A Study of Multiferroic BiFeO3/Epoxy Resin Composite as Potential Coating Materials for Microwave Absorption

A single layer of BiFeO3 (BFO)/epoxy resin composite with thickness of 3 mm was fabricated by polymerized 70 wt% of sintered BFO as fillers and 30 wt% of epoxy resin polymer as matrix. The electromagnetic and the microwave absorption properties of BFO/epoxy resin composite were reported. The reflection loss (RL) of the same composite sample was measured by two different techniques of measurement, S11a parameter (without metal backed reflector) and S11b parameter (with metal backed reflector) in the range of 8-18 GHz using a network analyzer. Minimum RL (RLmin) from S11b parameter for BFO/epoxy resin composite with metal backed is lower than the RLmin from S11a composite without metal backed reflector. In details, the results showed BFO/epoxy resin composite with metal backed can achieve a strong absorption with RLmin of -40.5 dB over a 1.31 GHz bandwidth

Microstructural, magnetic and dielectric properties of Bi1-xSmxFeO3 multiferroic materials

BiFeO3 (BFO) is a most common type of multiferroic materials that exhibits antiferromagnetic and ferroelectric order at room temperature. Based on previous reports, it was rather difficult to synthesize BFO in form of pure single phase due to narrow range of temperature stabilities. Hence, in this thesis, we report some research findings on the effect of different small ranges of calcinations and sintering temperature for preparing BFO. The best BFO sample could be determine by analyzing the phase transformation, magnetic and dielectric properties using XRD, VSM and impedance analyzer respectively. The effect of Sm substitution in the BFO system also has been studied. Samples of Bi1-xSmxFeO3 (BSFO) with x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 were prepared using solid state reaction method. There are three series of samples that have been prepared which are Sample A (both calcinations and sintering temperature at 800 ºC), Sample B (calcinations temperature at 800 ºC and sintering temperature at 825 ºC) and Sample C (both calcinations and sintering temperature at 825 ºC). The XRD pattern showed an improvement of crystallinity in pure BFO with the lower unwanted secondary phases by increasing the calcinations and sintering temperature at 825 ºC. However, the unwanted secondary phases disappeared in BSFO sample implying that Sm3+ substitution can stabilize the perovskite structure. SEM micrograph showed a well defines grain structures with clear grain boundaries in BFO sample. A larger grain sizes were observed as the calcinations and sintering temperature increase. However, BSFO have smaller average grain size than BFO sample. As the Sm composition increases from x = 0.0 to x = 0.5, the density values decreased for all series. The density increases proportionally with sintering temperature caused by elimination pores. The magnetization analysis showed that BFO compound have very narrow hysteresis loop exhibits antiferromagnetic behavior (Hc = 191 Oe and Mr = 1.81 x 10-3emu/g) at room temperature. The result showed magnetic properties were enhanced with higher calcinations and sintering temperature at 825 ºC. Larger hysteresis loop were obtained in BSFO indicates weak ferromagnetic behavior and the magnetization values increases when Sm composition increases. Sample C5 have highest magnetic properties with Hc = 3589.9 Oe and Mr = 7.52 x 10-2 emu/g. The dielectric permittivity, ε and dielectric loss, ε' decreased with increasing of frequency. The higher calcinations and sintering temperature, Sample C has the higher value of ε' and ε''. The value of ε' and ε'' increased with Sm composition and dielectric measuring temperature. The dispersion of ε' and ε'' are maximum for Sample C5 with ε' ~ 141 and ε'' ~ 5 at room temperature. Hence BSFO with x =0.5 with higher calcinations and sintering (825 ºC) is formed to be a better multiferroic material than pure BFO sample by resulting enhancement in magnetic and dielectric properties

Effect of BiFeO3/epoxy resin composite thickness on gigahertz microwave absorption properties

The microwave absorption properties of multiferroic BiFeO3 (BFO) epoxy resin composite with different thicknesses have been investigated. The BiFeO3 nanoparticles were synthesized by using high energy ball milling (HEBM). The BiFeO3 powders 70% by weight were mixed with epoxy resin as a matrix to form a composite with verified thicknesses of 1 mm, 2 mm and 3 mm. XRD was used to identify the phases and structures of the sample. The room temperature of magnetic characteristics of BFO composite was analyzed by using a vibrating sample magnetometer. The reflection loss value for the purpose of absorption performance was measured in the frequency range 8-18 GHz using a network analyzer. The absorption performances of different thickness of BFO epoxy resin composites were compared and analyzed. The results revealed that BFO epoxy resin composites with 3 mm thickness exhibited higher absorption performance with RLmin of –40.5 dB over a 1.31 GHz bandwidth (corresponding to RL below -10 dB)

Effects of crystalline phase formation of multiferroic BiFeO3on microwave absorption characteristics

This paper reports a study of the microwave absorption properties of multiferroic BiFeO3 (BFO) epoxy resin composites. The effects of various sintering temperatures on the crystalline phase of BFO and its microwave absorption characteristics were critically analyzed. BFO nanoparticles were synthesized by mechanical activation high energy ball milling (HEBM) with post heat treatment over various temperatures ranging from 700 to 800 °C. The XRD results showed by using the HEBM method, BFO phase is formed at a lower sintering temperature of 700 °C compared to conventional solid state reaction due to the enhanced diffusion rates. The phase composition and the grain sizes had significant influence on the permeability, permittivity and reflection loss values of BFO composites measured by a network analyzer in the frequency range from 8 to 18 GHz. It was observed that the purity fraction of BFO phase and the grain sizes increased with the sintering temperature. By increasing the sintering temperature up to 775 °C, the microwave absorption properties were enhanced over a broad working frequency range corresponding to the reflection loss below − 10 dB (i.e. 90% absorption) due to crystalline phase changes. BFO samples sintered at 775 °C demonstrated higher absorption ability with RLmin − 40.5 dB over a 1.31 GHz bandwidth, showing that BiFeO3 has great potential as a microwave absorbing material

A Study on microwave absorption properties of carbon black and Ni0.6Zn0.4Fe2O4 nanocomposites by tuning the matching-absorbing layer structures

Microwave absorption properties were systematically studied for double-layer carbon black/epoxy resin (cB) and ni0.6Zn0.4fe2o4/epoxy resin (F) nanocomposites in the frequency range of 8 to 18 GHz. The ni0.6Zn0.4fe2o4 nanoparticles were synthesized via high energy ball milling with subsequent sintering while carbon black was commercially purchased. The materials were later incorporated into epoxy resin to fabricate double-layer composite structures with total thicknesses of 2 and 3 mm. The CB1/F1, in which carbon black as matching and ferrite as absorbing layer with each thickness of 1 mm, showed the highest microwave absorption of more than 99.9%, with minimum reflection loss of −33.8 dB but with an absorption bandwidth of only 2.7 GHz. Double layer absorbers with F1/CB1(ferrite as matching and carbon black as absorbing layer with each thickness of 1 mm) structure showed the best microwave absorption performance in which more than 99% microwave energy were absorbed, with promising minimum reflection loss of −24.0 dB, along with a wider bandwidth of 4.8 GHz and yet with a reduced thickness of only 2 mm

Comparative study of single- and double-layer BaFe12O19-Graphite nanocomposites for electromagnetic wave absorber applications

The development of stealth technology for military applications and increasing concerns of electromagneticpollution have garnered interest to design microwave absorbing materials with wide absorption bandwidth andeffective absorption properties. Two batches of samples as a potential radar absorbing material were prepared inthis study: single-layer and double-layer nanocomposite mixtures of graphite and barium hexaferrite nano-particles. Characterizations of electromagnetic and microwave absorbing properties were carried out in thefrequency range of 8−12 GHz (X-band) and 12−18 GHz (Ku-band). Single-layer samples with thickness of 2 mmshowed optimal absorption properties with minimum reflection loss of -20.5 dB at 11.8 GHz for X-band and-20.7 dB at 14.7 GHz for Ku-band, displaying bandwidths of 0.6 GHz for the former and 3.8 GHz for the latter at-10 dB. On the other hand, double-layer samples made of 1 mm thick barium hexaferrite matching layer and2 mm thick graphite absorbing layer showed optimal absorption properties with minimum reflection loss of-30.0 dB at 9.2 GHz for X-band with narrower bandwidth of 0.6 GHz. The microwave absorption properties ofthese nanocomposites were attributed to combined effect of dielectric loss from graphite and magnetic loss from ferrite

Influence of nanometric microstructural development on thermophysical properties of lanthanum-doped strontium titanate

The evolution of imperfect crystal from a highly amorphous structure to an ordered crystalline structure via sintering has demonstrated a significant development onto the thermophysical properties. Therefore, a series of La-doped strontium titanate with different morphological properties have been synthesized via high energy ball milling with subsequent sintering. Doping of lanthanum tends to inhibit the grain growth where a significant reduction of grain size (range from 34 nm to 0.47 μm) could be observed. A large amount of grain boundaries presence with fine grains, resulting from lanthanum doping, has enhanced phonon scattering, thus yielding a low heat propagation in La-doped SrTiO3. Besides acting as a grain growth inhibitor, lanthanum also acts as a scattering centre due to imperfection created by the doping. The scattering mechanisms significantly decrease the phonon mean free path. Consequently, the thermal diffusivity has been efficiently reduced to 1.1 mm2/s as compared to that of pure SrTiO3 which showed a value of about 3.8 mm2/s, both observed for the complete phase polycrystalline materials. The systematic development of thermophysical and morphological properties of La-doped SrTiO3 can be served as a preliminary guide to engineer thermoelectric materials with low thermal diffusivity

Effects of different sintering temperatures on thermal, physical, and morphological of SiO2-Na2O-CaO-P2O5 based glass-ceramic system from vitreous and ceramic wastes

This research involved comprehensive studies on thermal, physical, and morphological properties of SiO2-Na2O-CaO-P2O5 (SNCP) glass-ceramic at various sintering temperatures. The study in SNCP glass-ceramic using soda-lime-silica (SLS) wastes glass and clam shell (CS) wastes as the main raw of materials via conventional melt-quenching technique and solid state sintering are interesting and challenging by considering the research using waste materials to fabricate novel SNCP glass-ceramic. The main peaks, Na3PO4 and Ca3Na6Si6O18 were assigned to high crystallization temperature (Tc) at 650-950 °C. The density of samples increases at 550-750 °C and decreases at 850-950 °C due to the increase of sample thickness and higher specific volume at high sintering temperature. FESEM micrograph showed that existed porous increased at sintering temperature 850-950 °C contributes effect to low densification of the sample