| Description |
127 pages. |
| Summary |
"The effect of minor additions of CaO dopant to a manganese zinc ferrite - Zn[subscript .25] Mn[subscript .75] Fe[subscript 2.17] O[subscript 4.0] - on its grain growth and densification kinetics in air at 1250°C., 1300°C., and 1350°C. was studied. Grain growth was controlled over a range of dopant levels. At a sintering temperature of 1350°C. and time of six hours a ferrite with the smallest dopant addition was sintered to the highest density - 98% of theoretical. Under the same sintering conditions ferrites with higher dopant levels also sintered with normal growth but sintered to lower densities. Due to discontinuous grain growth the ferrite without dopant additions sintered (at 1350°C. for six hours) to densities less than 98% of theoretical. In vacuum or nitrogen-oxygen gas mixture (P[subscript O₂] = 10⁻³ atm.) the sintered density was 95% of theoretical. In vacuum or nitrogen-oxygen gas mixture (P[subscript O₂] =10⁻² atm.) the sintered density was 93.5% of theoretical. In air the sintered density was 90% of theoretical. Intermediate stage sintering and grain growth models were applied to the densification and grain growth data for the doped ferrite. It appears that the effect of the dopant is to reduce the diffusion coefficient of oxygen-reducing the densification rate and to control grain growth by decreasing the grain boundary mobility. Magnetic hysteresis loops were obtained for several doped ferrite toroids sintered to densities ranging from 91% of theoretical to 98% of theoretical. It was found that the maximum magnetic induction, B[subscript max], increased with increasing sintered density and increasing grain size and reached a maximum of 5400 gauss at a sintered density of 98% of theoretical. It was found that the coercive force, H[subscript c], decreased with increasing sintered density and increasing grain size and reached a minimum of 0.3 oersteds at a sintered density of 98% of theoretical"--Abstract, leaves ii-iii. |
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