surface pretreatment by phosphate conversion coatings – a review
surface pretreatment by phosphate conversion coatings – a review
surface pretreatment by phosphate conversion coatings – a review
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160 T.S.N. Sankara Narayanan<br />
Fig. 13. Infrared spectra of α-hopeite and phosphophyllite<br />
in the region 4000<strong>–</strong>1400 cm -1 (Reprinted<br />
from Spectrochimica Acta Part A, Vol. 57, O.<br />
Pawlig, V. Schellenschlager, H.D. Lutz and R.<br />
Trettin, Vibrational analysis of iron and zinc <strong>phosphate</strong><br />
<strong>conversion</strong> coating constituents, pp. 581-590<br />
(2001) with permission from Elsevier Science).<br />
monitored. QCIS is also used to measure the change<br />
in viscoelasticity of zinc <strong>phosphate</strong> <strong>coatings</strong>, which<br />
decreases with increase in phosphating time and<br />
the concentration of sodium nitrite [330].<br />
The utility of GDOES in the analysis of <strong>phosphate</strong><br />
<strong>coatings</strong> has been attempted <strong>by</strong> several authors<br />
[331-334] and <strong>phosphate</strong> <strong>coatings</strong> deposited<br />
on cold-rolled, hot-dipped galvanized, galvanneled,<br />
electrogalvanized and Zn-Ni or Zn-Fe electroalloycoated<br />
sheets were characterized. It has been reported<br />
[331] that the profiles of the elemental distribution<br />
throughout the film thickness can be obtained<br />
with high sensitivity. GDOES provides more detailed<br />
information on the constituent elements, depth, di-<br />
Fig. 14. Infrared spectra of α-hopeite and phosphophyllite<br />
in the region 1200<strong>–</strong>100 cm -1 (Reprinted<br />
from Spectrochimica Acta Part A, Vol. 57, O.<br />
Pawlig, V. Schellenschlager, H.D. Lutz and R.<br />
Trettin, Vibrational analysis of iron and zinc <strong>phosphate</strong><br />
<strong>conversion</strong> coating constituents, pp. 581-590<br />
(2001) with permission from Elsevier Science).<br />
rection and the crystal growth process than conventional<br />
chemical and X-ray methods. Quantification<br />
of the results has also been attempted in the<br />
case of GDOES based on the integrated intensity<br />
of the constituent elements. Maeda et al. [331] have<br />
suggested the possibility of utilizing this method for<br />
quantitative determination, after establishing a linear<br />
relationship between integrated intensity and<br />
coating thickness of phosphorus and nickel.<br />
GDOES is considered to be the most appropriate<br />
method for depth profiling thick <strong>phosphate</strong> <strong>coatings</strong><br />
[335]. GDOES due to its higher detection sensitivity<br />
compared to XPS, confirms the adsorption of<br />
titanium <strong>phosphate</strong> on zinc coated steel [328].
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