Synthesis and characterization of magnetic nanoparticles for electromagnetic wave absorbers

Nano-kristalinični prah stroncijevega heksaferita (SrFe12O19) smo sintetizirali s klasičnim soobarjanjem in mikroemulzijsko metodo. Prekurzor, ki je bil pripravljen z obarjanjem Sr2+ in Fe2+ ionov z uporabo tetrametilamonijevega hidroksida, smo termično obdelali pri različnih temperaturah v območju od 400 °C do 1000 °C v zračni atmosferi. Proučevali smo vpliv molskega razmerja Sr2+ / Fe3+ in temperature termične obdelave na formiranje produkta in njegovih magnetnih lastnosti. Nanodelce SrFe12O19 z relativno visoko nasičeno magnetizacijo σs = 64 Am2/kg, remanentno magnetizacijo σr = 39 Am2/kg in koercitivnostjo Hc = 430 kA/m smo dosegli pri molskem razmerju Sr2+ / Fe3+ = 1 : 8 ter termični obdelavi pri 900 °C. Pripravljen prah SrFe12O19 smo okarakterizirali s pomočjo rentgenske praškovne analize (XRD), termogravimetrične analize (TGA), diferenčne termične analize (DTA), presevnega elektronskega mikroskopa (TEM), dinamičnega laserskega sipanja svetlobe (DLS) in z merjenjem specifične površine delcev z metodo BET. Magnetne lastnosti materiala smo določili z uporabo magneto-susceptometra DSM-10. V nadaljevanju smo se posvetili pripravi nanokompozitov za absorpcijo elektromagnetnega valovanja, ki temeljijo na magnetnem polnilu sestavljenem iz faz znotraj sistema SrO - Fe2O3, ki je homogeno vmešan v polimerno matrico iz polifenilensulfida (PPS) v utežnem razmerju 80 : 20. Nanodelce SrFe12O19 in Fe3O4, ki sta bili glavni magnetni fazi smo pripravili s klasičnim soobarjanjem pri različnem molskem razmerju Sr2+ / Fe3+ ter termično obdelavo v temperaturnem intervalu od 600 °C do 1000 °C v zračni atmosferi. Elektromagnetne parametre nanokompozitov smo merili z vektorskim mrežnim analizatorjem v frekvenčnem območju od 400 MHz do 32 GHz. Rezultati kažejo, da lahko pripravimo široko paleto mikrovalovnih absorberjev. Nanokompoziti, ki vsebujejo za magnetno polnilo delce spinelne faze so primerni za absorpcijo elektromagnetnega valovanja v nižjem GHz območju, medtem ko so nanokompoziti vsebujoč heksagonalno fazo primerni za delovanje v območju frekvenc nad 32 GHz.Nano-crystalline strontium hexaferrite (SrFe12O19) powder was synthesized using the classical co-precipitation and microemulsion methods. The precursors were obtained by precipitating Sr2+ and Fe2+ ions using tetramethylammonium hydroxide and calcinating at different temperatures ranging from 400 °C to 1000 °C in air. The influence of the Sr2+ / Fe3+ mol ratio and the calcination temperature on the product formation and their magnetic properties were studied. The formation of nanosized particles of SrFe12O19 with a relatively high saturation magnetization σs = 64 Am2/kg, remanent magnetization of σr = 39 Am2/kg and a coercitivity of Hc = 430 kA/m was achieved at a Sr2+ / Fe3+ mol ratio of 1 : 8 calcined at 900 °C. The formation of the SrFe12O19 was inspected using X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), differential thermal analysis (DTA), transmission electron microscopy (TEM), dynamic light scattering analysis (DLS) and specific surface area measurements (BET). The magnetic properties were inspected using magneto-susceptometer DSM-10. Furthermore, we have investigated nanocomposites designed for absorption of electromagnetic waves based on magnetic filler, composed of phases within the SrO - Fe2O3 system, embedded in a polymer matrix based on polyphenylene sulfide (PPS) with a concentration ratio of 80 : 20 by weight. The formation of the nanosized particles of SrFe12O19 and Fe3O4, as the principal magnetic phases, was achieved via the classical co-precipitation of Sr2+ / Fe3+ ions using different molar ratios. The various precursors obtained were calcined between 600 °C and 900 °C in air atmosfere. The electromagnetic parameters of the nanocomposites were measured with a vector network analyzer in frequency range from 400 MHz to 32 GHz. The results show that with a nancomposite composed of a complex magnetic filler comprising the nanoparticles of two magnetically diverse phases, i.e., a spinel phase as the electromagnetic wave absorber in the lower GHz range and a hexagonal phase operating at a higher GHz range, above 32 GHz, a microwave absorber with an broad absorption range can be prepared