Notranja oksidacija Cu-C in Ag-C kompozitov

The internal oxidation in copper-carbon and silver-carbon composites occurs when they are exposed to air or oxygen at high temperature. Solubility of carbon in copper or in silver is very low. The kinetics of oxidation at high temperature and activation energy were determined and the mechanism of internal oxidation was analysed. The kinetics of internal oxidation was determined for both cases and it is depended from the diffusion of oxygen following parabolic time dependence according to Wagner\u27s theory. The activation energy for Cu-C composite is 70.5 kJ/mol, and for Ag-C composite is 50.1 kJ/mol, what is in both cases close to the activation energy for the volume diffusion of oxygen in copper or in silver. In both cases gas products are formed during the internal oxidation of composites. In the internal oxidation zone pores, bubbles occur. The carbon oxidates directly with the oxygen from solid solution as long there is a contact, which breaks down with the presence of gas products. Then the oxidation occurs over the gas mixture of CO and CO2.Pri visokih temperaturah kompoziti bakra in srebra z ogljikom na zraku ali v kisiku reagirajo po mehanizmu notranje oksidacije. Topnost ogljika v trdnem bakru in trdnem srebru je zelo majhna. Analizirali smo kinetiko oksidacije kompozitov, določili aktivacijsko energijo in mehanizem notranje oksidacije. Kinetika oksidacije je pri obeh skupinah materialov odvisna od difuzije kisika in sledi parabolični odvisnosti od časa v skladu z Wagnerjevo teorijo. Aktivacijska energija procesa je za kompozit Cu-C enaka 70,5 kJ/mol, za kompozit Ag-C pa 50,1 kJ/mol, kar je blizu aktivacijski energiji za volumsko difuzijo kisika v trdnem bakru oziroma srebru. Pri oksidaciji kompozita nastajajo plinski produkti. Oksidacija ogljika poteka neposredno s kisikom iz trdne raztopine, ko pa se zaradi nastanka plinske faze stik prekine, pa preko plinske zmesi CO in CO2

Simulation of wastewater treatment processes and possible idea solution for upgrading WWTP Škofja Loka

In addition to building new treatment plants in recent years there is also increasingly taking place the upgrading of existing wastewater treatment plants. Need to upgrade is in larger extent because of failing to complie with effluent nutrient limits for parameters, such as nitrogen and phosphorus. One of the sewage facilities where upgrade of the processes for removal of nutrients has not yet been made is the Central Wastewater Treatment Plant Škofja Loka. This thesis has made preliminary studies of upgrade of WWTP Šk. L. by the simulation with a computer program Aquifas. The models are sets of mathematical equations that characterize the process and enable the simulation process. Activated sludge models (ASM) are being presented, of which ASM2d is a part of Aquifas application. As part of identifying possible solution for upgrading an overview of processes and technologies for the removal of nutrients has been done, and among them, as appropriate outline of possible solutions, the A2O process has been selected that I have regarding to the inflow of different parameters to the treatment plant tried to optimize with the program. The results for the effluent obtained from so conceived process and after optimization of various parameters are under regulatory limits. The thesis also presents important issues that need to be considered in upgrading existing facilities, including general selection factors, design and operation factors and the final selection of appropriate technology.\ud \u

Impact of friction stir welding parameters of highstrength aluminum alloys on residual stresses and corrosion resistance

V letalski industriji so aluminijeve zlitine pogosto v uporabi, predvsem zaradi ugodnega razmerja med trdnostjo in maso. Varjenje s trenjem in mešanjem (angl. Friction Stir Welding – FSW) oz. varjenje z gnetenjem počasi izpodriva klasično kovično spajanje zaradi boljših mehanskih lastnosti spojev, odprave zareznih učinkov ter lažje izvedbe. Vendar pa ima ta način spajanja tudi neugodne lastnosti. Med samim varjenjem se generira toplota, kar privede do sprememb v mikrostrukturi ter vnos nateznih in zaostalih napetosti, kar se odraža tudi v slabši korozijski odpornosti. V diplomski nalogi smo analizirali elektrokemične korozijske lastnosti in zaostale napetosti visoko-trdnostnih Al zlitin serije 2017A-T451 in 7075-T651, spojenih z FSW varjenjem, ob uporabi različnih varilnih parametrov. Iz vidika analize učinkov varjenja smo izmerili zaostale napetosti tako v osnovnih materialih kot tudi v samem zvarnem spoju. Meritev smo opravili trikrat, in sicer pred ter po odrezu z abrazivnim vodnim curkom in po izvedenih elektrokemijskih meritvah. S tem smo neposredno preučili vpliv različnih postopkov. Za analizo korozijske odpornosti smo uporabili različne elektrokemijske metode v agresivnem kloridnem okolju. Ugotovili smo, da se ob uporabi višjega razmerja obratov na podajanje (ONP) orodja med procesom varjenja generirajo manjše natezne zaostale napetosti v zvarnem spoju. Hkrati smo z elektrokemijskimi metodami potrdili najboljšo korozijsko odpornost zvarnega spoja v neposredni coni mešanja, kjer nastopa mikrostruktura z izredno finimi, enako-osnimi kristalnimi zrni. Meritve potenciala odprtega tokokroga so potrdile najplemenitejši korozijski potencial pri zlitini 2017A-T451, pri čemer pa FSW zvarni spoj izkazuje najboljšo korozijsko odpornost z najvišjo polarizacijsko upornostjo in možnostjo pasivacije ter repasivacije.In the aviation industry, aluminium alloys are often used, mainly because of their favorable strength to mass ratio. Friction stir welding (FSW) is slowly replacing classic rivet joining, because of better mechanical properties of joints, elimination of notching effect and easier construction. However, this joining also has some disadvantages. During the welding process, heat is generated, which leads to changes in the microstructure and the introduction of tensile residual stresses, which is also reflected in the lower corrosion resistance. In the thesis we analyzed electrochemical corrosion properties and residual stresses of high strength Al alloys series 2017A-T451 and 7075-T651 coupled with FSW welding using different welding parameters. From the point of view of the analyses of the effects of welding, residual stresses in the base materials and in the weld joint were measured. The measurement was performed three times, i.e. before and after the abrasive water jet cut and after electrochemical measurements. This enabled the full insight of the effect of the specific procedure. Various electrochemical methods have been used for corrosion resistance analysis in an aggressive chloride environment. It has been found that smaller tensile residual stresses in the weld are generated during the welding process using higher rotaion per feed (RPF) ratio. At the same time, the electro-chemical methods confirmed the best corrosion resistance of the weld joint, in the mixing zone with extremely fine, equiaxed grains. Open circuit potential measurements have confirmed the noblest corrosion potential with 2017A-T451 alloy, whereas the specimen taken from the FSW weld exhibited the best corrosion resistance with the highest polarization resistance and passivation and repassivation ability

Comparison of the simulation tools WEST and GPS-X in the case of MBBR reactor

The aim of this work was to evaluate two simulation tools, WEST and GPS-X, by setting a model of MBBR reactor. The evaluation was based on an existing simulations with a model constructed in GPS-X. Within this work, the same simulations were reconstructed by setting a model in WEST. To this end, the data from Central Wastewater Treatment Plant Domžale- Kamnik was used, where the laboratory pilot plant was operating from October 2005 to May 2006. The pilot MBBR was filled with K1 biocarriers, produced by AnoxKaldnes. Using artificial wastewater, good conditions for autotrophic biomass growth were achieved. A mathematical model of the MBBR reactor was built in WEST, which includes typical biochemical processes of wastewater treatment as well as the transport processes of the substrate from the bulk liquid into the biofilm. Using the model we performed three different simulations in WEST. For the first one, the same values of the parameters were used as those in GPS-X, which produced a simulation that differed significantly compared to the simulation obtained with GPS-X. After running the sensitivity analysis, we calibrated some parameters and achieved better (second) simulation, fitting well the simulation, obtained by GPS-X. The aim of the third simulation was verification of the WEST default parameter values. Slight modification of those parameters was needed in order to achieve good fit to the measured values on the pilot plant. Final result of this work is the comparison of the MBBR models applied in GPS-X and WEST\ud and of the parameter values used in both tools. Apart from some conceptual differences of the\ud two models, we also point to the differences in the computational times and to the numerical\ud stability of the simulation tools

Sestava in morfologija diboridov v zlitinah Al-Ti-B po žarjenju na 1873 K

In the investigation, Al-Ti-B alloys with different Ti/B ratios were annealed at 1873 K for 10 hours. Under this condition diboride particles were in contact with molten aluminium. During annealing considerable growth of remaining unmelted diboride particles took place. The composition of diboride particles shifted extremely close to the composition of pure TiB2 regardless of the Ti/B ratios in the alloys, indicating that in equilibrium almost pure TiB2 coexisted with a melt. Diboride particles were bound with well-defined crystal facets. Types and relative size of the facets depended on the Ti/B ratio. It is strongly indicated that an excess of Ti (B) in the melt over that needed to form TiB2 stabilizes crystal planes having planar arrangement of Ti (B) atoms.V tej raziskavi smo več zlitin Al-Ti-B, ki so imele različna razmerja Ti/B, žarili 10 ur pri 1873 K. V teh razmerah so bili delci diborida v kontaktu z aluminijevo talino. Med žarjenjem so diboridni delci močno zrasli. Njihova sestava se je v vseh raziskanih zlitinah močno približala sestavi čistega TiB2, kar kaže, da je v termodinamskem ravnotežju s talino praktično čisti TiB2. Diboridni delci so bili obdani s kristalnimi fasetami. Vrsta in relativna velikost faset je bila močno odvisna od razmerja Ti/B. Obstajajo trdni dokazi, da presežek Ti (B) nad vrednostjo, ki je potrebna za tvorbo TiB2, stabilizira kristalne ravnine, ki imajo ravninsko razporeditev Ti (B) atomov

The occurrences of nitrates and pesticides in the Water Supply System in Murska Sobota

Water supply systems in the past greatly influenced on the development of the society in various lands. However, today the water supply system represents an irreplaceable way of drinking water supply. This thesis presents the operation of the water system in Murska Sobota. It describes the facilities and equipment that ensure uninterrupted supply with drinking water in the municipalities of: Murska Sobbota, Moravske Toplice, Puconci and Cankova.Because this part of Pomurje is dominated by intensive farming, there are some problems with the supply of drinking water regarding to the presence of nitrates and pesticides. I gathered data from the archive and displayed them in transparent tables to determine the actual state of pollution of groundwater pumping stations and water supply\ud system. The data shows that the water in the system is clean. Some problems are occurring in the water supply station Črnska meja for which I have made several proposals for reduction of pollution. Before entering the water system the water mixes from all of water supply stations, thus ensuring adequate quality and quantity of drinking water in the system. Current state of the system is the result of good work in the past. Due to that it is necessary to continue to strive that in the future there will also be no difficulties in providing sufficient quantities of safe drinking water

Influence of the catchment area and management of the lake to the eutrophic and succession processes in the lake ecosystem - the case of fish ponds in the Draga Valley in the vicinity of Ig

Cycle of matter in lake ecosystems and the influence of loading with nutritional substances on eutrophic process are presented in the Graduation Thesis; abiotic factors are discussed, the role of planktonic and macrophyte vegetations and interactions that occur among them are described. In particular, the Thesis describes characteristics of eutrophication, ways of preventing it from appearing, especially bio-manipulation as a way of changing of biomass on higher trophic levels that by regulating the proportion between zooplankton and phytoplankton enables submerged macrophytes and leads to cleaner water. In connection with eutrophic process, land use in hydrographic hinterland, and the way of management, rules of succession process and its course dynamics in the lake ecosystems are presented. As well described is the influence of morphological characteristics of the lake to distribution of macrophyte vegetation and silting up. In the second part the existing conditions, management and problems in ponds in the Draga Valley near Ig are treated. In order to obtain a better insight into the condition of ponds, measurements of basic physical-chemical parameters with the Hydrolab Datasonder 4 probe were performed. Also, measurements of transparency with the Secchi Disc were carried out. Taking into account the results of the measurement, analysing of the existing condition of ponds and conditions for prospering of various biological communities, the regulation plan proposal is represented, whose basic purpose is improvement of the condition and renovation of the deserted ponds. Also given are basing points and directives for the management of ponds

Rail, key element in the railway superstructure

A rail is an important and the most heavily laden element in the railway superstructure, because it\ud functions as both the running surface used for vehicle guidance and the beam directly transmitting the\ud load of the vehicles to the ballast bed and the railway substructure. The first part of the thesis describes\ud the characteristics of rails and provides a theoretical background relating to rail stresses resulting from\ud traffic load, temperature change and production procedures.\ud When rail vehicles move, enormous contact stresses are produced in the contact zone between the\ud wheel and the rail, which often causes damage to the running surface. Curves with smaller diameters\ud cause particular wear of the rails because of the strongest dynamic effects of the vehicle on the rail.\ud The thesis thus presents the most common surface defects, defines rail wear and outlines currently\ud available techniques of rail grinding and lubrication.\ud In the last few decades, only continuous welded tracks have been consistently installed. To this end,\ud the second chapter describes the procedures and conditions for the construction and welding of rails\ud into continuous welded tracks as provided for in the Rules on railway line superstructure published in\ud the Official Gazette of the Republic of Slovenia, No. 92/2010. As for rail welding, special emphasis is\ud given to aluminothermic welding which is one of the most established procedures for rail welding on\ud the ground

Natural and anthropogenic impacts on hydrosphere in the range of Šmarješke Toplice

My thesis is divided into two main parts. The first part is focused on the properties of\ud phosphorous and nitrogen that are most important in the eutrophication process, while the second part\ud of the thesis presents the specifics of the water basin Jezero in Smarjeske Toplice.\ud The first part of the thesis describes the problem of pollution with nutrients in the aquatic environment\ud - eutrophication. Eutrophication is caused by excessive nutrient concentrations in the aquatic\ud environment, which is limited by the lack of one of the two presented nutrients in this thesis. The\ud thesis is focused on two nutrients, namely phosphorus and nitrogen.\ud The thesis presents the basic properties for phosphorus and nitrogen and the circulation of these two\ud nutrients in the environment. It also lists and describes the main anthropogenic activities, which\ud contribute the largest share of these nutrients into the environment.\ud In its next chapters the thesis presents the chemical and biological processes, removal of phosphorus\ud and nitrogen, and some common technologies developed for the purpose of disposing these two\ud nutrients from water. Then it presents some assumptions and actions for reducing the impact of these\ud two nutrients on the environment in the future. The first part of the thesis is concluded with the use of\ud nutrients in Slovenian agriculture in order to improve the productivity of its agricultural land.\ud The second part of the thesis delivers a presentation of the largest water basin in the Dolenjska region\ud – water basin Jezero in Šmarješke Toplice. It describes the legislation, regarding water resources on\ud the European, state and municipal level. It also presents the ways of determining water protection\ud areas, their different variations and its limits and restrictions. There is also a calculation of nutrient\ud concentration in the underground waters in this specific area. The final part of the thesis is a product of\ud collaboration with Komunala Novo mesto. It presents their plans for improving quantitative and\ud qualitative properties of the water that is pumped from the water basin Jezero