PREPARATION OF LOW-DENSITY XEROGELS AT AMBIENT-PRESSURE

For successful large-scale commercialization of aerogel technology to occur, aerogel costs must be dramatically reduced. Using a previously developed model for predicting gel shrinkage during drying, a number of approaches for producing aerogels under ambient pressure conditions are presented. The extent of drying shrinkage is governed by two parameters, the dimensionless group, P=A(s) gamma cos(theta)m rho(0)/K-0, which represents the relative magnitudes of capillary pressure and gel stiffness, and the parameter, m, which describes the stiffness variation with density. For P less than 1, the density increase upon drying is less than 10%. Necessary steps to produce aerogels which are commercially viable include: (1) the use of low-cost precursors such as sodium silicate; (2) the production of aerogel granules to greatly reduce diffusion and heat transfer-related process timescales; (3) development of a continuous aerogel process technology which employs a minimum of solvents (number and volume), does not require expensive high-pressure supercritical or surface modification techniques, which has short process times at each step and which is built upon existing unit operations. if possible, structural relaxation after the drying critical point should be enabled to yield lower density materials for a given P value.