A comparative study of the X-ray diffraction patterns and thermal transitions of metal soaps

Summary X-ray diffraction patterns at room temperature for soaps of barium, calcium, and lithium were found to be characteristic for different soaps of the same cation. This is true not only for palmitates and stearates but also (with minor variations) for mixed soaps containing up to at least 50% oleate, for pure calcium oleate, and even for lithium 12-hydroxystearate. Soaps of the same cation in mixtures approximating the composition of natural tallow fatty acids appear to form mixed crystals. The succession of phases formed on heating shows strongly the influence of the oleate in the mixture. Calcium resinates appear to crystallize imperfectly but definitely with a “head to head” arrangment of the abietate radicals in contrast to the acids which give evidence of a head to tail arrangement. This research was carried out as part of a project, “Phase Studies of Greases”, supported by the office of Naval Research; Contract Number N6onr-238-TO-2, NRO57057. Contribution from the Depatment of Chemistry, University of Southern California.     

Stress measurement in polymeric materials by X-ray diffraction

Experiments are described which show that stresses in amorphous polymers can be measured by diffracting X-rays at high Bragg angles from a filler consisting of crystalline particle or powders. The method is applicable, when calibrated, to both applied and residual stresses, to stress relaxation studies, to both tensile and compressive stresses, to both interior and surface positions in an object, and to composites of various types as well as to polymers that are substantially homogeneous. In the lower (Hookian) range, strains and stresses in metallic embedded particles increase linearly with applied stresses and strains in the matrix. When applied stresses exceed an apparent yield point, which correlates with the yield strength of the metallic filler, the elastic strains in the particles increase only slightly or even decrease as the matrix strains are increased, and with constant applied strain, the particles reveal changes due to relaxation. Strains in the particles are found to be smaller, and stresses higher, than in the matrix. Tests of graphite-fiber epoxy composites with embedded filings of silver or aluminum alloy show that compressive residual stresses from curing at 350°C and cooling to room temperature are registered in the particles as well as stresses externally applied to the cured composite. Precision of the order of 1000 psi (0.7 kg/mm² or 6.9 M Pa) was obtained with measurements made and evaluated rapidly and simply; with more refined techniques, much higher precision would be possible.     

Structural studies of nanodiamond by high-energy X-ray diffraction

The atomic scale structure of explosive diamond nanoparticles has been studied using high-energy X-ray diffraction. The diffraction data have been converted to the real space representation in the form of the radial distribution function. Spherical and truncated octahedron nanodiamond clusters containing from 729 to 1182 atoms have been computer generated and then relaxed using the molecular dynamics method with the reactive empirical bond order potential for carbon-carbon interaction and the Lennard–Jones potential with parameters for inter-layer interactions. Validity of such constructed models has been verified by comparison of the simulations and the experimental data in both real and reciprocal space. The obtained results show that the structure of the investigated diamond nanoparticles cannot be satisfactorily described in terms of the model based on the perfect diamond lattice. The core-shell model with an average size of 22.5–23.4 Å, consisting of the diamond core and the graphite-like shell, accounts very well for the experimental data.     

X-Ray diffraction study of sodium soaps of monounsaturated and polyunsaturated fatty acids

X-Ray powder diffraction patterns of the sodium soaps of 14 monounsaturated and polyunsaturated fatty acids were obtained at room temperature. The patterns of the soaps of 9,12-trans,trans-octadecadienoic acid, 11,14-cis,cis-eicosadienoic acid 11,14,17-allcis-eicosatrienoic acid and 5 monounsaturated fatty acids were typical of the crystalline lamellar phase. The patterns of the soaps of 9,12-cis,cis-octadecadienoic, allcis-9,12,15-octadecatrienoic, allcis-8,11,14-eicostrienoic, allcis-5,8,11,14-eicosatetraenoic, allcis-5,8,11,14,17-eicosapentaenoic and allcis-4,7,10,13,16,19-docosahexaenoic acids were indicative of the less ordered forms reported for sodium oleate at elevated temperature. The diffraction data from the less ordered soaps are consistent with the melted form of the hydrocarbon chains of the unsaturated acids at room temperature.     

Quantitative mineralogical analysis of hydraulic limes by X-ray diffraction

A combined selective dissolution/quantitative X-ray diffraction (QXRD) approach is proposed for the quantitative mineralogical phase analysis of hydraulic limes. The proposed methodology is validated by the analysis of two model mixtures. Afterwards two commercial hydraulic binders and one self-burned hydraulic quicklime were analysed. Chemical, thermal and microprobe analyses were performed to check the results. It is shown that the proposed selective dissolution/QXRD approach yields reliable quantitative mineralogical information for hydraulic limes in spite of their complex phase composition and the presence of amorphous material.     

Mixed impregnated thiosalt decomposition catalysts characterized by X-ray diffraction

We used the impregnated thiosalt decomposition method (ITD) to prepare catalysts of molybdenum sulfide promoted with cobalt in atomic ratios (r = Co/(Co + Mo)) ranging from 0.0 to 1.0. Measurements obtained by X-ray diffraction (XRD) show the presence of the MoS₂-2H phase in all mixed samples, and segregation of cobalt in two phases: Co₉S₈, forr 0.3, and CoS_1.035, for 0.3 r 0.5.     

Residual stress in particulate epoxy resin by X-ray diffraction

Residual stress in particulate epoxy resin was investigated by X-ray diffraction. Microdeformation of incorporated Al and α-SiO₂ crystal, which was induced by the residual stress, could be detected as a shift of X-ray diffraction peak. The residual stress at the interface between the adherend and the particulate epoxy resin was found to decrease with the increase of volume fraction of filler. It was shown that the difference in the thermal expansion coefficients between the adherend and the particulate epoxy resin is much more effective on residual stress than the increment of Young's modulus owing to the incorporation of filler. When epoxy resin was cured on the Al plate, incorporated particles were subjected to a tensile stress; while cured on polytetrafluoroethylene sheet, particles were subjected to a compressive stress. The incorporation of some inorganic particles is considered effective to reduce the residual stress.     

Radial distribution functions from molten polyethylene by X-ray diffraction

The short range ordering in molten polyethylene has been investigated by radial distribution function (RDF) methods. The intramolecular distances resolved are consistent with the presence of gauche conformations, whilst no long trans sequences are resolved. Broad peaks at ～5, 10 and 15 Å are attributed to intermolecular ordering, which is greater than that observed in glassy amorphous polymers. The results are not inconsistent with the polymer chains adopting a random coil configuration over distances greater than $\text{～20}\text{A}\text{?}$.     

Determination of matrix crystallinity of composites by X-ray diffraction

Determination of the degree of crystallinity of the matrix of polymer matrix composites by wide-angle X-ray diffraction is discussed. An extensive theoretical review is given, and many of the practical difficulties are also discussed. Poly(aryl ether ether ketone)-carbon fiber composites are used as example materials. It is shown that although wide-angle X-ray diffraction is potentially useful for unoriented samples, there are practical and theoretical difficulties in applying the technique to highly oriented materials.     

Microstructural evolution during charcoal carbonization by X-ray diffraction analysis

X-ray diffraction (XRD) of monolithic pieces of carbonized medium-density fiberboard (c-MDF) provided new insights on the microstructural evolution occurring during charcoal carbonization. Classical XRD theory was used to correlate the {002} peak intensity to the amount of carbon in large turbostratic crystallites and to bulk dimensional changes. This new analytical technique could be used to study the microstructural evolution of other monolithic carbon materials (including soft carbons) or of specific processes (including chemical activation). The quasipercolation model, a new ‘percolation-like’ model, was created based on XRD analysis of monolithic c-MDF. As the carbonization temperature (T_carb) increased above 600 °C, the large turbostratic crystallites grew very little, but the graphene sheets grew substantially. Volumetric shrinkage suggested that turbostratic crystallites were drawn closer together as the low-density disordered carbon was converted into high-density graphene sheets. At approximately 900 °C, the large graphene sheets and the large turbostratic crystallites significantly impinged on each other. The increased impingement of conductive phases with increasing carbonization temperature would cause the commonly observed nonmetal-metal transition of hard carbon materials. The quasipercolation model also suggested the source of the nanoporosity that is critical in activated carbons.     

Stress transmission in silica particulate epoxy composite by X-ray diffraction

Stress on particles in silica particulate epoxy composite under constant load was investigated by X-ray diffraction. Microdeformation of the crystal lattice of silica could be detected as a shift of the X-ray diffraction peak induced by the applied stress. When a tensile stress was applied to the particulate composite, incorporated particles were found to be subjected to a stress several times larger than the applied stress. The stress concentration onto particles in particulate composite material, which was considered to result in a mechanical reinforcement of the composite, depends on the volume fraction and size of particles. Quantitative relationships between the stress concentration coefficient, particle diameters and the increment of macroscopic Young's modulus with the incorporation of filler were stated.     

A study of branching in ethylene copolymers by X-ray diffraction

By slow cooling and annealing polyethylene a semiequilibrium crystallisation state is obtained. Under such crystallisation conditions changes in unit cell dimensions and crystallinities, as measured by X-ray diffraction, may be related to the size and number of branch groups in polyethylene copolymers. Thus methyl and ethyl groups may be accommodated within the crystalline lattice whereas butyl groups are not. The method may be used to determine the type and extent of branching in unknown ethylene copolymers.     

Orientation of aqueous stretched cottons as measured by X-ray diffraction

The structural changes produced by aqueous swelling and stretching in cotton is found to be irreversible. This article present the X-ray angle data of six varieties of cotton that belong to Gossypium hirsutum. A marked decrease in X-ray angles was found in all treated samples, thereby indicating better orientation. Improvement in the orientation is associated with ncrease in the stretch. The improvement is high in all tension-dried cottons, showing the impact of the tension drying. Similar improved orientation is found in all varieties, indicating the varietal response of G. hirsutum. © 1996 John Wiley & Sons, Inc.     

Microstructure of carbon blacks determined by X-ray diffraction profile analysis

The microstructure of carbon blacks is investigated by X-ray diffraction peak profile analysis. Strain anisotropy is accounted for by the dislocation model of the mean square strain in terms of average dislocation contrast factors. Crystallite shape anisotropy is modeled by ellipsoids incorporated into the size profile function. Different grades of carbon blacks, N990, N774 and N134, untreated, heat-treated and compressed at 2.5 GPa have been investigated. The microstructure is characterized in terms of crystallite size-distribution, dislocation density and crystallite shape anisotropy. Heat treatment results in increased vertical and lateral sizes of graphitic crystallites. Postproduction pressure treatment has little effect on the average sizes of the crystallites, however, it affects the crystallite size distribution function. The average sizes of the crystallites obtained by X-ray diffraction agree with those estimated from Raman spectra. Applied pressure affects the magnitude of strain within the crystallites.     

X射线粉末衍射法鉴定无标签化学试剂

运用X射线粉末衍射法，再结合红外光谱、形貌观察等方法来对失落标签的结晶化学试剂进行鉴定，从而为其使用或合理的回收打下基础。     

X-ray diffraction studies of some halatopolymers

The crystal structure and degree of crystallinity of a number of melt-spinnable halatopolymers has been investigated. These materials can be characterized by a well defined ‘ionic’ peak at low diffraction angle. In general they have a tetragonal unit cell, although the more perfectly crystalline materials may well belong to a triclinic crystal system. Changes in crystallinity were investigated in terms of method and conditions of preparation, and of thermal treatment. Stannous dicar?ylates had the most widely variable crystallinity.     

X-ray diffraction studies of iodine-doped polyacetylene

The results of an extensive X-ray and synchrotron radiation diffraction study of the structure of cis- and trans-polyacetylene doped with iodine are presented. Studies of rapidly and slowly iodine-doped samples confirmed that undoped regions of (CH)_x remain. The undoped regions of the initially cis-(CH)_x are shown to isomerize to the trans-(CH)_x structure during the doping process. Two new previously unreported X-ray reflections have been recorded for both doped cis- and doped trans-isomers. The data are in agreement with the model of intercalation of iodine between planes of close-packed polyacetylene chains.