Tuftran®

Infrared permeable windows are currently used on the optical covers of many airborne reconnaissance or navigation systems. The window material must not significantly reduce or add noise to the incoming signal and should be robust enough to withstand erosion from dust and rain during high-speed flights. CVD Zinc Selenide® (ZnSe) is an ideal candidate for this application due to its excellent transmission in the infrared range.

However, since ZnSe is a “soft” material (hardness = 110 Knoop, flexural strength = 8.000 psi), it does not effectively resist erosion from rain and dust during high-speed flight. Although zinc sulphide (ZnS) does not have the superior optical properties of zinc selenide, it is a “harder” material and therefore much more resistant to adverse environmental conditions.

Tuftran® combines the advanced optical and mechanical properties of both materials.

The Tuftran® infrared material consists of a polished ZnSe window over which a ZnS layer is chemically vapour-deposited. This ZnS layer protects the ZnSe window and improves the environmental resistance of the material, making it more resistant to rain, dust and dirt. Tuftran® has the broadband imaging properties (1-14 µm) of zinc selenide and the mechanical robustness of zinc sulphide. The resulting material offers high hardness, excellent imaging properties, is non-hygroscopic and easy to process.

Tuftran® has been custom ordered in sheets up to 24 inches in diameter. Blanks are manufactured to the surface area and zinc sulfide thickness specified by the customer. When ordering Tuftran®, please call CVD Ceramics for a technical discussion.

A coating of approximately 1 mm ZnS on a ZnSe blank is sufficient to produce a window with a rain erosion resistance equivalent to that of pure ZnS without any significant loss of the optical properties of the ZnSe. A sample of Tuftran® (25 mm diameter x 6 mm thickness, 1 mm ZnS, 5 mm ZnSe) coated on both sides with a rain erosion resistant coating COE 2203 ^*1 was tested for rain erosion resistance at the Royal Aerospace Establishment (RAE) under the following conditions:

After 20 minutes of erosion, the transmission of the sample between 8 and 12 micrometres decreased by an average of 3.0 %. This date confirms the superior performance against rain erosion.