NKR Fibers

Why NKR® fibers are different?

Because they are…

  • Single Crystal Fibers.
  • Pure.
  • Grown in the C-axis direction.
  • Of alpha-alumina (corundum).
  • With a very high aspect ratio.

Technical specifications

  • Increased strength.
  • High thermal stability.
  • Excellent performance in corrosive environments.
  • Significant reduction of creep and fatigue damage.
  • Significant increase in toughness.
  • Degree of flexibility adaptable on demand.
  • Electromagnetic transparency.
  • Processing flexibility.


  • Crystal Type: Alpha (sapphire) (Single Crystal).
  • Diameter, μm: 0.1-5.
  • Length, μm: 5-500.
  • Density, g/cm3: 4.
  • Purity, wt %: ~99 Al2O3.
  • Chemical composition: >99.7% Al2O3.
  • Tensile Strength: >6 GPa.
  • Aspect Ratio: >103.
  • Electrical: Insulator.
  • Melting point: 2050º C.
  • Environmental Resistance: Flammability, Fresh Water, Organic, Solvents, Oxidation, Sea Water, Strong Acid, Strong Alkalis, Wear...


Neoker has obtained the following certifications:

Neoker also is in the final stages of implementation of the following systems of quality management:

  • • R&D Certification: UNE 166001 and RD1432/2003.

See our Quality and Environmental Policy

NKR Fibers

¿What are the NKR® fibers?

NKR® single crystal alumina fibers improve the thermal performance and the chemical and mechanical properties of advanced composites. In addition, NKR® fibers provide benefits superior to those of other substitute materials:

Comparison of NKR® fibers properties vs. substitute materials*

Properties NKR® Fibers(Alumina Single Crystal Fibers) Alumina Polycrystal Fibers SiC Carbon Fibers
Purity: Present Phases One phase. Two phases, one of them limiting the performance. One phase. One phase.
Cristaline Structure Single crystal.No grain growth. Polycrystal.Grain boundaries: creep. Single crystal.No grain growth. Single / polycrystal
Thermal Very high thermal stability in all conditions. Service Tª: 1500º C. <1200º C Very high thermal stability. Service Tª: 1500º C, except in corrosive environments. Very high thermal stability. Service Tª: 1500º C, except in corrosive environments.
Chemical Stable even with strong acids, alkalies, corrosion environments… Not stable. Stable only with some acids. Not stable in presence of Oxygen, H2O, etc. Stable only with some acids. Not stable in presence of Oxygen, H2O, etc.
Mechanical Very high. Low. Very high, but not time-consistent. Very high, but not time-consistent.

*Reference: Krenkel, Walter (Ed.): Ceramic Matrix Composites. Fiber Reinforced Ceramics and their Applications. 2008, Wiley-VCH.

Uses of NKR® fibers

NKR® fibers are indicated for:

  • Aggressive environments (acids or bases).
  • Combustion environments (engines, turbines …).
  • A wide range of working temperatures: since its performance is stable from room temperature to high temperatures (melting point 2000° C, stable up to 1700° C, even in reducing atmospheres).
  • Improved creep resistance in MMC’s and CMC’s.
  • Increased hardness and abrasion resistance.
  • Improved impact resistance.

For more information on the different applicationsof the NKR® fibers, please visit Industries.

Forms of use

  • As part of MMC, CMC o PMC:
    • Used as a powder that is mixed with the original raw materials.
    • Developed as preforms for subsequent infiltration.
    • Applied to the composite through surface treatments.
  • As an insulator able to withstand high temperatures, aggressive environments and friction.

What formats are sold?

  • Fibers: Lower bulk density. Suitable for surface coating because of its insulating effect.
  • Fiber powder: Higher bulk density. Suitable for processing composite materials.

What is our intellectual property?

Neoker has designed and developed the processes for industrial manufacturing of the NKR®fibers. These processes are protected by several patents owned by Neoker.