The Study of the Influence of ZrO2 Precursor Type and the Temperature of Annealing on the Crystallization of the Tetragonal Polymorph of ZrO2 in Zirconia-Silica Gels

Abstract

Materials of the ZrO₂-SiO₂ system were obtained by the sol-gel method applying two different types of ZrO₂ precursors: zirconium (IV) n-propoxide Zr(OC₃H₇)₄ and zirconium (IV) acetate Zr(OOC₂H₃)₄ (organic acetic acid salt) while commonly used tetraethoxysilane TEOS was selected as SiO₂ introducing one. ZrO₂ concentration in synthesized samples varied from 20% to 50% (mol.). After drying for 28 days, all gels were annealed at 500 °C, 1000 °C, and 1200 °C in air. FTIR spectroscopy together with XRD diffraction was selected as the two main structure research methods. SEM microscopy was applied to analyze the local chemical compositions of samples and to observe the morphology of gels' surfaces. The analysis of FTIR spectra and XRD diffraction patterns allowed us to recognize different ZrO₂ polymorphs which appeared in the samples depending strongly as well on ZrO₂ precursor type as on the temperature of annealing. Samples synthesized by using the zirconium (IV) n-propoxide contained both cubic and tetragonal zirconia phases in general but showed the tendency of the increasing t-ZrO₂ content in gels richer in ZrO₂ and heated up to 1200 °C. However, in materials obtained applying zirconium (IV) acetate, the first detected at 500 °C phase was t-ZrO₂ which was then conversing to m-ZrO₂ form with the increasing temperature in case of samples rich in ZrO₂. Meanwhile, t-ZrO₂ was the predominant phase in samples of the lower content of ZrO₂ but annealed at higher temperatures. By the analysis of changes in band profiles and positions, one can draw conclusions that the structure of studied samples is mostly built up of an amorphous silica matrix, in which different types of zirconia polymorphs create their own crystal lattice. The presence of the particular polymorph depends strongly on the type of zirconia precursor and the temperature of annealing.

Keywords: FTIR spectroscopy; SEM; X-ray diffraction; ZrO2-SiO2 system; sol-gel method; t-ZrO2.

Figure 1

X-Ray diffraction pattern of pure ZrO₂ gel (4% weight ZrO₂) annealed at 500 °C, 1000 °C and 1200 °C in the air (m—monoclinic ZrO₂, T—tetragonal ZrO₂, c—cubic ZrO₂).

Figure 2

X-Ray diffraction patterns of: (a) 1T sample; (b) 2T sample; (c) 3T sample and (d) 4T sample. All samples were synthesized using zirconium (IV) n-propoxide and annealed at 500 °C, 1000 °C and 1200 °C in the air (*—undefined silica, T—tetragonal ZrO₂, c—cubic ZrO₂).

Figure 2

X-Ray diffraction patterns of: (a) 1T sample; (b) 2T sample; (c) 3T sample and (d) 4T sample. All samples were synthesized using zirconium (IV) n-propoxide and annealed at 500 °C, 1000 °C and 1200 °C in the air (*—undefined silica, T—tetragonal ZrO₂, c—cubic ZrO₂).

Figure 3

X-Ray diffraction pattern of: (a) 1C sample; (b) 2C sample; (c) 3C sample and (d) 4C sample. All samples were synthesized using zirconium (IV) acetate and annealed at 500 °C, 1000 °C and 1200 °C in the air (*—undefined silica, m—monoclinic ZrO₂, T—tetragonal ZrO₂, c—cubic ZrO₂).

Figure 3

X-Ray diffraction pattern of: (a) 1C sample; (b) 2C sample; (c) 3C sample and (d) 4C sample. All samples were synthesized using zirconium (IV) acetate and annealed at 500 °C, 1000 °C and 1200 °C in the air (*—undefined silica, m—monoclinic ZrO₂, T—tetragonal ZrO₂, c—cubic ZrO₂).

Figure 4

FTIR spectra of pure ZrO₂ (4% mas. ZrO₂), synthesized using zirconium (IV) n-propoxide and annealed at 500 °C, 1000 °C, and 1200 °C in air.

Figure 5

FTIR spectra of: (a) 1T sample; (b) 2T sample; (c) 3T sample and (d) 4T sample. All samples were synthesized using zirconium (IV) n-propoxide and annealed at 500 °C, 1000 °C and 1200 °C in the air.

Figure 5

FTIR spectra of: (a) 1T sample; (b) 2T sample; (c) 3T sample and (d) 4T sample. All samples were synthesized using zirconium (IV) n-propoxide and annealed at 500 °C, 1000 °C and 1200 °C in the air.

Figure 6

FTIR spectra of: (a) 1C sample; (b) 2C sample; (c) 3C sample and (d) 4C sample. All samples were synthesized using zirconium (IV) acetate and annealed at 500 °C, 1000 °C and 1200 °C in air.

Figure 6

FTIR spectra of: (a) 1C sample; (b) 2C sample; (c) 3C sample and (d) 4C sample. All samples were synthesized using zirconium (IV) acetate and annealed at 500 °C, 1000 °C and 1200 °C in air.

Figure 7

SEM images of: (a) 1T gel synthesized using zirconium (IV) n-propoxide; (b) 4T gel synthesized using zirconium (IV) n-propoxide; (c) 1C gel synthesized using zirconium (IV) acetate and (d) 4C gel synthesized using zirconium (IV) acetate. All gels were annealed at 1200 °C in air.

Figure 8

EDS analysis of 1T gel annealed at 1200 °C in the air (Figure 7a) at: (a) point 1; (b) at point 2 and (c) at point 3.

Figure 9

EDS analysis of the whole studied surface of gels: (a) 4T (Figure 7b); (b) 1C (Figure 7c) and (c) 4C (Figure 7d).