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. © 1990 Chapman and Hall Ltd.