Preparation and characterization of SrM₀.₅Fe₁₁.₅O₁₉ derived from mill scale with substitution M= Co, Cu, Ni, Zn, Ti, Nd via mechanical alloying

It is interesting to see the changes on structural and magnetic properties of strontium hexaferrites on the addition of metal element such as Co, Cu, Ni, Zn, Ti, and Nd for future device applications. Here the aims of the projects are to produce the undoped and doped strontium ferrite (Co, Cu, Ni, Zn, Ti, and Nd) from mill scales as raw iron compound by using a high-energy ball milling (HEBM) technique. Secondly to study the effect of Co, Cu, Ni, Zn, Ti, and Nd substitution in strontium hexaferrite and compare with undoped strontium hexaferrite on its structural, microstructure, magnetic, thermal and density properties. In order to achieve the first objective, the undoped and doped strontium hexaferrites, mill scales as the main sources of iron oxide Fe2O3 undergo two stages of purification process that are magnetic separation technique and curie temperature separation technique. The powders of 0.5 molar ratio of various metal oxides (Co, Cu, Ni, Zn, Ti, and Nd), strontium carbonate (SrCO3), and iron oxides (Fe2O3) were milling by employing HEBM following the formula SrM0.5Fe11.5O19. The resulting powder were then moulded into rod and pellets with diameters and height 10 mm × 10 mm and 10 mm × 2 mm respectively and sintered at 1300 ⁰C. For the second objective, the doped and undoped was characterized by XRD, FESEM, EDX, FTIR, VSM, BH-tracer, Photoflash Technique to measure thermal diffusivity (k) Precision Impedence Analyser to measure Curie temperature (Tc), and densimeter. The XRD patterns confirmed the formation of the single phase hexagonal ferrite structure for all samples, with space group P63/mmc. The XRD analysis exhibits an excess compound of Fe2O3 for Ti, Nd and Ni cations substitution. The analysis also shows increase in calculated lattice parameters a, c and cell volumes (Vcell) indicating the solubility of substituted cation in hexagonal structure of strontium ferrite. The average crystallite size from XRD for different substitution is in the range of 40 to 70 nm. From FESEM images, the samples with homogenous surface and hexagonal geometry have an average particle size in the range of 1 to 4 μm. The corresponding peaks of Co, Cu, Ni, Zn, Ti, and Nd were observed from EDX confirms the metal substitution. The FTIR spectra showed characteristic peaks for strontium hexaferrite was detected between 650 cm1 to 450 cm1 for all samples. The Tc values for undoped, Co, Cu, Ni, Zn, Ti, and Nd were 390, 330, 292, 290, 287, 270 and 266 °C respectively. From B-H tracer the value of Ms for undoped is 2546 Gs was in the range of common magnetic properties for ferrite 2000 to 3000 Gs (Cullity and Graham, 2009) while Ms for Zn = 3284 Gs and Ni = 3154 Gs doped was higher than that of common ferrite. The Hc of strontium hexaferrite decreases largely from a value of 1160 Oe for the pure samples to 332, 02, 281, 260, 127 and 64 Oe for Cu, Co, Zn, Ti, Nd and Ni metal cations, respectively. The substitutions have decreased the value of Hc and Mr compared with undoped strontium hexaferrite. The value of Mr for undoped strontium hexaferrite is 1576 Gs while the remanence for Zn, Cu, Co, Ni, Ti and Nd was 955, 873, 839, 727, 714 and 165 Gs, respectively.

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