An Electroacoustic Investigation of Concentrated Aqueous Suspensions of Calcium Pyrophosphate

The zeta potential of concentrated suspensions of calcium pyrophosphate were investigated using electroacoustics. The particles were negatively charged over the entire pH range studied. It proved impossible to reduce the pH of the suspension below 1.8, but the iso electric point could be estimated to occur at approximately pH 1. Two commercially available dispersants (one cationic and one anionic) were then added in small increments to the suspension in order to follow the change in zeta potential as the dispersants adsorbed onto the particles. From the shape of the curve it was possible to estimate the optimum adsorbed amount of dispersant required to fully coat the particles. The cationic dispersant adsorbed strongly and the optimum dosage was estimated at 2.5 ml of active polymer/kg of powder. Anionic dispersants are known to adsorb onto negatively charged ceramic oxide particles, but the anionic dispersant used in this study did not adsorb onto the negatively charged calcium pyrophosphate particles.     

A comparative study of the silent discharge treatment of saturated and unsaturated hydrocarbon polymers

Dielectric barrier air discharge treatment of polyethylene, polypropylene, polyisobutylene, polystyrene, and polyisoprene substrates has been characterized by x-ray photoelectron spectroscopy (XPS). The relative reactivities of these polymers towards silent discharge oxidation are rationalized in terms of ozone molecules interacting with an excited surface. © 1994 John Wiley & Sons, Inc.     

The 99Ru Mössbauer spectrum of β-RuCl3

The ⁹⁹Ru nuclear quadrupole interaction in β-RuCl₃ can be related to the large trigonal distortion at the ruthenium site. The ratio of the quadrupole moments has been determined to be Q_e/Q_g = +3.06 ± 0.10, and it is confirmed that Q_c and Q_g are both positive.     

The preparation,phase relationships,and Eu-151 Mössbauer spectroscopy of europium tungsten bronzes and related phases

Crystal chemistry and phase relations for the bronze-forming region of the EuWO system have been investigated. A bronze Eu_xWO₃ is stable up to 1000°C when x ? 0.125 and in the region 0.085 ? x ? 0.125 the symmetry is cubic. A tetragonal bronze exists at x = 0.05, and an orthorhombic bronze with a structure closely related to the orthorhombic form of WO₃ exists below x = 0.01. Mössbauer spectra at room temperature and at 80 K indicate that in all these phases the europium is highly ionized as Eu(III) with no electron localization to give (EuII) even at low values for x. The decomposition products of the bronzes have been established, and the Mössbauer parameters for the highly nonstoichiometric tungstates Eu_xWO₄ were determined. Both Eu(II) and Eu(III) resonances were obtained, and a cation vacancy model for Eu_xWO₄ was found to fit the data best. In conformity with the foregoing data, a sample of composition “Eu₂W₂O₇” was found not be be a pyrochlore but to comprise a mixture of Eu₆WO₁₂, Eu_xWO₄, and W. The phase relationships for the europium bronze system Eu_xWO₃ are compared with those of other ionic bronzes Na_xWO₃, Li_xWO₃, and Al_xWO₃.     

Hydrogen bonding in vitamin B6

Double-well potential energy surfaces for hydrogen bonding in crystalline vitamin B₆ have been associated with molecular environmental effects. New calculations, involving improved representations of a fragmentation model, include the introduction of a second pyridoxinium chloride system within the model in a “dimer-like” configuration. The new results confirm the double-well potential and the prediction of the experimentally observed position for the proton as being due essentially to environmental effects. Atomic difference maps are presented for the charge density distributions, which reflect the nature of the bonding as it depends on the proton position. Mulliken populations are examined particularly in relation to the “intermolecular” transfer of electrons.     

On the joint distribution of ladder variables of random walk

Summary The ladder timeN and ladder heightH of a random walk {S _n ,n1} as a pair (N, H) lie in the domain of attraction of a bivariate stable law ifS ₁ is in a domain of attraction, as was shown by Greenwood et al. (1982). In this paper we prove a converse. IfP(S _n >0) converges and (N, H) lies in a bivariate domain of attraction thenS ₁ is also in a domain of attraction.     

Organoruthenaborane Chemistry. X. The SM2-catalysed formation of [ l-(η6-C6Me6)-isocloso-RuB9H9], and some B-phenylamino derivatives. NMR and X-ray diffraction studies

The action of SMe₂ on the ten-vertex nido-ruthenaborane [6-(η⁶-C₆Me₆)RuB₉H_l3] ( 1 ) provides a high-yield route to the unsubstituted isocloso-ruthenaborane [1-(η⁶-C₆Me₆)RuB₉H₉] (2). The benzene analogue [1-(η⁶-C₆Me₆)RuB₉H₉] is prepared similarly. By contrast, reaction of (1) with PhNH₂ gives a variety of B-phenylamino isocloso derivatives, including orange crystals of [1-(η⁶-C₆Me₆)-2-(PhNH)-isocloso-1-RuB 9 H₈] ( 3 ), red-orange [1-(η⁶-C₆Me₆)-2,3-(PhNH)₂-isocloso-1-RuB₉H₇] ( 4 ) and dark-red [1-(η⁶-C₆Me₆)-5,6,7-(PhNH)₃-isocloso-1-RuB₉H₆] ( 5 ). Detailed ¹H and ¹¹B nmr properties of these various compounds are described. The structure of ( 3 ) has been established by a single-crystal X-ray diffraction study of the solvate [1-(η⁶-C₆Me₆)-2-(PhNH)-isocloso-1-RuB₉H₈] · 1/2 CH₂Cl₂; the crystals were monoclinic, space group C2/c, with a = 1895.1(3), b = 1556.6(3), c = 1716.4(3) pm, β = 104.37(1)° and z = 8.