Concentration Of Paramagnetic Centers Research Articles

Defect structure of nanosized mechanically activated MoO3

Defect structure of mechanically activated MoO3 has been studied with the use of X-ray diffraction, Raman spectroscopy, electron paramagnetic resonance, laser granulometry, and adsorption methods. Two stages of mechanical activation have been distinguished. At mechanical activation doses below 1 kJ/g, the fracture of oxide particles is the main process. At this stage, MoO3 particle sizes decrease from 30 μm to 60 nm and specific surface area linearly increases to 30 m2/g, the sizes of coherent-scattering regions decrease to 18 nm, paramagnetic centers are accumulated, and the Raman spectral bands corresponding to three different types of Mo-O bonds widen and shift. At doses above 1 kJ/g, the main process consists in the friction and aggregation of particles, which is accompanied by some reduction in the specific surface area and an increase in the particle sizes. At the stage of friction, the phase transition from an orthorhombic modification to a monoclinic modification of MoO3 occurs seemingly due to a shift of one layer of the material in plane (100). The shift is accompanied by the accumulation of lattice microstrains in the same plane, formation of “stressed” Mo-O-Mo bridge bonds, and a substantial rise in the concentration of Mo5+ radicals. The maximum total concentration of paramagnetic centers is 1 × 1018 g−1. It may be assumed that the radicals are formed due to the rupture of the most stressed molybdenum-oxygen bridge bonds.

Determination of adhesion interaction between carbon fiber and epoxy binder

Experimental results of the concentration of paramagnetic centers have been given for carbon fibers of Elur-0.1P, UOL-300, LUP-0.1, HTS-45, AS-4, T-300, and T-700 brands and carbon plastics designed on their basis with ENPB binder. The strength of carbon plastics at interlaminar shear has been used as a measure of adhesion interaction. It is shown that the highest concentration of paramagnetic centers and the highest strength of adhesion interaction are intrinsic to carbon plastics based on T-700 brand fiber. It is noted that the oxidation of carbon fibers leads to the increase in the concentration of paramagnetic centers on their surface.

The Use of Principle Component Analysis in Type Classification of Air-dry Peat

The use of principle component analysis (PCA) in the variant of projection on latent values with discriminant analysis (PLS-DA) in type classification of Siberian region air-dry peat by a set of properties is presented. A statistical analysis in principle component space by PCA of different physico-chemical properties of peat such as component composition, concentration of paramagnetic centers and IR-spectra is presented and shows a developed PLS- DA classification model allows estimating peat type by a set of physico-chemical properties with minimum prediction errors.

EPR and IR studies on the role of coal genetic type in plastic layer formation

Coal blends with all possible combinations of two pairs of isometamorphic coals of different sulfur levels were pyrolysed in centrifugal field, allowing to be separated into solid, fluid and gaseous products. It has been shown that the replacement of the low-sulfur by the high-sulfur coking coal of the same rank (≈83–88% Cdaf) in blends leads to a substantial increase of fluid product yield which can be of great practical value. Using the EPR and DRIFT-spectroscopy methods the structural peculiarities of the obtained products have been studied. An apparent relation between the content of sulfur in coal, paramagnetic centers in plastic layer and coal coking ability was established. It was demonstrated that the concentration of paramagnetic centers in fluid non-volatile products correlates with the yield of plastic layer responsible for coking ability.

Identification of the Chromophore in the Apatite Pigment [Sr10(PO4)6(CuxOH1−x−y)2]: Linear OCuO− Featuring a Resonance Raman Effect, an Extreme Magnetic Anisotropy, and Slow Spin Relaxation

A new chromophore has been identified in copper-doped apatite pigments having the general composition [Sr(10)(PO(4))(6)(Cu(x)OH(1-x-y))(2)], in which x=0.1, 0.3 and y=0.01-0.42. By using X-ray absorption spectroscopy, low-temperature magnetization measurements, and synchrotron X-ray powder structure refinement, it has been shown that the oxygenated compounds contain simultaneously diamagnetic Cu(1+) and paramagnetic Cu(3+) with S=1. Cu(3+) is located at the same crystallographic position as Cu(1+), being linearly coordinated by two oxygen atoms and forming the OCuO(-) anion. The Raman spectroscopy study of [A(10)(PO(4))(6)(Cu(x)OH(1-x-y))(2)], in which A=Ca, Sr, Ba, reveals resonance bands at 651-656 cm(-1) assigned to the symmetric stretching vibration (ν(1)) of OCuO(-). The strontium apatite pigment exhibits a strong paramagnetic anisotropy with an unprecedentedly large negative zero-field splitting parameter (D) of ≈-400 cm(-1). The extreme magnetic anisotropy causes slow magnetization relaxation with relaxation times (τ) up to 0.3 s at T=2 K, which relates the compounds to single-ion magnets. At low temperature, τ is limited by a spin quantum-tunneling, whereas at high temperature a thermally activated relaxation prevails with U(eff)≈48 cm(-1). Strong dependence of τ on the paramagnetic center concentration at low temperature suggests that the spin-spin relaxation dominates in the spin quantum-tunneling process. The compound is the first example of a d-metal-based single-ion magnet with S=1, the smallest spin at which an energy barrier arises for the spin flipping.

Free-radical cooligomerization of N-vinyl-4,5,6,7-tetrahydroindole with butyl vinyl ether

Oligo(N-vinyl-4,5,6,7-tetrahydroindole-co-butyl vinyl ethers) have been synthesized through free-radical cooligomerization with a yield of 84%. The copolymers are readily soluble in organic solvents (benzene, 1,4-dioxane, chloroform, and tetrahydrofuran), stable up to 380–400°C, and paramagnetic. (The concentration of paramagnetic centers is 1014 spin/g.) In addition, the copolymers exhibit the properties of organic semiconductors. (After being doped with iodine, σ = 1.1 × 10−7 S/cm.) The analysis of the 1H and 13C NMR spectra has shown that the oligomerization reaction is complicated by intramolecular cyclization involving carbon atoms located at the 2-position of pyrrole rings.

Copolymers of vinyl chloride obtained by polymer-analogous reactions of polyvinyl chloride with sodium salts of heteroaromatic H-N acids

By a reaction of PVC with sodium salts of pyrazole and 3,5-dimethylpyrazole we obtained copolymers possessing paramagnetic properties with a concentration of paramagnetic centers 1017–1019 spin g−1 and g-factor of 2.0024-2.0044.

Magnetic resonance study of annealed and rinsed N-doped TiO2 nanoparticles

Abstract Nanoparticles of nitrogen-modified TiO2 (N-doped TiO2) calcined at 300°C and 350°C, have been prepared with and without water rinsing. Samples were characterized by x-ray diffractrometry (XRD) and optical spectroscopy. The electron paramagnetic resonance (EPR) spectra from centers involving oxygen vacancies were recorded for all samples. These could be attributed to paramagnetic surface centers of the hole type, for example to paramagnetic oxygen radicals O−, O2−etc. The concentration of these centers increased after water rising and it further increased for samples annealed at higher temperature. Additionally, for samples calcined at 300°C, and calcined at 350°C and rinsed, the EPR spectra evidenced the presence of magnetic clusters of Ti3+ ions. The photocatalytic activity of samples was studied towards phenol decomposition under unltraviolet-visible (UV-Vis) irradiation. It was found that, in comparison to the starting materials, the rinsed materials showed increased photocatalytic activity towards phenol oxidation. The light absorption (UV-Vis/DRS) as well as surface Fourier transform infrared/diffuse reflectance spectroscopy (FTIR/DR) studies confirmed a significantly enhanced light absorption and the presence of nitrogen groups on the photocatalysts surfaces, respectively. A significant increase of concentration of paramagnetic centers connected with oxygen vacancies after water rising has had an essential influence on increasing their photocatalytic activity.

Reply to “Comment on ‘Self-doping effects in cobalt silicide CoSi: Electrical, magnetic, elastic, and thermodynamic properties’ ”

In the Comment, it is argued that concentrations of paramagnetic centers in our CoSi crystals were estimated incorrectly [Phys. Rev. B 86, 064433 (2012)]. Doubts also are raised about the temperature dependence of the resistivity of four CoSi crystals prepared in different laboratories. These criticisms, even if they were valid, do not invalidate our main conclusions [Phys. Rev. B 86, 064433 (2012)].

Sulfurization polyvinyl chloride

A sulfurized polymer comprising 57.64% of chemically bound sulfur characterizing by paramagnetism with the concentration of paramagnetic centers 2 × 1019 spins g−1 and g-factor 2.0043 was resulted n the treatment of industrial polyvinyl chloride by elemental sulfur.

EPR testing of the concentration of paramagnetic centers using standards

A calculation model for the evaluation of the concentrations of paramagnetic centers in specimens using their electron paramagnetic resonance spectra in the form of single derivatives of resonance curves is developed. It is shown that using a correcting factor to account for differences of the shapes of the resonance curves of standards, which are based on a polycrystalline radical of the α, α’-diphenyl-β-picrylhydrazyl type, and tested objects allows the error in the evaluation of the paramagnetic-center concentration to be reduced to a practically acceptable level of 30%.

Tuning the electronic structure, bandgap energy and photoluminescence properties of hexagonal boron nitride nanosheets via a controllable Ce3+ ions doping

The modification of electronic structure, bandgap energy and photoluminescence properties of hexagonal boron nitride (h-BN) nanosheets has been challenging due to the inherent inertness and chemical stability of h-BN. In the present work, we realized tuning the electronic structure and bandgap energy properties of h-BN nanosheets via a controllable Ce3+ ions doping through a one-step facile thermal chemical reaction route using HBO3, C3H6N6 and Ce(Ac)3·nH2O as reactant precursors. As the Ce3+ ions incorporating content is lower than the critical threshold saturation value of 1.25%, the Ce-doped BN samples show an obvious band gap monotonically narrowing trend from 4.42 eV of pure BN to 3.31 eV for 1.25% Ce-doped BN nanosheets. With incorporation of Ce3+ ions into the lattice of h-BN, the intensity of electron paramagnetic resonance (EPR) signals closely associated with the nitrogen vacancies in Ce-doped BN samples, displays a decline trend with increasing the concentration of the incorporated Ce3+ ions, suggesting a decrease in the concentration of paramagnetic centers. The introduction of Ce3+ ions can result in the formation of a doping energy level between the conduction and valence bands of BN, and thus shifts the absorption band to the large-wavelength region, corresponding to the bandgap energy narrowing of Ce-doped BN, resulting in a red shift of the absorption edge of the Ce-doped BN samples. The B–N–O–Ce bonding due to the Ce3+ ion doping is responsible for bandgap energy narrowing in the Ce-doped BN materials. As the concentration of the incorporated Ce3+ ions reaches the critical threshold value of 1.25%, no more nitrogen vacancies are available, so the bandgap energy narrowing effect from the Ce3+ ion doping is reduced.

Structural transformations in ZnS:Cu in the course of thermal annealing

The influence of annealing at 800°C on the photoluminescence, electron spin resonance, and X-ray diffraction spectra of powder-like ZnS:Cu, obtained by the self-propagating high-temperature synthesis of a charge, consisting of Zn, S, and CuCl, is studied. It is shown that variation in the material’s heating rate up to the annealing temperature leads to a nonmonotonic variation in the spectral location and full-width at half-maximum of the photoluminescence band in the blue-green spectral region, as well as in the Mn2+ paramagnetic center concentration. It is established that the cubic and hexagonal ZnS phases, as well as the ZnO and CuZn phases, are present in the powder after synthesis. It is shown that annealing of the obtained powder at 800°C leads to three processes: the transformation of the hexagonal ZnS phase into the cubic phase, the oxidation of ZnS and CuZn, and the diffusion of Cu into the bulk of the ZnS microcrystals from the CuZn phase. A model attributing the observed variations in luminescence and electron spin resonance spectra to the diffusion of Cu and Mn impurities into the microcrystal bulk, particularly from the CuZn phase, and to their accumulation at extended defects is suggested.

Obtaining of water soluble microbial melanin and study of its some properties

The effective sorption method for melanin isolation and purification from fermentation solutions of Bacillus thuringiensis serovar galleriae K1 has been elaborated, the principle process flowsheet is presented. The identification of obtained pigment with the samples of natural and synthetic melanin was done by IR-spectroscopy, and the intensity ratio of optical absorption at 650 and 500 nm allows to refer the isolated melanin to eumelanin class. By thermal treatment it was determined, that melanin's amorphous sediment is steady at up to 120 degrees C temperatures, at that the concentration of paramagnetic centers is changed from 0.053 x 10(18) spin/g (48 degrees C) to 0.25 x 10(18) spin/g (120 degrees C). The rising of the temperature of treatment up to 210 degrees C brings to substantial increase of the concentration of unpaired electrons, and at 280 degrees C its sharp growth is observed. At 350 degrees C growth stops, then sharp decrease is observed. The obtained results were confirmed by methods of IR spectroscopy and derivatographic analysis.

EPR Study of Iron Ion Complexes in Human Blood

Electronic states of iron ion complexes in human blood from patients with melanoma have been investigated by electron paramagnetic resonance (EPR). The measurements were performed at liquid nitrogen temperature (77 K) on an X-band EPR spectrometer. Numerous types of iron paramagnetic centers have been identified. In several kinds of protein complexes exemplified by methemoglobin, transferrin or ferritin, various forms of trivalent iron have been found. Three groups of patients with typical EPR spectra have been individualized. These groups differed in types and concentration of paramagnetic centers in peripheral blood. A good correlation has been found between the EPR results, the total iron ion complexes concentration and transferrin saturation.

Correlation between the sudden and regular releases of coal-bed methane and the structures of the organic matter of natural coals

A correlation between the structure of the organic matter of coal and the ability of coal to release gases upon thermal and mechanical actions was considered. It was found that coal-bed methane released in different modes (regular and sudden) during coal-bed mining is of mechanochemical rather than sorption nature. Relationships were proposed to determine the natural methane content of coals and the sorption capacity of coals from a metamorphic series for methane using a structure-chemical parameter: the concentration of paramagnetic centers calculated from a broad line of the EPR signal. The use of spectroscopic techniques provides an opportunity to considerably simplify and make cheaper a very labor intensive technology for the determination of natural gas content. The regulations of methane safety in coal mines should be corrected based on the original concepts of the nature of coal-bed methane.

Electron paramagnetic resonance (EPR) study of DOPA–melanin complexes with kanamycin and copper(II) ions

This work comprises the study of DOPA-melanin complexes with kanamycin and copper(II) ions made by electron paramagnetic resonance EPR spectroscopy. The high concentration of paramagnetic centers in melanin makes the use of EPR spectroscopy possible. The unpaired electron localized on the oxygen atom in indol-5,6-quinone groups is the paramagnetic centers in this polymer. The aim of this work was the analysis of EPR parameters of recorded spectra. For researches were pre- pared melanin complexes which differed in complexing order of drug and Cu(II) ions, and in concentration of CuCl2 solutions used during synthesis. The introduction of drugs and metal ions into melanin causes changes in EPR parameters of recorded spectra. Kanamycin causes the increase and copper(II) ions the decrease of concentrations of paramagnetic centres in melanin. Shape of EPR signal of DOPA-melanin was analyzed by fitting method. Results indicate that EPR line of DOPA-melanin is superposition of Gaussian and Lorentzian function.

Electron paramagnetic resonance (EPR) study of DOPA–melanin complexes with kanamycin and copper(II) ions

This work comprises the study of DOPA–melanin complexes with kanamycin and copper(II) ions made by electron paramagnetic resonance EPR spectroscopy. The high concentration of paramagnetic centers in melanin makes the use of EPR spectroscopy possible. The unpaired electron localized on the oxygen atom in indol-5,6-quinone groups is the paramagnetic centers in this polymer. The aim of this work was the analysis of EPR parameters of recorded spectra. For researches were prepared melanin complexes which differed in complexing order of drug and Cu(II) ions, and in concentration of CuCl2solutions used during synthesis. The introduction of drugs and metal ions into melanin causes changes in EPR parameters of recorded spectra. Kanamycin causes the increase and copper(II) ions the decrease of concentrations of paramagnetic centres in melanin. Shape of EPR signal of DOPA–melanin was analyzed by fitting method. Results indicate that EPR line of DOPA–melanin is superposition of Gaussian and Lorentzian function.

Comparative EPR Study of Monomer and Polymerized Phases of C60

Temperature dependences of EPR spectra of the monomer, 1D (orthorhombic), and 2D (tetragonal and rhombohedral) polymerized phases of C60 were studied in the range of 11–295 K. It was shown that the concentration of paramagnetic centers depends radically on the type of polymerized phases. The temperature dependences allow one to separate temperature-dependent and temperature-independent components of the main doublet signals, which were attributed to C60 + radical and to conducting electrons, respectively. Additional triplet EPR signals assigned to dimer centers formed by a coupling of two C60 + radical were observed for the tetragonal and rhombohedral phases.

EPR study of the crystalline polymerized phases of C60

AbstractComparative electron paramagnetic resonance (EPR) study of the monomer and 1D (orthorhombic) and 2D (tetragonal and rhombohedral) polymerized phases of C60 has been carried out. It was shown that the concentration of paramagnetic centers (PC) depends on the phase structure. Temperature dependences of the EPR spectra enabled separation of temperature‐dependent from temperature‐independent components of the main doublet signals, which were attributed to C radical (PC1) and to conducting electrons, respectively. Additional weak EPR signals, observed for the tetragonal and rhombohedral phases, were attributed to dimer PC2 formed by coupling of two PC1. Possible models for these centers are discussed.