Magnetite Samples Research Articles

Green Capping Agents and Digestive Ripening for Size Control of Magnetite for Magnetic Fluid Hyperthermia

Background: Magnetite is the most recognized iron oxide candidate used for various biological applications. Objective: This work is a complete study that addresses the synthesis of magnetic nanoparticles and investigates the feasibility of using green tea and ascorbic acid as capping agents. Methods: Synthesis of magnetite by two wet chemical methods namely: coprecipitation and solvothermal methods. The samples were characterized using X-ray diffraction (XRD), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). Results: The results reveal the impact of coating on the size and morphology of the particles. The study also proves that autoclaving the samples prepared by coprecipitation results in smaller particle size and narrower size distribution due to digestive ripening. In addition, a novel and facile methodology for coating magnetite with polyethylene glycol is presented. The potential of the particles to be used for magnetic fluid hyperthermia is assessed by measuring the specific absorption rate (SAR) of the samples. Conclusión: The results show that all the prepared magnetite samples showed a promising capacity to be used as magnetic fluid hyperthermia agents.

Heavy aggregate and different admixtures efffect on parquets: chrome, magnetite, and quartz-based surface hardener

This paper presents the mechanical and micro-structure results of concrete parquet blocks. The blocks were generated by utilizing the same part in the bottom part and by substituting different proportions (40%, 30%, 20%, and 10%) of heavy aggregate like chromite aggregate, magnetite aggregate, normal aggregate, and surface hardener in the upper part. The parquet sample tests were conducted on TS 2824 EN 1338. The test outcomes indicated that utilizing diverse aggregate and chemical materials boosted the abrasion resistance, 40% magnetite and quartz-based concrete parquet block samples demonstrated the best abrasion resistance values. Also, the minimum amount of mass loss was discovered in the samples that possess high water absorption at the freezing-thaw test. The different material substitutions in the sheet of the surface of the concrete parquet block samples altered the tensile strength of the samples, even though they did not bring about an outstanding variation in the compressive strength of the concrete parquet samples.

The use of block modeling to predict the variability of the bulk weight of titanomagnetite ore

The article presents the results of the performed studies using block modeling technologies to determine the volume weight of the titanium magnetite ore of the Northern deposit of the Gusevogorsky deposit, developed by EVRAZ KGOK OJSC. The methods used for laboratory studies of samples of titanium magnetite ore from exploration wells are described. The results of statistical processing of the obtained data are presented. The relationship between the bulk weight of the ore and the iron content in it has been established. Based on block modeling of the massif, a forecast was made for the deep horizons of the Northern Quarry of JSC EVRAZ KGOK on changes in the volume weight of ore and the total iron content in it, which will allow the company's specialists to use the obtained data in geological and technological calculations.

Effect of calcination temperature on structure evolution of hematite nanoparticles

The objective of this study is to investigate the transition structure of iron oxide, specifically the change from magnetite to hematite, as well as the influence of calcination temperature on the structural growth of hematite nanoparticles. The magnetite was extracted from the native iron sand in Indonesia using the coprecipitation procedure. To generate hematite, magnetite was calcined at various temperatures (350, 500, 650, and 800 °C). The structural changes resulting from the effect of calcination temperature were investigated by combining a number of characterisation methods. The crystal structure was examined using synchrotron x-ray diffraction (SRD) and the local structure was examined using x-ray absorption spectroscopy (XAS). Crystallite size was calculated using the Debye-Schrerrer equation at the most dominant SRD peak. Surface morphology was investigated using scanning electron microscopy (SEM). SRD data revealed that the sample calcined at 350 °C displayed both the Fe3O4 and α-Fe2O3 phases, while higher temperatures revealed the single-phase α-Fe2O3. Furthermore, an increase in calcination temperature was shown to be associated with an increase in crystallinity and crystallite size. For the samples H350 and H800, the crystallinity increased from 95.56 to 98.17%. In the magnetite, H350, H500, H650, and H800 samples, the crystallite size increased from 9.57 to 29.55, 16.40, 28,48, 29.26, and 29.55 nm. Higher calcination temperatures, on the other hand, increase the interatomic distance while decreasing the Debye–Waller factor, according to XAS fitting data. It can be inferred that around 500 °C, the transition from Fe3O4 to single-phase α-Fe2O3 was observed. While a greater calcination temperature of at least 800 °C would alter the structural parameters, it would not affect the phase.

A Raman Spectroscopic Study of Lightning‐Induced Glass Produced From Five Mineral Phases

AbstractLightning‐induced volcanic spherules (LIVS) are glasses produced by the rapid melting and solidification of molten volcanic ash grains. High temperatures generated by lightning will alter the physical and chemical properties of minerals exposed to the discharge. Laboratory experiments reveal that LIVS glass composition varies depending on the starting material, exhibiting heterogeneous compositional features common in other glasses created by cloud‐to‐ground lightning, nuclear explosions, and high velocity impact events. This study uses scanning electron microscopy, energy dispersive spectroscopy, and Raman spectroscopy to investigate the structure and Raman signatures of lightning‐induced glass spherules manufactured from five igneous minerals (<32 μm powders of albite, labradorite, augite, hornblende, and magnetite). LIVS were created through high‐current impulse experiments using peak currents of 25 and 40 kA. Analysis of the post‐experimental albite, labradorite, augite, and hornblende LIVS reveal primarily homogeneous silicate or aluminosilicate glasses with limited heterogeneity. Their amorphous Raman spectra are comparable to rhyolitic and mafic natural glasses along with Na2O‐K2O‐Al2O3‐SiO2, CaCO3‐Al2O3‐SiO2, and CaO‐MgO‐SiO2 synthetic glass networks. A few of the augite and hornblende LIVS spectra exhibit premelting effects, which occur below the melting point and represent the onset of cation disordering in phases that remain crystalline. Magnetite samples produced crystal‐rich, glass‐poor LIVS characterized by the growth of dendritic microcrystals and crystalline spectra that also contain a few bands alluding to the composition of their silicate–phosphate glass matrix. By understanding these chemical changes induced by lightning, we can extract information from other types of glasses produced during high temperature, short duration events.

Copper-substituted magnetite as a Fenton-like catalyst boosted with electromagnetic heating

Copper-substituted magnetite samples Fe3-xCuxO4 (x = 0.0; 0.02; 0.05; 0.1) were synthesized using the co-precipitation method. XRD data revealed that the synthesized samples retain the cubic spinel structure of magnetite. The obtained materials were tested as heterogeneous Fenton catalysts to destroy organic pollutants and inactivate bacteria. The model organic pollutants were oxytetracycline, Congo Red dye, and Methylene Blue dye having neutral, anionic, and cationic nature, respectively. These organic pollutants differ in their adsorption on magnetite surface: oxytetracycline < Congo Red < Methylene Blue. The same order stays for their decomposition rates. The copper-substituted magnetite catalysts also ensure effective inactivation of E.coli bacteria. A contact time of 60 min is sufficient to reduce the number of bacteria by 6-log. In all tests, the catalytic activity of magnetite increases with the increase in Cu content. The maximum catalytic activity was recorded for the Fe2.9Cu0.1O4 sample. Since the copper-substituted magnetite samples are ferromagnetic, they absorb a high-frequency electromagnetic field. Electromagnetic heating results in a significant increase in catalytic activity: the rate constants of the studied catalytic reactions are increased by 1.5–5 times. Thus, copper-doped magnetite is a hetero-Fenton catalyst capable of increasing activity by electromagnetic heating. The adjustable catalytic activity may be useful in water disinfection, where bacterial load varies greatly.

In situ Fe isotope analysis of Cr-rich iron oxides using pure chromium metal for isobaric interference corrections by femtosecond LA–MC–ICP–MS

Iron oxide minerals, such as hematite and magnetite, are commonly found in a wide range of geological environments. Their Fe isotopic composition acts as a potent geochemical tracer, finding applications across various realms of Earth sciences. However, natural iron oxide minerals often have a high Cr content up to percentile levels, necessitating correction of isobaric interference caused by 54Cr+ on 54Fe+ to ensure accurate and precise in situ Fe isotopic compositions. In this study, a pure chromium metal with homogeneous isotopic compositions was examined within the analysis sequence to obtain the fractionation factor of Cr (βCr) for isobaric interference correction. A femtosecond laser ablation system combined with wet plasma conditions was used to decrease the matrix effect. We synthesized a series of magnetite and hematite samples with simple matrix as well as natural magnetite samples with complex matrix to evaluate the feasibility of Cr interference correction. By employing our proposed correction method, the deviation caused by the isobaric interference of 54Cr+ was effectively eliminated. The corrected δ56Fe values for hematite and magnetite samples, even with a Cr/Fe ratio of as high as 1.27, exhibited good agreement with the reference values within the long-term reproducibility uncertainty of 0.10‰. These results indicate the robustness of Cr interference correction in obtaining accurate Fe isotopic compositions of Cr-rich iron oxides.

Effect of Mn2+ substitution on catalytic properties of Fe3-xMnxO4 nanoparticles synthesized via co-precipitation method

Mn-substituted magnetite samples Fe3-xMnxO4 (x = 0.0; 0.02; 0.05; 0.1; 0.15; 0.2; 0.25) were synthesized using the co-precipitation method. X-ray diffraction patterns confirmed the formation of pure, well-crystallized manganese ferrite with a cubic spinel structure. The crystallites size increases sharply for the minimum degrees of substitution, with a subsequent tendency to decrease with the growth of manganese ions content. The catalytic properties of Fe3-xMnxO4 were investigated for the degradation of oxytetracycline (ОТС) and inactivate E. coli. There is a correlation between particle size and catalytic activity. The Fe2.95Mn0.05O4 sample exhibited the highest catalytic activity in the destruction of OTC. The effect of electromagnetic heating (EMH) on the catalytic properties of iron oxides were investigated. The Fe2.9Mn0.1O4 sample with electromagnetic heating achieved 100 % efficiency in decomposing 5 mg/L of OTC. Fe3-xMnxO4 samples reduce the number of Gram-negative bacteria E. coli at concentrations of 104 and 106 CFU/mL. Electromagnetic heating experiments demonstrated high performance, achieving inactivation of 6 logs of E. coli in the presence of Fe2.98Mn0.02O4 and Fe2.95Mn0.05O4 catalysts within 135 minutes. Studies on ecotoxicity have shown that Daphnia magna is a sensitive bioindicator of residual H2O2 concentration. An increase in the Mn2+ content in the synthesized catalysts resulted in a decrease in the toxicity of purified water. The study suggests that Mn-substituted magnetite catalysts are effective materials for catalytic decomposition of OTC and inactivation of E. coli bacteria.

Spectral induced polarization responses of carbonate precipitation in gel-saturated media with and without electron conductors

SUMMARY Interest in the use of carbonate precipitation for the purposes of soil stabilization, carbon capture and environmental remediation has created a need for geophysical techniques capable of characterizing the 3-D extent of precipitation in the subsurface. The use of spectral induced polarization, a geophysical technique sensitive to mineral precipitation and dissolution processes, has been investigated in previous studies; nevertheless, debate still exists regarding measured induced polarization (IP) signals relating to the formation of calcite. In this study, calcite was precipitated within gel-saturated media through highly controlled double-diffusion methods. Three experiments were conducted to study both the inherent IP response of calcite in isolation, as well as the IP response when precipitated within a low-polarizability background medium (quartz sand) and a high-polarizability medium (a sand–magnetite mixture). The results support that in isolation, the polarization of the electrical double layer surrounding individual calcite grains is not a significant contributor to IP signatures from calcite precipitation. However, under certain circumstances the precipitation of calcite, in the quartz-sand and sand–magnetite mixtures, can produce a strong IP response when the precipitation blocks a current conduction pathway. If metallic mineral grains are present then they may act as conduits for current if they become embedded in an insulating calcite wall, creating a significant electrode polarization which dominates the IP signal. Equivalent circuit models indicate that the precipitation of calcite as a thin planar front normal to the current path is analogous to a simple lossy capacitor blocking most DC current but being thin enough to measurably polarize. Circuit models also suggest that the total impedance seen from the sand–magnetite sample is simply the sum of the impedance of the disseminated grains and the grains encased in the calcite front. The encased grains also have a higher relaxation time which may indicate a different polarization mechanism than from disseminated magnetite.

Preparation and Use of Iron on Carbon Foam for Removal of Organic Dye from Water: Batch Studies.

The presence of dyes in effluents from textile industries has a detrimental effect on aquatic ecosystems as it hinders the process of photosynthesis by reducing the penetration of sunlight. The adsorption capacity of a carbon foam-based iron oxide sorbent obtained from natural sources for the removal of organic methylene blue (MB) dye from water was investigated. The adsorption capacities were examined by batch experiments, wherein the impacts of varying iron content, sorbent dosage, contact time, dye concentration, and characterization were assessed. The physical characteristics and surface morphology of the synthesized carbon foam were also investigated. The carbon precursor and iron oxide precursor were coalesced within a singular container and subjected to carbonization process. This resulted in the formation of a porous structure that is capable of effectively providing support to the iron oxide particles. The carbon foam produced is a self-assembled formation that possesses the characteristic shape and underlying network structure reminiscent of bread. As the number of nanoparticles went up, so did the number of active sites. At elevated temperatures, the interactions between the dye molecules were enhanced, resulting in a more efficient process of dye removal. The magnetite sample exhibited endothermic adsorption, and all other samples exhibited exothermic adsorption. The adsorption of MB onto iron supported by carbon foam did not exhibit intraparticle diffusion as the only rate-limiting step for all samples. The adsorption rate was governed by a multistep elementary reaction mechanism in which multiple processes occurred simultaneously. The experimental data in this study may be accurately modeled by the pseudo-second-order kinetic model (R2 > 0.96). Additionally, the Freundlich isotherm best describes the adsorption equilibrium, which is supported by the outstanding fit of data to the model (R2 > 0.999). The findings suggest that the utilization of a natural carbon foam as a support for an immobilized iron oxide sorbent demonstrates considerable effectiveness in the removal of methylene dye from industrial effluent.

FEATURES OF VIBRATION CRUSHING OF GEOLOGICAL SAMPLES OF MATERIAL

An innovative method of vibro-impact grinding of geological samples, implemented in a vibrating jaw crusher with an inclined crushing chamber, is considered to obtain a product of -1 mm in one crushing cycle. The technique consisted in comparing the results of crushing quartzite and magnetite with a particle size of 60...80 mm according to the existing multi-stage technology using jaw and roller crushers, as well as the proposed single-stage technology using a vibrating jaw crusher. Three technological schemes for the preparation of samples of quartzite and magnetite were modelled with obtaining granulometric characteristics after each piece of equipment. The analysis of the results showed almost the same particle size distribution of the samples according to the multi-stage scheme: jaw crusher, screening -2mm, roller crusher, screening -1mm and single-stage: vibrating jaw crusher, screening -1mm. The output of the finished material was 80%. The studies substantiated the feasibility of creating a small-sized vibrating jaw crusher with a crushing ratio of i ≥ 100 for the preparation of geological samples, operating in an open cycle and replacing at least two pieces of crushing equipment, two screens and mounting elements, which significantly reduces the metal consumption of the structure, the occupied area and simplifies maintenance.

Quantifying Internal Stress and Demagnetization Effects for Natural Multidomain Magnetite and Magnetite‐Ilmenite Intergrowths

AbstractDemagnetizing effects and internal stress are difficult to distinguish in natural magnetite samples, but quantitative stress estimates can provide valuable information about microstructure formation, surface oxidation, impacts, tectonic stresses, or interface properties in exsolution structures. Quantifying demagnetizing effects informs about magnetite particle shape, magnetostatic interaction, or anisotropic texture. Here, we establish an improved measurement workflow to separate demagnetizing effects from internal stress for natural magnetite. The method is based on temperature‐dependent hysteresis measurements, and for natural samples require accurate estimates of Curie temperature and temperature‐dependent saturation magnetization to ensure that near‐end‐member magnetite is the dominant magnetic mineral, and to calibrate the temperature‐dependent scaled reversible work (SRW). SRW is the fundamental quantity to determine stress and demagnetizing factor. The improved SRW method is applied to three natural samples with different stress histories where it proves that large magnetite crystals in the metamorphosed Modum complex (Norway) have low internal stress (&lt;100 MPa), while in highly exsolved magnetite‐ilmenite intergrowths from Taberg (Sweden) and Bushveld (South Africa) the magnetite component is highly stressed (&gt;230 MPa). This confirms experimentally that interface strain in complex microstructures due to spinodal decomposition and partial oxidation creates large average internal stress in the magnetite minerals. Because sister specimens have similar internal stress but noticeably (&gt;20%) different demagnetizing factors, textural, and shape anisotropy contribute substantially to SRW in these samples.

Physio-chemical characterization, in-vitro biocompatibility, and antimicrobial activity of magnetite nanoparticles synthesized via sol-gel route

In the present study, the biocompatibility of the magnetic Fe3O4 nanoparticles was examined for biomedical applications. The Fe3O4 nanoparticles showed good antimicrobial activity and better biocompatibility with human peripheral blood mononuclear cells and red blood cells. The Fe3O4 nanoparticles were synthesized via the sol-gel route. The x-ray diffraction pattern of the Magnetite sample showed single-phase crystalline with a hexagonal spinel structure and the lattice parameters are a = b = 5.0360 Å and c = 13.747 Å. The Debye Scherer formula was used to analyze the average crystallite size (36.56 nm). The dumbbell and near-spherical morphology (80-200 nm average particle size) were observed by field emission electron microscopy followed by transmission electron microscopy analysis. The vibrating sample magnetometer analysis depicted the magnetic characteristics of the spinel ferrite as 66.15 emu/g of saturation magnetization. The antimicrobial assay revealed a significant zone of inhibition against Escherichia coli and Staphylococcus aureus bacteria.

Genesis of the Longwanggou iron deposit in the Yudongzi Complex, South China: Implications for the redox state of seawater at the onset of the Great oxidation Event

Banded iron formations (BIFs) deposited during the onset of the Great Oxidation Event (GOE) are crucial to understanding fundamental changes in the redox conditions of Earth’s surface environments, however, they are poorly understood in South China. Here, we investigate the petrographic, geochronological, and geochemical characteristics of a set of continuous magnetite quartzite samples from a drill core through the Longwanggou iron deposit in the Yudongzi Complex, South China. These magnetite quartzite samples exhibit diagnostic features of BIFs — 1) they comprise alternating magnetite and quartz layers at the centimeter–millimeter scales, 2) they are dominantly composed of SiO2 + Fe2O3T (87.8–95.8 wt%, average = 91.4 wt%), and 3) they are characterized by shale-normalized rare earth elements plus yttrium patterns similar to seawater. The maximum depositional age of the Longwanggou BIF (i.e., magnetite quartzite) is constrained to ca. 2.49 Ga based on U–Pb dating of detrital zircon grains from chlorite schist that is intercalated with the BIF. The metamorphic complex of the Yudongzi Complex that hosts the BIF was intruded by ca. 2.5–2.45 Ga granitoid gneisses, indicating that the BIF must be older than 2.45 Gyr. Accordingly, the depositional age of the Longwanggou BIF is constrained to ca. 2.49–2.45 Ga, coincident with the onset of the GOE. The positive Eu anomalies (1.3–4.2; average = 2.2) that occur throughout BIF samples suggest a continuous flux of submarine, high-temperature hydrothermal fluids to the ocean at the Archean–Proterozoic boundary. Based on elemental mass balance, the proportion of submarine, high-temperature hydrothermal fluids that contributed to the deposition of the BIF was less than 0.1%. Unlike BIFs deposited during the GOE, the Longwanggou BIF samples lack negative Ce anomalies, suggesting that the water column in which the BIF was deposited was at least locally anoxic during the onset of the GOE. Identification of the Longwanggou BIF provides new constraints for the Precambrian evolution of South China and lays the foundation for further study of the environmental changes at the Archean–Proterozoic boundary.

Trace element geochemistry of magnetite from Mabianshan skarn iron deposit in the Lu-Zong volcanic basin, Eastern China

The composition of host rocks is essential in determining the composition of hydrothermal magnetite formed via fluid-rock interactions in skarn deposits. The HuangLong ore field in the Luzong volcanic basin, Eastern China, hosts several stratabound iron (Fe) skarn deposits, including Mabianshan and Longqiao. In this paper, we analyse the composition of different lithologies of carbonate strata and trace element concentrations in magnetite from Mabianshan, which has complex lithology carbonate strata, and compare it with magnetite from Longqiao, which has uniform lithology carbonate strata. The objective is to investigate the influence of lithology variation on magnetite trace elements and enhance the indicative significance of magnetite trace elements in prospecting and exploration. Our results demonstrate that the lithology of ore-bearing carbonate strata varies greatly due to inversion and different degrees of denudation in the ore field, resulting in variations of Al, Si, Mg, Mn, and Ca in the protolith across different areas. The alteration mineral assemblage of the Mabianshan deposit primarily included epidote, chlorite, and magnetite, while only a few diopside-magnetite relatively high-temperature assemblages developed in the southeastern part of the deposit. Moreover, higher concentrations of Ti and V in magnetite samples from the southeastern area of the deposit suggest that the heat sources related to Fe mineralization may be located there. Compared with the regular spatial variations of Mg, Mn, Al, and Si in the magnetite from Longqiao, the magnetite from Mabianshan does not show evident spatial variations due to the complex lithology of the magnetite protolith in different regions. The protolith lithology of magnetite from Longqiao is relatively stable, mainly dolomitic limestone. However, the protolith lithology of magnetite from Mabianshan is complex and includes dolomitic marlstone, dolomitic limestone, dolomite, and Fe-Mn bearing dolomite, resulting in a significant increase of Si, Al, Mg, and Mn in magnetite. Therefore, it is difficult to effectively trace the temporal-spatial evolution of the hydrothermal fluids using these elements in magnetite. Special attention should be paid to the uniformity of the protolith lithology of the ore when using these elements in magnetite to trace the fluid source.

Obtention of magnetite nanoparticles via the hydrothermal method and effect of synthesis parameters

Magnetic nanoparticles (MNPs) have been widely studied for their properties and applications in the fields of electronics and medicine. Hydrothermal synthesis, in which the reaction parameters are extremely important because they influence the product characteristics, properties, and final applications, is an existing method for producing nanomaterials. Therefore, in this study, hydrothermal syntheses were performed to obtain nanomagnetite by varying the temperature, reaction time, and molar ratio, and their influences on the product particle size were analyzed using statistical analysis. The products were characterized in terms of composition and purity.Tthe purest samples were obtained at a reaction temperature of 214 ℃ and the longest reaction time of 6 h, with 96 % purity for the tests with a higher magnetite content. All syntheses produced products with particles on the nanometer scale. The purest magnetite samples exhibited an average hydrodynamic diameter of 220 nm and ferromagnetic behavior. Statistical analysis revealed that the reaction time was the only statistically significant parameter influencing magnetite particle size, with smaller sizes at longer reaction times. The cytotoxicity of MNPs was evaluated in non-tumor cells (NIH3T3 and RAW 264.7). Human erythrocytes did not exert any cytotoxic effects on non-tumor cells, indicating that MNPs are promising drug delivery systems.

Structural and optical properties of gadolinium doped-magnetite nano-crystal for photocatalytic application

Doped ferrite materials offer a combination of enhanced magnetic properties, multifunctionality, higher Curie temperature, biocompatibility, and potential energy applications. Their unique characteristics make them appealing for research in diverse fields, including materials science, electronics, biomedical engineering, and energy technology. In present work, Gadolinium-doped magnetite samples are synthesized following the co-precipitation method. The effects of doping on the structural and optical properties of Fe3O4 are studied. Structural parameters of the samples such as cell parameters, cell volume crystalline size, x-ray density, and average micro-strain are calculated from the analysis of x-ray diffraction (XRD) data via Rietveld refinement method. An increase in crystalline size and cell volume is observed while a reduction in micro-strain is observed with increase in doping concentration. The particle size estimated from FE-SEM data ranges from 9 to 16 nm and is in good agreement with XRD data and confirms the formation of nanoscopic phase of the particles. The presence of characteristic peaks concerned with tetrahedral and octahedral site vibrations in the Fourier transform infrared spectroscopy data approve the formation of inverse spinel structure. The distribution of Gd in the samples is determined with Energy dispersive x-ray analysis. The optical studies show that the direct and indirect band gaps decrease from 4.07 to 3.95 eV and 3.79–3.65 eV, respectively. These values of band gap are indicated the potential use of the synthesized nanoparticles for photocatalytic application.

Comparative Mössbauer and first principles calculations for selected iron oxides and ferrites nanoparticles

Magnetic ferrites and related iron oxides, such as Fe3O4 and γ -Fe2O3, are widely explored due to their commercial and scientific importance. While typical ferrites exhibit cubic structures, maghemite (γ-Fe2O3) has two probable phases at room temperature, namely cubic (C) and the lately discovered tetragonal (T) structures. Here, we explore the structural and electronic properties of these two distinct maghemite phases using density functional theory (DFT). To assure the reliability of our DFT calculations, we perform comparative calculations on the most stable inverse spinal structure, namely NiFe2O4, and the cubic magnetite (Fe3O4). We also explore the systematic oxidation of Fe3O4 into γ-Fe2O3 when a portion of Fe+2 ions, at octahedral sites, are oxidized into Fe+3 by controlling the vacancies ratio from one to three vacancies per cell. The obtained calculations are supported by X-ray diffraction (XRD), UV–visible, and Mössbauer spectroscopies measured for partially-oxidized magnetite, maghemite, and NiFe2O4 nanoparticle samples of different size, prepared by the conventional chemical methods. Comparative DFT calculations for C γ-Fe2O3 phase and Fe3O4, with tunable vacancies, showed that the smooth conversion of Fe3O4 into γ-Fe2O3 involves a slight reduction in the lattice parameters with increasing maghemite vacancy ratio, in agreement with the experimental XRD results for the prepared samples. Likewise, a clear signature of the successful fabrication of partially-oxidized Fe3O4 and γ-Fe2O3 phases was confirmed from Mössbauer results. The energy gap obtained from the calculated band structures for γ-Fe2O3 and NiFe2O4 were consistent with the values obtained from UV–visible spectroscopy. The present work demonstrates the effectiveness of DFT methods to predict and explain fine structural and physical properties of magnetic materials and iron oxides of different structures and complexity.

SEDIMENTATION OF TITANIUM DIOXIDE SUSPENSION UNDER THE ACTION OF MAGNETIC FLOCCULANTS

Magnetic flocculants are synthesized from magnetite (Fe3O4) nanoparticles and ionic and nonionic acrylamide copolymers having different concentrations of ionic units and molecular weights. The synthesis is carried out in two steps: two magnetite samples having different size and surface characteristics are precipitated with ammonia from a mixed aqueous solution of Fe(II) and Fe(III) chlorides; then, the obtained samples are mixed with aqueous solutions of polyacrylamide flocculants. Individual particles of magnetite, copolymers, and magnetic flocculants based thereon are characterized by dynamic light scattering. Effect of the nature and flocculating ability of magnetic flocculants on the process of sedimentation of a titanium dioxide suspension is estimated. Varying the sizes of magnetic nanoparticles and the molecular parameters of acrylamide copolymers in the magnetic flocculant makes it possible to obtain a highly efficient multifunctional flocculant for the selective separation of multicomponent disperse systems.

Superparamagnetic-like Micrometric Single Crystalline Magnetite for Biomedical Application Synthesis and Characterization

Single-crystalline magnetite (Fe3O4) particles having a size beyond the nanometric range (1 µm to 50 µm) and showing high (close to the bulk value) saturation-specific magnetization (σs = 92 emu/g), were obtained by the hydrothermal decomposition of the Fe-EDTA complex. The very low values of the magnetic remanence (σr = 0.82 emu/g) and coercitivity (μoHc = 1.53 mT) observed at room temperature (RT) suggest a superparamagnetic-like behavior, which is quite remarkable for such micrometric magnetite particles. As confirmed by vibrating sample magnetometer (VSM)-based measurements, minor changes in their magnetic properties occur between RT and 5K. Scanning electron microscopy (SEM) has revealed a morphology consisting of a combination of non-porous octahedral- and dodecahedral-shaped particles, energy dispersive X-ray analysis (EDX) has indicated high elemental (Fe and O) purity, whereas X-ray diffraction (XRD) has confirmed a single crystal structure. The nitrogen adsorbtion–desorption isotherm and pore size distribution are presented for the magnetite sample. Thermomagnetic records under zero field-cooled (ZFC) and field-cooled (FC) conditions have revealed a thermal hysteresis of the Verwey transition.The Verwey point (TV) at which the major step of the phase transformation takes place is located around 132 K for heating and around 122 K for cooling. These microcrystals do not remain agglomerated when the polarizing field is removed, an essential requirement in biomedical applications is met.