Sinterovani sistemi na bazi nano prahova teških metala i glinice

Ultra fini i nanokompozitni prahovi na bazi bakra, srebra i glinice mogu se vrlo uspešno koristiti za dobijanje disperzno ojačanih sinterovanih polikristalnih materijala sa submikronskom, odnosno nanokristalnom strukturom, koje karakteriše dobra kombinacija električna svojstva-mehanička svojstva, i koji nalaze široku primenu u oblasti elektronike i elektrotehnike. U skladu sa tim, u okviru ove doktorske disertacije dat je prikaz rezultata istraživanja dobijenih pri izučavanju sinterovanih sistema na bazi ultra finih i nano prahova teških metala i glinice. Sinteza dvokomponentnog nanokompozitnog Cu-Al2O3 praha izvršena je termohemijskim postupkom, polazeći od vodenih rastvora Cu(NO3)2 i Al(NO3)3, kao i mehaničkim legiranjem komercijalnog praha bakra dobijenog elektrolitičkim postupkom i prethodno sintetisane glinice sol-gel metodom. Trokomponentni Cu-Ag-Al2O3 prah dobijen je mehaničkim legiranjem prethodno sintetisanog nanokompozitnog Cu-Al2O3 praha termohemijskim postupkom i praha srebra dobijenog hemijskim putem, odnosno Cu-Ag praha dobijenog termohemijskim postupkom. Nakon karakterizacije dobijenih prahova, koja je obuhvatila hemijsku analizu, diferencijalnotermijsku i termogravimetrijsku (DT/TG) analizu, rendgenostrukturnu analizu (RDA), određivanje specifične površine čestica, nasipne gustine, tečljivosti, oblika, veličine i raspodele veličine čestica, kao i mikrostrukturna ispitivanja skanirajućom elektronskom mikroskopijom (SEM) i analitičkom elektronskom mikroskopijom (AEM) povezanom sa energetskom disperzivnom spektroskopijom (EDS), vršeno je presovanje prahova pritiskom presovanja od 500MPa. Sinterovanje dobijenih uzoraka Cu-Al2O3 sistema vršeno je u atmosferi vodonika u izotermskim uslovima u temperaturnom opsegu 800-1000oC u toku 15-120 minuta. Trokomponentni Cu-Ag-Al2O3 sistem sinterovan je u atmosferi vodonika u temperaturnom opsegu 600-800oC u toku 15-120 minuta. Karakterizacija dobijenih sinterovanih sistema obuhvatila je ispitivanja gustine, relativne promene zapremine, električnih i mehaničkih svojstava, kao i ispitivanja mikrostrukture skanirajućom elektronskom mikroskopijom (SEM), energetskom disperzivnom spektroskopijom (EDS), transmisionom elektronskom mikroskopijom (TEM) i transmisionom elektronskom mikroskopijom visoke rezolucije (HRTEM), ispitivanja metodom fokusiranja snopa jona (FIB – Focused Ion Beam) i ispitivanja selktovanih difrakcionih polja (SADP – Selected Area Diffraction Pattern). Dobijeni nanokompozitni prahovi, čija je struktura uz izvesne promene očuvana u strukturi krajnjeg proizvoda, obezbedili su dobijanje sinterovanih sistema sa homogenom raspodelom disperzoida, izuzetnim efektima ojačavanja i dobrom kombinacijom mehanička-električna svojstva. Uporednom analizom svojstava dobijenih sinterovanih sistema uočljivo je da su kod sistema na bazi Cu-Al2O3 nanokompozitnog praha sintetisanog temohemijskim postupkom u odnosu na ostale ispitivane sisteme postignuti značajniji efekti ojačavanja uz strukturnu stabilizaciju sistema na nižim temperaturama i u toku kraćih vremena sinterovanja

Postupak prerade otpadne olovne alkalne šljake u korisne proizvode

Postupkom prerade otpadne olovne alkalne šljake u korisne proizvode, dobijaju se frakcija +1mm, koja sadrži korisne komponente (metalno sulfidne, čvrste, nerastvorne) i koja se vraća u proces topljenja u cilju valorizacije korisnih komponenti. Postupkom se takođe dobija frakcija -1mm (jalovinska oksidno – sulfatna), optimalnog sastava i strukture, pogodna za postupak stabilizacije i solidifikacije u cementnoj matrici betona radi primene u građevinarstvu. Postupak obuhvata ispiranje u cilindričnom rotirajućem ispiraču – odvajaču (temperatura 22-43oC, brzina mešanja 6-25min-1, odnos čvrsto tečno 10-28% čvrstog), pri čemu se uklanjaju u vodi rastvorne komponente iz šljake, dobija stabilnija šljaka (frakcija -1mm) i izdvaja povratni metal i kamenac (frakcija +1mm) sa sadržajem korisnih komponenata, koje se valorizuju vraćanjem u proces topljenja. Koristan proizvod je i rastvor nakon tretmana sodnog sadržaja, koji se koristi u procesu proizvodnje natrijum(I) – sulfata, zajedno sa rastvorom iz faze desumporizacije olovne paste prerade otpadnih olovnih akumulatora, u cilju dobijanja komercijalnog proizvoda Na2SO4

Synthesis and Characterization of Dispersion Reinforced Sintered System Based on Ultra Fine and Nanocomposite Cu-Al2O3 Powders

Characterization of the obtained powder indicates a possibility of the synthesis of nanocomposite Cu-Al2O3 system by the thermochemical procedure, starting from water solutions Cu(NO3)2 and Al(NO3)3. AEM analysis indicates the presence of individual particles of 20-50 nm size. The shape of particles is irregular, with the presence of individual particles of nodular shape. The surface morphology is rough. Apart from that, the presence of an agglomerate with the magnitude of >100nm and of a sponge shape is noticeable. The obtained nanocomposite powders, with the structure basically preserved together with the final product, provided a significant reinforcement effect in the obtained sintered system. This is a consequence of the homogenous distribution of the elements in the structure, accomplished during the synthesis of powder and presence of the third phase which causes stabilization of dislocation substructure and achieves the relevant reinforcing effect. The analysis of the mechanical and electric properties of the sintered Cu-Al2O3 systems based on powders obtained by the thermochemical method shows that in the system with 3wt.%Al2O3, sintered at 900ºC, structural stabilisation occurs only after 30 minutes with considerable reinforcement effects. Since in other systems, the structural stabilisation process was not completed even after 120 minutes, the system with 3wt.% of dispersoids sintered at 900ºC for 30 minutes seems to be the optimum solution for the production of dispersively reinforced Cu-Al2O3 systems. This statement is confirmed by the corresponding analysis of the microstructure. In accordance with the previous statements, the EDS analysis of the sintered systems surface as well as FIB analysis show a homogenous distribution of elements, i.e. present phases. FIB analysis also indicates the size of microstructural constituents within the range of 50-250nm. TEM analysis of the sintered systems reveals the presence of copper crystals of 100 nm in size exposed to twinning, thus pointing to stabilization of the dislocation substructure. SADP of the examined nanocomposite Cu–Al2O3 sintered system shows spots and rings, where spots refer to the individual crystals of copper, and sharp circles (rings) originate from nanocrystals of alumina dispersed in the copper matrix. HRTEM analysis indicates the changes in the lattice parameter, which leads to the conclusion that the eutectic reaction occurred and the third, CuxAlyOz phase was formed on the grain boundary, which will be the subject of future studies based on a more precise approach to physical chemistry of system surfaces and of thermodynamic examinations of the influences of finely dispersed Al2O3 on the formation of the third phase and the increase in the system surface energy. In the end, all the above-mentioned examinations show that the reinforcement of Cu-Al2O3 system occurs via two mechanisms, which are: dispersion and reinforcement mechanism due to the homogenous dispersion of fine particles of Al2O3 in the matrix, and the mechanism of grain boundary reinforcement due to the appearance of the third phase

Disperzno ojačani materijali na bazi nanostrukturnih prahova u sistemu bakar-glinica

U okviru monografije, polazeći od teorijskog prikaza sinteze, strukture, svojstava i primene nanostrukturnih materijala, dati su originalni eksperimentalni rezultati uporedne analize različitim postupcima sintetisanih disperzno ojačanih nanostrukturnih kompozitnih Cu-Al2O3 materijala sledećih sistema: - nanokompozitnog Cu-Al2O3 sistema dobijenog mehaničkim legiranjem komercijalnog praha bakra dobijenog elektrolitičkim postupkom i glinice sintetisane sol-gel metodom, - nanokompozitnog Cu-Al2O3 sistema na bazi praha dobijenog termohemijskim postupkom, taloženjem iz tečne faze, - nanokompozitnog Cu-Al2O3 sistema dobijenog kombinacijom hemijskog postupka sinteze i mehaničkog legiranja

Innovative solutions for the extraction of technology metals from complex primary a nd secondary raw materials

Technological evolution and growing demand for various high-tech devices have increased need for metals, both in terms of their diversity and quantities, resulting in more intense use of natural resources and generation of huge amounts of various waste materials. In contrast to base metals, advances in material science have given rise to a new group of metals, which are used in small or trace amounts to alter drastically the properties of matter. Whether in composite materials, like semiconductors or minor elements in alloys, these trace metals shape modern-day technology and, hence, are termed as Technology Metals (TM). Metals such as Sb, Co, Ga, Ge, In, Ta, the Platinum Group Metals (PGMs) and the Rare Earth Elements (REEs) are among the TM in which Europe is 100% import dependent. Development of the novel processing technologies will aim not only in securing raw material supply, but will rather aim to establish sustainable metallurgical processing, meaning establishing technologies for de-complexing the advanced material products with the minimum environmental footprint. Hydro and electro metallurgical steps make essential base with synergy to primary production route, advanced mechanical and minor pyro pretreatment step. However, absence of such extraction technologies, successfully applied on industrial scale, is still notable. To secure a reliable and sustainable supply of critical materials, innovative solutions need to be developed along the entire value chain. This transition requires multi-stakeholder partnerships that foster innovation and entrepreneurship, which can be obtained by applying the Triple Helix concept. Presented compilation of scientific, theoretical and experimental results, promotes an innovative synergy of various metals and industrial activities in metallurgy, resulting in profitable transformation of by-products and waste materials into resources. Focusing on treatment of specific by-products from zinc and copper primary production, as well on specific waste streams like WEEE and waste automotive catalysts, group is actively contribute to the EU sustainability policies

Synthesis of nanocomposites of difference architectures and applications based on copper, nickel and alumina

Considering that nanostructural materials are expected to have special physical and mechanical properties, in the recent years the examinations of synthesis and characterization of the nanocomposite system attracts even greater scientific interest. This paper presents production of sintered contacts materials produced from nanocomposite powders obtained by combination of thermochemical synthesis of Cu-Al2O3 powder and mechanical alloying of atomized copper powder with previously sinthetized Cu-Al2O3 powder. Produced powders were characterized by X-ray diffraction and Analytical Electron Microscopy. Characterization of sintered samples included Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometry (EDS), measurement of hardness and specific electrical conductivity. By thermochemical method of Cu-Al2O3 nanocomposite synthesis, i.e. deposition from aqueous solutions, in combination with mechanical alloying, significant effects of reinforcement were achieved as a result of homogenous distribution of alumina in the nanocomposite system. In combination with conventional methods, thermochemical process of nanocomposite powders synthesis could be successfully applied for synthesis of new nanocomposite catalysts, which are characterized by a high degree of dispersion of the catalytically active component, respectively the catalyst with high activity and selectivity. The high degree of dispersion is the result of uniform distribution of the catalytically active component into alumina suspension, realized during the thermochemical treatment in the synthesis of nanocomposite catalysts. In accordance with this, the paper shows the synthesis of Ni/Al2O3 and Ni-Pd/Al2O3 nanocomposite catalysts with homogeneously dispersed Ni particles, as catalytically active component, and Pd, as activity modifier, supported on ceramic Al2O3 based foam. Namely, the previous synthesized monolith was soaked in a mixed alumina suspension with NiCl2, PdCl2 and appropriate organic additives in order to obtain a nanocomposite catalysts with homogeneous distribution of catalytically active components. Characterization of obtained Al2O3 foam, as the active catalytic components primary carrier, and synthesized nanocomposite catalysts included SEM, EDS, gas permeability and mechanical properties. Synthesis of nanocomposite materials with homogeneous distribution of particles on the nanometer level may lead to formation of new materials with improved or even unexpected properties

Sintering process optimization for Cu-Al2O3 powders synthesized by novel method

This paper presents sintered materials for use as contacts produced via novel synthesis method of starting powders by combination of explored conventional routes of thermochemical synthesis and mechanical alloying. Starting raw materials for powder synthesis by thermochemical route were soluble salts, nitrates of copper and aluminum of p.a. quality, dissolved in distilled water (50wt.% solution) in suitable ratio for final powder to contain 50wt.% of Al2O3 in structure. Nitrate solution was spray dried and subjected to heat treatment (900 ºC/1h). Obtained oxides were reduced in hydrogen atmosphere (flow rate 20L/h at 350 °C for 1h) in order to obtain composite of Cu-Al2O3. Produced powders were used for mechanical alloying of atomized copper (5h, 300 min-1). Final amount of alumina Al2O3 in composite powder were 1, 1.5 and 2 wt.%. After mechanical alloying obtained powders were compacted by a uniaxial pressing (8×32×3mm, 500 kN). Sintering of samples was performed in hydrogen atmosphere in isothermal conditions at five different temperatures in the range from 725-925 °C for 15 to 120 min. Results of characterization show, that increase of Al2O3 content has more noticeable effect on the electrical conductivity and hardness than sintering temperature and time. With increase of Al2O3 from 1 to 1.5 wt.% there is a slight decrease in both investigated properties, while with increase up to 2 wt.% Al2O3 significant decrease in electrical conductivity and hardness of sintered samples is observed. According to achieved results optimum sintering parameters for composite materials produced by novel synthesis method based on copper with dispersed 1% Al2O3 are 875 ºC/60 min. Based on the achieved results, this method provides production of contact materials with good combination of electrical and mechanical properties, but with estimated lower production costs

Sintering of Cu–Al2O3 nano-composite powders produced by a thermochemical route

This paper presents the synthesis of nano-composite Cu–Al2O3 powder by a thermochemical method and sintering, with a comparative analysis of the mechanical and electrical properties of the obtained solid samples. Nano-crystalline Cu–Al2O3 powders were produced by a thermochemical method through the following stages: spray-drying, oxidation of the precursor powder, reduction by hydrogen and homogenization. Characterization of powders included analytical electron microscopy (AEM) coupled with energy dispersive spectroscopy (EDS), differenttial thermal and thermogravimetric (DTA–TGA) analysis and X-ray diffraction (XRD) analysis. The size of the produced powders was 20–50 nm, with a noticeable presence of agglomerates. The composite powders were characterized by a homogenous distribution of Al2O3 in a copper matrix. The powders were cold pressed at a pressure of 500 MPa and sintered in a hydrogen atmosphere under isothermal conditions in the temperature range from 800 to 900 °C for up to 120 min. Characterization of the Cu–Al2O3 sintered system included determination of the density, relative volume change, electrical and mechanical properties, examination of the microstructure by SEM and focused ion beam (FIB) analysis, as well as by EDS. The obtained nano-composite, the structure of which was, with certain changes, presserved in the final structure, provided a sintered material with a homogenеous distribution of dispersoid in a copper matrix, with exceptional effects of reinforcement and an excellent combination of mechanical and electrical properties

Wear Resistance and Dynamic Fracture Toughness of Hypoeutectic High-Chromium White Cast Iron Alloyed with Niobium and Vanadium

The influence of mass fractions 1.5 % Nb and 1.5 % V, added singly and in combination, on the microstructural characteristics and properties relevant to the service performance of the hypoeutectic high-chromium white iron containing 18 % Cr and 2.9 % C, namely, the wear resistance and the fracture toughness, has been examined. The Fe-Cr-C-Nb-V alloy gives the best compromise between the wear resistance and the fracture toughness. The dynamic fracture toughness of this alloy is larger by about 42 % and the abrasion wear resistance is larger by about 33 % than the properties of the basic Fe-Cr-C alloy. The presence of NbC carbides in the structure, caused by adding niobium to the alloy, contributes to an improvement of the wear resistance and the dynamic fracture toughness. On the other hand, the higher fracture toughness was attributed to the strengthening during fracture, since very fine secondary carbide particles were present, mainly in the austenitic matrix (as a result of the vanadium addition). The secondary carbides that precipitate in the matrix regions also influence the abrasion behaviour. By increasing the matrix strength through a dispersion-hardening effect, the fine secondary carbides can increase the mechanical support of M7C3 eutectic carbides

Synergistic solid lubricants system based on selected sulfides of technology metals

Technology advances have resulted in a growing demand for the new tribology materials. In development of the properties of tribology materials, improvements can be achieved by combining materials in form of composites. The aim of this work was production of solid lubricants composites based on sulfides of technology metals. Selected solid lubricant powders, tin sulfide (SnxSy) and tungsten disulfide (WS2), were synthesized by pyrometallurgical method in rotary tilting tube furnace (ST-1200RGV). The chemical thermodynamic parameters of the synthesis were determined using HSC Chemistry software modeling package. Characterization of the obtained powders included analysis of chemical composition by optical emission spectroscopy, phase composition identification by X-ray diffraction (XRD) and microstructural examination by the scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Finally, the tribological properties of the as-synthesized powders in composite mixture were estimated. It has been shown the beneficial synergistic effect due to unique combination of properties between tin sulfides and tungsten sulfide in composite. In addition, advantage of synergistic tribology material (SnxSy/WS2) is simple method of synthesis and environmentally acceptable components of the composite