Structural differences between W, WC, and W2C?

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SUMMARY

The discussion focuses on the purity assessment of a tungsten sample, revealing a composition of 66% tungsten and 33% carbon, potentially indicating contamination with tungsten carbide (WC). The sample was analyzed using Focused Ion Beam (FIB) techniques, and a density measurement of 22 g/cm³ was obtained, significantly higher than the expected density for pure tungsten. The participant questions the impact of FIB on the sample and whether the observed carbon levels could be due to surface contamination or a layer of WC. The participant also considers discussing the findings with their principal investigator (PI) due to the discrepancies in purity claims.

PREREQUISITES
  • Understanding of tungsten and its alloys, specifically tungsten carbide (WC).
  • Familiarity with Focused Ion Beam (FIB) techniques for material analysis.
  • Knowledge of density measurement techniques and their implications for material purity.
  • Experience with spectroscopic methods, particularly spectrogram analysis.
NEXT STEPS
  • Research methods for performing density calculations to assess material purity.
  • Investigate common contaminants in tungsten samples, focusing on tungsten carbide.
  • Explore the effects of FIB processing on material properties and surface contamination.
  • Learn about the implications of density discrepancies in material characterization.
USEFUL FOR

Researchers in materials science, metallurgists, and quality control analysts involved in the analysis and purity assessment of tungsten and its alloys.

Sputki
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In my research group, I'm tasked with determining the purity of a tungsten sample sent from a supplier. Using FIB, we cut a 20 by 20 by 20 micron well into the sample and tested a wall of the well about 10 microns down from the surface.

After taking a spectrogram, there seemed to be a large amount of carbon, 66% W with 33% C by atomic percentage (tungsten carbide/tungsten semicarbide?)

Although we used 2 small strips of carbon tape to mount the sample (cylinder 2 cm tall 0.5 cm diameter), we don't think there should be that much carbon on the sample. I plan to do a simple density calculation to roughly determine purity tomorrow.

What is the next step in determining purity? Is there an obvious simple test I can perform (preferably without using expensive machinery first)? Is tungsten carbide a common contaminant of tungsten? Could this just be a small layer of WC on pure W?

This link is to the SEM and EDS images themselves http://imgur.com/a/qIwIL
(You're looking at a close up of the wall of the well)
 
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As a follow up, the tungsten cylinder was measured (rather crudely with a caliper but with a precise scale) to have a density of 22 g/cm^3, which (imho) is far from the supplier's guarantee that the sample was 99.9% pure W and as such would have an i(deal) density of 19.3 g/cm^3 at room temperature (which was calculated to be 19.5 g/cm^3 at 25 C).

Could the FIB work have this big effect on the sample (which had 1.2 cm height with 0.3 cm diameter)? Could WC have formed on the surface?

Should I bring up the discrepancy with my PI? (again, actual FIB SEM work is in an imgur album in the original post).
 
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Given that the density of tungsten cabide is lower than that of tungsten, and a density as high as 22 g/cm^3 is only reached by osmium and iridium, I have some doubts concerning the precision of you density determination.
 

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