calcite. Findings from a controlled USDA‐ARS sprinkler‐ versus furrow‐irrigation study suggested that changes in P dynamics occur slowly over time, as few differences were observed. Overall findings suggest that Fe redox chemistry or changes in calcium (Ca)‐associated P in flooded conditions altered P availability under furrow irrigation, even in aridic, calcareous soils, contributing to greater Olsen‐extractable P concentrations in long‐term furrow‐irrigated fields. Core Ideas Irrigation type may greatly affect soil P dynamics in calcareous systems. Furrow irrigated fields contained more plant‐available P than sprinkler irrigated fields. Furrow irrigation leads to Fe chemistry alterations, release of P, and increases available P. Available P increases under furrow irrigation could limit amendment application based on P, not N, crop needs. We still do not fully understand P dynamics in irrigated calcareous systems.

Ippolito, James A.↗
DOE OSTI2023

Single-crystal X-ray diffraction of fluorapatite to 61 GPa

Apatite is a mineral of widespread importance in Earth and planetary science. Here we examine the behavior of a natural fluorapatite (FAp) crystal from Durango (Mexico) under compression to 61 GPa. Single-crystal X-ray diffraction experiments were carried out in a diamond-anvil cell using a synchrotron source. The apatite structure persists up to 32.4 GPa. Birch-Murnaghan equation of state parameters were fit to the pressure-volume data for fluorapatite for two cases: fixing V 0 at its measured ambient value resulted in a bulk modulus, K 0T , of 97.0(8) GPa and a pressure derivative of the bulk modulus, K' 0T , of 3.3(1), while fixing V 0 and K 0T at its ambient value 90.5 GPa (derived from ultrasonically measured elastic constants) resulted in a K' 0T value of 4.1(1). At 35.6 GPa, fluorapatite transforms to a triclinic phase (P$\bar{1}$, Z = 4), designated here as fluorapatite II (FAp-II). This phase persists up to at least 61 GPa. The major structural differences between FAp and FAp-II involve the buckling of the Ca polyhedra along the c-axis and changes in the number and coordination of the Ca sites. Furthermore, our study extends the pressure range over which fluorapatite has been examined by more than a factor of three, providing new insights into its structural response to high-pressure conditions.

58 GEOSCIENCES↗