Interesting Examples of SEM Analyses
Syringe: Rubber or Silicone Rubber?
The question was raised as to the composition of the "rubber" used in a plastic hospital syringe. Using the variable pressure mode of the SEM, the only preparation required was to cut the plastic plunger arm and place the rubber fittings onto the adhesive carbon tape sample holder.
SEM analysis clearly showed two kinds of inner syringe fittings. One showed brighter BEI image and on closer examination of both the surface and internal structure, it could be seen to be silicone rubber containing filler particles of BaSO4 and Aluminum Silicates. The BaSO4 was most likely added for radiologic contrast should portions accidentally get into the patient. These particles range in diameter from <1 to >10 µ The other fitting was the same density and composition as the plastic of the syringe (Carbon and Sulfur) with irregular patches on the surface consistent with silicone oil lubrication. These findings are well demonstrated in the x-ray spatial distribution map.
During a re-roofing in 2003, samples of various materials, including various roofing nails, old asphalt shingles from ca. 1950 and ca. 1978, and new asphalt shingles from 2003, were collected for examination of the types of particulates by SEM/EDS. The roofing shingles consisted of a carbon-based material as a matrix, in which small stones, composed mainly of aluminum-silicates, iron, and titanium, were embedded. This matrix was reinforced by organic fibers in the older shingles, and by fibrous glass in the new shingles.
The roofing nails were composed mainly of zinc. One of the older nails showed deposits of lead scattered over its surface. The newest nails were soldered to copper wire, with an iron-based solder. This solder also contained particles composed of tungsten, rhenium, and selenium.
During a recent wall repair, samples of wall-building materials were collected for SEM/EDS analysis. Samples included "rock wool" fibrous glass from ca. 1950, new fibrous glass from 2003, and gypsum drywall from ca. 1950.
The "rock wool" showed numerous globules of glass among the fibers, while the new fibrous glass was more homogeneous, showing very few globules. The two differered compositionally as well; the "rock wool" showed large peaks of Ca, Mg, and Si, and a small peak of Al, while the new insulation showed large peaks of Na and Si with smaller peaks of Mg, Al, and Ca.
The drywall was composed of fibers of CaS, with numerous strontium-containing particles embedded among the CaS fibers. Strontium often is found associated with calcium.
What Particulate Matter is in Cardboard?
SEM/EDS investigation of dust exposures related to cardboard manufacture raised the question of what various samples of cardboard might contain. Therefore, samples of at-hand cardboard boxes were taken and examined in the SEM, using the variable pressure mode, so that no conductive coating was required.
This photo illustrates the two samples initially examined. One was white outer cardboard from a box used for shipping styrofoam-insulated containers. The other was a plain brown cardboard from a box at a local home supply store.
The SEM/EDS illustrations (left) of the white cardboard show the surface and internal paper fibers. Note higher BSE contrast for the surface than the internal fibers. This correlates with a general increase in Calcium(Ca) noted in the EDS analysis of areas of the paper fibers lacking additional particles within the resolution of the SEM under these operating conditions.