Preparation and properties Preparation and properties of Fe and Feof Fe and Fe33OO44

nanoparticlesnanoparticles embedded in embedded in ZrOZrO22 matrixmatrix

P. Roupcová1, 2, O. Schneeweiss1

1Institute of Physics of Materials AS CR, Czech Republic

2Institute of Materials Engineering, Brno University ofTechnology, Czech Republic

Aim

n Preparation of the nanocomposite in the form of α-Fe and Fe3O4 nanoparticles embedded in ZrO2matrix.

n Magnetic properties and phase composition of the composite.

n Determination of activation energy of transformation of iron oxide particles to α Fe by annealing in hydrogen.

Experimental detailsn The samples of the nanocomposite were prepared by mixing of

nanocrystalline Fe3O4/Fe2O3 (~30 nm) or Fe2O3 (>100 nm) and ZrO2 or ZrH2 (~60÷110 nm) in agate mortar.

n Magnetic measurements were carried out using vibrating sample magnetometer (VSM) during a measurement in high temperature (at 293÷1093K), in the vacuum (10-2 Pa) and in the pure hydrogen (5N) atmosphere.

n 57Fe Mössbauer spectra (MS) were collected by a standard transmission method at room temperature using 57Co/Rh source.

n XRD was performed using CoKα radiation. n Temperature dependence of the magnetic moment were measured

for determination of critical temperatures of magnetic transition and isothermal transformation. The points corresponding to 50% of isothermal transformation were selected for the calculation of general rate of diffusion transformation in hydrogen by means ofArhenius equation.

TEM

Selected area diffraction pattern from fine particles was identified as cubic form of ZrO2. The clusters of Fe3O4 are disseminated in zirconia matrix.

Cubic-ZrO2

Cubic-ZrO2

γ-Fe3O4

XRD (as-prepared samples)

0

100

200

300

Counts/s

Position [°2Theta]

40 50 60 70 80 90

0.0000 0.0000 0.0000 0.0000

Position [°2Theta]

30 40 50 60 70 80 90 100 110

Counts/s

25

100

225

400 ZrH2-Hem_3

mon-ZrO2+Fe3O4

ZrH2+Fe2O3

ZrH2+Fe3O4

cub-ZrO2+Fe3O4

83% - ZrH2

17% - Fe3O4 / Fe2O3

MS

-8 -4 0 4 8VELOCITY [mm/s]

0.970

0.980

0.990

1.000

RE

LATI

VE

TR

AN

SM

ISS

ION

α−Fe2O3Fe(III)

-8 -4 0 4 8VELOCITY [mm/s]

0.975

0.980

0.985

0.990

0.995

1.000

RE

LATI

VE

TRAN

SMIS

SIO

N

crystalline Fe3O4 / Fe2O3

amorphous Fe3O4 / Fe2O3

XRD Data

Magnetite - 42 nm, ZrO2c - 35 nm, Hematite - 51 nmZrO2 - 34 nm, Magnetite - 33 nm

Magnetite - 18%, ZrO2c - 75%, Hematite - 7%ZrO2c - 98%, Magnetite - 2%

Cubic-ZrO2 + Magnetite

Magnetite - 42 nm, ZrO2m - 25 nm, Hematite - 41 nmZrO2 - 30 nm, Magnetite - 30 nm

Magnetite - 42%, ZrO2m - 53%, Hematite - 5%ZrO2m - 99%, Magnetite - 1%

Monoclinic-ZrO2 + Magnetite

FeO-51nm, ZrO2m-38nm, Fe-16nm, ZrO2 t-22nmZrH2 - 108 nm, Magnetite - 30 nm

FeO-15%, ZrO2m-45%, Fe-15%, ZrO2t-25%ZrH2 - 98%, Magnetite - 2%

ZrH2 + Magnetite

FeO-42nm, ZrO2m-23nm, Fe3O4-36nm, Zr-25nm,Fe-45nmZrH2 - 110 nm, Hematite - 90 nm

FeO-30%, ZrO2m-20%, Magnetite -20%, Zr-20%,Fe-10%ZrH2 - 43%, Hematite - 57%

ZrH2 + Hematite

annealing at 800°C in vacuumas preparedphase composition/ mean size of particles

Temperature dependence of the magnetic moment and hysteresis loops of the as prepared powder (before and after TM)

0 200 400 600 800TEMPERATURE [°C]

0

0.01

0.02

0.03

REL

ATI

VE M

AGN

ETI

C M

OM

ENT 800°C in vacuum

800°C in hydrogen

α-Fe

Fe3O4

-10000 -5000 0 5000 10000MAGNETIC FIELD [Oe]

-0.8

-0.4

0

0.4

0.8

MA

GN

ETI

C M

OM

EN

T [e

mu]

800°C in vacuum800°C in hydrogen

-10000 -5000 0 5000 10000MAGNETIC FIELD [Oe]

-0.4

-0.2

0

0.2

0.4

MA

GN

ETI

C M

OM

EN

T [e

mu]

As-prep. samp.1As-prep. samp.2

XRD (annealed in hydrogen and in vacuum)

Position [°2Theta]

40 50 60 70 80 90 100 110 120

C ounts/s

0

100

200

300

ZrO2_Hem_772956-ICSD 57.4 %64998-ICSD 18.3 %90889-ICSD 24.3 %

Position [°2Theta]

40 50 60 70 80 90 100 110 120

C ounts/s

0

100

200

300

ZrO2_Hem_1189429-ICSD 75.2 %82137-ICSD 6.8 %82456-ICSD 18.1 %57,4% - tetr-ZrO2

24,3% - cubic-ZrO2

18,3% - α−Fe

75,2% - cubic-ZrO2

18,1% - Fe3O4

6,6% - Fe2O3

MS (annealed in hydrogen and in vacuum)

-8 -4 0 4 8VELOCITY [mm/s]

0.98

0.985

0.99

0.995

1

0.975

0.98

0.985

0.99

0.995

1

REL

ATI

VE

TRAN

SMIS

SIO

N

α-FeFe(III) IS=0.2Fe(III) IS=0.7

-8 -4 0 4 8VELOCITY [mm/s]

0.992

0.994

0.996

0.998

1

0.988

0.992

0.996

1

REL

ATIV

E T

RA

NS

MIS

SIO

N

HematiteMagnetiteFe(III) IS=0.7Fe(III) IS=0.2

MS and XRD data

18% Fe3O4

7% Fe2O3

75% c-ZrO2

3%Fe(III)IS=0.2

11% γ-Fe2O3

34% Fe2O3

50% Fe3O4

in vacuum

18% α-Fe

24% c-ZrO2

58% t-ZrO2

2% Fe(III)IS=0.7

8%Fe(III)IS=0.2

90% α-Fein H2

21% Fe3O4

79% c-ZrO2

nanocrystalline or/and amorphous structure of magnetite and maghemite

as-prepared

XRDMössbauer spectroscopyC-ZrO2+ Fe3O4

Phase composition of the samples (originally cubic ZrO2 + Fe3O4) annealed by measurement of thermomagnetic curve up to 800°C in hydrogen and in vacuum.

Isothermal curves + hysteresis loops

0 100 200 300Time [min]

0

0.01

0.02

0.03

Mag

netic

mom

ent [

emu]

580°C in hydrogen540°C in hydrogen

Start of transformation

50% of transformation

End of transformation

-400 -200 0 200 400

-0.08

-0.04

0

0.04

0.08

-10000 -5000 0 5000 10000MAGNETIC FIELD [Oe]

-0.8

-0.4

0

0.4

0.8

MA

GN

ETI

C M

OM

EN

T [e

mu]

As preparedAfter homogen.After 620°C in H2

y´ - rate of decrease magnetic moment Q - activation energyA - constantR - molar gas constant

n Activation energy of magnetic transformation:

n below transition temperature Q = 1 kJ/mol

n above transition temperature Q = 3.1 kJ/mol

Arhenius equation: (general rate of diffusion transformation)

TRQAy

TRQAy 1lnlnexp ⋅+=′⇒

⋅−⋅=′

1.12E-003 1.20E-003 1.28E-003TEMPERATURE [1/K]

5

6

7

8

9

10

11

TIM

E [ln

s]

TC = 830 K

-19%81%6%3%7%84%Annealed at 620°C6

-20%80%10%4%3%83%Annealed at 600°C5

-20%80%6%3%5%85%Annealed at 580°C4

-21%79%-3%2%95%Annealed at 540°C3

9%20%71%2%3%5%90%Annealed at 520°C2

-20%80%2%-7%90%Annealed at 500°C1

ZrO2-cα-FeZrO2-tFe(II)FeOFe(III)α-Fe

XRDMössbauer spectroscopy

0.950

0.960

0.970

0.980

0.990

1.000

REL

ATI

VE T

RA

NS

MIS

SIO

N

-6 -4 -2 0 2 4 6VELOCITY [mm/s]

0.950

0.960

0.970

0.980

0.990

1.000

RE

LATI

VE T

RA

NSM

ISS

ION

0.940

0.960

0.980

1.000

RE

LATI

VE T

RAN

SMIS

SIO

N

-6 -4 -2 0 2 4 6VELOCITY [mm/s]

-6 -4 -2 0 2 4 6VELOCITY [mm/s]

-6 -4 -2 0 2 4 6VELOCITY [mm/s]

annealed at 500°C in H2

annealed at 520°C in H2

annealed at 540°C in H2

0.940

0.960

0.980

1.000

REL

ATI

VE T

RA

NS

MIS

SIO

N

-6 -4 -2 0 2 4 6VELOCITY [mm/s]

0.950

0.960

0.970

0.980

0.990

1.000

RE

LATI

VE T

RA

NSM

ISS

ION

0.960

0.970

0.980

0.990

1.000

RE

LATI

VE T

RAN

SMIS

SIO

N

-6 -4 -2 0 2 4 6VELOCITY [mm/s]

-6 -4 -2 0 2 4 6VELOCITY [mm/s]

-6 -4 -2 0 2 4 6VELOCITY [mm/s]

annealed at 580°C in H2

annealed at 600°C in H2

annealed at 620°C in H2

α-FeFe(III) IS=0.2Fe(III) IS=0.4Fe(III) IS=0.6Fe(II) IS = 1Fe(II) IS = 1.4FeO

Conclusionsn The as-prepared powders consist of mixture of Fe3O4(30nm), Fe2O3

(90 nm), ZrO2-monoclinic (30 nm) and cubic (35 nm) and ZrH2 (110 nm) phases.

n The samples annealed in vacuum are formed by particles of FeO(50 nm), Fe3O4(45 nm), Fe2O3 (50 nm), ZrO2-monoclinic (25 nm), tetragonal (22 nm) and cubic (35 nm).

n Annealing in hydrogen causes reduction of iron oxides to pure iron particles (180 nm) and clusters of Fe atoms in ZrO2.

n The magnetic parameters confirm full transformation of iron oxides to α-Fe.

n The activation energy of transformation Fe3O4 to α-Fe calclulatedusing Arhenius equation exhibit different values below (QH = 1.0 kJ/mol) and above (QH = 3.1 kJ/mol) magnetic transition temperature (Hedvall effect).

Thank you for your attention

n Thank to Dr. N. Pizurová for the TEM analysis.

n This work was supported by the Czech Ministry of Education, Youth and Sports (1M6198959201) and Academy of Sciences of the Czech Republic (AV0Z20410507).