PROCESSING OF Cr³⁺/Cr⁴⁺ STABILIZED c-ZrO₂ NANOPARTICLES THROUGH THERMOMECHANICAL ATTRITION PROCESS

Abstract

Stabilized zirconia in nanoparticles in c-ZrO₂ polymorph has been synthesized with a small quantity of (5 mol%) additive of Cr³⁺ and Cr⁴⁺ cations by thermomechanical attrition (MA) process. The MA process allows the chromium cations to dissolve in the precursor in an amorphous state in order to obtain a stabilized phase in c-ZrO₂. This is not so easily possible by conventional methods. The synthesis process consists of a controlled Cr³⁺/Cr⁴⁺:c-ZrO₂ nucleation and growth from an energized amorphous precursor of the metal cations. It involves a reactive milling of dispersed Cr⁶⁺ cations by (NH₄)₂Cr₂O₇ in an amorphous precipitate of Zr⁴⁺ oxyhydroxide. During milling, the Cr⁶⁺ reacts with Zr⁴⁺ in producing a high-energy solid solution in an amorphous structure. The occurrence in the change from oxidation state is promoted by a plastic deformation and mixing between the two types of cations during the milling. The resulting precursor powder undergoes a self-controlled reconstructive thermal decomposition at 500°C and yields Cr³⁺/Cr⁴⁺ stabilized c-ZrO₂ nanoparticles. Average crystallite size is estimated from x-ray diffraction peak-widths in sample stabilized by 5 mol% Cr³⁺/Cr⁴⁺ in 20 hr of milling. The D value decreases from 18 to 15 nm by extending the milling time to 50 hr. The stabilized nanoparticles are found to exist in the c-phase up to a temperature as high as 1000°C. The results are analyzed and discussed in terms of x-ray diffraction, thermal analysis, scanning electron microscopy microstructure, and x-ray photoelectron and optical spectra.

Keywords:

• Processing of ZrO₂
• Stabilized c-ZrO₂
• Nanoparticles
• Nanopowder
• Cr³⁺/Cr⁴⁺ doped ZrO₂
• ZrO(OH)₂·xH₂O precursor
• Thermomechanical attrition
• Plastic deformation
• Crystallite size
• Solid solution
• X-ray diffraction
• Microstructure
• Thermal analysis
• X-ray photo electron spectroscopy
• Optical spectrum

ACKNOWLEDGMENTS

This work has been financially supported by the Council of Scientific and Industrial Research (CSIR), Government of India.