)] were prepared by the microwave combustion synthesis, using a stoichiometric mixture of metal nitrates and urea as the oxidizer and fuel to drive the reaction. The effect of microwave irradiation on the phase composition was favorable to promote the formation of fluffy foams and nanoparticles sizes. The fast internal heating with microwaves leads to a reduction in synthesis time, to only 2 min. The structural, chemical and magnetic properties of the nickel-doped cobalt ferrites were analyzed by XRD, TEM, SEM and BET. The XRD results confirmed the formation of pure and single-phase spinel structure. The crystallite size of the nanoparticles was in the range of 38 -50 nm. SEM images show nanoparticles with spherical shape and homogenous morphology. The TEM analysis shows necked near-spherical particles with an average size of ~30 -50 nm, reflecting the highly crystalline nature of these nanoparticles. The magnetic measurements of all the samples were recorded using vibrating sample magnetometer (VSM) at room temperature in 10 kOe. Increasing the nickel content directly affects the structural characteristics of the particles, causing a reduction in the coercive field.

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Studies of Fe‐contaminated Al‐based scraps have drawn attention for years. However, little has been researched about the effects of cobalt (Co) and nickel (Ni) additions to contaminated scraps both under slow solidification (directional solidification, DS) and fast solidification regime (copper mold centrifugal casting, CC). As such, the current study examines a representative low‐alloy Al–Si chemistry from industrial scraps, i.e., the Al–7%Si–0.6%Fe–0.35%Cu–0.25%Zn (% by weight). This alloy is changed independently using Ni and Co. It is observed that a mixture of uneven distributed α and β Fe‐bearing particles prevails for all tested alloys and solidification conditions. The coexistence of both phases agrees with the charts proposed by Gorny's work for the range of secondary dendritic spacing, λ 2, observed. Although the Fe‐containing particles are smaller for fast‐solidified samples, they still maintain the acute morphology and, in some cases, the Chinese script shape. This results in a reduction in ductility of the order of 65% for the nonmodified and Ni‐modified samples considering mean λ 2 varying from 20 μm (DS) to 6.5 μm (CC), despite improvements in mechanical strength. Furthermore, addition of Co results in a higher number of Fe‐based particles within the microstructure. In this case, the largest particle/α‐Al interfacial area results in slightly poor ductility (~6–8%) and higher strength (175–205 MPa), with less ductility loss when DS and CC samples are compared.

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