Novel methodology for hydrotalcite (Mg6Al2(OH)16CO3.4H2O) synthesis from aqueous suspensions of magnesium oxide (MgO) and aluminum hydroxide (Al(OH)3) and its application in porous ceramics for high temperature thermal insulation

Abstract

The combination of aluminum oxide (Al2O3) with hydrotalcite (Mg6Al2(OH)16CO3×4H2O) based poregenerators or double layered hydroxides (DLH) results in structures with high porosity (greater than 50 %) and with low sintering driving force, even at high temperatures (1500-1650ºC). Due to these effects, this system presents suitable properties for applications involving thermal insulation and high temperature filtration. Theconventional hydrotalcite (analytical grade) is usually obtained through co-precipitation methods from soluble Mg and Al salts, in alkaline medium. These methods require high purity reactants, present low output and residual cations (Na+ and K+) which require a further step of purification, such as centrifugation or filtration. Concerning its use in large scale as thermal insulating, it is necessary to develop a more effective and withless cost alternative method of synthesis for hydrotalcite. Previous works of the proponent of the present project (supported by FAPESP) have shown that hydrotalcite nanoparticles can be formed from the combination of magnesium oxide (MgO) and hydratable alumina (rho-Al2O3) or aluminum hydroxide (Al(OH)3) in aqueoussuspensions, in large quantities and without needing of purification steps. Due to this, this project aims to: 1)Optimize this novel synthesis technique for hydrotalcite , determining the best conditions for its formation (characteristics of the particles, mixing, kinetics, temperature and pH of the suspensions); 2) Evaluate thehydrotalcite synthesized as pore generator in porous ceramics (pores fraction, mechanical strength, refractoriness under load and thermal conductivity), comparing with the conventional material; 3) Establish the necessary background for the development of a novel product, attained from national raw materials and with high technological applicability. (AU)