Spinel solid solutions in the systems MgAl₂O₄–ZnAl₂O₄ and MgAl₂O₄–Mg₂TiO₄

Abstract

Phase relations in two binary systems MgAl 2 O 4 -ZnAl 2 O 4 and MgAl 2 O 4 -Mg 2 TiO 4 have been studied and phase diagrams for them have been constructed. Based on the data of x-ray phase and crystal-optical analyses, the formation of a continuous series of solid solutions with spinel structure between the terminal members of the systems studied has been established. In the MgAl 2 O 4 -ZnAl 2 O 4 system the solid solution is stable in the range from room temperature to melting temperature. In the MgAl 2 O 4 -Mg 2 TiO 4 system the solid solution decomposes below 1380 ± C, yielding the formation of limited regions of homogeneity on the basis of MgAl 2 O 4 and Mg 212d Ti 12d O 4 . Decomposition of the solid solution is accompanied by crystallization of MgTiO 3 .

Microstructural evolution of some MgO–TiO2 and MgO–Al2O3 powder mixtures during high-energy ball milling and post-annealing studied by X-ray diffraction

“…Namely, the fully developed MgTiO 3 phase in our experiments was detected in the 10 h milled sample after its post-anneal treatment for 1 h at 900 • C; whereas, in the case of Mg 2 TiO 4 phase post-anneal processing at 1200 • C lasted only 1 h. However, in the latter case besides the dominant Mg 2 TiO 4 phase in the sample appeared also a small amount of the MgTiO 3 phase. Presumably, the latter effect was a consequence of the thermodynamic instability of Mg 2 TiO 4 phase, also observed earlier [30,31]. 3.…”

“…We would like to point out here that this phenomenon presumably is a consequence of the thermodynamic stability of the spinel Mg 2 TiO 4 . Namely, it is known that this phase starts to decompose to MgTiO 3 plus MgO phases below some temperature chosen from the range 1000-1400 • C [30,31]. Finally, it is evident that in the milled samples were incorporated a minor amount of the WC impurity-phase which appeared as a consequence of the contamination effect of the milling assembly (a wearing-off or abrasion effect).…”

(1-x)MgAl2O4-xTiO2 dielectrics for microwave and millimeter wave applications

“…The density reported in Fig. 1 [18] pointed out that a stable solid solution is possible between similar structured MgAl 2 O 4 and Mg 2 TiO 4 . A previous investigation [8] revealed that presence of a low melting phase formed at the grain boundary during excess doping of TiO 2 caused micro cracks, which could degrade the densification of spinel.…”

Dielectric characteristics of the (1−x)Mg2TiO4–xSrTiO3 ceramic system at microwave frequencies

“…Second phase was not observed in our experiments. Petrova et al [14] proposed the following thermal decomposition mechanism to explain the formation of the MgTiO 3 phase.…”