Ishizaki Toshitaka, Nakano Hideyuki, Tajima Shin, Takahashi Naoko
Toyota Central R&D Labs., Inc., 41-1 Nagakute, Aichi 480-1192, Japan.
Nanomaterials (Basel). 2016 Dec 23;7(1):1. doi: 10.3390/nano7010001.
A thin, insulating layer with high electrical resistivity is vital to achieving high performance of powder magnetic cores. Using layer-by-layer deposition of silica nanosheets or colloidal silica over insulating layers composed of strontium phosphate and boron oxide, we succeeded in fabricating insulating layers with high electrical resistivity on iron powder particles, which were subsequently used to prepare toroidal cores. The compact density of these cores decreased after coating with colloidal silica due to the substantial increase in the volume, causing the magnetic flux density to deteriorate. Coating with silica nanosheets, on the other hand, resulted in a higher electrical resistivity and a good balance between high magnetic flux density and low iron loss due to the thinner silica layers. Transmission electron microscopy images showed that the thickness of the colloidal silica coating was about 700 nm, while that of the silica nanosheet coating was 30 nm. There was one drawback to using silica nanosheets, namely a deterioration in the core mechanical strength. Nevertheless, the silica nanosheet coating resulted in nanoscale-thick silica layers that are favorable for enhancing the electrical resistivity.
具有高电阻率的薄绝缘层对于实现粉末磁芯的高性能至关重要。通过在由磷酸锶和氧化硼组成的绝缘层上逐层沉积二氧化硅纳米片或胶体二氧化硅，我们成功地在铁粉颗粒上制备了具有高电阻率的绝缘层，随后用这些颗粒制备环形磁芯。用胶体二氧化硅涂层后，这些磁芯的堆积密度因体积大幅增加而降低，导致磁通密度恶化。另一方面，用二氧化硅纳米片涂层由于二氧化硅层更薄，导致电阻率更高，并且在高磁通密度和低铁损之间实现了良好的平衡。透射电子显微镜图像显示，胶体二氧化硅涂层的厚度约为700纳米，而二氧化硅纳米片涂层的厚度为30纳米。使用二氧化硅纳米片有一个缺点，即磁芯机械强度下降。然而，二氧化硅纳米片涂层形成了纳米级厚度的二氧化硅层，有利于提高电阻率。
