Viscosity and glass transition in amorphous oxides

An overview is given of amorphous oxide materials viscosity and glass-liquid transition phenomena. The viscosity is a continuous function of temperature, whereas the glass-liquid transition is accompanied by explicit discontinuities in the derivative parameters such as the specific heat or thermal expansion coefficient. A compendium of viscosity models is given including recent data on viscous flow model based on network defects in which thermodynamic parameters of configurons—elementary excitations resulting from broken bonds—are found from viscosity-temperature relationships. Glass-liquid transition phenomena are described including the configuron model of glass transition which shows a reduction of Hausdorff dimension of bonds at glass-liquid transition

Characterisation of corrosion of nuclear metal wastes encapsulated in magnesium silicate hydrate (MSH) cement

A novel low pH magnesium silicate hydrate cement system for encapsulating nuclear industry wastes have been developed using blends of MgO, silica fume (SF), MgCO3 and sand. Aluminium and Magnox swarf were encapsulated in both this new system and in a BFS/PC control system used in the nuclear industry. The interaction of the optimised mortar with the metal strips has been investigated, both in terms of rate of continued corrosion as well as the phases that form by reaction of the binder with different metal strips. Magnox swarf was better bound into the BFS/PC system than MgO/SF system whereas Al 1050 metal strips were bound better into the MgO/SF samples than into the BFS/PC reference mortar. No H2 generation was recorded when aluminium or magnox were encapsulated in the new binder, which is substantially better than what can be achieved with the reference system. Hence, the newly developed binder could potentially encapsulate mixtures of reactive metals better than the existing solution

Long-term field and laboratory leaching tests of cemented radioactive wastes

Experiments with real and simulated radioactive cementitious wasteforms were set up to compare the leaching behaviour of cementitious wasteforms containing nuclear power plant operational waste in field and laboratory test conditions. Experiments revealed that the average annual Cs-137 leach rate in deionised water was about thirty-five times greater compared with the measured average value for the 1st year of the field test. Cumulative leached fraction of Cs-137 for 1st year (3.74%) was close to values reported in literature for similar laboratory experiments in deionised water, however more than two orders of magnitude higher than the 1st year leached fraction of Cs-137 in the repository test (0.01%). Therefore, to compare field and laboratory test results, a scaling factor is required in order to account for surface to volume factor difference, multiplied by a temperature factor and a leach rate decrease coefficient related to the ground water composition. (C) 2011 Elsevier B.V. All rights reserved

Complications of dental whitening treatment

Rezumat. În prezent, datorită sporirii interesului faţă de aspectul estetic al corpului uman, tot mai multe persoane se adresează medicilor stomatologi pentru efectuarea procesului de albire a dinţilor. Faptul în cauză generează o atenţie sporită a stomatologului în prevenirea complicaţiilor sau a erorilor pe parcursul acestei medicaţii estetice.Summary. Nowadays, due to the increase of the interest in the aesthetic aspect of the human body, more and more people are going to the dentists to perform the teeth whitening process. This generates a greater attention of the dentist in preventing complications or errors during this aesthetic procedure

Vitreous Materials for Nuclear Waste Immobilisation and IAEA Support Activities.

Vitreous materials are the overwhelming world-wide choice for the immobilisation of HLW resulting from nuclear fuel reprocessing due to glass tolerance for the chemical elements found in the waste as well as its inherent stability and durability. Vitrification is a mature technology and has been used for high-level nuclear waste immobilization for more than 50 years. Borosilicate glass is the formulation of choice in most applications although other formulations are also used e.g. phosphate glasses are used to immobilize high level wastes in Russia. The excellent durability of vitrified radioactive waste ensures a high degree of environment protection. Waste vitrification gives high waste volume reduction along with simple and cheap disposal facilities. Although vitrification requires a high initial investment and then operational costs, the overall cost of vitrified radioactive waste is usually lower than alternative options when account is taken of transportation and disposal expenses. Glass has proven to be also a suitable matrix for intermediate and low-level radioactive wastes and is currently used to treat legacy waste in USA, and NPP operational waste in Russia and South Korea. This report is also outlining IAEA activities aiming to support utilisation of vitreous materials for nuclear waste immobilisation

Revealing structural changes at glass transition via radial distribution functions.

Transformation of glasses into liquids is discussed in terms of configuron (broken chemical bond or transformation of an atom from one to another atomic shell) percolation theory with structural changes caused. The first sharp diffraction minimum (FSDM) in the pair distribution function (PDF) is shown to contain information on structural changes in amorphous materials at the glass transition temperature (Tg). A method to determine the glass transition temperature is proposed based on allocating Tg to the temperature when a sharp kink in FSDM occurs. The method proposed is more sensitive compared with empirical criterion of Wendt-Abraham; e.g., for amorphous Ni the kink that determines Tg is almost twice sharper. Connection between the kink in fictive temperature behavior of PDF and Wendt-Abraham criterion is discussed

Thermodynamic parameters of bonds in glassy materials from viscosity-temperature relationships

Doremus's model of viscosity assumes that viscous flow in amorphous materials is mediated by broken bonds (configurons). The resulting equation contains four coefficients, which are directly related to the entropies and enthalpies of formation and motion of the configurons. Thus by fitting this viscosity equation to experimental viscosity data these enthalpy and entropy terms can be obtained. The non-linear nature of the equation obtained means that the fitting process is non-trivial. A genetic algorithm based approach has been developed to fit the equation to experimental viscosity data for a number of glassy materials, including SiO2, GeO2, B2O3, anorthite, diopside, xNa2O–(1-x)SiO2, xPbO–(1-x)SiO2, soda-lime-silica glasses, salol, and α-phenyl-o-cresol. Excellent fits of the equation to the viscosity data were obtained over the entire temperature range. The fitting parameters were used to quantitatively determine the enthalpies and entropies of formation and motion of configurons in the analysed systems and the activation energies for flow at high and low temperatures as well as fragility ratios using the Doremus criterion for fragility. A direct anti-correlation between fragility ratio and configuron percolation threshold, which determines the glass transition temperature in the analysed materials, was found

Characterisation of Al corrosion and its impact on the mechanical performance of composite cement wasteforms by the acoustic emission technique

In this study acoustic emission (AE) non-destructive method was used to evaluate the mechanical performance of cementitious wasteforms with encapsulated Al waste. AE waves generated as a result of Al corrosion in small-size blast furnace slag/ordinary Portland cement wasteforms were recorded and analysed. The basic principles of the conventional parameter-based AE approach and signal-based analysis were combined to establish a relationship between recorded AE signals and different interactions between the Al and the encapsulating cement matrix. The AE technique was shown as a potential and valuable tool for a new area of application related to monitoring and inspection of the mechanical stability of cementitious wasteforms with encapsulated metallic wastes such as Al

Complex therapeutic approach of children with diabetes and oral diseases

This material represents a theoretical and analytical approach to the problem of the correlation between type 1 diabetes in minors and diseases of the oral cavity. Following observations made in parallel by doctors specializing in dentistry and those in endocrinology, a clear interdependence between dental conditions and type 1 diabetes was found. This fact also requires an appropriate therapeutic tactic. Parallel actions with bio-psycho-social rehabilitation are of particular importance for minor patients

THE OPPORTUNITY FOR THE REHABILITATION OF MINORS WITH TYPE 1 DIABETES

Type 1 diabetes is a chronic disease that is globally widespread. Those most affected by this disease are minors: infants, children, teenagers, and young people up to the age of 18. To reduce some destructive consequences and avoid quite degrading health conditions caused by diabetes during mature life, it is necessary to apply rehabilitation measures. Following the research undertaken, it was established that the most suitable actions to fortify the health status of minors with diabetes are the rehabilitation procedures applied in the age range of 12-18 years. The recommended type of rehabilitation is the bio-psycho-social complex. The bio-psycho-social rehabilitation of minors with type 1 diabetes constitutes an original and innovative algorithm of therapeutic conduct with prospects of achieving visible success