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Military engineering
– Military reconnaissance
MILITARY ENGINEERING // MARINE // MILITARY RECONNAISSANCE // ARMAMENTS // PERSONAL AND EQUIPMENT PROTECTION
In equipment for military purposes, components made of oxide or non-oxide ceramics are used predominantly when the required performance features cannot be guaranteed with agreed reliability and precision.
For night-vision devices, for instance, windows made of transparent Al2O3 in the form of monocrystalline leucosapphire are used as this material is permeable to wavelengths in the range from 250 – 5 000 nm. As, on the basis of the MoMn process, the leucosapphire can be soldered and firmly bonded high-vacuum-tight with metallic partners like, for example, Ni42 (1.3917) or NiCo2918 (1.3981), welded joints with other equipment components can be realized. Soldered component diameters of 50 mm and larger can be realized without any problem with a suitable cut of the sapphire disc.
Some technical properties of the leucosapphire can be summarized as benchmarks with reference to standard conditions, the data areas specified in the following predominantly indicating the anisotropic character of its crystal structure:
- Optical transmission range: 250 – 5 000 nm
- Refractive index: (nw) = 1.767 – 1.772, (ne) = 1.759 – 1.763
- Birefringence: (δ) = 0.008 – 0.009
- Specific electrical resistance: 1014 Ohm*cm
- Dielectricity constant: 8.6 – 11
- Density: 3.99 g/cm³
- High resistance to wear and scratches
- Surface quality in line with MIL standards
- Tensile strength at room temperature: 185 MPa
- Compressive strength at room temperature: 2 000 MPa
- Modulus of eleasticity: 400 GPa
- High chemical corrosion resistance
- High thermal and thermomechanical strength
- Thermal expansion: 5.5 – 6.5 ppm/K
- Thermal conductivity: 35 – 40 W/m/K
As carriers for lens systems in satellites and unmanned aircraft, dense-sintered ceramic components made of Al2O3 and Si3N4 are expedient as these materials enable extremely high imaging precision. Selected important technical properties for such applications are listed in the following:
- Low component weight owing to low material density
- High strength level over long periods
- High fracture toughness
- High modulus of elasticity and consequently high stiffness of the structure
- Low thermal expansion
- No embrittlement at low temperatures
Both types of materials and here especially dense-sintered Si3N4 ceramics are suitable for such carrier systems as they enable an optimum combination of the above-listed properties.
