Synthesis and Characterization of SrFe11.2Zn0.8O19 Nanoparticles for Enhanced Microwave Absorption

Abstract

SrFe 12 O 19 /ZnFe 2 O 4 (SrFe 11.2 Zn 0.8 O 19 ) nanoparticles having superparamagnetic nature were synthesized by coprecipitation of chloride salts using 7.5 M sodium hydroxide solution. The resulting precursors were heat-treated at 900°C and 1200°C for 4 h in nitrogen atmosphere. During heat treatment (HT), transformation proceeds through instantaneous nucleation and three-dimensional diffusion-controlled growth with an activation energy of 175.9 kJ/mole. The hysteresis loops showed an increase in saturation magnetization from 1.044 emu/g to 61.227 emu/g with increasing HT temperature. As-synthesized particles had sizes in the range of 20 nm to 25 nm with spherical shape. Further, these spherically shaped nanoparticles tended to change their morphology to hexagonal plate and pyramidal shape with increasing HT temperature. The effects of this systematic morphological transformation of nanoparticles on dielectric (complex permittivity and permeability) and microwave absorption properties were estimated in the X-band (8.2 GHz to 12.2 GHz). The maximum reflection loss of the composite powder reached À29.81 dB at 10.37 GHz, making it suitable for application in radar-absorbing materials.

Microwave Absorbing Properties of NiFe2O4 Nanosheets Synthesized Via a Simple Surfactant-Assisted Solution Route

“…Compared to their bulk counterparts, the scientific interest on nano-sized ferrite is on the rising, due to their interesting chemistry and physical properties from the size effect and the low density 6 . Spinel nanoferrites (MFe 2 O 4 : M=Fe, Co, Ni, Mn, Zn, etc) have recently attracted a great deal of attention, due to the broad practical applications in several important fields such as magnetic refrigeration, ferrofluids making, magnetic resonance imaging and high density data storage 7 . Among them, nickel ferrite (NiFe 2 O 4 ) is one of the most important spinel ferrites.…”

Influence of Temperature on Reducing Gas Sensing Performance of Nanocrystalline Zinc Ferrite

“…As expected, the degree of crystallinity of ZnFe 2 O 4 nanoparticles is further increased by increasing the heat treatment temperature to 560°C. Moreover, the temperature of the heat treatment in present work (560°C) is much lower than that of the solid state synthesis and other reported methods [17][18][19], in which the mixed oxides with spinel structure are often obtained from reactions at about 1,000°C. This lowering of crystallization temperature favors the formation of fine powders with larger specific surface area ( Table 2).…”

“…The first exothermic peak, at about 285.46°C (Fig. 3), is attributed to the growth of desirable magnetic phase (ZnFe 2 O 4 ) synthesized in 'as synthesized' condition and conversion of hydroxide (left after the auto combustion) to oxides phase during heat treatment [18][19][20][21]. The second exothermic peak, at 491.03°C, is attributed to the synthesis of desirable magnetic phase (ZnFe 2 O 4 ) with loss of organic residues in the temperature ranging from 442.80 to 556.86°C.…”

“…5b). This process of crystal growth and morphological evolution can be described in terms of Ostwald ripening [18,19]. As the HT temperature is increased, small size nanoparticles slowly disappear except for the few that grow larger, at the expense of smaller ones.…”

“…It is a challenging task to synthesize pure phase, meso-porous, nanocrystalline spinel ferrite particles at lower temperature. Most ferrite powders are synthesized by heat treatment of mixed oxides, hydroxides or carbonates at temperatures in the range of 600-1,200°C [17][18][19].…”