Average Chemical Formula Research Articles

Thermal hazard analysis and fire risk assessment of rocket kerosene in oxygen-enriched environment

Fire hazard of liquid fuel exposed in oxygen-rich environment is significantly greater than that in air, which should be considered in the safety risk assessment of scenarios where oxygen and fuel coexist. To reveal the effect of oxygen concentration on fuel properties and combustion characteristics of liquid fuel, a series of experiments were conducted to measure the liquid-phase component, flash point, lower flammability limit, heat release rate and flame height of rocket kerosene at different oxygen concentrations. The results show that the flash point of rocket kerosene (with an average chemical formula of C11.98H22.64) decreases nonlinearly with the increased oxygen concentrations, while the oxygen concentration has a great enhancement effect on the heat release rate and visible flame height of rocket kerosene pool fire. Prediction models of the flash point and lower flammability limit based on the Clausius-Clapeyron equation, Le Chatelier rule and decreasing temperature assumption, as well as empirical equations of the heat release rate and visible flame height, were derived for different oxygen concentrations in this work, providing a new comprehensive understanding of the effect of oxygen concentration on the rocket kerosene, and could be further applied to fire risk assessment in liquid fuel and oxygen coexisting scenarios.

Methane Adsorption in Anthracite Coal under Different Pressures and Temperatures—A Study Combining Isothermal Adsorption and Molecular Simulation

In situ gas content is an important parameter associating coalbed methane, while the influence of pressure and temperature on methane adsorption and desorption still needs to be revealed. In this study, the molecular structure and methane adsorption capacity of anthracite coal collected from Diandong Coalfield (China) were studied based on 13C nuclear magnetic resonance (13C NMR), Fourier transform infrared spectroscopy (FT-IR), and methane isothermal adsorption experiment. The results show that the carbon skeleton of coal sample is mainly composed by aromatic carbon (72%), followed by aliphatic carbon structure (14.2%). Carbons connected to the oxygen atoms contribute 13.7% of the total carbons in coal molecule, and the oxygen atoms are mainly in the form of carbonyl. The 2-dimension structure and 3-dimension molecular structure of coal sample was also reconstructed. The average chemical formula of the coal molecule is C200H133O21N3. The experimental methane adsorption isothermal data of the coal sample under different temperatures shows that with increasing the temperature, the methane adsorption amount at each pressure decreases obviously. At 7 MPa and 20°C, the methane adsorption amount of the coal sample is 28.5 cm3/g. Comparably, at 100°C and 7 MPa, the methane adsorption amount is only 15.9 cm3/g, decreasing by 44%. In mesopores, temperature has stronger influence on methane adsorption under higher pressure than that of lower pressure. On the contrary, in micropores, temperature has weaker effects on methane adsorption at higher pressure than that at lower pressure. The results can be beneficial for understanding methane adsorption characteristics of deep coal.

Study on andorite-series minerals from Meleg Hill, Velence Mts., Hungary

During the last decades, different sulphosalts were observed in several samples that were investigated from the Meleg hill, Velence Mts. The investigated sample of this study was collected from the less studied north-eastern, stibnite-rich part of the hydrothermal breccia at the Meleg Hill. Based on the results of electron microprobe analysis, we found that the sample contained two sulphosalt minerals of the andorite series that have not been described from Hungary before. The andorite series is a subgroup of the lillianite homologous series. The individual minerals, andorite VI and roshchinite, within the andorite series were identified on the basis of their chemical composition and the andorite substitution percentage (L%). Andorite VI has Ag1.06Cu0.04Pb0.80Sb2.49Bi0.22As0.3S6 average chemical formula (normalized to 6 sulphur atoms) and L%=102.65–109.84, whereas roshchinite has Ag17.23Cu0.53Pb10.4Hg0.04Zn0.04Fe0.02Sb39.73Bi5.52As5.98S96 average chemical formula (normalized to 96 sulphur atoms) and L% = 119.52–123.48. Our results suggest that the formerly used comparative ternary diagrams of the system (Ag2S + Cu2S)–(Sb2S3 + Bi2S3 + As2S3)–(PbS + HgS + FeS + ZnS + CdS) is not adequate to differentiate the andorite-series minerals from each other, due to the highly variable element substitution of Me+, Me2+ and Me3+ cations. The andorite substitution percentage (L%) and the andorite homologue order value (N) are always necessary to calculate to distinguish the mineral species.

Chemical characterizations and molecular dynamics simulations on different rejuvenators for aged bitumen recycling

Molecular dynamics (MD) simulation is an advanced tool to explore the interaction mechanism between aged bitumen and rejuvenators at the nanoscale. However, the general MD molecular structures of rejuvenators led to the lower quantify and inaccuracy of the simulation outputs. This study aims at developing more realistic molecular models to represent the generic rejuvenators for MD simulation of aged bitumen recycling. Four types of rejuvenators (bio-oil, engine-oil, naphthenic-oil, and aromatic-oil) are characterized in terms of element analysis, functional groups distribution observed from Attenuated total reflectance-Fourier-transform infrared (ATR-FTIR) spectroscopy, and average molecular weight. Afterward, the average molecular structures of rejuvenators are determined and validated. Further, the MD simulations are performed to predict the energetic, dynamic, volumetric, and structural properties of various rejuvenators. Based on the chemical characteristics, the average chemical formula of bio-oil, engine-oil, naphthenic-oil, and aromatic-oil is derived as C19H36O2, C22H44, C26H48, C30H40. From MD simulations, the ranking of density and glass transition temperature for four different rejuvenators is AO > NO > BO > EO, which is same as the experimental results. It proves that the established average molecular structures of four rejuvenators are reasonable. Various rejuvenators display different thermodynamics and structural properties. The aromatic-oil exhibits the highest potential energy, cohesive energy density, and solubility parameter. Besides, the order of expansion coefficient and diffusion coefficient of the four rejuvenators is the same as BO > EO > NO > AO, while the viscosity presents the opposite sequence. Moreover, the fractional free volume values follow EO > BO > NO > AO. The occurrence probability between bio-oil and aromatic-oil molecules is higher than engine-oil and naphthenic-oil. This study develops the representative average molecular models for generic rejuvenators and helps understand the difference in chemo-physical and thermodynamics properties among various rejuvenators.

EMPA, XRD, and Raman Characterization of Ag-Bearing Djurleite from the Lubin Mine, Lower Silesia, Poland

The chalcocite group minerals are widely distributed among different hydrothermally affected rocks, the oxidized zone of copper sulfide deposits, or may be even crystalline from supersaturated volcanic gases. Some of the chalcocite group minerals form the main Cu orebodies. Djurleite (Cu31S16) is a rare member of the chalcocite group, with a very complex structure. The physical and chemical similarities between all members of the group make them almost unidentifiable by macroscopic and microscopic methods. In this study, Ag-bearing djurleite from the Kupferschiefer deposits, Lower Silesia, Poland, is characterized by EMPA (Electron Microprobe Analyses), XRD (X-Ray Diffraction), and Raman spectroscopy. Djurleite from the investigated site has the following general, average chemical formula: Cu30.86Ag0.1Fe0.04S16. The Ag content is up to 0.55 wt.%, while Fe is up to 0.19 wt.%. The presence of djurleite confirms a low-temperature (~90 °C), hydrothermal origin of the Cu-Ag deposit in Kupferschiefer, which is consistent with previously studies. Moreover, the authors believe that Ag-rich djurleite may often be mistaken for Ag-rich chalcocite, which used to be one of the main Ag-bearing minerals in the orebody from the Cu-Ag deposit in the Fore-Sudetic Monocline. However, the confirmation of such a statement requires more samples, which should be studied in detail.

Mineralogical characterization and evaluation of chromite ore in Grevena and Kozani Vourinos massif, Western Macedonia, Greece

Purpose. Chromite samples from Aetoraches mine area in the southern part of the Vourinos complex in Western Macedonia, Greece were examined from mineralogical-geochemical perspective. Methods. Χ-ray Diffraction (XRD) mineral phase analysis, elemental Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS) analysis and Thermogravimetry/Differential Thermogravimetry (TG/DTG) were carried out. Findings. The XRD results showed that all the samples contain mainly magnesium- and aluminum-chromite (“aluminum-picrochromite”) phases, along with forsterite (magnesian olivine), serpentine and chlorite occurrences. Based on the SEM-EDS results, the computed average chemical formula indicative of this specific chromite type is: (Fe0.4 Mg0.6) (Cr1.6 Al0.4/)O4. The TG-DTG weight losses found to be in the range of 4.4-14.36%, at temperatures between 600 and 750°C, indicated the presence of the hydroxyl-rich silicate minerals, serpentinite and chlorite, in agreement to the Loss of Ignition (LOI) results. The mineral phases detected in the present analyses appear in the dunite/diorite/harzburgite/peridotite main rocks of the ophiolitic complex that hosts the chromite ore. Originality.In the current research, an original characterization, via thorough elemental, phase and thermal analysis, is carried out aiming to enlighten the geochemistry aspects of the Vourinos chromite complex, Region of Western Macedonia, Greece, particularly of easily accessible and exploitable chromite deposits of the Aetoraches mine area. Practical implications. The chromite mineral, and especially the metallurgical type, is of substantial importance in metal industry. In that sense, the findings of the present investigation of chromite purity and mineral structure is a prerequisite for future exploitation of the Aetoraches chromite deposits in particular and broadly for the ongoing exploitation of chromite ore in the Vourinos complex, situated in Region of Western Macedonia, Greece, an area with high unemployment and rather slow economic growth. Keywords: chromite ore, Vourinos massif, Aetoraches mine area, mineralogical characterization, geochemistry, XRD, SEM-EDS, TG/DTG

Crystal structure determination of kosnarite, KZr2(PO4)3, from the Mario Pinto Mine, Jenipapo district, Itinga, Brazil

ABSTRACT The crystal structure of a natural kosnarite, KZr2(PO4)3 from the Mario Pinto Mine, Jenipapo district, Brazil, has been determined for the first time. Kosnarite and its related synthetic compounds (NZP) are open-framework orthophosphates of the type ([6]M′[8]M′′)L2(TO4)3 (where M = Li, Na, K, Rb, Cs; L = Ti, Zr, Hf; and T = P, Si). These compounds have been proposed as potential radioactive waste hosts as a result of their physiochemical properties and because their crystal structure allows for extreme isomorphism and incorporation of all 42 radioactive nuclides present in nuclear waste. Kosnarite from the Mario Pinto mine is hexagonal, Rc, with a = 8.7205(1), c = 23.9436(3) Å, and V = 1576.89(4) Å3. The average chemical formula (n = 75) is (K0.96Na0.02)Σ0.98(Zr1.93Hf0.08)Σ1.01(P2.99Si0.01)Σ3.00O12. The structure contains one six-coordinated Zr site (L), one four-coordinated P site (T), and a six-coordinated K site (M′); in kosnarite, the M″ site is vacant. The average bond lengths in the ZrO6 octahedra (2.0646 Å) and PO4 tetrahedra (1.5278 Å) are slightly larger than those observed in the synthetic analogue (<Zr–O> = 2.063 Å, <P–O> = 1.522 Å). The ZrO6 octahedra and PO4 tetrahedra share corners to form ribbons of [Zr2(PO4)3]– units parallel to the c axis, which are further joined by PO4 tetrahedra perpendicular to c to form a 3D network. Kosnarite is one of only five natural alkali zircono-orthophosphates, all of which are late-stage hydrothermal minerals. Although synthetic Na-dominant endmember analogues of kosnarite exist, the distortions in the structure with respect to the M and L octahedra, along with experimental evidence at hydrothermal temperatures, suggest that only K (or Li) endmembers are possible in nature.

Fosfohedyfán z opuštěného železnorudného ložiska Hraničná (Slezsko, Česká republika)

Abandoned iron skarn deposit Hraničná is located 16 km NW of Jeseník, Silesia, Czech Republic. It is situated in the Staré Město Crystalline Complex, belt of high grade metamorphic rocks, which suppose to be a meta-ophiolite of the initial Cambro-Ordovican rifting. The deposit itself is formed by two stratiform magnetite-hematite bands within the marbles and quartz-rich biotite gneisses. Marbles containing silicates are rich in Zn and Pb and give evidence for sedimentary of volcanosedimentary origin of the ore accumulation. We collected several samples at the adit and +20 m levels of the mine which yielded phosphohedyphane. Mineral forms irregular aggregates up to 100 μm within the calcite-dolomite-magnetite skarn. Its average chemical formula from 7 WDS spots is (Ca2.07Sr0.03Ba0.01Mg0.02Pb3.23Zn0.01Fe0.09Al0.01)Σ5.47[(PO4)2.53(AsO4)0.03(SO3)0.01(SiO4)0.24]Σ2.81[Cl1.05F0.20]Σ1.25 based on 13 O+Cl+F. Use of the normalization to Ca1 + Ca2 = 5 and employing the charge balance could lead to the possible presence of (CO3)2- up to 0.60 apfu, resp. 3.61 hm. % CO2; this possible content do not have any effect on mineral classification. It is, therefore, fifth reported occurrence of this mineral in the territory of the Czech Republic and the Bohemian Massif.

Crystallographic Changes Accompanying the Verwey Transition in a Magnetite from Steatite

The crystallographic structural analysis of the magnetite of a steatite rock at 298 K, (saturation magnetization, σ = 95.0 J T-1 kg-1) showed two cubic networks and, below Verwey temperature (TV ca.120 K) a monoclinic structure, basing on their cell dimensions and different transitional behaviors when reducing the temperature. A monoclinic structure was identified from their cell dimensions and different transition behaviors when reducing the temperature. The average chemical formula of this almost stoichiometric magnetite was deduced from the chemical analysis, 298 K-Mossbauer and the structural refinement. The Rietveld fitting of the 298 K X-ray pattern is Fe3+Fe0.953+Fe0.882+Cr0.043+Al0.043+Mg0.052+Ni0.022+⊗0.02O4, where [ ] and { } stand for cations in tetrahedral and octahedral coordination symmetries, respectively. The crystallographic structure below TV in this magnetite was observed from synchrotron X-ray diffraction data (XRD), collected at 15 K. It was identified three structures: two cubic (space group, Fd3m), with significantly different lattice parameters, and one monoclinic (P2/c).

Dellagiustaite: A Novel Natural Spinel Containing V2+

Dellagiustaite, ideally Al2V2+O4, is a new spinel-group mineral from Sierra de Comechingones, San Luis, Argentina, where it is found associated with hibonite (containing tubular inclusions, 5–100 μm, of metallic vanadium), grossite, and two other unknown phases with ideal stoichiometry of Ca2Al3O6F and Ca2Al2SiO7. A very similar rock containing dellagiustaite has been found at Mt Carmel (northern Israel), where super-reduced mineral assemblages have crystallized from high-T melts trapped in corundum aggregates (micro-xenoliths) within picritic-tholeiitic lavas ejected from Cretaceous volcanoes. In the holotype, euhedral grains of dellagiustaite are found as inclusions in grossite. The empirical average chemical formula of dellagiustaite is (Al1.09 V 0.91 2 + V 0.87 3 + Mg0.08 Ti 0.04 3 + Mn0.01)Σ3O4, but it may show limited replacement of V2+ by Mg and of V3+ by Al. As Al is the dominant trivalent cation, the ideal formula is Al2V2+O4 according to the current IMA rules. Dellagiustaite shows the usual space group of spinel-group minerals (Fd 3 ¯ m, R1 = 1.46%) with a = 8.1950(1) Å. The observed mean bond lengths <T–O> = 1.782(2) Å and <M–O> = 2.0445(9) Å, the observed site scattering (T = 13.3 eps, M = 22.5 eps), and the chemical composition show that dellagiustaite is an inverse spinel: T tetrahedra are occupied by Al3+, whereas M octahedra are occupied by V2+ and V3+, leading to the site assignment as TAlM( V 0.91 2 + V 0.88 3 + Al 0.09 3 + Mg0.08 Ti 0.03 3 + Mn0.01)O4.

Performance and emission analysis of OilJFWPB recovered by the oxidative thermal degradation of the mixture of waste polyethylene and Jute

Five blends of OilJFWPB were prepared with diesel and used as fuel in Kirloskar4 stroke IC engine to investigate the performance and emission characteristics at different engine loads. According to the GC/MS analysis, on the basis of the molecular structure the tentative average chemical formula of the OilJFWPB was calculated as C17.14H34.1401.85N and the theoretical air-fuel ratio of the OilJFWPB for the complete combustion was found to be 12.13. It was reported that EGT, BTE, ME increases and BSFC decreases with increase in load. It was also reported that NOx emission increases and CO emission decreases with increase in load for each blend of OilJFWPB as compared to diesel.

Formation of clay minerals on Mars: Insights from long-term experimental weathering of olivine

Laboratory experiments are useful to constrain the environmental parameters that have allowed the formation of the ancient hydrous mineralogical assemblages observed at the surface of Mars, which are dominated by ferric smectites. Weathering under a dense CO2 atmosphere on early Mars is a process frequently invoked to explain their formation, but has proven difficult to test in the laboratory due to low reaction rates. Here, we present a long-term weathering experiment (470 days, at 45 °C) of forsteritic olivine specially designed to increase as much as possible the amount of reaction products and thus allow their detailed mineralogical, petrological and chemical characterization by FTIR, SEM and TEM. Our results show the formation of crystalline smectites both under 1 bar of CO2 and under ambient air. However, important differences are observed between the two types of conditions. The smectite formed under CO2 has an average chemical formula per half unit-cell of Si3.92Al0.16Fe3+0.78Mg1.66 Cr0.01Ni0.06K0.04Ca0.04.O10(OH)2. It is thus intermediate between a trioctahedral Mg-rich saponite and a dioctahedral ferric smectite. It is also clearly enriched in Fe compared its counterpart formed under ambient air, which has an average chemical formula per half unit-cell of Si3.68Al0.12Fe3+0.37Mg2.61Cr0.01Ni0.02K0.04Ca0.25.O10(OH)2. This result demonstrates that the enrichment in Fe observed for Martian smectites is to be expected if they were formed by low-temperature weathering under a dense CO2 atmosphere. Another difference is the nature of the accompanying phases, which includes amorphous silica (in the form of opal spheres 10 to 100 nm in diameter) and Mg-carbonates under CO2, but is limited to rare kaolinite under ambient air. The observation of kaolinite particles under air and the significant amount of Al measured in smectites under both atmospheres, despite the Al-poor nature of the initial material, shows that this element is easily concentrated by low-temperature weathering processes. At a larger scale, this concentration mechanism could be responsible for the formation of Al-rich upper horizons, as frequently observed on Mars.

Characterisation of Authentic Lignin Biorefinery Samples by Fourier Transform Infrared Spectroscopy and Determination of the Chemical Formula for Lignin

Efficient methods for lignin characterisation are increasingly important as the field of lignin valorisation is growing with the increasing use of lignocellulosic feedstocks, such as wheat straw and corn stover, in biorefineries. In this study, we characterised a set of authentic lignin biorefinery samples in situ with no prior purification and minimal sample preparation. Lignin chemical formulas and lignin Fourier transform infrared (FTIR) spectra were extracted from mixed spectra by filtering out signals from residual carbohydrates and minerals. From estimations of C, H and O and adjustment for cellulose and hemicelluloses contents, the average chemical formula of lignin was found to be C9H10.2O3.4 with slight variations depending on the biomass feedstock and processing conditions (between C9H9.5O2.8 and C9H11.1O3.6). Extracted FTIR lignin spectra showed many of the same characteristic peaks as organosolv and kraft lignin used as benchmark samples. Some variations in the lignin spectra of biorefinery lignin residue samples were found depending on biomass feedstock (wheat straw, corn stover or poplar) and on pretreatment severity, especially in the absorbance of bands at 1267 and 1032 cm−1 relative to the strong band at ~1120 cm−1. The suggested method of FTIR spectral analysis with adjustment for cellulose and hemicellulose is proposed to provide a fast and efficient way of analysing lignin in genuine lignin samples resulting from biorefineries.

Single-crystal X-ray diffraction, EMPA, FTIR and X-ray photoelectron spectroscopy study of narsarsukite from Murun Massif, Russia

AbstractA crystal chemical study of narsarsukite from the Murun alkaline massif, Russia has been carried out combining single-crystal X-ray diffraction, electron microprobe analyses, micro-Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The narsarsukite single crystals are tetragonal (space group I4/m) with unit-cell parameters: 10.7140(1) ≤ a ≤ 10.7183(2) Å and 7.9478(1) ≤ c ≤ 7.9511(1) Å. The XPS analysis showed that Fe occurs in the mineral as Fe3+, whereas the FTIR spectrum showed that the sample studied is anhydrous. The average crystal chemical formula of the Murun narsarsukite is: Na2.04K0.01(V0.015+Ti0.74Zr0.01Al0.01Fe0.223+Mg0.01)1.00Si4.00(O10.74F0.23OH0.03)11.00. Structural disorder at octahedral and interstitial sites was modelled and also discussed in consideration of the main substitutional mechanism Ti4+ + O2– ↔ Fe3+ + (F–, OH–) active in the structure of the mineral.

Elemental analysis of various biomass solid fractions in biorefineries by X-ray fluorescence spectrometry

Elemental analysis by X-ray fluorescence spectrometry (XRF) of solid samples from a biorefinery process was performed to study the behaviour of mineral elements in a process involving hydrothermal pretreatment of biomass (wheat straw, corn stover, sugarcane bagasse, palm oil empty fruit bunches, poplar) followed by enzymatic hydrolysis and fermentation. For all the different biomasses, the biorefinery process concentrated silicon, aluminium, and calcium in the solid fraction, while potassium and magnesium were solubilised in the process and removed from the solid fraction. Sodium concentrations were in general low and they only increased in case of addition during the process. No general tendencies were observed for phosphorus, sulphur, and iron concentrations. A prerequisite for XRF elemental analysis was defining an average chemical formula for the organic matrix of process biomass samples. Based on ultimate elemental analysis of all biomasses, the formula for biomass was C6H8.4O3.5, which was used for all types of samples (raw biomass, pretreated biomass, and lignin residue) and can be used in future XRF analysis of samples of similar process and biomass feedstock as those used in this study.

XRD and TEM Studies on Nanophase Manganese Oxides in Freshwater Ferromanganese Nodules from Green Bay, Lake Michigan

AbstractFreshwater ferromanganese nodules (FFN) from Green Bay, Lake Michigan have been investigated by X-ray powder diffraction (XRD), micro X-ray fluorescence (XRF), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and scanning transmission electron microscopy (STEM). The samples can be divided into three types: Mn-rich nodules, Fe-Mn nodules, and Fe-rich nodules. The manganese-bearing phases are todorokite, birnessite, and buserite. The iron-bearing phases are feroxyhyte, goethite, 2-line ferrihydrite, and proto-goethite (intermediate phase between feroxyhyte and goethite). The XRD patterns from nodule cross sections suggest the transformation of birnessite to todorokite. The TEM-EDS spectra show that todorokite is associated with Ba, Co, Ni, and Zn; birnessite is associated with Ca and Na; and buserite is associated with Ca. The todorokite has an average chemical formula of Ba0.28p2+(Zn0.14p+2Co0.05p3+Ni0.02p2+) (Mn4.99p4+Mn0.82p3+Fe0.12p3+Co0.05p3+Ni0.02p2+) O12·nH2O. Barium is the main cation in the structural tunnels of the todorokite. The average chemical formula of birnessite and Ca-buserite are: Na0.14p+Ca0.19p2+(Mn1.48p4+Mn0.52p3+0.52) O4·nH2O and Ca0.27p2+(Mn1.46p4+Mn0.54p3+)O4·nH2O, respectively. Most nodules have a concretionary structure of alternating Fe/Mn layers, commonly with a core of reddish feldspar containing phyllosilicates and hematite micro-crystals. Other cores consist of goethite, cristobalite, tridymite, hercynite, hematite-bearing quartz, coal, and chlorite-bearing rock fragments. The hexagonal or hexagonal-like structures of hematite micro-crystals and clay minerals in the cores may serve as heterogeneous nucleation sites for the Mn-oxides and Fe-(oxyhydr)oxides. The alternating Fe/Mn layers in FFNs might be caused by oscillatory redox condition fluctuations at the sediment-water interface due to changes in water level.

Enantioselective silver nanoclusters: Preparation, characterization and photoluminescence spectroscopy

Herein, we report a new wet-synthesis method to separate some water-soluble chiral silver nanoclusters with high yield. The cluster material was obtained by the reduction of silver nitrate with NaBH4 in the presence of three ligands l-penicillamine (l-pen), d-penicillamine (d-pen) and racemic mixture of penicillamine (rac-pen), functioning as capping ligand. For characterizing all silver cluster samples, the particle size was assessed by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) and their average chemical formula was determined from thermogravimetric analysis (TGA) and elemental analysis (EA). The particles sizes of all three clusters are 2.1 ± 0.2 nm. The optical properties of the samples were studied by four different methods: UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), photoluminescence spectroscopy (PL) and circular dichroism (CD) spectroscopy. The spectra are dominated by the typical and intense plasmon peak at 486 nm accompanied by a small shoulder at 540 nm. Infrared spectroscopy was measured for the free ligand and protected silver nanoclusters, where the disappearance of the S-H vibrational band (2535–2570 cm−1) in the silver nanoclusters confirmed anchoring of ligand to the cluster surface through the sulfur atom. PL studies yielded the fluorescent properties of the samples. The main focus of this work, however, lies in the chirality of the particles. For all silver clusters CD spectra were recorded. While for clusters capped with one of the two enantiomers (D- or L-form) typical CD spectra were observed, no significant signals were detected for a racemic ligand mixture. Furthermore, silver clusters show quite large asymmetry factors (up to 3 × 10−4) in comparison to most other ligand protected clusters. These large factors and bands in the visible range of the spectrum suggest a strong chiral induction from the ligand to the metal core. Textural features of the prepared silver nanoclusters were investigated using nitrogen adsorption-desorption at −196 °C. Specific surface area SBET, pore volume and average pore diameter were calculated.

Oxo-magnesio-hastingsite, NaCa2(Mg2Fe3+3 )(Al2Si6)O22O2, a new anhydrous amphibole from the Deeti volcanic cone, Gregory rift, northern Tanzania

AbstractOxo-magnesio-hastingsite, ideally NaCa2(Mg2Fe3+3)(Al2Si6)O22O2, is a new anhydrous amphibole from the Deeti volcanic cone in the Gregory rift (northern Tanzania). The mineral occurs as megacrysts up to 12 cm in size in crystal-rich tuff. Oxo-magnesio-hastingsite is brown with a vitreous lustre and has a perfect {110} cleavage. The measured density is 3.19(1) g/cm3. Ferri-kaersutite is biaxial (–), α = 1.706 (2), β = 1.715(2), γ = 1.720(2) (Na light, 589 nm). 2V (calc.) = 73°. Dispersion: r > v, weak; orientation: Y = b; Z ^ c = 8°; pleochroism: strong, Z: dark brown, Y: brown, X: light brown. The average chemical formula of the mineral derived from electron microprobe analyses, Mössbauer spectroscopy and direct water determination is (Na0.67K0.33)Σ1.00(Ca1.87Na0.14Mn0.01)Σ2.02(Mg3.27Fe3+1.25Ti0.44Al0.08)Σ5.04(Al1.80Si6.20O22)(O1.40OH0.60)Σ2.00. It has monoclinic symmetry, space group C2/m and unit-cell parameters a = 9.8837(3), b = 18.0662(6), c = 5.3107(2) Å, b = 105.278(1)o, V = 914.77(5) Å3, Z = 2. The five strongest powder-diffraction lines [d in Å, (I/Io), hkl] are: 3.383 (62) (131), 2.708 (97) (151), 2.555 (100) (), 2.349 (29) () and 2.162 (36) (261). The isotopic composition of H and O, as well as the concentration of trace elements in oxo-magnesio-hastingsite suggest its formation from a melt originated from a mantle source metasomatized by slab-derived fluids.

Antiferromagnetic phase transition of K-Rb alloy nanoclusters incorporated in sodalite

We prepared Rb-rich K-Rb alloy nanoclusters arrayed in the regular nanospace of aluminosilicate sodalite which has a bcc arrangement of cages. The average chemical formula of the cluster is (K1.5Rb2.5)3+, where one unpaired s-electron is shared by four alkali cations and is confined in a cage. The magnetic susceptibility and the electron spin resonance clearly show an antiferromagnetic phase transition at a Neel temperature TN of approximately 90–100 K. The observed TN is higher than that in K43+ (TN = 72 K) and (K3Rb)3+ clusters (TN = 80 K) in sodalites. This result indicates a systematic enhancement of the antiferromagnetic exchange coupling between the adjacent nanoclusters by substituting Rb atoms for K ones. The size and the spatial distribution of the s-electron wave function in the nanocluster play a key role in the exchange coupling.

Average chemical properties and potential formation pathways of highly oxidized organic aerosol

Measurements of ambient organic aerosol indicate that a substantial fraction is highly oxidized and low in volatility, but this fraction is generally not reproduced well in either laboratory studies or models. Here we describe a new approach for constraining the viable precursors and formation pathways of highly oxidized organic aerosol, by starting with the oxidized product and considering the possible reverse reactions, using a set of simple chemical rules. The focus of this work is low-volatility oxidized organic aerosol (LV-OOA), determined from factor analysis of aerosol mass spectrometer data. The elemental composition and volatility of the aerosol enable the determination of its position in a three-dimensional chemical space (defined by H/C, O/C, and carbon number) and thus its average chemical formula. Consideration of possible back-reactions then defines the movement taken through this chemical space, constraining potential reaction pathways and precursors. This approach is taken for two highly oxidized aerosol types, an average of LV-OOA factors from ten field campaigns (average formula C10.5H13.4O7.3), and extremely oxidized LV-OOA (from Mexico City, average formula C10H12.1O8.4). Results suggest that potential formation pathways include functionalization reactions that add multiple functional groups per oxidation step, oligomerization of highly oxidized precursors, and, in some cases, fragmentation reactions that involve the loss of small, reduced fragments.