HOW THE RAREST GEMSTONES IN THE WORLD

High Temperature optical armor ceramics (spinel)
Spinel [MgAl2O4] is a cubic crystalline material with unique combination of ruggedness and excellent
transmission from the ultraviolet [0.2 mμ ] to the mid infrared [5 micrometer] region. This positions
spinel as the de facto material of choice for the numerous defense department and commercial infrared
window applications-DDG destroyer, submarine high energy lasers, domes of missiles and rockets, night
vision devices etc.
The poor quality of commercial spinel ceramics in attributed to the inhomogeneous mixing of the
sintering aid with spinel powders.
This leads to porosity and trapped sintering aid. NRL has developed a novel and patented process to
uniformly coat the sintering aid on to every spinel powder particle and enable it to be removed during
hot pressing process at around 16000
C. This enables full densification and fabrication of uniformly
transparent high optical quality spinel ceramic. It is possible to make thick windows and conformal
optics, including lenes and dome shapes.
Dr. Petrik has developed spinel making process by pressing powders obtained by sol gel method, which
gives high uniformity of the mixture. The workshop, which is deep in jungles was shown to us. The
facility has double screw press, electric furnace, a tank and control systems. It occupies a space of about
10 x 5 x 3 m.
The production of high quality transparent ceramic demands both careful powder synthesis and close
control during densification. Ballistic test were conducted on ceramics to check structural behavior.

The spinels produced by Prof. Petrik's lab were evaluated by defense institutes, measurement of sample
spectral characteristics confirmed high optical transmittance and X-ray structural checks confirmed that
delivered ceramic is a polycrystalline spinel. The technology for synthesis of transparent armor ceramics
is developed in Russia which has wide applications in items operating under extreme loads and
development of this ceramics is an outstanding scientific achievement

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