Surface and bulk properties of ancient Egyptian mortars,part II: Adsorption and infrared studies

Adsorption studies carried out on Ancient Egyptian mortars suggest that these materials are essentially nonporous with a certain degree of mesoporosity. Analysis of the adsorption data was achieved by means of two reference nonporous materials. Surface activity is observed as a result of heat-treatment. Infrared studies confirm that the samples contain gypsum, calcite and quartz sand with a clearcut predominance of gypsum in the mortars extracted from the Sphinx statue. A correlation is perceived between these results and the X-Ray Diffraction results obtained in Part I of this series.     

PdSiO2: I. In situ X-ray diffraction studies during treatment and hydrogenolysis

Simple techniques for studies of X-ray diffraction from $\text{Pd}\text{SiO}{}_2$ catalysts during catalytic reactions are reported here. The catalytic activity of $\text{Pd}\text{SiO}{}_2$ of low percentage metal exposed for methylcyclopropane hydrogenolysis at 0 °C is less for catalyst cooled from 450 °C in H₂ than for that cooled in He. This effect appears to result from differing amounts of hydride formation. Ease of formation of hydride decreases with decreasing Pd particle size. Exposing the catalysts with D_h = 13.8 and 29.3% to hydrogen at ~25 °C results in nearly complete conversion of particles of Pd to hydride. Purging with helium (even at 0 °C) reconverts the hydride to palladium, but this reconversion exhibits an induction period; hydride formation is more rapid. Passing hydrogen plus methylcyclopropane results in the conversion into hydride of a substantial fraction of catalyst particles originally present as palladium. The palladium hydride particles of catalyst produced by cooling from 450 °C in H₂ remain as PdH_0.7 during the hydrogenolysis reaction. The lattice parameter of palladium particles is indistinguishable from that of bulk palladium, at least for particle diameters ≥45 Å.     

Portland cement clinker: Mineralogical and chemical investigations: Part I Microscopy, X-ray fluorescence and X-ray diffraction

The phase and chemical compositions of 39 differently prepared and burned industrial clinkers from the “Holderbank” Group were investigated by microscopy, X-ray fluorescence, X-ray diffraction and electron microprobe. Based on microscopic analysis the clinkers can be divided into two groups. Examination with a conventional diffractometer showed that the determination of the crystallographic modifications of phases is not always clear. The lattice parameters of the alites are directly related to the amounts of incorporated MgO. A dependence on other impurities could not be detected.     

X-ray diffraction orientation studies on blown polyethylene films. I. Preliminary measurements

X-Ray diffraction pole figure measurements have been made on six films blown from high-density polyethylene. Five were prepared on an experimental unit; the sixth, blown on commercial equipment, had a higher degree of overall orientation thus enabling more extensive results for the a-, b-, and c-axis distributions to be obtained. The results provide information on the orientation present, how it may be related to the stress crystallization process of Keller and Machin, and the dependence of the tear strengths in the machine and transverse directions on the orientation. The typical behavior, with the a and c axes at 90° and both at an angle to the plane of the film, is shown to be the result of a composite process involving several types of stress during the blowing operation and a partial relaxation arising at one or possibly two stages of the process. The predicted relative tear strengths, obtained from the concentration of c axes inclined towards the machine direction, are in line with the experimental values. There is some evidence that transcrystallization in the surface layers of the films may lead to a better balance of the tear strengths in the machine and transverse directions.     

Quantitative X-ray diffraction analysis of ettringite,thaumasite and gypsum in concretes and mortars

A method for quantitative Xray diffraction analysis (QXDA) of three sulphate minerals frequently associated with building materials has been devised. Sulphate minerals which form within concretes, mortars and other cementitious-based materials include ettringite, (3CaO.Al₂O₃.3CaSO₄.31H₂O), thaumasite (CaSiO₃.CaCO₃.CaSO₄.15H₂O) and gypsum (CaSO₄.2H₂O). Calibration standards were prepared using pure samples of these minerals and incorporating boehmite as an internal standard. The equations obtained from the standard calibration curves were used to calculate the percentage of ettringite, thaumasite and gypsum in a) samples which contained known percentages of these minerals mixed together and b) laboratory prepared concrete cubes undergoing sulphate attack. The cubes contained 0%, 20% or 40% pulverized fuel ash (pfa) by weigth of cementitious material and had been stored in various sulphate solutions including sea water for one year.Quantitative Xray diffraction analysis of the standard mixtures successfully detected the expected ettringite, thaumasite and gypsum concentrations. The concrete cube results showed that the sulphate mineral concentration within the surface of the cubes decreased when larger amounts of pfa were used in the concrete mixes. This effect was less noticeable in the sea water cubes.     

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.     

Surface and bulk properties of glycidyl methacrylate modified polypropylene: Experimental and molecular modeling studies

Modifications of polypropylene (PP) are often carried out to either functionalize them or meet specific property demands. This study considered the process of PP grafting with glycidyl methacrylate (GMA) as an intermediate step to achieve improvements in surface properties of this polymer. Abundant literature is available on this grafting process but little is known about the surface properties of the grafted PP. Present work considered both experimental and computational approaches to attain this goal. Experimentally, it was established that the melting temperature of modified PP changed with the addition of GMA, and at higher concentrations of GMA in the PP matrix, heterogeneous nucleation took place. Experimental results revealed a decrease in the surface energy (SE) as well. To discern the underlying reasons behind these changes, molecular dynamics simulations were undertaken. The computational results revealed that the changes in SE could be associated with the location of the functional group. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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.     

DSC and synchrotron-radiation X-ray diffraction studies on crystallization and polymorphic behavior of palm stearin in bulk and oil-in-water emulsion states

The crystallization and polymorphic behavior of palm stearin (PS) in a bulk state and in oil-in-water (O/W) emulsion droplets (average diameter, 1.7±0.3 μm) was observed by using DSC, optical microscopy, and in situ X-ray diffraction with synchrotron radiation (SR-XRD). For the bulk sample the DSC measurements revealed three main exothermic peaks at approximately 31 (large), 21 (small) and 3°C (medium) on cooling, and broad endothermic peaks at approximate −3 (small), 8, 15 to 25 (medium), and 37 and 53°C upon heating. The SR-XRD patterns taken during cooling from 60 to −5°C clarified that the DSC exothermic peaks around 31 and 3°C corresponded to crystallization of the α form of high-melting and low-melting fractions, respectively, and that the occurrence of β′ corresponded to the small exothermic peak around 21°C. The XR-XRD patterns taken during heating from −5 to 60°C demonstrated that the DSC endothermic peaks corresponded to the following transformation processes: melting of α of the low-melting fraction (−3°C), melt-mediated transformation from α to ∇′ (15–25°C), melting of β′ (36°C), and melting of β (53°C) of the high-melting fraction. As for the O/W emulsion sample, the DSC and SR-XRD measurements during the cooling and heating processes exhibited basically the same behavior as that of PS in the bulk state, except that β′ did not crystallize during the cooling process, and the temperatures of crystallization of α, melt-mediated α→β′→β transformation, and melting of β were lower in the emulsion droplets than in the bulk state.     

Mercerization of cellulose. I. X-ray diffraction evidence for intermediate structures

A study of the mercerization of ramie cellulose was begun using x-ray diffraction, in order to determine the types of alkali–cellulose structures that occur as intermediates during the conversion of cellulose I to cellulose II. A total of five unique alkali–celluloses (Na–celluloses) could be generated reproducibly, depending only on the alkali concentration used. The reproducibility was enhanced by slowing down the mercerization process, by laterally compressing the fibers in capillary tubes. The five structures, named Na–celluloses I, IIA, IIB, III, and IV, were of two types based on their crystallographic fiber repeats. The first type was represented by Na–celluloses I, III, and IV, all exhibiting a ca. 10 Å repeat. The second type was represented by Na–celluloses IIA and IIB, with a ca. 15 Å repeat. The latter structures are possibly based on a threefold helical chain conformation, which has not been seen in crystalline celluloses. All Na–cellulose structures exhibited a reasonable degree of crystallinity and high degree of fibrous orientation. They formed a definite interconversion scheme, marked by crystalline-to-crystalline phase transformations.     

Diamond nanoparticles to carbon onions transformation: X-ray diffraction studies

Carbon onions prepared by high temperature annealing of ultradispersed diamond nanoparticles of about 5 nm in average diameter have been studied by X-ray diffraction using synchrotron radiation. The X-ray diffraction patterns show transformation of the diamond nanoparticles with sp³ bonds into spherical carbon onions containing remaining diamond-like core and then into polyhedral onions with facets on their outer part and pure sp² graphitic bonds. The prepared onions form concentric-shell particles which comprise of about ten shells with an intershell distance of 0.35-0.36 nm. The large intershell distance suggests a considerable reduction in intershell interaction when compared to perfect graphite. The X-ray data are related to the previously performed studies by electron energy-loss spectroscopy and electron spin resonance.     

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.     

Surface area and porosity, X-ray diffraction and chemical analyses

Texture, structure and composition of the fresh and the used EUROCAT oxide V₂O₅–WO₃/TiO₂ SCR catalysts have been investigated with aid of nitrogen adsorption/desorption at 77 K, mercury porosimetry, X-ray diffraction and chemical analyses. The BET specific surface area is around 47 and 46 m²/g for the fresh and the used catalyst, respectively. Both samples are essentially mesoporous, with pore diameters centred in the range 10–20 nm according to the data derived from the nitrogen adsorption and around 40 nm according to the mercury porosimetry. The anatase form of TiO₂ and traces of orthorhombic V₂O₅ are the only crystalline phases identified in both materials. According to the chemical analysis there are no significant differences in the contents of the main constituting elements between the fresh and the used catalyst. Selective dissolution with NH₃ aq. reveals that in the used catalyst the amount of vanadium component not susceptible to the treatment increases.     

X-ray diffraction studies in resins: Effect of entanglements and chain structure

X-ray diffraction halo of alkyd, amino, and epoxy resins were recorded. The effective d obtained from them was used to estimate certain physical parameters like cross-sectional area, number of carbon atoms per chain, and stiffness parameters from the empirical curves of Boyer and Miller. Amino resin was found to behave differently than the rest of the resins which have a benzene ring in their backbone. These ideas find a confirmation from the ultrasonic and dielectric measurements performed on these very samples.     

Graft copolymerization of wool using acrylate monomers. IV. X-ray diffraction studies

X-ray diffraction of wool graft-copolymerized with methylacrylate, ethylacrylate, n-butylacrylate and methylmethacrylate monomers was studied taking equatorial scans using an x-ray diffractometer. The prominent reflection arcs of wool remained unaffected by grafting as was evident from the x-ray photographs. The ratio of the two intensity peak heights increased with the percentage graft-on indicating an increase in the degree of order. The average crystallite size also increased with grafting showing a narrower spectrum of order in the case of grafted fibres.     

Thermal conductivity of traditional ceramics. Part I: Influence of bulk density and firing temperature

The thermal conductivity of traditional ceramics is known to be a function of their porosity or bulk density. However, the scatter in the thermal conductivity–bulk density data in certain studies, particularly when data from industrially processed brick are involved, suggests that thermal conductivity depends, apart from porosity, on other characteristics such as phase composition, microstructure, humidity or the presence of soluble salts.A red-firing clay used in brick manufacture has been used in this study with a view to systematising the impact of the different variables that could influence thermal conductivity and mechanical strength. This first paper presents the results obtained when the dry bulk density of the pieces and their firing temperature were modified.It was confirmed that thermal conductivity did not solely depend on the total porosity of the fired pieces, but that pore size distribution and pore interconnectivity need to be considered, which depend on the degree of firing attained, and may also be influenced by the phases present in the pieces, whose content and/or composition could vary with firing temperature.     

The preparation of lead dioxide for X-ray diffraction studies

Lead dioxide is the active constituent of the positive electrode in the lead-acid battery. Both the α- and the β-modifications are present in battery electrodes and X-ray diffraction techniques must be used to differentiate the role of each in the reactions occurring in the lead-acid battery system. Standard samples of the two forms of lead dioxide are necessary for this purpose, and samples prepared by various methods have been studied. Powder patterns of electrodeposited samples of both α- and β-lead dioxide showed preferred orientation effects which could not be removed by grinding. Chemically prepared samples of the two forms were well crystallised and did not produce preferred orientation effects. α-Lead dioxide prepared by the oxidation of yellow lead monoxide (using a fused mixture of sodium chlorate and sodium nitrate) and β-lead dioxide prepared by hydrolysis of lead tetra-acetate were chosen as standard samples for X-ray studies and their diffraction patterns have been recorded. A mechanism of nucleation has been proposed for the formation of α-lead dioxide in alkaline and neutral media, and the β-form in acid media.     

Positron annihilation and X-ray diffraction studies of cellulose and some derivatives

Positron lifetime measurements are reported over a temperature range from 290 to 380K on cellulose and certain of its derivatives. The lifetime spectra were resolved into three components each attributed to a different mode of positron annihilation in the polymer. The longest lifetime component is associated with the decay of ortho-positronium and is a function of the average cavity distribution in the sample. It is observed that significant differences exist in the lifetimes of positrons in cellulose and its derivatives which can be interpreted as evidence for changes in the free volume distribution in these materials. Comparison of positron decay in samples of cellulose acetate prepared at both room temperature and elevated temperature indicate that the phenomena of gelation in this material is accompanied by a reduction of free volume. The correlation of such observations with the dynamic properties of these polymers is discussed.