X-ray Amorphous Phase Research Articles

Синтез дисперсных мезопористых порошков твердого раствора Zr0,88Ce0,12O2 для носителей катализаторов конверсии метана в синтез-газ

The xerogels in the system 0.88 mol.% ZrO2 − 0.12 mol.% CeO2 were obtained by the method of coprecipitation in a neutral (pH = 7) and slightly alkaline (pH = 9) medium under the influence of ultrasound with the size of the agglomerates 70 – 230 nm. It is shown that the coprecipitation of hydroxides of zirconium and cerium at pH = 9 with the use of ultrasonic treatment facilitates the formation of a primary crystal is symbolic of the particles in the xerogel, whose size is ~ 5 nm, whereas the xerogel synthesized in a neutral environment consists only of the x-ray amorphous phase. The effect of pH-precipitation on deposition processes of dehydration of the xerogels and crystallization solid solution based on zirconia oxide in the metastable pseudocubic modification (с′-ZrO2) was discovered. It was found that in the temperature range 500 – 800 °C there is a phase transition с′-ZrO2 → t-ZrO2, the size of the crystallites of the formed tetragonal solid solutions is 8 and 11 nm. The method of low-temperature nitrogen adsorption were investigated dispersion properties and characteristics of the pore structure of the powders of the solid solution Zr0.88Ce0.12O2. It is determined that the specific surface area of t-ZrO2 samples obtained after firing at 800 °C is 117 and 178 m2/g, the total pore volume reaches 0.300 − 0.325 cm3/g, the pore size distribution is monomodal and is in the range of 2 − 8 nm. The effect of thermal “aging” at a temperature of 800 °C (40 h) on the structure and dispersion of the solid solution t-ZrO2 powders was studied.

Характеристика микросфер золы уноса для их использования в качестве сорбента

Работа посвящена изучению физико-химических свойств микросфер золы уноса (зольныхмикросфер) тепловых электростанций с целью последующего их использования в качестве сорбентадля очистки сточных вод от примесей различной природы. Определены химический и минералогический состав зольных микросфер. Выполнена оценка химической и механической стойкости, удельной поверхности, сорбционной способности материала. Анализ физических и химических свойств зольных микросфер показал, что исследованный материал соответствует требованиям ГОСТ Р 51641-2000 «Материалы фильтрующие зернистые. Общие технические условия» и является эффективным для использования, как в качестве самостоятельного сорбента, так и составляющей в системах водоочистки.

In situ XRD measurements to explore phase formation in the near surface region

Though X-ray diffraction (XRD) is a well-established technique—yet still continuously evolving—for characterization of thin films and diffusion layers, there are two inherent limitations due to the underlying physical principles leading to the diffraction: (i) all data are a weighted integral across the information depth and (ii) X-ray amorphous or nanocrystalline phases are very difficult to be detected. The purpose of this Perspective is to show how a straightforward combination of in situ XRD with depth profiling using a laboratory experiment in combination with a low-energy broad-beam ion source may allow us to overcome these limitations for functional surfaces. Whereas time-resolved investigations of diffusion and phase formation during ion implantation using reactive species are well established, using ion beam sputtering with nonreactive species for depth profiling of the phase composition during the measurements is a rather recent development. While employing analysis of differential spectra leads to a depth resolution below the information depth, ongoing in situ sputtering will lead to information obtained from layers deeper than the information depth. Keeping track of the total diffraction intensity permits the identification of phases without reflections in the XRD measurements, i.e., they appear to be amorphous, and their depth distribution. Selected examples drawn mainly from investigations of the nitriding kinetics of austenitic stainless steel will be used to demonstrate the potential and possible limitations of this method.

Synthesis of natural zeolite agglomerates: clinoptilolite-based geopolymers through aluminate activation

AbstractNatural zeolite (clinoptilolite)-based geopolymers were synthesized using alkali aluminate solution, including aluminate anodizing waste solution. The effect of calcination of the clinoptilolite sample at 900°C was investigated. The samples were studied by powder X-ray diffraction, thermal analysis, scanning electron microscopy and N2-specific surface area. The alkali aluminate-activated clinoptilolite geopolymers are characterized by satisfactory compressive strength (up to 37 MPa), low density and acceptable shrinkage. The clinoptilolite geopolymer obtained contains an X-ray amorphous phase and newly formed phillipsite and zeolite NaP. The presence of zeolite phases in the geopolymer agglomerate could be beneficial in products with specific qualities and properties, such as ion exchange, passive cooling, antimicrobial activity,etc.

Mechanical transformation of phyllite mineralogy toward its use as alkali-activated binder precursor

The mechanical activation of phyllite for use as an alkali-activated material was studied. Prolonged milling of phyllite resulted in reduced particle size and a structural reorganization of the material, leading to incremental increases in amorphous content, which further resulted in the improved reactivity of phyllite in an alkaline environment. Quantitative X-ray diffraction results showed that the phyllite consisted of quartz, muscovite, chamosite, albite, and X-ray amorphous phases. Among the crystalline phases, muscovite and chamosite underwent the most structural reorganization, leading to a more disordered structure due to prolonged and intensive milling. The structural reorganization was also established through Fourier-transform infrared spectroscopy. Dissolution tests in 6 M NaOH showed incremental increases in leached Al and Si elements with increased milling time. After geopolymerization of mechanically activated phyllite, calorimetric studies showed exothermic reactions, and a 28-day compressive strength of 25 MPa was achieved for paste samples cured at room temperature. This study ascertained the potential utilization of phyllite mineral waste in sustainable cement applications.

Influence of the reagent types on the characteristics of barium hexaferrites prepared by mechanochemical method

The phase composition, structure parameters, morphology and the basic magnetic characteristics of BaFe12O19 hexaferrites obtained by the method of soft mechanochemical synthesis with the following annealing in air for one hour at temperatures in the range from 800 to 1100 °C were studied. The influence of the reagent type on the phase composition and structural characteristics of hexaferrites are analyzed. It has been established that for the synthesis of a single-phase barium hexaferrite a reaction when only water-containing reagents are used is advantageous. In addition, the participation of water in the mechanochemical synthesis leads to an increase in the rate of reagent interaction. The saturation magnetization and the anisotropy fields were determined. The specific saturation magnetization of the sample obtained using the initial hydrous reagents (FeCl3·6H2O and BaCl2·2H2O) is higher than that of the sample obtained using the anhydrous barium chloride (BaCl2). Magnetocrystalline anisotropy of the synthesized materials is investigated by the ferromagnetic resonance method. Along with the high-anisotropic ВаM phase the samples contain the traces of a phase with a small field of magnetocrystalline anisotropy. It is caused by the presence of the X-ray amorphous phase in the samples. Another source of this phase is the superparamagnetic Ba-M hexaferrite nanoparticles.

Crystal Chemistry and High-Temperature Behaviour of Ammonium Phases NH4MgCl3·6H2O and (NH4)2Fe3+Cl5·H2O from the Burned Dumps of the Chelyabinsk Coal Basin

The technogenic mineral phases NH4MgCl3·6H2O and (NH4)2Fe3+Cl5·H2O from the burned dumps of the Chelyabinsk coal basin have been investigated by single-crystal X-ray diffraction, scanning electron microscopy and high-temperature powder X-ray diffraction. The NH4MgCl3·6H2O phase is monoclinic, space group C2/c, unit cell parameters a = 9.3091(9), b = 9.5353(7), c = 13.2941(12) Å, β = 90.089(8)° and V = 1180.05(18) Å3. The crystal structure of NH4MgCl3·6H2O was refined to R1 = 0.078 (wR2 = 0.185) on the basis of 1678 unique reflections. The (NH4)2Fe3+Cl5·H2O phase is orthorhombic, space group Pnma, unit cell parameters a = 13.725(2), b = 9.9365(16), c = 7.0370(11) Å and V = 959.7(3) Å3. The crystal structure of (NH4)2Fe3+Cl5·H2O was refined to R1 = 0.023 (wR2 = 0.066) on the basis of 2256 unique reflections. NH4MgCl3·6H2O is stable up to 90 °C and then transforms to the less hydrated phase isotypic to β-Rb(MnCl3)(H2O)2 (i.e., NH4MgCl3·2H2O), the latter phase being stable up to 150 °C. (NH4)2Fe3+Cl5·H2O is stable up to 120 °C and then transforms to an X-ray amorphous phase. Hydrogen bonds provide an important linkage between the main structural units and play the key role in determining structural stability and physical properties of the studied phases. The mineral phases NH4MgCl3·6H2O and (NH4)2Fe3+Cl5·H2O are isostructural with natural minerals novograblenovite and kremersite, respectively.

Sediment geochemistry and mineralogy from a glacial terrain river system in southwest Iceland

Abstract The weathering of basalt has implications for the global carbon cycle on Earth as well as for understanding sedimentary processes on other terrestrial bodies dominated by a basaltic crust (e.g., Mars), but yet studies in mafic terrains are limited in comparison to their felsic counterpart. Our work details the compositional transformations resulting from the sedimentation process of first-cycle sediments generated in a basalt dominated watershed of southwest Iceland. By sampling multiple sites along the Hvita S river transport pathway and analyzing the sedimentology, geochemistry, and mineralogy, this work provides a geologically integrated approach to understanding a fluvial source-to-sink system in mafic terrains. Environmental conditions such as climate, hydrology, and transport distance all influence the overall sediment composition, and in response, chemical weathering, physical abrasion, sorting, transport, and mixing are all sedimentary processes unraveled in the geochemical and mineralogical relationships of individual grain size bins. Chemical weathering initiates in the upper reaches of the watershed with the alteration of primary mafic phases to form secondary weathering products. As sediment continues to move downstream, the entire sediment suite becomes more altered, and the extent of chemical weathering is intensified, as evidenced by a higher abundance of clay minerals and glassy material. Fluvial sorting separates detritus by particle size and differentiates them by compositional gradients in geochemistry and mineralogy. As grain size decreases, mafic minerals become less abundant and the finer grain sizes are preferentially enriched in immature weathering minerals and mineraloids (e.g., smectite clays and X-ray amorphous phases). This grain size trend is also correlated with elemental fractionation, illustrated most notably by the clay size fraction (

Mechanical properties and oxidation behavior of W–Si–N coatings

Monolithic and multilayered WN and W–Si–N coatings were fabricated through direct current magnetron cosputtering at substrate holder rotation speeds of 0 and 5 rpm. The mechanical properties, structural evolutions, and oxidation behaviors of the WN and W–Si–N coatings were investigated through nanoindentation, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The mechanical properties of crystalline WN coatings correlated to their textures and residual stresses. The monolithic W77N23 samples located closest to the W target exhibited a high deposition rate of 18.0 nm/min, a strong (200) texture coefficient, a high nanoindentation hardness of 32.7 GPa, a high Young's modulus of 392 GPa, and a high residual stress of −3.2 GPa. The addition of Si into the WN matrix transformed the monolithic W–Si–N coating into an X-ray amorphous phase dominated structure that comprised Si3N4, W2N, and W constituents. Ion bombardment caused the formation of multilayered W78N22 samples with high residual stress and mechanical properties. The mechanical properties and residual stresses of the multilayered W–Si–N coatings decreased due to the preferential formation of Si3N4. By contrast, oxidation resistance was improved by adding Si content higher than 24 at.% with annealing at 600 °C in a 1% O2–99% Ar atmosphere.

Spectroscopic methods of investigation and the thermal stability of detonation nanodiamonds

The behavior of detonation nano- and microdiamonds at increased temperatures is studied by synchronous thermal analysis, X-ray diffraction analysis, and scanning electron microscopy. The X-ray analysis of survived samples shows that a part of the nanodiamond is stable under heating to 1500°C. At the heating to 600°C, we see the decreasing of nanodiamond phase. Appearance of graphite phase isn’t observed in the sample up to 1500°C. However, in the range Bragg angle 20-32° after heating to 1500°C, the x-ray amorphous graphite-like phase is observed. The analysis of microphotographs of samples before and after heating showed the influence of heating rate on the parameters of powder particles. A high thermal stability of detonation microdiamonds (above 1500°C) is established. Literature data on the radiation stability of diamond are analyzed. It is established that the character of the diamond damage depends on the type and dose of the irradiation.

A novel synthetic approach to low-crystallinity calcium deficient hydroxyapatite

Abstract Synthetic calcium deficient hydroxyapatite (CDHA, with the formula Ca9(HPO4)(PO4)5OH) is a promising material which could be potentially used in biomedicine. The aim of this study was to develop a simple and cost-effective synthesis route for the preparation of low crystalline CDHA granules. A method based on an incessant dissolution-precipitation reaction eventually resulting in a solid and shaped material consisting of the desired phase was utilized. The calcium sulphate hemihydrate was selected as the starting material. The synthesis products obtained were characterized by Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The monophasic calcium deficient hydroxyapatite granules of about 300–350 μm in diameter were synthesized by three slightly different preparative approaches at 70 °C temperature and compared. Independently of the composition of the raw granules synthesized ones were composed of low crystalline an apatitic phase. The granules were calcium deficient as contained HPO42− group in their structure. It was demonstrated that the addition of (NH4)H2PO4 or (NH4)2HPO4 into the raw granules could promote the growth of the CDHA crystallites. SEM revealed that the microstructure of synthesized materials was influenced by the chemical composition of the raw granules. Chemical composition and presence of no an X-ray amorphous phase in obtained samples was confirmed by reheating the obtained granules at 800 °C to get monophasic β-TCP. Our work provides a novel and simple approach to produce CDHA granules for various applications.

Preparation of TiO2/C Composites via Titanium Glycerolate Pyrolysis

Titania-based composites TiO2/C were manufactured by thermolyzing titanium glycerolate under an inert atmosphere at temperatures in the range 360–850°C. The structure of the compound was shown to be determined by Ti(C3H7O3)4 heat-treatment conditions. Composite formation (up to 400°C) involves the formation of an X-ray amorphous phase with the short-range order typical of anatase titania. A rise in thermolysis temperature (400–600°C) leads to the formation of anatase TiO2/C. The composites TiO2/C manufactured at temperatures above 600°C are anatase + rutile mixtures. TiO2/C particles have a rod-like morphology 100–250 nm in diameter and up to 6.5 μm long, retaining it up to 850°C. The presence of carbon in samples is verified by Raman spectroscopy and thermogravimetry.

Ferro-manganese nodules from the Kara Sea: Mineralogy, geochemistry and genesis

Sixteen ferromanganese nodules collected from a large area in the Kara Sea were studied by optical and scanning electron microscopy, X-ray powder diffraction, X-ray fluorescence analysis, inductively coupled plasma mass spectrometry, and electron microprobe analysis. The geological setting, chemical and mineralogical features suggest that Fe-Mn concretions of the Kara Sea mainly were formed by diagenetic process, while hydrogenetic process is secondary if present. The studied nodules are characterized by the alternation of Mn- and Fe-P-enriched laminae. The Fe-P-rich laminae are almost completely composed of an amorphous phase under X-ray. We consider that the phosphatization process did not occur during formation of the Fe-Mn crusts and nodules from the Kara Sea. Several Mn-bearing phases are present in the studied samples (buserite-1, birnessite and X-ray amorphous phase). All studied nodules have similar contents of the main chemical elements. In all cases, the samples are depleted in light REE, enriched in heavy REE, and have negative Ce and Y anomalies. Our data indicate that diagenetic crusts and nodules differ significantly in terms of chemical composition from other types of Fe-Mn concretions. Based on their Co, Ni, Cu, Ce, Zr and Mo contents, we could differentiate diagenetic concretions from hydrogenetic and hydrothermal (both high and low-temperature) concretions.

Chemical shrinkage of ye’elimite with and without gypsum addition

Ye’elimite (Ca4Al6O12SO4 or C4A3S-) is the main hydraulic mineral present in calcium sulphoaluminate cement (CSA). Its reaction is responsible for the (early) hydration and associated cement properties such as the chemical shrinkage. This paper discusses the evolution of chemical shrinkage and related hydration reactions of stoichiometric ye’elimite in the absence and presence of gypsum. The measurements reveal a transitory chemical expansion followed by recovery to the original value for both binders. The shrinkage evolution is linked to the changes within the X-ray amorphous phases formed during hydration. This amorphous component is composed of several metastable hydrates such as aluminium hydroxide gel, which undergo subsequent recrystallization with time. This causes the release of some of the bound water and coincides with the period during which the chemical expansion occurs.

Soil concrete based on waste of heat power engineering and siftings of rock grinding

The possibility of recycling large-tonnage waste of heat power engineer-ing and mining industry in road construction is shown. Compositions of road-building materials were researched, containing siftings of rock grinding, fly ash, Portland cement, modified with a stabilizing additive of polymeric nature. X-ray phase analysis showed availability of quartz in fly ash, calcite, feldspars, goethite and X-ray amorphous phase, what is consistent with the data of infrared spectroscopy. By atomic emission spectrometry with inductively coupled plasma it was revealed that fly ash is latent-active and can be disposed in compositions in the presence of a stabilizing additive. The X-ray phase analysis of grinding siftings showed that it contains quartz, feldspars, chlorite, calcite and dolomite. The specific activity of natural radionuclides (226Ra, 232Th, 40К) of fly ash and grinding siftings was 248 and 110 Bq/kg, which allows using such waste in construction without restrictions. It was revealed that the initial mineral raw materials belong to multiphase polymineral systems; therefore, when modifying them with stabilizing additives, binding of finely divided particles should be taken into account. It was revealed that the optimal content of Portland cement and fly ash in samples is 8 and 10 wt.%. It was found that an increase in the mass fraction of fly ash in the composition of soil-concrete up to 30 wt.% leads to softening of the samples and a decrease in their strength characteristics.

Tschermigite from thermal fields of Southern Kamchatka: high-temperature transformation and peculiarities of IR-spectrum

Tschermigite, (NH 4 )Al(SO 4 ) 2 ∙ 12H 2 O, is a widespread mineral in efflorescence at geothermal fields associated with Kambalny and Koshelevsky volcanoes (Southern Kamchatka, Russia). The determined temperature ranges of stability of tschermigite and products of its high-temperature evolution by in situ powder X-ray diffraction: tschermigite (23—60°C) → X-ray amorphous phase (70—200 °C) → godovikovite (210—390°C) → millosevichite (380—>620°C). This implies decomposition of tschermigite (23—60°C) first to the interim X-ray amorphous phase (probably melt) from which godovikovite is then formed, without direct transformation of tschermigite to godovikovite, as it was suggested in some papers previously. Deammonization of godovikovite to millosevichite occurs at 380—390°C. Thermal expansion coefficients are given for tschermigite, godovikovite and millosevichite with discussion on some peculiarities on their formation. Regarding IR bands that refer to ammonium ion: ν 3 (~1430 cm –1 ) split, ν 1 (~3100 cm –1 ) active, what attests about at least partial shift of N (NH 4 + ) in tschermigite crystal structure from site 4 b ( S 6 ) to site 8 c ( С 3 ). In O—H stretching region, higher wavenumber band (~3380 cm –1 ) corresponds to «extraframework» water, while the observed band ~2950 cm –1 corresponds to water coordinating Al.

Pseudo-equilibrium equation of calcium phosphate precipitation from aqueous solution.

An X-ray amorphous phase is frequently present at the early stage of calcium phosphate crystallization, and the relevant solution chemistry is essential for understanding the mechanism of reaction. Here, we report a quantitative study of a series of reaction systems at pseudo-equilibrium states. We determined the composition of solutions and the quantities of the precipitate samples, and characterized the long- and short-range order of the precipitate using X-ray diffraction and synchrotron X-ray absorption near-edge structure spectroscopy, respectively. We found that, in a particle with multiple structural units, only a fraction of the units was able to reach pseudo-equilibrium with the solution composition, which represents the average number of surficial clusters per unit. These findings enabled us to propose a general form of the equilibrium constant equation. The equation fits the pseudo-equilibrium data well, and it converts to the "solubility product (Ksp)" and the conventional "reaction quotient" in two limit cases, respectively. Further, using a cube model, we derived a "particle equation" that reveals the connection between the particle structure and the form of equilibrium constant equation. The dependency of the form of pseudo-equilibrium equation on the structure and size of the precipitate reveals a fundamental relation in chemistry, and its applicability remains to be examined in other reaction systems, such as those involving nanocrystals and porous materials.

Pressure-driven phase transitions and reduction of dimensionality in 2D silicon nanosheets

In-situ high-pressure synchrotron X-ray powder diffraction studies up to 21 GPa of CVD-grown silicon 2D-nanosheets establish that the structural phase transitions depend on size and shape. For sizes between 9.3(7) nm and 15.2(8) nm we observe an irreversible phase transition sequence from I (cubic) → II (tetragonal) → V (hexagonal) during pressure increase and during decompression below 8 GPa the emergence of an X-ray amorphous phase. High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and atomic force microscopy (AFM) images of this X-ray amorphous phase reveal the formation of significant numbers of 1D nanowires with aspect ratios > 10, which are twinned and grow along the <111> direction. We discovered a reduction of dimensionality under pressure from a 2D morphology to a 1D wire in a material with a diamond structure. MD simulations indicate the reduction of thermal conductivity in such nanowires.

DETERMINATION OF THE PHASE COMPOSITION OF INTERMEDIATE AND FINAL PRODUCTS OF SYNTHESIS OF SPINEL TYPE CATALYSTS Cu1Cr2O4 AND Cu1Fe2O4 BY DIFFERENTIATING DISSOLUTION METHOD

Traditionally, the X-ray analysis (XRD) method is used to study the phase composition of a solid. But phases with structural defects, poorly crystallized (with disordered structure and amorphous), microphases, phases of variable composition, surface phases and phases, distributed in various ways throughout the entire volume of the sample, often turn out to be X-ray amorphous. In these situations, the stochiographic DR method proves to be more effective, since it allows qualitatively and quantitatively to detect both the crystalline and X-ray amorphous phases listed above. The phase compositions of the spinel type catalysts Cu 1 Cr 2 O 4 and Cu 1 Fe 2 O 4 were studied by the stoichiographic method of differentiating dissolution (DR). It is established that the nature of the element and temperature influence the formation of the spinel structure, creating new shapes. The paper describes phase transformations occurring in the synthesis of catalysts, which was carried out by coprecipitation from a mixture of solutions of nitrate salts. It was found that the temperature of 85°C forms various stoichiometric formations, which are precursors of spinels. The 600°C temperature in the case of copper-chromium systems forms stoichiometric compounds of the spinel composition Cu 1 2+ Cr 2 3+ O 4 and structures with different degree of ordering. In the case of copper-iron systems at 600 °C, stoichiometric compounds of the Cu 1-x 2+ Fe 2 3+ O 4 spinel composition and structure are defective in copper. The 900°C temperature pro­vides the formation of compounds of a given spinel composition Me 1 2+ Me 2 3+ O 4 and structures in both systems. The results by the DR method were compared with the results of the XRD method. A comparative analysis has shown that the ordered or crystallized forms of spinels and oxides are detected by both methods, while disordered and defective forms of spinels, the shapes of disordered solid solutions, and also small amounts of oxides show only the DR method.

In Search of a Binding Agent: Nano-Scale Evidence of Preferential Carbon Associations with Poorly-Crystalline Mineral Phases in Physically-Stable, Clay-Sized Aggregates

Mechanisms of protecting soil carbon (C) are still poorly understood despite growing needs to predict and manage the changes in soil C or organic matter (OM) under anticipated climate change. A fundamental question is how the submicron-scale interaction between OM and soil minerals, especially poorly-crystalline phases, affects soil physical aggregation and C stabilization. Nano-sized composites rich in OM and poorly-crystalline mineral phases were presumed to account for high aggregate stability in the Andisol we previously studied. Here we searched for these nanocomposites within a sonication-resistant aggregate using scanning transmission X-ray microscopy (STXM) and near-edge X-ray absorption fine structure (NEXAFS) as well as electron microscopy (SEM, TEM). Specifically, we hypothesized that nanometer-scale spatial distribution of OM is controlled by poorly-crystalline minerals as both co-exist as physically-stable nanocomposites. After maximum dispersion of the cultivated Andisol A-horizon sample in water, one aggregate (a few µm in diameter) was isolated from 0.2–2 µm size fraction which accounted for 44–47% of total C and N and 50% of poorly-crystalline minerals in bulk soil. This fraction as well as &lt;0.2 µm fraction had much higher extractable Al and Fe contents and showed greater increase in specific surface area (N2-BET) upon OM oxidation compared to bulk and &gt;2 µm size fractions, implying high abundance of the nanocomposites in the smaller fractions. The isolated aggregate showed a mosaic of two distinctive regions. Smooth surface regions showed low adsorption intensity of carbon K-edge photon energy (284–290 eV) with well-crystalline mineralogy, whereas rough surface regions had features indicative of the nanocomposites: aggregated nanostructure, high C intensity, X-ray amorphous mineral phase, and the dominance of Si, O, Al, and Fe based on SEM/EDX and TEM/EDX. Carbon functional group chemistry assessed by NEXAFS showed the dominance of amide and carboxyl C over aromatic and aliphatic C with some variation among the four rough surface regions. Together with C and N isotopic patterns among the size fractions (relatively low C:N ratio, high 15N natural abundance, and more positive Δ14C of the &lt;2 μm fractions), our results provided the direct evidence of preferential binding of microbially-altered, potentially-labile C with poorly-crystalline mineral phases at submicron scale. The role of the nanocomposite inferred from this study may help to bridge the knowledge gap between physical aggregation process and biogeochemical reactions taking place within the soil physical structure.