Browsing by Author "Nemilov, Sergei V."

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    Ageing kinetics and internal friction of oxide glasses
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Nemilov, Sergei V.
    The detailed analysis of internal friction data of Silicate and phosphate glasses (frequencies of about 1 Hz) was done in comparison with the calculated temperature positions expected from the characteristic times of ageing which resulted from previous systematization of alkali-containing silicate glasses. As basis suggested for such comparison is the validity of secondary relaxation mechanism at high-temperature mechanical relaxation to that for ageing kinetics at room temperature. Practically in all cases the relaxadon times for the ageing process fit the distribution of relaxation times for internal friction. Thus the β-relaxation maximum (internal friction) may be considered as overlapping four narrow spectral components, at least. The characteristic times for ageing, contrary to continuous distribution for the mechanical relaxation, are discrete due to the condition of structure ordering. The nonbridging oxygens seem to be more probable participants of elementary relaxation events in both kinds of processes.
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    Physical ageing of silicate glasses
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Nemilov, Sergei V.
    The presented review has been devoted to the problem of volume-determined properties relaxation of siicate glasses at room temperature. It is shown that the experimental data are described by the simple Debye exponential law or by a superposition of two exponents. Their parameters are calculated and systematized. A molecular-kinetic model is proposed for these ageing processes. It proceeds from the possibility of volume relaxation due to the cooperative β-relaxation mechanism with no change in the system's topology. The characteristic ageing times can be calculated according to equations obtained based on the viscosity data in the glass transition range. The precision of the calculations is about ± 15 % at the time variations from a few weeks up to about 15 years. The system of calculated parameters is proposed which characterizes the completeness of ageing and its rate at any glass age. Optical and thermometric glasses have been ranked by their tendency to ageing. The scheme of future investigations predetermined by practice is defined.