Development of sol-gel synthesis and characterization of meso porous SiO2 nanopowder for improvement of nanomullite/SiC ceramic filter

Abstract

The study investigates the synthesis of mesoporous SiO2 nanoparticles with uniform spherical morphology via the sol-gel method. A strategic approach of this research was to control the particle size within the sol, achieved by incorporating ammonium polycarboxylate (APC) as an additive. The primary objective of this paper is to utilize these modified particles in the fabrication of ceramic filters for metal melt filtration, aiming to enhance their functional properties. Various analytical methods, including DLS, XRD, FTIR, DTA/TG, XPS, SEM, and TEM/EDS, were employed to evaluate the product formation mechanism during the sol-gel process. It was demonstrated that by controlling the pH within an acidic range of 3, precursor particles containing the Si source formed in sizes below 10 nm within the sol, a phenomenon that is fundamental in controlling the final product size to be under 50 nm. The addition of APC, through an electrosteric mechanism, contributed to the stability of the precursor particles within the sol. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) images revealed that the silica nanoparticles possess a spherical shape with a uniform size of approximately 25 nm. Nitrogen adsorption/desorption porosimetry indicated that the nanoparticles have mesoporous with an average pore size of 2.5 nm and a specific surface area of 120 m2/g. This method can be conveniently used to prepare silica nanoparticles with desirable morphology and mesostructure. Polyurethane foam filters were impregnated with nanosilica particles using a slurry casting method. Subsequently, the effects of varying percentages of nanosilica particles in the slurry on the compressive strength, density, and porosity of the ceramic foam filters were examined. Additionally, the impact of silica nanoparticles on the slurry's viscosity was studied using rheometry. The optimal sintering temperature was reported to be 1250 °C. XRD results indicated the formation of mullite phase alongside silicon carbide and alumina phases at 1250 °C. SEM microstructural analysis showed that the mullite phase formed in nanometric dimensions within the ceramic foam bodies. The emergence of the mullite phase in nanometric dimensions within the filter microstructure is one of the factors contributing to the reinforcement and enhancement of refractoriness.