Browsing by Author "Stachel, Dörte"

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    Analyses of aluminum traces in sorted amber cullet
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Pitzel, Christian; Ehrig, Reiner; Stachel, Dörte
    This paper deals with analyses of aluminum impurities in already sorted cullet. Some ways of minimizing the amount of pure aluminum in this amber cullet are shown and discussed. By the mechanism presented the aluminum is oxidized with an alkaline Solution at pH 7.5 up to 11.5, as found in outside stored cullet. This proves to be a useful way of minimizing metallic aluminum in cullet and reduction of interfering inclusions in glasses.
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    Comparison of metallic Silicon in clusions in industrial Container glass and laboratory melts
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Reisch, Renate; Stachel, Dörte; Tessmann, Elke
    Metallic silicon inclusions in glasses obtained from different Container glass companies and from laboratory melts by addition of metallic cuttings (aluminum, magnesium) were examined using light and Scanning electron microscopy The composition of the formed silicon spheres is always similar. The metallic inclusions are composed of silicon with a very small part of fmely distributed iron-Silicon alloys. In amber and green glass chromium, manganese and copper are additionally enriched as further main elements in these alloying phases. Differences in the composition of silicon spheres are due to the dwell time and the concentration of polyvalent ions in the melt.
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    Glass-ceramics with a zeolite phase
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2002) Erdmann, Mandy; Stachel, Dörte
    Zeolites are hydrated alumino-silicates. They crystallize in framework structures. Zeolites are used in the catalysis, adsorption, drying and separation technologies. Glass-ceramics are polycrystalline solid materials. They also have interesting properties. A new field of application can be opened by combination of the properties of zeolites and glass-ceramics. For example, material surfaces can be functionalized (membranes, foams) or special geometries for catalysis can be stabilized. The goal of the work was to design glassceramics with zeolite(s) as crystal phase(s). The glasses with zeolite compositions were melted from raw materials with partial substitution of NaF for Na2CO3. Samples of the glasses were crystallized at various temperatures. The zeolitic phase Na6[AlSiO4]6 was precipitated in K 1 1/2 samples at all temperatures. Na6[AlSiO4]6 is a zeolite of the sodalite type. The obtained zeolite does not correspond to the synthesis compositions of the glasses. It is remarkable that the zeolite itself is OH- and/or F- -free, although the presence of these anions is necessary for the zeolite formation.
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    Investigation of the dissolution of metallic Silicon spheres in a container glass melt
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Reisch, Renate; Stachel, Dörte; Traufelder, Steffi
    On laboratory scale, metallic silicon spheres obtained from industrial flint glass production and spectroscopically pure silicon were annealed in flint glass, amber glass and green glass cullet melts. The dissolution behavior of sihcon was investigated in the temperature range of 1200 to 1500°C in normal air a nd sulfur dioxide atmosphere. Silicon dissolves by formadon of a thin silicon dioxide layer at the surface of the spheres only at high temperatures and long annealing times. The dissolution of silicon is a process with low reaction rate and a complex reaction mechanism due to interactions of Silicon with oxygen, hydroxide ions and polyvalent ions in the Container glass melt.
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    Silicon in container glasses, its solution kinetics and dissolving potential in container glass furnaces
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Pitzel, Christian; Stachel, Dörte; Ehrig, Reiner
    The forming proeess of sihcon stones in differently colored container glasses under the action of different aluminum pieces will be discussed and some special features during the generation reported. The dissolution of formed silicon stones was analyzed in dependence on melting time, temperature and color of the glass. With the knowledge of these parameters the rate constant and the diffusion coefficient of the dissoludon were calculated. The main results are: first, it is not possible to generate large silicon stones anyway, indicated by big aluminum pieces which will be divided when they become liquid. Second, the dissolving of the silicon stones does not go on homogenously about the whole temperature range analyzed. But it can be divided into three fields: an area below, an area around and an area above the melting point of the silicon. The reason for these differences is found in the SiO2-rich layer around the stones which will be formed and dissolved by different rates in colored container glasses. On the basis of these dissolving rates and of the temperature profiles in glass meldng furnaces the dissolving potential in furnaces could be calculated. Three possible routes of silicon stones through special types of furnaces show the respective dissolving potential for silicon. The potential for dissolution of elementary Silicon for the calculated types of Container glass furnaces is nearly the same. The dissolution rates could be improved by raising the temperature of the glass bath in the furnace and by raising the dwell time of the silicon stones in the furnace.
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    Thermal behavior of metallic aluminum in a Container glass melt
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Reisch, Renate; Stachel, Dörte; Traufelder, Steffi; Tessmann, Elke
    The thermal behavior o f metallic aluminum was studied in the temperature ränge of 1100 to 1500°C in a Container glass melt. The dissolution of the metal was determined as a function of aluminum input, glass volume, melting time and the type of glass used. By analogy, melts containing magnesium cuttings were also investigated. With the aid of electron microscopy, it was possible to establish a reaction scheme of Oxidation and reduction processes. Only 2 to 3 % of the aluminum introduced causes the formation of silicon spheres. The main part will be oxidized through reactions with oxygen, hydroxide and polyvalent ions in the melt.
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    Zeolite-type and nepheline crystals in glass-ceramics
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Erdmann, Mandy; Stachel, Dörte
    Zeolites are hydrated alumino-silicates. They crystallize in framework structures. Zeolites are used in the catalysis, adsorption, drying and separation teehnologies. Glass-ceramies are polycrystalline solids prepared by controlled crystallization of glasses, with interesting properties. A new field of application can be opened by combination of the properties of zeolites and glass-ceramics. For example, material surfaces can be functionalized (membranes, foams) or special geometries for catalysis can be stabilized. It is possible to design glass-ceramics with a zeolite as crystal phase. In this study further investigations of the phase distribution and the interface between the crystal phases will be presented. Glasses with a composition similar to the stoichiometric composition of a zeolite were melted with partial subtitution of NaF for Na2CO3. Samples of these glasses were crystallized at various temperatures. The zeolitic phase Na6[AlSiO4]6 and the nepheline were precipitated in two of the glass compositions at all crystallization temperatures. Na6[AlSiO4]6 is a zeolite of the sodalite type. The interface between the zeolite and the nepheline will be shown. The nepheline seems to grow radially (epitaxially) on the zeolite. The obtained zeolite does not correspond to the synthesis compositions of the glasses.