Low Degree Of Order Research Articles

Mineralogical attenuation for metallic remediation in a passive system for mine water treatment

Passive systems with constructed wetlands have been consistently used to treat mine water from abandoned mines. Long-term and cost-effective remediation is a crucial expectation for these water treatment facilities. To achieve that, a complex chain of physical, chemical, biological, and mineralogical mechanisms for pollutants removal must be designed to simulate natural attenuation processes. This paper aims to present geochemical and mineralogical data obtained in a recently constructed passive system (from an abandoned mine, Jales, Northern Portugal). It shows the role of different solid materials in the retention of metals and arsenic, observed during the start-up period of the treatment plant. The mineralogical study focused on two types of materials: (1) the ochre-precipitates, formed as waste products from the neutralization process, and (2) the fine-grained minerals contained in the soil of the wetlands. The ochre-precipitates demonstrated to be poorly ordered iron-rich material, which gave rise to hematite upon artificial heating. The heating experiments also provided mineralogical evidence for the presence of an associated amorphous arsenic-rich compound. Chemical analysis on the freshly ochre-precipitates revealed high concentrations of arsenic (51,867 ppm) and metals, such as zinc (1,213 ppm) and manganese (821 ppm), indicating strong enrichment factors relative to the water from which they precipitate. Mineralogical data obtained in the soil of the wetlands indicate that chlorite, illite, chlorite–vermiculite and mica–vermiculite mixed-layers, vermiculite, kaolinite and goethite are concentrated in the fine-grained fractions (<20 and <2 μm). The chemical analyses show that high levels of arsenic (up to 3%) and metals are also retained in these fractions, which may be enhanced by the low degree of order of the clay minerals as suggested by an XRD study. The obtained results suggest that, although the treatment plant has been receiving water only since 2006, future performance will be strongly dependent on these identified mineralogical pollutant hosts.

Influence of the semiconductor thickness on the charge carrier mobility in P3HT organic field-effect transistors in top-gate architecture on flexible substrates

In this study, we report on the dependence of the charge carrier mobility μ on the organic semiconductor thickness in organic field-effect transistors (OFETs) fabricated in top-gate architecture on flexible and transparent plastic foils as substrates with regio-regular poly-(3-hexylthiophene) (rr-P3HT) as organic semiconductor and poly(methyl methacrylate) (PMMA) as gate insulator. The gate-voltage dependence of the charge carrier mobility is taken into account by analyzing the mobility according to the Vissenberg and Matters model for charge transport in disordered systems. The transistors exhibit high mobility of almost 0.01 cm 2/(Vs) and long-term stability. After a strong mobility increase by two orders of magnitude with P3HT thickness for very thin films of several nanometer, saturation was observed around 50 nm thickness. It was observed that the exponent of the mobility’s gate-voltage dependence increases from 1.2 to 3.2 when decreasing the semiconductor thickness. A larger exponent is related to a wider distribution of localized states in the tail of an exponential density of states and thus to higher disorder of the system. This finding explains the low mobility in these very thin films and is confirmed by phase contrast AFM measurements, which demonstrate the low degree of order in thin P3HT films.

Heteropolyacid/saponite-like clay complexes and their blends in amphiphilic SEBS

Abstract A synthetic saponite-like clay, Sumecton SA (SSA), was self-assembled with 12-phosphotungstic acid (PTA) heteropolyacid for the preparation of new hybrid nanocomposites for proton exchange membranes. Thermogravimetric analysis (TGA) and Fourier transformed diffuse reflectance spectroscopy (DRIFT) measurements indicate the formation of robust PTA–SSA complexes. The Keggin structure of PTA is preserved within the complexes and is thermally stable up to 450 °C. The amount of PTA incorporated into the clay depends on the PTA–SSA weight ratio used for the complex preparation. PTA incorporation achieved is approximately 2–3 times the PTA content of most reported literature. However, higher PTA incorporation is accompanied by a significant loss of structural clay integrity. Low PTA–SSA weight ratios tend to preserve clay structure, but do not preclude its general amorphization generated by the PTA acidic treatment. PTA–SSA complexes present a low degree of order. Inorganic complexes were blended by melt extrusion with chemically-modified styrene/ethylene-co-butylene/styrene block copolymer (SEBS). Poly(oxyethylene/oxypropylene)-grafted-SEBS is more efficient than maleic anhydride-grafted-SEBS at dispersing PTA–SSA complexes. For both nanocomposite systems, nanoparticles’ size varies between 30 and 300 nm.

Ductile Cu–Al–Mn based shape memory alloys: general properties and applications

Polycrystalline Cu–Al–Mn shape memory alloys (SMAs) with a low degree of order of the β (L21) phase show excellent ductility and exhibit shape memory (SM) properties such as superelasticity, the one way memory effect and the two way memory effect based on martensitic transformation. These SM properties can be greatly enhanced by controlling microstructural factors such as grain size and texture by thermomechanical treatments. In the present paper, the SM properties of ductile Cu–Al–Mn based SMAs and microstructure control to obtain excellent SM characteristics are reviewed. Furthermore, an example of the application of Cu–Al–Mn based SMAs to a guidewire for medical use is also presented.

Interaction, growth, and ordering of epitaxial graphene on SiC{0001} surfaces: A comparative photoelectron spectroscopy study

Thermally induced growth of graphene on the two polar surfaces of $6H\text{\ensuremath{-}}\mathrm{Si}\mathrm{C}$ is investigated with emphasis on the initial stages of growth and interface structure. The experimental methods employed are angle-resolved valence band photoelectron spectroscopy, soft x-ray induced core-level spectroscopy, and low-energy electron diffraction. On the Si-terminated (0001) surface, the $(6\sqrt{3}\ifmmode\times\else\texttimes\fi{}6\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ reconstruction is the precursor of the growth of graphene and it persists at the interface upon the growth of few layer graphene (FLG). The $(6\sqrt{3}\ifmmode\times\else\texttimes\fi{}6\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ structure is a carbon layer with graphene-like atomic arrangement covalently bonded to the substrate where it is responsible for the azimuthal ordering of FLG on SiC(0001). In contrast, the interaction between graphene and the C-terminated $(000\overline{1})$ surface is much weaker, which accounts for the low degree of order of FLG on this surface. A model for the growth of FLG on SiC{0001} is developed, wherein each new graphene layer is formed at the bottom of the existing stack rather than on its top. This model yields, in conjunction with the differences in the interfacial bonding strength, a natural explanation for the different degrees of azimuthal order observed for FLG on the two surfaces.

最近の研究から Ｌ１０型ＦｅＰｄ規則合金ナノ粒子の長範囲規則度

Hard magnetic properties of FePd nanoparticles originate from their L10-type tetragonal ordered structure with high magnetocrystalline anisotropy energy. In order to know correlations among the long-range order (LRO) parameter (S), the particle size and the anisotropy energy, we employed a new technique to determine LRO parameter of single L10-FePd nanoparticle using nanobeam electron diffraction (NBD) . The LRO parameter was determined by quantitative analysis of NBD intensities recorded on imaging plates together with intensity calculations considering the multiple scattering of electrons. In taking NBD patterns, hh0 systematic reflections were excited using a transmission electron microscope with a field emission gun operated at 300 kV. Specimen thickness was evaluated by electron holography. The obtained order parameters of individual nanoparticles larger than 8 nm are almost around the mean LRO parameter (S=0.79) determined by selected area electron diffraction. In contrast, the parameters gradually decrease as the particle size decreases below 8 nm (S=0.60-0.73) . The low degree of order in very small particles is responsible for the coercivity (anisotropy energy) decrease of the L10 nanoparticles in smaller sized region. Experimental conditions required for NBD analysis are presented in detail and the possible experimental errors of the determined LRO parameters are discussed.

Liquid crystalline hydrogen bonded oligo(p-phenylenevinylene)s

The thermotropic behaviour of a series of hydrogen bonded chiral and achiral oligo(p-phenylenevinylenes) (OPVs) has been investigated. The liquid crystalline properties are studied as a function of their molecular design that is based on hydrogen bonding units, the lengths of the π-conjugated and flexible segments and the branching of the side chains. Two-dimensional wide-angle X-ray scattering experiments indicate self-assembly of all OPVs into columnar superstructures which is the result of hydrogen bonds formed by the diaminotriazine or ureidotriazine units and π-stacking interactions accompanied by a local phase separation between the alkoxy side chains and the aromatic rods. The phase behaviour of the compounds bearing the diaminotriazine functionality depends on the length of the OPV segment. OPV trimers are already liquid crystalline at ambient conditions, while longer OPV tetramers are in a well-organized crystalline state at that temperature. In the liquid crystalline phase the intracolumnar order decreases due to molecular motion as confirmed by solid-state NMR studies. Interestingly, the introduction of branched (S)-2-methylbutoxy side chains increases significantly the π-stacking distance while the dimensions of the hexagonal unit cell decrease. The hydrogen bonding ureidotriazine groups decrease the thermal stability and lower the degree of order in comparison with the diaminotriazine derivatives. This low degree of order is probably the result of the ureidotriazine units that form hydrogen bonded dimers while the diaminotriazine arrays form hydrogen bonded hexameric rosettes. In the latter case a more densely packed columnar structure is formed.

Transmission electron microscopy of Co 2(Cr 1−xFe x)Al sputtered films and their magnetic tunneling junctions

The microstructures of Co 2FeAl and Co 2(Cr 0.4Fe 0.6)Al sputtered films and of their magnetic tunnel junctions (MTJs) have been investigated to discuss the possible reasons for an unexpectedly low tunneling magnetoresistance (TMR). The structure of the Co 2FeAl film changed from B2 to L2 1 with increasing substrate temperature, while that of the Co 2(Cr 0.4Fe 0.6)Al film remained B2 up to 500 °C. The thermodynamically predicted phase separation was not observed in the films. The low TMR values obtained from the MTJs using the Co 2FeAl and Co 2(Cr 0.4Fe 0.6)Al films are attributed to the low-spin polarization expected from the low degree of order in these films. The TMR values depend sensitively on the interfacial structure of the tunnel junctions when the degree of order of the film is low.

Long-range order parameter of single L10-FePd nanoparticle determined by nanobeam electron diffraction: Particle size dependence of the order parameter

The long-range order (LRO) parameter (S) of single isolated L10-FePd nanoparticle was determined by quantitative analysis of nanobeam electron diffraction (NBD) intensities and intensity calculations considering the multiple scattering of electrons. The obtained order parameters of the nanoparticles larger than 8nm are distributed around the mean LRO parameter (S¯=0.79) which was determined by selected area electron diffraction intensity analysis, while the parameters slightly decreased gradually as the particle size decreased below about 8nm (S=0.60–0.73). The low degree of order in very small particles is responsible for the coercivity decrease of the L10 nanoparticles in smaller-sized regions. Quantitative NBD intensity analysis is quite useful for the determination of the LRO parameter of individual L10-FePd single crystalline nanoparticle. Experimental conditions required for NBD analysis are presented in detail and the possible experimental errors of the determined LRO parameters are discussed.

Low-frequency noise in gallium nitride epitaxial layers with different degrees of order of mosaic structure

The correlation between the noise level 1/f and the degree of mosaic-structure order in gallium nitride epitaxial layers was studied for the first time. Samples with a doping level of Nd−Na≈8×1016 cm−3 and a relatively high degree of order were characterized by the Hooge parameter α≈1.5×10−3. This value is unprecedently low for thin GaN epitaxial films. The Hooge parameter was significantly higher for samples with Nd−Na≈1.1×1018 cm−3 and a low degree of order despite the fact that α generally decreases with increasing doping level at the same degree of order. Thus, the degree of mosaic-structure order affects not only the optical and electrical characteristics but also the fluctuation parameters of GaN epitaxial layers.

Industrial radioactive barite scale: suppression of radium uptake by introduction of competing ions

Incorporation of radioactive isotopes during the formation of barite mineral scale is a widespread phenomenon occurring within the oil, mining and process industries. In a series of experiments radioactive barite/celestite solid solutions (SS Barite–Celestite) have been synthesized under controlled conditions by the counter diffusion of 226Ra, Ba 2+, Sr 2+ and SO 4 2− ions through a porous medium (silica gel), to investigate inhibiting effects in Ra uptake associated with the introduction of a competing ion (Sr 2+). From characterization studies, the particle size and the morphology of the crystals appear to be related to the initial [Sr]/[Ba] molar ratio of the starting solution. Typically, systems richer in Sr produce smaller sized crystals and clusters characterized by a lower degree of order. The activity introduced to the system is mainly incorporated in the crystals generated from the barite/celestite solid solution as suggested by the activity profiles of the hydrogel columns analysed by γ-spectrometry. There is a relationship between the initial [Sr]/[Ba] molar ratio of the starting solution and the activity exhibited by the synthesized crystals. An effective inhibition of the 226Ra uptake during formation of the crystals (SS Barite–Celestite) was obtained through the introduction of a competing ion (Sr 2+): the higher the initial [Sr]/[Ba] molar ratio of the starting solution, the lower the intensity of the activity peak in the crystals.

N-acylated chitosan: hydrophobic matrices for controlled drug release

N-acylation of chitosan with various fatty acid (C 6–C 16) chlorides increased its hydrophobic character and made important changes in its structural features. Unmodified chitosan exhibited a low degree of order (DO) and a weak tablet crushing strength. Chitosan acylated with a short chain length (C 6) possessed similar properties, but exhibited significant swelling. Acylation with longer side chains (C 8–C 16) resulted in a higher DO and crushing strength but lower swelling. The best mechanical characteristics and drug release properties were found for palmitoyl chitosan (substitution degree 40–50%) tablets with 20% acetaminophen as a tracer. The high stability of these monolithic tablets appears to be due to hydrophobic interactions between side chains, as shown by a more organized structure. Infrared spectroscopy, X-ray diffractometry and proton nuclear magnetic resonance analyses of palmitoyl chitosan were consistent with a hydrophobic self-assembling model. Drug dissolution kinetics showed longer release times for higher degrees of functionalization, i.e. 30 h (for 47% substitution) and 90 h (for 69% substitution), suggesting palmitoyl chitosan excipients as interesting candidates for oral and subdermal pharmaceutical applications.

Long-Range Order Parameter of Oriented L1&lt;SUB&gt;0&lt;/SUB&gt;-FePt Nanoparticles Determined by Electron Diffraction

Two-dimensionally dispersed L10-FePt nanoparticles as small as 12 nm with orientation was fabricated by electron-beam evaporation and post-annealing at 873 K. After a prolonged annealing at 873 K for 86.4 ks, the increase of coercivity was almost saturated and coercivity reached 434 kAm−1 at 300 K, which is very small compared to recent reports on FePt nanoparticles with sizes larger than 20 nm. Long-range order parameter of the fabricated nanoparticles was determined by electron diffraction at 200 kV taking the multiple scattering into consideration. Obtained order parameter remained 0.55±0.02 for the nanoparticles with an axial ratio c⁄a of 0.961±0.003. The low degree of order is thought to be responsible for the small coercivity. Effect of Debye-Waller factor on the order parameter was discussed.

Characterization of the supermolecular structure of cellulose in wood pulp fibres

The hierarchic organization of cellulose fibrils (microfibrils) was investigated in holocellulose, sulphite pulp and kraft pulp using TEM, XRD, ED and FTIR. There were remarkable differences in both the fibril structure and fibril aggregation between the samples. TEM observations revealed more intimately associated fibrils in the kraft pulp compared to the sulphite pulp and the holocellulose, results in agreement with previous CP/MAS 13C-NMR data [Hult E.-L. et al. (2002) Holzforschung 56: 231–234]. Furthermore, the cellulose crystallinity was higher in the kraft pulp sample. With respect to the cellulose Iα and Iβ allomorphs, these samples were controversial when different analytical techniques were applied. Due to the small fibril size and the low degree of order of cellulose in these samples, the concept of crystalline triclinic and monoclinic components as determined by diffraction analysis may not be adequate. Instead the fibril can be regarded to have different degrees of lateral order (including paracrystalline ordering) that can be reoriented to Iβ type conformation and packing upon pulping.

Origin of pre-peak in structure factors of liquid Cu-Al-Ni alloys

Molten Cu-Al-Ni alloys have been investigated using the X-ray diffraction method. A distinct pre-peak has been found around a scattering vector magnitude of 18.5 nm-1 in the structure factor. The pre-peak increases in its intensity with decreasing temperature and the addition of Ni. The appearance of a pre-peak is a mark of medium range order. The structural unit size corresponding to the pre-peak is equal in magnitude to the (111) interplanar lattice spacing of the β phase. The appearance of a pre-peak is due to the existence of a cluster with a β phase-like structure in the melt. The size of the clusters increases with decreasing temperature but their structural unit size remains constant. Shape memory alloy ribbons can be fabricated by the rapid solidification technique. At a quenching temperature corresponding to that of the lower pre-peak, the structure of the martensite obtained has a lower degree of order and the temperature of the reverse martensitic transformation is lower. At a quenching temperature corresponding to a higher pre-peak, the structure of the martensite obtained has a higher degree of order and temperature of the reverse martensitic transformation is higher. These clusters can become crystal seeds of the β phase and β phase develops from these clusters, thus resulting in a correlation between the pre-peak and martensitic transformation.

Fabrication of oriented L1-FePt and FePd nanoparticles with large coercivity

Oriented L10-FePt and FePd nanoparticles with coercivities as large as 5 kOe (FePt) and 3 kOe (FePd) were fabricated by alternating deposition of Pt(or Pd) and Fe nanoparticles and their annealing at the temperatures between 773 and 873 K on single crystal NaCl and MgO. Atomic ordering reactions and degrees of order towards the L10-structure formation in these nanoparticles were investigated by high resolution electron microscopy and electron diffraction, and magnetic coercivities at low temperature were also measured. The long range order parameter of the FePt nanoparticles was ∼0.56 even after annealing at 873 K for 24 h. The coercivity of the FePt nanoparticles at 100 K was as high as twice the room temperature value. The low degree of order in the L10-structure formation and the thermal effect on magnetization have been found in the present FePt and FePd nanoparticles. These are closely concerned with the origin of the coercivity values which are very small in comparison with those expected from the single magnetic domain theory.

Prediction of the Crystalline Structure of a Novel Polythiophene Using Molecular Dynamics Simulations

A novel polythiophene, poly(3-acetamido-undecanoic-succinimidyl-thiophene), has been synthesized and characterized by using IR, RMN, X-ray, DSC, and density measurements. Powder X-ray analysis shows that the polymer crystallizes in a distinct lamellar structure with a spacing of ∼23 Å. Fine details at large diffraction angles indicated the presence of a three-dimensional crystalline structure although the data were insufficient to resolve the exact form of this structure. DSC measurements showed two distinct melting peaks a few degrees apart, which are possibly linked to a liquid-crystal intermediate phase. In a second stage, molecular dynamics (MD) simulations have been used in an attempt to predict the crystal structure and to shed light on the double melting peak behavior. Based on the initial assumption that the polymer backbones are parallel and the aliphatic side chains are linear (all trans), three trial starting configurations have been generated, energy minimized, and then allowed to relax by using constant pressure-constant temperature MD. Two of these systems have been followed for over 1 ns of elapsed time. Although both of these latter systems maintain a linear ordering of the polymer backbones, one shows a low degree of order in the arrangement of the side chains, whereas the other shows a high degree of order. Comparisons are made between the properties of the two systems and model X-ray diffractograms are presented and compared with experimental data.

Structural modifications produced by the incorporation of Ar within the lattice of Fe2O3 thin films prepared by ion beam induced chemical vapour deposition

Iron oxide thin films have been prepared at room temperature by ion beam induced chemical vapour deposition. The films were grown by bombardment of a substrate with O+2 or O+2+Ar+ mixtures, while a Fe(CO)5 volatile precursor was adsorbed on the surface. In both cases, the films were dense and had a low roughness. After preparation, the films prepared with O+2 ions consisted of hematite (α-Fe2O3), although with a low degree of order as revealed by grazing angle X-ray diffraction (GXRD), transmission infrared (IR) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy. A progress in the crystallisation process of these films occurred by annealing at 573 and 773K. In all cases, the crystallographic c axis of the hematite structure was oriented perpendicular to the film surface. Samples prepared with the O+2+Ar+ mixture were amorphous or badly ordered. Rutherford backscattering spectroscopy (RBS) showed that in these films Ar (∼4% atomic) became homogeneously incorporated within the Fe2O3 lattice. These Ar atoms remained incorporated even after annealing at 773K. At this temperature, a sudden crystallisation of α-Fe2O3 occurred, resulting in the same preferential orientation of the c axis as in the samples prepared in absence of Ar. The extinction of some GXRD peaks for these annealed samples is correlated with the presence of Ar atoms within the α-Fe2O3 lattice. The possibility of controlling the structure of thin films prepared by ion beam assisted methods by incorporation of Ar into their structure is discussed.

Side-Chain Liquid-Crystalline Polymers from the Alternating Copolymerization of Maleic Anhydride and 1-Olefins Carrying Biphenyl Mesogens

Side-chain liquid-crystalline copolymers (SCLCPs) were synthesized from the alternating copolymerization of maleic anhydride with mesogenic 1-olefins. These SCLCPs showed high glass transition temperatures and highly ordered smectic mesophases. The mesophase width increased with spacer length. The terminal alkyl group length determined the degree of order in the hexatic mesophase that was present just above the glass transition temperature. A terminal methoxy group induced a hexatic smectic B mesophase, intermediate terminal alkyl groups induced a smectic E mesophase, and long terminal alkyl groups induced a crystal smectic B mesophase. If the spacer was shorter than the terminal alkyl group, an interdigitated smectic A mesophase was found in which the terminal alkyl groups overlap. A strong correlation was found between the glass transition temperature and the temperature at which the hexagonal or orthorhombic ordered mesophase disappears. Introduction of an ester linkage between the spacer and biphenyl mesogen or replacing the terminal alkoxy group by a cyano terminal group induced a lowering of transition temperatures and a lower degree of order in the mesophase.

Lattice constants and compositions of the metastable Ni3Nb phase precipitated in a Ni-15Cr-8Fe-6Nb alloy

The lattice constants of γ and metastable γ″ (Ni3Nb) phases and the composition of the γ″ phase in a nickel-based superalloy (a modified JIS NCF 3-type alloy) are investigated using an X-ray diffractometer and an analytical electron microscope with an energy-dispersive X-ray (EDX) system. The lattice constant of the γ phase decreases and those of the γ″ phase increase during the aging time. The γ″ phase is composed of nickel, niobium, chromium, and iron. While the content of nickel in the γ″ phase increases and reaches a constant composition during the aging time, the chromium and iron content decrease and reach a constant value during aging. The niobium content maintains a constant value regardless of the time that the alloy has aged. The relationship between the lattice constants and the composition of the γ″ phase is discussed in detail. In the early stages of aging, there is the possibility that nickel (including chromium and iron) and niobium atoms mutually substitute for one another, resulting in a somewhat lower degree of order than would normally be expected.