Process for producing low thermal conductivity high strength silica foam

Claim 1

IN A PROCESS FOR THE PREPARATION OF INORGANIC SILICA FOAM WHEREIN AN AQUEOUS ALKALI METAL SILICATE CHASEN FROM SODIUM NOT POTASSIUM SILICATES IS FORMED AND SAID FOAM IS CURED IN THE PRESENCE OF AN ALKALI METAL OR ALKALINE EARTH METAL SILICOFLUORIDE ISOLUBILIZER, RESULTING IN A RIGID FOAMED STRUCTURE HAVING CELL WALLS FORMED OF SILICA, AND CONTAINING INTERSTITIAL ALKALI METAL FLUORIDE REACTION PRODUCT, AND TREATING SAID CURED FOAM FOR THE REMOVAL OF ALKALI METAL FLUORIDE, THE IMPROVEMENT WHICH COMPRISES PREVENTING DEGRADATION AND WEAKENING OF THE STRENGTH AND INSULATION PROPERTIES OF THE FOAMED MASS BY CARRYING OUT SAID LEACHING STEP PRIOR TO THE OCCURANCE OF SUBSTANTIAL DAMAGING CRYSTAL GROWTH OF ALKALI METAL FLUORIDE IN THE WET FOAMED MASS, AND BY LEACHING THE CURED, WET FOAM WITH AN AQUEOUS SOLUTION OR COLLIDAL AQUEOUS SUSPENSION OF AN ACID OR ACIDIC SALT LEACHING AGENT, SAID LEACHING AGENT BEING NON-REACTIVE WITH RESPECT TO SILICA, SAID LEACHING AGENT HAVING THE ABILITY TO FORM WATER SOLUBLE OR WATER DISPERSIBLE FLUORIDE COMPOUNDS OR COMPLEXES HAVING REDUCED AFFINITY FOR THE SILICA STRUCTURE.