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Silica powders for powder evacuated thermal insulating panel and method

  • US 5,395,604 A
  • Filed: 05/03/1994
  • Issued: 03/07/1995
  • Est. Priority Date: 07/09/1993
  • Status: Expired due to Fees
First Claim
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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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