Papers by Keyword: Selective Dissolution

Abstract: The use of some additions as cement replacement has played an important role in the amount of clinker reduction. Due to its huge worldwide availability one of the most important and recognised replace agent is the fly ash, but is also estimated that only 30 to 40% of fly ash is used, although there are some challenges to be overcome, such as the reactive potential quantification. Chemical analysis is typically determined by the oxides content and does not take into account the vitreous and crystalline phase ratio. Therefore, this paper describes in detail one selective dissolution method, based in the hydrofluoric acid attack, to the quantification of the vitreous phase (reactive) and crystalline phases (not reactive). Fly ash from Portuguese Pego thermoelectric power plant was submitted to different attacks. To confirm the method and its effects, chemical and physical analysis were performed, such as STA, XRF, XRD with Rietveld refinement, SEM, EDS and laser diffraction granulometry. The results can be used to quantify the potential reactivity of this type of fly ash. The best results were achieved with 1% hydrofluoric acid attack during 6 hours.

Abstract: We synthesized Sr0.7La0.2[ ]0.1Bi2Ta2O9 (SBTL , [ ] vacancy), and measured their photocatalytic activity for water decomposition under UV light irradiation after acid treatment. They showed the high photocatalytic activity under UV light irradiation (H2 evolution (213μmol / h) , O2 evolution (82μmol / h)).

Abstract: It is well known that the Al-Fe system intermetallic compound particles on the aluminum and its alloys are detrimental to the corrosion for aluminum materials. Trial and error efforts reveal that Al3Fe intermetallic compound particles exposed on aluminum are preferentially and selectively removed by electrochemically treatment in cathodic current. These treatment combined by two steps: the first step is selective dissolution of aluminum component in the Al3Fe intermetallic compound by electrochemical reaction. The second step is intensive removal of the iron-enriched intermetallic particles on which vigorous hydrogen bubbling has been took place. The electrochemical measurement and surface observation show that the aluminum and its alloys with free intermetallic compound particles treated by aboves have excellent corrosion resistance in a NaCl solution. It is also found that the intermetallic compound-free surface is preferable for the pretreatment surface for the surface finishing.

Abstract: Unidirectional solidification of Al-In, Cu-Pb and Cu-Pb-Al monotectic alloys was performed under static magnetic fields up to 10T for formation of the regularly aligned-rod structure. mThe imposition of static magnetic fields exceeding 4T suppressed movement of the In liquid droplets at the Al solidifying front and enhanced the engulfment of the In droplets into the front. As a result, the eutectic-like structure was obtained in the Al-10 and 15at%In hypermonotectic alloys. The micro X-ray tomography indicated that the continuous In rods with diameters of 10-20 µm were aligned parallel to each other. In the case of the Cu-Pb and the Cu-Pb-Al alloys, the imposition of static magnetic fields also enhanced the formation of the aligned Pb rods. The electrochemical etching by using a 10% HNO3 solution successfully removed the minor phase, and the porous aluminum and copper with deep pores were fabricated.