Zdeněk Weiss

X-ray diffraction phase analysis of crystalline copper corrosion products after treatment in different chloride solutions

The corrosion products Cu2(OH)3Cl, Cu2O, and CuCl2 were identified on the surface of copper plates after their four days treating in three different sodium chloride, sodium/magnesium, and sodium/calcium chloride solutions using X-ray diffraction powder analysis. However, the quantitative proportions of individual corrosion products differ and depend on the type of chloride solution used. Treating of copper plates only in the sodium chloride solution produced the mixture of corrosion products where Cu2O is prevailing over the Cu2(OH)3Cl and CuCl2 was not identified. The sample developed after treating of the cooper surface in the sodium/magnesium chloride solution contains Cu2(OH)3Cl and CuCl2 prevailing over the Cu2O, while the sample developed after treatment of copper in sodium/calcium chloride solution contains Cu2(OH)3Cl prevailing over CuCl2 and Cu2O was not identified.

Polymer/clay nanocomposites based on MMT/ODA intercalates

Natural Na-montmorillonite (MMT) with the formula (Na0.67K0.01Ca0.02)(Al2.90Mg0.59 Fe3+ 0.49Ti0.01)(Si7.92Al0.08)O20(OH)4was intercalated with octadecylamine (C18H39N) (ODA) with varied MMT/ODA ratios. The basal spacings d(00l) of natural and intercalated Na-MMT with ODA were determined by XRD analysis. The set of basal diffractions: d(001) = 56 Å, d(002) = 28 Å, d(003) = 18 Å, d(004) = 14 Å, d(005) = 11 Å for the saturated Na-MMT/ODA intercalate indicates existence of highly ordered periodic structure with the ODA double-layer intercalated in the silicate interlayer spacing. Molecular modeling calculations were applied to the Na-MMT/ODA saturated intercalation system. Stable structure with d-spacing 53 Å has been calculated which is in a good agreement with the experimental data. Such structure gives good conditions for the organosilicate layered structure exfoliation and nanocomposite production. Na-MMT/ODA intercalates were compounded with polypropylene. In accordance with theoretical predictions, XRD analysis applied to compounded structures have proved that a high degree of the organoclay exfoliation was achieved.

Molecular simulations of montmorillonite intercalated with aluminum complex cations. Part I: Intercalation with [Al13O4(OH)(24+x)(H2O)(12−x)]((7−x)+)

AbstractThe structure of montmorillonite intercalated with [Al13O4(OH)24+x(H2O)12−x](7−x)+ cations (Al13(7− x)+ for short), where x = 0,2 an 4, has been studied using the Cerius2 modeling environment. The Crystal Packer module used in the present study takes into account only the nonbonded interactions between the silicate layer and the Keggin cations. Minimization of the total sublimation energy led to the following conclusions: the structure of the interlayer (that is, the orientation of Keggin cations and the basal spacing) depends on the charge of cations (that is, on the degree of hydrolysis, x). The values of basal spacings in the range 19.38–20.27 Å have been obtained, depending on the charge and arrangement of cations in the interlayer. The dominating contribution to the total sublimation energy comes from the electrostatic interactions. Translations of Al13(7−x)+ cations along the 2:1 layers give only small fluctuations of the total sublimation energy and basal spacings. No preference for the position of Al13(7− x)+ cations in the interlayer of montmorillonite was found during translation along the 2:1 layers. This result confirmed the inhomogeneous distribution of cations in the interlayer and turbostratic stacking of layers.

INTERCALATION AND GRAFTING OF VERMICULITE WITH OCTADECYLAMINE USING LOW-TEMPERATURE MELTING

Octadecylamine (ODA) was used to intercalate a fine-grained and a coarse-grained fraction of natural Mg-vermiculite (VER) using a low-temperature melting procedure. Mixtures of Mg-vermiculite fractions and powdered ODA in the molar ratios of 2:1, 1:1, 1:2 and 1:6 were homogenized and heated for 1, 3, 15 and 30 h at 80°C to prepare intercalated samples. X-ray powder diffraction analysis of intercalated samples was combined with molecular modeling to investigate their interlayer structure. Significant amounts of non-intercalated vermiculite and diffuse peaks with very low intensity and basal spacings close to 29 Å were identified when the lowest concentration (molar ratio VER:ODA = 2:1) was used. According to molecular modeling, this indicates the initial stage of a one-layer arrangement of distorted ODA molecules in the interlayer. If the concentration of ODA molecules and treatment time were increased, a two-layer arrangement of ODA molecules with a different ODA chain-disorder and interlayer-space saturation was identified. Interlayer ODA molecules were inclined to the vermiculite basal plane with an inclination angle for two-layer arrangements that ranged from 76 to 95°. Experimental basal spacings with these two-layer arrangements varied from 52 to 58 Å and were in agreement with molecular modeling results. A fully-saturated 58 Å two-layer ODA arrangement was identified when higher ODA concentrations (VER:ODA = 1:2 and 1:6) and 15 and 30 h treatment times were used. There was no significant difference between ODA-intercalated samples prepared using fine-grained and coarse-grained Mg-vermiculite fractions. A grafted ODA-chain nano-layer with a 49.6(2.1) Å average height was observed on the surface of thin ODA-intercalated micro-flakes using atomic force microscopy. Grafted ODA chains not only created an homogeneous surface nano-layer, but also variable-width channels between the ODA molecules.

Molecular simulations of montmorillonite intercalated with aluminum complex cations; Part II, Intercalation with Al(OH) 3 -fragment polymers

The Crystal Packer module in the Cerius2 modeling environment has been used to study the structure of montmorillonite intercalated with Al(OH)3-fragment (gibbsite-like) polymers. Basal spacings in gibbsite-like polymers arranged in 2 layers in the interlayer of montmorillonite varied in the range 19.54–20.13 Å, depending on the type and arrangement of Al(OH)3 fragments. The inhomogeneous distribution of intercalating species in the interlayer and, consequently, the turbostratic stacking of layers has been found for gibbsite-like polymers as well as in the case of Keggin cations (Čapková et al. 1998). The dominating contribution to the total sublimation energy comes from electrostatic interactions for both intercalating species, gibbsite-like polymers and Keggin cations.

Calculation of element distributions between inorganic and organic parts of coal

A procedure for calculation of the quantitative element distribution between inorganic and organic parts of coal is proposed. Individual coal fractions with different contents of inorganic matter are prepared from the original coal sample and the following input data are determined for each coal fraction: (1) weight of the fraction; (2) concentration of elements for the distribution to be calculated; (3) sum of crystalline phases and the ash content. Furthermore, during the procedure the following assumptions were used: (a) non-crystalline phases in coal are neglected; (b) concentrations of elements bonded to the organic part of coal are constant and independent of the content of crystalline phases in individual coal fractions; (c) the relation between the mass of the inorganic part of coal fractions and the concentration of elements bonded on the inorganic part can be approximated by a quadratic function. Using two samples of different coals the procedure was applied for calculation of the distribution of Pb, Ge and As between inorganic and organic parts of coal.

Montmorillonite Co-intercalated with Octadecylamine and Stearic Acid by Low Temperature Melting and its Influence on PP Nanocomposites

Abstract Organically modified Na-montmorillonite (MMT) samples were prepared by co-intercalation of octadecylamine (ODA) and stearic acid (STA) using a low-temperature melting procedure A blend of MMT and ODA (with the ratio 1: 0.5) was stirred for one minute at 80°C in a laboratory mixer and then different amount of STA (weight ratios of MMT + ODA: STA = 1 : 0.3 and 1 : 1) were added and stirred for another five minutes. The resulting mixture was annealed at the same temperature for one hour. X-ray diffraction (XRD) powder patterns of two co-intercalated samples contain a non-regular set of d spacings of basal diffractions. The first basal diffraction with d = 4.8 nm probably gives evidence for prevalent bilayer molecular arrangement in the interlayer and the non-regular set of d spacings of basal diffractions indicates possible mixed-layer interstratification and/or disorder in the bilayer arrangement of the interlayer space. The set of basal diffractions in the XRD patterns of co-intercalated samples significantly differs from the set of basal diffractions in the patterns of the samples intercalated by only ODA or STA. XRD patterns of Na-montmorillonite sample intercalated with ODA (in the ratio of MMT: ODA = 1:0.5) and with STA (in the ratio of MMT: STA = 1: 1) contain broadening peaks. Polypropylene (PP) nanocomposite samples were prepared by mixing MMT modified in the described mode into the PP matrix. To improve the PP affinity to intercalated MMT, maleic anhydride modified PP as a compatibilizer was used. The level of PP nanocomposites exfoliation was evaluated by XRD technique. The influence of the nanofiller on mechanical properties was measured by tensile tests, and an improvement of mechanical properties was noticed.

Structure Analysis of Intercalated Clays Using Combination of Molecular Simulations, Powder Diffraction and IR Spectroscopy

Combination of molecular simulations with x-ray powder diffraction and TR spectroscopy has been used to study the structure of montmorillonites, intercalated with aluminium complex cations. Two different intercalating species have been investigated: (1) Keggin cation - ideal and hydrolysed and (2) gibbsite-like polymers, arranged in two layers in the interlayer of montmorillonites. The results of molecular simulations showed, that for Keggin cations, the crystal packing depends on the degree of hydrolysis, exhibiting the basal spacings within the range 19.38 - 20.27 (10(-10)m). I, case of gibbite-like polymers, arranged in two layers in the interlayer, basal spacings within the range 19.58 - 20.06 (10(-10)m) have been found, in dependence on the mutual position of Al-OH polymers. Results of molecular simulations showed, that no two-dimensional ordering of complex cations and no reggular stacking of layers can occure in the interlayer of montmorillonites. All the conclusions of modelling were in agreement with the results of XRD analysis.