The first report about carbon as a foaming agent for cellular glass

logo_smallPatent US3666506 with inventers JH Cowan and D. Rostoker from Corning Glass Works  have developed cellular glass from rocks in 1969. For the first time, carbon is mentioned as foaming agent. The patent has further other interesting information: they mention

  • already the large production cost of cellular glass, foamed from a special glass composition in closed molds.
  • the need for a reducing atmosphere and for that reason a closed mold.
  • batch materials like clay, vulcanic ash, flux, cellulating agent and maximum 800°C
  • organic foaming agents as carbon source instead of carbon black or graphite are preferred
  • the flux added to give the proper visocity to the clay (rocks) with  sodium silicate (water glass) as the favorite one
  • a table with working and not working foaming agents
  • the need for 10% particles smaller than 5 micron in the clay
  • the use of a ball mill to mix and grind
  • producing pellets to avoids molds
  • 30 foaming recipes
  • densities between 150 and 650 kg/m³

The drive for this patent was to avoid the melting of a glass and the use of molds. Today, GLAPOR has replaced the clay by recycled bottles and the molds by a continuous foaming system. And as a consequence, very competitive prices around 200€/m³ are possible for large quantities. Cowan and Rostoker, both eminent scientists with a view should be satisfied.

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