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

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

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

Topologically disordered systems at the glass transition

The thermodynamic approach to the viscosity and fragility of amorphous oxides was used to determine the topological characteristics of the disordered network-forming systems. Instead of the disordered system of atoms we considered the congruent disordered system of interconnecting bonds. The Gibbs free energy of network-breaking defects (configurons) was found based on available viscosity data. Amorphous silica and germania were used as reference disordered systems for which we found an excellent agreement of calculated and measured glass transition temperatures. We reveal that the Hausdorff dimension of the system of bonds changes from Euclidian three-dimensional below to fractal 2.55 ± 0.05-dimensional geometry above the glass transition temperature

The essence of the biopsychosocial model in medical rehabilitation

Universitatea de Stat de Medicină şi Farmacie „Nicolae Testemiţanu”, Chişinău, Republica MoldovaIntroduction. The biopsychosocial model is an approach that establishes the existence of multiple factors that influence a person's development and well-being in the context of a disease, disorder, or disability. There are three types of factors: biological (genetics, anatomy, biochemical disorders, endocrine, etc.), psychological (thinking, emotions, behavior) and social (socio-economic factors, factors of the social microenvironment, cultural factors). Rehabilitation includes various aspects and methods and aims at both mental and physical health, the integrity of the body. Aim of study. Highlighting the biopsychosocial aspects within the complex medical rehabilitation actions in order to make the therapy more efficient and increase the quality of life. Methods and materials. In this literature review were analyzed publications from PubMed, NCBI, Hinari, Elseiver, etc., using the terms «rehabilitation» and «biopsychosocial». Results. The analysis of scientific sources published highlights the important role of the biopsychosocial model in the medical rehabilitation process. Highlighting the biopsychosocial context represents an advance in understanding health in general, because before it, the prevailing model was the medical or biological model (a traditional model, where only biological factors matter). Biopsychosocial factors affect the patient's subjective experience, clinical outcomes, and effective treatment throughout the rehabilitation process or the course of an illness. Essential emphases in the rehabilitation process according to a biopsychosocial model initially consist in a thorough assessment of the general state of health of the body and the psycho-emotional and social components, then in the monitoring and optimization of treatment, psychological counseling and a complex of medical education. Through special medical, psychological and educational actions, the negative impact of the disease on physical and psycho-emotional development can be reduced and and improve a person's abilities to integrate into the family or social environment. Conclusion. 1. The biopsychosocial model is based on understanding the dynamic nature of the various factors that affect the patient's condition and the final results of rehabilitation. 2. The doctor must be aware of the correlation of all the factors that influence the person's state of health. 3. The effective application of the biopsychosocial model, within the complex rehabilitation processes, offers effective possibilities for improving the quality of life. factors that influence a person's development and well-bei ng in the context of a disease, disorder, or disability. There are three types of factors: biologica l (genetics, anatomy, biochemical disorders, endocrine, etc.), psychological (thinking, emotions, behavi or) and social (socio-economic factors, factors of the social microenvironment, cultural factors) . Rehabilitation includes various aspects and methods and aims at both mental and physical health, the integrity of the body. Aim of study. Highlighting the biopsychosocial aspects within the complex medical rehabilitation actions in order to make the therapy more efficient and increase the quality of life. Methods and materials. In this literature review were analyzed publications from PubMe d, NCBI, Hinari, Elseiver, etc., using the terms «rehabilitatio n» and «biopsychosocial». Results. The analysis of scientific sources published highlights the important role of the biopsychosocial model in the medical rehabilitation proces s. Highlighting the biopsychosocial context represents an advance in understanding health in gen eral, because before it, the prevailing model was the medical or biological model (a traditiona l model, where only biological factors matter). Biopsychosocial factors affect the patient's s ubjective experience, clinical outcomes, and effective treatment throughout the rehabilitation proces s or the course of an illness. Essential emphases in the rehabilitation process according to a bio psychosocial model initially consist in a thorough assessment of the general state of health of the body and the psycho-emotional and social components, then in the monitoring and optimization of treat ment, psychological counseling and a complex of medical education. Through special medical, psychological and educational actions, the negative impact of the disease on physical and psycho-e motional development can be reduced and and improve a person's abilities to integrate into the fa mily or social environment. Conclusion. 1. The biopsychosocial model is based on understanding the dynamic nature of the various factors that affect the patient's condition and t he final results of rehabilitation. 2. The doctor must be aware of the correlation of all the factors tha t influence the person's state of health. 3. The effective application of the biopsychosocial model, wit hin the complex rehabilitation processes, offers effective possibilities for improving the quality of life

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

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

Combined Quantitative X-ray Diffraction, Scanning Electron Microscopy, and Transmission Electron Microscopy Investigations of Crystal Evolution in CaO–Al2O3–SiO2–TiO2–ZrO2–Nd2O3–Na2O System

Glass-ceramics, with a specific crystalline phase assembly, can combine the advantages of glass and ceramic and avoid their disadvantages. In this study, both cubic-zirconia and zirconolite-based glass-ceramics were obtained by the crystallization of SiO2-CaO-Al2O3-TiO2-ZrO2-Nd2O3-Na2O glass. Results show that all samples underwent a phase transformation from cubic-zirconia to zirconolite when crystallized at 900, 950, and 1000 °C. The size of the cubic-zirconia crystal could be controlled by temperature and dwelling time. Both cubic-zirconia and zirconolite crystals/particles show dendrite shapes, but with different dendrite branching. The dendrite cubic-zirconia showed highly oriented growth. Scanning electron microscopy images show that the branches of the cubic-zirconia crystal had a snowflake-like appearance, while those in zirconolite were composed of many individual crystals. Rietveld quantitative analysis revealed that the maximum amount of zirconolite was ∼19 wt %. A two-stage crystallization method was used to obtain different microstructures of zirconolite-based glass-ceramic. The amount of zirconolite remained approximately 19 wt %, but the individual crystals were smaller and more homogeneously dispersed in the dendrite structure than those obtained from one-stage crystallization. This process-control feature can result in different sizes and morphologies of cubic-zirconia and zirconolite crystals to facilitate the design of glass-ceramic waste forms for nuclear wastes

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