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Fe2W-type ferrite BaFe2+2Fe3+16-xO27± (x =−0.8, −0.4, 0.0, 0.4, 0.8, 1.2) fine powders and magnets were synthesized by a facile ceramic route. The lattice and microstructure of the fine powders were studied by x-ray diffraction (XRD). The results show that a single magnetoplumbite structure is obtained under the condition of Fe change (x =−0.8, −0.4, 0.0, 0.4, 0.8, 1.2). The morphology of the sintered magnet was studied by scanning electron microscopy (SEM). The influence of iron content on the magnetic characteristics of BaFe2+2Fe3+16-xO27± was systematically studied by controlling the pre-sintering temperature of 1300°C. The change in the remanence (Br) of BaFe22+Fe16-x3+O27± magnets with different iron content first increased and then decreased, which confirmed that the change trend of the Br was consistent with the variation in the saturation magnetization (Ms). Meanwhile, the coercivity (Hcj) and (Hcb) of the magnets was consistent with the change characteristics of the coercive force (Hc) of magnetic powder. At iron change (x) = −0.4, Ms, Br, Hc, Hcj, Hcb, and maximum energy product ((BH)max) reach maximum.

BaCoxFe2−x W-type hexagonal ferrites with nominal composition $$ {\text{BaCo}}_{x} {\text{Fe}}_{2 - x}^{2 + } {\text{Fe}}_{16}^{3 + } {\text{O}}_{27} $$ (x = 0.0, 0.5, 1.0, 1.5) were prepared by conventional solid-state reaction in nitrogen at high annealing temperature of 1350 °C. X-ray diffraction and scanning electron microscopy were used to find out the structural and physical properties of BaCoxFe2−x W-type hexaferrites. Vibrating-sample magnetometry was used to measure hysteresis (M vs. H) loops. Furthermore, magneto-crystalline anisotropy constant (K), Bohr magneton (nB), initial permeability (μi), and magnetic anisotropy fields (Ha) of Co in BaCoxFe2−x W-type hexaferrites were also calculated. Finally, the magnetic characteristics of magnets were also analyzed by B–H measuring equipment.

Effect of oleic acid on precipitation ratio, agglomeration and morphology of gibbsite was investigated at selected conditions. The results of titrimetric analysis suggest that oleic acid inhibit gibbsite precipitation from seeded sodium aluminate liquors, and the inhibitory effect is stronger at 65 °C than that at 75 °C. The variations of particle size distribution (PSD) indicate that the agglomeration of gibbsite is significantly enhanced when the concentrations of oleic acid are in a low range (0.01 g/L–0.05 g/L). However, relatively higher concentrations of oleic acid (> 0.1 g/L) suppress agglomeration. The morphology of gibbsite was examined with scanning electron microscope (SEM). It shows that low concentrations of oleic acid in the sodium aluminate liquors lead to the formation of compact gibbsite particles, while high concentrations of oleic acid favor the growth of smooth texture of gibbsite surfaces, that is, the growth habit of gibbsite crystal changes under the influence of oleic acid.

Effects of tetracarbon additives, 1-butanol, 1,4-dioxane and tetrahydrofurane on gibbsite precipitation from caustic seeded sodium aluminate liquor were investigated. The additive was charged into supersaturated seeded sodium aluminate liquor, then the precipitation ratio of aluminate liquor in 10 h was evaluated and compared, and the particle size distribution of product was measured. The Mulliken atomic charge of oxygen in the additive molecule was calculated with DMol3 program. The results show that 1-butanol has little effect on gibbsite crystallization, while the precipitation ratios under the effect of 1,4-dioxane and tetrahydrofurane are 1.7% and 3.6% higher than that of the blank, respectively. The agglomeration efficiency of the product is also enhanced obviously by the addition of 1,4-dioxane and tetrahydrofurane. The precipitation ratio is inversely proportional to Mulliken atomic charge of oxygen atom, which implies that functional group in the additive molecule is involved in the gibbsite precipitation process more fundamentally than carbon chain.

The effect of mannitol and 1,2-octanediol on gibbsite crystallization from seeded sodium aluminate liquor was investigated and compared. The inhibitory effect of mannitol increases with its concentration, in good agreement with other strong inhibitors. Low concentrations of 1,2-octanediol have no apparent influence on crystallization but above 1.0 mmol/L severe inhibition occurs with crystallization rate rapidly decreasing until completely stopped 2.0 mmol/L. Unlike with mannitol, the inhibition cannot be alleviated by doubling the seed amount or by adding oleic acid. Unseeded experiments also show that a high concentration of 1,2-octanediol inhibits Al(OH) 3 nucleation while the influence of low concentration of 1,2-octanediol is negligible. 1,2-octanediol appears to be a unique inhibitor for alumina crystallization. The effect is evident below the critical micelle concentration of 1,2-octanediol in sodium aluminate solution indicating it is a molecular effect. Infrared spectroscopy indicates that the structure of the solution might be changed when the concentration of 1,2-octanediol is relatively high. Clearly the inhibition by mannitol derives from adsorption on the active surface sites, while inhibition by 1,2-octanediol appears to be due to changing the characteristic of sodium aluminate liquor.