Search

The incorporation of nanosized particles into the building materials can significantly influence their properties. Such noticeable modification of the properties of cement-based composite is not possible with traditional cement binders and mineral additives. Heavyweight cement concretes are used for production of the radiological shields in the objects exposed to ionizing radiation. In the case of nuclear reactors, concrete is also exposed to a high temperature at the moment of failure. In the presented work authors investigated the properties of the cement composites modified with core-shell type nanostructures. The study is aimed at the development of new material solution showing improved shielding properties of the concrete. Magnetite nanoparticles coated with silica shell were applied to increase the resistance of concrete to elevated temperature, without deterioration of its shielding ability. Plain cement paste and cement paste containing 5 wt% magnetite/silica core-shell structures were prepared. The samples were exposed to temperatures elevated to 300 o C and 450 o C, respectively. Nanoindentation technique was applied for the analysis of mechanical properties of cement pastes. The results have confirmed the favorable role of the Fe 3 O 4 /nSiO 2 nanoparticles in the protection of the cement matrix from the high temperature. [ABSTRACT FROM AUTHOR]

Pristine nanoparticles of magnetite were coated by solid silica shell forming core/shell structure. 20 nm thick silica coating significantly enhanced the chemical and thermal stability of the iron oxide. Chemical and thermal stability of this structure has been compared to the magnetite coated by mesoporous shell and pristine magnetite nanoparticles. It is assumed that six-membered silica rings in a solid silica shell limit the rate of oxygen diffusion during thermal treatment in air and prevent the access of HCl molecules to the core during chemical etching. Therefore, the core/shell structure with a solid shell requires a longer time to induce the oxidation of iron oxide to a higher oxidation state and, basically, even strong concentrated acid such as HCl is not able to dissolve it totally in one month. This leads to the desired performance of the material in potential applications such as catalysis and environmental protection. [ABSTRACT FROM AUTHOR]