Influence of Crystallite Size of Nickel and Cobalt Ferrites on the Catalytic Pyrolysis of Buckwheat Straw by Using TGA-FTIR Method

Pyrolysis of buckwheat straw with or without catalysts was investigated using the TGA-FTIR method to determine the influence of nickel and cobalt ferrites on the distribution of pyrolysis products. According to the obtained results, the overall shape of the thermogravimetric and derivative thermogravimetric curves is unchanged in the presence of nickel and cobalt ferrites but different weight losses were observed. All catalysts contribute to the formation of solid residue from BWS pyrolysis. The presence of cobalt ferrites exhibited the highest bio-oil yields, whereas the highest non-condensable gas yield and the lowest bio-oil yield was obtained with the addition of NiFe2O4 (1) catalyst. According to the obtained results, the ability of nickel and cobalt ferrites to catalyze deoxygenation reactions depends on the crystallite size. The nickel or cobalt ferrites with smaller crystallite size (15-22 nm) show a higher ability to catalyzed dehydration reaction than catalysts with larger crystallite size (45-54 nm).

Catalytic Behavior of Iron-Containing Cubic Spinel in the Hydrolysis and Hydrothermolysis of Ammonia Borane

The paper presents a comparative study of the activity of magnetite (Fe3O4) and copper and cobalt ferrites with the structure of a cubic spinel synthesized by combustion of glycine-nitrate precursors in the reactions of ammonia borane (NH3BH3) hydrolysis and hydrothermolysis. It was shown that the use of copper ferrite in the studied reactions of NH3BH3 dehydrogenation has the advantages of a high catalytic activity and the absence of an induction period in the H2 generation curve due to the activating action of copper on the reduction of iron. Two methods have been proposed to improve catalytic activity of Fe3O4-based systems: (1) replacement of a portion of Fe2+ cations in the spinel by active cations including Cu2+ and (2) preparation of highly dispersed multiphase oxide systems, involving oxide of copper.

Effect of milling time on microstructure of cobalt ferrites synthesized by mechanical alloying

Purpose: of this paper is to determine the effect of manufacturing conditions, especially milling time, on the microstructure and phase composition of CoFe2O4 cobalt ferrite. Design/methodology/approach: Cobalt ferrite (CoFe2O4) has been synthesised from a stoichiometric mixture of CoCo3 and α-Fe2O3 powders in a high energy planetary mill. Annealing at 1000°C for 6 hours after milling was used to improve the solid-state reaction. Calcinated samples were analysed by X-ray diffraction (XRD), and transmission electron microscopy (TEM). The relationship between the milling time of powders, their microstructure, as well as their properties were evaluated. Particles size distribution and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) examination were also made. Findings: CoFe2O4 ferrites were successfully synthesized by mechanical alloying of α-Fe2O3 and CoCO3 powders. The powder particles had undergone morphological changes with the increasing milling time. However, the milling time does not affect the ferrite formation rate. It is expected that the improvement of fabrication parameters can further enhance the properties of cobalt ferrite presented in this work. Research limitations/implications: Contribute to research on the structure and properties of cobalt ferrites manufactured by mechanical alloying. Practical implications: The reactive milling and subsequently annealing is an efficient route to synthesise cobalt ferrite powder. However, using steel milling equipment risks powder contamination with iron and chromium from the vials and balls. Originality/value: The results of the experimental research of the developed ferrite materials served as the basis for determining material properties and for further investigation.

Development of Graphene Based Cobalt-Ferrites Nanocomposites for Microwave Shielding

The study is related to cobalt ferrites nanocomposites embedded with graphene nanosheets, prepared by co-precipitation method. Various doping of graphene from 0.1% up to 1% were applied within the cobalt ferrite structure to study its microwave and mechanical effects on the nanocomposites. Microstructural analysis confirms the homogeneous dispersion and successful adhesion of graphene nanosheets within the cobalt ferrite matrix. Microwave absorbing capacity of these samples was studied by Agilent network analyzer in low frequency band of microwave (1MHz to 2 GHz), Results reveals that graphene incorporation not only improved the absorption capacity of cobalt ferrites (13dB-17d), but also widened its maximum absorption peak. This change was supposed to be due to inhomogeneity and combine effects of electric (graphene), and magnetic dielectric nature (cobalt ferrites). Further mechanical characterizations reveal that our composites samples have higher flexural strength (19.92 MPa for 1% loading) and improved toughness (>6000 J/mm2) compare to pure cobalt ferrites (10.28 MPa, 1000 J/mm2).

Crystal Chemistry, Rietveld Analysis, Structural and Electrical Properties of Cobalt-Erbium Nano-Ferrites

Synthesis of Cobalt-Erbium nano-ferrites with formulation CoErxFe2-xO4 (x = 0, 0.005, 0.010, 0.015, 0.020, 0.025, and 0.030) using technique of citrate-gel auto-combustion was done. Characterization of prepared powders was done by using XRD, EDAX, FESEM, AFM and FTIR Spectroscopy, DC resistivity properties respectively. XRD Rietveld Analysis, SEM, TEM and EDAX analysis were taken up in studying spectral, structural, magnetic and electrical properties. XRD pattern of CEF nano particles confirm single phase cubic spinal structure. The structural variables given by lattice constant (a), lattice volume (v), average crystallite size (D) and X-ray density(dx), Bulk density (d), porosity (p), percentage of pore space (P%), surface area (s), strain (ε), dislocation density (δ), along with ionic radii, bond length and hoping length were calculated. SEM and TEM results reveal homogeneous nature of particles accompanied by clusters having no impurity pickup. TEM analysis gives information about particle size of nanocrystalline ferrite while EDAX analysis confirm elemental composition. Emergence of two arch shaped frequency bands (ν1 and ν2) that represent vibrations at tetrahedral site (A) and octahedral site(B) was indicated by spectra of FTIR. The samples electrical resistivity (DC) was measured between 30°C -600°C with Two probe method. XRD Rietveld analysis confirm crystallite size lying between 20.84 nm–14.40 nm while SEM analysis indicate formation of agglomerates and TEM analysis indicate particle size ranging between 24 nm–16 nm. DC Electrical measurements indicate continuous decrease in resistivity with increasing temperature while increasing doping decreases curie temperature. The Magnetic parameters such as Saturation magnetization (Ms), Remanent magnetization (Mr), Coercivity (Hc) and Squareness ratio (R = Mr/Ms), Magnetic moment (nB) were altered by doping of Er+3 content in the increasing order (x = 0.00 to 0.030). The increasing erbium content decreases magnetization thus converting the sample into soft magnetic material. Observations indicated strong dependence of magnetic properties on Erbium substitution and coercivity varies in accordance with anisotropy constant. Due to the presence of magnetic dipole Erbium substituted cobalt ferrites can be used in electromagnetic applications. The present study investigates the effect of different compositions of Er3+ replaced for Fe on structural properties and electrical resistivity of cobalt ferrites.