Low temperature phase equilibria and ordering in the ZrO2-rich region of the system ZrO2-CaO

Thermodynamic Reassessment of ZrO2–CaO System

“…T he ceramic materials based on ZrO 2 –CaO system are widely used in many industrial areas, such as high‐temperature electrolytes in fuel cells oxygen gas sensors, piezoelectric oscillator transducer, heat‐resistant linings in furnaces, and protective coatings on alloys 1 . Therefore, lots of researchers pay much more attention to the phase diagram and thermodynamic properties of this system 1–13 . The first experimental phase diagram of ZrO 2 –CaO system was reported by Ruff 2 where the intermediate compounds CaZrO 3 was discovered, of which melting point was determined to be 2330°C.…”

“…Subsequently, Wartenberg 3 confirmed the existence of CaZrO 3 and its melting point was 2550°C. From then on, many researchers made the considerable efforts to measure the scales of different phase regions in this system 7,8,11,14–21 . Recently, the existence of another two intermediate compounds CaZr 4 O 9 (Φ1) and Ca 6 Zr 19 O 44 (Φ2) have been well established, however, the reports for their stability are controversial, generally, Ca 6 Zr 19 O 44 is accepted as a stable phase now, while the stability of CaZr 4 O 9 is still debated among the different researchers 1,5–7,11,14 .…”

“…A series of thermodynamic assessments on the ZrO 2 –CaO system have been performed by several groups 1,4–6 . For example, the first calculation of this system was carried out by Kaufman 4 based on minimal experimental data, the recently reported phase relations 7–11 in this system cannot be reasonably described by Kaufman's calculations. On the basis of the collection of a lot of experimental data and the review of a very exhaustive revision of thermodynamic assessment of this system, Du 1 indeed made a detailed assessment and calculated the phase diagram, however, when one try to reproduce this work, two stoichiometric compounds (Φ1‐CaZr 4 O 9 , Φ2‐Ca 6 Zr 19 O 44 ), which should be stable below 1650 K, still appeared above 2500 K. Recently, the recalculations of this system were implemented by Yin 5 and Serena 6 their disadvantage is that, Φ2 phase was not included in their calculations and the tetragonal solid solution was even stable below 500 K using their optimized model parameters for reproduction.…”

Thermodynamic assessment of the system ZrO2–CaO–MgO using new experimental results

“…The experimental data considered with a high weight were: for liquidus surface those reported by Stubican and Ray, 34 Traverse and Foex, 35 and Noguchi et al; 36 for the c-ZrO 2 and t-ZrO 2 compatibility field those reported by Stubican and Ray, 34 Garvie, 37 Stringer, 38 Duran et al, 39 and Yin and Arget; 33 and for the c-ZrO 2 and CaZrO 3 compatibility field those proposed by Stubican and Ray, 34 Duran et al, 39 Strickler, 40 Cocco, 41 Tien Subbarao, 42 and Nishimo. 43 For the solidus CaO-rich region of the system, the data provide by Noguchi et al 36 were allocated a high weight.…”

Determination of CaO activity in the mixture {xCaO + (1 −x)ZrO2} at the temperature 1270 K by a galvanic cell involving calcium-ion conducting solid electrolyte

“…The phase diagram of {xCaO + (1−x)ZrO 2 } has been investigated by many authors. A detailed description of it was given by Duran et al (1) There is little literature available on the thermodynamics of the system. Measurements of the thermodynamic properties are not easy from the experimental point of view.…”