Abrasion Resistant thin Partially Stabilised Zirconia Coatings by Sol-gel Dip-coating

H. Ivanković, J. Macan, M. Ivanković and K. Grilec

Abstract
Thin partially stabilised zirconia coatings were prepared by dip-coating from sols. Zr(O-nC4H9)4 was used as zirconia precursor in sol-gel synthesis, making use of yttria to stabilise the high-temperature zirconia modifications. The effect of synthesis parameters for sol, such as molar ratio of Zr(O-nC4H9)4, 2,4-pentadione, water and nitric acid on the stability of ZrO2 sols, was determined. The gelling time was largely extended from 0 to 4200 h by increasing the molar ratio of 2,4-pentadione to Zr(O-nC4H9)4 from 0 to 0.8. The acid displayed a marked catalytic and, combined with 2,4-pentadione, synergistic effects on the hydrolysis rate of Zr(O-nC4H9)4. Crystallographic analysis showed that only tetragonal zirconia crystallized at 673 K, and that it remains stable until ∼1173 K. Optical microscopy of thin zirconia coatings showed that increased firing temperature facilitated the grain growth of zirconia. The mechanical properties (microhardness and abrasion resistance) of the coating-substrate system also increased with increasing the firing temperature and viscosity of the coating solution.

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Keywords
sol-gel, dip-coating, zirconia, thin coatings, tribology