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Permeable hollow particles having an outer shell of mechanically rigid porous material

  • US 5,770,416 A
  • Filed: 06/03/1993
  • Issued: 06/23/1998
  • Est. Priority Date: 05/26/1989
  • Status: Expired due to Fees
First Claim
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1. A method for the preparation of permeable hollow particles having an outer shell of a mechanically rigid porous material, the size of the particles being within the range from 1 μ

  • m to 5000 μ

    m, the method comprising;

    (a) taking impermeable, substantially spherical, hollow, particles having an outer shell of a mechanically rigid material, the outer shell comprising a member selected from the group consisting of anhydrous forms of silicon dioxide, metal silicates, metal borosilicates, metal oxides, and boric oxide, the size of the particles being within the range from 1 μ

    m to 5000 μ

    m, and(b) treating said hollow particles with one or more reagents selected from the group consisting of acids and bases capable of rendering said hollow particles permeable by the formation of through-going pores in the outer shell by chemical reaction or solvent/solute dissolution so as to form substantially spherical permeable hollow particles having a cavity defined by the inner surface of the outer shell, said cavity being connected with the surroundings by the through-going pores, the permeability of said particles being such as to permit chemical species to traverse their outer shell via said through-going pores, wherein step (b) is carried out at a temperature of about 20°

    C. to the boiling point of said acid or base obtained under reflux conditions open to the atmosphere;

    with a first proviso that, if step (b) includes treatment with hydrochloric acid, then said treatment is not employed as the only treatment or as an initial treatment when said particles of step (a) are soda-lime borosilicate glass,and with a second proviso that, if step (b) includes treatment with orthophosphoric acid, then said treatment is not employed as the only treatment or as an initial treatment when said particles of step (a) are siliceous particles obtained as a component of the fly-ash formed upon combustion in a combustion plant, andwith a third proviso that said mechanically rigid material is not a material selected from metal and alloys thereof.

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