INFLUENCE OF ZnO INCORPORATION ON PHASE STABILITY, MORPHOLOGY AND APPARENT DENSITY OF TiO₂-BASED SPRAY FEEDSTOCK POWDERS

Muhamad Akmal  Mohd Sani; Yusliza Yusuf; Jariah  Mohamad Juoi; Azhar Shah  Abu Hassan; Sarita Morakul

Muhamad Akmal Mohd Sani Fakulti Teknologi Dan Kejuruteraan Industri Dan Pembuatan, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia.
Yusliza Yusuf Fakulti Teknologi Dan Kejuruteraan Industri Dan Pembuatan, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia.
Jariah Mohamad Juoi Fakulti Teknologi Dan Kejuruteraan Industri Dan Pembuatan, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia.
Azhar Shah Abu Hassan Fakulti Teknologi Dan Kejuruteraan Industri Dan Pembuatan, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia.
Sarita Morakul Department of Mechanical Engineering, Chulalongkorn University, Phayathai Road Pathumwan, Bangkok 10330, Thailand.

Keywords: ZnO, TiO₂, plasma spraying, feedstock powder

Abstract

TiO₂ based ceramic coatings are extensively used in plasma spray applications due to their excellent hardness, wear resistance, and chemical stability. Nevertheless, the performance of plasma sprayed coatings is strongly influenced by the physical and microstructural characteristics of the feedstock powders. This study investigates the influence of ZnO incorporation on the phase composition, morphology, microstructure, particle distribution, and apparent density of TiO₂-based plasma spray feedstock powders. ZnO was selected due to its favourable chemical compatibility and complementary physical properties with TiO₂, which may enhance phase stability, particle cohesion, and powder packing behaviour. TiO₂ and ZnO powders were blended at different weight ratios of 90 wt.% TiO₂/10 wt.% ZnO, 80 wt.% TiO₂/20 wt.% ZnO, and 70 wt.% TiO₂/30 wt.% ZnO using wet mixing followed by planetary ball milling without milling balls to promote homogeneous agglomeration while preserving particle integrity. X-ray diffraction (XRD) analysis confirmed the coexistence of anatase and rutile TiO₂ phases together with the ZnO wurtzite phase without the formation of secondary phases, indicating good phase compatibility and homogeneous ZnO distribution within the powder matrix. FESEM observations revealed angular and well-defined TiO₂ particles, while ZnO appeared as finer irregular aggregates distributed around the TiO₂ surfaces. Incorporation of 10 wt.% ZnO resulted in more uniform particle dispersion, reduced agglomeration, and improved packing through effective filling of interparticle voids. Apparent density analysis showed that moderate ZnO incorporation enhanced bulk density and packing efficiency, whereas excessive ZnO addition increased interparticle voids and reduced powder density. Among all compositions, the 90 wt.% TiO₂/10 wt.% ZnO feedstock exhibited the most balanced combination of phase stability, morphology, and packing characteristics, demonstrating strong potential for dense and wear-resistant plasma-sprayed coating applications.