Silica powders for powder evacuated thermal insulating panel and method
First Claim
1. A method for making ultrafine silica particles for use in powder evacuated insulation panels with said silica particles being of a median size less than about 100 nanometers in diameter and having internal porosity sufficiently small to substantially restrict motion of gas molecules therein, a pour density of about 0.6 g/cm3, and an external surface area greater than 90 m2 /g and formed of an agglomeration of substantially spherical porous silica particulates each of a size less than about 10 nanometers in diameter, comprising the steps of reacting a solution consisting essentially of a tetraalkyl silicate with a sufficient concentration of ammonia and water in the presence of an alcohol solvent and for a sufficient duration to form in the solution solid substantially spherical silica particles of a size less than about 100 nanometers in diameter, distilling the solution to remove therefrom the ammonia and alcohol for forming an aqueous slurry containing agglomerates of the silica particles, drying the slurry for removing water from the silica particles to define internal and external pores in the silica particles, and milling the resulting dried agglomerates of silica particulates for a sufficient duration to form discrete silica particles of a size less than about 100 nanometers in diameter.
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Abstract
A powder evacuated thermal insulating panel using generally spherical and porous silica particles of a median size less than about 100 nanometers in diameter, a pour packing density of about 0.4 to 0.6 g/cm3 and an external surface area in the range of about 90 to 600 m2/ g is described. The silica powders are prepared by reacting a tetraakyl silicate with ammonia and water in an alcohol solvent, distilling the solution after the reaction to remove the ammonia and recover the alcohol. The resulting aqueous slurry was dried, ball-milled, and dried again to provide the silica particles with defined internal and external porosity. The nanometer size and the large external surface area of the silica particles along with the internal and external porosity of the silica particles provide powder evacuated thermal insulating panels with significantly higher R-values than obtainable using previously known silica powders.
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9 Claims
- 1. A method for making ultrafine silica particles for use in powder evacuated insulation panels with said silica particles being of a median size less than about 100 nanometers in diameter and having internal porosity sufficiently small to substantially restrict motion of gas molecules therein, a pour density of about 0.6 g/cm3, and an external surface area greater than 90 m2 /g and formed of an agglomeration of substantially spherical porous silica particulates each of a size less than about 10 nanometers in diameter, comprising the steps of reacting a solution consisting essentially of a tetraalkyl silicate with a sufficient concentration of ammonia and water in the presence of an alcohol solvent and for a sufficient duration to form in the solution solid substantially spherical silica particles of a size less than about 100 nanometers in diameter, distilling the solution to remove therefrom the ammonia and alcohol for forming an aqueous slurry containing agglomerates of the silica particles, drying the slurry for removing water from the silica particles to define internal and external pores in the silica particles, and milling the resulting dried agglomerates of silica particulates for a sufficient duration to form discrete silica particles of a size less than about 100 nanometers in diameter.
Specification