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Infrared transparent ceramic windows 2 for high-speed vehicles

 
: Ragulya, Andrey; Kolesnichenko, Valeriy; Herrmann, Mathias

:

Palestini, Claudio (Ed.):
Advanced Technologies for Security Applications : Proceedings of the NATO Science for Peace and Security 'Cluster Workshop on Advanced Technologies', 17-18 September 2019, Leuven, Belgium
Dordrecht: Springer Netherland, 2020 (NATO Science for Peace and Security. Series B, Physics and biophysics)
ISBN: 978-94-024-2020-3 (Print)
ISBN: 978-94-024-2021-0 (Online)
ISBN: 978-94-024-2022-7
ISBN: 978-94-024-2023-4
pp.85-96
Cluster Workshop on Advanced Technologies <2019, Leuven>
English
Conference Paper
Fraunhofer IKTS ()
IR transparent ceramic domes; Nanopowders of MgF2 and MgAl2O4; spark plasma sintering; sinter-forging

Abstract
The project has created new technical approaches to manufacture large size transparent ceramic windows (transparency 85% and higher in the IR part of spectrum) using advanced consolidation techniques such as 3D printing (binder jet printing of green prototypes up to 120 mm in diameter) and spark plasma sintering (enable to form domes of 70 mm in diameter). The proposed approach has required the development of ceramic nanopowders specifically formulated by internal structure to be applied in 3D binder-jet technology of meniscus-shape domes. The technologies for the synthesis of nanopowders of magnesium fluoride (MgF2) and magnesium-aluminum spinel (MgAl2O4) have been developed, and batches of 3 kg of the both powders have been manufactured. According to the results of the analysis, it was found that the powders are thermally, mechanically and optically-suitable for the manufacture of IR-transparent windows. The specific surface of MgF2 powder is 38–40 m2/g, for MgAl2O4 powder it is 27 m2/g. Shaping technologies by slip casting and 3D-printing suitable for sintering under pressure have been developed. Granules from KPI powders and Baikovsky powders have been prepared. Based on the granules a printing process has been developed using CJP 360 printer. Before sintering stage, the FEM calculations of the press instrument design and shape were carried out and optimal construction providing uniform temperature and strain rate distributions were defined. FEM simulation of the sample under pressure consolidation conditions (spark-plasma sintering and hot pressing) resulted in manufacturing of molds valid for the pilot production of dome-shaped windows. Optimization of the graphite press mold using FEM allows five times shortening of operation regime. The developed technologies of spark-plasma sintering (SPS) and hot pressing (HP) are key-enable technologies to produce transparent (88% and above) in the IR range. It has been shown that rapid sintering conditions (heating rates above 100 °C/min) and variable pressure application can achieve high values of density (above 99.95% of theoretically possible) and optical transparency (up to 91%) and avoid excessive grain growth. In this way, SPS-forging allows manufacturing of infrared lenses from both MgF2 and MgAl2O4 for complex windows for sensors. For spark-plasma sintering in sinter- forging mode, it was first performed for optical materials. It was found that the strain rates at high temperatures correspond to the superplastic deformation rates 1*10−3 to 5*10−3 s−1. The experimental batch of 10 pieces was used for aerokinetic tests. Studies of the properties of manufactured samples of IR-windows have demonstrated the feasibility of the proposed technological approaches (spark-plasma sintering or hot pressing) for the pilot production of dense homogeneous ceramics from magnesium fluoride (MgF2) and magnesium-aluminum spinel (MgAl2O4) with a fairly high level of transparency (higher than 88–91%) in the infrared diapason. Specific design of this graphite instrument was helpful to manufacture optically transparent domes with uniform transparency up to 91%.

: http://publica.fraunhofer.de/documents/N-596829.html