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Biološka denitrifikacija
No full textUbrzani napredak industrije, poljoprivrede i domaćinstva su pogodovali povišenim koncentracijama dušika u vodenom ekosustavu, što uzrokuje
eutrofikaciju. Dušik se iz otpadne vode uklanja procesom biološke denitrifikacije. U ovom preglednom radu dan je osvrt na denitrifikaciju, s aspekta
mikroorganizama, koncentracije otopljenog kisika, donora i akceptora elektrona
Microstructure and microhardness of Cu-Al-Mn-Zr alloys before and after heat treatment
No full textIn this work preliminary results of the heat treatment effect on microstructure and microhardness of Cu-8.5Al-10Mn-(0.25-1.00)Zr alloys were presented. Ingots (8 mm in diameter and 15 mm in length) were produced by melting and casting process. Production of investigated alloys was performed in laboratory electric arc furnace. Melting was carried out using the heat produced by electric arc and by a water-cooled, specially constructed copper anode that also served as a casting mould. The samples were analysed in as-cast state and after heat treatment at 900 °C/15 min/water. Microstructural analysis was performed by optical microscopy (OM), scanning electron microscopy (SEM) equipped by device for energy dispersive spectroscopy (EDS). Preliminary optical microscopy analysis of investigated alloys confirmed that microstructure was consisted of martensite only in Cu-8.5Al-10Mn-0.25Zr alloy in as-cast and heat treated state. SEM analysis show the start of martensite formation in some places at all investigated alloys in both, as-cast and heat treated state. A microhardness measurement was performed by Vickers method. Microhardness values of Cu-8.5Al-10Mn-(0.25-1.00)Zr alloys were up to 215.8 HV1 after casting and up to 224.5 HV1 after heat treatment
The effect of annealing time on microstructure and impact energy of stainless steel AISI 316L
No full textIn this work the results of microstructural analysis and impact energy testing of austenitic stainless steel AISI 316L were carried out. Investigations were performed before and after annealing at 850 °C. Annealing time in this investigation varied from 30 to 90 minutes. After annealing, the samples were cooled in room temperature air. Microstructural analysis of initial rolled and different annealed states was performed by optical microscopy (OM) and scanning electron microscopy (SEM) equipped with device for energy dispersive spectroscopy (EDS). Impact tests were performed on Charpy V-notch specimens at room temperature. Initial rolled state of investigated steel showed the presence of typical elongated polygonal grains austenite and delta ferrite while annealed states showed the presence and evolution of sigma phase in microstructure. Impact energy value of initial rolled state was 260 J and by increasing annealing time it decreases
Influence of the return material on the AlSi9Cu3(Fe) alloy properties
No full textStandardna AlSi9Cu3(Fe)aluminijska legura najčešće se koristi za proizvodnju odljevaka tehnologijom visokotlačnog lijevanja, a primjenjuje se u automobilskoj industriji za izradu nosača motora, kućišta mjenjača, kućišta generatora, kućišta turbopunjača itd. Prednosti AlSi9Cu3(Fe) legure su relativno visoka mehanička svojstva, čvrstoća i tvrdoća uz nešto nižu otpornost na istezanje i koroziju. Na razvoj mikrostrukture i mehanička svojstva legure pored kemijskog sastava, tehnološke obrade taline, procesa lijevanja te mogućnosti toplinske obrade, značajno utječe sastav uložnog materijala. Porast udjela povratnog uložnog materijala utjecat će na razvoj mikrostrukture tijekom skrućivanja te uzrokovati smanjenje mehaničkih svojstava konačnog proizvoda.
Cilj ovog rada je usporediti mehanička svojstva uzoraka AlSi9Cu3(Fe) legure neposredno nakon te 4 i 80 tjedana nakon lijevanja proizvedenih uz primjenu 100% povratnog uložnog materijala. Metalografska ispitivanja pokazala su da mikrostruktura ne odstupa značajno od uobičajene prakse primjenom 50% i 100% povratnog uložnog materijala. Uočeni su sljedeći mikrostrukturni konstituenti: dendritna mreža primarnog αAl, eutektik (αAl + βSi), primarni βSi, β – Al5FeSi u obliku iglica, α – Al15(Mn,Fe)3Si2 u poligonalnom obliku i obliku kineskog pisma, te Al2Cu nepravilnog oblika izlučen u interdendritnom području. Mehanička ispitivanja pokazala su odstupanje granice razvlačenja od zahtijevanih vrijednosti odmah i 4 tjedna nakon lijevanja unatoč istim mikrostrukturnim konstituentima. Nakon 80 tjedana uočava se učinak prirodnog starenja koje doprinosi porastu granice razvlačenja te slijedom navedenog zadovoljavanje zahtjeva norme EN 1706.The standard AlSi9Cu3(Fe) aluminium alloy is mostly used for the production of the castings with the use of high-pressure casting. It is used in the car industry for manufacturing engine block carriers, gearbox housings, generator housings, turbocharger housings, etc.The AlSi9Cu3(Fe) alloys are characterized by relatively high mechanical properties, strength, and hardness, with slightly lower resistance to strain and corrosion. Besides chemical composition, melt treatment and the possibility of various heat treatments, the microstructure and mechanical properties of the alloy are significantly influenced by the composition of the return material.The development of microstructure is influenced by the increase of the returnable material in the melt during solidification and it can decrease mechanical properties of the final product.
The aim of this research is to compare the mechanical properties is the comparison of the mechanical properties of the AlSi9Cu3(Fe) alloy immediately after,4 and 80 weeks after casting obtained with the application of 100 % returnable material. The metallographic testing showed that the microstructure of such alloy does not deviate significantly from usual practice obtained by using 50% or 80% of returnable material. Following microstructural constituents wereidentified: dendritic network of primary αAl, eutectic (αAl + βSi),primary βSi,needle-shaped β – Al5FeSi, α – Al15(Mn,Fe)3Si2 in polygonal shape and in the shape of Chinese scriptalong with irregularly shaped Al2Cu precipitated the interdendriticareas. Mechanical testing showed deviation of the yield strength from required values immediately after casting and 4 weeks after casting despite the same microstructure constituents. After 80 weeks, the effect of natural ageing led to the increase in yield strength and achievement of satisfactory mechanical properties in accordance with EN 1706 standard
Characterization of welded duplex stainless steel after annealing
No full textIn this work microstructure analysis and microhardness testing was carried out on duplex stainless steel X2CrNiMoN22-5-3 after welding and annealing. Investigated stainless steel was welded using two welding procedures. The root of weld join was performed with TIG process and for filling SMAW process was used. Analysis of microstructure and microhardness was carried out before and after annealing. Annealing of welded joint was performed at temperature of 850 °C in duration for 60 minutes followed by cooling in air. After annealing, the samples were metallographic prepared. Optical microscopy and scanning electron microscopy with energy dispersive spectrometer were used for characterization of microstructure. Results shows that before annealing microstructure was consisted of ferrite and austenite, and after annealing presence of sigma phase was determined in weld metal. Microhardness values of samples before and after annealing was determined by Vickers method. A significant increase in microhardness values was observed in weld metal after annealing (from 294.9 HV1 to 357.0 HV1)
Biodegradation of materials base on thermoplastic strach by composting process
No full textPrekomjerna uporaba polimernih ambalažnih materijala dovela je do prevelike zasićenosti planeta ambalažnim otpadom te velike potrebe za pronalaskom zamjenskog biorazgradivog polimernog materijala koji bi mogao zadovoljiti potrošačku kao i ekološku svrhu.
Upravo u ovom radom ispitana je mogućnost biorazgradnje polimernih mješavina polietilena niske gustoće (PE-LD) i termoplastičnog škroba (TPS) procesom kompostiranja. Tijekom procesa kompostiranja praćeni su fizikalno kemijski parametri značajni za samu provedbu procesa kompostiranja, kao i mikrobiološka analiza kompostne mase. Proces kompostiranja proveden je u adijabatskom reaktoru na laboratorijskoj razini tijekom 16 dana. Provedena je optimizacija procesa kompostiranja primjenom kinetičkog modela prvog reda važna za dizajniranje i rad postrojenja za kompostiranje. Biorazgradnja polimernih PE-LD/TPS mješavina pratila se gubitkom mase kao i promatranjem promjena morfološke strukture svjetlosnim i pretražnim elektronskim mikroskopom prije i nakon procesa kompostiranja.
Dodatak TPS-a polietilenu niske gustoće utjecao je i potaknuo biorazgradnju polimernih PE-LD/TPS mješavina. Veći udio TPS-a omogućio je veći gubitak mase, odnosno bržu razgradnju. TPS pogoduje biorazgradnji polimernih PE-LD/TPS mješavina zbog naglašene amorfne strukture kao i hidrofilnog karaktera TPS-a, te je i dobar izvor hrane mikroorganizmima koji su upravo odgovorni za biorazgradnju polimernih mješavina tijekom procesa kompostiranja.Excessive use of polymeric packaging materials has led to an oversaturation of the planet with packaging waste and a great need to find a replacement biodegradable polymeric material that could meet consumer as well as environmental purposes.
This paper investigates the possibility of biodegradation of polymer blends of low density polyethylene (PE-LD) and thermoplastic starch (TPS) by composting. During the composting process, physicochemical parameters important for the implementation of the composting process were monitored, as well as microbiological analysis of the compost mass. The composting process was carried out in an adiabatic reactor at the laboratory level for 16 days. The optimization of the composting process was carried out using a first-order kinetic model important for the design and operation of the composting plant. Biodegradation of polymer PE-LD/TPS blends was monitored by weight loss as well as by observing changes in morphological structure with a light and scanning electron microscope before and after the composting process.
The addition of TPS to low density polyethylene affected and promoted the biodegradation of polymer PE-LD/TPS blends. A higher share of TPS enabled higher mass loss, i.e. faster decomposition. TPS favors the biodegradation of polymer PE-LD/TPS blends due to the pronounced amorphous structure and hydrophilic character of TPS. It is a good source of food for microorganisms that are responsible for their biodegradation during the composting process
Application of Immobilized TiO<sub>2</sub> for Removal of Cu(II) Ions
No full textU ovoj studiji istraživana je adsorpcija Cu(II) iona na smjesi anatasa i rutila, dviju polimorfnih formi TiO2. Istražen je učinak vremena kontakta adsorbens/adsorbat i učinak početne koncentracije Cu(II) na adsorpciju. Rezultati su pokazali da ravnoteža nastupa već nakon jedne minute kontakta Cu(II) i TiO2 te da kapacitet adsorpcije raste s porastom početne koncentracije Cu(II) iona. Eksperimentalni podatci obrađeni su Langmuirovom i Freundlichovom izotermom. Dobiveni rezultati ukazuju da Freundlichov model bolje opisuje ispitivani adsorpcijski sustav te da je adsorpcija fizikalne prirode.
Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.The adsorption of Cu(II) ions on a mixture of anatase and rutile, two polymorphic forms of TiO2, was investigated. The influence of the adsorbent/adsorbate contact time as well as the influence of the initial concentration of Cu(II) on the adsorption was monitored. The results showed that equilibrium occurred after only one minute of contact of Cu(II) and TiO2, and that the adsorption capacity increased with initial concentration of Cu(II) ions. Experimental data were processed by Langmuir and Freundlich isotherm. The obtained results showed that the Freundlich model better described the investigated adsorption system, and that the adsorption was of a physical nature.
This work is licensed under a Creative Commons Attribution 4.0 International License
Influence of cold reduction on the structure and hardness of cold drawn copper wire
No full textThe production of copper wires involves the application of various processing operations thatlead to
the certain structural changes. The electrical properties of wire depend on certain structural changes.
Research was carried out on copper wire produced by the UPCAST process. Copper wire was
subsequently subjected to the cold drawing through the dies in multiple passes. The structural
changes in the process of cold drawing of Cu-wire were observed. During the cold drawing of Cu-wire
through dies, a significant change in deformed structure occurred in relation to the initial cast
structure. The microstructure analysis and hardness values of the deformed sample indicated that
during the initial reduction the majority of the deformation was performed at the surface area of the
Cu-wire that was in contact with the die. The initial equiaxed grains at the surface of the Cu-wire
elongated in the drawing direction as a consequence of the deformation degree increase
Inhibitory effect of commercial inhibitor VCI 379/611 on corrosion behavior of X153CrMoV12 tool steel for cold work
No full textIn this paper, the influence of water and the influence of the commercial inhibitor VCI 379/611 on the corrosion processes of X153CrMoV12 tool steel for cold work were investigated. The research was carried out by electrochemical methods: by measuring the potential of an open circuit, by determining the corrosion parameters using the method of electrochemical impedance spectroscopy (EIS) and method of Tafel extrapolation. After each measurement, the sample surface was analyzed using an optical microscope. The obtained corrosion parameters showed a high efficiency of the applied inhibitor in the protection of tool steels for cold work from corrosion. For the sample that was exposed to distilled water medium with the addition of inhibitor, a significantly lower corrosion rate was registered and no damage to the sample surface was visible. Metallographic images of the electrode surface after polarization measurements in tap water indicate the occurrence of pitting corrosion
Diffusion in metals and metal alloys
No full textU ovom radu definiran je pojam difuzije te su navedene i pobliţe objašnjene vrste difuzijskih procesa. TakoĎer su prikazani različiti mehanizmi difuzije karakteristični u metalima i metalnim legurama te su navedene direktne i indirektne metode mjerenja difuzije. Definiran je koeficijent difuzije kao mjera brzine difuzije te je opisana njegova ovisnost o temperaturi, tlaku i obliku kristalne rešetke. Navedeni su Fickovi zakoni difuzije za stacionarno i nestacionarno stanje te su istaknuti primjeri primjene difuzije u metalurgiji.In this paper, the term diffusion is defined and the types of diffusion processes are listed and explained in more detail. Various diffusion mechanisms characteristic of metals and metal alloys are also presented and direct and indirect methods of diffusion measurement are given. The diffusion coefficient is defined as a measure of the diffusion rate and its dependence on the temperature, pressure and shape of the crystal lattice is described. Fick's laws of diffusion for stationary and non-stationary states are given, and examples of applications of diffusion in metallurgy are highlighted