Influence Of Iron Substitution Research Articles

Influence of iron substitution on the microstructure and properties of ettringite in calcium sulfoaluminate cement: A comprehensive study on the Al/(Fe+Al) ratios

Ettringite, as the dominant hydration product of calcium sulfoaluminate cement, significantly contributes to cement strength. Its formation is closely related to the Fe and Al ratio in raw materials. During cement hydration, Fe present in ferrite can replace some of the Al in ettringite, which notably affects the microstructure and properties of the latter. To understand the relationship between the Al/(Fe + Al) ratios and the ettringite phase, we synthesized ettringite with varying Al/(Fe + Al) ratios using a chemical synthesis method. The microstructure was then characterized to determine the formation process of this phase. Various analysis methods, including X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscope (TEM), and N2 adsorption-Brunauer Emmett Teller (BET), were used to study the solid phases. For aqueous solutions, inductively coupled plasma emission spectroscopy (ICP-OES) was employed. Our results reveal that Fe replacing Al leads to regular changes in the ettringite crystal's microstructure. As the Al/(Fe + Al) ratio decreases, there is a reduction in the ettringite unit cell parameter a, an increase in c, and an enlargement of the unit cell volume. Concurrently, Fe substitution shrinks the crystallinity and grain size of ettringite crystals. SEM-TEM and BET demonstrate that Fe substitution boosts ettringite's particle size and aspect ratio, while the specific surface area contracts with a decreasing Al/(Fe + Al) ratio. Moreover, Fe substitution tends to lower ettringite's thermal stability and OH group binding ability. When the Al/(Fe + Al) ratio reached 80%, the ettringite crystal exhibited optimal thermal stability.

Influence of iron substitution on structural, magnetic, and magnetocaloric properties of Tb2Fe17−xAlx compounds synthesized by arc melting

In the present work, the structure and magnetic and magnetocaloric properties of the Tb2Fe17−xAlx compounds with x=0,0.25,0.5,0.75, and 1 were studied. These compounds were synthesized by arc furnace without subsequent annealing. Their crystal structure is a Th2Ni17 hexagonal structure with a P63/mmc space group. The Rietveld refinement of the X-ray diffractograms allowed for determining the structural parameter variations with different amounts of aluminum. Lattice parameters and the unit cell volume increase with aluminum amounts while the c/a ratio remains nearly constant. The Tb2Fe17−xAlx compounds exhibit a second-order magnetic phase transition from a ferromagnetic state to a paramagnetic state. The Curie temperature (TC) increases with the aluminum content, the observed effect is due to the magnetovolumic effect. The saturation magnetization (MS) decreases with the increase of Al content. Magnetic entropy and relative cooling power (RCP) decrease as the aluminum content increases. Tb2Fe17−xAlx compounds have a moderate magnetocaloric effect and a tunable operating temperature interval.

Structural and magnetostrictive properties of intermetallic (Tb,Ho)(Fe,Co)[formula omitted] compounds

The influence of iron substitution by cobalt on the structural and magnetostrictive characteristics of (Tb,Ho)(Fe, Co)2-type compounds is investigated. It is established that cobalt doping of the Tb0.16Ho0.84Fe2 compound leads to an increase in the Curie temperature and a decrease in the lattice constant. It is shown that the anisotropic magnetostriction of the Tb0.16Ho0.84Fe2−xCox (x≤0.4) compounds significantly exceeds the volumetric one in the moderate (up to 1.2T) magnetic fields. The Tb0.16Ho0.84Fe1.8Co0.2 composition with the highest saturation magnetostriction and magnetostrictive susceptibility is found.

Influence of iron substitution on the ferromagnetic ordering and magnetic entropy variation in La1-xNaxMn1-yFeyO3 (x = 0.1, 0.2 and y = 0, 0.1)

In the present work, the magnetocaloric effect of La1-xNaxMn1-yFeyO3 (x = 0.1, 0.2 and y = 0, 0.1) was investigated using magnetic characterization data. The X-ray diffraction confirms that all samples synthesized by flash combustion and calcined at 1000 °C have been crystallized in a rhombohedral structure with an R3¯c space group. According to the magnetization versus temperature results, LaMnO3 is a ferromagnetic material with a Curie temperature TC = 95 K. The substitution of the rare earth La by alkali magnetic metal Na leads to an increase of TC to 265 and 330 K accompanied with large magnetic entropy change/-ΔSMmax/ of 2.88 and 4.88 J.Kg-1K−1 for x = 0.1, 0.2, respectively. The addition of 10% of Fe in La1-xNaxMn1-yFeyO3 decreases the Curie temperature and the magnetic entropy change, while, the relative cooling efficiency increases. The Mössbauer spectrum recorded at room temperature represents a paramagnetic character of the manganites and proves the distribution of Fe3+ in the samples.

Influence of iron substitution on structural and dielectric properties of nano ZnMn2O4

Influence of iron substitution on structural and dielectric properties of nano ZnMn2O4

Influence of iron substitution by selected rare-earth ions on the properties of NiZn ferrite fillers and PVC magneto-polymer composites

Nickel-zinc ferrites are very important soft magnetic materials from the point of view of diverse technical applications (such as, e.g., various electronic devices and components) for their high magnetic permeability and permittivity, low core loss, high resistivity, high Curie temperature as well as mechanical strength and chemical stability. Due to their good absorbing properties, they can be used as microwave absorbing and shielding materials with the aim of decreasing the environmental pollution caused by non-ionizing microwave radiation. The ferrite material incorporated into the polymer matrix creates qualitatively new magneto-polymer composite material taking benefits from both components. The properties typical for polymers (elasticity, mouldability, etc.) are combined with good high-frequency magnetic parameters, thus allowing to utilize these materials, e.g., in high-frequency applications where especially flexibility of composite materials plays a key role. Small amounts of selected rare-earth (RE) ions, in particular Y3+, La3+, Eu3+ and Gd3+ have been embedded into the nickel-zinc ferrite that has been used as the magnetic filler in magnetic polymer composites with polyvinylchloride (PVC) acting as the polymeric matrix. The effect of various types of rare-earth ions on the structural as well as quasi-static and dynamic (electro)magnetic properties of the ferrite fillers as well as ferrite/PVC composites, in particular the frequency dispersion of the complex permeability, has been studied.

The influence of iron substitution on the electrochemical properties of Li1+xTi2−xFex(PO4)3/C composites as electrodes for lithium batteries

The Li1+xTi2−xFex(PO4)3/C series with 0 ≤ x ≤ 0.4 was prepared by a sol–gel method. XRD patterns showed a rhombohedral phase and minor contribution of an orthorhombic phase. The local environment of the phosphate structure was analyzed by 31P MAS NMR spectroscopy. The electrochemical lithium insertion revealed two reversible regions for Fe3+/Fe2+ and Ti4+/Ti3+ reactions as confirmed by 57Fe Mossbauer spectroscopy. Capacity values as large as 130 mA h g−1 were recorded for Li1.2Ti1.8Fe0.2(PO4)3/C after 40 cycles. The drastic decrease in capacity observed for LiTi2(PO4)3/C cycled at C/2 was explained in terms of a lower kinetic response at the electrode–electrolyte interphase.

SYNTHESIS AND PROPERTIES OF Fe-MODIFIED CALCIUM-DEFICIENT HYDROXYAPATITE NANOCRYSTAL FOR MRI CONTRAST AGENT

In order to achieve for a better magnetic resonance imaging (MRI) contrast agent, the synthesis, degradation and magnetic properties of Fe -modified calcium deficient hydroxyapatite nanoparticles ( Fe -CDHAP, ( Ca , Fe )10-x( HPO 4)x( PO 4)6-x( OH )2-x), which synthesizes using ultrasonic assisted precipitation at low temperature, were investigated. The MRI contrast agent should be stable, biodegradable and also with great magnetism. The synthesized sample demonstrates needle-like morphology with dimension less than 50 nm in width and 300 nm in length under SEM. The structure and crystal deformation were studied by X-ray diffraction (XRD), which show 0.2% shrinkage in cell volume, through the pattern shifting and the lattice parameters calculations. Thermal gravity analysis (TGA) analysis indicated Fe -CDHAP were stable up to 1200°C and confirmed the structure of the Fe -CDHAP, which is stable. Fourier transform infrared spectroscopy (FTIR) assisted to define the influence of iron substitution and gave the hint of internal structure variation on [Formula: see text] sites that reflect on the great amount of phosphate ions release in acidic solution. The methods above prove the structure of Fe -CDHAP and also indicate the effect to [Formula: see text], which is caused by the doping of iron ions. The degradation test confirms the biodegradability of Fe -CDHAP that can degrade faster than CDHAP and also release a great amount of phosphate ions in a short time. The magnetic property of CDHAP and Fe -CDHAP were determined with VSM to and found the transformation of diamagnetic into paramagnetic.

Influence of iron substitution on formation and structure of Cu-based mixed oxides derived from layered double hydroxides

Cu/Zn/Fe/Al mixed metal oxides were prepared by calcination of layered double hydroxides (LDHs) carbonate precursors. The iron content had significant influence on the crystallinity, purity and thermal stability of as-synthesized Cu/Zn/Fe/Al-LDHs as well as the structure and composition of resultant mixed oxides obtained at 773 K. The mixed oxide with the Fe/Al ratio of 0.3:0.7 exhibited highest catalytic activity for oxidation of phenol by hydrogen peroxide. Moreover, the Fe-containing mixed oxides had stronger oxidation abilities than the Fe-free ones. The difference of catalytic activity is probably related to the difference in the amounts and types of composite oxides containing Cu 2+ and/or Fe 3+ cations on the surface of calcined products depending on the pristine nature of the starting LDHs precursors.

On the nature of metastable high-spin states formed during spin transitions in iron(II) complexes

The metastable high-spin (HS) state of iron is formed and fixed in iron(II) complexes during irradiation of a low-spin (LS) sample at low temperatures (~15 K) with green laser light at a wavelength of 514.5 nm [1]. This phenomenon was studied further in [2-4] (see also references in the above papers). In particular, it was shown that the metastable HS form is transformed back to the LS form by irradiation of crystals with red laser light at a wavelength of 752.7 nm. This effect may be of interest for molecular electronics, because molecular systems reversibly changing their state during irradiation with laser light may be used as optical keys in devices for processing and storage of optical data. M/Sssbauer spectroscopy is an essential tool for investigating light-induced spin transitions. The main results obtained by this method are the ratios between the LS and HS forms of iron, determined in various experimental conditions. The aim of this work is to draw attention to a new possibility offered by this method in studying the nature of the metastable HS state of Fe(II) formed in light-irradiated samples. Formulation of the problem will ftrst demand several explanations concerning the nature of the HS and LS forms of iron that are simultaneously observed in a particular temperature range during sharp spin transitions (ST) caused by temperature variations. In some papers (e.g., review [5]), it was shown that the HS form, which appears at increased temperatures, as well as the LS form, which appears during cooling, exist in crystals in the form of domains, i.e., certain regions in which all iron atoms are in the same spin state. An alternative form is chaotic distribution of iron atoms, which do not create regular regions. The domain structure of the LS and HS forms during ST is proved by hysteresis on the curves of the temperature dependences of the effective magnetic moment of the complex [5]. Let us consider the crystal in which the HS form appears during irradiation with light. It would be reasonable to ask whether this state exists in the crystal as dom~in~ or individual paramagnetic centers. The idea of using MiSssbauer spectroscopy for solving this problem is based oft the following fact. The HS state appears in the matrix of the LS state, in which iron atoms participate in cooperative interactions; hence the reaction of the atoms of the LS state to an admixture of the metastable HS state will depend on whether the atoms of the HS state form domains or individual paramagnefic centers in the low-spin matrix. We can assume that in the case of domains their influence on the structure of the LS state will be negligible due to the relatively low content of the neighboring pairs of atoms with different values of spins. The case is different when the HS centers are chaotically distribfited in the LS matrix. The changes in the spin states of iron atoms as a result of irradiation with light can lead to changes in the electronic states of the neighboring iron atoms of the LS matrix because of considerable differences in the metal-ligand distances of the LS and HS forms [7] and due to cooperative interactions in the LS matrix. The effect of the "large" paramagnetic admixture on the structure of the LS matrix will be more simaiflcant for crystals with strong cooperative interactions and for crystals with higher concentrations of admixtures. The "large" paramagnetic admixture loosens the structure of the LS matrix and decreases the covalence of the metal-ligand bond of the LS form, thus increasing the chemical shift c3LS of the M/Sssbauer line for the I~ form. Recently, we reported on a similar effect in [6], in which we studied the influence of iron substitution by zinc on the ST in the polynuclear Fe(ATr)3(NO3) 2 complex (ATr = 4-amino-l,2,4triazole). We found that the chemical shift of the LS form of the complex measured at 78 K monotonically increases with the concentration of zinc atoms. Tiffs effect was explained in terms of the model of steric strai-~ arising in crystals