Prepared Powder Samples Research Articles

Complete spin crossover in tris(pyridylbenzimidazole) iron(II)

The magnetic properties of a hexacoordinated iron(II) complex with the bidentate ligand pyridylbenzimidazole (pybzim), [Fe(pybzim) 3](ClO 4) 2 · H 2O, ( 1), have been investigated by AC susceptometry, 57Fe-Mössbauer, ESR and NMR spectroscopy. The temperature dependence of the AC magnetic susceptibility for a powder sample showed essentially diamagnetic behaviour below 85 K and paramagnetism ( μ eff/ μ B = 4.5−5.3, S = 2) above 160 K, obeying the Curie-Weiss law. Spin crossover behaviour can be found within the temperature range 90–160 K; it is centered at 141 K. The Mössbauer spectra confirm the susceptibility measurements: the area fraction of the high-spin quadrupole doublet plotted against temperature shows a curve similar to that deduced from susceptibility measurements. The complex is ESR silent in the X-band mode: neither the powder sample (77 K and 300 K) nor a methanolic solution exhibit an ESR signal. NMR measurements in methanol, acetone, nitromethane, acetonitrile and dimethylsulfoxide show an increasing magnetic moment μ eff/μ B from 1.6 (220 K, acetone) to 5.2 (325 K, DMSO), respectively. The spin-crossover transition of a freshly prepared powder sample is complete. However, time evolution causes (within months) an increasing admixture of iron(III), which was proved by magnetic susceptibility measurement, 57Fe-Mössbauer, ESR and electronic spectra of the complex.

A TEM characterization of precipitates evolution and their effect on the grain-growth behavior of gas atomized superalloy A-286

It is generally accepted that the refined grain size and stable grain boundaries observed in rapid-solidification-processed (RSP) materials are due to the fine precipitates produced during and after the processing. This is based on the observation of the materials after consolidation of the powders. Though there is little doubt that the as-atomized powder structure is crucial for the understanding of the consolidated sample, there are few studies of the powder. This is mainly because of the difficulty in preparation of thin electron-transparent samples.The most common method of powder sample preparation uses two or three different embedding materials whose polishing conditions are usually not identical. In this study, a monolayer of powder was gold coated, electroplated with nickel, and then electropolished. Electropolishing provided a nice and smooth surface without any surface artifact. In this study, as-atomized and heat treated powders were studied by TEM (JEOL JEM 200CX) and STEM (VG HB501). Because of the fineness of the defects involved, TEM observation is crucial.

Neutron diffraction investigation of structures of ‘RE124’ (RE = Dy, Ho, Er) and ‘Nd247’ superconductors; 2D antiferromagnetism in ‘Dy124’

High resolution neutron diffraction studies were performed on carefully prepared powder samples of the high- T c superconductors REBa 2Cu 4O 8 (RE = Dy, Er, Ho) (‘R124’) and on Nd 2Ba 4Cu 7O 15 (“Nd247’) at temperatures down to 7 mK. The structure parameters of these compounds, which are isostructural to the R = Y systems (Ammm), were refined. In agreement with Zhang et al. two-dimensional (2D) antiferromagnetism exists in ‘Dy124’ below T N≈1.1 K. It appears to be stable down to T = 7 mK.

Research on Buckminsterfullerene Continues To Proliferate

Research on the chemistry of buckminsterfullerene, the 60-carbon atom molecule with the geometry of a soccer ball, continues to appear in the literature at a rapid clip. In the past few weeks, new data from several laboratories on superconducting C 60 , metal derivatives of C 60 , and the physical and chemical properties of buckminsterfullerene have been published. At the University of California, Los Angeles, chemistry professors Francois N. Diederich and Robert L. Whetten, visiting physics professor Karoly Holczer, and coworkers have confirmed and extended the findings of AT&T Bell Laboratories researchers on the superconducting properties of C 60 doped with alkali metals [ Science , 252, 1154 (1991)]. The UCLA chemists prepared powder samples of C 60 doped with potassium under carefully controlled conditions and used diamagnetic shielding as a measure of superconductivity. While earlier research at Bell Labs unambiguously demonstrated that potassium-doped C 60 is a superconductor with a superconducting...

Inverse AC Josephson effect on multiphased high temperature oxide superconductors

The measurement of the microwave-induced voltage across a granular sample due to the inverse AC Josephson effect provides a technique to detect a superconducting phase in a multiphase system. For the systematic investigation of this technique the authors prepared powder samples from two Y-Ba-Cu-O compounds of different oxygen content and therefore different critical temperature. They measured the microwave induced DC voltage as a function of temperature of varying concentration of the higher Tc compound. External magnetic field, power and frequency of incident microwaves were also varied.

Optimisation of LiF:Cu,Mg,P for Radiation Protection Dosimetry

Abstract The results of our investigations of various parameters of the preparation procedure of thermoluminescent LiF:Cu,Mg,P are reported. The parameters under investigation are: (i) the relative concentration of the incorporated Mg, Cu and (PO4)-3 dopants; (ii) the influence of incorporation of oxygen; (iii) particle size distribution of the prepared powder samples; (iv) emission wavelength; (v) high temperature '300 oC, 10 min' pre-irradiation annealing. Incorporation of oxygen in the molten stage plays an essential role in the creation of thermoluminescence: 0.5 mol.% oxygen leads to a TL material with approximately twenty times the intensity of TLD-100. We also find that the relative intensity of the undesirable high-temperature TL (270 oC) shows no apparent correlation with oxygen or other dopant concentrations. The loss in TL sensitivity following 300 oC, 10 min annealing shows similar behaviour.

Low-pressure, automated, sample packing unit for diffuse reflectance infrared spectrometry

An automatic, low-pressure packing unit has been designed with control of packing time and pressure to prepare powder samples for diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This unit also provides a polished packing surface that ensures constant measurement height of the sample in the spectrometer. Use of this unit coupled with sample rotation during measurement and control of particle size and size distribution, provides excellent precision in obtaining DRIFTS spectra. For example, repackings by a single person or by several untrained people gave coefficients of variation from 0.8% to 2.3% for each digital spectral value for a coal sample and from 1.3% to 3.7% for thymol blue, a sharp spectral featured organic, rather than the 15%–30% normally found for repackings of the same sample. Thus representative DRIFTS spectra can be obtained quickly and efficiently from a powder sample with a single spectrum using this low-pressure, mechanical packing device, control of particle parameters, and sample rotation as opposed to previous efforts requiring the repacking of several samples and averaging of the spectra.

A Tubular Aerosol Suspension Chamber for the Preparation of Powder Samples for X-Ray Diffraction Analysis

AbstractHighly uniform fine powder sample layers may be prepared for X-ray diffractometry by aerosol suspension and collection on glass fiber filter substrates. A tubular aerosol suspension chamber (TASC) has been fabricated for this purpose. Essential components include a 500 ml gas buret, 4.7-cm filter cassette, rotameter, and rotary pump. Aerosol particles are generated within the TASC buret by convection within a fluidized bed of glass beads mixed with the sample. Exceptional uniformity of load and randomness of particle orientation has been demonstrated for samples prepared with this system. For quantitative analytical work accurate intensities may be obtained using corrections to raw intensities based on fundamental sample and filter properties.

Tetrametaphosphates — a new quasi-one-dimensional magnetic system

In the tetrametaphosphates M 2 P 4 O 12 of monoclinic structure (C2/ c ) the divalent cations M form characteristic zigzag chains. We prepared powder samples of M 2 P 4 O 12 ( M = Mn, Co, Ni, Cu) and investigated them by magnetic measurements and neutron scattering between 1.7 and 300 K, The copper compound showed no LRO down to 1.7 K. The other substances form antiferromagnetic structures below T N ( k = [010]). The intrachain interaction turned out to be ferromagnetic in the Ni and Co compounds, but antiferromagnetic in the case of Mn. The interchain coupling is always weakly antiferromagnetic leading to quasi-one-dimensional behavior. Critical exponents, magnetic moments, and their angles relative to the a - and b -axis were derived.

Trace element analysis of silicates by means of energy‐dispersive x‐ray spectrometry

AbstractThree methods for the energy‐dispersive x‐ray spectrometric analysis of trace elements in silicate rock samples were compared. The comparisons were based on three new USGS reference samples, DNC‐1, W‐2, and BIR‐1, and two established reference samples, G‐1 and W‐1. A loose powder sample preparation was used in the analysis of selected trace elements, including Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb and Ba. For one method, the ratio of analyte line intensity to either Compton or Compton and Rayleigh scatter intensity for a series of standards was used to construct calibration graphs. The other two methods involved fundamental parameter calculations which required a knowledge of the total sample compositions in order to perform the necessary matrix corrections. The results showed good accuracy for all three methods, but those obtained from the ratio–calibration graph method were slightly better than those from the other two methods.

A new procedure of powdered sample preparation by melting for x‐ray emission spectrometry

AbstractA new procedure of powder sample preparation for x‐ray emission analysis by melting has been worked out in detail. The mixture sample‐flux was melted and cooled in graphite crucible. The resulting glass disk was ready for direct measurement. The re‐fused graphite electrode of an electric arc furnace was used as the material for the graphite crucible. The dimension and shape of the crucible bottom were determined on the basis of sample holder dimension and sample behaviour during the cooling step. The reproducibility of Kα line measurement was below 1%. Resistance of the crucible to handling and the influence of graphite on Fe Kα, Ca Kα, SKα, Si Kα and Mg Kα line intensities also were investigated.

Routine analysis of iron ores by X-ray spectrometry

A number of iron ores from all parts of the world were analysed with a powder sample preparation technique. Calibration curves were plotted for Fe, Ca, Si, Al and Mg in wide concentration ranges using 32 international and a few local standards. All iron ores were divided into 5 groups related to mineralogical differences; however, the calibration curve for Ca is common for all samples. For hematites and magnetites the relationship FeO + Fe 2O 3 = f(Fe) was experimentally established. The total time for sample preparation and analysis is about 5 min. A good correlation of chemical and X-ray results was obtained in this routine work.

Disintegration of powder particle agglomerates under the action of an alternating electric field

1. A study was made of the process of disintegration of powder particle agglomerates in an alternating electric field generated by a plane capacitor with a narrow electrode gap. It is shown that the disintegration process could be employed for the preparation of powder samples for particle-size analysis. 2. It has been established that the process of disintegration of powder particle agglomerates involves the action of both electrical forces and mechanical forces set up during collisions of particles with the electrode surfaces and with one another. 3. Experiments have shown that in the disintegration of Al2O3 and Al powder particle agglomerates the best results are obtained at a field intensity E = (6–7) · 105 V/m, a frequency f = 225–300 Hz, and a treatment time t=4–6 min.

Dissolution Studies with a Multichannel Continuous-Flow Apparatus

A multichannel continuous-flow apparatus for dissolution rate measurements is described. Typical data are presented to demonstrate its utility for studies with bulk drug powders as well as with tablets and capsules without any change of setup. Procedures are given for the preparation of powder samples for dissolution studies and for a simple method of changing pH for “retard” tablets. The precision in dissolution rates obtained with this apparatus and method is 1–10% mean RSD. The advantages of the method are flexibility, reproducibility, and ability to obtain data in integral or differential form.

A method of preparation of powder samples for Debye–Scherrer–Hull X-ray diffraction

A method of preparation of powder samples for Debye–Scherrer–Hull X-ray diffraction

The preparation of powder samples

The preparation of thick isotope samples for several types of neutron cross-section measurements is described. In the ideal case, these kinds of measurements are performed on metallic samples. If it is not possible to use the isotope in its metallic form, samples are prepared from its compounds. The three preparation methods used are direct compacting of powders, compressing in a container, and sedimentation. The experimental setup including the chemical treatment, the purification, the preparation of the samples, the canning, and the decontamination are discussed. In most cases, the samples are canned under vacuum. Special care is given to the yield and the quantitativity of the method in the treatment and recovery of the sample material. Problems encountered during the preparation of radioactive samples are outlined. Some examples of prepared samples are given, e.g., 241Am, 241Pu, and 237Np.

Simple techniques to prepare powder samples for spark-source mass-spectrometric analysis

Simple techniques to prepare powder samples for spark-source mass-spectrometric analysis

X-Ray Study on the Binding Properties of Cu2O and Ag2O Crystals

Crystallographical properties of the chemically prepared powder samples of Ag 2 O and Cu 2 O were investigated by an X-ray diffractometer, in relation to their bonding characters. The lattice constant is 4.720±0.004A for Ag 2 O and 4.268±0.001A for Cu 2 O. The thermal expansion coefficient of the lattice is 1.9×10 -6 for Cu 2 O. The root-mean-square amplitude of the thermal lattice vibration is determined as 0.26A for Cu 2 O and 0.40A for Ag 2 O at room temperature. The mean lattice strain is 1.4% for Ag 2 O and 0.15% for Cu 2 O, respectively. The thermal decomposition of Ag 2 O was also observed. The obtained results suggest that the binding force between metallic and oxygen atoms is much weaker in Ag 2 O than in Cu 2 O, which can not be expected from the purely ionic model for the present crystals.