Heterogeneous Chemical Composition Research Articles

Advanced Icephobic Coatings

Adhesion and excessive accumulation of atmospheric ice on the surface of exposed objects such as conductors of overhead power lines, cables and conductors in aluminum can have devastating economical and safety consequences as it was the case during the 1998 and 2007 ice storms in Canada and USA. Recent advances in the understanding of ice adhesion on various substrates and in materials science have spurred interest in developing new intrinsic icephobic materials. The aim of this paper is to review the most relevant research activities related to ice adhesion mechanisms and icephobic coating development during the recent years. This will allow a better comprehension of ice adhesion, and help determine more reliable and cost effective ways to develop icephobic coatings, In order to develop icephobic coatings three main groups of materials or surface treatment can be considered: (i) self-assembled monolayers with –CH3 or –CF3 groups oriented outward to the ice surface, (ii) coatings with a heterogeneous chemical composition of at least two highly hydrophobic components to disrupt the structure of the liquid-like layer, and finally (iii) a porous or superhydrophobic deposits to promote the presence of tiny air pockets at the ice/solid interface to disrupt bonding by creating stress concentrations.

Electrodeposition and characterization of manganese–bismuth system from chloride based acidic bath

In this work, Mn–Bi system has been successfully electrodeposited on Cu/Si substrates from aqueous ammonium chloride containing electrolyte. A thermodynamic study of the electrolysis bath highlights the possible formation of manganese complexes ( MnCl + , MnCl 2 , MnC l 3 − ) and bismuth complexes ( BiCl 2+ , BiC l 2 + , BiCl 3 , BiC l 4 − , BiC l 5 2 − , BiC l 6 3 − ) . The mechanism process involving Mn and Bi electrodeposition is investigated by cyclic voltammetry. Mn–Bi films can be grown under potentiostatic control. The physico-chemical, morphological and structural characterizations of the deposits were carried out by scanning electron microscopy (SEM) and X-rays analysis (XRD). The results reveal a granular surface quality and a heterogeneous chemical composition of the films. The energy dispersive spectroscopy (EDS) analysis reveals the presence of manganese and bismuth peaks whose relative intensities vary according to the imposed potential and the position on the sample. The X-rays diffraction analysis showed three different crystalline phases: α-manganese (body centred cubic system), γ-manganese (body centred tetragonal system) and bismuth (rhombohedral system).

Characterization of Ethylene Copolymers with Liquid Chromatography and Melt Rheology Methods

AbstractSummary: Melt rheology and polymer chromatography methods were applied to characterize molecular heterogeneities in products of free radical copolymerization of ethylene with methyl acrylate and vinyl acetate comonomers performed in continuously stirred tank and tubular reactors. We found that the ethylene–vinyl acetate copolymers made in both reactors had similar linear viscoelastic properties typical to branched products of the high pressure process. But the ethylene–methyl acrylate copolymers obtained in the tubular reactor had unusually high melt viscosity at low shear rate and much lower onset of shear thinning despite the narrower molecular weight distribution and the lower overall amount of long‐chain branches compare to their autoclave counterparts with similar average molecular weight and chemical composition. Using interaction polymer chromatography method called gradient elution at critical point of adsorption we found that ethylene‐acrylate copolymers from the tubular reactor had very broad chemical composition distribution, which was consistent with a significant difference in reactivity ratios between ethylene and acrylate comonomers. Such chemical composition heterogeneity can be a reason for the observed unusual rheological properties of these copolymers.

Low-energy X-ray fluorescence microscopy opening new opportunities for bio-related research

Biological systems are unique matter with very complex morphology and highly heterogeneous chemical composition dominated by light elements. Discriminating qualitatively at the sub-micrometer level the lateral distribution of constituent elements, and correlating it to the sub-cellular biological structure, continues to be a challenge. The low-energy X-ray fluorescence microspectroscopy, recently implemented in TwinMic scanning transmission mode, has opened up new opportunities for mapping the distribution of the light elements, complemented by morphology information provided by simultaneous acquisition of absorption and phase contrast images. The important new information that can be obtained in bio-related research domains is demonstrated by two pilot experiments with specimens of interest for marine biology and food science. They demonstrate the potential to yield important insights into the structural and compositional enrichment, distribution and correlation of essential trace elements in the lorica of Tintinnopsis radix, and the lateral distribution of trace nutrients in the seeds of wheat Triticum aestivum.

Microwave heating of different commercial categories of olive oil: Part II. Effect on thermal properties

Abstract The effect of microwave heating of commercial categories of olive oil for human consumption (extra virgin olive oil [EVOo], olive–pomace oil [Po] and olive oil [Oo]) on DSC thermal properties was evaluated at different times of microwave treatment. Marked changes of DSC cooling profiles were found for EVOo and Po subjected to microwaving, with the major exotherm that shifted towards lower temperature and decreased height with increasing treatment time. Thermal properties (during DSC cooling analysis) changed in all samples: crystallisation enthalpy significantly decreased and the phase transition developed over a larger temperature range, due to more heterogeneous chemical composition of all oils that resulted from triacylglycerol lysis to the formation of lipid oxidation products. Heating profiles of EVOo and Po were also modified by microwave treatment, as the minor endotherm progressively disappeared, significantly shifting offset temperature of transition towards lower temperature. Oo did not exhibit such changes of thermal properties and phase transition profiles as described for EVOo and Po. This may be mainly related to its lower water content although the simultaneous presence of small amounts of antioxidant molecules (polyphenols) may have contributed to partially prevent thermal degradation of this oil in comparison with the others. These preliminary results suggest that DSC can be useful, not only for monitoring modifications of chemical composition with increasing microwave treatment time, but also to discriminate amongst olive oils according to their response to microwave exposure.

Fluoride optical nanoceramics

The methods for preparation of highly transparent optical ceramics based on simple and complex fluoride compounds of elements of the first, second, and third Group in the Periodical system are considered. The use of precursors as nanopowders and processes of their self-assembling on heating results in maximally homogeneous, transparent, and mechanically strong ceramics. The resulting calcium fluoride ceramics possess optical losses of 10−2–10−3 cm−1 at 1.06 μm and shock resistance characterized by the fracture toughness K1C = 4.7±0.3 MPa m1/2 (for comparison, for a calcium fluoride single crystal K1C = 1.5±0.15 MPa m1/2). Regularities of the chemistry of fluoride nanopowders were considered in comparison with the oxide nanopowders: the fluorides are prone to hydrolysis, and powder nanoparticles precipitated from aqueous solutions have complex and heterogeneous (over the volume) chemical composition. The spectral luminescence properties of the ceramics activated by rare-earth metals (Ce3+, Nd3+, Er3+, Yb3+) or containing active color centers are presented. The generation properties of the lithium fluoride ceramics with the color centers and the ternary Ca-Sr-Yb fluoride during diode laser pumping are describe

Synthesis of Core−Shell Ferrite Nanoparticles for Ferrofluids: Chemical and Magnetic Analysis

A chemical core−shell strategy is developed here for the synthesis of ferrofluids based on nanoparticles of different ferrites with different mean sizes. A heterogeneity of chemical composition, associated with a superficial enrichment of iron, allows to obtain chemically stable ionic colloids. We propose here a core−shell model to describe the synthesized nanoparticles, which is tested by chemical and magnetic measurements performed at the various steps of the synthesis. The thickness of the superficial layer, rich in iron, is ranging between 0.4 and 1.3 nm, depending on the nanoparticle size and on the underlying ferrite. Its density is found close to that of maghemite, and its magnetization depends on the core ferrite. It is low with a cobalt ferrite core and larger for the three other ferrites investigated here (NiFe2O4, CuFe2O4, and ZnFe2O4). Magnetic measurements prove that there is a strong redistribution of Zn2+ ions inside the core of the synthesized nanoparticles based on ZnFe2O4.

TOF‐SIMS analysis of cometary particles extracted from Stardust aerogel

Abstract— Sections of seven cometary fragments extracted from the aerogel collector flown on the Stardust mission to comet 81P/Wild 2 were investigated with TOF‐SIMS. These grains showed a rather heterogeneous chemical and mineralogical composition on a submicrometer scale. However, their average chemical composition is close to bulk CI chondritic values, which is consistent with analyses of numerous Stardust samples using various techniques. As a result, the TOF‐SIMS analyses support the conclusion that Wild 2 has a CI‐like bulk composition. The cometary particles resemble anhydrous chondritic porous interplanetary dust particles, which have previously been suggested to originate from comets. For one of the fragments, polycyclic aromatic hydrocarbons that could possibly be attributed to the comet were observed.

Dynamical equilibrium in nanoalloys

Using Monte Carlo simulations on a lattice-gas model, we study the segregation isotherm of a cluster made of thousands of atoms for a system that tends to phase separate, e.g., Cu-Ag. We show that the Ag segregation involves the vertices first, then the edges and finally the (111) and (100) facets. In these facets, the segregation starts on the outer shells, leading to a heterogeneous chemical composition. When the nominal Ag concentration (or the chemical potential difference delta(mu)c between Ag and Cu), is increased a dynamical equilibrium replaces the progressive evolution of the segregation towards the core of the facets: the whole facet oscillates between one pseudo Ag-pure state and another one corresponding to a rather Cu-pure core surrounded by Ag-enriched outer shells. A remarkable consequence is that very different concentrations can be observed for facets of equivalent orientation. This dynamical equilibrium occurs in a delta(mu) range that is very close to the critical value delta(mu)c associated with the first-order phase transition of the Fowler-Guggenheim type that affects the surfaces of semi-infinite alloys. These results, which have been obtained in the grand-canonical ensemble, can also be derived in the canonical ensemble due to a sufficient number of facets that behave with each other as a reservoir.

Role of composition heterogeneity on fracture micromechanisms of nodular cast iron

The aim of the present study is to explain the role of chemical composition and heterogeneity within the microstructure of nodular cast iron on the micromechanisms of fracture. The heterogeneity in chemical composition is revealed by a thorough study of the microstructure using scanning electron microscopy, Auger electron spectroscopy and colour etching. The ferritic phase surrounding the graphite globules is enriched by silicon and depleted of manganese in the range of micrometres. Maximum manganese concentration is found in regions distant from these particles and in pearlitic regions. Simultaneously, ferritic grain boundaries in the vicinity of the graphite particles are enriched in phosphorus in the nanometer range. This interfacial segregation, reaching nearly 15 at.-%P, is most probably responsible for an embrittlement of these regions and the appearance of intercrystalline decohesion. An elastic-plastic finite element analysis of the ferritic/pearlitic microstructure demonstrates that a heterogeneous microstructure is locally subjected to heterogeneous stresses and strains, which are also expected to affect fracture mechanisms.

2.61 Ga potassic granites and crustal reworking in the western Dharwar craton, southern India: Tectonic, geochronologic and geochemical constraints

We present combined field, structural data and spot image analysis, petrographic data, U–Pb zircon ages, Nd isotopes and whole-rock geochemical data for the late Archaean granite plutons from Arsikere–Banavara (AB suite) and Chitradurga–Jampalnaikankote–Hosdurga (CJH suite), in the western Dharwar craton (WDC). AB plutons are syn-kinematic with respect to the development of dome-and-basin patterns resulting from partial crustal diapiric overturn (D1), whilst CJH suite plutons show deformation patterns resulting from the superimposition of large-scale regional strike-slip shearing (D2) onto D1 syn-emplacement fabrics. SIMS U–Pb zircon ages of 2614±10Ma for the Chitradurga pluton (CJH) and of 2617±3Ma for the Arsikere pluton (AB) define the minimum age of the D1 strain pattern.The CJH and AB suites are mainly high-K granites whose origin is to be sought in partial melting of an old (>3.0Ga) depleted lower crust of intermediate composition. The CJH and AB suites correspond mainly to the CA1- and CA2-types of Archaean calc-alkaline granites and some facies to the transitional TTG. Their heterogeneous chemical compositions indicate involvement of various sources and also significantly different depths of partial melting to produce these granites.These results allow documenting regional partial reworking of the WDC 2615Ma ago, requiring an HT event to have taken place before 2.61Ga and thus different from the 2.55 to 2.51Ga granulite facies metamorphic episode associated to regional-scale strike-slip shearing (D2) that affected the entire craton. Partial reworking of the older lower crust at 2.61Ga and associated deformation would result from heat advection and/or crustal thickening that may relate to voluminous mafic greenstone volcanism and moderate shortening at that time.

Monitoring of Petroleum-Related Environmental Contamination Using Fluorescence Fingerprinting

Petroleum and its refined products are considered the most complex contaminants frequently impacting the environment in significant quantities. They have heterogeneous chemical composition and alterations occur during environmental weathering. No single analytical method exists to characterize the petroleum-related environmental contamination. For monitoring, the analytical approaches include gravimetric, spectrometric and chromatographic methods having significant differences in their selectivity, sensitivity and cost-effectiveness. Recording fluorescence fingerprints of the cyclohexane extracts of the water, suspended solids, sediment or soil samples and applying appropriate statistical evaluation (e.g. by correlating the concatenated emission spectra of the fingerprints of the samples with arbitrary standards (e.g. petroleum products)), provides a powerful, cost-effective analytical tool for characterization of the type of oil pollution and detecting the most harmful aromatic components of the petroleum contaminated matrix. For monitoring purposes, the level of the contamination can be expressed as the equivalent concentration of an appropriate characteristic standard, based on the fluorescence intensities at the relevant characteristic wavelengths. These procedures are demonstrated in the monitoring of petroleum-related pollution in the water and suspended sediment in the Danube river basin

Influence of accompanying substances of hemp fibres on their electric resistance

Hemp fibres belong to the group of natural, cellulose bast fibres. These fibres have exceptional properties such as: antimicrobial effect, absence of allergy effect, extraordinary sorption properties, good electro-physical properties (small static electricity in regard to other cellulose fibres) as well as high values of breaking strength (the natural fibre with the highest strength). However, hemp fibres have some defects: heterogeneous chemical composition, large quantity of accompanying substances (lignin pectins, waxes) and unsatisfactory fineness and eveness. It is possible to a great extent to eliminate or reduce, the defects of hemp fibres by of appropriate modification treatments. In order to determine the appropriate modification treatment of hemp fibres, the dependences between the chemical composition, fineness and electric resistance of hemp fibres were presented in this paper. In the experimental part of the paper, by the application of a procedure for the determination of the chemical composition, the accompanying supstances of hemp fibres were gradually removed. After each phase some fibrous substrates were separated. After that the fineness and electric resistance were determined. This experiment was conducted in order to define the influence of each component of hemp fibres on the fineness and electric resistance. In this paper, hemp fibres were modified by an aqueous solution of sodium hydroxide, under different conditions of modification. The influence of modification conditions on the fineness and electric resistance were studied.

Permeability Change of Crystalline Silicate Mineral-Packed Bed Column by Highly Alkaline Plume

AbstractFor the construction of the geological disposal system, the use of the cementitious material may affect the permeability change of the natural barrier around the repository. In practice, the construction requires a large amount of cement to maintain the mechanical stability of the repository system, particularly in Japan. Since such material alters the pH of ground water to highly alkaline region, also the permeability change of natural barrier is one of the notable factors for the performance assessments of geological disposal system.In the high pH region, the solubility of silicic acid is very high compared to that in the natural pH (around 8). Therefore, the highly alkaline groundwater would dissolve and alter a part of rock surface. Usui et al. (2005) reported that the change of the pore structure due to the chemical reaction is the key factor to consider the change of the permeability. Moreover, such a change of the pore structure was considered as the result of the spatial heterogeneity of chemical composition. Since such spatial heterogeneity exists also in the sedimentary rocks consisted of crystalline minerals such as quartz and feldspar, we need to examine natural rock, in order to obtain more reliable understanding about the change of permeability induced by the highly alkaline groundwater (plume).In this study, as crystalline mineral, silica sand was packed in the column, and the effect of dissolution induced by the highly alkaline plume on the permeability-change was examined. The silica sand particles mainly consist of SiO2 partially including Al2O3, CaO, Na2O3, and K2O. The volumetric flow rate and the pressure difference between the inlet and outlet of the column were measured, and the permeability was calculated. At the same time, the concentration of elements in the fluid was measured by the ICP-AES.The experimental result showed that permeability decreased gradually, although the silica sand was continuously dissolved in the column. The behavior of the permeability is considered to be the result from the rearrangement of the particles. In the column test using the silica sand as packed mineral, the flow-path seems to be clogged by the rearrangement of the particles rather than the increase of the pore between the particles.

Compositional Mapping of Polymer Surfaces by Chemical Force Microscopy Down to the Nanometer Scale: Reactions in Block Copolymer Microdomains

AbstractThe laterally resolved analysis of the chemical surface composition of surface‐treated block copolymers by atomic force microscopy (AFM) pull‐off force mapping in the force volume (FV) mode and the automated analysis of the FV data is discussed. Poly(tert‐butyl acrylate) (PtBA) microdomains residing in a polystyrene (PS) matrix at the surface of cyclohexane‐treated polystyrene‐block‐poly(tert‐butyl acrylate) (PtBA‐b‐PS) block copolymer thin films were domain‐selectively deprotected, activated and chemically modified, as also shown by fluorescence microscopy. AFM pull‐off force mapping in conjunction with an automated analysis of the data provided real space evidence for the successful conversion of reactive esters located in the PtBA domains and showed that AFM and related approaches, such as chemical force microscopy (CFM), can indeed contribute to assess changes in heterogeneous surface chemical composition of polymers down to sub‐50 nm length scales.

Spatially inhomogeneous crystallinity in heterogeneous ethylene‐α‐olefin copolymers

AbstractThe crystallinity development in heterogeneous ethylene‐1‐butene copolymers is compared with that in ethylene copolymers, with more bulky 1‐heptene as a comonomer. The thermal transitions of the 1‐heptene based copolymers persistently occur at higher temperatures than of the corresponding 1‐butene copolymers. The earlier crystallization onset is reflected in thicker primary crystals, which in turn are associated with the presence of longer ethylene sequences because of the inaccessibility of 1‐heptene to sterically shielded catalytic sites. In addition, the 1‐heptene based copolymers are characterized by a higher degree of primary crystallinity, whereas the 1‐butene copolymers exhibit more prominent secondary crystallization. The 1‐butene based copolymers thus have a less heterogeneous chemical composition distribution. At high comonomer contents, the highly heterogeneous nature of the 1‐heptene copolymers is emphasized by a more pronounced presence of low crystalline spherulite inclusions accomplished by the liquid–liquid phase separation of dissimilar polymeric chains before crystallization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3000–3018, 2005

Effect of Temperature on the Adsorption of Water in Porous Carbons

We report experimental and simulation studies to investigate the effect of temperature on the adsorption isotherms for water in carbons. Adsorption isotherms are measured by a gravimetric technique in carbon-fiber monoliths at 378 and 423 K and studied by molecular simulation in ideal carbon pores in the temperature range 298-600 K. Experimental adsorption isotherms show a gradual water uptake, as the pressure increases, and narrow adsorption-desorption hysteresis loops. In contrast, simulated adsorption isotherms at room temperature are characterized by negligible uptake at low pressures, sudden and complete pore filling once a threshold pressure is reached, and wide adsorption-desorption hysteresis loops. As the temperature increases, the relative pressure at which pore filling occurs increases and the size of the hysteresis loop decreases. Experimental adsorption-desorption hysteresis loops are narrower than those from simulation. Discrepancies between simulation and experimental results are attributed to heterogeneities in chemical composition, pore connectivity, and nonuniform pore-size distribution, which are not accounted for in the simulation model. The hysteresis phase diagram for confined water is obtained by recording the pressure-density conditions that bound the simulated hysteresis loop at each temperature. We find that the hysteresis critical temperature, i.e., the lowest temperature at which no hysteresis is detected, can be hundreds of degrees lower than the vapor-liquid critical temperature for bulk model water. The properties of confined water are discussed with the aid of simulation snapshots and by analyzing the structure of the confined fluid.

P–T–fO2 controls on a partly inverse chromite-bearing ultramafic intrusive: an evaluation from the Sukinda Massif, India

The chromites from the alpine type ultramafic intrusive of Sukinda, India, display a typical partly inverse spinel form and occur in two distinct zones: Brown Ore Zone (BOZ) and Grey Ore Zone (GOZ). The host ultramafites are mostly altered and are represented by the serpentinite, tremolite-talc(chlorite) schist, talc-serpentine schist and chlorite rock. The less altered variants are dunite, harzburgite and websterite. A dyke of orthopyroxenite runs through the main ultramafic body.The composition of olivine (Fo92), orthopyroxene (En92–89) and Al2O3 contents of the parental liquid (10.40–11.45%) determined from chromites, suggest that the parent melt is of boninitic affinity. The chemical plot of TiO2 content against cr# of chromites corroborates a boninitic parental melt. The Fe–Mg partitioning in olivine and chromite depicts the temperature for chromitites as 1200 °C. A compositional plot of mg# and cr# suggests crystallization at high pressure conditions, corresponding to the kimberlite xenolith field. From the P–T diagram of pyrolite melting and mineral assemblage, the pressure of crystallization is stipulated to be ≥1.2 GPa. The fO2 values estimated from Fe3+/Cr+Al+Fe3+ ratios range from 10−8.3 to 10−9.3 for the GOZ and 10−7.1 to 10−7.3 for the BOZ. The fO2 values together with the pressure range suggest crystallization at upper mantle conditions. The heterogeneity in chemical composition and fO2 conditions for the GOZ and BOZ could be linked to heterogeneity in the upper mantle.

Laboratory observations and mathematical modeling of colloid‐facilitated contaminant transport in chemically heterogeneous systems

In the work reported here, I examine colloid‐facilitated solute transport through a natural porous medium that exhibits grain‐scale heterogeneity in chemical composition. I conducted six column experiments using the contaminant hydroxyatrazine (HA) and either homogeneous clay‐colloid suspensions or mixtures of clay colloids and dissolved organic matter. The transport of colloids composed of illite and montmorillonite, although not conservative, is only slightly affected by rate‐limited mass transfer reactions with the oxide‐coated aquifer material. Coinjection of HA with monomineralogic suspensions of illite colloids produces modest increases in effluent concentrations of HA relative to experiments performed with colloid‐free influent solutions. Montmorillonite colloids have a much higher capacity to bind HA than illite colloids and substantially increase the transport rate of HA in the column experiments. Suwannee River humic acid (SRHA) does not strongly complex aqueous phase HA, but its addition to column influent mixtures that contain HA and montmorillonite suppresses HA adsorption to the clay colloids and promotes a decline in HA mobility. A model for colloid‐facilitated transport, formulated to account for nonuniformity in the kinetics of colloid deposition and HA adsorption, closely describes HA transport in experiments performed with monomineralogic clay‐colloid suspensions, heterogeneous suspensions made of both illite and montmorillonite, and mixtures of montmorillonite and SRHA.

Evidence for crustal components in the mantle and constraints on crustal recycling mechanisms: pyroxenite xenoliths from Hannuoba, North China

Spinel and garnet pyroxenite xenoliths in Cenozoic basalts from Hannuoba, North China show extremely heterogeneous chemical and isotopic compositions ( ε Nd=−27 to +34). Most of these pyroxenites are relatively young, probably late Mesozoic in age, although a few Al-pyroxenites could be very old (∼2 Ga). While their texture and major element compositions suggest an origin of high pressure cumulates, the trace element and isotopic compositions of the Hannuoba pyroxenites require multiple segregation processes from different parental magmas. Strong LREE enrichment, ubiquitous HFSE depletion and some Eu anomalies of the Al- and Cr-pyroxenites indicate the involvement of crust components in their source. Their Sr–Nd isotopic ratios are negatively correlated and plot below the MORB–OIB–IAB–sediment trend, suggesting that the parental melts of the Cr- and Al-pyroxenites may have been derived from a mixture of asthenospheric melts and a long-term evolved continental crust. The garnet pyroxenites significantly deviate from the isotopic array defined by the Al-pyroxenites, due to their relatively high 87Sr/ 86Sr at given ε Nd. They thus more likely represent segregates from melts derived from partial melting of hydrothermally altered oceanic crust (basalts+marine sediment). If the crustal component involved in the Al-pyroxenites is subducted terrigenous sediments or other continental materials from the Archean Sino-Korean Craton, the Al-pyroxenites and garnet pyroxenites may have formed contemporaneously at a palaeo-convergent plate margin. This may be related to the subduction of the Mongol–Okhotsk plate beneath North China during the late Jurassic. Alternatively, if the delaminated lower crust was involved, it implies that most of the Al-pyroxenites are younger than the garnet pyroxenites, and their formation may be temporally correlated with lithospheric thinning during the Cretaceous. This model is attractive because the inferred tectonic evolution from a convergent setting to an extensional environment is consistent with the geologic record in the area.