Nondestructive testing of defects in adhesive joints

composites containing nano additives as well as conducting PANI should improve tremendously
the barrier properties of coatings as well as self healing effect giving large advantage in
anticorrosion behaviour. Hence, the present studies were carried out on the preparation of nano
TiO2-PANI hybrid coating formulations using polyvinyl butyral (PVB) as the matrix and
investigating their suitability for anticorrosive coatings.
2. Experimental:
2.1 Material
Aniline (ANI) ( AR, Spectrochem Pvt. Ltd. India ) was purified by distillation, 38% hydrochloric
acid ( AR,Ranbaxy), TiO2 particles, ammonium peroxodisulphate ( APS, AR, Spectrochem Pvt.
Ltd, India) and methanol (E Merk ) were used as such. Poly vinyl butyral (PVB) with M.W.
60,000 was obtained as granules from ABC Chemicals Exporter, Mumbai, India.
2.2 Preparation of PANI-TiO2 composites of different PANI-TiO2 ratio
To prepare PANI-TiO2 composites of different ratios, the following steps were followed. 0, 0.1,
0.2, 0.3 and 0.5 g of TiO2 nanoparticles (prepared according to procedure reported earlier ) were
added into a mixture of 1ml aniline and 90ml 1N HCl in a set of reaction vessels. The mixtures
were stirred with magnetic stirrers in ice water baths for one hour to get a uniform suspension of
TiO2. To these mixtures, 100 ml pre-cooled 1N HCl solutions containing 2.5 g APS were added
drop wise. The resulting mixtures were allowed to react in ice bath for about four hours. From
these reactions we get pure PANI and TiO2-PANI composites with compositions given in Table-
1A. The products were washed with distilled water for several times and at last washed with
methanol to remove low molecular weight oligomers along with other impurities. Then all
samples were dried in an oven for 12 hours. These samples were characterized by UV, IR, XRD,
SEM and TEM in the usual manner.
2.3 Preparation of PANI-TiO2 dispersion formulations for coating
PVB (2g) was dissolved in methanol (20 ml) with continuous stirring for 6hr and then in a
sonicator for few hours. The 10 wt % of PANI-TiO2 powder having different compositions was
crushed and slurry was made with small quantity of methanol. The slurry was added and mixed in
the PVB solution and subjected to sonication for 24 Hrs. This yielded a uniform dispersion of
PANI-TiO2 in the PVB solution with no settling. The stainless steel coupons (50mmx 10mmx
1mm) with rounded corners and edges were polished by C- 800 emery paper, washed with
acetone and dried. The substrates were dip coated for 30 sec in PVB/PANI-TiO2 dispersion and
dried at room temperature for 30 min followed by baking in air circulating oven at 50 0 C for 4 hr.
The samples were cooled and then subjected for measurement of corrosion inhibition properties..
2.4 Testing of corrosion resistance properties
Tafel plot and impedance measurements were carried out in 3.5 % NaCl solution as electrolyte.
All measurements were performed on computerized electrochemical analyzer (supplied by CH
instruments, USA). Stainless steel plates coated with the PANI-TiO2 composites were used as
working electrode while Pt and SCE were the counter and reference electrodes respectively. The
voltammograms were measured between +1 to –1 V at a scan rate of 50 mV/s. Tafel plots was
recorded at a scan rate of 10 mV/s. After initial measurements all the coupons were immersed in
an external bath with hot 3.5 % NaCl solution (65 o C) for a period of 4 hrs so that accelerated
testing could be carried out. The coupons were then again subjected to electrochemical
measurements at an interval of 4 hours as described above [10, 19]. Micrographs of corroded
samples were recorded on polarized optical microscope fitted with digital camera (model Leica
Stereoscan 440, UK).