Development of Radar Absorbing Nano Crystals under Thermal Irradiation

Abstract

) were synthesized by a modified flux method that combines the controlled chemical co-precipitation process for nucleation and complete uniform growth during in-situ annealing with NaCl flux under vacuum furnace. Uniform structure morphological transformation of nano crystals from spherical to prism faces were noticed after annealing with increasing temperatures from 200 to 1200 o C for 4 h in vacuum. XRD results showed the single phase nanocrystals of BaFe 18 O 27 with increasing crystallanity and size from 10 to 90 nm during annealing. FESEM and TEM were used to investigate the systematic growth processes of various morphologies of nano crystals. The effect of such systematic morphological transformation of nanocrystals was observed in dielectric, dynamic magnetic and refection loss (RL) properties in Kuband (12.4 -18.0 GHz). A significant increment from -15.23 dB to -43.65 dB with wide range of bandwidth in RL loss is noticed due to the symmetric morphological growth of single phase nano crystals of RAM during annealing. This process of crystal growth, morphology evolution and RL enhancement with respect to increasing temperature were also explained in terms of ostwald ripening and quantum size effect. IntroductionThe electromagnetic interference (EMI) problems have been attracting more attention recently due to the extensive growth in the application of electronic devices such as computer local area networks, mobiles phones, laptops, microwave oven etc [1][2][3]. EMI can cause severe interruption on electronically controlled systems. Furthermore, larger exposure to microwave energy can be potentially harmful to biological systems and human beings. To overcome EMI problems, it is suggested that electromagnetic wave absorbing materials with the capability of absorbing unwanted electromagnetic signals are to be used. For significant absorption of electromagnetic waves, the radar absorption material (RAM) should have electric and/or magnetic dipoles that interact with the electromagnetic fields in the radiation. Microwave absorption materials from magnetic to dielectric related materials used in a high frequency are particularly noticed. But, pure dielectric or magnetic materials are insufficient for absorbing radiation energy. The efficiency of magnetic-dielectric absorbers is high because the complex permittivity (ε΄-jε˝) and permeability (µ΄-jµ˝) differ from zero [4][5][6]. In general, the suitable values of RAM can be achieved by adding lossy fillers and/or magnetic particles to a light weight that are physically and chemically stable one and of course have a high ability to absorb electromagnetic wave radiation [7][8][9][10]. The composite approach has been used to improve various material properties, including mechanical, chemical, structural, optical and electrical/magnetic etc [11][12][13][14][15][16][17].

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

“…This makes the process fast, and hexaferrite particles crystallize out completely with hexagonal pyramidal or plate-like shape after cooling in the furnace. [21][22][23][24] Similar morphologies were obtained by Sharma et al for barium hexaferrite and are reported elsewhere. 23,24 In view of the discussion above, the present investigation deals with synthesis of zinc-substituted strontium hexaferrite nanoparticles by the modified flux method.…”

“…It is reported that barium and strontium hexaferrite nanoparticles with hexagonal pyramidal and hexagonal plate-like morphology are potential materials for radarabsorption applications. [22][23][24] The magnetic measurements of SrFe 12 O 19 / ZnFe 2 O 4 nanoparticles showed almost negligible coercivity and remanence values (Fig. 9) in the as-synthesized condition, showing the superparamagnetic behavior of the material.…”

Reaction kinetic studies of strontium hexaferrite nanoparticles synthesized by co-precipitation method

“…These strontium hexaferrite nanoparticles with hexagonal pyramidal and plate shaped morphologies are effective radar absorbing materials, RAM. Here the crystallite size is in nano range ~ 38 nm so these nano crystals can also be called as NRAM [18]. These particles shows the three dimensional growth (Fig 5) which is also confirmed by 'n' values lying in the range of 3.54 to 3.58 [13,14].…”

“…When reaction temperature is increased to 1200ºC, the pure SrFe 12 O 19 nano particles were obtained with hexagonal pyramidal shape. According to literature [17][18][19], barium and strontium hexaferrite nano particles with hexagonal pyramidal and hexagonal plate like morphology are best for the electromagnetic wave absorption applications. These strontium hexaferrite nanoparticles with hexagonal pyramidal and plate shaped morphologies are effective radar absorbing materials, RAM.…”

Structural and magnetic properties of nanocrystalline BaFe12O19 synthesized by microwave-hydrothermal method

“…The plate-like shape of the grains clearly indicates the formation of barium hexaferrites at 950°C, which is confirmed from the XRD. According to literature (Sharma et al 2008(Sharma et al , 2009), barium and strontium hexaferrite nanoparticles with hexagonal pyramidal and hexagonal plate-like morphology are best for the electromagnetic wave absorption applications, effective radar absorbing materials (RAM). The average grain sizes of the sintered samples were found to be in the range of 185-490 nm.…”