Substitutions of Ti and Cu in ZrO 2 .MgO (Z), cause transformation from monoclinic (m) to cubic (c) and tetragonal (t). According to the vacancy model and solid solution formation models, neither CuO nor TiO 2 cause zirconia stabilization, which derives from other phenomena. Data analysis by TMA using the CRH (constant rate of heating) method shows a solid state reaction of ZrO 2 .MgO.TiO 2 (Z.TiO 2 ) demonstrating a dominant mechanism of volume diffusion (n=1). However, the sintering of ZrO 2 .MgO.CuO (Z.CuO) shows a viscous flow mechanism (n=0), a similar phenomena to that of by sintering of glass. Transformations, such as: CuO to Cu 2 O at 1000 o C, ZrO 2 (m) to ZrO 2 (t) at 1100 o C and Cu 2 O (s) to Cu 2 O (l) at 1230 o C cause successive rearrangements of microstructure inside of region I (sintering process) and lead to interpretation errors when the Bannister equation is used.