Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

20000064096 NASA Glenn Research Center, Cleveland, OH USA
Mechanical, Chemical and Microstructural Characterization of Monazite-Coated Silicon Carbide Fibers
Bansal, N. P., NASA Glenn Research Center, USA; Wheeler, D. R., NASA Glenn Research Center, USA; Chen, Y. L., DYNACS
Engineering Co., Inc., USA; June 2000; 24p; In English
Contract(s)/Grant(s): RTOP 523-31-13
Report No.(s): NASA/TM-2000-210208; E-12328; NAS 1.15:210208; No Copyright; Avail: CASI; A03, Hardcopy; A01, Microfiche
Tensile strengths of as-received Hi-Nicalon and Sylramic fibers and those having monazite surface coatings, deposited by
atmospheric pressure chemical vapor deposition, were measured at room temperature and the Weibull statistical parameters determined.
The average tensile strengths of uncoated Hi-Nicalon and Sylramic fibers were 3.19 +/- 0.73 and 2.78 +/- 0.53 GPa with
a Weibull modulus of 5.41 and 5.52, respectively. The monazite-coated Hi-Nicalon and Sylramic fibers showed strength loss of
approx. 10 and 15 percent, respectively, compared with the as-received fibers. The elemental compositions of the fibers and the
coatings were analyzed using scanning Auger microprobe and energy dispersive X-ray spectroscopy. The LaPO4 coating on Hi-
Nicalon fibers was approximately stoichiometric and about 50 nm thick. The coating on the Sylramic fibers extended to a depth
of about 100 to 150 nm. The coating may have been stoichiometric LaPO4 in the first 30 to 40 nm of the layer. However, the surface
roughness of Sylramic fiber made this profile somewhat difficult to interpret. Microstructural analyses of the fibers and the coatings
were done by scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction. Hi-
Nicalon fiber consists of fine beta-SiC nanocrystals ranging in size from 1 to 30 mn embedded in an amorphous matrix. Sylramic
is a polycrystalline stoichiometric silicon carbide fiber consisting of submicron beta-SiC crystallites ranging from 100 to 300 nm.
Small amount of TiB2 nanocrystallites (approx. 50 nm) are also present. The LaPO4 coating on Hi-Nicalon fibers consisted of
a chain of peanut shape particles having monazite-(LA) structure. The coating on Sylramic fibers consisted of two layers. The
inner layer was a chain of peanut shape particles having monazite-(LA) structure. The outer layer was comprised of much smaller
particles with a microcrystalline structure.
Author
Silicon Carbides; Fiber Composites; Microstructure; Mechanical Properties; Coating; Amorphous Materials; Chemical Composition
20000064098 NASA Marshall Space Flight Center, Huntsville, AL USA
Metallurgical Evaluations of Depainting Processes on Aluminum Substrate Final Report
McGill, Preston, NASA Marshall Space Flight Center, USA; December 1999; 25p; In English; Original contains color illustrations;
No Copyright; Avail: CASI; A03, Hardcopy; A01, Microfiche
In December 1993, the Environmental Protection Agency (EPA) Emission Standards Division and the National Aeronautics
and Space Administration’s (NASA’s) Marshall Space Flight Center (MSFC) signed an Interagency Agreement (IA) initiating
a task force for the technical assessment of alternative technologies for aerospace depainting operations. The USA Air Force
(USAF) joined the task force in 1994. The mandates of the task force were: (1) To identify available alternative depainting systems
that do not rely on methylene chloride or other ozone-depleting, chlorinated, and volatile organic carbon solvents. (2) to determine
the viability, applicability, and pollution prevention potential of each identified alternative. (3) to address issues of safety, environmental
impact, reliability, and maintainability. Through a Technical Implementation Committee (TIC), the task force selected and
evaluated eight alternative paint stripping technologies: chemical stripping, carbon dioxide (CO2) blasting, xenon flashlamp and
CO2 coatings removal (FLASHJET(R)), CO2 laser stripping, plastic media blasting (PMB), sodium bicarbonate wet stripping,
high-pressure water blasting (WaterJet), and wheat starch abrasive blasting (Enviro-Strip(R)). (The CO2 blasting study was discontinued
after the first depainting sequence.) This final report presents the results of the Joint EPA/NASA/USAF Interagency
Depainting Study. Significant topics include: (1) Final depainting sequence data for the chemical stripping, PMB, sodium bicarbonate
wet stripping, and WaterJet processes. (2) Strip rates for all eight technologies. (3) Sequential comparisons of surface
roughness measurements for the seven viable depainting technologies. (4) Chronological reviews of and lessons learned in the
conduct of all eight technologies. (5) An analysis of the surface roughness trends for each of the seven technologies. (6) Metallurgic
evaluations of panels Summaries of corrosion and hydrogen embrittlement evaluations of chemical stripping panels, detailed
descriptions of which appear in previous reports. Because the requirements for alternative systems are diverse, as are initial setup,
training, and on-going operational considerations, this study does not recommend a particular product or process. Users of this
study will draw their own conclusions from the data presented herein.
Author
Carbon Dioxide; Carbon Dioxide Removal; Environment Protection; Exhaust Emission; Exhaust Gases; Maintainability; Methylene;
Paint Removal; Pollution Control; Technology Assessment
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