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Lead Glass

Lead glass is made by using lead oxide instead of calcium oxide, and potassium oxide instead of all, or most of, the sodium oxide. The lead is not readily extractable from the silicate matrix. Lead glass has a high refractive index, making it sparkle brightly, and a relatively soft surface so that it is easy to decorate by grinding, cutting, and engraving, which makes it popular for drinking glasses, decanters, and other decorative objects. Lead glass is also used for radiation shielding and can be found in cathode ray tubes which are used, for example, in TV and monitors.

The type of glass is very important when making fine powders for polymer applications, as these often require particle sizes below 10 pm. Commercial (soda- lime) glass is difficult to prepare and use at such small size, largely due to the water sensitivity of the composition. This leads to caking under humid conditions and problems with wet grinding. Borosilicate and alumina borosilicate are much less soluble and so can be produced at such low sizes more readily.

The main potential sources of glass powder are.

  • 1. Dust fractions of soda-lime glass collected during crushing operations: These are usually too fine to be used in the glass furnaces.
  • 2. Borosilicate glass: This has too high a melting point for recycling through conventional furnaces.
  • 3. Glass fibers: These can be ground down to be used as particulate fillers. These can be soda-lime or alumina borosilicate. Because of the solubility issues, the main interest is in alumina borosilicate powders.

Despite being widely available and relatively low cost, recycling of glass into polymer fillers is fairly limited. This is mainly due to its high abrasiveness, which makes use in many polymer-processing lines using softer fillers such as carbonates and talcs, impractical. The water sensitivity of soda-lime glass also makes it difficult to make and store at very small particle size.

 
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