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  • Articles: DFG German National Licenses  (3)
  • 1990-1994  (2)
  • 1985-1989  (1)
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  • Articles: DFG German National Licenses  (3)
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  • 1
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Goethite waste, originated in the hydrometallurgy of zinc, was characterized and recycled, in combination with raw materials, for producing glass-ceramic (GC) materials. Four base compositions were prepared with an Fe2O3 content ranging from 15 to 25 wt%. The mixtures were melted at 1400–1450 °C and quenched to obtain the glass. The nucleation and crystallization temperatures and the activation energy of the crystallization process were determined by differential thermal analysis. The glass samples were nucleated at 660 °C for times ranging from 1 to 4 h and crystallized at 800–900 °C for 1 to 4 h. X-ray diffraction and fluorescence analysis were performed on the glasses and GC samples and the crystalline phases characterized. The percentage of crystallinity was determined as a function of the temperature and duration of the thermal treatment. The fractional factorial experimental approach was carried out on the 20 wt% Fe2O3 composition with the aim of evaluating the influence of the nucleation temperature and time, the crystallization temperature and time and the presence of a reducing agent on the glass devitrification process.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The kinetics of decomposition ofα-goethite were investigated, under vacuum conditions, in the temperature range 170–250° C. The experimental thermogravimetric traces were interpreted according to the shrinking core model for cylindrical particles. The Arrhenius plot of InK (kinetic constant) against 1/T yielded an activation energy of 119±9 kJ mol−1 at 210° C. The highest specific area,S BET=118.4±5.5 m2 g−1, of the reaction productα-hematite, was obtained by decompsition at 225° C. Information about the formation of micropores and their evolution with temperature was also obtained.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 27 (1992), S. 448-452 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The nucleation and crystallization processes of Li2O-Al2O3-SiO2 glass-ceramics were investigated by differential thermal analysis. The crystalline phases produced during thermal treatment at different temperatures and the residual glassy phase were characterized by X-ray diffraction, SEM and image analysis techniques. The activation energy of the crystallization process was calculated as E=380±20 kJ mol−1. The influence of nucleating agents (TiO2, ZrO2) was evaluated to obtain glass-ceramics transparent to visible light. The stability of the glassy phase in cooling was determined by means of temperature-time-transformation curves.
    Type of Medium: Electronic Resource
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