Elektrohemijsko taloženje i karakterizacija prahova metala i legura trijade gvožđa i prahova legure nikla sa molibdenom

Abstract

Elektrohemijsko taloženje prahova Fe-Ni legura iz rastvora amonijumhloridnog i natrijum-sulfatnog pomoćnog elektrolita različitih odnosa koncentracija Ni/Fe jona i prahova Mo-Ni-O legura iz rastvora amonijum-hloridnog i amonijumsulfatnog pomoćnog elektrolita različitih odnosa koncentracija Ni/Mo jona ispitivano je snimanjem polarizacionih krivih. Sve polarizacione krive su imale isti oblik okarakterisan dvema prevojnim tačkama. Prva prevojna tačka odgovarala je početku taloženja legure uz nagli porast gustine struje usled paralelnog izdvajanja vodonika, dok je druga prevojna tačka odgovarala potencijalu na kome brzina ukupnog procesa na katodi postaje ograničena brzinom formiranja mehurova vodonika. Morfologija, hemijski i fazni sastav istaloženih prahova Fe-Ni i Mo-Ni-O legura ispitivani su pomoću SEM, EDS, XRD, DSC, TGA, AAS, TEM i SAED analize. Ustanovljeno je da morfologija istaloženih prahova Fe-Ni legura zavisi od odnosa koncentracija Ni/Fe jona, kao i od prisustva Fe(III) ili Fe(II) vrsta u rastvoru. Zajednička karakteristika morfologije svih prahova Fe-Ni legura je prisustvo sfernih zrna i šupljina konusnog oblika, koje odgovaraju mestima gde su se formirali mehurovi vodonika. U prahovima istaloženim pri odnosu Ni/Fe = 9/1 iz rastvora oba pomoćna elektrolita uočeni su kristali oblika pagode, koji pripadaju FeNi3 fazi. EDS analiza sastava prahova potvrdila je pojavu anomalnog taloženja Fe i Ni pri svim ispitivanim odnosima koncentracija Ni/Fe jona, pri čemu je anomalan karakter taloženja bio izraženiji u rastvorima Fe(III) soli. Nakon odgrevanja na 400, 600 i 700°C u atmosferi vazduha došlo je do oksidacije prahova i formiranja NiO, NiFe2O4 i Fe2O3 faza, čiji je sadržaj u odgrevanim prahovima zavisio od sastava istaloženih prahova. Ustanovljeno je da NiFe2O4, poznat kao magnetni materijal sa širokim opsegom primene, predstavlja dominantnu fazu u prahu istaloženom pri odnosu Ni/Fe = 1/3 nakon odgrevanja na 600°C. Utvrđeno je da odnos koncentracija Ni/Mo jona utiče na morfologiju i hemijski sastav prahova Mo-Ni-O legura. Morfologija prahova Mo-Ni-O legura okarakterisana je prisustvom dve vrste sfernih aglomerata: aglomerata sa kompaktnom, relativno glatkom površinom i aglomerata sa razvijenom površinom sastavljenom od kristala nanometarskih dimenzija. Rezultati EDS analize ukazali su na prisustvo i do 70 at. % kiseonika u talogu, kao i na nehomogen sastav čestica prahova. Istaloženi prahovi su bili nanokristalni, bez pojave oštrih pikova na difraktogramima. Tokom uzastopnih termičkih tretmana prahova na 300, 400, 500 i 600°C u atmosferi azota došlo je do povećanja dimenzija kristalita sa temperaturom odgrevanja, uz pojavu pikova MoO3 i NiMoO4 faza na difraktogramima već nakon odgrevanja na 300°C. Nakon odgrevanja na 600°C u uzorku praha istaloženog pri odnosu Ni/Mo = 1/0,3 XRD analizom je ustanovljeno da dominira NiMoO4 faza, a v Izvod da je u manjoj meri prisutna i MoNi4 faza. TEM analiza istaloženih prahova je pokazala istovremeno prisustvo amorfnih i kristalnih čestica. Kristalne čestice svih prahova sadrže pretežno MoO3 i MoNi4 fazu, dok je kod praha istaloženog pri odnosu Ni/Mo = 1/0,3 uočeno i prisustvo NiO faze. Otkriveno je da je formiranje NiMoO4 faze posledica reakcije u čvrstom stanju između NiO i MoO3 na povišenim temperaturama. Na osnovu rezultata TEM analize pretpostavljen je mehanizam elektrohemijskog taloženja prahova legura Mo-Ni-O sistema po prvi put u svetskoj literaturi.

Electrodeposition of Fe-Ni alloy powders from ammonium chloride and sodium sulfate containing solutions of different Ni/Fe ions concentration ratios and Mo-Ni-O alloy powders from ammonium chloride and ammonium sulfate containing solutions of different Ni/Mo ions concentration ratios was investigated by the polarization measurements. All polarization curves have the similar shape characterized by two inflection points. The first inflection point corresponds to the beginning of the alloy deposition, which is accompanied with the sharp increase of the current density due to the simultaneous hydrogen evolution reaction, while the second inflection point reflects the moment when the total cathodic process becomes controlled by the rate of the hydrogen bubbles formation. The morphology, chemical and phase composition of the electrodeposited Fe-Ni and Mo-Ni-O alloy powders were examined using SEM, EDS, XRD, DSC, TGA, AAS, TEM and SAED analysis. The morphology of electrodeposited Fe-Ni alloy powders was found to depend on the Ni/Fe ions concentration ratio, as well as on the presence of Fe(III) or Fe(II) ions in the solution. A common characteristic of the morphology of all Fe-Ni alloy powders was the presence of rounded agglomerates and cone shape cavities corresponding to the positions where the hydrogen bubbles were formed. In the powders electrodeposited at the ratio Ni/Fe = 9/1 from both solutions, pagoda like crystals, corresponding to the FeNi3 single phase, were detected. The EDS analysis of alloy powders confirmed anomalous co-deposition of Fe and Ni at all investigated Ni/Fe ratios, being more pronounced using solutions of Fe(III) salt. After annealing in air at 400, 600 and 700°C all alloy powders oxidized forming NiO, NiFe2O4 and Fe2O3 phases in different proportions depending on the original powder composition. The NiFe2O4 phase, one of the most important magnetic materials with wide range of applications, was found to be the dominant one in the sample electrodeposited at Ni/Fe = 1/3 after annealing at 600°C. It was found that the morphology and the chemical composition of the Mo-Ni-O alloy powders were influenced by the Ni/Mo ions concentration ratio. The morphology of the Mo-Ni-O alloy powders is characterized by the presence of two types of rounded agglomerates: agglomerates with compact, relatively smooth surface and agglomerates with rough surface comprised of nanosized crystals. Results of the EDS analysis revealed the presence of up to 70 at. % of oxygen in the deposit as well as the non-homogeneous composition of powder particles. The asdeposited alloy powders were nanocrystalline, showing no peaks in diffractograms. During the stepwise annealing of powders at 300, 400, 500 and 600°C in nitrogen atmosphere the dimension of crystallites increased with increasing the annealing temperature and the peaks corresponding to the MoO3 and NiMoO4 phases appeared in diffractograms already after annealing at 300°C. After annealing at 600°C in the powder electrodeposited at the Ni/Mo = 1/0.3 the predominant NiMoO4 phase together with a small amount of MoNi4 phase was detected by the XRD. The TEM analysis showed that two types of particles were present in the as-deposited powders: amorphous and crystalline. Among the crystalline particles in all powders MoO3 and MoNi4 phases prevail, while in the powder electrodeposited at the Ni/Mo = 1/0.3 NiO phase was also detected. It was discovered that the NiMoO4 phase was formed by solid state reaction between NiO and MoO3 at elevated temperatures. From the results of the TEM analysis the mechanism of the electrodeposition of alloy powders of the Mo-Ni-O system has been proposed for the first time in the world literature.