Morphological and microchemical phenomena in the high-temperature oxidation of binary Al-Li alloys

The high-temperature oxidation behavior of binary Al-Li alloys has been characterized by scanning electron microscopy and secondary ion mass spectrometry in order to understand the mechanism of rapid oxidation in these alloys and to correlate the oxide morphology to its microchemistry. The oxide scale developed on polished specimens during short exposures in air at 530°C shows characteristic nodules that usually nucleate at grain boundaries. Examination of the alloy surface after removal of the oxide layer shows that the initial growth of the oxide nodules occurs laterally in addition to thickening normal to the oxide/alloy interface. Microchemical analysis of the oxide film with a scanning ion microprobe reveals a thick Li-oxide layer at the oxide/gas interface indicating preferential oxidation of Li at the free surface; the rest of the oxide film is composed of both Al- and Li-rich oxides, probably Li₂O and LiAlO₂ The presence of trace impurities (K, Na, F, and Cl) in the oxide scale was also detected. A microstructural model for the development of the oxide film in the Al-Li system is presented on the basis of both morphological and microanalytical data obtained in this study; this new model is compared with existing models.     

Microstructure and Hydrogen-Induced Failure Mechanisms in Fe and Ni Alloy Weldments

The microstructure and fracture morphology of AISI 8630-IN625 and ASTM A182-F22-IN625 dissimilar metal weld interfaces were compared and contrasted as a function of postweld heat treatment (PWHT) duration. For both systems, the microstructure along the weld interface consisted of a coarse grain heat-affected zone in the Fe-base metal followed by discontinuous martensitic partially mixed zones and a continuous partially mixed zone on the Ni side of the fusion line. Within the partially mixed zone on the Ni side, there exists a 200-nm-wide transition zone within a 20-??m-wide planar solidification region followed by a cellular dendritic region with Nb-Mo?Crich carbides decorating the dendrite boundaries. Although there were differences in the volume of the partially mixed zones, the major difference in the metal weld interfaces was the presence of M₇C₃ precipitates in the planar solidification region, which had formed in AISI 8630-IN625 but not in ASTM A182-F22-IN625. These precipitates make the weldment more susceptible to hydrogen embrittlement and provide a low energy fracture path between the discontinuous partially mixed zones.     

Power line carrier systems for industrial control applications

This paper addresses the potential applications of power-line-carrier (PLC) communications technology within the field of industrial plant/equipment control. The special needs and requirements for this application (in terms of such factors as system integrity and response times) are considered in comparison with those for other types of PLC application. Existing PLC technologies are discussed and their suitability (or otherwise) for this application considered     

Development for the electric utilities networks towards thenational information infrastructure

With an increasing competitive environment, electric utility companies face a window of both necessity and opportunity. The necessity to investigate and assess the information and telecommunications capabilities they will need to be competitive in their main operations, and the opportunity to consider new sources of revenue that such capabilities may make possible. Irrespective of approach a utility takes to integrating its main activities with the emerging information superhighway, only a confluence of energy and information technologies can meet the national challenge of efficiently managing energy demand, supply and transmission. Utilities will be driven to become more competitive in deploying both supply-side and demand side energy information services in order to control access to the customer and prevent erosion of their customer base. However at the same time, utilities have the potential to become significant players in the communications field especially towards the superhighway by providing nonenergy value added services through telecommunications infrastructures. Structuring a telecommunications architecture and strategy for a particular utility is difficult because it involves many interconnected technological, economic, competitive and financial considerations. This considers these key points including telecommunications networks, supply side information services and energy information services. The changes in architecture and technologies of communications systems leading to new services plus additional attributes to current services is covered     

Compositional changes in

The compositional changes in Al-Li-(Mg)-(Cu) alloys induced by oxidation at high temperature (450 °C to 570 °C) were investigated by secondary ion mass spectrometry (SIMS). It was found that the alloy surface beneath the oxide layer was depleted in both Li and Mg as a consequence of the selective oxidation of these elements, whereas Cu concentration was nearly constant or slightly increased in the affected zone. The measured-concentration profiles of Li and Mg were modeled using a diffusion equation to obtain diffusion data for the alloys. The depletion profiles also provided information regarding the interfacial-alloy composition and the depletion depth. The effect of alloying elements on the oxidation and depletion behavior is discussed. Secondary ion mass spectrometry data were quantified using the relative sensitivity factor method, and the quantification procedure is described in detail.     

An electron microprobe study of a mature cement paste

A portland cement paste 23 years old, and essentially fully hydrated, was studied by electron probe microanalysis. X-ray images indicated that the shapes of the original, largely polymineralic cement grains, and those of the regions occupied by the individual phases within them, are substantially preserved in the hydrated material. This was shown especially clearly by the Mg and Fe images, probably because these elements do not readily migrate in the alkaline medium. Estimation of individual phase compositions is rendered uncertain because of possible admixture of phases on or below a micrometer scale, but the atomic ratios relative to Ca are, approximately: Mg 0.03, Al 0.08, Si 0.60, S 0.03 and Fe 0.015 (Ca:Si 1.67) for the C-S-H, and Al 0.40, Si 0.33 and Fe 0.27 for the hydrogarnet.