Final Report - Strategic Environmental Research and Development ...

number of counts. However, the counts could not be converted to concentration, so the signal
intensity indicated only the relative magnitude of elemental concentration at each pixel.
In this analysis there was no correction for absorption atomic number or fluorescence. A
technique was developed to make comparative assessments of particle dissolution. The average
(Ave) of the elemental X-ray signal intensity in a fixed area on a particle was used to estimate
particle dissolution. Increasingly larger areas with radii of 5, 10 and 15 pixels were analyzed
depending on the size of the particle. The center of the circle in which analysis was conducted
was set as that with the highest average signal intensity across the selected pigment within radius
of 5 pixels. The center selected did not only rely on its own intensity value, but the intensity
values of the pixels around it. This method eliminated the possibility of selecting single pixel
with unusually high intensity, which might not have seen the real center of the particle. When
selecting a single particle for analysis, it was found that sizes and shapes of the particles were
varied, even though the particles had similar elemental types. In order to limit the differences
caused by shape and size, the pigments selected were larger than 30 pixels in any direction and
the shape was close to spherical. However, the size of pigments could not be too large in case
that the center of the pigments did not dissolve during exposure due to its large size. As an
example, the fixed area for calculating average of calcium intensity within Hentzen 16708 TEP
was shown in Figure 6.26. A similar evaluation was done for calcium and praseodymium within
Deft 02N084, and barium within Sicopoxy 577-630. For the deft primer, the size of
praseodymium-enriched pigments was small, so the radius of fixed area was limited to 5 and 10
pixels respectively. The percentage decrease of elemental signal intensity within fixed area was
collected in order to see whether particle dissolved and soluble products spread out through the
surrounding polymer. The calculation for estimating decrease in elemental signal intensity was:
(eq. 6.3.1)
where I 5 is the average signal intensity of the fixed area within radius of 5 pixels and I b is the
average signal intensity of within radius of 10 or 15 pixels depending on the area selected. The
smaller the percentage residue, the higher the dissolution rate during the same amount of time.
Calculations were carried out for each element on multiple particles. Only the values of average
percentage decrease (APD) are shown in Tables 6.8—6.11. Average intensity of the fixed area of
particles within each primer is shown in Appendix 6A.
302