Revitalization of bucket wheel excavator SRS 1301 24/2.5 drive number 10 – mining basin Kolubara

Rotorni bager SRs 1301 24/2.5, pogonski broj G-10, koji je u vlasništvu polja „D“, 30.04.2014. godine zadesila je teška havarija. Usled odrona velike količine jalovinske mase koju je bager otkopavao došlo je do loma konstrukcije strele radnog točka. Nakon stabilizacije sprave i demontaže neupotrebljivih delova pristupljeno je izradi nove konstrukcije strele radnog točka kao i pripadajućih delova i sklopova. Montažom  nove konstrukcije, sanacijom prslina na obrtnoj platformi nastalih usled udara i montažom novoizrađenih sklopova i podsklopova bager je za manje od osam meseci doveden u stanje pogonske spremnosti.Bucket-wheel excavator SRs 1301 24/2.5, the drive number G-10, which is owned by mining basin „Kolubara“- field „D“, 30.04.2014. was strucked by heavy accident. Due to landslide of large amount of waste mass, that the excavator was exploited, there was a fracture of bucket wheel construction. After stabilization of excavator and removal of unusable parts we accessed the creation of a new structure of the bucket wheel construction and related parts and components. Installation of new construction, repair cracks in the rotary platform caused by shock and assembly of newly assemblies and subassemblies excavator for less than eight months was in a state of operational readiness

New materials and technologies in aero and space research

Space technology plays an integral and indispensable role in our daily lives. Whether we are talking about live broadcasts of World Cup matches, satellite-assisted emergency management efforts, or the nightly weather forecast, one thing is true: our lives would be very different without satellite images or satellite-based communication and navigation systems. Space technology is key to our modern, knowledge-based society. Today space makes a vital contribution when it comes to promoting research and development, education and innovation, economic growth, providing highly qualified jobs, improving our quality of life, protecting the Earth, ensuring our security and defence and furthering international cooperation. Military platforms—such as ships, aircraft, and ground vehicles— rely on advanced materials to make them lighter, stronger, and more resistant to harsh environmental conditions. Currently, the process for developing new materials frequently takes longer than a decade. This lengthy process often means that developers of new military platforms are forced to rely on decades-old, mature materials, because potentially more advanced materials are still being developed and tested and are considered too large a risk to be implemented into platform designs. Al alloys have been the primary material for the structural parts of aircraft because of their well known performance, well established design methods, manufacturing and reliable inspection techniques. Fiber reinforced polymer composites have been increasingly used in aerospace. Fiber Metal Laminate (FML) is a new kind of hybrid composite. Materials used to construct spacecraft and protective gear—including the International Space Station and space suits for astronauts—must be lightweight yet strong enough to guard against cosmic dust that travels at hypervelocity

Study of Barium Bismuth Titanate Prepared by Mechanochemical Synthesis

Barium-bismuth titanate, BaBi4Ti4O15 (BBT), a member of Aurivillius bismuth-based layer-structure perovskites, was prepared from stoichiometric amounts of barium titanate and bismuth titanate obtained via mechanochemical synthesis. Mechanochemical synthesis was performed in air atmosphere in a planetary ball mill. The reaction mechanism of BaBi4Ti4O15 and the preparation and characteristics of BBT ceramic powders were studied using XRD, Raman spectroscopy, particle analysis and SEM. The Bi-layered perovskite structure Of BaBi4Ti4O15 ceramic forms at 1100 degrees C for 4 h without a pre-calcination step. The microstructure of BaBi4Ti4O15 exhibits plate-like grains typical for the Bi-layered structured material and spherical and polygonal grains. The Ba2+ addition leads to changes in the microstructure development, particularly in the change of the average grain size

Characterization of Barium Titanate Ceramic Powders by Raman Spectroscopy

Barium titanate, BaTiO3 ceramic powders were prepared by mechanochemical synthesis and by the Pechini method. A powder mixture of BaO and TiO2 was treated in a planetary ball mill in an air atmosphere for Lip to 1 h, using zirconium oxide vial and zirconium oxide balls as the milling medium. After 60 min BaTiO3 phase was formed. In both ways BaTiO3 ceramics were sintered after 2 h on 1300 degrees C without pre-calcinations step. The heating rate was 10 degrees C min(-1). The formation of phase and crystal structure of BaTiO3 was approved by X-ray diffraction analysis and the Raman spectroscopy. The morphology and microstructure of obtained powders were examined by scanning electron microscopy method. Sharp phase transition from ferroelectric to paraelectric state was observed. The hysteresis loop is very well performed with regular sharp characteristic of ferroelectric materials

Effect of Fe2+ (Fe3+) Doping on Structural Properties of CeO2 Nanocrystals

We have measured the Raman scattering and magnetization of pure and Fe2+(Fe3+) doped CeO2 nanopowders at room temperature. The Raman scattering spectra revealed the existence of CeO2 fluorite cubic structure for all investigated samples. The Raman active mode at about 600 cm(-1), seen in all samples, can be ascribed to the CeO2 intrinsic oxygen vacancies. Additional Raman modes at 720 cm(-1), 1320 cm(-1) and 1600 cm(-1), which appear in the spectra of doped samples, can be assigned to maghemite (gamma-Fe2O3) cation deficient structure, to 2 omega(LO) IR-allowed overtone and two magnon structure, respectively. This implies that our powders are composed of mixed valence states and have defective structure. Presence of oxygen defect states and magnetic ions can be responsible for the observed ferromagnetism at room temperature in both pure and Fe doped samples.Symposium on Raman Scattering in Materials Science, Sep 15-19, 2008, Warsaw, Polan

Vibrational and magnetic properties of nano-sized CoFe2O4 obtained by various synthesis techniques: a comparative study

Nanocrystalline CoFe2O4 has been synthesized by various synthesis methods. The obtained monodomain nanoparticles are similar in sizes (15.8-19 nm), but with different internal stresses, size distributions and cation inversion coefficients (0.51 - 0.90) due to different synthesis routes. The structure and cation distribution are investigated by XRD diffraction analysis, Raman and FIR spectroscopy. Measurement of magnetization, i.e. coercivity, enable the calculation of the anisotropy coefficient K1 = (3.6-5.12)·105 J cm-3, which is very high in cobalt ferrite. The anisotropy coefficient directly depends on the nanoparticle size. It has been shown that magnetization linearly depends on the cation inversion, except in the sample with the largest nanoparticles (19 nm), where the more regular crystal structure prevails and higher values of magnetization were obtained. The average magnetic moments at 300 K are: μFe = 3.6μB and μCo = 2.5μB. It is obvious that with small adjustments in the synthesis, desirable nanoparticle properties can be obtained

Magnetism in oxide nanomaterials

U ovoj disertaciji je proučavan fenomen feromagnetnog uređenja na sobnoj temperaturi u nanokristalnim uzorcima CeO2 dopiranog gvožđem i prazeodimijumom. Razređeni magnetni oksidi, tj. oksidi dopirani malim procentom magnetnih elemenata, a koji pokazuju feromagnetno uređenje na sobnoj temperaturi, u poslednjoj deceniji predstavljaju jednu od najaktuelnijih oblasti istraživanja u fizici čvrstog stanja. Ovi materijali su viđeni kao veoma pogodni materijali za upotrebu u spintronici. S druge strane, istraživanja su takođe stimulisana činjenicom da je fenomen feromagnetizma u ovim materijalima po mnogo čemu atipičan i u velikoj meri preispituje dosadašnje poznavanje magnetizma. Posebno je interesantna činjenica da se feromagnetizam u ovim materijalima javlja samo kada su oni u nano-fazi, tj. kod uzoraka u obliku tankih slojeva ili nanočestica, dok se u voluminoznim uzrocima ne javlja. Takođe, istraživanja pokazuju da je poreklo feromagnetnog uređenja povezano sa izraženim prisustvom defekata i kiseoničnih vakancija u nanouzorcima. Mogući mehanizmi uspostavljanja feromagnetnog uređenja u ovim materijalima se i dalje istražuju, pri čemu model vezanog magnetnog polarona ili mehanizam transfera naelektrisanja u ovom trenutku deluju kao najizgledniji kandidati. U disertaciji su proučavani uzorci čistog i CeO2 dopiranog gvožđem različitih valenci Fe2+/Fe3+: 2 0.88 0.12 2- Ce Fe O d + , 2 3 0.88 0.06 0.06 2- Ce Fe Fe O d + + , 3 0.88 0.12 2- Ce Fe O d + , kao i CeO2 dopiranog prazeodimijumom, Ce1-xPrxO2-d sa sadržajem 0≤x≤0.4. Uzorci su dobijeni metodom samopropagirajuće sinteze na sobnoj temperaturi. Dobijeni nanokristalni uzorci pokazuju postojanje feromagnetnog uređenja na sobnoj temperaturi. Za ispitivanje i karakterizaciju uzoraka su korišćena magnetna merenja, Ramanova, infracrvena, XPS i Mesbauereova spektroskopija, AFM merenja i fotoluminescencija. U slučaju Fe2+/Fe3+ dopiranih CeO2 nanokristala, magnetnim merenjima je dobijeno da uzorci pokazuju osobine superparamagnetizma. Krive magnetizacije u funkciji magnetnog polja na sobnoj temperaturi pokazuju vrlo malo koercitivno polje i mogu se fitovati otežinjenom Lanževenovom funkcijom. Na osnovu merenja ZFC i FC krivih i zavisnosti koercitivnog polja sa temperaturom je dobijeno da je temperatura blokiranja oko 20 K. Raman merenja su pokazala da F2g mod na 457 cm-1 pokazuje neočekivano omekšavanje i asimetrično širenje pri Fe dopiranju i porastu valence od Fe2+ ka Fe3+, što se može objasniti efektom sprezanja elektrona i molekulskih vibracija. Ponašanje Ramanovog F2g moda ukazuje da dolazi do delimične delokalizacije Ce 4f 1 i Fe 3d elektrona, i njihovog transfera na Ce(Fe)-O(VO)-Ce(Fe) veze, dovodeći do promene konstante sile i rezultujući u omekšavanju i širenju Ramanovog moda. Korišćenjem Alenove formule, određena je konstanta elektron-fonon sprezanja za nedopirane i Fe-dopirane uzorke, kao i gustina stanja na Fermijevom nivou. Na osnovu dobijene vrednosti gustine stanja na Fermijevom nivou se može zaključiti da je Stonerov kriterijum za feromagnetizam višestruko ispunjen, što sve znači da je zonska teorija feromagnetizma, odnosno model transfera naelektrisanja, primenjiv u Fe-dopiranim CeO2 uzorcima, pri čemu se uspostavljeno feromagnetno uređenje, usled nanometarskih dimenzija kristalita, ispoljava u formi superparamagnetizma. U slučaju Pr-dopiranih CeO2 nanokristala, magnetnim merenjima je ustanovljeno da uzorci pokazuju feromagnetizam na sobnoj temperaturi, pri čemu saturaciona magnetizacija drastično opada pri dopiranju. Istraživanja su pokazala da se Pr ugrađuje supstitucionalno u celom ispitivanom opsegu, delimično u obliku Pr4+ a delimično u obliku Pr3+ jona, pri čemu relativni udeo Pr3+ jona raste sa Pr dopiranjem. Takođe je ustanovljeno da na površini nanokristala dolazi do segregacije Pr, pri čemu je ta segregacija najizrazitija za male koncentracije dopiranja, kao i da se većina Pr na površini nanokristala nalazi u obliku Pr3+ jona. Istraživanja su pokazala da pri Pr dopiranju sadržaj kiseoničnih vakancija raste. Obzirom da kod razređenih magnetnih oksida porast sadržaja kiseoničnih vakancija tipično dovodi do jačanja feromagnetizma, ustanovljeno opadanje saturacione magnetizacije je bilo iznenađujuće. Da bi se ono objasnilo predloženo je objašnjenje bazirano na mehanizmu izmene preko F centara. Nedopirani nanokristali CeO2 na sobnoj temperaturi ispoljavaju feromagnetizam koji se uspostavlja posredstvom kiseoničnih vakancija sa jednim zarobljenim elektronom (F+ centara). Prisustvo Pr3+ jona u tankom površinskom sloju nanokristala, gde su kiseonične vakancije uglavnom smeštene, dovodi do drastične degradacije feromagnetizma. Do ovoga dolazi usled formiranja kompleksa kao što su Pr3+-VO-Ce3+ ili Pr3+-VO-Pr3+, lokalizacije elektrona na vakancijama i kreiranja kiseoničnih vakancija bez zarobljenih elektrona (F0 centara), ili sa dva zarobljena elektrona (F2+ centara), koje ne doprinose feromagnetizmu. Formiranje F2+ i F0 centara smanjuje koncentraciju F+ centara i narušava feromagnetizam u Pr-dopiranim CeO2 uzorcima. Rezultati istraživanja prikazani u disertaciji pokazuju da feromagnetizam u nanokristalnim oksidima može izrazito da zavisi od dopirajućeg elementa i njegovog valentog stanja, kao i od forme kiseoničnih vakancija i njihove mogućnosti odnosno nemogućnosti da prenose feromagnetizam

Surface optical phonon and multi - phonon transitions in YVO4: Eu3+ nanopowders

In this paper two methods of preparation of yttrium orthovanadate nanopowders were presented: Solid State Reaction (top - down approach) and Solution Combustion Synthesis (bottom - up approach). For starting structural characterization, X - Ray Powder Diffraction (XPRD) and Field Emission Scanning Electron Microscopy (FESEM) were used. We report the change in reflection spectra in europium doped YVO4 nanopowders with comparison to its bulk analog. In UV-Vis reflection spectra we consider the change in values of band gap in these structures, after resizing it from bulk to nanomaterial. In Far - Infrared (FIR) reflection spectra, we registered the existence of Surface Optical Phonon (SOP) and different multi - phonon processes which alter the reflection spectra of bulk YVO4 . The influence of Eu ions is reflected through multi - phonon processes that occur and are connected with energy transfer from YVO4 lattice to Eu ions. All IR spectra were modeled using classical oscillator model with Drude part added which takes into account the free carrier contribution. Since our samples are distinctively inhomogeneous materials, we use Effective Medium theory in Maxwell Garnett approximation to model its effective dieletric function

Structural and optical characterization of titanium–carbide and polymethyl methacrylate based nanocomposite

The rich chemistries and unique morphologies of titanium carbide MXenes, made them strong candidates for many applications like sensors and electronic device materials. During the synthesis procedure, chemical etching, oxidation occurs and residual materials, like titanium-dioxide nanocrystals and nanosheets are often present in resulting material. As titanium-carbide MXenes are suggested to be used as additive in organic polymer matrices for production of nanocomposites, it is essential to consider the presence of the oxides and other residuals together with MXene flakes in synthesis results, and consequently in produced nanocomposite. In this study we present structural and optical characterization of such polymer nanocomposite titanium carbide/PMMA (Polymethyl methacrylate) consisting of Ti3C2, TiC2 MXenes and TiC, and TiO2 residues of synthesis in PMMA matrix, as a multicomponent nanocomposite. Using XRD, infra-red and Raman spectroscopy, followed by comparative study on the vibrational properties using density functional theory calculations, we characterize this nanocomposite. Further, the SEM measurements are performed, demonstrating the produced titanium-carbide-based flakes in nanocomposite are well defined and separated to nanosized grains, allowing us to use Maxwell–Garnet model to analyse infrared spectrum. This enables us to determine the presence of the optical modification of polymer matrices corresponding to a volume fraction of 0.25