The Development and Qualification of Thermal Control Coatings for Snap Systems Page: 51 of 75
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
The temperature dependence of the rate of diffusion follows the equation
D =Do -Q/RT (11)
where
D (cm 2/sec) = rate of diffusion,
Do = constant which is a function of the square of the interatomic
distance of the solvent,
Q (k cal/mol) = identified with activation energy and is dependent on the melting
point of the solvent,
R = gas constant, and
T = absolute temperature.
A material with a low value of Do and a high value of Q should act as a
good diffusion barrier. Thus, a material having a high melting temperature and
a closely packed crystal structure should be an excellent diffusion barrier.
Results obtained from the effort performed were unsatisfactory based on
system objectives. However, a discussion of this work is presented to provide a
foundation for future development. Work performed in development of diffusion
barriers included the investigation of metallic barriers to interpose between the
SS substrate and the low-emittance gold surface. The metallic barriers investi-
gated were chromium, nickel, palladium and rhodium. These metals, especially
the palladium system, have much higher melting points than does the gold. Both
type 316 and type 405 SS were used as the metallic substrates. Chromium and
nickel exhibit similar properties in that complete diffusion between these metals
and a gold coating surface occurs within short exposure times, < 100 hr, at
elevated temperature, 1000*F.
Initial effort performed on the palladium and rhodium diffusion barrier
systems indicated these materials were successful for high temperature expo-
sures up to 70 hr in duration. However, electrolytic deposition of a palladium
or rhodium coating between a SS substrate and a gold surface causes severe
blistering of the composite coating system at elevated temperatures. To prevent
this blistering, the SS is treated in a high-temperature hydrogen atmosphere to
remove all surface oxides and contaminants. This is only partly successful in
NAA-SR -9 908
47
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Crosby, J. R. The Development and Qualification of Thermal Control Coatings for Snap Systems, report, September 30, 1965; Canoga Park, California. (https://digital.library.unt.edu/ark:/67531/metadc1028869/m1/51/?rotate=270: accessed July 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.