Preface

Journal of Thermal Analysis and Calorimetry -     

XRD study of the dehydration and rehydration behaviour of Al-pillared smectites differing in source of charge

The swelling properties of Al-pillared clays, obtained from five different smectites, were studied using X-ray diffraction. These clays, the dioctahedral beidellite and montmorillonite and the trioctahedral saponite, hectorite and laponite differ in source of isomorphic substitution and represent a series of decreasing basicity along the siloxane plane. An Al oxyhydroxy cation was inserted between the layers to form the respective pillared clays and these clays were heated incrementally to 600°C. The XRD peaks at each stage of heating were recorded as well as the same samples subsequently wetted. Basal spacings of each clay at each stage of dehydration d rehydration indicated that the swelling of tetrahedrally substituted saponite and beidellite was indeed restricted, compared with the other three clays. This was attributed to greater basicity of the oxygen plane of beidellite and saponite due to tetrahedral substitution of Si by Al, resulting in an increase in the strength of hydrogen bonds between either water or the interlayer polyhydroxy cation and the clay.The data from the XRD analyses helped in addition, to clarify the thermal transformations of the Keggin ion itself. According to the changes in thed-spacings of the pillared clays it was concluded that the Keggin ion lost its structural water at 200°C and dehydroxylated in a range beginning at 350°C. Between 500 to 600°C this polymer cation, which is thought to form the Al₂O₃ oxide, did not rehydrate.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthdayThe authors wish to thank Laporte Industries, Inc., U.K. for the laponite sample.     

Thermo-XRD-analysis of Co-, Ni- and Cu-montmorillonite treated with anionic alizarinate

Co- and Ni-montmorillonites adsorb in aqueous suspensions up to 13 mmol alizarinate per 100 g clay, onto the broken-bonds whereas Cu-clay adsorbs up to 25 mmol dye per 100 g clay into the interlayer space. Unloaded Co-, Ni- and Cu-clays and samples loaded with increasing amounts of alizarinate, were gradually heated in air to 360°C and analyzed by X-ray diffraction. All diffractograms were curve-fitted. Fitted diffractograms of non-heated samples, showed two peak components labeled C and D, at<span lang=EN-US style='font-size:10.0pt;font-family:Symbol;mso-bidi-font-family: Symbol;mso-ansi-language:EN-US'>?1.22 and<span lang=EN-US style='font-size:10.0pt;font-family:Symbol;mso-bidi-font-family: Symbol;mso-ansi-language:EN-US'>?1.32 nm, characterizing tactoids with mono- and non-complete bilayers of water, respectively. After heating at 120°C component D decreased or disappeared and two new components A and B appeared at<span lang=EN-US style='font-size:10.0pt;font-family:Symbol;mso-bidi-font-family:Symbol; mso-ansi-language:EN-US'>?0.99 and<span lang=EN-US style='font-size:10.0pt;font-family:Symbol;mso-bidi-font-family: Symbol;mso-ansi-language:EN-US'>?1.08 nm, representing collapsed tactoids and tactoids with interlamellar oxy-cations, respectively. At 250°C, C and D decreased or disappeared but A and B appeared in all fitted diffractograms. Co- and Ni-clay after heating at 360°C did not show C and D. Components A and B proved that these clays collapsed indicating that initially there was no alizarinate in the interlayers. At 360°C, C and D persisted in the fitted-diffractograms of Cu-clay, representing tactoids with interlamellar charcoal formed from the partial oxidation of adsorbed dye initially located in the interlayers.     

The effect of the exchangeable metallic cation on the colloid properties of laponite treated with acridine orangea spectrophotometric study

The adsorption of the cationic dye acridine orange (AO) by different monoionic laponites leads to changes in the colloid properties of this synthetic mineral in aqueous solutions. The organic cation is adsorbed by the mechanism of cation exchange. Small amounts of adsorbed dye keep the clay in a peptized state with all metallic cations. Greater amounts of AO result in the neutralization of the electric charge of the clay, and its flocculation. In excess AO the charge of the clay platelets becomes positive and the clay is peptized. The colloid properties are studied by absorbance curves in which the absorbance is described as a function of the degree of saturation with constant clay concentrations or with constant dye concentrations. In the absorbance curves three regions can be identified. The transition between the first and second or the second and third regions depend on the exchangeable metallic cation initially present in the clay. The spectrophotometric method is useful in identifying the presence of tactoids and flocculation mechanism, whether it results in card-house or in book-house flocs.     

Computations and application of classical phase space integrals in reactive molecular collisions

Classical treatment of the evaluation of prior distribution functions (PDF) of product state and recoil energy distributions in reactive collisions is presented. It is shown that for any diatomic potential a single one dimensional numerical (or often analytical) integration suffices to determine the relevant PDF. The conservation of total angular momentum leads to an explicit dependence of the resulting distributions on the maximal total angular momentum of the reactants. The evaluation of prior cross section and branching ratios in collision induced dissociation necessitates the estimation of the radius of the interaction zone. A method for the estimation of the interaction radius and the evaluation of the priors is presented.     

Thermo-XRD analysis of the adsorption of Congo-red by montmorillonite saturated with different cations

The adsorption of the organic anionic dye Congo red (CR) by montmorillonite saturated with Na⁺, Cs⁺, Mg²⁺, Cu²⁺, Al³⁺ and Fe³⁺ was investigated by XRD of unwashed and washed samples after equilibration at 40% humidity and after heating at 360 and at 420°C. The clay was treated with different amounts of CR, most of which was adsorbed. Clay samples, untreated with CR, after heating showed collapsed interlayer space. Unwashed and washed samples, which contained CR, before heating were characterized by three peaks or shoulders, labeled A (at 0.96-0.99 nm, collapsed interlayers), B (at 1.24-1.36 nm) and C (at 2.10-2.50 nm). Peak B represents adsorbed monolayers of water and dye anions inside the interlayer spaces. Peak C represents interlayer spaces with different orientations of the adsorbed water and organic matter. Diffractograms of samples with small amounts of dye were similar to those without dye showing peak B whereas diffractograms of most samples with high amounts of dye showed an additional peak C. Heated unwashed and washed samples were also characterized by three peaks or shoulders, labeled A' (at 0.96 nm), B' (at 1.10-1.33 nm) and C' (at 1.61-2.10 nm), representing collapsed interlayers, and interlayers with charcoal composed of monolayers or multilayers of carbon. When the samples were heated from 360 to 420°C some of the charcoal monolayers underwent rearrangement to multilayers. In the case of Cu the charcoal decomposed and oxidized. The present results show that most of the adsorbed dye was located inside the interlayer space.This revised version was published online in November 2005 with corrections to the Cover Date.     

Translational energy disposal in molecular collisions: The transfer of momentum constraint

A Franck—Condon type argument, which requires the least transfer of momenta to the nuclei during a collision is outlined and applied to the analysis of translational energy disposal and its dependence on the initial translational energy. Using the maximal entropy procedure of information theory we are able to proceed directly from the assumed (model) constraint to the product state distribution.     

Phase-locked InGaAsP laser array with diffraction coupling

A phase-locked array of InGaAsP lasers has been fabricated for the first time. The array utilized diffraction coupling between 10 adjacent lasers to achieve phase locking. Threshold current as low as 200 mA is obtained for arrays with 250 m cavity length. Smooth single-lobe far field patterns with beam divergence as narrow as 3° have been achieved.     

Mechanochemical Adsorption of Phenol by Tot Swelling Clay Minerals

The mechanochemical adsorption of phenol by laponite, saponite, montmorillonite, beidellite and vermiculite was studied by IR and X-ray spectroscopy. Mixtures containing phenol and clay in the ratio of 6:10 were manually ground by a mortar and pestle for 1,3,5 and 10 min and the ground mixtures were investigated. Depending on the basicity of the clay mineral and the time of grinding, two different associations between interlay er cations, water and phenol were identified. In these associations phenol can act either as a proton acceptor or donor (Configurations I and II, respectively). The phenol is more acidic than water and in most cases phenol acts as a proton donor. With montmorillonite and beidellite phenol acts as a proton acceptor. In this association the aromatic ring forms π bonds with atoms of the oxygen planes of the tetrahedral sheets which donate electrons to the anti-bonding π orbitals of the phenol.