Melt interphase

Apart from the most electropositive metals, most other metals extracted through molten salt routes are recovered as solids these include many important refractory and other transition metals, the lanthanides, and some actinides. Particularly interesting problems arise in the electrowinning of the refractory metals. Attempts to deposit these metals in a coherent, massive form of theoretical density usually meet with a number of difficulties. Deposits may be dendritic, for example, if electrodeposition proceeds under mass transfer control, or they may be powdery and nonadherent if secondary reactions, such as alkali metal deposition, followed by backreaction with the solute, occurs. Moreover, powdery deposits may also arise if low oxidation states, formed as intermediates during the reduction process, disproportionate in the metal-melt interphase. Charge-transfer-controlled electrodeposition or coupled chemical steps appear to be a prerequisite for obtaining dense, coherent, and adherent deposits. Such deposits have been obtained... 

Under certain conditions, it will be impossible for the metal and the melt to come to equilibrium and continuous corrosion will occur (case 2) this is often the case when metals are in contact with molten salts in practice. There are two main possibilities first, the redox potential of the melt may be prevented from falling, either because it is in contact with an external oxidising environment (such as an air atmosphere) or because the conditions cause the products of its reduction to be continually removed (e.g. distillation of metallic sodium and condensation on to a colder part of the system) second, the electrode potential of the metal may be prevented from rising (for instance, if the corrosion product of the metal is volatile). In addition, equilibrium may not be possible when there is a temperature gradient in the system or when alloys are involved, but these cases will be considered in detail later. Rates of corrosion under conditions where equilibrium cannot be reached are controlled by diffusion and interphase mass transfer of oxidising species and/or corrosion products geometry of the system will be a determining factor. 

The thickness of interphases in polymer melts and solutions may be much greater than in low-molecular matrices owing to the greater size of their macromolecules and existence in them of submolecular associates [51],... 

Rheological methods of measuring the interphase thickness have become very popular in science [50, 62-71]. Usually they use the viscosity versus concentration relationships in the form proposed by Einstein for the purpose [62-66], The factor K0 in Einstein s equation typical of particles of a given shape is evaluated from measurements of dispersion of the filler in question in a low-molecular liquid [61, 62], e.g., in transformer oil [61], Then the viscosity of a suspension of the same filler in a polymer melt or solution is determined, the value of Keff is obtained, and the adsorbed layer thickness is calculated by this formula [61,63,64] ... 

The recourse to the above-described procedure permitted the derivation [74] of an exact expression for function G(pi,p2). It is of utmost importance for the construction of a phase diagram of a melt or solution of interphase copolymerization products, since this function enters in the equations for the cloud point curve [82]. 

The interphases between MDs should not be able to cause nucleation of the semicrystalline phase. If the interphase displays nucleation activity, first-order crystallization kinetics may be obtained however, the supercooling at which dynamic crystallization from the melt occurs will not be the maximum that could be possibly attained if homogeneous nucleation were in place. 

As Table 2 shows, non-treated fillers and reinforcements have high energy surfaces. During the almost exclusively used melt mixing procedure, the forces discussed in the previous section lead to the adsorption of polymer chains onto the active sites of the filler surface. The adsorption of polymer molecules results in the development of a layer which has properties different from those of the matrix polymer [43-47]. Although the character, thickness and properties of this interlayer or interphase are much discussed topics, its existence is now an accepted fact. 

Decreased mobility of adsorbed chains has been observed and proved in many cases both in the melt and in the solid state [52-54] and changes in composite properties are very often explained by it [52,54]. Overall properties of the interphase, however, are not completely clear. Based on model calculations the formation of a soft interphase is claimed [51], while in most cases the increased stiffness of the composite is explained by the presence of a rigid interphase [55,56]. The contradiction obviously stems from two opposing effects. Imperfection of the crystallites and decreased crystallinity of the interphase should lead to lower modulus and strength and larger deformability. Adhesion and hindered mobility of adsorbed polymer chains, on the other hand, decrease deformability and increase the strength of the interlayer. 

DSC measurements showed that the crystallization ability of this interphase region was reduced by the silane modification of the glass beads. Despite an increase in the amount of amorphous material with increasing number of silane layers, a decrease in the intensity of the fourth lifetime was observed. This decrease in the free volume is in accordance with the earlier observed reduced mobility in the interphase region measured by dynamic-mechanical spectroscopy in the melt state [9,10] and creep and stress relaxation measurements in the solid state [12]. 

Molecular Weight Dependence of Phase Structure. Similar line shape analysis was performed for samples with molecular weight over a very wide range that had been crystallized from the melt. In some samples, an additional crystalline line appears at 34.4 ppm which can be assigned to trans-trans methylene sequences in a monoclinic crystal form. Therefore the spectrum was analyzed in terms of four Lorentzian functions with different peak positions and line widths i.e. for two crystalline and two noncrystalline lines. Reasonable curve fitting was also obtained in these cases. The results are plotted by solid circles on the data of the broad-line H NMR in Fig. 3. The mass fractions of the crystalline, amorphous phases and the crystalline-amorphous interphase are in good accord with those of the broad, narrow, and intermediate components from the broad-line NMR analysis. 

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