Amorphous phase boundary

Beside the crystalline material, a certain portion of amorphous lead dioxide is always observed. In the working electrode such amorphous material is apparently hydrated and forms a gel structure at the phase boundary between the solid material and the electrolyte (cf. Ref. [6]). 

The oxidation of the crystalline phase occurs 15 times more slowly than the oxidation of the amorphous phase and is likely localized in the boundary regions. The autoxidation of PE and PP occurs at the rate, which is slower at higher crystallinity of polymers and vice versa, as indicated by the amount of the oxygen consumed. Based on the evidence accumulated, it is safe to say that PE and PP are oxidized in their amorphous regions [12,33,34,42,67],... 

Said this, we can let the reader to recall Fig. 1.15, where we depicted amorphous-like phase regions at grain boundaries as the pathways open for preferential diffusion of hydrogen atoms. Apparently, an alloy can benefit from some fraction of amorphous phase to improve kinetics of hydrogen absorption, but complete amorphization of crystalline lattice lowers capacity for storing hydrogen [156]. Mechanochemical activation is therefore a complex process where kinetic and thermodynamic effects must be firstly well understood, and then optimized. 

There are two possibilities first, nonuniform or multicomponent polymer materials. Internal stresses may appear due to differences in the properties of various parts of an article and the existence of phase boundaries. Second, uniform materials, which seem quite homogeneous, can be amorphous or polycrystalline.The physics of the development of residual stresses in such materials will be discussed in this section. 

This approach has been applied for Si-Al-O-N ceramics. The results can explain the existence of the amorphous phase in the grain boundaries (Fig. 24), depending on the overall composition of the system ([equ% O] = 16, 12, 8 and [equ% Al] = 10.6) and on the strength of interaction (Ap). In a strict sense it must be concluded that the conventional phase diagrams of Si3N4 ceramics are incomplete representations of materials containing an amorphous intergranular phase. 

Fig. 24. Driving force for an amorphous grain boundary phase in equilibrium with /tes as a function of composition in the system Si-N-O-Al and strength of interaction [330]...

The specific heat of Si3N4 ceramics is in the temperature range 293 up to 1200 K [Cp (293 K) = 0.67 KJ (K kg)-1] nearly independent of the composition of the additives. The isobaric specific heat values agree well with the isochoric specific heat calculated by Debye s theory. Also the Dulong Petit s rule can applied as an approximation of the Cv values [25 J(K mol)-1] at temperatures >1100 K [371]. From the Cp values at around 100 K the amount of the amorphous grain boundary phase can be calculated [371]. 

In this overview, we will first discuss how transmission electron microscopy (TEM) techniques can be used to determine the presence or absence of intergranular amorphous phases at interphase boundaries in structural... 

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