Line Profile Study Research Articles

Microstructure of calcite deformed by high-pressure torsion: An X-ray line profile study

Calcite aggregates were deformed to high strain using high-pressure torsion and applying confining pressures of 1–6GPa and temperatures between room temperature and 450°C. The run products were characterized by X-ray diffraction, and key microstructural parameters were extracted employing X-ray line profile analysis. The dominant slip system was determined as r{101¯4}⟨2¯021⟩ with edge dislocation character. The resulting dislocation density and the size of the coherently scattering domains (CSD) exhibit a systematic dependence on the P-T conditions of deformation. While high pressure generally impedes recovery through reducing point defect mobility, the picture is complicated by pressure-induced phase transformations in the CaCO3 system. Transition from the calcite stability field to those of the high-pressure polymorphs CaCO3-II, CaCO3-III and CaCO3-IIIb leads to a change of the microstructural evolution with deformation. At 450°C and pressures within the calcite stability field, dislocation densities and CSD sizes saturate at shear strains exceeding 10 in agreement with earlier studies at lower pressures. In the stability field of CaCO3-II, the dislocation density exhibits a more complex behavior. Furthermore, at a given strain and strain rate, the dislocation density increases and the CSD size decreases with increasing pressure within the stability fields of either calcite or of the high-pressure polymorphs. There is, however, a jump from high dislocation densities and small CSDs in the upper pressure region of the calcite stability field to lower dislocation densities and larger CSDs in the low-pressure region of the CaCO3-II stability field. This jump is more pronounced at higher temperatures and less so at room temperature. The pressure influence on the deformation-induced evolution of dislocation densities implies that pressure variations may change the rheology of carbonate rocks. In particular, a weakening is expected to occur at the transition from the calcite to the CaCO3-II stability field, if aragonite does not form.

Line profile study of transitions in the 30012 ← 00001 and 30013 ← 00001 bands of carbon dioxide perturbed by air

In this work we present a line profile study for air-broadened carbon dioxide transitions in the 30012 ← 00001 and 30013 ← 00001 vibrational bands. The room temperature spectra were recorded at a resolution of 0.008 cm −1 using a Fourier Transform spectrometer. The air-broadening, air-shift, and air-line mixing coefficients were derived from a simultaneous fitting of spectra using the Voigt model and a Speed-Dependent Voigt lineshape model. The results obtained are consistent with other studies in addition to the theoretically calculated values. Exponential Power Gap (EPG) and Energy Corrected Sudden (ECS) scaling laws were used to calculate the relaxation matrix elements.

Diode-laser spectroscopy: Temperature dependence of R (0) line in the ν4 band of CH 4 perturbed by N 2 and O 2

In this paper, we present a line profile study of the R (0) line in the ν 4 band of methane diluted in nitrogen and oxygen, from room temperature to 153 K. The measurements were performed over a total pressure range from 14 to 128 mbar. The collisional broadening and narrowing (Dicke effect) coefficients are derived from a fit of the experimental spectra by using the soft and hard collision models, taking into account the Dicke effect. For higher pressures, we have fitted the data with a model taking into account simultaneously the Dicke narrowing and the speed dependence effect. Finally, we have deduced the parameter n of the temperature dependence (inverse power law) of the broadening coefficients for the CH 4–N 2 and CH 4–O 2 gas mixtures.

Line profile study by diode laser spectroscopy in the 12CH 4ν2 + ν4 band

We present a complete study on four methane lines for two atmospheric micro-windows (in the ν 2 + ν 4 absorption band) used for the determination of atmospheric methane concentrations with ground-based Fourier transform spectrometers. Thanks to our tunable diode laser (TDL) spectrometer with active wavenumber control and step-by-step recording mode we have improved the accuracy on intensity, broadening, narrowing, and pressure shift parameters. To make our results directly useable in atmospheric models which usually assume a Voigt line shape, we have parameterised an effective-broadening parameter γ Voigt ( P) for each line and each gas mixture (CH 4–N 2 and CH 4–O 2). When this parameterisation is used to fit a “true” line profile, the same concentration as with more sophisticated models is retrieved using a consistent set of spectroscopic parameters in both approaches.

Line profile study down to 80 K of R(7) in the 13CO (1–0) band perturbed by Ar and 13CO collisional cooling with He at 6.9 K

We present a line profile study at 150, 110 and 80 K for the R(7) line in the fundamental band of 13CO perturbed by Ar in a new stabilized low-temperature cell cooled by liquid nitrogen. The broadening, shifting and narrowing parameters are determined taking into account the absorber speed dependence by simultaneous least-squares fitting of spectra over a 4–300 Torr pressure range recorded using a frequency-stabilized diode laser spectrometer. When the cell is cooled by liquid helium the (1–0) R(2) line of 13CO in collision with helium is observed at a temperature of 6.9 K.

Line profile study with tunable diode laser spectrometers

In this paper, we present the different theoretical line profiles, which can be used to describe a shape of molecular transitions in dilute gases: the Voigt, Galatry, Rautian and speed dependence models. We discuss their limitations and their advantages, and present for illustration different comparisons of model results with experimental data obtained with several diode laser spectrometers suitable for precise line shape measurements.

Line profile study from diode laser spectroscopy in the 12CH 4 2 ν3 band perturbed by N 2, O 2, Ar, and He

We present a line profile study for two lines in the 2 ν 3 band of CH 4 recorded with a frequency stabilized tunable diode laser spectrometer. The broadening and narrowing (Dicke effect) parameters of the R(0) line perturbed by N 2, O 2, and He are derived from a simultaneous fitting of spectra at pressures from 20 to 300 Torr by using the soft and hard collision models. These parameters are determined for the A and F components of the unresolved R(3) manifold perturbed by N 2, Ar, and He from the line profile analysis of spectra at pressures between 50 and 500 Torr. The line mixing effect between the two F components is also taken into account and the absorber speed dependent effect on broadening is estimated for N 2 and Ar.

A Flower on a WIRE: Asteroseismology of a Massive Star

AbstractRecently it became clear from a line profile study that the β Cephei star β Crucis (Mimosa) is multiperiodic with at least three modes excited. Observations of this star by the star tracker of the WIRE satellite have now confirmed the multiperiodicity in the light variations. A total of 5 million observations covering 17 days was analysed and the three main periods are in perfect agreement with the line profile results. The amplitudes are small (3, 2.7 and 0.6 millimag for the dominant modes), but this is not surprising in view of the mode identifications derived from the line profiles. More periods could still be present, including the one earlier suggested by the radial velocity data.

Effect of alloying on the microstructure and mechanical properties of Ni3Al

Microstructural characterisation of four compositions of Ni3Al based alloys (industrially designated as 463, 465, 790 and 794) prepared by a vacuum gas atomization technique has been done in the powder and hot pressed forms of the materials by adopting the most recent version of X-ray line profile studies (assuming pV functions) along with high resolution optical and scanning electron microscopy. Mechanical properties of the hot pressed samples has been measured by microhardness studies. X-ray line profile study reveals the defect related features of the microstructures in terms of the parameters such as change in the lattice parameters, stacking and multilayer fault densities (α and β), particle (domain) sizes, r.m.s strains, dislocation density, degree of long range order, antiphase boundary (APB) probability, APB domain size etc. The results revealed considerably higher values of α on hot-pressing with anisotropic values of domain sizes and r.m.s strains. The domain sizes decrease and r.m.s strains increase on hot-pressing. A dislocation density as high as 1011 cm cm−3 has been observed in hot-pressed samples. With increasing alloying additions and on hot-pressing the degree of long-range order decreases. A broadening study of superlattice reflections reveals an increase in APB probability and a decrease in APB domain sizes in the hot pressed states of the materials. Grain sizes are reduced on hot pressing with most complex alloy 790 having smallest grain sizes. The values of hardness and work hardening coefficients are high on Cr containing alloy (465, 790) compared to Fe containing (794) and unalloyed (463) alloys.

Discrimination of Ceramics—Study on the Microstructures of Ceramics

Abstract A method for discrimination of alumina ceramics was developed based on the observation of the surface morphology of etched surfaces, density, X-ray diffraction line profiles and grain size distributions. The experimental observations of the surface microstructure were made, using the scanning electron microscopy (SEM), on several different alumina ceramics with high (>99%), middle (96 to 98%) and low (approximately 92%) alumina content in order to identify them. The samples were prepared with a sulfuric acid (4.5 mol/L) etching method performed at 150 ≈ 200°C for 2 h on low and middle purity alumina ceramics and for 4 h on high purity alumina ceramics. The results indicate that the SEM observation coupled with computerized image analysis to determine grain size distribution is a powerful tool to discriminate among alumina ceramics that exhibit similar morphological characteristics. The X-ray diffraction line profile study is suggested as an additional useful index for the determination of microcrystalline structure.

A X-ray line profile study on as-polymerized isotactic polypropylene

The line profile analysis of high-resolution wide angle X-ray diffraction spectra (WAXS) has been employed to characterize two polypropylenes polymerized by: a) “conventional” Ziegler-Natta catalyst (PP-A) and b) “high-yield” new supported catalyst (PP-B). The observed differences in line-width are most reasonably due to a marked crystallite size anisotropy, more pronounced for PP-A. The smallest size is along the crystallographic a-axis, which is the preferred direction of growth of crystallites. Paracrystalline fluctuations, on the whole larger in the high-yield polymer than in the conventional one, are present. The diffuse background resulting from line profile analysis is preliminarily investigated here in terms of scattering from a microcrystalline array.

A line profile study of the 193.76 nm arsenic emission line from lamps used in atomic absorption spectroscopy

The width of the 193.7 nm line of arsenic has been measured for a commercial hollow cathode lamp (HCL), a pumped hollow cathode lamp and a commercial electrodeless discharge lamp (EDL). The measurements were made using an echelle spectrometer and operating the lamps under a wide range of conditions. The line widths for the commercial HCL and for the EDL were found to be 0.91 pm (9.10 mÅ) and 0.895 pm (8.95 mÅ) respectively when operated under the recommended unpulsed operating conditions, and the EDL line was seven times as intense as that from the HCL. When the lamps were pulsed, the widths of the lines increased to 1.009 pm (10.09 mÅ) in the case of the HCL and to 0.904 pm (9.04 mÅ) for the EDL. The arsenic HCL, with neon as a carrier gas, suffers from severe spectral interference which arises from the presence of the 193.89 nm and 193.01 nm Ne II lines. This could account for most of the curvature of the absorbance-vs-concentration calibration curve.