Werner Vogel

Glass formation, properties and structure of glasses in the TeO2ZnO system

Glass formation occurs in the zinc tellurite system in the region of the eutectic (21 mol% ZnO) on the TeO2-rich side of the phase diagram. Glasses are characterized by a high refractive index which increases with TeO2 content. The glasses are transmitting from about 400 nm to about 6 μm with Oue5f8H absorption bands at 3.3 and 4.4 μm. Short range order of the glasses was deduced with neutron diffraction, infrared and Raman spectroscopy by comparison with the spectra of the synthesized crystalline α-TeO2, Zn2Te3O8 and ZnTeO3. Glasses consist of disordered TeO4, TeO4, TeO3+ and TeO3 building units. The number of the TeO3+1 units is limited by ZnO addition. There is a relatively strong structural correlation between the glasses and the crystalline compound Zn2Te3O8 in accord with the phase diagram.

Development of machineable bioactive glass ceramics for medical uses

Abstract Following a controlled, two-stage phase separation in glasses of the system Na2O/K2Oue5f8MgOue5f8Al2O3ue5f8SiO2ue5f8CaOue5f8P2O5ue5f8F, annealing results in both fluorophlogopite and apetite crystallization. The phlogopite mica crystals make the material machineable, whereas the apatite crystals provide for its bioactivity. Animal tests show direct intergrowth with the bone. Bone cells and blood vessels can be found in the immediate neighbourhood of the implant.

Development, structure, properties and application of glass-ceramics for medicine

Abstract Glass-ceramics of the type Bioverit can be used as implants for hard tissue (bones). The structures of four biomaterials of the type Bioverit are discussed: biocompatible machineable glass ceramics with mica crystals; bioactive machineable glass ceramics with mica and apatite crystals; bioactive phosphate glass ceramics with apatite and AlPO4-crystals; and a new composite material. Applications of Bioverit are possible in orthopaedics, head and neck surgery and stomatology.

Electron-microscopical studies of glass

Abstract During the past 25 years, the use of the electron microscope in glass research has substantially expanded our knowledge of the microstructure of glasses, for instance of the phase separation processes in glasses. The use of electron microscope in glass research calls for special knowledge the lack of which would certainly lead to misinterpretations and wrong conclusions. Direct electron transmission of the specimen: low voltage beams create images of high contrast. On the other hand, there is always the risk of altering the specimen. If very high beam voltages are employed this is at the expense of image contrast. The optimum beam voltage range in the direct electron transmission of glass is 50 to 120 kV, depending very much on the kind of glass to be examined. The replica technique: this technique in electron microscopical investigations of glasses has more advantages than disadvantages but a highly developed technique is necessary. The most important factors will be described. Surface treatment of glass samples prior to making the replica: suitable etching processes of a freshly fractured glass surface sometimes help to enhance the visibility of structural peculiarities but faulty preparations have to be avoided. Use of the scanning electron microscope and the electron-beam microprobe: enormous advantages and problems will be described. Finally selected examples of electron-optical examinations of glass will be given.

29SiMASNMR investigation on silica glass prepared by the drying control chemical additives method

Abstract High-resolution 29 Siue5f8NMR measurements in solids are performed to study the effect of DCCA (drying control chemical additive) formamide on the tempering of silica gel glass in the range of 200 to 900°C. The Ftue5f8MASue5f8NMR spectra yield quantitative results and indicate only the existence of O 3 (HOSi(-OSi≡) 3 ] and Q 4 [Si(OSi≡) 4 ] groups in the limits of error. The increasing polycondensation is shown by an increasing content of Q 4 groups which goes from about 75% at 200°C to about 95% at 900°C. Additionally CPue5f8MASue5f8NMR experiments give the qualitative evidence of small parts of Q 2 [(HO) 2 Si(-OSi≡) 2 ] groups in all tempering steps.

Some aspects of property tailoring of sol-gel derived thin SiO2 films

Abstract The sol-gel process in the dip-coating variant opens an interesting way for the production of thin metal oxide or transition metal oxide films with useful properties. This paper present result on the desposition and the characterization of thin SiO 2 films. The influence different process parameters, such as the composition and the aging behaviour of the coating solution, the withdrawal speed and the thermal treatment on important properties such as refractive index, film thickness, crystallinity and topography was tested. Viscosity and transmission measurements, Fourier transformation infrared reflection spectroscopy (FTIRS), transmission electron microscopy (TEM) and reflection high energy electron diffraction (RHEED) were used.

Perspective of the development of bioactive glass ceramics for biomedical applications

Abstract The development of new materials for application in human medicine, especially for replacement of bones or other tissue, is a young field of research in the world. New results lead to extra-ordinary progress in human medicine. Necessary lines of development of bio-materials are mentioned. As an example, the development of a glass ceramic, which is both machinable and highly bioactive, is described.

The coordination of Ni11 in glasses and glass-ceramics of the system MgOAl2O3SiO2

Abstract Differences in strength connected with colour variations in NiO-containing Mg-alumosilicate glass ceramics give rise to a remission spectroscopic analysis of the Ni-on. In the base glass, Ni11 occupies tetrahedral and octahedral positions of the dark green Niue5f8Al spinel. An increase of the Mg-component and a rise of the melting intensity promote the octahedral nickel coordination and along with it the formation of the strength-reducing, light green Ni-forsterite. The demand for a strong final product is thus met by the technologically desirable shortening of the melting time.

Crystallization of Glasses

One of the most important causes of defective glass is crystallization, which is, after all, the equilibrium stage of the solidifying melt. From this viewpoint, the manufacture of glass is based on tricking the melt so that it will not attain the low-energy state it strives to assume. Whether one wishes to avoid crystallization or to control it, it is necessary to master theoretically the phenomena of nucleation and crystal growth.

Structure investigations on Ba(PO3)2-glass with neutron diffraction and wideline-NMR-technique

Abstract The combination of nuclear magnetic resonance (NMR) and neutron diffraction allowed in connection with computer-model-simulations the construction of a detailed structural model of Ba(PO3)2 glass. The starting point was the structure of crystalline Ba(PO3)2. A computer program has generated the transition to the amorphous state by rotation of the PO4-tetrahedra at a random angle and by translation of the Ba-positions into the three space directions by means of the Monte Carlo procedure. As a result the essential peaks of the distribution function, obtained from scattering data, could be described with certain atomic pairs of the model. Up to a distance of 0.55 nm the simulated structure adequately describes the experimental data of the neutron diffraction. Therefore, conclusions with respect to the amorphous atomic arrangement are possible. The results of 31P-NMR based on dipolar interactions support the existing structural conceptions. Additional information comes from the anisotropic chemical shift of 31P and the 1H resonance.