Showing papers on "Chemical binding published in 1995"

Mössbauer spectra of tin in float glass

Abstract: Tin is not a major constituent of window glass, but is found at high concentrations in the lower surface of float glass which has been in contact with the molten tin bath. It does not extend far into the surface, but causes the physical and chemical behaviour to differ from that of the upper surface. It is important, therefore, to understand the structural role of tin in silicate glasses and thus its effect on various properties. Mossbauer spectra were taken of three series of glassy materials, namely binary glasses (SnO and SiO2) in varying proportions, re-melted float glass containing tin, and float glass from a production plant. The binary glasses contained between 20 and 70% tin which was found to be mainly Sn2+, with very small amounts of Sn4+ in some of them. The spectra showed a small decrease in isomer shift with increase in tin content, which is ascribed to the change in molar volume. The re-melted samples were float glass which was mixed with stannous oxalate in appropriate conditions to try and maintain tin in the 2+ state, and contained up to 15% tin by weight. The spectra show both Sn4+ and Sn2+ with rather more in the 4+ oxidation state. The change in the spectra as a function of temperature revealed a large difference in thef-factor (and hence the chemical binding) of the two states. A series of spectra was taken between 17.5 and 900 K for the sample containing 15% tin. From the absorption as a function of temperature thef-factor was determined for both oxidation states, and hence enabled the relative amounts of Sn4+ and Sn2+ present in each sample to be estimated. Measurements of the shift as a function of temperature were also made. The float samples were surface material produced by grinding away all but 0.1 mm of the lower surface of industrially produced float glass. The Mossbauer spectra showed them to be predominantly Sn2+, as expected from the reducing atmosphere in the float plant. The concentration and oxidation state of the tin may be estimated from the value of thef-factors and isomer shifts.

New characteristic signatures from time‐dependent static light scattering during polymer depolymerization, with application to proteoglycan subunit degradation

Abstract: Models were developed for the time-dependent light scattering intensity for simply branched (“comb”) polymers undergoing one or more of three distinguishable degradation mechanisms: (a) stripping off the side chains, (b) randomly degrading off the side chains, and (c) randomly degrading the backbone. The model equations were applied to the analysis of different types of degradation of simply branched biopolymers—bovine nasal cartilage proteoglycan subunits (or “monomers”); NaOH stripped off the glycosaminoglycan (GAG) chains from the protein backbone [mechanism (a)], whereas hyaluronidase seemed to randomly cleave the GAG side chains [mechanism (b)], and HCl both stripped the GAG side chains and randomly cleaved the protein backbone [combined mechanisms (a) and (c)]. The reactions were followed with time-dependent multiangle, static light scattering. The time-resolved total scattering technique allowed degradation rate constants and percentage of material in the branched polymer backbone and side chains to be determined, in addition to the mechanisms involved. These new time-dependent light scattering profiles are added to the growing library of functions from which deductions can be made concerning polymer structure and associated degradation mechanisms and kinetics. These conclusions, drawn from time-dependent “batch” light scattering, are substantiated by preliminary size exclusion chromatography results and chemical binding assays for sulfated GAGs. © 1995 John Wiley & Sons, Inc.

Viscous effects in capillary electrophoresis: theory and experiment.

Abstract: Simple theory which relates the viscous effects of additives used in capillary electrophoresis (CE) to resolution and resolution per unit time are developed for small molecule separations in the absence of sieving effects. The resolution theory shows that there is no advantage to using viscous additives for resolution improvement unless either a binding energy difference exists between the solutes and additive, or viscous effects cause a reduction in the vector sum of electrophoretic and electroosmotic velocities when these are of opposite sign. In general, increasing the viscosity is shown to result in a loss of resolution per unit time. Theory demonstrates that in cases where only binding is considered to be present, the maximum resolution increase is found to be at relatively small amounts of additive. In addition, specific regions of the elecctrophoreogram may demonstrate resolution enhancement at a specific concentration while other regions exhibit a resolution decrease, as compared to no additive present. CE separations of the components in a Triton surfactant, conducted using a polyethylene glycol (PEG) additive, demonstrate that improved resolution for some of the peaks exists at a specific PEG concentration. These results are mostly explained through the reduction in electroosmotic flow velocity that takes place through additive adsorption to the capillary wall, although some binding is present.

Negative electron affinity spark plug

Abstract: A spark plug having a positive electrode spark tip which is covered with aery thin layer (≦20 nanometers) of very hard NEA material having very large chemical binding energies such that most elements, including carbon and nitrogen, will not bind to its surface. The NEA material may be sapphire, or may be an n-type impurity-doped semiconductor material such as n-type AlN, cBN, or GaAlN having a bandgap exceeding 5.5 eV.

An empirical neutron scattering kernel for plexiglas

Abstract: An empirical scattering kernel is proposed for thermal neutrons in plexiglas. The kernel is based on the Radkowsky prescription, but takes into account the chemical binding of hydrogen also in the energy transfer by an effective mass. The parameters are fitted to experimental results on the energy dependent total cross section of plexiglas and refined by fitting two parameters to neutron pulse measurements, using the P3L2 approximation. A reasonably good fit has been obtained.

Process for the preparation of mixtures of used plastic containing halogen components for use in refinery plants

Abstract: The residual chlorine contents in thermally degraded mixtures of used plastic containing a halogen component were to be reduced as much as possible. The mixtures of used plastic are comminuted, freed from entrained impurities and pre-degraded at elevated temperature and under shear forces in an extruder, where, at the end of the extrusion process, alkali or alkaline earth metal compounds are added to the mixtures of used plastic after removal of the thermolysis gases, and the resultant mixture is homogenized in a connected static mixer. The chemical binding of the residual halogen after thermal dehalogenation enables the mixtures of used plastic from domestic plastic garbage to be processed without difficulty in refinery plants.