A modified structural model describing the interference-function of pyrolized non-graphitizing carbon

A modified structural model taking into account strains within the hexagonal network was used to describe the interference function of PFA and PP. The measurements were performed using monochromatic Ag K_α-radiation. The results show that determination of the crystallite size $\text{L}\text{?}{}_{\mathrm{a}}$ can lead to serious disagreement between the calculated and real $\text{L}\text{?}{}_{\mathrm{a}}$ values if strain is not considered to modify the scattering profiles.     

Aluminium and silicon base coatings for high temperature alloys—Process development and comparison of properties

The paper is concerned with systematic studies on the formation of overlay coatings on nickel and iron base superalloys to improve their resistance against high temperature oxidation and hot corrosion. In contrast to the simpler case of aluminizing nickel base alloys, the problems arising in aluminizing iron base superalloys and in siliconizing nickel base alloys have not yet been solved.A new and economical coating procedure is presented, which involves a reaction sintering process of unalloyed powder mixtures to obtain overlay coatings. The influence of the compositions of the layer and the substrate on the chemical compatibility of the whole layer composite is described in detail. It is shown that overlay coatings containing high concentrations of silicon can only be applied on nickel base superalloys if elements that are able spontaneously to form reaction barriers are present within the substrate alloy (e.g. aluminium) or in the as-preformed interlayer. Refractory metals have proved to be the most advantageous.To obtain a ductile coating, silicon-rich donor phases in the form of isolated precipitates were incorporated into a matrix containing low concentrations of silicon. These coating systems can also be applied to improve the aluminization of iron base alloys. The high temperature oxidation and corrosion behaviours of the coated samples were tested in burner gas or air at 1000°C and in molten salts at 900°C.     

Thin coatings on carbon fibers as diffusion barriers and wetting agents in Al composites

This paper describes the preparation of CVD coatings (Ta, TiC, TiN, TiNC and SiC) on carbon fibers and the effect of the deposition parameters on the mechanical properties of the fibers. Ta does not influence the fiber strength, whereas for the other coating materials the deposition conditions must be optimized in order to retain the original fiber properties.In view of the application of such coated carbon fibers in composites, their wetting behavior with liquid aluminum as well as the behavior of the coatings as diffusion barriers were studied. The coatings are instantly wetted only at temperatures so high that a partial penetration of aluminum through the thin coatings and hence a reaction at the surface of the carbon fiber leading to the formation of aluminum carbide become inevitable. The fiber strength of high performance fibers is then considerably impaired although low strength fibers are hardly affected.Wetting by liquid aluminum below 800°C can be achieved by using additional thin nickel layers. In this way the infiltration of coated carbon fiber bundles can be realized and theoretical fiber strength yields in accordance with the rule of mixtures can be obtained. This improved wetting behavior was found not to depend on the type of coating.The barrier effect of the coatings allows heat treatments at up to 600°C for short times with high fiber strength yields. Heat treatments of the order of 100 h, however, gradually decrease the composite strength. In order to retain high fiber strength during long heat treatments at high temperatures, a minimum coating thickness of some microns is needed. The preparation of such thicker coatings is discussed in detail. With such a procedure, one can obtain reinforcing elements comparable with commercially available boron or silicon carbide monofilaments.     

Mitigation of saturation in dynamic voltage restorer connection transformers

During the transient period at the start of a voltage sag, a DVR injection transformer can experience a flux-linkage that is up to twice its nominal steady-state value. In order to prevent the transformers from saturating it is normal to choose a rating flux that is double that of the steady-state limit. An alternative method is to limit the flux-linkage during the transient switch-on period, thus preventing saturation. It is shown through both simulation and experimental results that an adaptive form factor can be applied to the DVR injected voltage, which minimizes the disturbance seen by a sensitive load, while at the same time preventing saturation. The proposed method removes the need for rating the series injection transformers for the DVR transient switch-on period, and therefore removes the redundancy normally associated with their steady state operation. In economic terms, this may reduce the total cost of a DVR system, thus making it a more attractive solution for voltage sag mitigation.