Browsing by Author "Vogel, Jürgen"
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- ItemChemical solubility of phosphate glasses in the system Na2O-CaO-MgO-P2O5-Al2O3-TiO2 in aqueous solutions of different pH values(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Vogel, Jürgen; Wange, Peter; Knoche, Silke; Rüssel, ChristianPhosphate glasses of different composition ranges show very different solubility behaviour in aqueous solutions of pH 4 and 5.8. With inereasing P2O5 concentrations between 38 and 52 mol% , in the system Na2O-CaO-MgO-P2O5-Al2O3-TiO2 , the dissolution rate generally increases, however, the most notable increase is observed at P2O5 concentrations larger than 48 mol%. Additives of TiO2 and AI2O3 increase the stability to corrosion. Glasses with compositions in the metaphosphate range show larger dissolution rates in slightly acidic medium than glasses near the invert glass range. Glasses in the invert glass range show a stronger increase in the dissolution rates with decreasing pH value and also deceleration of the dissolution with time.
- ItemCrystallization and vicosity of phosphate melts in the system Na2O-CaO-MgO-P2O5-Al2O3-TiO2(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Wange, Peter; Vogel, Jürgen; Knoche, Silke; Rüssel, ChristianGlasses in the system Na2O-CaO-MgO-P2O5-Al2O3-TiO2 were studied with respeet to their crystallization and viscosity. Glasses in the metaphosphate range are composed of phosphate chains, and possess a comparably small tendeney to crystallization. Here, AlPO4 in a cristobalite-like modification and Ca2P2O7 are formed. Glasses in the intermediate range between metaphosphate and invert glass structures are composed of smaller phosphate units and show higher erystal growth velocities as well as higher viscosities. Additions of MgO, AI2O3 and TiO2 result in a strengthening of the glass network, and hence, inereasing viscosities and a notably smaller tendeney to crystallization.
- ItemEffect of composition changes on the structure and properties of phosphate glasses in the pyrophosphate region(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Vogel, Jürgen; Wange, Peter; Hartmann, PeterThe structures of phosphate glasses in the ultra- and polyphosphate region are well-investigated. Discontinuous changes of the properties in the composition ränge around 50 mol% P₂O₅ (transition from network to chain-like structures) are known. The present work is concerned with the structural transition of chain-like phosphate glasses to pyrophosphate glasses. ³¹P MAS N M R in vestigations were used for the quantitative structural analyses of pyrophosphate and mixed pyrophosphate/orthophosphate glasses. Several chemical and physical properties of these glasses were determined in dependence on composition and structure. The in vestigated phosphate invert glasses are very sensitive to additives. Therefore, some important properties of phosphate invert glasses and glass-ceramics can be controlled by addition of relatively small and highly charged cations.
- ItemPhosphate glasses and glass-ceramics for medical applications(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Vogel, Jürgen; Wange, Peter; Hartmann, PeterModified calcium phosphate glass Systems meet the requirements for the development of different biomaterials. Bioactive, longterm stable phosphate glass-ceramics and resorbable phosphate glasses were prepared in the Systems P₂O₅ - CaO - Al₂O₃ - Na₂O and P₂O₅ - CaO - MgO - Na₂O . Due to their high thermal expansion coefficients the bioactive phosphate glass-ceramics are excellently suited for coating metals. Using a salt-sintering process, porous resorbable glasses can be obtained. The properties of glassceramic coatings on cobalt/chromium alloys and the production of porous resorbable phosphate invert glasses are described.
- Itemstructural investigations of SiO₂-containing phosphate glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Vogel, Jürgen; Jana, Carsten; Hartmann, PeterThe incorporation of SiO₂ into phosphate glasses is interesting in view of the development of phosphatic biomaterials. The present investigation is concerned with the incorporation of SiO₂ into phosphate base glasses possessing different phosphate structures. Due to their structural characteristics, they can be classified into three groups: glasses with long phosphate chains or rings formed by Q² phosphate structural groups, glasses with shorter phosphate chains formed by Q² and Q¹ groups and glasses with phosphate invert glass structure, possessing ortho(Q°)- and pyrophosphate groups (two Q¹ groups) exclusively. The structures of these glasses in dependence on the incorporated silica were investigated by transmission electron microscopy and by ³¹P MAS NMR. The principles of incorporation are discussed.