Investigation on sol–gel Al2O3 and hybrid phosphate-alumina insulation coatings for FeSiAl soft magnetic composites

Abstract

Alumina has been prepared by sol-gel method as the coating layer in the fabrication of FeSiAl soft magnetic composites (SMCs). Influence of the Al 2 O 3 content on the magnetic properties of the SMCs has been studied, and optimized effective permeability (l e = 116.3) and core loss (P cv = 331.2 mW cm -3 ) measured at 50 kHz, 100 mT was achieved with 0.8 wt% Al 2 O 3 . Hybrid phosphate-alumina coating has also been used to prepare the FeSiAl SMCs with a total addition of 0.8 wt%. Significantly improved performance of the SMCs can be achieved with the hybrid coating compared to single phosphate or alumina coating. The addition of 0.2 wt% H 3 PO 4 and 0.6 wt% Al 2 O 3 gives rise to the optimal magnetic properties (l e = 123.4; P cv = 226.4 mW cm -3 ) of the FeSiAl SMCs. For the hybrid coating, the inner phosphate layer grown by direction reaction at the powder surfaces gives rise to excellent adhesion. Also, investigation on the thermal stability of the coatings indicates that the outer Al 2 O 3 layer hinders the decomposition of the phosphate layer, leading to enhanced magnetic performance of the SMCs.

The role of microstructural evolution during spark plasma sintering on the soft magnetic and electronic properties of a CoFe–Al2O3 soft magnetic composite

“…Organic polymer SMCs yielded moderate resistivity, on the order of 100 lXÁm, but typically are not thermally stable above 300 °C and have low J s , less than 1.0 T [11,12]. In other approaches, consolidated SMCs made with coatings of Al 2 O 3 , SiO 2 , or even CaF 2 on ferromagnetic powder particles reached high resistivities on the order of 100-1000 lXÁm, and moderate J s , approximately 1.0-1.5 T [13][14][15][16][17][18][19][20][21][22]. The high resistivity of Al 2 O 3 containing SMCs is attributed to the high electrical resistivity of Al 2 O 3 , on the order of 10 17 lXÁm.…”

“…The high resistivity of Al 2 O 3 containing SMCs is attributed to the high electrical resistivity of Al 2 O 3 , on the order of 10 17 lXÁm. Additionally, the Al 2 O 3 phase has a higher thermal stability than organic polymers and other insulating phases such as phosphates or fluorides which may degrade at comparably lower temperatures [19][20][21][22][23][24]. However, the processes used to coat powders with Al 2 O 3 are relatively of small scale and have not enabled large production volumes of SMCs.…”

Preparation and properties of the anodized film on Fe-Cr-Al alloy surface

“…To insulate the electrothermal components, a layer of insulating material was usually coated on the surface of the alloy (Liu et al, 2018a). At present, the types of surface coating applied include magnetron sputtering (Bartzsch et al, 2003), high-temperature oxidation and sol-gel spin coating (Liu et al, 2015;Peng et al, 2016;Zhong et al, 2010). However, the films prepared by these methods have poor insulation, often cannot meet the actual requirements in high temperature, and show weak adhesion to the alloy substance in the process of repeated heating and cooling (Wang et al, 2017).…”

Formation Process of the Integrated Core(Fe-6.5wt.%Si)@Shell(SiO2) Structure Obtained via Fluidized Bed Chemical Vapor Deposition

“…The design and preparation of SMCs and ferromagnetic/inorganic C-S structures using diverse insulative oxide coatings including Al 2 O 3 [8,9], SiO 2 [10], Fe 3 O 4 [11], MgO [12], and ZnO [13] were reported. Yan and coworkers investigated the influence of processing parameters on the magnetic properties of SMCs [14][15][16]. Shokrollahi and coworkers studied the mechanisms by which C-S structures influenced the magnetic properties of SMCs [17,18].…”