The purpose of this study is to investigate the interface reaction between Mn-Zn ferrite single crystal and bonding glasses, and its effect on the magnetic properties of the ferrite.
In chapter 3, the residual stress caused by the difference in thermal expansion coefficient of Mn-Zn ferrite single crystal and $61SiO_2-23PbO-6ZnO-3Na_2O-2K_2O$(mol%) glass after bonding them was measured by Vicker's indentation technique. It was revealed that the residual stress in the ferrite depended upon cooling rate: The mean values of residual stress in the ferrite were estimated to be 9.0, 6.7, and 5.8 MN/㎡ when the cooling rates were 10, 5, and 1℃/min, respectively. It was also found that holding the temperature at 450℃ for 1 h during cooling at 5℃/min reduced the residual stress to 5.1 MN/㎡; this indicates that slow cooling near the glass transition temperature is important in reducing the residual stress.
The initial permeability of the ferrite bonded with the glass decreased with the increase of the residual stress: At 100 kHz, the initial permeabilities of the ferrites with the residual stress of 9.0 and 5.1 MN/㎡ decreased to 67% and 55%, respectively, of that of the ferrite without glass.
In chapter 4, the interface reactions between Mn-Zn ferrite single crystal and $SiO_2$-PbO-MO (M = Zn, Mn, Fe) ternary glasses, and $SiO_2$-PbO-ZnO-MnO quarternary glasses were investigated using SEM, EPMA (WDX), and XRD. When ZnO was added in the $SiO_2$-PbO binary glass, the formation of an intermediate phase was inhibited and the dissolution of the ferrite was suppressed. The interface morphology became a dendrite structure with the increase of ZnO concentration in the glass. Appearance of the anomalous concentration profile of Zn and Mn ion at the ferrite adjacent to the interface was interpreted in terms of the difference in their dissolution rate from the ferrite into the glass. It was found that Zn ion has dissolved from the ferrite into the glass during the reaction and Mn ion in the ferrite dissolved into the glass faster than Zn ion, making the undissolved ferrite adjacent to the interface Zn-rich. The source of the hump of Zn concentration was considered to be the undissolved and accumulated Zn ions at the ferrite adjacent to the interface. A model of the interface reaction between Mn-Zn ferrite and $SiO_2$-PbO-ZnO glass was suggested. The effect of addition of MnO and $Fe_2O_3$ in the glass on the interface reaction was interpreted by the same mechanism as that of ZnO.
When 6 mol% MnO and 4 mol% ZnO, the ratio of which was similar to that in the ferrite, were added in the $SiO_2$-PbO binary glass, the hump of Zn concentration has appeared at the ferrite adjacent to the interface, which was caused by the higher dissolution rate of Mn ion into the glass from the ferrite than that of Zn ion. It was found that when 7 mol% MnO and 3 mol% ZnO, the ratio of which was higher than that in the ferrite, were contained in the glass, the concentration of Zn and Mn hardly changed at the ferrite adjacent to the interface.
In chapter 5, the effect of interface reaction between Mn-Zn ferrite single crystal and $61SiO_2$-23PbO-6ZnO-$3Na_2O$-$2K_2O$ (mol%) glass on the magnetic properties of the ferrite was investigated. After the reaction, the hump of Zn concentration appeared at the ferrite adjacent to the interface. The initial permeability of the ferrite bonded with the glass at 700℃ was 1766 at 100 KHz and reduced to 907 after reaction at 1000℃. This permeability degradation was attributed not only to the size diminution of the ferrite due to the its dissolution into the glass but also to the residual stress due to the difference in expansion coefficient between the ferrite and the diffusion layer-the region of the hump of Zn concentration-adjacent to the interface.