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Article: Cubic zirconia

Cubic zirconia

Introduction and Overview of Cubic Zirconia

  • Cubic zirconia is a cubic crystalline form of zirconium dioxide (ZrO2).
  • It is a synthesized material that is hard and usually colorless, but can be made in different colors.
  • It should not be confused with zircon, which is a zirconium silicate.
  • Cubic zirconia is a cost-effective and durable alternative to diamonds.
  • Its main competitor as a synthetic gemstone is synthetic moissanite.
  • Cubic zirconia was discovered in 1937 as a natural counterpart to the synthetic product.
  • Commercial production of cubic zirconia began in 1976.

Technical Aspects and Properties of Cubic Zirconia

  • Cubic zirconia is crystallographically isometric.
  • Stabilizers like yttrium or calcium oxide are used to form and maintain cubic crystals.
  • It has a density between 5.6 and 6.0 g/cm3, about 1.65 times that of diamond.
  • Cubic zirconia is relatively hard, scoring 8-8.5 on the Mohs scale.
  • Its refractive index is high at 2.15-2.18, and it exhibits an Adamantine luster.
  • Cubic zirconia has no cleavage and shows a conchoidal fracture.
  • It has a high dispersion of 0.058-0.066, exceeding that of diamond.
  • Under shortwave UV, it typically fluoresces yellow, greenish yellow, or beige.
  • Colored cubic zirconia stones may exhibit a strong rare earth absorption spectrum.
  • Due to its high hardness, it is generally considered brittle.

Synthesis and Phase Relations of Cubic Zirconia

  • The primary method of synthesis is the skull-melting method.
  • This method allows for high temperatures and choice of gas atmosphere.
  • The process involves a cup-shaped crucible surrounded by RF activated copper coils.
  • Zirconium dioxide mixed with a stabilizer is fed into the cold crucible.
  • The resulting crystals are formed through controlled crystallization and cooling.
  • Phase relations in zirconia solid solutions: cubic phase crystallizes first, followed by tetragonal and monoclinic phases.
  • Concentration of yttrium determines the resulting product (PSZ or monophasic cubic crystals).
  • Crystals below 14% concentration tend to be opaque, indicating partial phase separation.

Uses and Innovations of Cubic Zirconia

  • Yttrium cubic zirconia (YCZ) is used for windows, lenses, prisms, filters, and laser elements.
  • YCZ is used as a window material for monitoring corrosive liquids in the chemical industry.
  • Partially stabilized zirconia has high hardness, shock resistance, low friction coefficient, and high chemical and thermal resistance.
  • Partially stabilized zirconia is used as a building material in the bio-engineering industry.
  • It is used to make super-sharp medical scalpels compatible with bio-tissues.
  • Coating cubic zirconia with a film of diamond-like carbon (DLC) makes it harder and more lustrous.
  • DLC coating quenches excess fire of cubic zirconia and improves its refractive index.
  • Vacuum-sputtering a thin layer of precious metal or metal oxides creates an iridescent effect.
  • Precious metal coatings are not durable compared to the cubic zirconia substrate.
  • Innovations aim to improve the appearance and properties of cubic zirconia.

Comparison to Diamonds and Impact on the Diamond Market

  • Cubic zirconia has a hardness rating of approximately 8 on the Mohs scale, while diamond has a rating of 10.
  • Cubic zirconia has a higher density than diamond, allowing for differentiation by weight.
  • Refractive index of cubic zirconia is lower than that of diamond, leading to immersion techniques for identification.
  • Dispersion of cubic zirconia is higher than that of diamond.
  • Cut and color of cubic zirconia can differ from diamonds.
  • Cubic zirconia can reduce demand for conflict diamonds.
  • De Beers Company held a monopoly on the diamond market and engaged in price-fixing practices.
  • The price of diamonds continues to increase due to demand in emerging markets.
  • Cubic zirconia offers a lower-priced alternative for jewelry buyers.
  • The Kimberley Process aims to deter the trade of conflict diamonds, but is not fully effective in all markets.

Cubic zirconia Mentions

Cubic zirconia Data Sources

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