The preparation of a core/shell structure with alumina coated spherical silica powder

In this work, a SiO2@Al2O3 core/shell structure was prepared through a sol–gel approach. Various techniques were used to characterize the as-prepared products, including thermogravimetric analysis and differential scanning calorimeter (TG-DSC), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and laser flash thermal diffusivity apparatus. The TG-DSC and XRD results showed a SiO2@Al2O3 structure comprised of amorphous silica and α-Al2O3 at a calcination temperature of 1000 °C. In addition, the FESEM images and EDS results revealed that the α-Al2O3 shell had a thickness of around 90 nm. The presence of SiO and AlO was confirmed through FTIR analysis. Different modification surfactants were investigated, revealing the superior properties of polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) for dispersing and coating spherical silica powders. We obtained smooth spherical SiO2@Al2O3 particles by changing Al2O3 sol adding rate. The results confirmed that spherical silica powders had been uniformly coated by alumina powders with the size less than 50 nm. The SiO2@Al2O3 powders demonstrated higher thermal conductivity than raw spherical silica powders. The thermal conductivity of spherical silica powders was 0.24 Wm−1 K−1, while that of SiO2@Al2O3 powders reached 0.46 Wm−1 K−1.