Network Structures and the Properties of Na-Ca-Sr-Borophosphate Glasses

Borophosphate glasses were prepared with the nominal molar compositions 16Na2O-(24-y)CaO-ySrO-xB2O3-(60-x)P2O5 (mol%), where 0≤x≤60 and y=0, 12, and 24. Information about the compositional dependence of borate and phosphate site speciation and next nearest neighbor linkages was obtained by 11B and 31P MAS NMR and Raman spectroscopies, and by high pressure liquid chromatography (HPLC). With the initial replacement of P2O5 by B2O3, tetrahedral borate sites linked to four phosphate anions, B(ØP)4, are created in the glass structure, and the average phosphate anion becomes smaller as bridging PØP bonds are replaced by bridging PØB bonds. With further increases in the B2O3 content, borate units, including B-triangles, replace phosphate units linked to the B-tetrahedra. Compositional trends for the glass transition temperature (Tg) and molar volume are explained by considering the number and types of bridging oxygens per glass former, consistent with topological models reported elsewhere

Burnout in Organizational Life

Burnout is a psychological response to work stress that is characterized by emotional exhaustion, depersonalization, and reduced feelings of personal accomplishment. In this paper, we review the burnout literature from 1993 to present, identifying important trends that have characterized the literature. We focus our attention on theoretical models that explain the process of burnout, the measurement of burnout, means of reducing burnout, and directions for the future of burnout research.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Dissolution rates of borophosphate glasses in deionized water and in simulated body fluid

Particles of borophosphate glasses with the nominal molar compositions 16Na2O-(24-y)CaO-ySrO-xB2O3-(60-x)P2O5 (mol%), where 0 ≤ x ≤ 60 and y = 0, 12, and 24, were reacted in deionized water and in simulated body fluid (SBF) at 37 °C. For the dissolution experiments in water, the pH of the solution at the conclusion of the experiments increased systematically, from 2.1 to 9.5, for y = 0 glasses when ‘x’ increased from 0 to 60. The reaction rates over the first 8–24 h of dissolution in both SBF and deionized water followed linear kinetics, with reaction rates dependent on glass composition. For glass particles in SBF, replacing P2O5 with up to 20 mol% B2O3 decreased the dissolution rate (fraction dissolved) by two orders of magnitude, from 7.0 × 10−3 h−1 for x = 0 to 2.0 × 10−5 h−1 for x = 20. Further replacement of P2O5 by B2O3 increased dissolution rates by three orders of magnitude, to 2.3 × 10−2 h−1 at x = 60. The compositional dependence of the dissolution rates is explained by changes in the glass structure, with the most durable glasses possessing the greatest fraction of tetrahedral borophosphate sites in the glass network. Crystalline brushite was detected on Ca-glasses with 35 and 40 mol% B2O3, but the dominant precipitation phase on both the Ca- and Sr-glasses is an x-ray amorphous material constituted from orthophosphate and pyrophosphate anions

The Structure and Properties of XZnO-(67-x)SnO-33P₂O₅ Glasses: (IV) Mechanical Properties

The Vickers hardness, Young\u27s modulus, and shear modulus of xZnO-(67-x)SnO-33P2O5 glasses increase with increasing values of x, in agreement with predictions that consider the quantitative structural information regarding coordination numbers of Zn2+ and Sn2+ ions by diffraction methods, and phosphate anion distributions by NMR methods, reported in an earlier study. The compositional dependence of the shear modulus falls into two ranges which correlate with trends in photoelasticity, and the elastic and photoelastic properties are explained considering changes in ion packing ratio and average bond strengths when ZnO replaces SnO

Characterization of 20Na₂O·30((1−x)CaO·xSrO)·50P₂O₅ Glasses for a Resorbable Optical Fiber Application

Resorbable glasses with nominal molar compositions of 20Na2O·30[(1−x)CaO·xSrO]·50P2O5, where x = 0, 0.25, 0.50, 0.75, and 1, were prepared and characterized. With the replacement of CaO by SrO, the molar volume, refractive index, and coefficient of thermal expansion increased, and the glass transition temperature, crystallization temperature, and viscosity decreased. The replacement of CaO by SrO decreased the dissolution rate in 37°C water by nearly an order of magnitude. Resorbable glass fibers drawn from melts of the 20Na2O·30CaO·50P2O5 glass exhibited decreasing transmission of laser light (632 nm) in a predictable way as the fiber dissolved in a phosphate buffer solution. This demonstrated that these glasses could be used to produce resorbable fibers for temporary biosensing or therapeutic applications