Test settings

2.2.2.1 Field corrosion tests

The influence of the urban environment on the bronze corrosion was studied by exposing the three alloys for 5 weeks (from March 2010 to April 2010) at the Department of Analytical Chemistry (Ghent University, Belgium) towards the North-West. Others samples sets were exposed at the Faculty of Engineering (Sapienza University of Rome) towards South and at 45^° of inclination from January 2011 to June 2011. The set-up is shown in Figure 2.7

Fig. 2.7: Photographs of the in field urban exposition in Ghent (left) and in Rome (right).

For the marine environment the samples were exposed in a coastal town (Fiumicino) from January 2011 to May 2011.The weather conditions during the exposure tests are reported in Table 2..

Months Average

°C

Min

°C

Max

°C RH%

Average wind Km/h

Rain days

Storm days

Fog days GHENT 2010

March 7 3 11 72 14 15 2 3

April 10 5 16 64.8 11 10 0 2

ROME 2011

January 7.6 4.3 12.1 83.5 4.8 13 3 /

February 7.3 3 13.9 72.2 4.4 5 3 3

March 10.2 6.1 14.8 79.4 6.4 12 6 2

April 14.5 9.4 20.2 73.8 5.3 10 3 1

May 18.2 12.3 24.3 69.3 6 8 8 0

Jun 22.6 17.3 27.9 68.1 6 7 3 0

FIUMICINO 2011

January 8.5 4.7 12.7 83.6 6.8 16 1 5

February 7.8 2.8 13.4 74 8.8 6 3 6

March 10.7 6.5 14.6 79.8 9 11 2 2

April 14.6 9.1 19.7 76.2 7 10 1 3

May 18.1 11.9 23.5 73.2 8 9 2 4

Jun 22.1 16.9 26.5 75.6 8.1 8 2 1

The samples were oriented towards the south and had an inclination of 45° following the ISO 9223 standard as in Rome [37]. Figure 2.8 shows the set-up.

Fig. 2.8: Rake expositor in field urban exposition in Rome and Fiumicino (Italy).

2.2.2.2 Laboratory tests

A chamber for the corrosion tests was assembled in order to have homogeneous vapor diffusion and deposition. The position of the vapor exit hole on the chamber (volume: 45 cm³) from which the vapor was introduced, as well as the flow rate of the solutions vapor, was optimized to avoid the formation of water film on the surface and to obtain a drop deposition.

The circular coupons were installed on columns of 2 cm in height, inclined to 45° and 1.5 cm far from each other to avoid contamination between samples.

Figure 2.9: Chamber for the corrosion tests.

Wet and dry cycles were performed six times per day, spraying 0.66 mL of vapor per cycle.

The daily wet and dry cycles were carried out as follows: 30 minutes between the first three vaporizations; 2 hours between the 3^rd and 4^th hour; 30 minutes between the 4^th-5^th and 5^th-6^th hour; 17

hours between the last vaporization and the first vaporization of the following day. After seven days of cycles, the samples were dried for two days.

In order to simulate an urban environment, synthetic acid rain was sprayed on samples. In order to simulate a marine environment synthetic sea water was sprayed.

Figure 2.10 shows the graphs of the relative humidity (RH%) during the wet and dry tests performed at 25°C. The measurements were done after 2 hours, 4 hours, 24 hours, 48 hours, 96 hours, 240 hours as suggested by ISO 4536 [38].

0 50 100 150 200 250 300 350 400 450

Fig. 2.10: R.H.% during the wet and dry tests in the vapor chamber. (a) during the week; (b) after the weekend.

The samples were vaporized with the above wet and dry cycles with a synthetic solution of acid rain [39] and synthetic sea water [40]. The compositions are reported in Table 2.3.

Tab. 2.3: Synthetic acid rain and sea water solutions composition [39-40].

The effects on the bronze corrosion of long time wetness was tested with immersion in the solution of synthetic acid rain and in its major acid constituent (H2SO4 and HNO3 both 0.1 M) for five weeks.

ACID RAIN SEA WATER

Component (mg/dm³) Component (g/dm³)

H2SO4 (96%) 31.85 KBr 0.1

Figure 2.11: Immersion corrosion test in synthetic acid rain and in 0.1 M H2SO4 and 0.1 M HNO3.

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