University of Ioannina INVESTIGATING THE PROPERTIES OF IRON

University of Ioannina INVESTIGATING THE PROPERTIES OF IRON IN INORGANIC POLYMERS WITH 57 Fe MÖSSBAUER SPECTROSCOPY Alexios P. Douvalis Physics Department University of Ioannina-Greece 5 th International Slag Valorisation Symposium

University of Ioannina Outline q Slags and Inorganic Polymers (IP): why Spectroscopy. 57 Fe Mössbauer § Brief introduction and basic parameters. q The state of iron and its properties in synthetic Slags made of binary Fe. Ox-Si. O 2 (Bi) and ternary Fe. Ox-Ca. O-Si. O 2 (Te) oxide systems and the corresponding IPs, as seen by 57 Fe Mössbauer Spectroscopy. § Estimating the valence, atomic environment and structure. § Identifying the iron-bearing phases. § Suggesting paths to explain the role of iron in the IP formation. q Following the evolution of the 57 Fe Mössbauer spectra at different reaction stages of the Slag with the activating Si. O 2/Na 2 O-H 2 O/Na 2 O solution. § Monitoring the oxidation of Fe 2+ to Fe 3+. 5 th International Slag Valorisation Symposium

University of Ioannina Recoil-free γ-ray nuclear resonant emission and absorption simply: Mössbauer spectroscopy Ee Ee γ Ε 0 Recoil Energy Eγ Εg Source Εg Free Atom M ER=Eγ 2/2 Mc 2≈E 02/2 Mc 2 Eγ=E 0 - ΕR Absorber-Sample Nuclear Energy Levels Mössbauer spectroscopy “works” only in solids (those that are, or can become under experimental measuring conditions), and only with particular nuclei, not in soft matter (gases/liquids/loosely bound solids), because the process needs to be recoilless. 5 th International Slag Valorisation Symposium

University of Ioannina 57 Fe Mössbauer Spectroscopy Source-emission (stable & identical chemical environment) γ-rays 57 Co(Rh) 57 Fe Ee Ε 0 Εg γ Eγ Ee Hyperfine Interactions (multiple transitions) Εg Sample-absorption (different iron spices in the same phase or in different phases, or both, will appear as different contributions in the spectra) 5 th International Slag Valorisation Symposium

57 Fe Mössbauer Spectroscopy University of Ioannina γ-ray energy modulation is required to achieve absorption resonance Transmission geometry Hyperfine Interactions-Mössbauer Parameters sample IS γ ray detector 1 Source velocity modulation 2 ε 3 4 Bhf 5 6 IS Electronics/Recording 1 2 3 4 Bhf Superposition of several contributions 5 6 IS 1 QS 2 • valence state Absorption area (A) Fe 2+a Fe 2+b Fe 3+ Α(Fe 3+): A(Fe 2+a): A(Fe 2+b)=2: 1: 1 Ratios of Absorption Areas of individual components proportional to the ratios of populations of specific Fe atoms or ions in sample IS & Bhf & Quadrupole Shift (2ε) • atomic environment IS & Hyperfine Magnetic Field (Bhf) • coordination • structure • magnetic properties IS & Quadrupole Splitting QS IS 1 Isomer Shift (IS) 5 th International Slag Valorisation Symposium

University of Ioannina 57 Fe Mössbauer Spectroscopy 0 -1. 50 100 - 400 Bhf (k. G) QS (mm s-1) 0 - 4. 00 450 -550 Expected values of Mössbauer Parameters for high spin Fe 3+ (S=5/2) and Fe 2+ (S=2) in Oxides 0. 25 -0. 55 Fe 3+ 0. 75 -1. 50 IS* (mm s-1) *IS relative to α-Fe @ 300 K Fe 2+ 0. 25 -0. 55 Fe 3+ 0. 75 -1. 50 IS* (mm s-1) Fe 2+ Coordination: IS(Fe 3+/2+)tetrahedral< IS(Fe 3+/2+)octahedral 5 th International Slag Valorisation Symposium

University of Ioannina Synthetic binary Fe. Ox-Si. O 2 (Bi) and ternary Fe. Ox-Ca. O-Si. O 2 (Te) Slags and the corresponding IPs Table 1. (XRF) Starting Bi Te Mixture (wt. %) Components Fe. O 73 48 Si. O 2 27 35 Ca. O 17 • Activating solutions with molar ratios Si. O 2/Na 2 O=1. 2 and H 2 O/Na 2 O=22. • Curing ~ 4 weeks. Table 2. XRD-Rietveld analyses (external standard-based) wt. % Fayalite (Fe 2 Si. O 4) Ca-Fayalite (Fe 2 -x. Cax)Si. O 4 Magnetite (Fe 3 O 4) Quartz (Si. O 2) Wollastonite (Ca. Si. O 3) Wüstite (Fe. O) Amorphous Bi-Slag 53. 7 - 1. 5 0. 4 - 2. 5 41. 9 Bi-IP 42. 2 - 1. 2 0. 0 - 2. 0 54. 6 Te-Slag 0 4. 3 - 0. 7 0. 9 93. 4 Te-IP 0 4. 9 - 0. 3 0. 5 94. 0 5 th International Slag Valorisation Symposium

University of Ioannina Complete analysis Bi samples 5 th International Slag Valorisation Symposium

University of Ioannina Complete analysis Bi samples 5 th International Slag Valorisation Symposium

University of Ioannina Complete analysis Te samples 5 th International Slag Valorisation Symposium

University of Ioannina Complete analysis Te samples 5 th International Slag Valorisation Symposium

University of Ioannina Bi-Te samples 77 K Mössbauer spectra comparison Fe 3+ IS=0. 49 QS=1. 24 ΔQS=0. 32 A=7% (Fe 3+) IS=0. 43 QS=1. 04 ΔQS=0. 53 A=4% Fe 2+ IS=1. 26 QS=3. 05 ΔQS=0. 14 A=85% R(Fe 3+IP)≈4 x. R(Fe 3+Slag) Fe 2+2 Slag IS =1. 12 QSSlag=2. 02 ΔQS=0. 55 A=51% R(Fe 3+IP)≈4 x. R(Fe 3+Slag) Fe 3+ IS=0. 42 QS=0. 82 ΔQS=0. 41 A=16% Fe 3+ IS=0. 48 QS=0. 81 ΔQS=0. 39 A=27% Fe 2+ IS=1. 26 QS=3. 05 ΔQS=0. 13 A=73% Te[R(Fe 3+IP)]≈1. 5 x. Bi[R(Fe 3+IP)] Γ/2=(0. 14 ± 0. 02) mm/s IS, QS, ΔQS in mm/s (± 0. 02 mm/s) Fe 2+1 IS=1. 28 QS=2. 63 ΔQS=0. 42 A=39% Fe 2+1 IS=1. 28 QS=2. 81 ΔQS=0. 32 A=28% Fe 2+2 IS=1. 12 QS=2. 12 ΔQS=0. 55 A=40% ΔQS(Fe 2+)-Te > ΔQS(Fe 2+)-Bi enhancement of glass phase formation with Ca addition 5 th International Slag Valorisation Symposium

University of Ioannina 57 Fe Bi Mössbauer Spectroscopy Te Increase of the amount of Fe 3+ with Ca addition 5 th International Slag Valorisation Symposium

University of Ioannina 57 Fe Mössbauer Spectroscopy Weighted average values Bi Te Influence of Ca addition to the electronic configuration & coordination of Fe 2+/Fe 3+ 5 th International Slag Valorisation Symposium

University of Ioannina 57 Fe Mössbauer Spectroscopy Weighted average values Bi Te Influence of Ca addition to the electronic configuration & coordination of Fe 2+/Fe 3+ 5 th International Slag Valorisation Symposium

University of Ioannina 57 Fe Mössbauer Spectroscopy Weighted average values Bi Te Enhancement of glass phase formation with Ca addition 5 th International Slag Valorisation Symposium

Suggestions for relative phases hosting Fe 2+ and Fe 3+ ions University of Ioannina Fe 2+ in Slag precursor and IP: • Fayalite-type Fe 2+2 Si. O 4 (crystalline & amorphous for Bi) • Ca-Fayalite-type (Fe 2+2 -z. Caz)Si. O 4 and Ca-Ferrosilite-type (Fe 2+2 -z. Caz)Si 2 O 6 (amorphous for Te) Fe 3+ in Slag precursor and IP: • Ferrifayalite-type (Fe 2+2 -x□y. Fe 3+x)Si. O 4 (crystalline & amorphous for Bi) • Ca-Ferrifayalite-type (Fe 2+2 -x-z. Caz□ye 3+x)Si. O 4 (amorphous for Te) Fe 3+ in glass structure: The large drop in QS values from the Slags to the IPs reflect a shift in the coordination (O) number most probable from 6 (nn) to 5 or 4 the ferric ion could behave like silicon in the IP binder, i. e. it could act as a network former. Crystal structure of Fayalite (olivine-type) Fe 2+2 Si. O 4 Bi & Te samples Crystal structure of Ferrosilite (pyroxene-type) Fe 2+2 Si 2 O 6 Te samples 5 th International Slag Valorisation Symposium

University of Ioannina Evolution of the 77 K 57 Fe Mössbauer spectra at different reaction stages 7 w 4 w 1 d 3 d Starting Mixture Components wt% Fe. O Si. O 2 Ca. O Al 2 O 3 Mg. O 47 34 12 5 2 • Activating solutions with molar ratios Si. O 2/Na 2 O=1. 6 and H 2 O/Na 2 O=20. 5 th International Slag Valorisation Symposium

Conclusions University of Ioannina Ø Emphatic appearance of Fe 3+ contributions in the IP samples resulting by oxidation of the Fe 2+ states existing in the Slags after chemical reaction with the activating solutions. Ø The amorphous part of the slags is the most active component of the starting Slag material, while the crystalline part is more resistive to oxidation. Ø The addition of Ca seems to favor the formation of the amorphousglass phase and enhance the presence of Fe 3+ states both in the Slags and, more pronounced, in the IPs. Ø A shift in the Mössbauer parameters of the ferric ions from the slags to the IPs indicates a change in their O-coordination, suggesting that these ions could act as network formers similar to the role of Si. Ø The oxidation of Fe 2+ to Fe 3+ in the curing period of the IPs is fast for the initial 1 -3 days, then slower up to 4 weeks and persists further up to at least 7 weeks. 5 th International Slag Valorisation Symposium

University of Ioannina Collaborators KU LEUVEN • Arne PEYS • Silviana ONISEI • Yiannis PONTIKES 5 th International Slag Valorisation Symposium

University of Ioannina-Greece Mössbauer Spectroscopy & Physics of Materials Laboratory Physics department, University of Ioannina http: //pml. physics. uoi. gr 5 th International Slag Valorisation Symposium