Industrial Applications

Zircon, baddeleyite or manufactured zirconia are all useful refractory materials. They are valued for the preparation of special moulds and refractory bricks. High-grade zircon melts at about 2190ºC, softens between 1600ºC and 1800ºC and shows little shrinkage upto 1750ºC. Zircon exhibits many characteristics that make it very suitable for super refractory purposes. In addition to a high melting point it was very low thermal expansion and good resistance to abrasion. Zircon is used when acidic refractory is required while zirconia refractories are considered to be basic. A cheaper type of zircon-refractory is prepared with mixing zircon with alumina. It is reported to have refractory properties as good as those of zircon. At high temperatures the following reaction takes place:

2ZrSiZO₄ + 3Al₂O₃ = 2ZrO₂ + 3Al₂O₃. 2SiO₂

The dissociation of zircon starts at 1400ºC and at about 1600ºC a complete reaction takes place forming a stable product of zirconia and mullite. The high grade zircon sand is largely used in foundry as mould. It does not wet the molten metal, thus giving a better and smoother surface to the casting. It is estimated that about 75% of the total world zircon production is used as moulding sand and in the manufacture of refractory bricks, zirconium compounds and ceramics. Only 25% is used for the extraction of metal or in the manufacture of alloys.

Prepared zirconia and also zircon are extensively used in the glass and ceramic industry for opacifying enamels, porcelain and glazes.

Zircon sands bonded into bricks are also used in large quantities as refractory bricks in glass and aluminium industries. Zircon has special properties of resistance to spalling and wetting by glass and aluminium which makes it suitable for the above purpose. Finely powdered zircon and zirconia are used as an abrasive in polishing optical glasses.