Abstract
In this study, we apply silica-assisted sintering to develop porous yttria stabilized zirconia (YSZ) ceramics with tailored electrostatic surface potential and adsorption capacity as a promising alternative to chemical functionalization. The porous bodies were formed by partial sintering at 1050 °C and were investigated regarding the influence of admixtures of silica particles on sintering behavior, microstructural evolution and the resulting mechanical and surface properties of the material, particularly the surface potential. With increasing silica concentration, the sintering mechanism was gradually changed from solid state to liquid phase sintering, due to the wetting of YSZ by liquid silica and a resulting inhibition of mass transport, particle growth and diffusion-induced densification. Most importantly, due to the silica layer development, the isoelectric point (IEP) of the YSZ/silica material surfaces was systematically shifted towards the IEP of silica from pH 9.4 to 1.2 resulting in a more pronounced negative surface potential at neutral pH. The relationship between surface IEP and silica concentration was mathematically described using the IEPs of the starting materials, the YSZ particle radius and the glass layer thickness. This estimation allows us to tailor the surface coverage of the YSZ matrix with silica as well as the resulting electrostatic surface potential. We further demonstrate how the applied processing route can be effectively used to develop ceramics with specified adsorption capacities for protein immobilization for use in filtration, bioprocessing or biomaterial applications.
Highlights
The surface charge of oxide ceramic materials [1,2,3,4] critically determines the material’s performance in application areas such as filtration [2,5], biomaterials, biomedical devices [6,7] and catalyst supports [8,9]
The fabrication and systematic study of porous yttria stabilized zirconia (YSZ)/silica ceramics with varying silica content has shown the strong influence of silica addition on the densification behavior, sintering mechanism, on their microstructural evolution, mechanical properties and electrostatic surface potential and adsorption capacity (Fig. 8)
A silica melt was formed which gradually changed the sintering process from solid state sintering to liquid phase sintering with increasing silica concentration (0–20 vol%)
Summary
The surface charge of oxide ceramic materials [1,2,3,4] critically determines the material’s performance in application areas such as filtration [2,5], biomaterials, biomedical devices [6,7] and catalyst supports [8,9]. Like silanization [9,10,11], is frequently used to modify surface charge and other characteristics of ceramic materials without affecting their bulk properties [12,13]. Such strategies often require poorly scalable protocols, especially if a well-defined, ultrathin surface coating is desired and they can show a limited stability against hydrolysis, especially at extreme pH conditions or against decomposition at elevated temperatures [12,13,14,15]. Crystallographic defect structures [19], the nature and concentration of the surrounding electrolyte and especially the solid’s stoichiometry and phase composition [2,4,8] have a strong impact on the zeta potential
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