Powder Spectra Research Articles

Defect properties of cobalt-doped hexagonal barium titanate ceramics

X-ray diffraction (XRD) patterns, electron paramagnetic resonance (EPR) powder spectra (9 and 34 GHz) and the magnetic susceptibility of BaTiO3 + 0.04 BaO + x/2 Co2O3 (0.001 ⩽ x ⩽ 0.02) ceramics were studied to investigate the incorporation of Co ions in the BaTiO3 lattice and their valence states as well as the development of the hexagonal phase (6H modification) in dependence on doping level x and sintering temperature Ts. At Ts = 1400 °C the 6H modification begins to occur at a nominal Co concentration x of about 0.001 and for x > 0.005 the samples are completely hexagonal at room temperature. Two different EPR spectra were observed in the 6H modification of BaTiO3, which were both assigned to paramagnetic Co2+ ions located at the two crystallographically non-equivalent Ti sites in 6H-BaTiO3. The EPR g tensor values as well as the molar paramagnetic susceptibility, measured in the temperature range 5 K–300 K at a magnetic field of 9 T, were analyzed in the framework of the ligand field theory using the program CONCORD. The combination of EPR and magnetic measurements reveals that in air-sintered 6H BaTiO3, the incorporated Co occurs as a mixture of paramagnetic Co2+ and diamagnetic Co3+ ions, whereas in samples annealed in reducing atmosphere the majority of Co is in the divalent state. The occurrence of Co4+ can be excluded for all investigated samples. The sample color caused by Co2+ and Co3+ ions is beige/light yellow and dark grey/black, respectively. The majority of the Co2+ ions substitutes Ti in the exclusively corner-sharing oxygen octahedra possessing nearly cubic symmetry. The corresponding ligand field parameter amounts to about −28 000 cm−1 (Wybourne notation, 10Dq ≈ 20 000 cm−1). In the reduced samples nearly 5% of the detected Co2+ ions occupy the Ti site in the face-sharing oxygen octahedra, which are significantly trigonally distorted. The negative sign of the obtained ligand field parameter ≈ −7300 cm−1 reflects a compression of this octahedron in direction of the hexagonal c-axis.

Analysis of Nickel Defect in Diamond with Photoluminescence upon Excitation near 200 nm

Photoluminescent (PL) spectra of synthetic diamond powders at temperatures between 10 and 300 K were excited with synchrotron radiation in the wavelength range 125-375 nm. Prominent spectral PL features were detected at 484.6 and 489.0 nm (2.559 and 2.535 eV), associated with nickel defect. During our measurement of PL excitation (PLE) spectra of Ni defect in diamond, we observed a distinct PLE line at 215 nm for the first time. We thereby suggest the use of UV-PL spectra excited in the region 200-220 nm to analyze and to identify nickel defect in diamonds.

Improvement of Luminescence Properties and Particle Growth of AlN Phosphors By Si-Doping

Aluminum Nitride (AlN) has been regarded as a promising material for ceramic phosphors. Recently, we have developed a high efficiency blue AlN phosphor by co-doping with Si and Eu [1-2]. It has been proven that particle have grown rapidly with the highest luminescent intensity on the proper Si doping. Now, it is important to understand the role of Si on AlN particle growth and luminescence enhancement. For this purpose, AlN powders doped with Si from 0 to 4 at. % were prepared using gas-pressure sintering (GPS) furnace at 1950°C in N2 atmosphere. Firstly, particle size, phases and luminescence spectra of Si-doped AlN powder were investigated using SEM, XRD and CL. Secondly, the defect were evaluated by EPR to identify the defects transitions. Finally, the particle growth mechanism was clarified by cross-sectional CL-EDS. From 0.4 to 2.0 % Si, particle growth of AlN powders as well as ultraviolet emissions at 290 and 350 nm are enhanced. The 350 nm emission may be attributed to native AlN defects such as vacancy-oxygen complexes. The shoulder at 290 nm and 450 nm can be ascribed to the different states of Si related defects in AlN by EPR analysis. Cross sectional CL images show that the 1.6 % Si-doped AlN yields 280 nm emission at the surfaces of AlN particles (Fig. 1). Many particles are connected to each other with these bright surfaces. It suggests that the Si-rich surface may act as the binder of AlN particles and enhance the Ostwald growth.

Effect of ultrasound on the physico-chemical properties of poorly soluble drugs: Antisolvent sonocrystallization of ketoprofen

In the present study, power ultrasound (US) using the antisolvent sonocrystallization technique (ASC) was used to improve the physicochemical properties of ketoprofen which is a poorly water-soluble drug. The powders produced were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectrophotometry (FTIR), Differential Scanning Calorimetry (DSC) and X-ray Diffraction (XRD). The effect of process variables on particle size, solubility and dissolution were studied. Flowability, compressibility and mechanical properties of the produced powders were also assessed. Using ASC led to considerable decrease in the particle size. SEM studies showed that the ASC produced particles were almost spherical with regular size. Thermal behavior, XRD patterns and FT-IR spectra of raw ketoprofen and powders obtained by ASC have shown no significant differences. Although the solubility of the produced powders in HCl (pH=1.2, 37°C) was not increased, the rate and extent of dissolution were enhanced significantly. While process parameters did not significantly affect dissolution profile due to particle agglomeration. On the other hand, flowability and compressibility were improved. In conclusion, antisolvent sonocrystallization (ASC) technique was successfully developed for engineering small particles of ketoprofen with drug concentration of 100mg/ml, US amplitude of 75% for 5min in acetone at 25°C.

EMR study and superposition model analysis of Cr3+ and Fe3+ impurity ions in mullite powders used in aerospace industry

Abstract In this work, the electron magnetic resonance (EMR) spectra of the mullites powders were measured for different grain sizes (0.07 and 0.12 mm). We have used EMR spectroscopy at X-band, combined with superposition model (SPM) calculations to reveal electronic structure and establish correlations between structure, and surroundings of these complexes.

Research of reducing and emulsifying abilities of vegetable and fruit powder

The problem of investigating reducing and emulsifying abilities of cabbage powders, obtained by drying with the mixed heat supply at temperatures of 50 and 70°C, as well as spinach and banana powders of low temperature drying was considered in the paper. These methods allow to obtain a dried product with a moisture mass fraction of no more than 7 %, maximally preserve the nutritional value of the dried products and reducing ability. Dispersion of cabbage, spinach and banana powders was determined by a microscopic method. It was shown that the majority of the cabbage powder particles at drying temperatures of 50 and 70 °C have sizes of up to 40 microns - 75...85 % and only about 15...25 % - 60...100 microns. Powders obtained by low-temperature drying contain medium and large particles (over 40 microns) – 29 % in spinach and 47 % in banana. The structure of cabbage, spinach and banana powders was investigated using the microscopic method. It was shown that the powder cabbage obtained by MHS-drying at a temperature of 50 °C has more compacted particle structure (at magnification by 1000 times) than at 70 °C. Spinach powder is represented by separate small particles, banana powder - by spherical-shaped particles, uniform throughout the mass. The rehydration ability of powders was investigated. It was found that at the process duration of t£10 min, the behavior of vegetable and banana powders is characterized by intense swelling in water at 20 °C. After 30 min, the swelling process ends up and reaches a maximum value for the cabbage powder at 70 °C – 920 %, for the spinach powder – 380 %, cabbage powder of MHS-drying at 50 °C takes an intermediate value. The banana powder swells least of all. Powder cabbage of MHS-drying at 50 °C absorbs less water than at 70 °C. Spinach and banana powders have the WA (water amount) value by 2...3 times lower than the cabbage samples. Structural analysis of IR spectra of fresh vegetable and powders obtained after drying at temperatures of 50 and 70 °C was performed. Studies indicate minor changes in the chemical composition of the raw material during drying at temperatures of 50 °C and 70 °C. The regularities of increase in water retention, fat retention and emulsifying abilities of cabbage powder of MHS-drying at the process temperature increase was revealed: the sample shows high values of the studied parameters compared to the sample of MHS-drying at 50 °C. Spinach and banana powders show low values of these technological properties.

Origin of electron paramagnetic resonance signal in anthracite

Anthracite, with carbon content of 93.5wt% and 2.7wt% of hydrogen, was studied by electron paramagnetic resonance (EPR), electrical conductivity and static magnetic susceptibility measurements, in the temperature range of 2–300K. The EPR measurements were carried out on powder and bulk samples. The EPR signal of the thin bulk sample represented a single Lorentzian line, while the spectrum of the powder samples was composed of two Lorentzian lines having identical g-factors and different linewidths. The study of the temperature dependencies of the linewidths revealed that the narrow component of the powder spectra corresponds to the signal of the thin sample. The intensities of all EPR signals, proportional to the dynamic paramagnetic susceptibility, showed Curie-type dependency. The static magnetic susceptibility was dominated by the Pauli-type paramagnetism. This led to a conclusion that paramagnetism of anthracite is due to the conducting electrons, but part of them become isolated due to the granular structure of the material. In EPR, these non-interacting electrons yield a Curie-type contribution to susceptibility. The two-component structure of the powder EPR spectra was explained by the size distribution of grains and a more effective scattering of conduction electrons by the surface roughness in smaller grains.

Two-dimensional second-order quadrupolar exchange powder spectra for nuclei with half-integer spins. Calculations and an experimental example using oxygen NMR

Two-dimensional chemical exchange spectra are determined for powders containing half-integer quadrupolar nuclei that evolve under the second-order quadrupolar interaction. For simple exchange processes it is shown that the calculated exchange patterns depend sensitively on the jump angles, the tensor parameters, and the rotation axes characterizing the geometry of the underlying molecular motion. The inclusion of other interactions is discussed. To demonstrate the feasibility of the experimental method a two-dimensional second-order quadrupolar exchange spectrum was recorded for a clathrate hydrate using oxygen NMR. Simulations based on a motional model involving a six-site jump capture the essential features of the experimental results.

Uniformly dispersion of carbon nanotube in aluminum powders by wet shake-mixing approach

Since its discovery, carbon nanotube (CNT) was proposed as an ideal reinforcement material for metal matrix composite for its high strength, excellent electrical and thermal conductivity. CNT reinforced aluminum matrix composite has attracted most attention at the beginning of 21st century due to the need for advanced lightweight alloys for aerospace, automotive and defense industries. However, few researchers have successfully incorporated pristine and undamaged CNT into matrix to enhance the properties of the composite. Both traditional and novel powder metallurgical routes have been explored, nevertheless, challenges like the poor distribution of CNT in Al matrix, the agglomeration of CNTs and the damage of essential CNT tubular structure impeded the full translation of CNT potential into various matrix. To achieve a uniform dispersion of CNT without damaging the CNT structure, the authors have applied a novel wet shake-mixing method which combined the advantages of ultrasonication, turbular mixing and ball milling to fabricate an homogenous Al–0.5wt.% multi-walled carbon nanotube (MWNT) composite. The original structure and morphology of MWNTs and aluminum powders were well preserved even after all the processing procedures in the as-produced powders. This is confirmed by scanning electron microscopy and X-ray diffraction analysis, particle size distribution and the Raman spectra of the as-produced composite powders.

Microscopic, mechanical and thermal properties of spark plasma sintered ZrB2 based composite containing polycarbosilane derived SiC

ZrB2-SiCp (w/w 80:20) composites were spark plasma sintered at 1900, 2000 and 2100°C with ton=50ms and toff=5ms conditions under 50MPa pressure for 15min. SiC was obtained by in situ pyrolysis of polycarbosilane during sintering. The FTIR spectra of semi-pyrolysed ZrB2-SiCp powder showed that pre-ceramic PCS polymeric bands such as Si-CH2-Si, Si-CH3 and Si-H weakened and few characteristic bands like Si-C, Si-O and C = C peaks appeared strong in the spectra. In ZrB2-SiCP composition, uniform distribution of ZrB2 and secondary SiC phases were found in the sintered sample. The interfaces between hexagonal ZrB2 and needle shaped SiC were found in high resolution bright field TEM images. The Vickers' micro-hardness, fracture toughness (measured by DCM) of ZrB2-SiCp composite sintered at 2000°C achieved up to 16.22GPa and 3.69MPa√m, respectively. The critical energy release rate (GIC) value was 27.46J·m−2 implying that the composite resists fracture during indentation. Wear resistance coefficient and wear rate values of all the composites were found to be very low. Thermal conductivity values of all the composites varied from 78.09 to 57.20W/m·K in 100°C to 1000°C range.

The Effect of Blood Contamination on the Chemical Characterization of Hydrated Mineral Trioxide Aggregates and Their Dentin-Interface: A Comparative Study

The presence of blood contamination could affect the chemical characterization of mineral trioxide aggregates as endodontic repair material during surgical approach. The aim of this study was to assess and compare the chemical characterization of two white mineral trioxide aggregates (ProRoot and Angelus) mixed with blood versus water. ProRoot and Angelus were mixed with either distilled water, fresh human blood, or diluted blood and analyzed using Fourier transform infrared spectroscopy. The same materials were packed inside holes in dentin blocks for scanning electron microscopy with energy-dispersive X-ray. Gray Portland cement was used as a control. The infrared spectra of unhydrate powders showed an increase in alite in ProRoot and Angelus, belite in Portland cement, and calcium hydroxide in Angelus. Upon hydration, changes in these bands were detected. Energy-dispersive X-ray displayed significantly higher calcium, aluminum, and phosphorous in hydrated Angelus and silicon in hydrated ProRoot (p < 0.05). No phosphorous was detected in ProRoot. Traces of iron were detected in blood groups. A granular pattern was observed at the hydrated material of all tested groups. Definitive gaps were detected at certain areas within hydrated material and its dentin-interface, particularly in blood-contaminated groups. It was supported with the appearance of new bands assigned to Amide I and II of blood protein. It was concluded that the presence of blood during the hydration process of mineral trioxide aggregates produced small gaps of protein impurities within the hydrated material, affecting its chemical behavior and dentin/material-interface integrity.

Indium doped ZnO nano-powders prepared by RF thermal plasma treatment of In2O3 and ZnO

Indium doped ZnO nano-powders were synthesized by the RF thermal plasma treatment of In2O3 and ZnO. For this purpose, micron-sized ZnO powder was mixed with In2O3 powder at the In/Zn ratios of 0.0, 1.2, and 2.4 at. % by ball milling for 1 h, after which the mixtures were injected into RF thermal plasma generated at the plate power level of ∼140 kV A. As observed from the field emission scanning electron microscopy (FE-SEM) images of the RF plasma-treated powders, hexagonal prism-shaped nano-crystals were mainly obtained along with multi-pod type nano-particles, where the number of multi-pods decreased with increasing In/Zn ratios. In addition, the X-ray diffraction (XRD) data for the as-treated nano-powders showed the diffraction peaks for the In2O3 present in the precursor mixture to disappear, while the crystalline peaks for the single phase of ZnO structure shifted toward lower Bragg angles. In the UV–vis absorption spectra of the as-treated powders, redshifts were also observed with increases of the In/Zn ratios. Together with the FE-SEM images and the XRD data, the redshifts were indicative of the doping process of ZnO with indium, which took place during the RF thermal plasma treatment of In2O3 and ZnO.

Temperature dependent Raman and DFT study of creatine

Temperature dependent Raman spectra of creatine powder have been recorded in the temperature range 420–100K at regular intervals and different clusters of creatine have been optimized using density functional theory (DFT) in order to determine the effect of temperature on the hydrogen bonded network in the crystal structure of creatine. Vibrational assignments of all the 48 normal modes of the zwitterionic form of creatine have been done in terms of potential energy distribution obtained from DFT calculations. Precise analysis gives information about thermal motion and intermolecular interactions with respect to temperature in the crystal lattice. Formation of higher hydrogen bonded aggregates on cooling can be visualized from the spectra through clear signature of phase transition between 200K and 180K.

Quantitative reflectance spectra of solid powders as a function of particle size.

We have recently developed vetted methods for obtaining quantitative infrared directional-hemispherical reflectance spectra using a commercial integrating sphere. In this paper, the effects of particle size on the spectral properties are analyzed for several samples such as ammonium sulfate, calcium carbonate, and sodium sulfate as well as one organic compound, lactose. We prepared multiple size fractions for each sample and confirmed the mean sizes using optical microscopy. Most species displayed a wide range of spectral behavior depending on the mean particle size. General trends of reflectance versus particle size are observed such as increased albedo for smaller particles: for most wavelengths, the reflectivity drops with increased size, sometimes displaying a factor of 4 or more drop in reflectivity along with a loss of spectral contrast. In the longwave infrared, several species with symmetric anions or cations exhibited reststrahlen features whose amplitude was nearly invariant with particle size, at least for intermediate and large size sample fractions: that is, ≳150 μm. Trends of other types of bands (Christiansen minima, transparency features) are also investigated as well as quantitative analysis of the observed relationship between reflectance versus particle diameter.

Tribological Properties of Muscovite/La2O3 Composite Powders as Lubricant Additives

Muscovite/La2O3 composite powders were prepared by ball-milling solid-state chemical reaction at room temperature. The phase composition and micromorphology of the composite powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The tribological properties of different samples were tested and compared using four-ball wear testing on an MMW-1A multifunctional friction and wear testing machine. The SEM micrography and energy spectrum of the composite powders illustrated that La2O3 particles were coated on the surface of muscovite particles. The results of the friction tests indicated that lubrication oil with muscovite/La2O3 composite powders presents better friction reducing and antiwear properties than that of the base oil, and the friction coefficients and diameters of wear scars decreased by 47.6 and 11.2% using 500SN base oil with 0.6g/L of muscovite/La2O3 composite powders as additives, respectively. The composite powders with 5 wt% La2O3 present the best comprehensive tribological properties. The micromorphology and chemical composition of the worn surface were analyzed by SEM and EDX, which confirm that the composite powders directly participate in the complicated physicochemical process of reactions on the worn surfaces, therefore improving the tribological properties of the base oil.

A comment on powder averaging in wide line NMR

Computer calculations of wide line NMR spectra of powders usually involve numerical evaluation of double integrals over two Euler angles. Practice confirms intuition-based expectations that the integration results should be independent from the choice of the crystal-fixed (or molecule-fixed) coordinate system used in the calculations. However, a closer inspection of the relevant integration formulas may make one wonder why this is so. The present paper provides a rigorous mathematical proof of the validity of these intuitive predictions, by formulating the problem in terms of surface integrals on a sphere, which has presumably no precedence in the NMR literature.

Exploring the Variance of Authentic Skim and Non-Fat Dry Milk Powder Spectra

investigated by the Unites States Pharmacopeia (USP) in an effort to develop a successful non-targeted solution for milk powder. A significant challenge to be faced in this study is the normal physicochemical variability of pure milk powders. The existence of these variations will have the effect of widening the boundaries for any potential non-targeted method which may have the effect of decreasing the method’s ability to detect adulterants present at low concentrations. This problem is especially true for NIR diffuse reflectance spectroscopy, with its inherent limitations in the accurate detection of chemical components which are present below approximately 0.1% w /w in a sample matrix. In this report, the variance of NIR spectra from 41 different bovine skim milk powders and non-fat dry milk powders was explored. Spectral data were examined to identify influential sources of variance using princi pal component score trends and spectral signatures in rotated principal component loadings. Chemical analysis of samples of interest was also used to support the interpretations of the rotated principal components.

FTIR, XRD and SEM Analysis of Ginger Powders with Different Size

The grinding treatment could modify and change the chemical property of ginger powder. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to detect the chemical functional groups and structure of ginger powders with different sizes. FTIR showed that the absorption bands of different sizes of ginger powders were similar, but the intensity of bands decreased with reduce ginger particle size. The spectra of ginger superfine powder with a particle size of 8.34 μm were shifted compared with spectra of the particle sizes of 300, 149, 74 and 37 μm. It was concluded that the rigid and ordered structure of the cellulose was deteriorated by the superfine grinding treatment. XRD revealed that as the powder size decreased, the crystallinity and intensity of crystal peaks increased. The results of SEM showed that the superfine pulverizing was effective to change the original structure of the ginger powders. Practical Applications Superfine grinding is a novel technology in food processing and can improve the physicochemical properties of food materials. In addition, the knowledge provided by this work may promote the application of superfine grinding in the food industry.

Magnetic Anisotropy of Cr(III) Ions in Polymeric Oxalate Complexes as Revealed by HF-ESR Spectroscopy

Two new Cr(III) paramagnetic polymeric complexes: {[CaCr2(phen)2(C2O4)4]·0.33H2O} n (CrPhen) and {[CaCr2(bpy)2(C2O4)4]·0.83H2O} n (CrBpy), where phen = 1,10-phenanthroline and bpy = 2,2 $$'$$ -bipyridine, have been studied by high-field high-frequency electron spin resonance (HF-ESR) spectroscopy. From the oriented powder spectra, recorded in the frequency range 83–332 GHz in magnetic fields up to 16 T, the spin-Hamiltonian parameters, $$g$$ , $$D$$ and $$E$$ , have been obtained. Both chromium complexes have a small negative (easy axis) magnetic anisotropy $$|D|<1$$ K. CrPhen complex is biaxial, i.e., besides axial $$D$$ , there is also significant rhombic zero-field splitting (ZFS) parameter, $$E$$ . Contrary to CrPhen, CrBpy complex is uniaxial, but described by two sets of axial ZFS parameters. Despite very similar crystallographic structures of both complexes, HF-ESR spectroscopy resolved the existence of two magnetically inequivalent Cr(III) ions in CrBpy complex. The results fully support the earlier X-ray, SQUID magnetization and powder X-band ESR studies.

Production and Characterisation of PCL/ES Scaffolds for Bone Tissue Engineering

The combination of bio-fillers with synthetic polymers has been an exciting route for developing tissue engineering scaffolds, in particular for bone tissue regeneration. In this study, poly(ɛ-caprolactone) (PCL) scaffolds were produced using an additive manufacturing technique and eggshell (ES) powder was used as a filler. The morphology of PCL and PCL/ES scaffolds were analysed and the effect of ES in the polymer matrix was characterized using techniques of Differential Scanning Calorimetry and Thermogravimetric Analysis, Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Diffraction (XRD). Morphological observation revealed that the incorporation of ES in the polymer matrix modifies the flow behaviour of the material in spite of the same processing parameters, resulting in a decrease of scaffold pore size. Thermal analysis showed that the addition of the bio-filler improves the crystallization properties and thermal stability of the PCL. FT-IR spectra of ES powder showed characteristic bands of calcium carbonate and processed materials spectra indicated no changes on the functional groups compared to non-processed materials. Crystalline nature of ES was demonstrated through a characteristic broad peak in XRD pattern around 30o, which was also observed in the composites XRD spectra. The results indicate the potential of ES powder to be used as a filler for bio-based polymer scaffold composites.