Transparent spinel ceramics

Topic

transspinell

Fine-grained microstructure (example: grain size 0.4 µm) enables improved mechanical performance of transparent spinel ceramics (Vickers hardness HV10 ≈ 15 GPa, 4-point bending strength 200-250 MPa).

spinellgr

Fully transparent window of 5 mm thick sub-µm spinel ceramic (90 x 90 mm2)

trns spinell3

Defect-free processing and high purity give rise to high transmission from UV through IR.

Transparent components with almost thickness independent high transmission at UV, visible and IR wavelengths are made from commercial powders and, optionally, by new syntheses.

Because of birefringence the transmission of 1 mm thin ceramics with non-cubic crystal structure (e.g. corundum - α-Al2O3) hardly exceeds 80 % of the theoretical maximum, and their transparency is rather sensitive to thickness. On the contrary, cubic Mg-Al spinel can become fully transparent even with a centimeter of thickness if last hundredths of porosity percents are eliminated. Commonly, this is achieved by sintering at high temperatures > 1700 °C which results in very coarse grain sizes and reduced mechanical parameters. The new fine-grained grades from IKTS (Fig. 1) avoid such shortcomings.

 

Advantages

 

  • Real in-line transmission (RIT) > 80 % which is 0.95 of the theoretical maximum (measured at λ = 640 nm with aperture 0.57° at 5 mm thickness). Low dependence of transmission on thickness (Fig. 2)
  • High transmission from ultraviolet through infrared (Fig. 3)
  • High hardness (HV10 ~ 15 GPa) by small grain sizes down to the sub-µm range. As a consequence, the ballistic strength (AP ammunition) comes close to sub-µm Al2O3 armor and outperforms even sapphire

 

Products and services offered

 

  • Powder technology for highly transparent spinell ceramics with high hardness starting from commercial spinel powders
  • Technological options: reactive sintering, new chemical synthesis
  • Technological investigations for upscaling supporting the development of new products
  • Investigations of the technical performance in various applications