Synthesis,structural, mechanical,and in vitro evaluations of NiFe2O4/ZrO2 composites

NiFe₂O₄/ZrO₂ composite with varied compositional ratios was formed through solution-based sol-gel synthetic route. The ability to retain NiFe₂O₄/ZrO₂ composite structures was dependent on the concomitant effect of temperature gradient and precursor concentration. The crystallization of t-ZrO₂ alongside the incidence of NiFe₂O₄ and NiO was evident at 900°C. However, the gradual elimination of NiO and simultaneous enhancement in NiFe₂O₄ content is inevitable at 1300°C. Morphological analysis of the composite revealed discrete distribution of ZrO₂ and NiFe₂O₄ grains and also portrays the dense and pore-free microstructures. Despite the presence of varied amount of NiFe₂O₄ in the composites, the resultant mechanical properties displayed relatively better values and exhibited good similarities with the hard tissue. As expected, a gradual increment in the ferrimagnetic properties as a function of enhanced NiFe₂O₄ content was induced. Further, in vitro analysis delivered good biocompatibility features of the investigated NiFe₂O₄/ZrO₂ composite.     

Efficient catalytic wet oxidation of phenol using iron acetylacetonate complexes anchored on carbon nanofibres

Iron acetylacetonate complexes anchored on oxidized carbon nanofibres (CNFs) were prepared by a three steps procedure: (i) oxidation of commercial CNFs by treatment with HNO₃, (ii) synthesis of acetylacetonate (acac) functional groups on the oxidized CNFs surfaces (acac/CNFs) and (iii) iron ions complexation on the acac sites of the CNFs (Fe-acac/CNFs). The surface groups exposed on the functionalized CNFs were characterized by using attenuated total reflectance Fourier transform infrared spectroscopy, temperature programmed desorption, thermogravimetric analysis and X-ray photoelectron spectroscopy. The functionalized CNFs and the iron complexes anchored on the CNFs were tested as heterogeneous catalysts for the wet oxidation of phenol with pure oxygen. Complete phenol conversion and high mineralization values were achieved with fresh and reused Fe-acac/CNFs catalysts, which demonstrate the improved stability of the catalysts under the phenol degradation reaction conditions. Furthermore these conditions are comparatively mild, typically 413 K of reaction temperature and 2.0 MPa of oxygen pressure.     

Microwave absorption study of carbon nano tubes dispersed hard/soft ferrite nanocomposite

Nickel substituted strontium hexaferrite, SrNi₂Fe₁₀O₁₉·(SrFe₁₂O₁₉/NiFe₂O₄) nanoparticles have been synthesized by low combustion method by citrate precursors using sol to gel (S–G) followed by gel to nano crystalline (G–N) conversion. The resulting ‘as-synthesized’ powder is heat treated (HT) at 800 and 1000 °C for 4 h in nitrogen atmosphere. The hysteresis loops show an increase in saturation magnetization from 27.443 to 63.706 emu/g with increasing HT temperatures. The multiwalled carbon nano tubes (CNTs) were synthesized by thermal decomposition of acetylene gas over iron-catalyst deposited on silicon wafer in the temperature range of 750–800 °C. A microwave absorbing medium is prepared by adding CNTs in the nickel substituted strontium hexaferrite nanoparticles. Addition of certain mass of CNTs improves the microwave absorption properties and wave band of SrFe₁₂O₁₉/NiFe₂O₄ absorbent. When 10 wt% CNTs is mixed with SrFe₁₂O₁₉/NiFe₂O₄ nanoparticles to fabricate a composite with 2 mm thickness, the maximum reflection loss reaches to ?36.817 dB at 9.292 GHz and ?10 dB bandwidth reaches 3.27 GHz.     

Magnetic sputtering of FeNi/C bilayer film on SiC fibers for effective microwave absorption in the low-frequency region

It is a great challenge in promoting a microwave absorber with excellent absorbing properties in the low-frequency region. Herein, SiC fibers (SiC_f) coated by a bilayer of FeNi/C (SiC_f/FeNi/C) are fabricated via a two-step magnetron sputtering method. Owing to the improved dielectric loss, magnetic loss, and impedance matching, the reflection loss of SiC_f/FeNi/C is remarkably enhanced. Accordingly, the minimum reflection loss of SiC_f/FeNi/C reaches ?26.18 dB at a low-frequency region of 3.44 GHz. Besides, the mechanic strength of SiC_f/FeNi/C maintains at 2.32 GPa as compared to as-received SiC_f. Thus, SiC_f/FeNi/C is expected to be an ideal structure material to meet low-frequency microwave absorption requests.     

One-step hydrothermal synthesis and microwave electromagnetic properties of RGO/NiFe2O4 composite

The reduced graphene oxide (RGO)/NiFe₂O₄ composite was synthesized by a facile one-pot hydrothermal route, which avoided the usage of chemical reducing agent. The reduction of graphene oxide (GO) and the crystallization of NiFe₂O₄ crystals happened in a one-step hydrothermal process. The morphology, microstructure and magnetic properties of the composite were detected by means of XRD, XPS, TEM, EDX, TG-DSC and VSM. The maximum R_L of the RGO/NiFe₂O₄ composite is −39.7 dB at 9.2 GHz with the thickness of 3.0 mm, and the absorption bandwidth with the R_L below −10 dB is up to 5.0 GHz (from 12.7 to 17.7 GHz) with a thickness of 1.9 mm. The introduction of RGO signally enhanced microwave absorption performance of the NiFe₂O₄ NPs. It is believed that such composite will be applied widely in microwave absorbing area.     

An attempt to produce NiFe2O4 powder from electrodeposited Fe–Ni alloy powders by subsequent recrystallization in air

The electrodeposition of the Fe–Ni powders from citrate-ammonium chloride containing electrolytes for different Ni/Fe ions concentration ratios at pH 4.0 was investigated by the polarization measurements. The morphology, chemical composition, and phase composition of the obtained powders were investigated using SEM, EDS, and XRD analysis. EDS analysis of as-deposited alloy powders confirmed anomalous co-deposition of Fe and Ni. A common characteristic for all as-deposited powder samples was the presence of cone-shaped cavities and nodules on the big agglomerates of the order of 200–400 μm. After annealing in air at 400, 600, and 700 °C for 3 h, all alloy powders oxidized forming NiO, NiFe₂O₄, and Fe₂O₃ phases in different proportions depending on the original powder composition. The NiFe₂O₄ phase was found to be dominant in the sample with the highest percentage of Fe after annealing at 600 °C.     

Study of Electromagnetic Properties of Fabricated NiFe2O4/Polyurethane Nanocomposites

Nickel ferrite loaded (NiFe₂O₄) segmented polyurethane (SPU) nanocomposites prepared by melt mixing method using microcompounder at temperature 185 °C in recirculation mode to ensure proper dispersion and distribution of nanoparticles at optimized residency time of 5 min. Three different weight percentages of nanocomposites (3, 5, and 10 wt %) was prepared and studied the electromagnetic property of nanocomposites obtained from complex permittivity and permeability. The effect of nanofiller (NiFe₂O₄) has been studied to assess their thermal properties using thermogravimetric analysis, differential scanning calorimetry, and thermomechanical analysis. The nanocomposites (NiFe₂O₄/SPU) have further been studied using FE-SEM, and the micrographs show embedded NiFe₂O₄ filler uniformly dispersed in SPU matrix without agglomeration (size 20–40 nm). It is also evident that further loading of nanofiller resulted in saturation effect yielding no applicable change in thermal behavior and revealed lesser melting enthalpy due to the coalescence of the nanofillers. X-ray diffraction and vibrating sample magnetometer also support the formation of the nanocomposite. The electric and magnetic properties of NiFe₂O₄ incorporated nanocomposite (NiFe₂O₄/SPU) may have potential application in microwave absorption. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48645.     

Polypyrrole/NiFe2O4 composites with improved hexavalent chromium removal from aqueous solution

Polypyrrole/NiFe₂O₄ (PPy/NiFe₂O₄) composites were prepared by ultrasonic oxidative polymerization in the presence of NiFe₂O₄ nanoparticles (NPs). The nanostructure of PPy/NiFe₂O₄ was confirmed by the X‐ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM) examinations. The adsorption of Cr(VI) onto the PPy/NiFe₂O₄ composite was lowly pH dependent and the adsorption kinetics followed the Pseudo‐second‐order model. The Langmuir isothermal model well described the adsorption isotherm data and the maximum adsorption capacity increased with the increase of temperature. The maximum adsorption capacity of the PPy/NiFe₂O₄ for Cr(VI) ions was up to 50 mg/g at pH 2.0. The excellent adsorption characteristic of PPy/NiFe₂O₄ composite will render it a highly efficient and economically viable adsorbent for Cr(VI) ions removal. POLYM. COMPOS., 38:2779–2787, 2017. © 2015 Society of Plastics Engineers     

Effect of preparation conditions on mechanical,dielectric and microwave absorption properties of SiC fiber/mullite matrix composite

Silicon carbide fiber-reinforced mullite matrix (SiC_f/Mu) composites were fabricated via an infiltration and sintering method. Effects of sintering parameters on microstructure, mechanical, dielectric and microwave absorption properties of SiC_f/Mu composites have been investigated. The flexural strength is significantly improved with increasing sintering temperature, and the highest flexural strength of 213?MPa is obtained in vacuum at 1000?°C for 2?h. The performances of composites with different holding time are further studied at 1000?°C. The flexural strengths of composites sintered at 1000?°C for 2 and 4?h reach 213 and 219?MPa, respectively. The failure displacement of the composite sintered at 1000?°C for 4?h reaches 0.39?mm. The excellent microwave absorption properties are achieved for the composite sintered at 1000?°C for 2?h. The minimum reflection loss (RL) reaches ?38?dB with a thickness of 2.9?mm?at 12?GHz and the effective absorbing bandwidth (RL?≤??10?dB) with a thickness of 3.4?mm covers the whole X?band, which indicate that SiC_f/Mu composite is a good candidate for microwave absorbing materials. These results provide valuable solutions to obtaining structural-functional materials for microwave absorption applications in civil and military areas.     

Assessment of redox behavior of nickel ferrite as oxygen carriers for chemical looping process

This study investigated the suitability of using nickel ferrite (NiFe₂O₄) oxygen carriers for a chemical looping process. NiFe₂O₄ powder was prepared by ball milling equimolar NiO and Fe₂O₃ in a high temperature solid-state reaction. Material characteristics of NiFe₂O₄ samples were investigated by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area measurements, and scanning electron microscopy (SEM). Redox cycling of NiFe₂O₄ oxygen carriers was performed by thermogravimetric (TGA) measurement under pure CH₄ gas and O₂/Air atmospheres, respectively. After five successive cycles, NiFe₂O₄ powder with a single phase of spinel structure demonstrated higher redox cycling behavior and better stability than standard NiO and Fe₂O₃. We also addressed the mechanism underlying the redox cycling by NiFe₂O₄ spinel powder. Our results demonstrate the feasibility of using the proposed preparation of NiFe₂O₄ as an oxygen carrier in a reversible chemical looping process (CLP).     

High dielectric and microwave absorption properties of ultra-thin 1-xSrTiO3-δ − xSrAl12O19 films

To reduce the thickness of the microwave absorbing materials, we have prepared 1-xSrTiO_3-δ?xSrAl₁₂O₁₉ ceramics by hot?pressing sintering in the vacuum. The microstructure, dielectric, thermogravimetric analysis and microwave absorbing properties of 1-xSrTiO_3-δ?xSrAl₁₂O₁₉ were systematically investigated and discussed. The 0.95SrTiO_3-δ??0.05SrAl₁₂O₁₉ has high permittivity, the real part is from 1662.2 to 704.9 and the imaginary part is from 208.6 to 12. The absorption bandwidth (reflection loss ≤?5?dB) of 0.95SrTiO_3-δ??0.05SrAl₁₂O₁₉ can cover 8.6???12.4?GHz and its thickness is only 0.232?mm which is much thinner than these recently reported by other researchers. For 0.942SrTiO_3-δ??0.058SrAl₁₂O₁₉, the peak value of reflection loss is up to ??58.5?dB with a thickness of 0.75?mm. The 1-xSrTiO_3-δ?xSrAl₁₂O₁₉ films could be excellent candidates for highly efficient and ultra?thin microwave absorbing materials.     

A self‐repairing cermet anode: Preparation and corrosion behavior of (Cu–Ni–Fe)/NiFe2O4 cermet with synergistic action

In this paper, the cermet (Cu–Ni–Fe)/(NiFe₂O₄–10NiO) anodes were prepared through the powder metallurgy method, followed by being evaluated in the bench scale (200 A) electrolysis tests for more than 1000 hour. The results showed that the as‐prepared anodes exhibited excellent corrosion resistance with corrosion rate less than 0.99 cm/a, which satisfied the requirements of the aluminum industry. The analysis results were confirmed by SEM, EDS, and XRD. The results showed that the outstanding corrosion resistance of the anodes relied on a continuous and dense NiFe₂O₄ film formed on the surface of the anode material, which protected the inner structure of anode material during electrolysis. Finally, a model based on the synergistic action between the metal phase and the ceramic phase was built to illustrate the forming mechanism of the NiFe₂O₄ passivating film.     

Template‐Free Synthesis of Porous Fe3O4/SiOC(H) Nanocomposites with Enhanced Catalytic Activity

We present a template‐free synthesis of Fe₃O₄/SiOC(H) nanocomposites with in situ formed Fe₃O₄ nanoparticles with a size of about 50 nm embedded in a nanoporous SiOC(H) matrix obtained via a polymer‐derived ceramic route. Firstly, a single‐source precursor (SSP) was synthesized by the reaction of allylhydridopolycarbosilane (AHPCS) with Fe‐acetylacetonate [Fe(acac)₃] at 140°C. The SSP was heat‐treated at 170°C to generate Fe₃O₄ nanocrystals in the cross‐linked polymeric matrix. Subsequently, the SSP was pyrolyzed at 600°C–700°C in argon atmosphere to yield porous Fe₃O₄/SiOC(H) nanocomposites with the high BET surface area up to 390 m²/g, a high micropore surface area of 301 m²/g, and a high micropore volume of 0.142 cm³/g. The Fe‐free SiOC(H) ceramic matrix derived from original AHPCS is nonporous. The in situ formation of Fe₃O₄ nanoparticles embedded homogeneously within a nanoporous SiOC(H) matrix shows significantly enhanced catalytic degradation of xylene orange in aqueous solution with H₂O₂ as oxidant as compared with pure commercial Fe₃O₄ nanoparticles.     

Facile fabrication approach for a novel multifunctional superamphiphobic coating based on chemically grafted montmorillonite/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-polydimethylsiloxane binary nanocomposite

In this paper, a novel multifunctional superamphiphobic coating for anticorrosion was successfully prepared on aluminum substrate via a simple spraying technique. Al₂O₃ nanoparticles were chemically grafted onto montmorillonite (MMT) nanosheets via coupling effect of NH₂-C₃H₆-Si(OC₂H₅)₃ (KH-550) and then modified by low surface energy material polydimethylsiloxane (PDMS). The ethylene tetrafluoroethylene (ETFE) composite coating with 25 wt% MMT/Al₂O₃-PDMS binary nanocomposite exhibited well-designed nano/μ structures and possessed superamphiphobicity with high contact angles towards water (164°), glycerol (158°) and ethylene glycol (155°). This coating demonstrated outstanding self-cleaning ability and strong adhesive ability (Grade 1 according to the GB/T 9286). The superhydrophobicity could be maintained after 8000 times abrasion or annealing treatment for 2 h under 350 °C. The coating still retained high water-repellence after immersion in 1 mol/L HCl (146°), 1 mol/L NaOH (144°) and 3.5 wt% NaCl (151°) solutions for 30 d. It should be noted that this superamphiphobic coating revealed excellent long-term corrosion protection with extremely low corrosion rate (4.3 × 10^?3 μm/year) and high protection performance (99.999%) after 30 d immersion in 3.5 wt% NaCl solutions based on electrochemical corrosion measurements. It is believed that such integrated functional coating could pave new way for self-cleaning and anticorrosion applications under corrosive/abrasive environment.     

Fabrication of high-density NiFe2O4 ceramics by slip casting and pressureless sintering

High-density NiFe₂O₄ ceramics with homogeneous microstructure were produced by slip casting and pressureless sintering. The slurry stability, sintering behavior, and microstructure of NiFe₂O₄ ceramics were investigated. A stable slurry can be obtained by adding 12.5 wt% NiFe₂O₄ nanoparticle and 5 wt% nano-binder at a slurry pH around 11.0. The linear shrinkage and linear shrinkage rate for both NiFe₂O₄ ceramic green bodies shaped by cold press molding and slip casting showed nearly the same trends. The temperature associated with the maximum linear shrinkage rate of slip casted green body was 1263.5°C, which was lower than that of cold press molded sample (1272.0°C). The sintering activation energy of slip casted green body was also lower than that of cold press molded sample (279.18 vs 288.47 kJ mol⁻¹), owing to high density and homogeneity of slip-casted green compact. A high-density NiFe₂O₄ ceramics with uniform grain size distribution can be produced by slip casting and pressureless sintering at 1350°C for 6 hours, attributed to the ability of slip casting to minimize agglomerates and micropores. It demonstrated that slip casting was more suitable to prepare high-density NiFe₂O₄ ceramics with good homogeneity.     

Dielectric and ferroelectric properties of multilayer BaTiO3/NiFe2O4 thin films prepared by solution deposition technique

In this work different lead-free multilayered structures, composed of perovskite BaTiO₃ and spinel NiFe₂O₄ thin layers, were obtained by solution deposition method. Structural characterization of the sintered thin films confirmed the well-defined layered structure with overall thickness from 160 to 600 nm, crystalline nature of perovskite BaTiO₃ and spinel NiFe₂O₄ phases without secondary phases (after sintering below 900 °C) and grains on nanometer scale. Dielectric properties of the multiferroic multilayer BaTiO₃/NiFe₂O₄ thin films were analyzed in temperature and frequency range from 30 °C to 200 °C and 100 Hz to 1 MHz, respectively. In comparison to the pure BaTiO₃ films, the introduction of ferrite layer reduces dielectric response and increases low frequency permittivity dispersion of the multilayer thin films. The multilayer samples have shown relatively low dielectric loss with stronger contribution of conductivity at higher temperatures, and characteristic broad peak representing “relaxation” of the interface charge accumulation.     

Sintering kinetics and properties of NiFe2O4-based ceramics inert anodes doped with TiN nanoparticles

Sintering kinetics of NiFe₂O₄-based ceramics inert anodes for aluminum electrolysis doped 7 wt% TiN nanoparticles were conducted to investigate densification and grain growth behaviors. The linear shrinkage increased gradually with the increasing sintering temperature between 1000 and 1450°C, whereas the linear shrinkage rate exhibited a broad peak. The maximum linear shrinkage rate was obtained at 1189.4°C, and the highest densification rate was achieved at the relative density of 75.20%. Based on the pressureless sintering kinetics window, the sintering process was divided into the initial stage, the intermediate stage, and the final stage. The grain growth exponent reduced with increased sintering temperature, whereas the grain growth activation energy decreased by increasing sintering temperature and shortening dwelling time. The grain growth was mainly controlled by atomic diffusion. NiFe₂O₄-based ceramics possessed high-temperature semiconductor essential characteristics. The electrical conductivity of NiFe₂O₄-based ceramics first increased and then decreased with increasing sintering temperature, reached their maximum value (960°C) of 33.45 S/cm under 1300°C, mainly attributed to the relatively dense and uniform microstructure. The thermal shock resistance of NiFe₂O₄-based ceramic was improved by a stronger grain boundary bonding strength and lower coefficient of linear thermal expansion.     

NiFe2O4/SiO2 nanostructures as a potential electrode material for high rated supercapacitors

Engineered materials are crucial for the higher efficiency of supercapacitors. Current work presents roughly shaped spherical NiFe₂O₄ nanoparticles dispersed in the SiO₂ matrix NiFe₂O₄/SiO₂ as a newfangled electrode material for supercapacitors with remarkable performance. Designing the NiFe₂O₄/SiO₂ nanostructure with a sol-gel method followed by the Stober method to grow silica has instigated NiFe₂O₄/SiO₂ as dynamic material with higher electrochemical activity. Physicochemical aspects of NiFe₂O₄/SiO₂ nanostructures are evaluated using Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analysis. The electrochemical activity is evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) representing the comparable efficiency and reversibility of the electrode materials. The prepared electrode shows a capacitance of 925 F/g (154.1 mAh/g or 555 C/g) at 1 A/g, with 95.5% capacitance retention after 5000 cycles at 20 mA/cm². The improved electrochemical performance of the NiFe₂O₄/SiO₂ electrode can be subjected to prompt diffusion process provided by NiFe₂O₄/SiO₂ and enhanced redox reactions owing to the high surface area. The mentioned features decrease the total impedance of the electrodes as suggested by electrochemical impedance spectroscopy (EIS).     

Characterization of carbon nanofibers synthesized by microwave plasma-enhanced CVD at low-temperature in a CO/Ar/O2 system

The low-temperature synthesis of carbon nanofibers by microwave plasma-enhanced chemical vapor deposition using a CO/Ar/O₂ system and their characterizations were performed. At the optimum oxygen concentration of O₂/CO = 7/1000, vertically aligned CNFs can be synthesized at temperatures as low as 180 °C with growth rates of 4–6 nm/s. The diameter of bulk CNFs is about 50–100 nm and the surface of CNFs is covered by branching fibers and their nuclei with a diameter of about 5–20 nm. Not only the peaks originating from carbon chains, but also oxygen containing groups, such as CO and COC, are observed in the FTIR spectra. The CNFs growth rate is almost independent from the substrate temperature and it is concluded that an elementary process not on the substrates, but in the gas phase, is the rate-determining step in the present CO/Ar/O₂ microwave-plasma-enhanced CVD system.     

PREPARATION OF PEROVSKITE 0.75Pb(Ni1/3Nb2/3)O3-0.25PbTiO3 CERAMICS USING SEMICHEMICAL METHODS AND RELATED REACTION MECHANISMS

This article discusses a mechanism for preparing perovskite powders, 0.75Pb(Ni_1/3Nb_2/3)O₃-0.25PbTiO₃ (PNN-PT), using a semichemical method (SCM).Precursors were prepared by adding aqueous Ni(Ac)₂ solutions to an alcohol slurry of PbO, Nb₂O₅, and TiO₂. The TG-DTG and DSC analysis of the precursors and XRD analysis of the powders at different thermal treatment temperatures showed that the reaction mechanisms in this method differ from those in the conventional mixed-oxide method. The aqueous Ni(Ac)₂ solution reacted with PbO to form Pb(Ac)₂ · Pb(OH)₂ · H₂O and Ni(OH)₂, which decomposed to form nascent PbO and NiO, thereby improving the reactivity and distribution of PbO and NiO. Pb₃Nb₂O₈ and NiNb₂O₆ formed and were easily converted into the perovskite phase during the thermal treatment process. At a thermal treatment temperature of 850°C, the content of the perovskite phase reached 98%. Pyrochlore-free PNN-PT ceramic was obtained after 2 h of sintering at 1100°C, and its dielectric properties were found to be excellent at temperatures ranging between ?55 and 120°C.