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 amonijumhloridnogi natrijum-sulfatnog pomoćnog elektrolita različitih odnosa koncentracijaNi/Fe jona i prahova Mo-Ni-O legura iz rastvora amonijum-hloridnog i amonijumsulfatnogpomoćnog elektrolita različitih odnosa koncentracija Ni/Mo jonaispitivano je snimanjem polarizacionih krivih. Sve polarizacione krive su imale istioblik okarakterisan dvema prevojnim tačkama. Prva prevojna tačka odgovarala jepočetku taloženja legure uz nagli porast gustine struje usled paralelnog izdvajanjavodonika, dok je druga prevojna tačka odgovarala potencijalu na kome brzinaukupnog procesa na katodi postaje ograničena brzinom formiranja mehurovavodonika.Morfologija, hemijski i fazni sastav istaloženih prahova Fe-Ni i Mo-Ni-Olegura ispitivani su pomoću SEM, EDS, XRD, DSC, TGA, AAS, TEM i SAEDanalize.Ustanovljeno je da morfologija istaloženih prahova Fe-Ni legura zavisi ododnosa koncentracija Ni/Fe jona, kao i od prisustva Fe(III) ili Fe(II) vrsta urastvoru. Zajednička karakteristika morfologije svih prahova Fe-Ni legura jeprisustvo sfernih zrna i šupljina konusnog oblika, koje odgovaraju mestima gde suse formirali mehurovi vodonika. U prahovima istaloženim pri odnosu Ni/Fe = 9/1 izrastvora oba pomoćna elektrolita uočeni su kristali oblika pagode, koji pripadajuFeNi3 fazi. EDS analiza sastava prahova potvrdila je pojavu anomalnog taloženja Fei Ni pri svim ispitivanim odnosima koncentracija Ni/Fe jona, pri čemu je anomalankarakter 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 sastavaistaloženih prahova. Ustanovljeno je da NiFe2O4, poznat kao magnetni materijal saširokim opsegom primene, predstavlja dominantnu fazu u prahu istaloženom priodnosu Ni/Fe = 1/3 nakon odgrevanja na 600°C.Utvrđeno je da odnos koncentracija Ni/Mo jona utiče na morfologiju ihemijski sastav prahova Mo-Ni-O legura. Morfologija prahova Mo-Ni-O leguraokarakterisana je prisustvom dve vrste sfernih aglomerata: aglomerata sakompaktnom, relativno glatkom površinom i aglomerata sa razvijenom površinomsastavljenom od kristala nanometarskih dimenzija. Rezultati EDS analize ukazali suna prisustvo i do 70 at. % kiseonika u talogu, kao i na nehomogen sastav česticaprahova. Istaloženi prahovi su bili nanokristalni, bez pojave oštrih pikova nadifraktogramima. Tokom uzastopnih termičkih tretmana prahova na 300, 400, 500 i600°C u atmosferi azota došlo je do povećanja dimenzija kristalita sa temperaturomodgrevanja, uz pojavu pikova MoO3 i NiMoO4 faza na difraktogramima već nakonodgrevanja na 300°C. Nakon odgrevanja na 600°C u uzorku praha istaloženog priodnosu Ni/Mo = 1/0,3 XRD analizom je ustanovljeno da dominira NiMoO4 faza, avIzvodda je u manjoj meri prisutna i MoNi4 faza. TEM analiza istaloženih prahova jepokazala istovremeno prisustvo amorfnih i kristalnih čestica. Kristalne čestice svihprahova sadrže pretežno MoO3 i MoNi4 fazu, dok je kod praha istaloženog priodnosu Ni/Mo = 1/0,3 uočeno i prisustvo NiO faze. Otkriveno je da je formiranjeNiMoO4 faze posledica reakcije u čvrstom stanju između NiO i MoO3 na povišenimtemperaturama. Na osnovu rezultata TEM analize pretpostavljen je mehanizamelektrohemijskog taloženja prahova legura Mo-Ni-O sistema po prvi put u svetskojliteraturi.

Electrodeposition of Fe-Ni alloy powders from ammonium chloride andsodium sulfate containing solutions of different Ni/Fe ions concentration ratios andMo-Ni-O alloy powders from ammonium chloride and ammonium sulfatecontaining solutions of different Ni/Mo ions concentration ratios was investigatedby the polarization measurements. All polarization curves have the similar shapecharacterized by two inflection points. The first inflection point corresponds to thebeginning of the alloy deposition, which is accompanied with the sharp increase ofthe current density due to the simultaneous hydrogen evolution reaction, while thesecond inflection point reflects the moment when the total cathodic processbecomes controlled by the rate of the hydrogen bubbles formation.The morphology, chemical and phase composition of the electrodepositedFe-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 todepend on the Ni/Fe ions concentration ratio, as well as on the presence of Fe(III) orFe(II) ions in the solution. A common characteristic of the morphology of all Fe-Nialloy powders was the presence of rounded agglomerates and cone shape cavitiescorresponding to the positions where the hydrogen bubbles were formed. In thepowders electrodeposited at the ratio Ni/Fe = 9/1 from both solutions, pagoda likecrystals, corresponding to the FeNi3 single phase, were detected. The EDS analysisof alloy powders confirmed anomalous co-deposition of Fe and Ni at allinvestigated 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 formingNiO, NiFe2O4 and Fe2O3 phases in different proportions depending on the originalpowder composition. The NiFe2O4 phase, one of the most important magneticmaterials with wide range of applications, was found to be the dominant one in thesample electrodeposited at Ni/Fe = 1/3 after annealing at 600°C.It was found that the morphology and the chemical composition of theMo-Ni-O alloy powders were influenced by the Ni/Mo ions concentration ratio. Themorphology of the Mo-Ni-O alloy powders is characterized by the presence of twotypes of rounded agglomerates: agglomerates with compact, relatively smoothsurface 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 thedeposit as well as the non-homogeneous composition of powder particles. The asdepositedalloy powders were nanocrystalline, showing no peaks in diffractograms.During the stepwise annealing of powders at 300, 400, 500 and 600°C in nitrogenatmosphere the dimension of crystallites increased with increasing the annealingtemperature and the peaks corresponding to the MoO3 and NiMoO4 phases appearedin 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 phasetogether with a small amount of MoNi4 phase was detected by the XRD. The TEManalysis showed that two types of particles were present in the as-depositedpowders: amorphous and crystalline. Among the crystalline particles in all powdersMoO3 and MoNi4 phases prevail, while in the powder electrodeposited at theNi/Mo = 1/0.3 NiO phase was also detected. It was discovered that the NiMoO4phase was formed by solid state reaction between NiO and MoO3 at elevatedtemperatures. From the results of the TEM analysis the mechanism of theelectrodeposition of alloy powders of the Mo-Ni-O system has been proposed forthe first time in the world literature.