Induced crystallization of glass-forming melts : Part 1. Heterogeneous nucleation. Effect of noble metal microcrystals on the crystallization of calcium metaphosphate glasses

The possibilities of initiating crystallization in glass-forming melts are analyzed, using experimental evidence, obtained with several model glass-forming systems. In the present Part 1 of the investigation the process of heterogeneous nucleation, catalyzed by insoluble crystallization cores is studied, using a new theoretieal thermodynamie model. The nucleation activity coefficient, Φ, of the aubstrates is described by the adhesion energy, β, at the interface crystallization core/overgrowing crystal. Lattice disregistry is accounted for as an additional correlation factor, influencing the thermodynamie work of adhesion. The crystallization of calcium metaphosphate glass-forming melts, initiated by noble metal microerystals (Ag, Au, Pd, Pt, Rh, Ru, Ir, Os), is studied by differential thermal analysis, optical and scanning electron microseopy. Ir microerystals show highest nucleation activity promoting intensive bulk crystallization in the Ca(PO3)2 systems investigated. The activity of other crystallization cores decreases in the following sequence: Ru > Rh > Os > Pt > Pd > Au > Ag. The above outlined thermodynamic theory of nucleation activity is used to correlate experimental data and to calculate activity coefficients, Φ, in dependence on the properties of the substrates employed. Under tangential stress, applied by pressure in extrusion experiments, the metal microcrystals in the glass samples are stratified in concentric rings with particle density increasing towards the sample surface. Thus a new method of formation of pre-oriented glass-ceramic materials is indicated. In Part 2 of the investigation the effect of soluble oxide additives on nucleation and crystallization in glass-forming melts is considered

Hippuric Acid as a Significant Regulator of Supersaturation in Calcium Oxalate Lithiasis: The Physiological Evidence

At present, the clinical significance of existing physicochemical and biological evidence and especially the results we have obtained from our previous in vitro experiments have been analyzed, and we have come to the conclusion that hippuric acid (C6H5CONHCH2COOH) is a very active solvent of Calcium Oxalate (CaOX) in physiological solutions. Two types of experiments have been discussed: clinical laboratory analysis on the urine excretion of hippuric acid (HA) in patients with CaOX lithiasis and detailed measurements of the kinetics of the dissolution of CaOX calculi in artificial urine, containing various concentrations of HA. It turns out that the most probable value of the HA concentration in the control group is approximately ten times higher than the corresponding value in the group of the stone-formers. Our in vitro analytical measurements demonstrate even a possibility to dissolve CaOX stones in human urine, in which increased concentration of HA have been established. A conclusion can be that drowning out HA is a significant regulator of CaOX supersaturation and thus a regulation of CaOX stone formation in human urine. Discussions have arisen to use increased concentration of HA in urine both as a solubilizator of CaOX stones in the urinary tract and on the purpose of a prolonged metaphylactic treatment

The vitreous state: thermodynamics, structure, rheology, and crystallization

This book summarizes the experimental evidence and modern classical and theoretical approaches in understanding the vitreous state, from structural problems, over equilibrium and non-equilibrium thermodynamics, to statistical physics. Glasses, and especially silicate glasses, are only the best known representatives of this particular physical state of matter. Other typical representatives include organic polymer glasses, and many other easily vitrifying organic and inorganic substances, technically important materials, amidst them vitreous water and vitrified aqueous solutions, and also many metallic alloy systems. Some of these systems only form glasses under particular conditions, e.g. through ultra-rapid cooling. This book describes the properties and the formation of both every-day technical glasses and especially of such more exotic forms of vitreous matter. It is a unique source of knowledge and new ideas for materials scientists, engineers and researchers working on condensed matter. The new edition emphasizes latest experimental findings and modern theories, explaining the kinetics of glass formation, the relaxation and stabilization of glasses and their crystallization in terms of new models, derived from the framework of the thermodynamics of irreversible processes. It shows how the properties of common technical glasses, window glass, or the vitreous ice kernel of comets can be used to develop a new understanding of the existence of matter in various, unusual forms. The developed theoretical models can find application even in the description of lasers and in unusual processes in the universe