A.R. Lashin1, O. Schneeweiss1, P.Sajdl2

1Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, CZ-616 62 Brno, Czech Republic

2Institute of Chemical Technology, Department of Power Engineering, Technicka 3, 16628 Prague, Czech Republic

Aim

Investigation of phase composition atsurface of bcc Fe94Si6 alloy based on heat

treatment.

Experiment

XPS 1.4867 keV

~1nm

CEMS~100nm

14.4 keVSGMS

~1000nm

Samples: 11×11 × 0.3 mm plates of Fe–3wt.%Si(grain oriented steel sheet) polished using the

best metallography procedure.

Mössbauer spectroscopy

1- Standard Mössbauer spectra were measured in scattering geometry with detection 14.4 keV gamma radiation using 2π proportional counter.

2- 57Fe CEMS spectra were measured using 57Co in Rh source at room temperature in gas-filled detector

XPS spectra were taken in Institute of Chemical

Technology, Department of Power Engineering, Prague, Czech Republic for this sample using ESCA equipment using 1.4867 keV X-ray radiation on Fe 2p edge. Surface cleaning by repeated Ar sputtering was carried out in situ.

1- CEMS spectra for the polished sample contains three sextets

S1: δ= 0.00 mm/s, σ=0.00 mm/s, Bhf=33.1 TS1: δ= 0.05 mm/s, σ=0.00 mm/s, Bhf=30.9 TS1: δ= 0.11 mm/s, σ=-0.04 mm/s, Bhf=27.4 T

2- CEMS spectra for the polished and etched sample (in HF+H2O2) showed:

a) Three sextets for the Substrate.b) Fe (III), δ=0.36 mm/s and εQ=0.82 mm/s,

with A=0.11.

3-CEMS spectra after annealing in vacuum for 2 hours at 780 oC showed:

a) Three sextets for the substrate.b) Fayalite Fe2SiO4, δ=1.15 mm/s and εQ=2.72

mm/s, with A=0.04.c) Fe(III) δ=0.42 mm/s and εQ=0.78 mm/s ,

with A=0.01.-15 -10 -5 0 5 10 15

Velocity [mm/s]

0.98

1

1.02

1.04

1.06

1.08

1.11

1.02

1.04

1.06

1.08

1.1

Rel

ativ

e em

issi

on

1

1.02

1.04

1.06

1.08

1.1

Ground and polishedExperimental dataThe fitting curveFe with 0 Si in nnFe with 1 Si in nnFe with 2 Si in nn

Ground,polished and etchedExperimetal dataThe fitting curveα-FeSiFe(III)

Ground, polished, etched and annealedExperimental dataThe fitting curveα-FeSiFayalite Fe2SiO4Fe(III)

(1)

(2)

(3)

1-SGMS spectra for the polished sample showed:Three sextets for the substrateS1: δ= 0.00 mm/s, σ=0.00 mm/s, Bhf=33.1TS1: δ= 0.04 mm/s, σ=0.00 mm/s, Bhf=30.6T S1: δ= 0.10 mm/s, σ=0.00 mm/s, Bhf=27.4T

2- SGMS spectra for the polished and etched sample (in HF+H2O2)

3-SGMS spectra after annealing in vacuum for 2 hours at 780 oC

-15 -10 -5 0 5 10 15

Velocity [mm/s]

0.99

1

1.01

1.02

1.03

1.04

1.05

0.99

1

1.01

1.02

1.03

1.04

1.05

Rel

ativ

e em

issi

on

0.99

1

1.01

1.02

1.03

1.04

1.05

Experimental DataThe fitting curveFe with 0 Si in nnFe with 1 Si in nnFe with 2 Si in nn

(1)

(2)

(3)

XPS measurement

O min - zakladni stav

Su3 3

Fe 2

pFe

2p

Fe 2p1/2 Fe 2p3/2Fe 2p

x 10-2

30

40

50

60

70

80

90

100

110

120

CPS

735 730 725 720 715 710 705Binding Energy (eV)

3O min

Su3 3

Fe 2

p3/2

Fe 2p1/2 Fe 2p3/2Fe 2p

x 10-1

20

30

40

50

60

70

80

CPS

730 725 720 715 710 705 700Binding Energy (eV)

95 min

Su3 3

Fe 2

p3/2

Fe 2p1/2 Fe 2p3/2Fe 2p

2

4

6

8

10

CPS

730 725 720 715 710 705Binding Energy (eV)

155 min

Su3 3

Fe 2

p3/2

Fe 2p1/2 Fe 2p3/2Fe 2p

2

4

6

8

10

12

14

16

CPS

735 730 725 720 715 710 705Binding Energy (eV)

215 min

Su3 3

Fe 2

p3/2

Fe 2p1/2 Fe 2p3/2Fe 2p

2

4

6

8

10

12

14

16

18

20

22

CPS

730 725 720 715 710 705Binding Energy (eV)

275 min

Su3 3

Fe 2

p3/2

Fe 2p1/2 Fe 2p3/2Fe 2p

5

10

15

20

25

30

CPS

730 725 720 715 710 705Binding Energy (eV)336 min

Su3 3

Fe 2

p3/2

Fe 2p1/2 Fe 2p3/2Fe 2p

5

10

15

20

25

30

CPS

720 710Binding Energy (eV)

477 min

Su3 3

Fe 2

p3/2

Fe 2p1/2 Fe 2p3/2Fe 2p

5

10

15

20

25

30

CPS

720 710Binding Energy (eV)

The depth profile

0 40 80 120 160 200DEPTH [nm]

0

20

40

60

80

100

CONTE

NT

[%]

Fe0

SiOFe3+ & Fe2+

Annealing in oxygen

Four samples have been ground and polished both sides and then annealed in oxygen for 10 minutes at 500 oC, 600 oC, 700 oC and 780 oC respectively.

The CEMS measurements for the four samples showed hematite α-Fe2O3 , Fe with 0 Si in nn (pure iron) on the surface of these samples in addition to the substrate which contains α-FeSi.

The CEMS measurements for the four samples showed:

1-Hematite α-Fe2O3 ( )a) At 500 oC

δ= 0.36 mm/s, σ=-0.14 mm/s, Bhf=51.2 T

b) At 600 oCδ= 0.37 mm/s, σ=-0.16 mm/s, Bhf=51.5 T

c) At 700 oCδ= 0.37 mm/s, σ=-0.16 mm/s, Bhf=51.5 T

d) At 780 oCδ= 0.37 mm/s, σ=-0.16 mm/s, Bhf=51.6 T

2- Fe with 0 Si in nn ( )3- α-FeSi ( )

-15 -10 -5 0 5 10 15

Velocity [mm/s]

1

1.04

1.08

1.12

1.16

1

1.04

1.08

1.12

1.16Rea

ltive

em

ission

1

1.02

1.04

1.06

1.08

1

1.02

1.04

1.06

1.08

1.1

Experimental dataThe fitting curveHematite Fe2O3Fe with 0 Si in nnα-FeSi

500 oC

600 oC

700 oC

780 oC

The concentration of hematite which has been detected on the surface of these samples increases by increasing the

annealing temperature

Relative intensity of Hematite verus annealing temperature

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

450 500 550 600 650 700 750 800

annealing temperature T (oC)

Rel

ativ

e in

tens

ity o

f Hem

atite

Annealing in Ar

Two samples have been ground, polished and annealing in oxygen for 10 minutes at 500 oC and 600 oC and then polished once more and annealed in Ar for 10 minutes at 500 oC and 600 oC respectively.

CEMS spectra for these two samples showed magnetite Fe3O4, fayalite Fe2SiO4, and Fe(III) where the concentration of magnetite at 500 oC was greater than that at 600 oC.

1-At 500 oC, CEMS showed:(a) Magnetite Fe3O4 ( ) (~ 1:2)

S1: δ=0.24 mm/s, σ=0.00 mm/s, Bhf=48.6 TS2: δ=0.65 mm/s, σ=0.00 mm/s, Bhf=45.8 T

(b) Fe with higher content of Si ( )δ=0.28 mm/s, σ=0.10 mm/s Bhf=21.3 T

(c) α-FeSi ( )(d) Fayatite Fe2SiO4 ( )

δ=1.36 mm/s, εQ=1.42 mm/s, with A=0.02(e) Fe (II/III) ( )

δ=0.62 mm/s, εQ=0.69 mm/s with A=0.01

2-At 600 oC, CEMS showed:(a) Magnetite Fe3O4 ( ) (0.42: 0.58)

S1: δ=0.26 mm/s, σ=0.00 mm/s Bhf=48.4 TS2: δ=0.65 mm/s, σ=0.00 mm/s Bhf=45.8 T

(b) Fe with 0 Si in nn ( ) δ=0.00 mm/s, σ=0.00 mm/s Bhf=32.9T

(c) α-FeSi ( )(c) Fayalite Fe2SiO4( )

δ=1.22 mm/s and εQ=2.62 mm/s, with A=0.04(d) Fe(III) ( )

δ=0.49mm/s, εQ=0.83mm/s, with A=0.02

-15 -10 -5 0 5 10 15

Velocity [mm/s]

0.98

1

1.02

1.04

1.06

1.08

Rel

ativ

e em

issi

on

0.99

1

1.01

1.02

1.03

1.04

1.05Experimental dataThe fitting curveMagnetite Fe3O4α-FeSiFe with high Si contentFayalite Fe2SiO4Fe(II/III)

Experimental dataThe fitting curveMagnetite Fe3O4Fe with 0 Si in nnα-FeSiFayalite Fe2SiO4Fe(III)

0.42

0.58

0.370.63

600 oC

500 oC

Summary

1-Influence of Surface preparationa) Ground and polished sample showed only α-FeSib) After etching this sample in HF+H2O2 , Fe3+ formedc) After annealed in vacuum fayalite Fe2SiO2 and Fe3+are formed.d) Oxide and fayalite phases were confirmed by XPS measurement.

2-Annealing in Oxygena) In the temperature range 500 oC to 780 oC exhibiting the formation of

hematite α-Fe2O3 on the surface of the samples. b) The relative concentration of hematite increases with increasing

temperature.3-Annealing in Argon

a) Annealing in Ar at 500 oC caused the formation of magnetite, fayalite Fe2SiO4 and Fe3+.

b) Annealing at 600 oC caused the formation of magnetite, Fe with 0 Si in nn and fayalite on the surface.

c) The relative concentration of magnetite ate 500 oC is higher than that at 600 oC.

AcknowledgementsThe project was supported by the Grant Agency of the Academy of Sciences of the Czech Republic (Contract No. IAA1041404).