Aerogels and aerosils are highly porous solid bodies in that the predominant portion of their volume consists of pores. Aerogels can be based for example on silicate but also on plastics or carbon. The diameter of aerogel pores is in the nanometer range. Owing to their high pore volume, aerogels are particularly useful as insulating materials combining outstanding insulation properties with low density. Aerogels are initially present as particles, and can be subjected with the use of binders to a shaping process to form panels by pressing for example.
Aerogels are also described in the literature as gels with air as dispersion medium. Aerogels are obtainable by drying a suitable gel. The shaping process of the aerogel is concluded during the sol-gel transition. Once the solid gel structure has become developed, the outer form can only be changed by comminution, for example grinding. Aerogel in the context of the present invention also comprehends xerogels and cryogels.
EP-A-1 146 070 A2 and WO-A-2007/23118 disclose the impregnation of melamine-formaldehyde foams with an ammonium salt and with sodium silicate, respectively.
DE-A-10 2007 009127 A1 discloses fiber-reinforced foams based on melamine-formaldehyde resins having a fiber content from 0.5% to 50% by weight. Short or long fibers of glass, carbon or melamine resin are used as fibrous filler.
WO-A-2009/021963 A1 discloses a process for producing an abrasive foam based on a melamine-formaldehyde condensation product and comprising from 0.01% to 50% by weight of inorganic nanoparticles based on the weight of the precondensate.
US-2009/029147 A1 discloses aerogel-foam composite materials having a density of <150 g/L and a thermal conductivity of <50 mW/m*K. The sol-gel process is carried out in the foam. The drying is done in the supercritical state.
DE 19533564 A1 discloses a composite material comprising from 5% to 97% by volume of aerogel particles, at least one binder and at least one fiber material, a process for its production and also its use. The test specimen thus obtained has a very high density (380 g/l) and thermal conductivity (37 mW/mK).
The properties of known materials are no longer in line with increased expectations, especially in respect of thermal conductivity and acoustical absorption.