Effect of zinc oxide on wollastonite: Structural, optical, and mechanical properties

Abstract

Partial substitution of ZnO for CaO in the wollastonite formula was performed via wet precipitation. The effects of ZnO/CaO replacement on the structure, porosity, morphology, optical, and mechanical properties of the CaO–SiO2 ceramic were examined. Structural results and Fourier transform infrared (FTIR) spectra indicated the existence of mixed phases of wollastonite with hardystonite and willemite with hadystonite composites, depending on the ZnO content. The calculated crystallite size confirmed that the formed composites were in the nanoscale range. The FTIR results verified the mixed phases of the prepared samples. The optical band gap energy (Eg) values of 3.3 and 4.56 eV referred to the willemite phase in samples with high ZnO content. Addition of ZnO increased the bulk density and decreased the porosity of the wollastonite. The reduced porosity controlled the mechanical behavior of the prepared composites. The maximum stress (σu) increased from ∼4.10 to ∼26.68 N/mm2 as the porosity decreased from 52.20% to 40.17% for a ZnO content increased from 0% to 50%. The fracture load increased with the ZnO content. The degradability of samples revealed that the higher the ratio of ZnO to the nominal wollastonite, the more influential it was on the degree of weight loss % and the variation in the pH value. The bioactivity test estimated that all samples surface exposed development of a newly formed apatite layer, consequently evidencing the bioactivity of the prepared ceramic composites. Therefore, such substitution can be used in vital applications.