Wrocław University of Technology

About: Wrocław University of Technology is a education organization based out in Wrocław, Poland. It is known for research contribution in the topics: Laser & Computer science. The organization has 13115 authors who have published 31279 publications receiving 338694 citations.

The study of photocatalytic activities of titania and titania–silica aerogels

Abstract: Titania and titania–silica aerogels have been prepared by sol–gel method The pH of their point of zero charge (pHPZC), SBET, volumes of the micro- and mesopores were determined Considering titania–silica aerogels FTIR analyses were carried out Three phenol para-derivatives (p-chlorophenol, p-nitrophenol, 4-hydroxybenzoic acid) were chosen as model compounds in photodegradation processes All aerogels indicated photocatalytic activity However, titania aerogels were more efficient photocatalysts comparing to titania–silica aerogels The results can be explained by the percentage content of two phases (5, 10 and 20 wt% SiO2 in TiO2) The ratio of SiO2:TiO2 results in the presence of two separated phases that hinders photocatalytic processes The identified by-products of p-chlorophenol and p-nitrophenol degradation are hydroquinone, benzoquinone as well as chloride ions and nitrate ions, respectively The pHPZC of all catalysts changed between 62 and 67 Between the pHPZC and photoactivity there was no direct correlation The course of the photodegradation did not depend on surface area and pores volumes of the catalysts but on the kind of pollutant

Arc effect on single-phase reclosing time of a UHV power transmission line

Abstract: One of the important operational conditions of a single-circuit ultra-high-voltage transmission line is the power transmission by two phases during the clearance of a temporary single-phase short circuit. Such a condition may be sustained for an interval of 1 s without losing the dynamic stability of the system. The influence of the arc on the single-phase reclosing time of an ultra-high-voltage power transmission line is investigated on the basis of the primary and the secondary arc models incorporated into the transient program EMTP. The validity of the models used is proven by comparison with field test results on an actual 1150-kV power transmission line from Ekibastuz to Kokchetav in Northern Kazakhstan. The processes of this power transmission in the "dead time" of the single-phase reclosing cycle are simulated. It is shown in the paper that simplified short-circuit simulation without the incorporation of the dynamic arc model leads to erroneous results. Mathematical analysis and field experiments show that natural secondary arc extinguishing in a highly compensated 1150-kV power transmission line cannot be reached in a reasonable time (e.g., less than 1 s). It is shown in the paper that this problem can be solved by automatic phase shunting (APS) of the faulted phase.