Thermal decomposition of magnesium sesquicarbide

1983 ◽  
Vol 48 (7) ◽  
pp. 1963-1968 ◽  
Author(s):  
Bohumil Hájek ◽  
Pavel Karen ◽  
Vlastimil Brožek
Keyword(s):  
Thermal Decomposition ◽  
Kinetic Data ◽  
Arrhenius Equation ◽  
Kinetic Equations ◽  
Decomposition Reaction ◽  
Point Of View ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffraction Patterns ◽  
Thermal Stability Of

The structure of Mg2C3 and the course of its decomposition were studied. The powder X-ray diffraction patterns were analyzed to obtain the lattice parameters for hexagonal Mg2C3, a = 743.4 ± 0.5 pm, c = 1 056.4 ± 1.6 pm. Thermal decomposition data were obtained for temperatures 670-740 °C and pressure 130 Pa; they could be fitted satisfactorily by kinetic equations for various processes, including the 1 st order decomposition reaction, and so the controlling phenomenon of the reaction cannot be deduced based on the kinetic data. The 1 st order rate constants and reaction halflives were evaluated for various temperatures and approximated by the Arrhenius equation to calculate the parameters AA = 1.97 . 1014 s-1, EA = 333 kJ mol-1. The conditions of synthesis of Mg2C3 are discussed from the point of view of the choice of a suitable hydrocarbon for the reaction with magnesium. The thermal stability of the sesquicarbide increases with increasing pressure; it could be formed from dicarbide and sustained even at a temperature of 1 450 °C by applying a pressure as high as 6 GPa.

Synthesis and thermal decomposition of magnesium dicarbide

1983 ◽  
Vol 48 (7) ◽  
pp. 1969-1976 ◽  
Author(s):  
Bohumil Hájek ◽  
Pavel Karen ◽  
Vlastimil Brožek
Keyword(s):  
Thermal Decomposition ◽  
Arrhenius Equation ◽  
Kinetic Equations ◽  
Optimum Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Gaseous Products ◽  
Controlled Porosity ◽  
Diffraction Patterns ◽  
High Yields

The conditions of formation of magnesium dicarbide from magnesium and acetylene were investigated; the optimum temperature, reaction period, and acetylene flow rate were sought so as to achieve high yields of dicarbide and minimize the free carbon deposit. The porosity of the magnesium dust was found to have a pronounced effect upon the yield; a considerable improvement was achieved by pressing the dust into pellets with controlled porosity. The powder X-ray diffraction patterns of MgC2 samples were studied. The intense reflection could be indexed for the bet symmetry (a = 392.9 ± 0.6 pm, c = 503.7 ± 1.2 pm), but as the intensity calculations for dicarbide models with different arrangements of the C22- groups indicate, the symmetry of the MgC2 lattice will be lower than tetragonal. The thermal decomposition of the dicarbide leading to sesquicarbide was examined in dependence on time and temperature by hydrolyzing the samples and analyzing the gaseous products by GLC. Due to the thermal decomposition, traces of sesquicarbide appear even during the dicarbide synthesis. The decomposition process was approximated by kinetic equations. The Arrhenius equation constants, in the temperature region of 485-560 °C, are AA = 4.97 . 1012 s-1, EA = 257 kJ mol-1.

Infrared spectroscopic study of the YPO4-YCrO4 system

1985 ◽  
Vol 50 (10) ◽  
pp. 2139-2145
Author(s):  
Alexander Muck ◽  
Eva Šantavá ◽  
Bohumil Hájek
Keyword(s):  
Spectroscopic Study ◽  
Infrared Spectra ◽  
Point Of View ◽  
Mixed Crystals ◽  
Crystal Symmetry ◽  
Infrared Spectroscopic Study ◽  
X Ray Diffraction ◽  
X Ray ◽  
Infrared Spectroscopic ◽  
Diffraction Patterns

The infrared spectra and powder X-ray diffraction patterns of polycrystalline YPO4-YCrO4 samples are studied from the point of view of their crystal symmetry. Mixed crystals of the D4h19 symmetry are formed over the region of 0-30 mol.% YPO4 in YCrO4. The Td → D2d → D2 or C2v(GS eff) correlation is appropriate for both PO43- and CrO43- anions.

Algorithms for the calculation of X-ray diffraction patterns from finite element data

2010 ◽  
Vol 43 (6) ◽  
pp. 1287-1299 ◽  
Author(s):  
E. Wintersberger ◽  
D. Kriegner ◽  
N. Hrauda ◽  
J. Stangl ◽  
G. Bauer
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Point Of View ◽  
X Ray Diffraction ◽  
Displacement Fields ◽  
X Ray ◽  
Si Substrates ◽  
Diffraction Patterns ◽  
Simulation Point ◽  
Ccd Detectors

A set of algorithms is presented for the calculation of X-ray diffraction patterns from strained nanostructures. Their development was triggered by novel developments in the recording of scattered intensity distributions as well as in simulation practice. The increasing use of two-dimensional CCD detectors in X-ray diffraction experiments, with which three-dimensional reciprocal-space maps can be recorded in a reasonably short time, requires efficient simulation programs to compute one-, two- and three-dimensional intensity distributions. From the simulation point of view, the finite element method (FEM) has become the standard tool for calculation of the strain and displacement fields in nanostructures. Therefore, X-ray diffraction simulation programs must be able to handle FEM data properly. The algorithms presented here make use of the deformation fields calculated on a mesh, which are directly imported into the calculation of diffraction patterns. To demonstrate the application of the developed algorithms, they were applied to several examples such as diffraction data from a dislocated quantum dot, from a periodic array of dislocations in a PbSe epilayer grown on a PbTe pseudosubstrate, and from ripple structures at the surface of SiGe layers deposited on miscut Si substrates.

In Situ X-Ray Diffraction Study of Thermal Stability of Cu and Cu-Zr Samples Processed by ECAP

2013 ◽  
Vol 753 ◽  
pp. 279-284 ◽  
Author(s):  
Radomír Kužel ◽  
Zdeněk Matěj ◽  
Miloš Janeček
Keyword(s):  
In Situ Measurements ◽  
X Ray Diffraction ◽  
X Ray ◽  
Abnormal Growth ◽  
Angular Pressing ◽  
Dislocation Densities ◽  
Diffraction Patterns ◽  
Number Of Passes ◽  
Thermal Stability Of

X-ray diffraction (XRD) studies of ECAP (equal-channel angular pressing) materials were performed after annealing and by in-situ measurements in XRD high-temperature chamber for samples prepared by different number of passes and number of revolutions, respectively. Main attention was given to Cu and Cu-Zr samples. Significant dependence on number of passes was found for ECAP samples. In-situ measurements were focused not only on temperature dependence but also on time evolution of the diffraction line profiles. Evaluation in terms of dislocation densities, correlation and crystallite size and its distribution was performed by our own software MSTRUCT developed for total powder diffraction pattern fitting. Abnormal growth of some grains with annealing is well-known for copper and leads to the creation of bimodal microstructure. Therefore a special care must be given to the evaluation and a model of two Cu components (larger and smaller crystallites) was fitted to the data if an indication of some crystallite growth appears either in the XRD line profile shape or in two-dimensional diffraction patterns.

Massive Transformation in High Niobium Containing TiAl-Alloys

2004 ◽  
Vol 842 ◽  
Author(s):  
A. Bartels ◽  
S. Bystrzanowski ◽  
H. Chladil ◽  
H. Leitner ◽  
H. Clemens ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Sheet Material ◽  
Massive Transformation ◽  
X Ray Diffraction ◽  
Tial Alloys ◽  
X Ray ◽  
Boundary Triple ◽  
Triple Points ◽  
Diffraction Patterns ◽  
Thermal Stability Of

ABSTRACTMassive transformation in high Nb bearing γ-TiAl-based alloys, Ti-45Al-7.5Nb and Ti-46Al-9Nb (at.%), and the thermal stability of the resulting microstructure were investigated. Using a quenching dilatometer, a nearly complete massive transformation in Ti-45Al-7.5Nb was found at about 1050°C after annealing at 1305°C for 10min and subsequent cooling with a rate of 55K/s. Higher starting temperatures and higher cooling rates lead to incomplete massive transformation and small transformed areas situated at the grain-boundary triple points of the parent α-grains are observed. By means of EBSD only in one case the same orientation of the close-packed planes of parent α-grains and of massively transformed γM-areas was observed.The thermal stability of the microstructure of massively transformed Ti-46Al-9Nb sheet material was tested by annealing samples for 1 hour between 400 and 1200°C. Above 800°C a drop of hardness was measured and X-ray diffraction patterns show an increasing separation of (200)γ and (002)γ reflections as expected from a tetragonal γ-TiAl lattice. After annealing at 1100°C α2-phase segregates at grain boundaries and after 1200°C α2-lamellae appear insides the γM-grains parallel to all four {111}γ-planes.

The Effect of Al on Phase Stability and Oxidation Behavior in Ternary Nb-Ti-Si Alloys

2014 ◽  
Vol 556-562 ◽  
pp. 310-313
Author(s):  
Yong Jun Jiang
Keyword(s):  
Room Temperature ◽  
Oxidation Behavior ◽  
Point Of View ◽  
Transition Elements ◽  
X Ray Diffraction ◽  
X Ray ◽  
Room Temperature Ductility ◽  
Oxidation Properties ◽  
Diffraction Patterns ◽  
And Control

In this paper, we report a significant improvement in mechanical and oxidation properties of near eutectic Nb–Si alloys by the addition of aluminum (Al) and control of microstructural length scale. Thus in order to develop new alloys, we have to choose proper alloying elements keeping all the above issues in mind. Among the non-transition elements such as Al, Ga, Ge, Sn, and Al is most attractive from the point of view of enhancing the oxidation resistance and room temperature ductility due to substitution of Si with metallic Al . Al forms oxides which are even more thermodynamically stable than Si and Nb based oxides. Al is also soluble in Nb to a greater degree in conjunction with other refractory elementsFig.1 The figure shows composite X-ray diffraction patterns of each sample exposed to air for one hour in a TGA furnace at above mention temperatures.

scholarly journals INCORPORAÇÃO DE NB EM ZEÓLITAS: USO COMO CATALISADORES NA DECOMPOSIÇÃO DO PERÓXIDO DE OXIGÊNIO

2017 ◽  
Vol 36 (3) ◽  
pp. 47
Author(s):  
Selma Calgaroto ◽  
Cléber Calgaroto ◽  
Fábio G. Penha ◽  
Sibele B. C. Pergher ◽  
Luiz Carlos A. Oliveira
Keyword(s):  
Catalyst Activity ◽  
Decomposition Reaction ◽  
Textural Analysis ◽  
X Ray Diffraction ◽  
N2 Adsorption ◽  
X Ray ◽  
H2o2 Decomposition ◽  
Diffraction Patterns ◽  
Ionic Change ◽  
Partial Destruction

In this work, the comercial zeolites ZSM-5 and Y were submitted to previous ionic change with NH4NO3, followed by the addition of Nb. The incorporation of Nb on its structure aims increasing the acidity and improved the catalyst activity of these zeolites. The materials obtained are characterized by X-Ray diffraction patterns, chemical analysis, SEM and textural analysis by N2 adsorption. Furthermore, the materials were avaliated by decomposition reaction of the H2O2. The Nb presence improved the catalytic activity for H2O2 decomposition. Moreover, high amounts of Nb incorporated into zeolites caused a partial destruction of the structure of the materials as evidenced by X-Ray diffraction patterns. 

scholarly journals Activated Carbon as a Support of Catalysts for the Removal of Nitrogen Oxides

Mineralogia ◽  
2020 ◽  
Vol 51 (1) ◽  
pp. 9-16
Author(s):  
Anna Białas ◽  
Joanna Szlendak ◽  
Cezary Czosnek ◽  
Monika Motak
Keyword(s):  
Activated Carbon ◽  
Nitrogen Oxides ◽  
Catalytic Reduction ◽  
Textural Properties ◽  
Carbon Support ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffraction Patterns ◽  
Thermal Stability Of ◽  
Microporous Solids

Abstract Activated carbon was oxidised with concentrated nitric acid and impregnated with urea to form nitrogen-containing groups. Such a support was impregnated with cobalt, copper or silver nitrates to obtain catalysts for the selective catalytic reduction of nitrogen oxides with ammonia. Infrared spectra confirmed the formation of carboxylic and other organic oxygen-containing groups during oxidation. Nitrogen-containing species resulted from urea thermal decomposition. The metal-containing samples were hydrophilic. Cobalt and copper were present in the samples as small Co3O4 and CuO crystallites, while silver occurred in the form of large metallic crystallites, as seen from the X-ray diffraction patterns. Low temperature N2 sorption revealed that all samples were microporous solids, and the chemical and thermal treatment did not change their textural properties. The copper admixture caused the highest NO conversion, but worsened the selectivity and thermal stability of functionalised carbon support.

scholarly journals Synthesis and Characterization of Dodecylbenzene Sulfonic Acid doped Tetraaniline via Emulsion Polymerization

2012 ◽  
Vol 9 (3) ◽  
pp. 1342-1346 ◽  
Author(s):  
K. Basavaiah ◽  
K. Tirumala Rao ◽  
A. V. Prasada Rao
Keyword(s):  
Sulfonic Acid ◽  
X Ray Diffraction ◽  
Visible Spectroscopy ◽  
X Ray ◽  
Molar Ratios ◽  
Uv Visible ◽  
Dodecylbenzene Sulfonic Acid ◽  
Diffraction Patterns ◽  
Thermal Stability Of

In this work, we report preparation and characterization of dodecylbenzene sulfonic acid (DBSA) doped tetraaniline via micelles assisted method using ammonium per sulphate (APS) as an oxidant. Here, DBSA act as dopant as well as template for tetraaniline nanostructures. The synthesized DBSA doped tetraaniline have been well characterized by X-ray diffraction patterns, Fourier transform infrared spectroscopy, UV-Visible spectroscopy, Scanning electron microscopy and thermogravimetry. The morphologies of tetraaniline were found to be dependent on molar ratios of N-phenyl-1, 4-phenylenediamine to DBSA. The spectroscopic data indicated that DBSA doped tetraaniline. Thermogravimetry studies revealed that the DBSA doping improved the thermal stability of tetraaniline.

The structure of bacterial flagella: the packing of the polypeptide chains within a flagellum

1961 ◽  
Vol 260 (1303) ◽  
pp. 558-573 ◽  
Keyword(s):  
Point Of View ◽  
X Ray Diffraction ◽  
Detailed Structure ◽  
Satisfactory Explanation ◽  
X Ray ◽  
Bacterial Flagella ◽  
Diffraction Patterns ◽  
Polypeptide Chains ◽  
Ray Patterns ◽  
Single Flagellum

The X-ray diffraction patterns from specimens of bacterial flagella taken by Astbury, Weibull and others consist essentially of three sets of reflexions, two sets on the meridian and one set on the equator. The equatorial set gives information on the packing arrange-merit of the polypeptide chains within a single flagellum. This paper is concerned with the interpretation in terms of a physical model of the equatorial diffraction from flagella from Proteus vulgaris for which the published diffraction data are most detailed. The polypeptide chains are all assumed to be in the α -helical form though the meridional diffraction gives some indication that a smaller ‘cross- β ’ component may also be present. The separation (121 Å) between the flagella in the X-ray specimens is inferred from the spacings of the equatorial reflexions and two alternative models (model I and model II) for the detailed structure of a flagellum are inferred from the intensity data. The structures proposed are similar in outline but differ in detail and postulate that a flagellum is composed of a number of identical interwoven filaments which themselves comprise a limited number of α -helices in a centred hexagonal or pseudo-hexagonal array. In model I the flagella are assumed to be in contact in the X-ray specimens and the structure comprises three filaments of diameter 56 Å each containing 19 single α -helices. In model II the flagella are not in contact and each of the seven filaments of diameter 33 Å contains seven α -helices; the diameter of the flagellum on this model is about 100 Å. The equatorial X-ray patterns from the two models are calculated in detail including effects due to the packing of the flagella within an X-ray specimen, for comparison with the observed diffraction. Both calculated patterns give a satisfactory explanation of the spacings of the observed reflexions and show reasonable agreement with the experimental intensities. The relative merits of the two models are discussed from the diffraction point of view and in conjunction with available data from electron microscopy. The diffraction pattern from model II is in better agreement with the experimental results than the pattern from model I but the latter agreement may be improved if the hexagonal packing of the α -helices within a filament is slightly modified; a cylindrical lattice is considered from this point of view. It is concluded that, at the present time, there is insufficient evidence to differentiate between the two models of a flagellum presented.

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