Densification and microstructure development in the reaction sintering process of yttrium iron garnet

Factors affecting the densification and microstructure development in the reaction sintering process (RSP) of yttrium iron garnet were investigated. Three different powder mixtures were used: Fe₂O₃/Y₂O₃, Fe₂O₃/YFeO₃ (1100 ° C calcined), and Fe₂O₃/YFeO₃ (1200 ° C calcined). The conventionally prepared garnet powder was also adopted as a reference material. It was found that the RSP using Fe₂O₃-YFeO₃ systems has a beneficial effect on densification from the dilatation occurring along with the reaction of garnet formation. On the other hand, it has a detrimental effect due to the local contraction induced by the reaction in the Fe₂O₃-Y₂O₃ system. The densification rate and ultimate density achievable are also affected by the YFeO₃ powder adopted in RSP. A high grain-growth rate was obtained for garnet when the 1200 ° C calcined YFeO₃ powder was used. This leads to a high densification rate at low temperature. However, the densification ability deteriorates at temperatures above 1425 ° C due to the trap of pores in the fast-grown grains. Conversely, the grain-growth rate in RSP with 1100 ° C-calcined YFeO₃ was moderate, and although it gives a slower densification rate at low temperature, the ultimate density can be raised to 99% theoretical density at 1450 ° C.