Papers by Keyword: Opals

Abstract: In this work, we present a modification of the sol-gel based, Stöber, Fink and Bohn’s (SBF) procedure for the preparation of nanometric spheres of silica with a monomodal distribution of size and controlled diameter. In the SBF method, tetraethyl orthosilicate (TEOS) is used as a precursor molecule and hydrolysis and condensation reactions to form chains and branches of Si-O bonds are carried out. The novelty of this work consists in the use of an aqueous ammonium hydroxide solution as ammonia source. Graphics of particle size as a function of reagent contents are presented (reaction yield control) and differences to the results from the original SBF method are discussed. This procedure is the very first step for the development of a sol-gel synthetic opals preparation process. As a result, the best route to prepare monodisperse spheres in the whole range of 250 to 850 nm is that of keeping constant the TEOS and NH3 contents at 0.28:1M varying water contents in the range of 8 – 12.5 M.

Abstract: Templating methods provide an alternative approach for fabricating macroporous solids with three-dimensionally ordered arrays of pores with diameters from tens to hundreds of nanometers. The main goal of this work is the fabrication of thermoelectric-opal composite and inverse opals made of thermoelectric material in order to obtain enhanced performance by reducing the thermal conduction. Chemical bath deposition (CBD) has been employed and thermodynamic modelling was used to obtain optimum conditions for the desired phase of particle formation within the channels of the opal-like structures. The wetting behaviours of opals were considered in the choiceof the appropriate solvents. When loading is finished, the precursor is decomposed and reduced when appropriate. The opal template is then removed by pyrolysis to obtain the macroporous structures. The structural properties of materials produced were investigated.