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.

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.

scholarly journals Complexes of 4-chlorophenoxyacetates of Nd(III), Gd(III) and Ho(III)

2018 ◽  
Vol 35 (1) ◽  
pp. 67
Author(s):  
W. Ferenc ◽  
M. Bernat ◽  
J. Sarzyński ◽  
H. Głuchowska
Keyword(s):  
Thermal Decomposition ◽  
Magnetic Moments ◽  
X Ray Diffraction ◽  
Magnetic Studies ◽  
Bridging Ligands ◽  
X Ray ◽  
Gaseous Products ◽  
Carboxylate Groups ◽  
One Step ◽  
Ligand Fields

The complexes of 4-chlorophenoxyacetates of Nd(III), Gd(III) and Ho(III) have been synthesized as polycrystalline hydrated solids, and characterized by  elemental analysis, spectroscopy, magnetic studies and also by X-ray diffraction and thermogravimetric measurements. The analysed complexes have the following colours: violet for Nd(III), white for Gd(III) and cream for Ho(III) compounds. The carboxylate groups bind as bidentate chelating (Ho) or bridging ligands (Nd, Gd). On heating to 1173K in air the complexes decompose in  several steps. At first, they dehydrate in one step to form anhydrous salts, that next decompose to the oxides of respective metals. The gaseous products of their thermal decomposition in nitrogen were also determined and the magnetic susceptibilites were measured over the temperature range of 76-303K and the magnetic moments were calculated. The results show that 4-chlorophenoxyacetates of Nd(III), Gd(III) and Ho(III) are high-spin complexes with weak ligand fields. The solubility value in water at 293K for analysed  4-chlorophenoxyacetates is in the order of 10-4mol/dm3.

Heptamanganese tricarbide Mn7C3

1983 ◽  
Vol 48 (10) ◽  
pp. 2740-2750 ◽  
Author(s):  
Bohumil Hájek ◽  
Pavel Karen ◽  
Vlastimil Brožek
Keyword(s):  
Concentration Distribution ◽  
Radical Mechanism ◽  
Structural Elements ◽  
X Ray Diffraction ◽  
Reduced Pressure ◽  
X Ray ◽  
Gaseous Products ◽  
Diffraction Patterns ◽  
Structure Assignment ◽  
Covalent Nature

A procedure was examined for the preparation of Mn7C3 by reaction of manganese dust with n-pentane at 850 °C and a reduced pressure. The identity of the product was confirmed by chemical and X-ray diffraction analysis; no other carbide was found to be present. The powder X-ray diffraction patterns were investigated in terms of the structure assignment either to the hexagonal P63mc or the orthorhombic Pnma symmetry. The reflection intensities fit better the latter structure, but the possibility of hexagonal indexing indicates that the octahedral structural elements do not arrange coherently during the synthesis. The composition of the products of hydrolysis is also consistent with the formula Mn7C3. The gaseous products contain hydrogen, methane, and a number of other hydrocarbons, mostly saturated, whose concentration decreases with increasing number of carbon atoms in the molecule. The concentration distribution of the hydrocarbons is discussed in terms of the radical mechanism of the hydrolysis; the data are borne out indicating that in Mn7C3 the covalent nature of the bonds is more pronounced than in salt type carbides.

Evaluation of Freezing Methods by Low Temperature X-Ray Diffraction

1977 ◽  
Vol 35 ◽  
pp. 330-333
Author(s):  
T. Gulik-Krzywicki ◽  
M.J. Costello
Keyword(s):  
Biological Materials ◽  
Molecular Organization ◽  
X Ray Diffraction ◽  
Glass Capillary ◽  
X Ray ◽  
Rate Dependent ◽  
Before And After ◽  
Freeze Etching ◽  
Diffraction Patterns ◽  
Set Up

Freeze-etching electron microscopy is currently one of the best methods for studying molecular organization of biological materials. Its application, however, is still limited by our imprecise knowledge about the perturbations of the original organization which may occur during quenching and fracturing of the samples and during the replication of fractured surfaces. Although it is well known that the preservation of the molecular organization of biological materials is critically dependent on the rate of freezing of the samples, little information is presently available concerning the nature and the extent of freezing-rate dependent perturbations of the original organizations. In order to obtain this information, we have developed a method based on the comparison of x-ray diffraction patterns of samples before and after freezing, prior to fracturing and replication.Our experimental set-up is shown in Fig. 1. The sample to be quenched is placed on its holder which is then mounted on a small metal holder (O) fixed on a glass capillary (p), whose position is controlled by a micromanipulator.

Examination of Rabbit Fc Crystals

1968 ◽  
Vol 26 ◽  
pp. 140-141
Author(s):  
J. P. Robinson ◽  
P. G. Lenhert
Keyword(s):  
Molecular Weight ◽  
Flat Plate ◽  
Phosphate Buffer ◽  
Asymmetric Unit ◽  
X Ray Diffraction ◽  
X Ray ◽  
Neutral Ph ◽  
Small Crystals ◽  
Carbon Coated ◽  
Diffraction Patterns

Crystallographic studies of rabbit Fc using X-ray diffraction patterns were recently reported. The unit cell constants were reported to be a = 69. 2 A°, b = 73. 1 A°, c = 60. 6 A°, B = 104° 30', space group P21, monoclinic, volume of asymmetric unit V = 148, 000 A°3. The molecular weight of the fragment was determined to be 55, 000 ± 2000 which is in agreement with earlier determinations by other methods.Fc crystals were formed in water or dilute phosphate buffer at neutral pH. The resulting crystal was a flat plate as previously described. Preparations of small crystals were negatively stained by mixing the suspension with equal volumes of 2% silicotungstate at neutral pH. A drop of the mixture was placed on a carbon coated grid and allowed to stand for a few minutes. The excess liquid was removed and the grid was immediately put in the microscope.

Control of the phase composition of advanced calcium phosphates using an x-ray diffractometer with a curved position-sensitive detector

2020 ◽  
Vol 86 (6) ◽  
pp. 29-35
Author(s):  
V. P. Sirotinkin ◽  
O. V. Baranov ◽  
A. Yu. Fedotov ◽  
S. M. Barinov
Keyword(s):  
Phase Composition ◽  
Calcium Phosphates ◽  
Position Sensitive Detector ◽  
Sensitive Detector ◽  
X Ray Diffraction ◽  
X Ray ◽  
Impurity Phases ◽  
Position Sensitive ◽  
Diffraction Peaks ◽  
Diffraction Patterns

The results of studying the phase composition of advanced calcium phosphates Ca10(PO4)6(OH)2, β-Ca3(PO4)2, α-Ca3(PO4)2, CaHPO4 · 2H2O, Ca8(HPO4)2(PO4)4 · 5H2O using an x-ray diffractometer with a curved position-sensitive detector are presented. Optimal experimental conditions (angular positions of the x-ray tube and detector, size of the slits, exposure time) were determined with allowance for possible formation of the impurity phases during synthesis. The construction features of diffractometers with a position-sensitive detector affecting the profile characteristics of x-ray diffraction peaks are considered. The composition for calibration of the diffractometer (a mixture of sodium acetate and yttrium oxide) was determined. Theoretical x-ray diffraction patterns for corresponding calcium phosphates are constructed on the basis of the literature data. These x-ray diffraction patterns were used to determine the phase composition of the advanced calcium phosphates. The features of advanced calcium phosphates, which should be taken into account during the phase analysis, are indicated. The powder of high-temperature form of tricalcium phosphate strongly adsorbs water from the environment. A strong texture is observed on the x-ray diffraction spectra of dicalcium phosphate dihydrate. A rather specific x-ray diffraction pattern of octacalcium phosphate pentahydrate revealed the only one strong peak at small angles. In all cases, significant deviations are observed for the recorded angular positions and relative intensity of the diffraction peaks. The results of the study of experimentally obtained mixtures of calcium phosphate are presented. It is shown that the graphic comparison of experimental x-ray diffraction spectra and pre-recorded spectra of the reference calcium phosphates and possible impurity phases is the most effective method. In this case, there is no need for calibration. When using this method, the total time for analysis of one sample is no more than 10 min.

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.

scholarly journals Deep learning for visualization and novelty detection in large X-ray diffraction datasets

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Lars Banko ◽  
Phillip M. Maffettone ◽  
Dennis Naujoks ◽  
Daniel Olds ◽  
Alfred Ludwig
Keyword(s):  
Thin Film ◽  
Crystal Structure ◽  
Artificial Intelligence ◽  
Deep Learning ◽  
Novelty Detection ◽  
Structural Similarity ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffraction Patterns ◽  
Post Hoc

AbstractWe apply variational autoencoders (VAE) to X-ray diffraction (XRD) data analysis on both simulated and experimental thin-film data. We show that crystal structure representations learned by a VAE reveal latent information, such as the structural similarity of textured diffraction patterns. While other artificial intelligence (AI) agents are effective at classifying XRD data into known phases, a similarly conditioned VAE is uniquely effective at knowing what it doesn’t know: it can rapidly identify data outside the distribution it was trained on, such as novel phases and mixtures. These capabilities demonstrate that a VAE is a valuable AI agent for aiding materials discovery and understanding XRD measurements both ‘on-the-fly’ and during post hoc analysis.

scholarly journals Simultaneous Multi-Bragg Peak Coherent X-ray Diffraction Imaging

Crystals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 312
Author(s):  
Florian Lauraux ◽  
Stéphane Labat ◽  
Sarah Yehya ◽  
Marie-Ingrid Richard ◽  
Steven J. Leake ◽  
...  
Keyword(s):  
Bragg Reflection ◽  
Volume Ratio ◽  
X Ray Diffraction ◽  
X Ray ◽  
Crystal Substrate ◽  
In Series ◽  
Diffraction Imaging ◽  
Diffraction Patterns ◽  
Lattice Planes ◽  
Oriented Parallel

The simultaneous measurement of two Bragg reflections by Bragg coherent X-ray diffraction is demonstrated on a twinned Au crystal, which was prepared by the solid-state dewetting of a 30 nm thin gold film on a sapphire substrate. The crystal was oriented on a goniometer so that two lattice planes fulfill the Bragg condition at the same time. The Au 111 and Au 200 Bragg peaks were measured simultaneously by scanning the energy of the incident X-ray beam and recording the diffraction patterns with two two-dimensional detectors. While the former Bragg reflection is not sensitive to the twin boundary, which is oriented parallel to the crystal–substrate interface, the latter reflection is only sensitive to one part of the crystal. The volume ratio between the two parts of the twinned crystal is about 1:9, which is also confirmed by Laue microdiffraction of the same crystal. The parallel measurement of multiple Bragg reflections is essential for future in situ and operando studies, which are so far limited to either a single Bragg reflection or several in series, to facilitate the precise monitoring of both the strain field and defects during the application of external stimuli.

scholarly journals Rapid four-component synthesis of dihydropyrano[2,3-c]pyrazoles using nano-eggshell/Ti(IV) as a highly compatible natural based catalyst

BMC Chemistry ◽  
2021 ◽  
Vol 15 (1) ◽  
Author(s):  
Arefeh Dehghani Tafti ◽  
Bi Bi Fatemeh Mirjalili ◽  
Abdolhamid Bamoniri ◽  
Naeimeh Salehi
Keyword(s):  
Thermo Gravimetric Analysis ◽  
Reaction Times ◽  
Diffraction Field ◽  
Gravimetric Analysis ◽  
X Ray Diffraction ◽  
X Ray ◽  
Solvent Free Conditions ◽  
High Yields ◽  
Work Up

AbstractNano-eggshell/Ti(IV) as a novel naturally based catalyst was prepared, characterized and applied for the synthesis of dihydropyrano[2,3-c]pyrazole derivatives. The characterization of nano-eggshell/Ti(IV) was performed using Fourier Transform Infrared spectroscopy, X-ray Diffraction, Field Emission Scanning Electron Microscopy, Energy-Dispersive X-ray Spectroscopy, and Thermo Gravimetric Analysis. Dihydropyrano[2,3-c]pyrazoles were synthesized in the presence of nano-eggshell/Ti(IV) via a four component reaction of aldehydes, ethyl acetoacetate, malononitrile and hydrazine hydrate at room temperature under solvent free conditions. The principal affairs of this procedure are mild condition, short reaction times, easy work-up, high yields, reusability of the catalyst and the absence of toxic organic solvents.

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