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Modifying Barium Hexaferrite Magnets by Adding SoleGel Synthesized Cobalt Ferrite Phase
(2023-01-01)
Charoensuk, Thanida
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Thongsamrit, Wannisa
;
Hunyek, Anuchit
;
Chokprasombat, Komkrich
;
Jantaratana, Pongsakorn
Combining various types of ferrites brings about magnetic properties desirable for different applications. This study aims to modify barium hexaferrite (BaFe<inf>12</inf>O<inf>19</inf>) by physically mixing it with cobalt ferrite (CoFe<inf>2</inf>O<inf>4</inf>). BaFe<inf>12</inf>O<inf>19</inf>/CoFe<inf>2</inf>O<inf>4</inf> magnets were produced by ball-milling and pressing solegel-derived ferrite powders. The ferrite composites showed variations in magnetic properties from BaFe<inf>12</inf>O<inf>19</inf> magnets with a saturation magnetization of 69.46 emu/g and a maximum energy product of 0.4529 MGOe. For the BaFe<inf>12</inf>O<inf>19</inf>:CoFe<inf>2</inf>O<inf>4</inf> weight ratio of 4:1, both saturation and remanent magnetizations were increased due to the addition of CoFe<inf>2</inf>O<inf>4</inf> with high magnetizations. However, the magnetizations were reduced when the BaFe<inf>12</inf>O<inf>19</inf>:CoFe<inf>2</inf>O<inf>4</inf> ratio was reduced to 2:1. On the other hand, the coercivity was monotonously decreased with increasing CoFe<inf>2</inf>O<inf>4</inf>. Interestingly, the maximum energy product in this study was linearly decreased with the bulk density of the magnets from 3.59 to 3.15 g/cm3. It is concluded that magnetic properties could be modified from a facile physical mixing of ferrites.
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Paste-Injection of Low-Density Barium Hexaferrite Magnets with Soft Magnetic Iron Phase
(2022-10-01)
Thongsamrit, Wannisa
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Jantaratana, Pongsakorn
;
Charoensuk, Thanida
;
Sirisathitkul, Chitnarong
Permanent magnets of varying shapes and sizes are increasingly produced. For hexaferrite magnets, it is challenging to incorporate polymers and a soft magnetic phase in the form of paste before injection molding or extrusion free-forming. In this study, hard magnetic barium hexaferrite/soft magnetic iron composites with a density of 2.28–2.34 g/cm3 are obtained after paste-injection molding and subsequent sintering at 1150 °C for 5 h. Variations of the binder (143.5–287.0 mg poly(vinyl alcohol), PVA) and the plasticizer (75–150 mg poly(ethylene glycol), PEG-400) in the ceramic–polymer paste give rise to comparable remanent magnetization (33.10–33.63 emu/g) and coercivity (3854–3857 Oe). Unlike all-ferrite systems, the presence of a soft magnetic metal phase is not detrimental to the coercivity. However, the remanent and saturation magnetizations are not substantially increased. The addition of 1% and 5% of iron oxide in the ceramic–polymer paste gives rise to hard/soft composites with lower densities of 2.11 and 2.14 g/cm3. The coercivity is increased to 3942–3945 Oe; however, the maximum energy product is reduced.
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Enhanced Coercivity of Low-Density Barium Hexaferrite Magnets from Paste-Injection Molding
(2022-04-01)
Thongsamrit, Wannisa
;
Jantaratana, Pongsakorn
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Charoensuk, Thanida
;
Sirisathitkul, Chitnarong
Ceramic–polymer paste-injection molding is demonstrated as a facile fabrication route for barium hexaferrite magnets. Interestingly, these low-density (1.90–2.35 g/cm3 ) magnets exhibit substantial coercivity of 3868–4002 Oe. When ceramic paste without polymeric additives is used, reduced coercivity and slightly increased magnetizations are obtained from a magnet with the density of 2.55 g/cm3 . Their magnetizations are also higher than those obtained from compactions of sol–gel-derived powders. For compact magnets (3.46–3.77 g/cm3 ), the DI water addition results in a slightly higher magnetization but lower coercivity than dry-pressed magnets. Compactions into disk and bar magnets give rise to comparable magnetic properties. The morphological characterizations reveal smaller barium hexaferrite particles leading to larger coercivity, and the density and shape of magnets have a less pronounced effect.
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Loading effect of sol-gel derived barium hexaferrite on magnetic polymer composites
(2021-03-01)
Charoensuk, Thanida
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Thongsamrit, Wannisa
;
Ruttanapun, Chesta
;
Jantaratana, Pongsakorn
;
Sirisathitkul, Chitnarong
Solution–processing methods were investigated as viable alternatives to produce the polymer-bonded barium hexaferrite (BaM). BaM powders were first synthesized by using the sol-gel auto-combustion method. While the ignition period in two synthesis batches varied, the morphology of hexagonal microplates and nanorods, as well as magnetic properties, were reproduced. To prepare magnetic polymer composites, these BaM powders were then incorporated into the acrylonitrile-butadiene-styrene (ABS) matrix with a weight ratio of 80:20, 70:30, and 60:40 by using the solution casting method. Magnetizations were linearly decreased with a reduction in ferrite loading. Compared to the BaM loose powders and pressed pellet, both remanent and saturation magnetizations were lower and gave rise to comparable values of the squareness. The squareness around 0.5 of BaM samples and their composites revealed the isotropic alignment. Interestingly, the coercivity was significantly increased from 1727–1776 Oe in loose BaM powders to 1874–2052 Oe for the BaM-ABS composites. These composites have potential to be implemented in the additive manufacturing of rare-earth-free magnets.
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Effects of carbon doping and annealing temperature on magnetic MnAl powders and MnAl polymeric composites
(2021-03-01)
Thongsamrit, Wannisa
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Charoensuk, Thanida
;
Saetang, Panissa
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Jantaratana, Pongsakorn
;
Ruttanapun, Chesta
Process parameters leading to magnetic polymer composites, an essential ingredient in the additive manufacturing of rare-earth-free magnets, are investigated. The induction melting of manganese (Mn) and aluminum (Al), and subsequent annealing at 450, 500, or 550 °C for 20 min, gave rise to ferromagnetic τ-MnAl phase, as well as other phases. The nonmagnetic Al<inf>4</inf>C<inf>3</inf> and oxide phases were then removed by the magnetic separation. Magnetic powders from the magnetic separation were incorporated in polylactic acid (PLA) matrix via a solution route. The remanent magnetization as high as 4.3 emu/g in the powder form was reduced to 2.3-2.6 emu/g in the composites. The reduction in coercivity was minimal, and the largest value of 814 Oe was obtained when the powder annealed at 450 °C was loaded in the composite. The phase composition and hence magnetic properties were even more sensitive to the carbon (C) doping. Interestingly, the addition of 3% C led to coercivity as high as 1445 Oe in MnAl-C powders without further annealing. The enhanced coercivity was attributed to the domain wall pinning by the AlMn<inf>3</inf>C phase, and magnetizations are likely increased by this phase.
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Ferromagnetism of manganese-aluminium alloyed with 0–3% carbon from direct induction melting and subsequent annealing
(2020-01-01)
Charoensuk, Thanida
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Saetang, Panissa
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Ruttanapun, Chesta
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Phrompet, Chaiwat
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Pinitsoontorn, Supree
The transformation from ε to τ phase is investigated in manganese-aluminium (Mn<inf>55</inf>Al<inf>45</inf>) alloyed by the induction melting. By annealing Mn<inf>55</inf>Al<inf>45</inf> at 450–550°C for 2 h, the ferromagnetic τ-MnAl is enhanced at the expense of ε phase. The largest coercivity of 1139 Oe and remanent magnetization of 3.71 emu/g are obtained after annealing at 550°C. The additions of 1 and 2% carbon affect the phase and magnetic properties of Mn<inf>55</inf>Al<inf>45</inf> but the 2 h annealing at 550°C still leads to the largest coercivity. Interestingly, substantial coercivity and magnetizations are directly obtained in (Mn<inf>55</inf>Al<inf>45</inf>)<inf>98</inf>C<inf>2</inf> and (Mn<inf>55</inf>Al<inf>45</inf>)<inf>97</inf>C<inf>3</inf> by the induction melting without further heat treatments.

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