Title: Glass transition temperature its exploitation and new conception of fragility
Other Titles: Teplota skelného přechodu jeho využitelnost a nová koncepce křehkosti
Authors: Kozmidis-Petrovic, Ana
Šesták, Jaroslav
Citation: KOZMIDIS-PETROVIC, A., ŠESTÁK, J. Glass transition temperature its exploitation and new conception of fragility. Physics and Chemistry of Glasses-European Journal of Glass Science and Technology Part B, 2018, roč. 59, č. 6, s. 259-266. ISSN 1753-3562.
Issue Date: 2018
Publisher: Soc Glass Technology
Document type: článek
URI: http://hdl.handle.net/11025/33860
ISSN: 1753-3562
Keywords: Sklo;přechod teplota;vykořisťování;křehkost
Keywords in different language: Glass;transition temperature;exploitation;fragility
Abstract: Vztahy mezi velikostí změny poměru teplot krystalizace a tání a skelného přechodu, tj. Tc / Tg a Tm /Tg, určují hodnoty relativní změny parametrů stability skla dKH / KH (Hrubý), dKW / KW Weiberg) a dKLL / KLL (Lu a Liu). Obě závislosti Sc (T) a ScVFT (T) mají stejný teplotní profil a téměř se překrývají. Pomocí buď Sc (T) nebo ScVFT (T), získáme hodnotu indexu křehkosti. Ze závislosti lnSc (T) versus lnT to je možné úspěšně předpovědět vztahy mezi hodnotami m u různých skel. Lineární korelace mezi novými parametry GS FK a FKA, je lepší než korelace KLL. Exponent roztažení se zvyšuje jako lineární funkce T / Tg v intervalu 1≤T / Tg <1 pro dané hodnoty parametru dynamické křehkosti, m. Termodynamický termín, který má dominantní roli v křehkosti, může být určen výrazy pro konfigurační entropii a konfigurační tepelnou kapacitu. Porovnávali jsme Sc (T) s funkcí teplotní závislosti konfigurační entropie, kterou získali autoři Sipp et al a ScVFT (T) Oba Sc (T) a ScVFT (T) mají stejnou teplotní závislost a téměř se překrývají. Proto pomocí Sc (T) nebo ScVFT (T) získáme stejnou hodnotu indexu křehkosti a ze závislosti lnSc (T) versus lnT je možné úspěšně předpovědět vztahy mezi hodnotami m u různých typů skel
Abstract in different language: When cooled or pressurised, melts exhibit a tremen-dous reduction in molecular mobility. If the process is performed at a high enough rate, the structural relaxation time of the liquid eventually exceeds the time allowed for equilibration. This brings the system out of equilibrium, and the liquid is operationally defined as a glass – a solid lacking long range order. Despite almost 100 years of research on the liquid/glass changeover, it is not yet clear which molecular mechanisms are fully responsible for such a unique slow down in molecular dynamics.(1–3) The major characteristic of this transformation process is the single minded glass transition tem-perature Tg which is a conceivably distinguishable democratic average (simple arithmetic mean) value of temperatures labelling the glass transformation region (GTR) becoming often the source of disput-able interpretations and various scrutiny. It can be operationally defined via near equilibrium scans, where physical quantities are measured as a function of thermodynamic variables (e.g. temperature, pres-sure) scanning from the glassy to the liquid state and vice versa. Such an obtained Tg denomination can be referred to as pseudo thermodynamic, or thermal resem-bling value which in the case of the most commonly performed experiments via DTA/DSC experiments is a common subject of customary determination. Let us mention that even if computationally appealing for its simplicity, this Tg numerical value always implicates averaging and thus bears certain accidental subjec-tivity. Tg may also incorporate the impact of other inclusive properties, such as for a thin layered sample the Tg value would approach the bulk (standard) value with the reciprocal film thickness dependence. Treatments of experimental effects are not the subject of our contribution(4–9) even though significant. Though not uniquely and specifically definable (just on the previously prepared glass) Tg became one of the e nsuing parameters capable of yielding valuable predictive numbers. Glass forming ability (GFA) and consequent glass stability (GS) of the associated constrained (i.e. frozen-in) state are ac knowledged to hold substantial meaning for all those who are interested in various applications to which glassy materials lend themselves and thus worth reconsideration. When a glassy material turns out to be experimentally accessible upon a suitable melt quenching (critical cooling rate, Rc) from its well dis-tinguishable melting point (Tm) down through GTR, demarcated as shown above by the temperature, Tg, certain data became accessible for material identifica - tion. (10) A liquid with good GFA exhibits a low value of R for the glass formation, which has remained a lon
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