Microwave Sintering of Nanocrystalline Ni1−xZnxFe2O4 Ferrite Powder and Their Magnetic Properties

Nanocrystalline Ni_1?xZn_xFe₂O₄ (0 ≤ x ≤ 1.0) powder with grain size of 30 nm was prepared using the spraying‐coprecipitation method. The obtained nanocrystalline Ni_1?xZn_xFe₂O₄ powder was sintered using conventional and microwave sintering techniques. The results show that the microstructure and magnetic properties of the sintered samples are obviously improved by microwave sintering of nanocrystalline Ni_1?xZn_xFe₂O₄ ferrite powder. The initial permeability of Ni_1?xZn_xFe₂O₄ ferrite increases with the increase in zinc concentration, although its resonance frequencies shift from high frequency to low frequency. The maximum initial permeability for microwave‐sintered Ni_0.4Zn_0.6Fe₂O₄ ceramic obtained at the temperature of 1170°C for 30 min reaches up to 360.9, and its resonance frequency is ~10 MHz. It may be attributed to the nanocrystalline Ni_1?xZn_xFe₂O₄ raw powder as well as the microwave sintering process, which results in a synergistic effect on improvement of the microstructure and magnetic properties.     

Low‐Temperature Sintering and Microwave Dielectric Properties of CaMoO4‐Based Temperature Stable LTCC Material

The CaMoO₄–xY₂O₃–xLi₂O ceramics were prepared by the solid‐state reaction method. The sintering behavior, phase evolution, microstructure, and microwave dielectric properties were investigated. CaMoO₄ solid solution was obtained when x = 0.030, and two‐phase system including tetragonal CaMoO₄ phase and cubic Y₂O₃ phase formed when 0.066 ≤ x ≤ 1.417. A temperature stable CaMoO₄‐based microwave dielectric ceramic with ultralow sintering temperature (775°C) was obtained in the CaMoO₄–xY₂O₃–xLi₂O system when x = 0.306, which showed good microwave dielectric properties with a low permittivity of 9.5, a high Q_f value of 63 240 GHz, and a near‐zero temperature coefficient of resonant frequency of +7.2 ppm/°C.     

High performance of la‐promoted Fe2O3/α‐Al2O3 oxygen carrier for chemical looping combustion

Iron oxide supported oxygen carrier (OC) is regarded to a promising candidate for chemical looping combustion (CLC). However, phase separation between Fe₂O₃ and supports often occurs resulted from the severe sintering of supports during calcination, which leads to the sintering and breakage of Fe₂O₃ thus the decrease of redox reactivity. In this article, La‐promoted Fe₂O₃/α‐Al₂O₃ were used as OCs for CLC of CH₄ and for the first time found that the OC with the addition of 18 wt % La exhibited outstanding reactivity and redox stability during 50 cycles of CLC of CH₄. Such a superior performance originated from the formation of LaAl₁₂O₁₉ hexaaluminate (La‐HA) phase with not only small particle size but also excellent thermal stability at CLC conditions, which worked as a binder to prevent the phase separation thereby the sintering and breakage of active species α‐Fe₂O₃ were avoided during reaction. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2827–2838, 2017     

Investigations of Structural and Magnetic Properties of Nanostructured Ni0.5+xZn0.5‐xFe2O4 Magnetic Feeders for CSEM Application

Marine CSEM is a new technique for detection of deep target hydrocarbons. Aluminum EM antenna was developed, and nanostructured NiZn magnetic feeders were used to increase the field strength from EM antenna for deep hydrocarbons. The doping of Ni²⁺ was aimed at the optimization of initial permeability and magnetic losses. Ni_0.5+xZn_0.5‐xFe₂O₄ (x = 0.3) samples sintered at 950°C presented highest initial permeability (106.23) and low magnetic loss (0.0002) as compared to other samples. Due to better magnetic properties, Ni_0.5+xZn_0.5‐xFe₂O₄ (x = 0.3) samples were used as magnetic feeders for EM antenna. Magnitude of EM waves from the antenna increased up to 186%.     

Flow Cytometry Analysis of Cytotoxicity In Vitro and Long‐Term Toxicity of HA‐40 wt% BaTiO3 Nanoparticles In Vivo

The development of new implantable biomaterials requires bone‐mimicking physical properties together with desired biocompatible property. In continuation to our earlier published research to establish compositional dependent multifunctional bone‐like properties and cytocompatibility response of hydroxyapatite (HA)‐BaTiO₃ composites, the toxicological property evaluation, both in vitro and in vivo, were conducted on HA‐40 wt% BaTiO₃ and reported in this work. In particular, this work reports in vitro cytotoxicity of mouse myoblast cells as well as in vivo long‐term tissue and nanoparticles interaction of intra‐articularly injected HA‐40 wt% BaTiO₃ and BaTiO₃ up to the concentration of 25 mg/mL in physiological saline over 12 weeks in mouse model. The careful analysis of flow cytometry results could not reveal any statistically significant difference in terms of early/late apoptotic cells or necrotic cells over 8 d in culture. Extensive histological analysis could not record any signature of cellular level toxicity or pronounced inflammatory response in vital organs as well as at knee joints of Balb/c mice after 12 weeks. Taken together, this study establishes nontoxic nature of HA‐40 wt% BaTiO₃ and therefore, HA‐40 wt% BaTiO₃ can be used safely for various biomedical applications.     

Poly(Caprolactone)‐Poly(N‐Isopropyl Acrylamide)‐Fe3O4 Magnetic Nanofibrous Structure with Stimuli Responsive Drug Release

Poly(caprolactone; PCL)—poly(N‐isopropylacrylamie; PNIPAAm)—Fe₃O₄ fiber, that can be magnetically actuated, is reported. Here, a structure is engineered that can be utilized as a smart carrier for the release of chemotherapeutic drug via magneto‐thermal activation, with the aid of magnetic nanoparticles (MNPs). The magnetic measurement of the fibers revealed saturation magnetization values within the range of 1.2–2.2 emu g^?1. The magnetic PCL‐PNIPAAm‐Fe₃O₄ scaffold shows a specific loss power value of 4.19 W g^?1 at 20 wt% MNPs. A temperature increase of 40 °C led to a 600% swelling after only 3 h. Doxorubicin (DOX) as a model drug, demonstrates a controllable drug release profile. 39% ± 0.92 of the total drug loaded is released after 96 h at 37 °C, while 25% drug release in 3 h at 40 °C is detected. Cytotoxicity results show no significant difference in cell attachment efficiency between the MNP‐loaded fibers and control while the DOX‐loaded fibers effectively inhibited cell proliferation at 24 h matching the drug release profile. The noncytotoxic effect, coupled with the magneto‐thermal property and controlled drug release, renders excellent potential for these fibers to be used as a smart drug‐release agent for localized cancer therapy.     

Structural and Magnetic Property of Co1‐xNixFe2O4 Nanoparticles Synthesized by Hydrothermal Method

The cobalt nickel ferrite (Co_1‐xNi_xFe₂O₄ x = 0–1.0) nanoparticles were synthesized by a hydrothermal method. Effects of nickel content and organic template on the microstructure and magnetic property of the nanoparticles were studied. The experimental results indicate that Ni²⁺ substitution for Co²⁺ and special synthesis technique leads to obvious change in microstructure and magnetic property of the ferrites. The ferrites show nonlinear variations in the saturation magnetization and the coercivity with nickel substitution, which are explained by shape anisotropy and supernormal cation distribution. The organic template also leads to variation in the microstructure and properties of the nanoparticles.     

Effects of Mg‐Doping and of Reinforcing Multiwalled Carbon Nanotubes Content on the Structure and Properties of Hydroxyapatite Nanocomposite Ceramics

Surfactant‐assisted hydrothermal synthesis of magnesium‐doped hydroxyapatite (Ca_10?xMg_x(PO₄)₆(OH)₂) with 0 ≤ x ≤ 1) was realized in aqueous solution at 90°C. β‐TCP phase was formed in the Mg_0.6‐HA sample after heat treatment at 1000°C. Magnesium was found to degrade the sintering ability of Mg_x‐HA ceramics. Flexural strength (σ_f) was found to decrease as a function of Mg‐doped HA. The using of carbon nanotubes as reinforcing agents mitigated the strength loss of Mg‐HA ceramics. The flexural strength of Mg_0.6‐HA was then increased by nearly 20% from approximately 33 to 39 MPa with an optimum addition of 3 wt% of multi‐walled nanotubes.     

Preparation of Fe3Si‐Al2O3 Nanocomposite Powders by Mechanochemical Reaction of Fe3O4‐Si‐Al Powder Mixtures

Phase evolution and morphology of Fe₃O₄‐Si‐Al powder mixtures during ball milling from 30 min to 20 h were investigated. A 3‐h critical milling was necessary for the occurrence of mechanically activated combustion reaction. The reaction results in the formation of Fe (Si), Fe₃Si, and α‐Al₂O₃. During ball milling from 3 to 20 h, Fe (Si) and Fe₃Si were combined into disordered Fe₃Si intermetallic and Fe₃Si‐Al₂O₃ composite powder was formed. The presence of in situ formed alumina leads to a decrease in crystallite and particle sizes. The Fe₃Si‐Al₂O₃ particles after milling for 20 h had a crystalline size of 10~12 nm.     

Structural,Raman, and Dielectric Studies on Multiferroic Mn‐doped Bi1−xLaxFeO3 Ceramics

Multiferroic Bi_1?xLa_xFeO₃ [BLFO (x)] ceramics with x = 0.10–0.50 and Mn‐doped BLFO (x = 0.30) ceramics with different doping contents (0.1–1.0 mol%) were prepared by solid‐state reaction method. They were crystallized in a perovskite phase with rhombohedral symmetry. In the BLFO (x) system, a composition (x)‐driven structural transformation (R3c→C222) was observed at x = 0.30. The formation of Bi₂Fe₄O₉ impure phase was effectively suppressed with increasing the x value, and the rhombohedral distortion in the BLFO ceramics was decreased, leading to some Raman active modes disappeared. A significant red frequency shift (~13 cm^?1) of the Raman mode of 232 cm^?1 in the BLFO ceramics was observed, which strongly perceived a significant destabilization in the octahedral oxygen chains, and in turn affected the local FeO₆ octahedral environment. In the Mn‐doped BLFO (x = 0.30) ceramics, the intensity of the Raman mode near 628 cm^?1 was increased with increasing the Mn‐doping content, which was resulted from an enhanced local Jahn–Teller distortions of the (Mn,Fe)O₆ octahedra. Electron microscopy images revealed some changes in the ceramic grain sizes and their morphologies in the Mn‐doped samples at different contents. Wedge‐shaped 71° ferroelectric domains with domain walls lying on the {110} planes were observed in the BLFO (x = 0.30) ceramics, whereas in the 1.0 mol% Mn‐doped BLFO (x = 0.30) samples, 71° ferroelectric domains exhibited a parallel band‐shaped morphology with average domain width of 95 nm. Dielectric studies revealed that high dielectric loss of the BLFO (x = 0.30) ceramics was drastically reduced from 0.8 to 0.01 (measured @ 10⁴ Hz) via 1.0 mol% Mn‐doping. The underlying mechanisms can be understood by a charge disproportion between the Mn⁴⁺ and Fe²⁺ in the Mn‐doped samples, where a reaction of Mn⁴⁺ + Fe²⁺→Mn³⁺ + Fe³⁺ is taken place, resulting in the reduction in the oxygen vacancies and a suppression of the electron hopping from Fe³⁺ to Fe²⁺ ions effectively.     

Low‐Temperature Sintering Li2MoO4/Ni0.5Zn0.5Fe2O4 Magneto‐Dielectric Composites for High‐Frequency Application

The coexistence of Li₂MoO₄ (LMO) and Ni_0.5Zn_0.5Fe₂O₄ (NZO) has been proven and their low‐temperature‐sintered magneto‐dielectric composites (1?x)LMO–xNZO (volume fraction factor x = 0.1, 0.3, 0.5, 0.7) were prepared by the conventional solid‐state reaction method and were sintered below 700°C. It is found that the optimal sample (x = 0.5) has good and relatively stable magneto‐dielectric performance in the frequency range from 10 MHz to 1 GHz with permittivity between 7.14 and 6.84, dielectric loss tangent between 0.09 and 0.02, and permeability between 5.23 and 3.30, magnetic loss tangent between 0.06 and 0.65, respectively. Furthermore, the verified chemical compatibility with silver indicates that the LMO–NZO ceramics are potential for low‐temperature cofired ceramic application and their multifunctional magneto‐dielectric properties also make them for potential applications in electronic devices.     

Decolorization of methylene blue by heterogeneous Fenton reaction using Fe3−xTixO4 (0 ≤ x ≤ 0.78) at neutral pH values

In this work, a series of Fe_3−xTi_xO₄ (0 ≤ x ≤ 0.78) was synthesized using a new soft chemical method. The synthetic Fe_3−xTi_xO₄ were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy, thermogravimetric and differential scanning calorimetry (TG–DSC) analyses. The results showed that they were spinel structures and Ti was introduced into their structures.Then, decolorization of methylene blue (MB) by Fe_3−xTi_xO₄ in the presence of H₂O₂ at neutral pH values was studied using UV–vis spectra, dissolved organic carbon (DOC) and element C analyses. Furthermore, the degradation products remained in reaction solution after the decolorization were identified using ionic chromatography (IC), ¹³C nuclear magnetic resonance spectra (NMR), liquid chromatography and mass spectrometry (LC–MS). Although small amounts of MB were mineralized, the aromatic rings in MB were destroyed completely after the decolorization. Decolorization of MB by Fe_3−xTi_xO₄ in the presence of H₂O₂ was promoted remarkably with the increase of Ti content in Fe_3−xTi_xO₄ due to the enhancement of both adsorption and degradation of MB on Fe_3−xTi_xO₄.     

Ferrite‐Based Exchange‐Coupled Hard–Soft Magnets Fabricated by Spark Plasma Sintering

Ferrite‐based, hard‐soft magnetic nanocomposites with the composition (100%?x)SrFe₁₂O₁₉–xCoFe₂O₄, where x = 5, 10, and 15 wt%, were prepared by mixing the constituent powders, followed by spark plasma sintering. In order to control the particle size of the constituent materials, the SrFe₁₂O₁₉ and CoFe₂O₄ powders were synthesized using the hydrothermal method, mixed and then consolidated with spark plasma sintering. The conditions during the spark plasma sintering process (sintering temperature, time, and applied pressure) were varied in order to prepare composites with a high density and exchange‐coupled hard and soft magnetic phases, leading to an increase in the maximum energy product, when compared with pure SrFe₁₂O₁₉. The microstructural analysis revealed that the relative density of the sintered composite exceeded 90% of the theoretical value and that the CoFe₂O₄ was uniformly distributed in the SrFe₁₂O₁₉ matrix. Magnetic measurements of the sintered composites showed a single‐phase magnetic behavior. When compared with the single‐phase SrFe₁₂O₁₉ used in this study, the SPS composites exhibited a 22% increase in the maximum energy product (26.1 kJ/m³).     

Structural and Physical Properties of Mixed‐Layer Aurivillius‐Type Multiferroics

Different from the homogeneous layer structure of famous Bi_n+1Fe_n?3Ti₃O_3n+3 compounds with integer n values, the mixed‐layer structure of the compounds with fractional n values and their related physics have been rarely reported in recent years. In this work, the mixed‐layer compound Bi₁₁Fe₃Ti₆O₃₃ (n = 4.5) was synthesized by the modified Pechini method, and its structure was characterized as an inhomogeneous phase generating from the disordered intergrowths of the n = 4 and 5 perovskite slabs. Multiferroic properties of this compound were discussed in detail, compared with two adjacent homologous Aurivillius phases Bi₅FeTi₃O₁₅ (n = 4) and Bi₆Fe₂Ti₃O₁₈ (n = 5). Significantly, the ferroelectric polarization of the mixed‐layer sample at room temperature is higher than that of the adjacent homologous phases with integer n, mainly arising from the intrinsic mixed‐layer structure. The ferroelectric Curie temperature (~992 K) and a magnetic transition temperature (~7 K) of the 4.5‐layer phase of Bi₁₁Fe₃Ti₆O₃₃ fall in between those of the homogeneous 4‐ and 5‐layer phases, conforming to the change trends of such oxides with integer n. These results provide important contributions to understand the Aurivillius‐type materials and open up a new avenue to enhance multiferroic properties in single‐phase multiferroics.     

Formation Behavior and High Electrical Conductivity of Metastable Lithium Iron Silicate Crystals in Rapid Quenching of Li2O–Fe2O3–SiO2 Melts

The formation behavior of spinel‐type LiFeSiO₄ crystals in the quenching of melts in the Li₂O–Fe₂O₃–SiO₂ system was examined. It was found that high quenching rates of 10³ ~ 10⁶ K/min are favorable for the formation of LiFeSiO₄ crystals. The rapid quenched samples showed high electrical conductivities of the order of 10^?2–10^?4 S/cm at room temperature and low activation energy for conduction of 0.1–0.2 eV. Both valences of Fe²⁺ and Fe³⁺ were present in the melt‐quenched samples, and rapid‐quenched samples showed ferrimagnetism. It is proposed that the chemical composition of LiFeSiO₄ formed in the rapid quenching of melts would be spinel‐type Li_1 + xFe³⁺_1 ? xFe²⁺_xSiO₄. Because the Li_1 + xFe³⁺_1 ? xFe²⁺_xSiO₄ crystalline phases are metastable, the rapid quenching technique is necessary for their synthesis. The effects of quenching rate and composition on the formation of spinel‐type LiFeSiO₄ and on the electrical conductivity of quenched samples were discussed.     

Structure‐Dependent Microwave Dielectric Properties and Middle‐Temperature Sintering of Forsterite (Mg1–xNix)2SiO4 Ceramics

The crystal structure, microstructure, and microwave dielectric properties of forsterite‐based (Mg_1–xNi_x)₂SiO₄ (x = 0.02–0.20) ceramics were systematically investigated. All samples present a single forsterite phase of an orthorhombic structure with a space group Pbnm except for a little MgSiO₃ secondary phase as x > 0.08. Lattice parameters in all axes decrease linearly with increasing Ni content due to the smaller ionic radius of Ni²⁺ compared to Mg²⁺. The substitution of an appropriate amount of Ni²⁺ could greatly improve the sintering behavior and produce a uniform and closely packed microstructure of the Mg₂SiO₄ ceramics such that a superior Q × f value (152 300 GHz) can be achieved as x = 0.05. The τ_f value was found to increase with increasing A‐site ionic bond valences. In addition, various additives were used as sintering aids to lower the sintering temperature from 1500°C to the middle sintering temperature range. Excellent microwave dielectric properties of ε_r~6.9, Q × f~99800 GHz and τ_f~?50 ppm/°C can be obtained for 12 wt% Li₂CO₃‐V₂O₅‐doped (Mg_0.95Ni_0.05)₂SiO₄ ceramics sintered at 1150°C for 4 h.     

Effect of Ga2O3 on Sintering and Phase Stability of Sc2O3‐Doped Tetragonal Zirconia Prepared via Aqueous Solution Route

The effects of the presence of Ga₂O₃ on low‐temperature sintering and the phase stability of 4, 5, and 6 mol% Sc₂O₃‐doped tetragonal zirconia ceramics (4ScSZ, 5ScSZ, and 6ScSZ, respectively) were investigated. A series of zirconia sintered bodies with compositions (ZrO₂)_0.99?x(Sc₂O₃)_x(Ga₂O₃)_0.01, x = 0.04, 0.05, and 0.06 was fabricated by sintering at 1000°C to 1500°C for 1 h using fine powders that were prepared via the combination of homogeneous precipitation method and hydrolysis technique using monoclinic zirconia sols synthesized through the forced hydrolysis of an aqueous solution of zirconium oxychloride at 100°C for 168 h. The presence of 1 mol% Ga₂O₃ was effective in reducing sintering temperature necessary to fabricate dense bodies and enabled to obtain dense sintered bodies via sintering at 1100°C for 1 h. The phase stability, that is, low‐temperature degradation behavior of the resultant zirconia ceramics was determined under hydrothermal condition. The zirconia ceramics codoped with 1 mol% Ga₂O₃ and 6 mol% Sc₂O₃ (1Ga6ScZ) fabricated via sintering at 1300°C for 1 h showed high phase stability without the appearance of monoclinic zirconia phase, that is the tetragonal‐to‐monoclinic phase transformation was not observed in the 1Ga6ScZ after treatment under hydrothermal condition at 150°C for 30 h.     

High lithium ionic conductivity in the garnet‐type oxide Li7−2xLa3Zr2−xMoxO12 (x=0‐0.3) ceramics by sol‐gel method

Lithium garnet‐type oxides Li_7?2xLa₃Zr_2?xMo_xO₁₂ (x=0, 0.1, 0.2, 0.3) ceramics were prepared by a sol‐gel method. The influence of molybdenum on the structure, microstructure and conductivity of Li₇La₃Zr₂O₁₂ were investigated by X‐ray diffraction, scanning electron microscopy, and impedance spectroscopy. The cubic phase Li₇La₃Zr₂O₁₂ has been stabilized by partial substitution of Mo for Zr at low temperature. The introduction of Mo (x≥0.1) can accelerate densification. Li_6.6La₃Zr_1.8Mo_0.2O₁₂ sintered at lower temperature 1100°C for 3 hours exhibits highest total ionic conductivity of 5.09 × 10^?4 S/cm. Results indicate that the Mo doping LLZO synthesized by sol‐gel method effectively lowers its sintering temperature and improves the ionic conductivity.     

Magnetic Properties of Iron Phosphate Glass and Glass‐Ceramics

Magnetic properties of crystallized iron phosphate glasses and relationship between structural and magnetic properties modifications that occur during crystallization have been investigated. Iron phosphate glass exhibits the spin‐glass (SG) behavior and represents a prototype of solid with disordered spatially distributed magnetic moments. Glass of the composition 43Fe₂O₃–57P₂O₅ (wt%) was heat‐treated in air at 893, 923, and 1073 K for 24 h. The samples were studied using X‐ray diffraction, Raman spectroscopy, and dc magnetic measurements. The magnetic measurements show dominant antiferromagnetic (AF) interactions for all samples. The starting glass exhibits SG behavior, whereas magnetic behavior of samples heat‐treated at 893 and 923 K, which contain Fe₃(P₂O₇)₂ crystalline phase embedded in glass matrix, is ascribed to a mixture of superparamagnetism and SG behavior. In the sample heat‐treated at 1073 K, several peaks in the magnetization curves were observed which correspond to the various crystalline phases present in the sample: Fe₃(P₂O₇)₂, Fe₄(P₂O₇)₃ and Fe(PO₃)₃. Hysteresis loops show paramagnetic behavior at 300 K. Small curvature is present at low temperature (5 K) that can be ascribed to the AF ordering in the samples.     

The Synthesis of Ba‐ and Fe‐ Substituted CsAlSi2O6 Pollucites

Barium‐substituted CsAlSi₂O₆ pollucites, Cs_xBa_(1?x)/2AlSi₂O₆, and barium‐ and iron‐substituted pollucites, Cs_xBa_(1?x)/2Al_xFe_1?xSi₂O₆ and Cs_xBa_1?xAl_xFe_1?xSi₂O₆ were synthesized with 1 ≥ x≥ 0.7 using a hydrothermal synthesis procedure. Rietveld analysis of X‐ray diffraction data confirmed the substitution of Ba for Cs and Fe for Al, respectively. The crystallographic analysis also describes the effects of three different types of pollucite substitutions on the pollucite unit cell: Ba²⁺ for Cs¹⁺ cation results in little effect on cell dimensions, intermediate concentrations of Ba²⁺ and Fe³⁺ substitution result in net minor expansion due to Fe³⁺ addition, and large Ba and Fe substitutions result in overall framework contraction. Elemental analysis combined with microscopy further supports the phase purity of these new phases. These materials can be used to study the stability of CsAlSi₂O₆ as a durable ceramic waste form, which could accommodate with time Cs and its decay product, Ba. Furthermore, success in iron substitution for aluminum into the pollucite lattice predicts that redox charge compensation for Cs cation decay is possible.