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Modelling and parameter comparison of equivalent circuits on the basis of impedance measurements of stainless steels
Mojca Slemnik, 2006, izvirni znanstveni članek

Opis: In our former work [1] we have discussed the impedance of differently heat treated steels X20Cr13 in 0.1 M H2SO4, undergoing an active passive transition. Impedance spectra were interpreted in terms of a model by Armstrong [2, 3], describing the electrochemical reaction at interfaces with adsorbed intermediates. The present work was performed in order to study this phenomenon in more detail, with computer simulations of a new created and more convenient equivalent circuit in comparison with the former model. Computer simulations of equivalent circuits were also made in the region of passivity which was also continuation of our earlier work [4]. In this sense the entire study for these steels was completed by collating distinctive parameter values, demonstrating electrochemical characteristics of steel X20Cr13, undergoing different heat treatments in the active-passive and passive region.
Ključne besede: electrochemical impedance spectroscopy, equivalent circuits, stainless steel, heat treatment of steel
Objavljeno: 30.05.2012; Ogledov: 1049; Prenosov: 21
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The influence of thread twist on alterations in fibers` mechanucl properties
Andreja Rudolf, Jelka Geršak, 2006, izvirni znanstveni članek

Opis: In order to design high-quality threads, it is necessary to know the properties of threads and fibers, as well as the loadings and deformations which may occur during the sewing process. Thread properties depend on the mechanical properties of the fiber and the constructional parameters of the thread and its surface treatment, which directly influence sewing performance.The mechanical properties of a thread primarily depend on the fiber mechanical properties and the amount of twist. Knowledge of the thread dynamic loadings during the sewing process, depending on the number of turns and the lubrication method, is important for planning the required processing properties of the thread. This paper presents research into the influence of thread twist and the lubrication method on the mechanical properties and dynamic load of PES core-spun thread and its fibers. Research into the mechanical properties of the different twisted and surface treated threads, and separated fibers was carried out for this purpose. The influence of threaddynamic load during a sewing process was also researched regarding any alterations in the mechanical properties of the threads and separated fibers. Analyses of the results show that the amount of twist depends on the mechanical properties of the thread and its constituent fibers, whilst the method of surface treatment is based on the specific mechanical properties of the thread. A dynamic load causes greater or smaller thread deformations, which is reflected in changes in the thread and fiber mechanical properties. The occurred changes depend on dynamic load, amount of twist, and the lubrication method, which is confirmed with statistical analysis of the measured results.
Ključne besede: garment manufacturing, sewing, threads, textile fibres, surface treatment, dynamic loads, mechanical properties, amount of twist
Objavljeno: 30.05.2012; Ogledov: 1447; Prenosov: 17
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Methodology for determination of anaerobic digestion kinetics using a bench top digester
Marko Tramšek, Andreja Goršek, Peter Glavič, 2007, izvirni znanstveni članek

Opis: This paper presents a methodology for determining the microbial growth kinetics of an ideal anaerobic process in a non-ideal laboratory anaerobic digester (Armfield). Some laboratory experiments were performed, to confirm the proposed methodology. Having the same zero biomass concentration, some process parameters were changed and their influence on substrate outlet concentration was monitored. The specific growth rate of the biomass, the saturation constant of the substrate, and the yield coefficient were calculated, on the basis of the measured values. These parameters enabled us to perform a dynamic simulation of an anaerobic process in ideal continuously-stirred tank reactors (CSTR). The results represented the mass concentration profiles for substrate and biomass, from which the time required for reaching the steady state (60 d), where the operation is optimal, could be determined. The laboratory anaerobic digester provided operational process data, which are applicable for wastewater treatment plant design purposes.
Ključne besede: wastewater treatment, anaerobic digester, kinetics, dynamic simulation
Objavljeno: 31.05.2012; Ogledov: 1278; Prenosov: 40
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Magnetic water treatment for scale control in heating and alkaline conditions
Viljem Kozic, Anton Hamler, Irena Ban, Lucija Črepinšek-Lipuš, 2010, izvirni znanstveni članek

Opis: Magnetic water treatment (MWT), an alternative solution for scale control, is discussed with emphasis on the construction of the magnetic devices and the mechanism of MWT influence on the scale formation. Two applications in high-temperature and high-pH conditions are presented. The treatment noticeably reduced the scale thickness on the heating spiral and removed preciously precipitated scale from hot tap-water outlet pipe; on the walls in the zone with heated alkaline water, instead of hard scale, only thin, brittle coating was formed. The morphology analyses showed the acceleration of aragonite nucleation and raised formation of fine suspended particles.
Ključne besede: scale control, magnetic sater treatment, crystallization
Objavljeno: 31.05.2012; Ogledov: 1354; Prenosov: 50
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Removal efficiency of COD, total P and total N components from municipal wastewater using hollow-fibre MBR
Irena Petrinić, Mirjana Čurlin, Jasmina Korenak, Marjana Simonič, 2011, strokovni članek

Opis: The membrane bioreactor (MBR) integrates well within the conventionally activated sludge system regarding advanced membrane separation for wastewater treatment. Over the last decade, a number of MBR systems have been constructed worldwide and this system is now accepted as a technology of choice for wastewater treatment especially for municipal wastewater. The aim of this work was to investigate and compare submerged MBR with conventionally-activated sludge system for the treatment of municipal wastewater in Maribor, Slovenia. It can be concluded from the results, that the efficiencies being determined by the parameters were satisfied, such as, chemical oxygen demand, total phosphorous, and total nitrogen, which were 97%,75%, and 90%, respectively. The efficiencies of ultrafiltration membrane for the same parameters were also determined, and compared with biological treatment. The results of this analysis show an additional effect regarding an improvement in the quality of the permeate but primary treatment is also very important. For successfully application of MBR system smaller grid for primary treatment is needed.
Ključne besede: municipal wastewater treatment, membrane bioreactor, membrane filtration, biological treatment
Objavljeno: 01.06.2012; Ogledov: 1088; Prenosov: 42
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The interaction ability of cellulosic materials as a function of fine structure and Helmholtz surface energy
Tatjana Kreže, Karin Stana-Kleinschek, Volker Ribitsch, Zdenka Peršin, Majda Sfiligoj-Smole, 2005, izvirni znanstveni članek

Opis: Many chemical or physical modification processes significantly influence the accessibility of fiber forming polymers by causing structural changes. The wettability and sorption ability improvements of polymeric materials are major tasks during finishing processes. Different pre-treatment processes are used in order to improve the accessibility of dissociable groups, hydrophilicity, dyeability, and whiteness. These are usually alkaline purification, chemical bleaching and mercerization. In a previous paper we presented the data for structural characteristics (density, crystallinity index, molecular orientation, void volume, diameter and the specific inner surface of void, etc.) of untreated regenerated cellulose fibers (viscose, modal and lyocell) [41]. We now compare the influence of different pre-treatment processes on fiber structure and the accessibility of the chemical groups of these fibers. In order to improve the accessibility, two pre-treatment processes were used: chemical bleaching of fibers and tensionless alkali treatment. The influence of these pre-treatment processes on the structure parameters was evaluated using viscosity measurements (determination of polymerization degree (DIN 54 270)) and iodine sorption ability measurements according to the Schwertassek method (determination of crystallinity index) [13, 16]. The reactivity and accessibility in a polar environment was determined using tensiometry. Contact angles between the fibers and liquids of different polarities were determined using the powder contact angle method and calculated from a modified Washburn equation [26, 28]. The surface free (Helmholtz) energy of differently treated fibers was determined from the contact angle data using the Owens-Wendt-Raeble-Kaelble approximation [30, 33, 35]. The differences in the accessibility of raw and pre-treated regenerated cellulose fibers obtained using tensiometry are compared with the results of the conventional method used to determine moisture adsorption (DIN 54 351, DIN 53 802). In regard to raw fibers, viscose shows the most hydrophilic characteristic: adsorbs the highest amount of moisture, has the fastest penetration velocities (Fig. 6), the smallest contact angle, and the highest SFE (Fig. 8). Modal fibers have the largest contact angle, the lowest SFE, and they adsorb the smallest amount of water vapor. Pre-treatments increase the sorption ability and the surface free (Helmholtz) energy while they decrease the contact angle. This makes the material more accessible to water and chemicals used in the finishing processes although the crystallinity index increases. The main modification in polymer properties caused by the treatments is an increase in the fiber SFE caused by an increase of the fiber surfaces because of swelling in the alkaline medium (washing, slack-mercerization), and due to an increase of accessible OH- and COOH-groups (bleaching). This enables the formation of an increased number of hydrogen bridges between the water molecules and the OH- and COOH-groups. Our investigations confirm the results published earlier thatthe main property necessary for the proper sorption behavior of cellulose materials are the accessible, less ordered regions and not the degree of crystallinity.
Ključne besede: regenerated cellulose fibers, fiber pre-treatment, iodine sorption, cristallinity, tensiometry, contact angle, Helmholtz surface energy, water adsorption
Objavljeno: 01.06.2012; Ogledov: 1572; Prenosov: 19
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Removal of vat and disperse dyes from residual pad liquors
Vera Golob, Alenka Ojstršek, 2005, izvirni znanstveni članek

Opis: The efficiency of three wastewater treatment techniques, coagulation/flocculation, adsorption and ultrafiltration, has been studied for the removal of vat and disperse dyes from residual pad liquors. Three inorganic coagulants Al2(SO4)3 18H2O, FeSO4 7H2O, FeCl3 6H2O and commercial cationic flocculant, as individuals and in combination, were tested for the coagulation/flocculation methods. Granular activated carbon was used as an adsorbent in the adsorption technique. Ultrafiltration was performed using a polyethersulfone membrane with a molecular weight cut-off of 10 kDa. Dye removal was evaluated as the difference between concentrations of dyes in pad liquors before and after a particular treatment using absorbance measurements.The obtained results indicated over 90% of dye removal using appropriate coagulants and only 40% using activated carbon. The best results, dye removal over 98%, were achieved using the ultrafiltration technique.
Ključne besede: textile dyeing, disperse dyes, wastewater, decoloration, wastewater treatment, coagulation, flocculation, adsorption, ultrafiltration, vat dyes
Objavljeno: 01.06.2012; Ogledov: 1199; Prenosov: 32
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Wastewater treatment after reactive printing
Sonja Šostar-Turk, Marjana Simonič, Irena Petrinić, 2005, izvirni znanstveni članek

Opis: Membrane filtration of wastewater after textile printing with reactive dyes isdescribed. The wastewater from a Slovenian factory, whose output is approx. 80% reactive dyes printed and dyed on cotton, was studied. In particular, the presence of urea, sodium alginate, oxidation agent and reactive dyes, used forthe printing paste preparation, in the wastewater was studied. Chemical analyses of actual, non-purified, wastewater showed that many Slovenian regulations were exceeded. The study of membrane filtration is based on a pilot wastewater treatment plantČ ultrafiltration (UF) and reverse osmosis (RO) units. The quality of the wastewater was improved by ultrafiltration, butits effluent still does not conform to the specification of concentration limits for emission into water. Permeate coming from RO meets the required specification and, therefore, could be re-used in the washing process of printed textiles.
Ključne besede: textile printing, reactive dyes, wastewater treatment, membrane filtration, pilot plant
Objavljeno: 01.06.2012; Ogledov: 1519; Prenosov: 25
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Efficiency of the coagulation/flocculation method for the treatment of dyebath effluents
Vera Golob, Aleksandra Vinder, Marjana Simonič, 2005, izvirni znanstveni članek

Opis: Textile dyeing processes are among the most environment-unfriendly industrial processes, because they produce coloured wastewaters that are heavily polluted with dyes, textile auxiliaries and chemicals. The coagulation/flocculation method was studied as a wastewater treatment technique for the decolourization of residual dyebath effluents after dyeing cotton/polyamide blends using reactive and acid dyes. It was discovered that acombination of aluminium sulphate and a cationic organic flocculant yields an effective treatment for residual dyebath wastewaters since almost complete decolourization was achieved, TOC, COD, AOX, BOD and the anionic surfactants were reduced and the biodegradability was increased.
Ključne besede: textile industry, reactive dyes, acid dyes, wastewater, čiščenje odpadnih vodwastewater treatment, flocculation, coagulation, ecological analyses, wastewater decoloration, Jar-tests
Objavljeno: 01.06.2012; Ogledov: 1265; Prenosov: 26
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