scientific report 2014 (in Romanian)- Raport_stiintific_Etapa1_MAGNEF_cod_0971_contract_275_2014_1

scientific report 2015(in Romanian)- Raport_stiintific_tehnic_MAGNEF_Etapa_2_an_2015

scientific report 2016 (in Romanian)-Raport_stiintific_si_tehnic_Et3_2016_MAGNEF_275_2014

scientific report 2017 (in Romanian)-Raport stiintific si tehnic etapa 4 an 2017 MAGNEF PCCA2013 contract 275_2014

final report of the project (in Romanian)-Raport final MAGNEF PCCA2013 contract 275_2014

Main results from 2014

1. Literature review concerning compositions and preparation routes which will be used to prepare Fe₁₆N₂ magnetic particles with improved properties

2. Studies concerning optimization of the compositions and preparation routes which will be used to prepare bonded magnets based on Fe₁₆N₂ particles

3. Wet chemistry preparation methods and structural investigation of the oxyhydroxides with needle-like morphology

(i) Goethite obtained by controlled oxidation of Fe²⁺ salts

(ii) Goethite obtained from FeNO3/ KOH with molar ratio Fe³⁺:OH^-  of  1:6

(iii) Goethite obtained from FeNO3/KOH with molar ratio Fe³⁺:OH^- of 1:12

Main results from 2015

Calculations were performed using the SPRKKR code for evaluation of the magnetic moments for Fe16N2 doped with Ti.  Fe substitution with Ti increases the thermodynamic stability of Fe16N2 but slightly reduces magnetic properties.

(i) Energy of formation for Fe₁₅XN₂ compound (X = metal)

Calculations of energy bands with WIEN2k program showed increased thermodynamic stability of Fe16N2 for the substitution of Fe with Ti or V, among many possible iron substution with metals, and these predictions allow the design of future preparation in order to increase the  thermodynamic stability of Fe16N2.

(ii) monodisperse hematite nanoparticles obtained by hydrothermal route

(iii) as prepared iron oxyhydroxide obtained by microwave route

(iv) hematite obtained by annealing in air at 400 ⁰C of  iron oxyhydroxide by microwave route)

using heat treatment of iron salts solutions in microwave field were obtained amorphous particles of iron oxyhydroxide which turns in crystalline hematite particles by further annealing in air at 400 ⁰C.

(v) X-ray diffraction data for S1 (goethite nitrided at 140 ⁰C), S2 (hrmatite nitrided at 140 ⁰C), S3 (goethite nitrided at 150 ⁰C) and S4 (processed goethite nitrided at 140 ⁰C)

By treating goethite particles in H2 / Ar  flow at 450 ⁰C and then nitriding in ammonia flow at lower temepratures was possible to obtain a significant amount of Fe₁₆N₂ and small amount of metallic iron phase.

(vi) SEM image of goethite reduced and then nitrided

The Fe₁₆N₂ particles retain the needle-like structure of the goethite precursor even after the reduction in H2 / Ar  flow at 450 ⁰C and subsequent treatment in ammonia flow.

(vii) hysteresis loop at ambient temperature of nitrided goethite

(viii) hysteresis loop at ambient temperature of nitrided goethite pressed in magnetic field

Preliminary  permanent magnets were produced by compressing and heating Fe16N2 particles in magnetic field. There is an increase of the remanence from 29% for the original particles up to 38% for the particles oriented and pressed under magnetic field while saturation magnetization (Ms) and coercive field (Hc) remain approximately constant.

Main results from 2016

1. Preparation of elongated particles of β-FeOOH (akaganeite) by wet chemistry which were afterwards reduced in 5%H2/Ar and nitrided in ammonia flow

(A)                                                                      (B)

(i) SEM images of β-FeOOH (akaganeite): as prepared (A) and reduced and nitrided (B)

2. Preparation of transition metal substituted α-FeOOH (goethite) acicular particles by wet chemistry which were afterwards reduced in 5%H2/Ar and nitrided in ammonia flow

(A)                                                                      (B)

(ii)  SEM image (A) and XRD pattern (B) of α-Fe(Ni)OOH (goethite) with 5 at% Ni

3. Preparation of transition metal substituted amorphous iron oxide by microwave route. After reduction and subsequent long time nitriding it was obtained a mixture or Fe16N2 and Fe

(A)                                                                  (B)

(iii) XRD spectra of 5at%Ni substituted amorphous iron oxide prepared by microwave route: (A) as prepared, (B) after reduction and subsequent long time nitriding

(iv) XRD spectra for Fe16N2 milled composites after various milling time and subsequent annealing

(v) Hysteresis loops for the milled composites containing Fe16N2. Above is presented the full range, while below is shown the central part with higher magnification

It can be observed that the magnetization of saturation decreased strongly after milling and it has values much lower than that of nitrided goethite. However, the coercive field is higher for the composites milled long time than that of nitrided goethite.

5. Based on Mossbauer spectroscopy data we obtained the type of phases (even amorphous or poorly crystallized with superparamagnetic behaviour) and the relative amount of each phase. The samples obtained via microwave route were reduced at 420 ⁰C and subsequently nitrided at various temperatures. At a nitridation temperature of 130 ⁰C was formed mainly metallic iron while above 150 ⁰C, besides the main Fe16N2 phase, appeared also Fe4N and Fe3N with detrimental effect on magnetic properties. The Fe16N2 is characterized by 3 magnetic sextets with hyperfine magnetic fields of about 40.25 T pentru Fe(4d), 31.55 T pentru Fe(8h) si 29.65 T for Fe(4e) crystallographic positions. The other sextets were assigned to Fe, Fe3N and Fe4N, while the central doublet and singlet were assigned to superparamagnetic iron oxide and superparamagnetic iron nitride, respectively.

(vi) Mossbauer spectra of samples obtained via microwave route and reduced and subsequently nitrided at various temperatures: 140 ⁰C (A), 150 ⁰C (B), 160 ⁰C (C).

6. The goethite was reduced at various temperatures and subsequent nitrided. At low reduction temperatures were obtained also other Fe-N phases besides Fe16N2 which decrease the total magnetization at saturation

(vii) (A) - goethite reduced at 350 ⁰C, (B) - goethite reduced at 355 ⁰C and nitrided at 140 ⁰C, (C) - goethite reduced at 360 ⁰C and nitrided at 135 ⁰C, (D) - goethite reduced at 385 ⁰C and nitrided at 140 ⁰C, (E) - goethite reduced at 425 ⁰C and nitrided at 140 ⁰C

7. The maximum coercivity was obtained for samples reduced at low temperatures while the maximum magnetization at saturation was obtained for samples reduced at high temperatures

(A)                                                              (B)

(viii) Hysteresis loops measured at ambient temperature for samples: (A) - reduced at 360 ⁰C and nitrided at 135 ⁰C, (B) - reduced 470 ⁰C and nitrided at 140 ⁰C

8. Goethite reduced at 470 ⁰C and nitrided at 140 ⁰C was pressed (0.8 GPa) perpendicular to applied field (0.3 T). There is a high difference between the remanence measured in plane of the sample and that one measured perpendicular to the plane of the sample

(A)                                                              (B)

(ix) Hysteresis loops measured at ambient temperature for goethite pressed perpendicular to magnetic field and measured with the magnetic field applied: (A) - parallel to the plane of the sample, (B) - perpendicular to the plane of the sample

9. By mixing the milled composites with epoxy resin and solidificate them in magnetic field there is a significant difference between the remanence measured for magnetic field applied parallel and perpendicular to the sample during solidification

(x) Hysteresis loops and magnetization curves measured at ambient temperature for milled composites mixed with epoxy resin and solidificated in magnetic field oriented parallel and perpendicular to the sample during solidification

Main results from 2017

1.  Starting from Fe:Zr powders with mass ratio of 19:1 and by mixing Fe, Zr, Fe₄N powders with mass ratio 15.2:0.8:2 were prepared milled composites using a planetary mill in order to see the substitution of Fe by Zr. The reason for this substitution is that, according to first principles simulations, by replacing 1 atom of Fe from Fe₁₆N₂ with Ti, Zr or V the stability of Fe₁₆N₂ phase increases. The parameters used for miling: 4 h and 8 h miling time, ball to powder ratio 10:1. The samples were subsequent heat treated in 5%H2/Ar flow at 450 ⁰C and nitrided under nitrogen and ammonia flow at temperatures between 160 ⁰C - 300 ⁰C

2. Mossbauer spectroscoy and XRD data proved that Fe₁₆N₂ phase was not formed for the milled composites heat treated under ammonia and nitrogen flow. At 220 ⁰C a  very low amount of Fe-N phase (not Fe₁₆N₂₎ was detected in the sample annealed in ammonia. Magnetic measurements proved soft magnetic behaviour.

Mossbauer spectra for Fe-Zr milled composites heat treated under ammonia flow ( A - not heated , B - heated at 160 ⁰C , C - heated at 220 ⁰C)

X-Ray diffractograms for Fe-Zr milled composites heat treated under ammonia flow ( A - not heated , B - heated at 160 ⁰C , C - heated at 220 ⁰C)

Ambient temperature hysteresis loops for Fe-Zr milled composites heat treated under nitrogen proving soft magnetic behaviour

3.  Fe₁₆N₂ was prepared by a new route starting from goethite (alpha-FeOOH) produced by controlled oxidation of Fe²⁺ iron salt solution. For this purpose, deoxygenated aqueous solutions of Na₂CO₃ and FeSO₄ . 7H₂O were mixed and immediately afterwards a controlled air flow (2-4 L/min) passed through reactant solutions for 2 - 4 h at temperatures between 40 - 60 ⁰C. Acicular goetite particles with various morphology depending on reaction conditions were obtained by this route.

(A)                                                                     (B)

(C)                                                                        (D)

SEM images for goethite samples prepared starting from FeSO₄/Na₂CO3 aqueous solutions and  heat treated in air flow: (A) - 4h/40 ⁰C, (B) - 8h/40 ⁰C, (C) – 2h/40 ⁰C, (D) – 4h/ 60 ⁰C . Suitable morphology and dimensions in order to get Fe₁₆N₂ with good magnetic properties are obtained for (A) - 4h/40 ⁰C

4. Fe₁₆N₂ was obtained from goethite produced by  Fe²⁺ carbonated route by reducing under 5% H₂/Ar flow at 350 - 450 ⁰C and nitridation under ammonia flow at 140 - 150 ⁰C. The amount of Fe₁₆N₂ is very low for sample reduced at 450 ⁰C and afterwards nitrided at 143 ⁰C due to the large Fe grains difficult to nitridate. The samples reduced at lower temperatures are easy to nitridate.

(A)                                                                              (B)

SEM images for Fe₁₆N₂ produced from goethite via Fe²⁺ carbonated route subsequently processed:   (A) - reduced 3h/ 380 ⁰C and nitrided 25h / 143 ⁰C, (B) - reduced 3h/ 450 ⁰C and nitrided  25h / 143 ⁰C

X-ray diffractograms for goethite via Fe²⁺ carbonated route subsequently processed: (A) - not heat treated, (B) - reduced 3h/360 °C, (C) – reduced 3h/380 °C and nitrided 25h/143 °C, (D) - reduced 3h/390 °C and nitrided 25h/143 °C, (E) – reduced 3h/450 °C and nitrided 25h/143 °C

The sample obtained by reducing at 450 ⁰C and nitriding at 143 ⁰C the goethite obtained via Fe²⁺ carbonated route exhibits soft magnetic behaviour (low amount of Fe₁₆N₂) whereas the sample reduced at 360 ⁰C and nitrided at  143 ⁰C (high amount of Fe₁₆N₂) shows much higher coercivity and remanence

Hysteresis loops measured at ambient temperature for: (A)- sample reduced at 380 ⁰C and nitrided at 143 ⁰C (B) - sample reduced at 450 ⁰C and nitrided at 143 ⁰C

5. Starting from goethite synthesized by coprecipitation from KOH and Fe(NO₃)₃.9H₂O was prepared Fe₁₆N₂ by reducing and nitridation. Fe₁₆N₂ nanoparticles obtained by this route have magnetization at saturation Ms=193 emu/g, coercivity H_c= 1120 Oe and remanence R=29.3 %. Paralelipipeds (length= 8 mm, width= 2 mm) were produced starting from this powder using a nonmagnetic mold built specially for this project.

(A) - stainless stell nonmagnetic mold for pressing  almost paralelipipedic shapes in magnetic field starting from Fe₁₆N₂ powder

(B) almost paralelipipedic Fe₁₆N₂ magnet

6. The paralelipipedic magnets pressed in magnetic field were annealed under nitrogen flow at temperatures between 150 - 200 ⁰ C for sintering purpose. The cross section SEM images show that grains remain elongated after pressing in magnetic field, but after sintering at 200 ⁰C the structure becomes more compact

(A)                                                                       (B)

Cross section SEM images for paralelipipedic magnets from Fe₁₆N₂ (goethite reduced and nitridated) powder pressed in magnetic field in paralelipipedic shapes: (A) - without subsequent annealing, (B) annealed under nitrogen flow at 200 ⁰C.

X-ray diffraction data for paralelipipedic magnets obtained by pressing Fe₁₆N₂ in magnetic field and subsequent annealing under nitrogen flow: (A) - not annealed, (B) - annealed at 170 ⁰C , (C) - annealed at 200 ⁰C.

The sample not annealed contains only Fe₁₆N₂. By annealing at 170 ⁰C the phase Fe₄N begins to form.  After annealing at 200 ⁰C the main part of Fe₁₆N₂ decomposes, forming Fe₄N and metallic iron. This behaviour is supported also by Mossbauer spectroscopy measurements

(A)

 (B)

Hysteresis loops measured at ambient temperature for the Fe₁₆N₂ paralelipipeds pressed in magnetic field and subsequent processed: (A) - not sintered, (B) - sintered at 200 ⁰C.

The magnetic field is applied during measurement in the plane of the paralelipipedic sample  (on the direction of the magnetic field used to orientate the acicular nanoparticles during pressing and perpendicular to the pressing direction)

After sintering at temperatures 170 - 200 ⁰C, magnetization at saturation M_s, coercivity H_c and remanence R decrease compared with the not sintered sample due to formation of Fe₄Nphase

The remanence bot for the not sintered sample and for the sample sintered at 200 ⁰C increased compared with the remanence of not pressed powder due to shape anisotropy.

NATIONAL PATENTS:

OSIM PATENT REQUEST No. A 00686 from 20.09.2017 entitled (in Romanian)

 “Material magnetic pe baza de nanoparticule de nitrura de fier ordonata cu structura martensitica si procedeu de obtinere a lui”

Published ISI articles:

1. “Structural, magnetic and Mossbauer investigation of ordered iron nitride with martensitic structure obtained from amorphous hematite synthesized via microwave route”, Palade, P., Plapcianu, C., Mercioniu, I., Comanescu, C. C., Schinteie G., Leca, A., Vidu, R., Industrial & Engineering Chemistry Research, 56(11) (2017) 2958-2966

2. “Significant change of local atomic configurations at surface of reduced activation Eurofer steels induced by hydrogenation treatments”, Greculeasa, S. G., Palade, P., Schinteie, G., Kuncser, A., Stanciu, A., Lungu, G. A., Porosnicu, C., Lungu, C. P., Kuncser, V., Surface Science, 402 (2017) 114-119

3. “Electronic structure and magnetic properties of the Fe₁₆N₂ doped with Ti”, Benea, D., Isnard, O., Pop, V., J. Magnetism and Magnetic Materials 420 (2016) 75-80.

4. “Mossbauer and magnetic investigation of iron nitride with martensite structure synthesized from oxy-hydroxide type precursor”, Palade, P., Plapcianu, C., Mercioniu, I., Comanescu, C. C., Schinteie, G., Digest J. of Nanomaterials and Biostructures 11(1) (2016) 53-63.

5. “Small interfacial distortions lead to significant changes of the half-metallic and magnetic properties in Heusler alloys: The case of the new CoFeZrSi compound”, Birsan A., J. Alloys and Compounds 710(2017) 393-398

6. “Neutron diffraction study of the itinerant-electron metamagnetic Hf_0.825Ta_0.175Fe₂ compound”, Diop, L.V.B., Isnard, O., Suard, E., Benea, D., Solid State Communications229 (2016)16-21.

7. "Cross over between ferro and antiferromagnetic order in Fe itinerant electron magnetism: An experimental and theoretical study of the model (Hf,Ta)Fe₂ Laves phases”, Diop, L.V.B., Benea, D.,  Mankovsky, S.,Isnard, O., J. of Alloys and Compounds 643 (2015) 239–246.

Published BDI articles:

1. “Fe₂O₃ particles as precursors for α”-Fe16N2 phase synthesis”, One, R.A., Bortnic, R., Mican, S., Barbu-Tudoran, L., Pop, V., Studia Univ. Babes-Bolyai, Physica 61(1) (2016) 93-98.

2. "Surfactant effect on the structural and magnetic properties of Fe powders prepared by wet milling",  Hirian, R., Mican, S. Neamtu, B., Pop, V., Studia Univ. Babes-Bolyai, Physica, 60 (2) (2015) 53-58.

Book chapter:

1. “Transition metal/ Carbon Nanocomposites” in Carbon Nanomaterials Sourcebook: Nanoparticles, Nanocapsules, Nanofibers, Nanoporous Structures and Nanocomposites,   vol II,  V. Kuncser, P. Palade, G. Schinteie, F. Dumitrache, C. Fleaca, M. Scarisoreanu, I. Morjan, G. Filoti, p. 597-619,  CRC press, K. D. Sattler eds., (24 March 2016), 724 pages, ISBN 9781482252705.

International conferences:

1. “Hard Magnetic Materials: Present and Perspectives”, Pop, V., invited lecture at  International Conference on Powder Metallurgy & Advanced Material (RoPM-AM 2017), 17-20 september 2017 - Cluj-Napoca, Romania

2."Synthesis, structural, electronic and magnetic properties of α”-(Fe_1-xM_x)₁₆N₂ (M = Ti, Zr)", One R.,A., Mican S., Benea, D., Pop, V., poster presented atThe 11^th International Conference on Physics of Advanced Materials (ICPAM 2016), 8-14 september 2016 - Cluj-Napoca, Romania.

3. "Electronic Structure and Magnetic Properties of the Fe₁₆N₂ doped with Ti", Benea, D., Isnard, O., Pop, V., oral presentation at The 8th International Conference on Advanced Materials (ROCAM 2015), 7-10 july 2015, Bucharest.