Magnetite nanocrystals from a single source metallorganic precursor: metallorganic chemistry vs biogeneric bacteria

Magnetite nanocrystals, which are normally formed by magnetogeneric bacteria, have been prepared using a single source metallorganic precursor

Influence of CaO/FeO ratio on the formation mechanism and properties of alkali-activated Fe-rich slags

In the search for CO2 mitigating cement technologies, alkali-activated Fe-rich slags present a possible alternative. The influence of the chemical composition of the synthetic Fe-silicate slag on the reaction mechanisms is assessed by varying the CaO/FeO molar ratio. The alkali-activated Fe-rich slags consist of trioctahedral layers that are shown to be hydroxylated and in contact with silicates, in a similar way to phyllosilicate minerals. The formation of this phyllosilicate-like structure is hindered during the first days for samples with high CaO/FeO ratios, because of the partial incorporation of Ca in the trioctahedral layers. At later ages, the samples with higher CaO/FeO ratios gain in reaction extent, to exceed the reaction extent of low CaO/FeO ratios at 28 days and beyond. The increase in compressive strength is even more pronounced than the effect on the reaction extent, which underlines the importance of Ca on the inherent strength of the binding phases

Impact of the solidification path of FeOx-SiO2 slags on the resultant inorganic polymers

status: publishe

Inorganic polymers from CaO-FeOx-SiO2 slag : the start of oxidation of Fe and the formation of a mixed valence binder

Belonging to the family of alternative cementitious materials, inorganic polymers are rising in importance because of the drive to decrease CO2 emissions of concrete production. A synthetic Fe-rich slag resembling industrial copper or lead slags, was mixed with a sodium silicate activating solution. Fe-57 Mossbauer spectra analyses indicate that the oxidation reactions are taking place simultaneously with the polymerization reactions. The slag contains Fe2+ states and a small amount of Fe3+. During polymerization a new octahedral Fe2+ state is formed, while oxidation is manifested through the appearance of an additional Fe3+ state. The reactions continue after setting, lowering the relative contributions of the slag in the Mossbauer and FTIR spectra of the samples. The Na+/Fe3+ molar ratio in the mixture that makes up the binder after 28 days is similar to 1, suggesting the participation of tetrahedral Fe3+ in the silicate framework, charge balanced by Na+

Nové magnetické nanohybridy: od nanočástic oxidu železitého po nanočástice karbidu železa vypěstovaných na nanodiamantech

The synthesis and characterization of a new line of magnetic hybrid nanostructured materials composed of spinel-type iron oxide to iron carbide nanoparticles grown on nanodiamond nanotemplates is reported in this study. The realization of these nanohybrid structures is achieved through thermal processing under vacuum at different annealing temperatures of a chemical precursor, in which very fine maghemite (γ-Fe2O3) nanoparticles seeds were developed on the surface of the nanodiamond nanotemplates. It is seen that low annealing temperatures induce the growth of the maghemite nanoparticle seeds to fine dispersed spinel-type non-stoichiometric ~5 nm magnetite (Fe3−xO4) nanoparticles, while intermediate annealing temperatures lead to the formation of single phase ~10 nm cementite (Fe3C) iron carbide nanoparticles. Higher annealing temperatures produce a mixture of larger Fe3C and Fe5C2 iron carbides, triggering simultaneously the growth of large-sized carbon nanotubes partially filled with these carbides. The magnetic features of the synthesized hybrid nanomaterials reveal the properties of their bearing magnetic phases, which span from superparamagnetic to soft and hard ferromagnetic and reflect the intrinsic magnetic properties of the containing phases, as well as their size and interconnection, dictated by the morphology and nature of the nanodiamond nanotemplates. These nanohybrids are proposed as potential candidates for important technological applications in nano-biomedicine and catalysis, while their synthetic route could be further tuned for development of new magnetic nanohybrid materials.V této studii je uvedena syntéza a charakterizace nové řady magnetických hybridních nanostrukturovaných materiálů složených z nanočástic oxidu železa typu spinel na karbid železa pěstovaných na nanodiamantových nanotemplátech. Realizace těchto nanohybridních struktur je dosažena tepelným zpracováním ve vakuu při různých teplotách žíhání chemického prekurzoru, ve kterém byla na povrchu nanodiamantových nanotemplate vyvinuta velmi jemná semena nanočástic maghemitu (γ-Fe2O3). Je vidět, že nízké teploty žíhání indukují růst semen nanočástic maghemitu na jemné dispergované nestechiometrické ~ 5 nm magnetitové (Fe3-xO4) nanočástice spinelového typu, zatímco střední teploty žíhání vedou k tvorbě jednofázového ~ 10 nm cementitu (Fe3C) nanočástice karbidu železa. Vyšší teploty žíhání vytvářejí směs větších karbidů železa Fe3C a Fe5C2, což současně spouští růst velkých uhlíkových nanotrubiček částečně naplněných těmito karbidy. Magnetické vlastnosti syntetizovaných hybridních nanomateriálů odhalují vlastnosti jejich nosných magnetických fází, které sahají od superparamagnetických po měkké a tvrdé feromagnetické a odrážejí vnitřní magnetické vlastnosti obsahujících fází, jakož i jejich velikost a vzájemné propojení diktované morfologií a povaha nanodiamantových nanotemplate. Tyto nanohybridy jsou navrženy jako potenciální kandidáti na důležité technologické aplikace v nano-biomedicíně a katalýze, zatímco jejich syntetická cesta by mohla být dále vyladěna pro vývoj nových magnetických nanohybridních materiálů

The influence of air and temperature on the reaction mechanism and molecular structure of Fe-silicate inorganic polymers

Fe-rich inorganic polymers are rising in importance because of their low CO2 emissions during production and their potential in upcycling metallurgical residues. Here, the oxidation of Fe during formation of the binder from 0.4CaO-1.2FeOx-SiO2 slag is investigated in more detail using 57Fe Mossbauer spectroscopy. It was shown that the oxidation at early stages is not influenced by (O2 in the) air. Later, the quadrupole split Fe2+ state in the binder transforms to Fe3+ when the samples are crushed and exposed to air as powder for 28 days at room temperature or 1 h at ≥200 °C. This transformation does not affect the connectivity of the silicate network according to infrared spectroscopy. During heating of the inorganic polymer powder, the Mossbauer spectra remain stable until 400–500 °C. At 400 °C the Fe2+ in the slag starts to be oxidized, showing the formation of new Fe3+ components.status: publishe

Intriguing Prospects of a Novel Magnetic Nanohybrid Material: Ferromagnetic FeRh Nanoparticles Grown on Nanodiamonds

A novel endeavor based on the synthesis, characterization and study of a hybrid crystalline magnetic nanostructured material composed of bimetallic iron–rhodium nanoalloys, grown on nanodiamond nanotemplates, is reported in this study. The development of this hybrid magnetic nanomaterial is grounded in the combination of wet chemistry and thermal annealing under vacuum. In order to assess, evaluate and interpret the role and special properties of the nanodiamond supporting nanotemplates on the growth and properties of the bimetallic ferromagnetic Fe–Rh nanoparticles on their surfaces, unsupported free FeRh nanoparticles of the same nominal stoichiometry as for the hybrid sample were also synthesized. The characterization and study of the prepared samples with a range of specialized experimental techniques, including X-ray diffraction, transmission and scanning transmission electron microscopy with energy dispersive X-ray analysis, magnetization and magnetic susceptibility measurements and 57Fe Mössbauer spectroscopy, reveal that thermal annealing of the hybrid sample under specific conditions (vacuum, 700 °C, 30 min) leads to the formation of a rhodium-rich FeRh alloy nanostructured phase, with an average particle size of 4 nm and good dispersion on the surfaces of the nanodiamond nanotemplates and hard ferromagnetic characteristics at room temperature (coercivity of ~500 Oe). In contrast, thermal annealing of the unsupported free nanoparticle sample under the same conditions fails to deliver ferromagnetic characteristics to the FeRh nanostructured alloy phase, which shows only paramagnetic characteristics at room temperature and spin glass ordering at low temperatures. The ferromagnetic nanohybrids are proposed to be exploited in a variety of important technological applications, such as magnetic recording, magnetic resonance imaging contrast and magnetic hyperthermia agents

Intriguing Prospects of a Novel Magnetic Nanohybrid Material: Ferromagnetic FeRh Nanoparticles Grown on Nanodiamonds

A novel endeavor based on the synthesis, characterization and study of a hybrid crystalline magnetic nanostructured material composed of bimetallic iron–rhodium nanoalloys, grown on nanodiamond nanotemplates, is reported in this study. The development of this hybrid magnetic nanomaterial is grounded in the combination of wet chemistry and thermal annealing under vacuum. In order to assess, evaluate and interpret the role and special properties of the nanodiamond supporting nanotemplates on the growth and properties of the bimetallic ferromagnetic Fe–Rh nanoparticles on their surfaces, unsupported free FeRh nanoparticles of the same nominal stoichiometry as for the hybrid sample were also synthesized. The characterization and study of the prepared samples with a range of specialized experimental techniques, including X-ray diffraction, transmission and scanning transmission electron microscopy with energy dispersive X-ray analysis, magnetization and magnetic susceptibility measurements and 57Fe Mössbauer spectroscopy, reveal that thermal annealing of the hybrid sample under specific conditions (vacuum, 700 °C, 30 min) leads to the formation of a rhodium-rich FeRh alloy nanostructured phase, with an average particle size of 4 nm and good dispersion on the surfaces of the nanodiamond nanotemplates and hard ferromagnetic characteristics at room temperature (coercivity of ~500 Oe). In contrast, thermal annealing of the unsupported free nanoparticle sample under the same conditions fails to deliver ferromagnetic characteristics to the FeRh nanostructured alloy phase, which shows only paramagnetic characteristics at room temperature and spin glass ordering at low temperatures. The ferromagnetic nanohybrids are proposed to be exploited in a variety of important technological applications, such as magnetic recording, magnetic resonance imaging contrast and magnetic hyperthermia agents

The effect of high dose rate gamma irradiation on the curing of CaO-FexOy-SiO2 slag based inorganic polymers: Mechanical and microstructural analysis

In search for alternative cementitious materials for radioactive waste encapsulation, geopolymers and inorganic polymers (IPs) have received wide attention. Moreover, Fe-rich IPs offer an interesting alternative to high density concretes for use in radiation shielding applications. Materials can however be altered when subjected to ionizing radiation, creating the necessity to evaluate the material’s behaviour under irradiation conditions. In this study the effect of high dose rate (8.85 kGy/h) gamma irradiation is investigated on CaO-FexOy-SiO2 slag-based IPs. Samples with different curing times (1 h, 24 h and 28 days) prior to the irradiation were irradiated to a dose of 200 kGy using a60Co source. The effect of gamma radiation is observed to be highly dependent on the curing time prior to irradiation. 28 days cured samples are found to be resistant to the irradiation for the dose (rate) and properties tested without any significant change in strength, indentation characteristics, porosity and Fe3+ content. The IPs studied show a different behaviour when irradiated immediately after casting or after 24 h of curing. It is therefore thought that the mechanism behind the effect of irradiation is different for the non-hardened samples compared to hardened samples. For the 1 h cured samples prior to irradiation multiple effects were observed: an increase of the compressive strength by a factor 2.20, a decrease in hardness of the binder by a factor of 0.73, a lower Young’s-modulus of the binder by a factor of 0.67, a decrease of creep in time for the binder by a factor of 0.72, a decrease in porosity by a factor of 0.92 and an increase of the Fe3+/ΣFe ratio by a factor of 1.95.JRC.G.I.3-Nuclear Fuel Safet

Employment of 2-pyrrole aldoxime in iron cluster chemistry: Trinuclear and hexanuclear clusters

The reaction of Fe(ClO4)3·9H2O with 2-pyrrole aldoxime (pyroxH2) and two equivalents of sodium benzoate in MeCN afforded the complex {[FeIII6O2(OH)2(pyroxH)2(PhCOO)10(H2O)2]·[FeIII3O(pyroxH2)2(PhCOO)6(MeCN)](ClO4)·6.6MeCN} (1·6.6MeCN) in moderate yield. Repeating the same reaction in EtOH gave the complex [FeIII6O2(OH)2(pyroxH)2(PhCOO)10(EtOH)2] (2) in good yield. The crystal structures of 1 and 2 have been determined by single-crystal X-ray crystallography. Complex 1 contains two different clusters in the crystal: a trinuclear [FeIII3] molecule and a hexanuclear [FeIII6] unit, both of which contain different forms of the 2-pyrrole aldoxime ligand. Complex 2 is a hexanuclear [FeIII6] cluster almost identical with the hexametallic unit found in 1, with the difference being the presence of two terminal EtOH molecules in 2 versus two terminal H2O molecules in the hexametallic sub-unit of 1. DC magnetic susceptibility studies were performed on polycrystalline sample of 2, revealing the presence of strong antiferromagnetic interactions within the cluster leading to a well isolated diamagnetic ground-state. The oxidation state of the iron atoms in 2 were further established by Mössbauer studies performed at 77 K