X-ray diffraction analysis of ultradisperse systems: The Debye formula

Problems of X-ray diffraction analysis of ultradisperse systems with the particle size up to 5 nm are discussed in the review. A method for calculating X-ray diffraction patterns using the Debye formula within the kinematic theory of X-ray scattering (Debye Function Analysis-DFA) is presented. The DFA method makes it possible to obtain information on the atomic structure, shape and size of nanoparticles, and verify hypotheses on the presence of deformations, stacking faults and other structural features of ultradisperse and nanostructured systems. The method is applicable for modeling the diffraction patterns of objects with an arbitrary (not necessarily crystal) structure. Applications of the method for examining the structure of various objects are discussed.     

Thermal analysis and X-ray diffraction of synthesis of powellite

Powellite (calcium molybdate) is an essential industrial product used as additive material to steel and for smelting of ferromolybdenum. Powellite often occurs as a secondary mineral and as pseudomorph after molybdenite in the oxidation zone of molybdenite deposits. The present work reports a thermal analysis study of synthesis of powellite by sintering of molybdite (molybdenium oxide) with calcite or calcium oxide using a derivatograph. The reaction products were identified microscopically and by using a Siemens Crystalloflex diffractometer. The DTA curve of sintering of molybdite with calcite shows the beginning of the reaction at 480°C with the formation of powellite. The intensive formation of powellite is represented by the medium and wide endothermic peak at 630°C. This is followed by a small endothermic peak at 790°C, representing the melting of unreacted molybdite. This is followed directly by large and sharp endothermic peak at 880°C, representing the dissociation of unreacted calcite. The wide and large endothermic peak at 1155°C represents the boiling of unreacted molybdite with appreciable vaporization. The DTA curve of sintering of molybdite with calcium oxide shows a medium and wide endothermic peak at 525°C representing the intensive formation of powellite and also the dehydration of calcium oxide. The small endothermic peak at 730°C represents the loss of carbon dioxide due to some carbonatization of calcium oxide with carbon dioxide from air. The medium endothermic at 790°C represents the melting of unreacted molybdite. The produced powellite is yellow in thin sections, has indistinct cleavage, crystallizes in the tetragonal system in the form of tabular crystals and is optically positive. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structure of organoclays--an X-ray diffraction and thermogravimetric analysis study

X-ray diffraction has been used to study the changes in the surface properties of a montmorillonitic clay through the changes in the basal spacings of montmorillonite (SWy-2) and surfactant-intercalated organoclays. Variation in the d-spacing was found to be a step function of the surfactant concentration. High-resolution thermogravimetric analysis (HRTG) shows that the thermal decomposition of SWy-2-MMTs modified with the surfactant octadecyltrimethylammonium bromide takes place in four steps. A mass-loss step is observed at room temperature and is attributed to dehydration of adsorption water. A second mass-loss step is observed over the temperature range 87.9 to 135.5 degrees C and is also attributed to dehydration of water hydrating metal cations such as Na+. The third mass loss occurs from 178.9 to 384.5 degrees C and is assigned to a loss of surfactant. The fourth mass-loss step is ascribed to the loss of OH units through dehydroxylation over the temperature range 556.0 to 636.4 degrees C. A model is proposed in which, up to 0.4 CEC, a surfactant monolayer is formed between the montmorillonitic clay layers; up to 0.8 CEC, a lateral-bilayer arrangement is formed; and above 1.5 CEC, a pseudotrimolecular layer is formed, with excess surfactant adsorbed on the clay surface.     

Chemical transformations of lanthanide nitrate complexes: Synthesis and X-ray diffraction analysis

The complexes [Dy(NO₃)₃(Bipy)₂], (HBipy)[Gd(NO₃)₄(Bipy)], and [Fe^III(Me₂Bipy)₃][La(NO₃)₅(H₂O)]NO₃ and the precursor of the latter, [Fe^IIPc₂(Me₂Bipy)](CHCl₃) · 1.5H₂O (where Bipy is the 2,2′-bipyridyl, Me₂Bipy is the 4,4′-dimethyl-2,2′-bipyridyl, and Pc^? is the pyridine-2-carboxylate anion), were obtained and characterized by X-ray diffraction analysis. Depending on the conditions of the synthesis and the reagents, the number of coordinated nitrate groups in the lanthanide complex increases from three to five: [Dy(NO₃)₃(Bipy)₂], [Gd(NO₃)₄(Bipy)]^?, and [La(NO₃)₅(H₂O)]^2?.     

X-ray diffraction analysis of the fine structure of carbon fiber

X-ray diffraction analysis showed that the material of carbon fibers prepared from polyacrylonitrile is heterogeneous. Its component composition is determined by the fiber preparation conditions and depends on the angle at which the coherent scattering domains are oriented relative to the thread axis. The size of coherent scattering domains increases in going to components corresponding to lower d₀₀₂ values and depends on the orientation angle φ relative to the thread axis.     

The structure of benzoyldimedone from X-ray diffraction analysis

The structure of benzoyldimedone was established by X-ray diffraction analysis. The only tautomer was found. In this tautomer, the enol proton is covalently bound to the oxygen atom that is remote from the phenyl group. The role of steric and electronic factors in stabilization of the enol structure is analyzed. The geometric characteristics of the ring formed through an intramolecular hydrogen bond are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1074–1076, June, 2000.     

Preparative scale mass spectrometry: A brief history of the calutron

Calutrons were developed in the laboratory of E. O. Lawrence at the University of California at Berkeley. They were a modification of the cyclotrons he had invented and used in his Noble Prize winning investigations of the atomic nucleus. At the time their construction was undertaken, calutrons represented the only certain means of preparing enriched uranium isotopes for the construction of a fission bomb. The effort was successful enough that every atom of the 42 kg of ²³⁵U used in the first uranium bomb had passed through at least one stage of calutron separation. At peak production, the first stage separators, α tanks, yielded an aggregate 258-g/d ²³⁵U enriched to about 10 at. % from its natural abundance level of 0. 72 at. %. The second stage separators, β tanks, used the 10 at. % material as feedstock and produced a total 204-g/d ²³⁵U enriched to at least 80 at. %. The latter, weapons grade, material was used in fission bombs. Under typical operating conditions, each α tank operated at a uranium beam intensity at the collectors of approximately 20 mA and each β tank at a beam intensity of approximately 215 mA at the collectors. Bulk separation of isotopes for bomb production ceased in 1945. Since that time calutrons have been used to separate stable isotopes, but on a more limited scale than wartime weapons production. Stable isotope separations since 1960 have taken place using one modified beta tank.     

Preparative scale mass spectrometry: A brief history of the calutron

Calutrons were developed in the laboratory of E. O. Lawrence at the University of California at Berkeley. They were a modification of the cyclotrons he had invented and used in his Nobel Prize‐winning investigations of the atomic nucleus. At the time their construction was undertaken, calutrons represented the only certain means of preparing enriched uranium isotopes for the construction of a fission bomb. The effort was successful enough that every atom of the 42 kg of ²³⁵U used in the first uranium bomb had passed through at least one stage of calutron separation. At peak production, the first stage separators, α tanks, yielded an aggregate 258‐g/day ²³⁵U enriched to about 10 at. % from its natural abundance level of 0.72 at. %. The second stage separators, β tanks, used the 10 at. % material as feedstock and produced a total 204‐g/day ²³⁵U enriched to at least 80 at. %. The latter, weapons grade, material was used in fission bombs. Under typical operating conditions, each α tank operated at a uranium beam intensity at the collectors of approximately 20 mA and each β tank at a beam intensity of approximately 215 mA at the collectors. Bulk separation of isotopes for bomb production ceased in 1945. Since that time calutrons have been used to separate stable isotopes, but on a more limited scale than wartime weapons production. Stable isotope separations since 1960 have taken place using one modified β tank.     

Hetero-arylboroxines: the first rational synthesis, X-ray crystallographic and computational analysis

A novel series of hetero-arylboroxines were synthesized and structurally characterized by X-ray diffraction, NMR and computational analysis. The solid-state structures of the hetero-arylboroxines represent the first report of AB(2)-type hetero-arylboroxines.     

Thermal analysis and high-temperature X-ray diffraction study of BiNbO4

Journal of Thermal Analysis and Calorimetry - Phase transformations of bismuth orthoniobate BiNbO4 were studied by the methods of differential scanning calorimetry and high-temperature X-ray...     

Thermal analysis and high-temperature X-ray diffraction of nano-tricalcium phosphate crystallization

Calcium phosphate biomaterials have long ago attracted the interest of world-wide scientists because they form the main inorganic constituent of the human bones and teeth. Classical approaches to synthesize this ceramic material did not give satisfactory results until present, so new approaches are required. In this article the tricalcium phosphate achievement by a method which is a combination of sol–gel and classic precipitation from solution is presented, starting from CaCl₂ as calcium precursor and H₃PO₄ as phosphorus precursor, without pH adjustment. The reaction mixture was allowed to maturate for 2 months, the time influence on the precipitated material being presented in previous articles. Present studies aimed at the influence of temperature on the structural characteristics of precipitated and maturated material, by means of thermal analysis, X-ray diffraction, infrared spectroscopy, and high-temperature X-ray diffraction. A complex type thermal decomposition takes place while heating the sample to 1000 °C, with superposed and parallel processes. The sample goes through alternative amorphous and crystalline stages before final crystallization of β-tricalcium phosphate takes place. The high-temperature XRD studies offered the great advantage of being both a synthesis and a physico-chemical characterization technique, which along with thermal analysis and infrared spectroscopy, gave a lot of useful information in a very short time.     

NMR assignments and single-crystal X-ray diffraction analysis of deoxyloganic acid

7-Deoxyloganic acid (1), citrusin C (2), 3,4-dihydroxyl benzoic acid (3) and (E)-caffeic acid (4) were isolated from the water-soluble fraction of ethanol extracts of Morina nepalensis var. alba Hand.-Mazz. and their structures were determined on the basis of spectroscopic evidence. The total assignments of 1H and 13C NMR spectra of 1 in solvents CD3OD, D2O and CDCl3 were reported, in addition to the single-crystal X-ray diffraction analysis of its tetraacetate 1a. All compounds were obtained from Morina genus for the first time.     

High-throughput powder X-ray diffraction, IR-spectroscopy and ion chromatography analysis of urinary stones: A comparative study

The instrumental qualitative analysis of urinary stones is a critical step in clinical practice and urological research. A powder X-ray diffraction, IR-spectroscopy and ion chromatography have been applied for the qualitative analysis of 20 urinary stones. Suggestions for a sample preparation and an optimal measurement strategy were formulated. The main difficulties for the powder X-ray diffraction qualitative analysis are a limiting amount of the sample and a preferential orientation of crystals, both issues should be minimized by the special sample preparation. Urinary stones samples have been clustered into four groups using different sets of numerical input data (cation and anion content, phase composition). At the same time a high-throughput multivariate clustering has been applied for powder X-ray diffraction and IR-spectroscopy data. The multivariate whole-profile approach can be used as a tool for a high-throughput time reducing technique for clinical practice, when a quick and stable classification of samples is required. All three sets of the data can be automatically separated into three clusters: oxalate-reach, oxalate-pure and non-oxalate samples. Uricite-pure and uricite-rich samples can be easily clustered.      

Thermal analysis of ammonium nitrate by energy-dispersive X-ray diffraction

Ammonium nitrate was heated and cooled in consecutive steps in a high temperature device mounted on a X-ray goniometer. Diffraction patterns were measured at each temperature, using a Si-Li detector together with a multichannel analyzer. The results strongly support the existence of a phase II'. They show that the phase change IV/III goes via a transition state similar to or consistent with phase II'.

---

Zusammenfassung Ammoniumnitrat wurde in einer Hochtemperaturkammer auf einem Röntgengoniometer schrittweise aufgeheizt und abgekühlt. Bei jeder Temperatur wurde ein Beugungsdiagramm aufgenommen mit einem Si-Li-Detektor und angeschlossenem Vielkanalanalysator. Die Ergebnisse unterstützen die Annahme einer Phase II'. Sie zeigen, daß die Phasenumwandlung IV/III über einen Übergangszustand verläuft ähnlich oder identisch mit der Phase II'.

---

Résumé Le nitrate d'ammonium était chauffé et refroidi pas à pas dans un four fixé sur un goniomètre de rayons X. A chaque température, des diagrammes de diffraction étaient mesurés par un détecteur semiconducteur, combiné avec un sélecteur multicanaux. Les résultats supportent l'existence d'une phase IF. Ils montrent, que la transition des modifications IV/III procède par une phase de transition, qui ressemble à la phase II'.

---

, . , Si-Li . II. , IV/III , II.

     

X-ray diffraction structure analysis of MCM-48 mesoporous silica

The structure of MCM-48 mesoporous silicate materials has been fully characterized from X-ray diffraction data by applying recently developed methods of mesostructure analysis and full-profile refinement. The pore wall thickness of both as-made and calcined MCM-48 was determined with high precision to be 8.0(1) Angstrom. No regular variations of the wall thickness were detected, but its density was found to be ca. 10% higher in the low-curvature regions. The surfactant density in the pores was assessed around 0.6-0.7 g/cm(3) and was found to have a distinct minimum in the pore center similar to that detected previously in MCM-41. A new extended model function of the density distribution in MCM-48 is proposed on the basis of the structural features that were revealed.     

Phase composition of ceramic-based alkali-activated polymers: combination of X-ray diffraction and thermal analysis

Journal of Thermal Analysis and Calorimetry - Thermal properties and fire propagation performance were studied for the new and aged electrical wires. Two fine electrical wires were tested using the...