A silver plated steel c-ring used to seal two steel pieces together was found to have contamination upon disassembly. Auger and x-ray fluorescence spectroscopy and mapping were used to identify the contaminate as molybdenum disulfide lubricant. Recommendations were made to avoid such contamination in the future

Mills, Bernice

Vu-Nguyen, Thien Q

English

DigitalCommons@CalPoly

This material is based upon work supported by the S.D. Bechtel, Jr. Foundation, National Marine Sanctuary Foundation, Carnegie Corporation of New York, and/or National Science Foundation under Grant Nos. 0952013 and 0833353. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the funders. The STAR program is administered by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the California State University. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.   SAND 2013-6428 C C-Ring Contaminate Identification by Spectroscopy and Elemental Mapping Thien Vu-Nguyen1, Bernice Mills2 1STAR, California Polytechnic State University- San Luis Obispo, 2Sandia National Laboratory, Livermore, CA A silver plated steel c-ring used to seal two steel pieces together was found to have contamination upon disassembly. Auger and x-ray fluorescence spectroscopy and mapping were used to identify the contaminate as molybdenum disulfide lubricant. Recommendations were made to avoid such contamination in the future. Abstract Background •Elastomeric o-rings had been used in a high pressure application at various temperatures. •To improve confidence of performance at  -55°C, i.e. below the glass transition temperature of the polymer, a switch was made to a metallic c-ring, a drop-in replacement. •Contamination was found on one c-ring during disassembly. Recommendation •A change from MoS2 lubricant to silver plated bolts, which serve the same purpose,  was recommended to prevent contamination. •Several advantages come from implementing the silver plated bolts. •Fewer step are required to use the bolts in the system. •No drying period is required. •The cost increase is kept to a minimum by purchasing silver plated steel bolts. Auger Spectra Spectroscopy •Auger spectroscopy is used to identify the elements in the near-surface. •Auger is sensitive to all elements except H and He. •An electron from a higher level fills the missing lower level core electron providing enough energy to release another electron, the Auger electron. •X-ray fluorescence (XRF) is similar to Auger, but instead of releasing an electron, the excess energy is released as an x-ray. •Each element has characteristic energy levels which is compared to standard spectra in a reference manual. •X-rays penetrate matter more easily than electrons; therefore XRF samples much deeper than Auger. XRF Imaging •Spectra of the debris and a clean portion of the c-ring are shown. •Silver and carbon were the principle elements on the clean portion of the c-ring. •Sulfur, molybdenum, and carbon were found on the debris. •S, Mo, C, and Ag were chosen for mapping on the basis of the spectroscopy. Figure 3. Auger spectra of the background and contaminate. Auger Imaging •Optical photography is used to locate the contamination with respect to holder before introduction into the vacuum for Auger.  •Once in the Auger Microprobe, secondary electron microscopy (SEM) is used to locate the feature for spectroscopy and mapping.  Figure 1. Optical images showing areas of interest.  •XRF, having lower spatial resolution than Auger, a larger area was mapped. That area is seen to the right in the optical image (Figure 4). •Ag, S and Mo were seen in the spectrum of the entire area. •Carbon x-ray peak at 0.282 KeV, is below the detection limit for the XRF detector, therefore no carbon map can be  shown. Figure 6. XRF spectrum of the entire mapped area. Auger Electron X-ray Figure 2. The  core hole decays emitting either an Auger electron or an x-ray. Results and Conclusion • The debris was identified as molybdenum disulfide, MoS2, commonly used as a lubricant to prevent seizing, particularly in high temperature applications. • The MoS2 may have may have been introduced during component production which included: • Spay on MoS2 lubricant to the bolts • Let the bolts dry • Install the bolts on the component Figure 8. MoS2 lubricant is applied to the bolts indicated above to prevent cold welding. XRF Spectra Ag S C Mo Figure 5. The concentration of each element is shown as false color. Figure 7. XRF images verify the contaminate to contain Mo and S. Ag S Mo Figure 4. Optical (upper left) and SEMs used to locate the area for maps. •False color is used to indicate relative concentration in the Auger elemental maps. •Molybdenum and sulfur have concentrations in similar areas which indicate the possibility of a compound. •Silver is present where there is little contamination. •Carbon is ever-present in Auger, but large concentrations indicate contaminate includes carbon. •XRF imaging shows high concentrations of molybdenum and sulfur in the same area. • The silver map is not as clear for several reasons: •The signal range is much smaller than for Mo and S. •The depth of penetration of x-rays means that we are sampling some silver through the debris. Optical SEM SEM SEM 

C-Ring Contaminate Identification by Spectroscopy and Elemental Mapping

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C-Ring Contaminate Identification by Spectroscopy and Elemental Mapping

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