Zirconium oxide crystal phase: The role of the pH and time to attain the final pH for precipitation of the hydrous oxide

Abstract

Precipitated hydrous zirconium oxide can be calcined to produce either a monoclinic or tetragonal product. It has been observed that the time taken to attain the final pH of the solution in contact with the precipitate plays a dominant role in determining the crystal structure of the zirconium oxide after calcination at 500 °C. The dependence of crystal structure on the rate of precipitation is observed only in the pH range 7–11. Rapid precipitation in this pH range yields predominately monoclinic zirconia, whereas slow (8 h) precipitation produces the tetragonal phase. At pH of approximately 13.0, only the tetragonal phase is formed from both slowly and rapidly precipitated hydrous oxide. The present results, together with earlier results, show that both the pH of the supernatant liquid and the time taken to attain this pH play dominant roles in determining the crystal structure of zirconia that is formed after calcination of the hydrous oxide. The factors that determine the crystal phase are therefore imparted in a mechanism of precipitation that depends upon the pH, and it is inferred that it is the hydroxyl concentration that is the dominant factor.

Identification of tetragonal and cubic structures of zirconia using synchrotron x-radiation source

“…The resulting product was washed to a negative test for chloride ion (ca. 10 washings) and then calcined at 500 °C for 200 h. [11][12] Samples D and E were prepared in a manner similar to that reported by Benedetti et al 21 Sample D, which corresponds to sample III in Ref. 21, was washed twice while sample E (sample II in Ref.…”

Zirconia: A Review of a Super Ceramic

“…The material precipitated at a pH of 2.95 was predominantly the tetragonal phase following a 4 hour heating period; however, during the 200 hour heating period there was a gradual transformation to the monoclinic phase. 41 Precipitations were also carried out at a pH of 10.4 by the slower addition of base. In this slower precipitation procedure, a calculated amount of base was added dropwise to a stirred zirconium salt solution at a rate to produce the desired pH at a targeted time.…”

In-Situ Synchrotron X-ray Characterization of Corrosion Products in Zr Artificial Pits in Simulated Physiological Solutions

“…48,49 Hydrolytic polymerization of ZrOCl 2 ·8H 2 O solutions produces a hydrated amorphous gel of ZrO 2 , which can be transformed into crystalline phases such as monoclinic and tetragonal ZrO 2 on heating, with the phase formed dependent on the precipitation conditions. 49 It is reported that the crystal structure of ZrO 2 is dependent on the pH of the precipitation solution and the time taken to attain this pH, although the thermodynamic stable phase of crystalline ZrO 2 is monoclinic at room temperature. 49,50 Tetragonal ZrO 2 was found to be formed more effectively in precipitation solutions of higher pH and with slower precipitation rates.…”

“…49 It is reported that the crystal structure of ZrO 2 is dependent on the pH of the precipitation solution and the time taken to attain this pH, although the thermodynamic stable phase of crystalline ZrO 2 is monoclinic at room temperature. 49,50 Tetragonal ZrO 2 was found to be formed more effectively in precipitation solutions of higher pH and with slower precipitation rates. Further studies also propose that the tetragonal phase can be stabilized against transformation to monoclinic if the particle size is less than 30 nm.…”

“…[49][50][51] In this study, tetragonal ZrO 2 was found dispersed above the ZrOCl 2 ·8H 2 O salt layer toward the pit mouth (less acidic compared with the solution deep in the pit) when Zr artificial pits were grown for 3-5 h. Although the exact formation mechanism is not fully understood as there is no thermal factor evident, it is not unreasonable to propose that less acidic pH conditions found toward the pit mouth and a slow precipitation process facilitated the formation of tetragonal ZrO 2 by polymeric hydrolysis of ZrOCl 2 ·8H 2 O solutions. 49,50 The effect of H 2 O 2 and/or albumin on formation of Zr corrosion products and biomedical implications.-As seen in Figure 9, the addition of H 2 O 2 and/or albumin in physiological saline did not have a significant effect on the passive current densities and pitting potentials of the bulk Zr samples. A comparison of pit morphologies showed a similar characteristic 'honeycomb' morphology as well as rough pit surface regardless of the presence of H 2 O 2 and/or albumin in physiological saline (Figure 10).…”