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Osmium Alloys and UV reflection

by rppearso
Tags: alloys, osmium, reflection
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rppearso
#1
Jul29-14, 08:22 PM
P: 107
So I was reading that Osmium will break down into a poison oxide gas if it is heated in the presence of air. If Osmium is blended into an alloy will that eliminate its ability to oxidize in such a manner.

I have been looking at Osmium as a UV reflective material but poison gas break down is an extremely negative side effect.

Are there any other materials that have a VERY high reflection of very short wave length UV radiation, far from the visible spectrum?
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Baluncore
#2
Jul30-14, 09:10 AM
Sci Advisor
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P: 1,958
There may always be a problem with osmium in the presence of UV generated ozone.
If you vacuum deposit onto a surface, then toxicity problems may occur when the vacuum chamber is opened.

Does osmium oxide form on a UV radiated surface?
Does osmium evaporate from a UV radiated surface?
Osmium metal is very hard, what is the bond energy?

Alloys usually have a lower temperature eutectic than either of the alloy components. So I doubt if it will be any advantage to alloy osmium compared to the pure metal in the presence of short UV and ozone.

Osmium is usually found alloyed with iridium, as the mineral “osmiridium” or “iridosmium”.
They were once used predominantly to electroplate the nibs of fountain pens to give a very hard polished finish.

If you are coating a non-conductive material, it should be possible to first vacuum deposit a film of say copper or platinum, then follow that by electroplating with osmium. The selection of the base metal may influence the osmium evaporation or oxidation rate.

Is it possible to eliminate oxygen from the mirror by flooding the chamber with a heavy inert gas?
Baluncore
#3
Aug3-14, 10:09 AM
Sci Advisor
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P: 1,958
Extracts from;

Osmium atomic-oxygen protection by an iridium overcoat for increased extreme-ultraviolet grating efficiency.
Richelieu Hemphill, Mark Hurwitz, and Maria G. Pelizzo
1 September 2003 Vol. 42, No. 25 APPLIED OPTICS 5149

ABSTRACT.The deposition of a 30-Å-thick layer of iridium upon a 250-Å-thick osmium reflective layer for use as a diffraction grating in the Cosmic Hot Interstellar Plasma Spectrometer #CHIPS# satellite observatory has provided sufficient protection from an expected maximum orbital atomic-oxygen fluence of 1 # 1016 atoms#cm2. The grating parameters of groove constant and depth, efficiencies of zeroth-order, first and second inside orders, and first inside-order efficiency positional uniformity as well as stray light near the first inside order of the Ir–Os-coated grating were measured within a CHIPS spectral bandpass of 90–260 Å. Stray-light measurements were also made near the first inside spectral order at 304, 584, and 1216 Å. The results make the Ir–Os coat an acceptable grating reflectivity layer for CHIPS and other spaceborne extreme-ultraviolet spectrometers that employ grazing-incidence reflection optics.
© 2003 Optical Society of America
OCIS codes: 050.2770, 290.5820, 310.1620, 310.6860.
2. Ir–Os–Ir Layer Reflectivity.
Before we proceeded with deposition of the grating coating, a sample consisting of an Ir–Os bi-layer on top of an Ir-coated glass slide #Ir–Os–Ir# was designed, fabricated, and characterized to verify the EUV optical properties of the Ir–Os bilayer.
3. Ir–Os–Rh-Coated Grating.
Given the Ir–Os–Ir flat’s reasonable measured reflectivity values at the input light’s grating facet angles for greater than 90% of CHIPS bandpass and its ability to withstand the environmental constraint of atomic O, a CHIPS grating that had been poorly coated with 150 Å of Rh was overcoated with 250 Å of Os and then 25 Å of Ir to permit the grating’s EUV diffraction efficiency and scattering along its dispersion direction to be examined. The original Rh coating of the grating was deemed to be poor owing to its low-EUV first-, second-, and zero-order measured efficiencies compared to five other otherwise identical gratings also coated with Rh.


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