On Aging of Acid-Catalyzed Silica Sols—A Dynamic Light Scattering Study

Dynamic light scattering experiments in acid-catalyzed silica sols are discussed. It is shown that in spite of limited parameter accuracy and limited absolute knowledge of the particle sizes, the scattering data from various experiments are comparable with one another and give information about structural differences. Measurements at various angles indicate changes between non-spherical and nearly spherical particles and allow the estimation of gelling times before gelation.     

On the role of dissociative ionization in the formation of argon dimer ions

The formation of Ar ₂ ⁺ ions has been investigated by means of the threshold photoelectron photoion coincidence (TPEPICO) technique. Two pathways for the formation of Ar ₂ ⁺ ions are important. One is a direct path via excitation of Rydberg states of Ar₂ with consecutive autoionization. The other path is dissociative ionization of larger argon clusters, in this case argon trimers. These two pathways lead to Ar ₂ ⁺ ions with different internal energy. The pathways are easily distinguished in the TPEPICO-TOF spectra by the kinetic energy released (KER) in the dissociative ionization. The KER for the reaction Ar ₃ ⁺ → Ar ₂ ⁺ + Ar was measured as a function of the photon energy and compared to the KER expected from statistical theory. The agreement is satisfying and confirms that Ar ₃ ⁺ ions do indeed dissociate at the thermochemical threshold. At higher photon energy the excited²Π(3/2)g state of Ar ₃ ⁺ is also detected from a second component in the KER. By applying a kinetic energy discrimination it is possible to measure cluster ion spectra in the presence of larger clusters but essentially without interference from the latter.     

Thermodynamics of the Laminar Donnan System

Thermodynamic quantities of a polyelectroyte immersed in salt solution are derived modeling the polyelectrolyte by a sequence of charged parallel flat plates. The starting point for the analysis is the derivation of the Gibbs free enthalpy in its canonic variables pressure (p) and temperature (T), i.e., as a thermodynamic potential. From this, further thermodynamic quantities such as Helmoltz free energy, entropy, internal energy, compressibility, isobar and isochor heat capacities, and expansive force are derived in analytical expressions by differentiation. All these formulas contain the parameter plate surface charge density (sigma) that provides a measure of the discontinuity of the polymer charge distribution that can be used to fit the theory to experimental data. Thermodynamic quantities are also known from the classical Donnan equilibrium that treats the polyelectroyte charge network as a charge continuum. A limiting process is used to perform the transition from the laminar Poisson- Boltzmann model to the continuous Donnan equilibrium. In general, the expressions of the Donnan system are recovered for plate charge density sigma-->0, number of plates Z-->infinity, and sigma Z=constant. Copyright 2000 Academic Press.     

Strength and fatigue of some binary and ternary silicate glasses

A survey represented mainly by means of glasses of the borosilicate system shows the generally valid limits of the applicability of the crack growth model and the essential influence of the corrosion of glasses on fatigue. A close correlation between macroscopic crack growth and fatigue was affirmed for samples with fresh, slightly corroded cracks. If the state of corrosion of the samples is advanced, the influence of region 2 is reduced and the fatigue limit is increased. Processes of corrosion during the measurement influence the fatigue curve prevailingly in the range of great time-to-failure, in particular the slope in region 1. The results indicate the high complexity of the effective chemomechanical processes during the fatigue measurements.     

Modelling thermoplastic material behaviour of dual-phase steels on a microscopic length scale - numerical treatment

On a microscopic length scale dual-phase steels exhibit a polycrystalline microstructure consisting of ferrite and martensite. In this work it is assumed that the martensitic phase behaves purely thermoelastic while for the ferritic phase a thermoplastic material model was developed based on the assumption that the driving mechanism for persistent deformation is the movement of dislocations on preferred planes in preferred directions. The necessary shear stress to move dislocations at a certain temperature and deformation rate is assumed to possess contributions from the atomic lattice, alloying atoms and the dislocation structure. To consider the influence of the dislocation structure, dislocation densities are introduced as state variables for which temperature and deformation rate dependent evolution equations are formulated. Since for general loading histories the model equations cannot be integrated analytically, a time discretized form of the model equations with an appropriate solution algorithm is presented. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Identification and classification of organic and inorganic components of particulate matter via Raman spectroscopy and chemometric approaches

In this paper, a novel method for developing a tree‐like classifier which differentiates between organic and inorganic particulate matter by means of Raman spectroscopy is introduced. The algorithm is fully automatic and optimises itself without any human interaction. This method uses a tree‐like structure to classify Raman spectra as a decision tree. On every knot of this tree, the optimal classifier is automatically obtained, tested and trained. The optimal classifier is an artificial neural network, linear discriminant analysis or a support vector machine, where different kernels are possible. The support vector machine is optimised by the simulated annealing method to achieve the best possible classifier. After the training, a hold‐out experiment with two completely independent sets of Raman spectra was tried to show the abilities of this method for real‐world application. Copyright © 2010 John Wiley & Sons, Ltd.