Nondestructive testing of defects in adhesive joints

This is further evidenced from the impedance plots (Bode) indicated in Figures 5 recorded after
40 hrs exposure to hot saline conditions. It can be seen from these figures that PANI-TiO2-4.18%
has higher resistance than the coatings without TiO2 especially at low frequency which is
associated with ionic transport through the film. This continues to remain high even after
exposure to the corrosive environment. The accelerated testing conditions used in the present case
are equivalent to testing for more than 800 hrs at room temperature which is derived using the
reported logarithmic relations for corrosion rate of steel with temperature which gives about 10X
as acceleration constant [21,22 ]. Thus, there is excellent corrosion protection obtained in these
coatings especially when PANI-TiO2 (4.18%) powder is used as an additive even at low level of
loading (10wt %).
Log IZI (Ohm)
1.00E+06
1.00E+05
1.00E+04
1.00E+03
1.00E+
00
1.00E+
01
1.00E+
02
1.00E+
03
Frequency (Hz)
1.00E+
04
1.00E+
05
2.3% TiO2
2.8% TiO2
4.18% TiO2
0% TiO2
Figure: 5.Bode plots of PVB/PANI-NanoTiO2 coatings after 40 hr immersion at 65 0 C saline
solution
The low frequency data in Bode plots has been associated with the diffusion processes and as
mentioned above it indicates to some extent that nano-TiO2 leads to such improvement. However,
there is also an additional cause for further improvement of corrosion resistance especially when
one considers that the total concentration of the additive in the formulation was same (10%) in all
cases.
4. Conclusions:
The conducting PANI nano-particulate TiO2 hybrid composites prepared by in situ
polymerization were used for coating with PVB as the matrix. The effect of addition of nano
TiO2 on the improvement of has been clearly brought out The novelty of these coatings lies in
generation of corrosion inhibition by three mechanisms operating simultaneously viz.
improvement of barrier properties, redox behaviour of PANI and formation of p-n junctions
preventing easy charge transport when coating is threatened to be destroyed due to scratch or
scribble. Even if the main resin is damaged, the additives give a healing effect and prevent
catastrophic failure. Apart from the prevention of corrosion, these coatings have good gloss and
shiny surface, which is not easily obtained in conventional coating, prepared with commercial
micron size particle additives. Such systems can be used as a primer coat or even as a single
coating on steel where colour is not a very important criterion.