The Low‐Temperature Sintering Mechanism of Sr Hexaferrite Using the Addition of CuO

Abstract

We have investigated the sintering behavior of Sr hexaferrite (SrFe 12 O 19 ) and the effects of adding CuO, which partly substituted for the Fe 2 O 3 and the Fe deficiency during the sintering. For the experiments, samples with nominal compositions of SrCu x Fe yÀx O 19Àd (x = 0-1.0, y = 11-12) were prepared with a solid-state reaction at 1000°C. The overall shrinkages and the shrinkage rates were followed using dilatometry during the sintering. The addition of CuO was found to enhance the sintering rate of the Sr hexaferrite significantly at temperatures below 1100°C, whereas the Fe deficiency had only a moderate effect on the sintering above 1100°C. The relative densities of the Sr hexaferrite ceramics containing Cu sintered at 1000°C for 3 h were above 90%, whereas the Cu-free Sr hexaferrite ceramics only started to sinter at 1000°C. We have shown that the addition of CuO enabled the reactive liquidphase sintering of Sr hexaferrite at 1000°C. P. Joy-contributing editor Manuscript No. 30767.

Co/Ti-substituted M-type hexagonal ferrites for high-frequency multilayer inductors

“…This shrinkage behavior is also reflected in the densification of green compacts; after sintering at 900°C the density of samples is 4.7-5.0 g/cm³ with a maximum density of 5.0 g/cm³ for x ¼1.3, corresponding to 95% of the theoretical density. It was already shown, that BaM ferrites without low-melting additives require a sintering temperature of T 41000°C for achieving sufficiently high density [19]. Similar results were reported for Co/Ti-substituted ferrites [21] and BBSZ glass was suggested as a possible candidate of a liquid-phase sintering aid.…”

“…Low-temperature sintering (900°C) of pure BaFe 12 O 19 was also demonstrated with a resulting permeability of m′¼1-2 [18]. The low-temperature sintering behavior of Sr hexaferrite with CuO addition or Fe-deficiency was also studied; however, sintering at 900°C does not seem to be possible for those samples [19]. Chen et al proposed BaCu-borate as sintering aid and reported on a sufficient densification with 4 wt% additive at 900°C; however, they did not give any permeability data [20].…”

Low-Temperature Sintering of Barium Hexaferrites With Bi₂O₃/CuO Additives

“…The eutectic melting point of ceramic composites (bismuth copper oxide and bismuth oxide) plunges to 770º C [20]. D. Lisjak et al [11], [12] had suggested that the lowtemperature formation (copper ferrites) in the grains is also propitious to promote the ion and vacancy transformation among and in the grains, and then beneficial to promoting the sintering of barium and strontium hexaferrites. By introducing collectively driving force in the grains and on the grain boundaries, the sintering temperature of barium hexaferrites with Bi 2 O 3 +CuO additives is therefore reduced to 920º C, and the sintered samples become also dense.…”

“…N RECENT years, barium hexaferrites [M-type BaFe 12 O 19 (BaM)] have been extensively applied in microwave devices, permanent magnets and magnetic recording materials for their fairly large magnetocrystalline anisotropy (17.5kOe), high Curie temperature (450º C), relatively large density (5.28g/cm 3 ) and magnetization (380kA/m) [1]- [3]. As a conventional permanent magnetic material, the sintering temperature of barium hexaferrites without additives could reach up to 1300º C [4], [5].…”

“…This driving force is relatively small as compared with the chemical driving force from the chemical reaction [12]. Many studies related to decreasing the sintering temperature of barium hexaferrites have been concentrated on introducing the liquid-phase sintering and low-temperature formation [13]- [16].…”