Interface degradation

An overview of the most important phenomena in interface science related to studying solar materials is presented in this section. The methods for characterizing interfaces and those deemed likely to have the largest near-term impact on solving the problems of interface degradation are then mentioned. 

Encapsulants/coatings Polymers/metal (oxides) Photodegradation, interface degradation... 

Kinetic Monte Carlo and hyperdynamics methods have yet to be applied to processes involved in thermal barrier coating failure or even simpler model metal-ceramic or ceramic-ceramic interface degradation as a function of time. A hindrance to their application is lack of a clear consensus on how to describe the interatomic interactions by an analytic potential function. If instead, for lack of an analytic potential, one must resort to full-blown density functional theory to calculate the interatomic forces, this will become the bottleneck that will limit the size and complexity of systems one may examine, even with multiscale methods. 

Fig. 8 Electroluminescence spectrum of an ITO/PF/A1 device (solid line), of the same device after continuous operation under air showing changes due to electrooxidative degradation (dotted line), and under operation of a different device in argon showing changes due to interface degradation (line with symbols)...

Corrosion of the material used is another factor that limits the selection of the electrocatalyst. The electrochemical corrosion of pure noble metals is not as important as in the case of binary or ternary alloys in strong acid or alkaline solutions, since these catalysts are widely used in electrochemical reactors. In the case of anodic bulk electrolysis, noble metal alloys used in electrocatalysis mainly contain noble metal oxides to make the oxidation mechanism more favorable for complete electron transfer. The corrosion problem that occurs from this type of catalyst is the auto-corrosion of the electrode surface instead of the electrode/electrolyte solution interface degradation. The problem of corrosion is considered in detail in Chapter 22. 

Interface degradation apparently does not result from any appreciable reaction of the coated mirror with corrosive gases permeating in from the atmosphere. Thus, when the degraded polymer was dissolved off the mirror of a weathered PIB/Ag/glass sample and the mirror analyzed by X-ray/scanning electron microscopy, the Interface contained no sulfur (0.1% detection limit) and no more chlorine than did an unweathered control. 

Other variables investigated with respect to fracture toughness include processing parameters, e.g.. production schedules and postcure cycles [166.171] for thermosets, and cooling rates for thermoplastics [171] matrix composites, and moisture content. A study [171] on composites based on epoxy and vinyl ester matrices has shown that whilst matrix plasticization improves mode I fracture toughness, mode II fracture toughnc.ss deteriorates due to interface degradation. The sensitivity of (Jut to water absorption has been demonstrated even for matrices that absorb very small amounts of water such as pol propy lene [168]. 

Adhesion and stability of bonding at the fibre surface is important against resistance to creep, particularly in the presence of moisture, and selection of fibre finishes should ensure compatibility with choice of the resin system to optimise against interface degradation. 

Chung and co-workers [187-191] have investigated piezoresistivity in carbon fiber composites and how the effect can be used to advantage. Piezoresistivity was observed in cement-matrix composites with 2.6-7.4 vol% unidirectional continuous carbon fibers [191]. The DC electrical resistance in the fiber direction increased upon tensile loading in the same direction, such that the effect was mostly reversible when the stress was below the level of tensile modulus reduction. The increase in resistance was due to fiber-matrix interface degradation, which was mostly reversible. Above the stress at which the modulus started to decrease, the resistance abruptly increased with stress/strain, due to fiber breakage. 

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