Production of porous element comprises impregnating first porous material with second porous material of lower porosity which then gels

摘要

An initial element is made of a first porous material with a first porosity and a solution is made which is designed to gelify to form a second porous material with a lower porosity that the first material. The initial element is impregnated with the solution before its gelification, and the liquid phase of the solution eliminated once the initial element is impregnated. The initial element is a material with open pores. The first porous material is inox, glass or alumina. The gelification used is chemical and/or physical. The solution of the second porous material tends to polymerize in the liquid phase for a chemical gelification. The second porous material is a porous oxide such as porous silica, with a porosity of the order of 10 nm. The element thus obtained has a porosity of the order of 10 to 100 nm. The porosity of the element is adjusted by choosing the ratio of proportions of the two porous elements; the volumic concentration of the second material, or using specific drying to eliminate the liquid phase of the solution when the first material is impregnated. The specific drying method is direct drying; drying after exchange of the liquid phase, or supercritical drying. The constitution of the gel is made using a sun-gel method. The liquid phase is eliminated by supercritical drying on a liquid phase of CO2. Prior to the supercritical CO2 drying, the initial liquid phase is replaced so the first element is impregnated with liquid CO2. The process includes, at the end of the liquid elimination phase, a consolidation reheating of the porous element at a temperature greater than 300[deg]C, preferably of the order of 700[deg]C in an atmosphere containing a mixture of argon and hydrogen. Specifically, the reheating occurs under Noxal 4 for two hours at a temperature of the order of 700[deg]C, immediately after the drying process. The gel is made by diluting TEOS in a solution of EtOH; diluting an acid aqueous solution in the EtOH and adding it to the EtOH solution, diluting after 30 minutes with an aqueous solution of NH4OH in EtOH and adding to the EtOH solution; in particular, diluting 37 units of TEOS by volume in a solution of 12 units of EtOH by volume; diluting 1.5 units of an acid aqueous solution (HCl 10-2M) by volume in two units of EtOH by volume and adding to the EtOH solution; diluting after 30 minutes 4.5 units of an aqueous solution of NH4OH (5.10-2M) by volume in 6 units of EtOH by volume and adding it to the EtOH solution.