A Strategy to Promote American Undergraduate STEM Programs to International Students

In this project, STEM education in the United States and other parts of the world was analyzed. There has been an increasing number of international students studying STEM programs but not at the undergraduate level, with the exception of China and other countries. To understand what shapes the destination of students to a specific program various factors were taken into consideration: Financing, Language barrier, culture, and standardized testing

Photoluminescence et cristallochimie des polyphosphates de formule Na1-xAgxM(PO3)4 (M (la, Y) à l'état cristallisé ou vitreux)

Ce travail s inscrit dans le cadre d une étude systématique des propriétés physico-chimiques de polyphosphates à l argent permettant d avancer sur de nouvelles voies pour les dispositifs tels que l éclairage, les lasers accordables dans le visible, la radiophotoluminescence. L'objectif de ce travail vise la compréhension des mécanismes de luminescence de l ion Ag+ dans les composés Na1-xAgxLn(PO3)4 (Ln = La et Y) dont la structure a été parfaitement déterminée. La luminescence des monocristaux provient des ions Ag+, dans des sites isolés et proches de lacunes positives (Ag2+) résultant de la photosensibilité aux UV pour les cristaux au lanthane. La luminescence des verres Na1-xAgxLa(PO3)4 (seuls vitrifiables) a été élucidée grâce à une étude après irradiation et à celle des verres Na2-xAgxZnP2O7. Elle est due aussi aux ions Ag+ dans des sites isolés.This work focuses on keeping with the general pattern of investigations of physical-chemical properties of silver-polyphosphates to find new ways for devices such as lighting, visible range laser applications and radiophotoluminescence. The goal of this study aims at understanding the processes of Ag+ luminescence in Na1-xAgxLn(PO3)4 (Ln = La et Y) compounds which structure has been completely determinated. The luminescence of the single crystals is induced by Ag+ ions in isolated sites and close to hole centers (Ag2+) resulting in UV photosensitivity for the lanthanum crystals. The photoluminescence of the Na1-xAgxLa(PO3)4 glasses (glass-forming only) has been resolved owing to UV irradiation investigations and comparison with the luminescence of Na2-xAgxZnP2O7 glass. Both are also due to Ag+ ions in isolated sites.PESSAC-ICMCB (333182204) / SudocBORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Kinetic dissolution of phosphate glasses containing toxic heavy metals

The dissolution kinetics of a series of phosphate glasses with the compositions 50P2O5–15ZnO–(35−x)PbO–xCdO (x=20 and 35) and (100−y)[50P2O5–15ZnO–15PbO–20CdO]–yAl2O3 (y=6 and 8) have been studied in aqueous solution. The dissolution process of aluminium free metaphosphate glasses is interpreted as hydration of glass surface with a congruent dissolution for x=35 and controlled by both mechanisms with incongruent dissolution for x=20. The addition of Al2O3 in metaphosphate glass (x=20) considerably improves the corrosion resistance..

Physical properties and chemical durability of zinc-lead-iron phosphate glasses

This study provides experimental data on the physical properties and the chemical durability of zinc-lead-iron phosphate glasses with the general composition (100-x) (50P2O5-15ZnO-35PbO)-xFe2O3. The physical properties show that the addition of Fe2O3 results in a high reticulation of the glass network in the composition range 0 £ x £ 10. As a consequence, a drastic improvement of the chemical durability was noticed and the dissolution mechanism was found to be controlled by a hydrolysis reaction with a non congruent dissolution

Physical properties and chemical durability of zinc-lead-iron phosphate glasses

This study provides experimental data on the physical properties and the chemical durability of zinc-lead-iron phosphate glasses with the general composition (100-x) (50P2O5-15ZnO-35PbO)-xFe2O3. The physical properties show that the addition of Fe2O3 results in a high reticulation of the glass network in the composition range 0 £ x £ 10. As a consequence, a drastic improvement of the chemical durability was noticed and the dissolution mechanism was found to be controlled by a hydrolysis reaction with a non congruent dissolution

Luminescent properties of the potassium zinc phosphates of composition K1−xTlxZn(PO3)3

Crystalline and glassy K1−xTlxZn(PO3)3 polyphosphates have been synthesized and characterized. UV–visible spectroscopy was systematically used in order to analyze the optical properties of Tl+ ions both in crystalline and glassy forms with the similar compositions. The investigated polyphosphates can be considered as a model system since the spectroscopic properties of Tl+ ions in the glasses could be deduced by comparison with those in crystals. From structural point of view, in the crystalline forms the thallium ions are six-fold coordinated in a dissymmetrical oxygenated sites. Three luminescences (α, AX, AT) have been then observed and were attributed to the isolated Tl+ ions. In the glassy forms, an additional luminescence (D) has been detected in the low-energy range and was assigned to the Tl+ pairs formation. The relationship between the Tl+ site symmetry and its optical properties is discussed in the context of the Fukuda's model

Innovative Formulations of Phosphate Glasses as Controlled-Release Fertilizers to Improve Tomato Crop Growth, Yield and Fruit Quality

Three phosphate glass compositions, VF1, VF2, and VF3, containing macro and micronutrients with different [K2O/(CaO+MgO)] ratio, were formulated to be used as controlled release fertilizers for tomato crop, depending on their chemical durability in water and their propriety with respect to the standards of controlled-release fertilizers. This study investigated the influence of [K2O/(CaO+MgO)] ratio variation on glass properties. For this, the elaborated glasses have undergone a chemical characterization using inductively coupled plasma atomic emission spectroscopy, a thermal characterization using differential thermal analysis, a physicochemical characterization based on density and molar volume measurements, and a structural characterization using Raman spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. In addition, the chemical durability was determined by measuring the percentage of weight loss and the pH. Results revealed that the glass structure and composition have the mean role in controlling the release of nutrients in water. By increasing [K2O/(CaO+MgO)] ratio, the dissolution rates of the glasses increased due to the shrinking in the rate of crosslinking between phosphate chains, accompanied with a diminution in transition and crystallization temperatures, and an increase in the molar volume. An agronomic valorization of VF1 and VF2 glass fertilizers, which showed dissolution profiles adequate to the criteria of controlled-release fertilizers, was carried out to evaluate their efficiency on tomato crops. These glass fertilizers improved soil mineral content and tomato performances in comparison to the control and NPK treatments with the distinction of VF2. The results highlight the effectiveness of these smart fertilizers toward their potential large-scale application to improve crop production and quality for high nutritional value foods

Structure of zinc-lead-iron phosphate glasses

A structural characterization of (100-x)(50P2O5-15ZnO-35PbO)-xFe2O3 phosphates glasses was accomplished using Raman, XPS, EPR and Mössbauer spectroscopies..

Study of the Effect of Calcium Substitution by Magnesium in the Vitreous System 3P2O5-2K2O-(1 − x) CaO-x MgO

Phosphate glasses have potentially interesting properties that can be used in various applications. Recently, different studies are focusing on their dissolution behaviours that can be modified to suit some environmental applications, such as controlled-release fertilisers. In this work, magnesium had been suggested to improve the glass durability of 3P2O5-2K2O-(1 − x)CaO-xMgO glasses (0 ≤ x ≤ 1). Indeed, its effect on glass structure, thermal properties and most important dissolution behaviours were studied, in order to evaluate their suitability of being used as controlled-release fertilisers. Various compositions in which calcium was partially replaced by magnesium were prepared by melting at 800 °C. The samples were characterised by differential scanning calorimetry, density measurements, X-Ray diffraction, FTIR spectroscopy and Raman spectroscopy. The dissolution behaviours were investigated using inductively coupled plasma optical emission spectrometry ICP-OES, pH measurements and SEM. Substitution of calcium by magnesium reduced the glass density, owing to the lower atomic weight of magnesium compared to calcium, and caused an increase in glass transition and crystallisation temperatures. Magnesium substitution significantly improved the chemical durability of the glasses due to more covalent Mg–O bond than the Ca–O bond. This study demonstrated that 3P2O5-2K2O-0.3CaO-0.7MgO (x = 0.7) had a dissolution profile adequate to the criteria of controlled-release fertilisers and could be used to nourish the plants with phosphorus, potassium, calcium and magnesium