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Magnetne in mehanske lastnosti magnetov SrFe12O19, stisnjenih s konvencionalnim sintranjem (CS) in sintranjem s pulzirajočim tokom (SPS), so bile optimizirane s spreminjanjem različnih parametrov: dodajanjem različne količine celuloznih nanovlaken (CNF), različne količine Bi2O3, časom sintranja, temperaturo sintranja in tlakom zgoščevanja. Optimalni pogoji sintranja so bili določeni na podlagi dobljenih magnetnih in mehanskih lastnosti. Ugotovila sem, da so v CS magnetih prisotni le uklonski maximumi SrFe12O19. Pri SPS magnetih je zaradi delne razgradnje SrFe12O19 prišlo do precejšnjega upada trdomagnetnih lastnosti, saj nastajajo železovi oksidi in nižji SrxFeyOz oksidi. Pri magnetih brez CNF je bila najvišja vrednost BHmax (16,3 kJ/m^3 ) za magnet SPS, sintran pri 950 °C 5 minut z uporabljenim tlakom 90 MPa ter brez dodatka Bi2O3. Če primerjamo magnete CS in SPS z 1 mas. % CNF, sintranje SPS večinoma negativno vpliva na magnetne lastnosti vzorcev. Najvišja vrednost BHmax (10,9 kJ/m^3 ) je bila izmerjena za magnet CS, sintran pri 1250 °C 2 uri s tlakom stiskanja zelencev 150 MPa. Enak vzorec lahko opazimo pri magnetih z 2 mas. % CNF. Najvišja vrednost BHmax (10,1 kJ/m^3 ) je bila izmerjena za magnet CS, sintran pri 1200 °C 30 minut s tlakom stiskanja zelencev 100 MPa in dodatkom 4 mas. % Bi2O3. Točke zloma in upogibne trdnosti pri CS magnetih z 1 mas. % CNF so bile veliko višje od tistih brez CNF. Najvišja točka zloma (2500 MPa) je bila prikazana v magnetu CS z 1 mas. % CNF s tlakom stiskanja 100 MPa, ki je bil sintran pri 1200 °C 4 ure. Magneti s CNF se nagibajo k psevdoduktilnemu obnašanju in dodajanje celuloznih nanovlaken je izboljšalo mehanske lastnosti CS sintranih feritov. Tu predstavljeni rezultati kažejo potencial CS in SPS stiskanja SrFe12O19 z visokimi mehanskimi lastnostmi in prikazujejo učinek CNF na zmanjšanje magnetnih lastnosti. The magnetic and mechanical properties of SrFe12O19 magnets consolidated by Spark Plasma Sintering (SPS) or Conventional Sintering (CS) were optimised by varying addition of cellulose nanofibers (CNF), the addition of Bi2O3, sintering parameters and consolidation pressure. The optimum sintering conditions were identified based on the resulting magnetic and mechanical properties. In CS magnets, only the diffraction maxima of SrFe12O19 were present. In SPS magnets, there was a considerable decline in their hard-magnetic properties due to partial decomposition of SrFe12O19, while iron oxides and lower SrxFeyOz oxides were formed. The highest BHmax (16.3 kJ/m^3 ) was found for the SPS magnet sintered at 950 °C for 5 minutes with an applied pressure of 90 MPa and with no addition of CNF or Bi2O3. Comparing CS and SPS magnets with 1wt.% CNF, SPS sintering negatively affects the magnetic properties of the samples. The best BHmax (10.9 kJ/m^3 ) was measured for the CS magnet sintered at 1250 °C for 2 hours with a consolidation pressure of 150 MPa. The same can be observed in magnets with 2 wt.% CNF. The best BHmax (10.1 kJ/m^3 ) was found for the CS magnet sintered at 1200 °C for 30 minutes with consolidation pressure of 100 MPa and an addition of 4 wt.% Bi2O3. The fracture points and bending strengths in CS magnets with 1 wt.% CNF tend to be much higher than those without CNF. The highest fracture point (2500 MPa) was exhibited in a CS magnet with 1 wt.% CNF, sintered at 1200°C for 4h. Magnets with CNF are leaning toward pseudo-ductile behaviour, and the addition of CNF improved the mechanical properties of CS ferrites. The presented results show the potential of CS and SPS consolidation of SrFe12O19 with high mechanical properties and display the effect of CNF on the decrease in magnetic performance. |
