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Fraunhofer Nanotechnology Alliance
 

  High-strength transparent components of sub-µ-Al2O3 ceramics

Sub-µm-and nano-technologies for transparent components exhibiting highest strength, hardness and wear resistance together with an extreme thermal and chemical stability

Known "transparent" alumina ceramics exhibit low mechanical parameters and a low in-line transmission of unscattered light (< 15 %) because of coarse micro-structures (> 20 µm); in fact, they are optically not clear and rather translucent than transparent. The new sub-µm corundum ceramics (a-Al2O3, Fig. 1), avoid these shortcomings and can be manufactured with very complex shapes.

 

Transparent components of sintered corundum with sub-Ám microstructure
Fig. 1: Transparent components of sintered corundum with sub-µm microstructure. 4-point bending strength 650-700 MPa (3-pt: ~800 MPa), hardness HV10 > 2000. The transparency of the hollow component is demonstrated by a central wire and the XXX-marker on the backside.

  Advantages

  • In-line transmission (wave length = 640 nm, aperture = 0.57 °) > 50 % at thickness 0.8 mm (Fig. 2).
  • Same high infrared transmission as sapphire in the 3-5 µm range (Fig. 4).
  • Extremely high strength (600-850 MPa), hardness (Fig. 4), scratch and wear resistance.
  • High chemical stability in acids, bases, and agressive gases.
  • Flexible shaping by casting (discs, tiles, complex hollow shapes); technology to be used also for other materials.
clear appearance of highly dense Al2O3 with sub-Ám grain sizes
Fig. 2: High transmission of unscattered light ("clear" appearance)
of highly dense Al2O3 with sub-µm grain sizes.
 We offer

  • Development of high-strength transparent ceramics, e.g. on the basis of corundum (a-Al2O3) with sub-µm/ nano microstructures.
  • Alternative developments with commercial or with nanoscale raw materials.
  • Technological investigations for upscaling supporting the development of new products; screening of raw materials and shaping approaches.
  • Investigations of the technical performance in various applications.
infrared transmission of sintered sub-Ám Al2O3 as sapphire
Fig. 3: Same infrared transmission of sintered sub-µm Al2O3 as sapphire in the important 3-5 µm range.


thermally and chemically stable a-Al2O3 corundum-ceramics due to reduced grain size
Fig. 4: Reduced grain sizes of thermally and chemically stable a-Al2O3 corundum-
ceramics associate transparency with highest strength and hardness.

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