Vitreous transition temperature

Whatever the mobile ion is, all the vitreous electrolytes have a transport number of unity and below their vitreous transition temperature, ionic conductivity follows an Arrhenius law ... 

A microscopic model for ionic transport above the vitreous transition temperature... 

Above the vitreous transition temperature Tg, ionic conductivity increases steeply as represented in Fig. 4.6 from data obtained in the Agl-AgMoQ mixture. Above Tg, ionic conductivity is no longer represented by an Arrhenius law (4.1) and experimental results are better represented by an empirical relationship... 

It is important to select the components of the substrates with care and particularly to pay attention to the physical parameters they act upon, in particular the vitreous transition temperature (7g ) of the deep-frozen vaccine [20-25,30]. This temperature, also referred to as vitreous eutectic temperature, does indeed play a critical role in the deformation and collapsing of freeze-dried pellets [20,25], and possibly in the loss of infectivity titers. This temperature is dependent on the nature and concentration of the substrate molecules and may be determined in several ways [20,29,35,36]. In industrial practice, the most commonly utilized techniques are differential scanning calorimetry (DSC) as well as resistance and/or dielectric constant measurements. 

Nevertheless, the reliability of the assessment of the drop in titer by accelerated aging is disputable. The whole calculation principle relies on the fact that the kinetics follow laws of the Arrhenius type throughout the whole studied temperature domain. It so happens that this particular point is not that obvious if the dehydrated product contains an amorphous phase, which is quite frequently the case. As a matter of fact, a freeze-dried vaccine whose substrate contains sugars and proteins often has a vitreous transition temperature (Tg Lyo) greater than zero [12,25]. 

It was shown that the laws governing the evolution of physicochemical parameters according to temperature varied depending on whether one was above or under the vitreous transition temperature of the product [25]. 

For instance, if a freeze-dried vaccine with a vitreous transition temperature equal to 25°C is submitted to accelarated storage tests at temperatures lower than 25°C, Arrhenius s law is applicable. On the other hand, for temperatures above 25°C, there exists a potential risk of error in the prediction. The implementation of the accelarated storage test is thus submitted to the level of the Tg Lyo. 

The vitreous transition temperature (Tg) of the paint resin can be one of the important properties in order to get an uniform film of a significant thickness. The resin is known to change its... 

Figure 7.- Scheme of the nucleation rate (Vn) and growth (Vc) respectively, based on the temperature. Tl = temperature of liquidus Tg = vitreous transition temperature... 

In the case of ceramics with intergranular vitreous phase (materials sintered with additives), the transition is smooth and allows the vitreous transition temperature of the secondary phase at a lower temperature limit (Tg =1,000°C for the sialons), [ROU 93]. Furthermore, the finer the grains, the earlier the appearance of BDT (low temperature). There is finally the effect of size, which is evident from the dependence of the BDT with respect to the structure studied and reflects the time it takes for a confined soft zone to spread on both sides of the stmctiue [RIE 81], On the normal timescale for plastic deformation forming processes (from a few seconds... 

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