Towel bar - Al Alloy - Modern Times - France

Towel bar - Al Alloy - Modern Times - France

Towel bar

Christian. Degrigny (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland)

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Credit HE-Arc CR, J.Schröter.

Fig. 1: Front and back sides of a towel bar,

Towel bar with traces of use and a broken section (Fig. 1). White deposits have developed on the metal surface. Dimensions: L = 45cm.

Household implement

Château de Germolles, Mellecey, Bourgogne, France

Unknown

Modern Times

19th - 20th century

Indoor atmosphere

Château de Germolles, Mellecey, Bourgogne

Château de Germolles, Mellecey, Bourgogne

None

Not conserved

Complementary information

Nothing to report.

Credit HE-Arc CR, J.Schröter.

Fig. 2: Detail of the back side of the towel bar showing the location of the sampling area,

Stratigraphic representation: none.

Credit HE-Arc CR, J.Schröter.

Fig. 3: SEM image of the cross-section showing the location of Fig. 5,

Sample cut from the back side of the towel bar (Fig. 2).

Al Alloy

None

HE-Arc CR, Neuchâtel, Neuchâtel

HE-Arc CR, Neuchâtel, Neuchâtel

2017, the EtICAL project (a study of corrosion forms of aluminium alloys)

Complementary information

Nothing to report.

Analyses performed: 
Metallography, SEM/EDS.

The metal is a relatively pure aluminium alloy with numerous inclusions (Fig. 5). From their chemical composition they can be interpreted as Al3Fe intermetallic compounds (Fig. 6). Pitting corrosion as well as a start of intergranular corrosion develops locally under the deposits, outlining some of the grains (Fig. 5). 

Credit HEI Arc, S.Ramseyer.

Fig. 5: SEM image of the metal sample from Fig. 3 (detail), BSE-mode. We observe the presence of numerous inclusions,

Credit HEI Arc, S.Ramseyer.

Fig. 6: EDS spectrum of the inclusions of Fig. 5,

None

Al

Fe

Complementary information

Nothing to report.

A very thin and loose oxide film has formed on the metal surface (CP1) and is locally covered by white deposits (D1). Intergranular corrosion has developed under the deposits (Fig. 7). Analysis by SEM-EDS indicates that the Al and O-rich oxide layer is contamined with P and Si (area 1 on Fig. 7 and Fig. 8). These elements are even more present at the interface between CM1 and CP1 with Cl and S (area 2 on Fig. 7 and Fig. 9). The concentration of P and Si decreases in CM1 (area 3 on Fig. 7 and Fig. 10) while the concentration of S and Cl increases (Fig. 11). The deposit is mainly constituted of Ca, O, C and Si (probably CaCO3 and SiO2, area 4 on Fig. 7 and Fig. 12).

Credit HEI Arc, S.Ramseyer.

Fig. 7: SEM picture with location of EDS analyses of areas 1 to 4), BSE-mode. From bottom to top: the metal (M1) in light grey, the corroded metal (CM1), CP1 and D1,

Credit HEI Arc, S.Ramseyer.

Fig. 8: EDS spectrum of area 1 of Fig. 7,

Credit HEI Arc, S.Ramseyer.

Fig. 9: EDS spectrum of area 2 of Fig. 7,

Credit HEI Arc, S.Ramseyer.

Fig. 10: EDS spectrum of area 3 of Fig. 7,

Credit HEI Arc, S.Ramseyer

Fig. 11: EDS Linescan from CM1 to M1,

Credit HEI Arc, S.Ramseyer.

Fig. 12: EDS spectrum of area 4 of Fig. 7,

Multiform - intergranular

None

Complementary information

Nothing to report.

Fig. 4: Stratigraphic representation of the object in cross-section using the MiCorr application. This representation can be compared to Fig. 9, Credit HE-Arc CR, C.Degrigny.

Corrected stratigraphic representation: none.

This aluminium alloy has a composition similar to a primary aluminium with an Al content between 99 and 99.8 mass%. The main impurity is Fe forming intermetallic (Al3Fe) inclusions. It is covered by a thin oxide layer (probably aluminium oxide). Pitting corrosion has formed under calcareous white deposits with a local distribution. It seems to develop as intergranular corrosion.

References object

1. Degrigny, C. (2018) Etude, identification des objets en aluminium patriminoniaux et classification de leurs forms de corrosion - projet EtICAL, rapport interne HE-Arc CR.

References sample

2. Degrigny, C. (2018) Etude, identification des objets en aluminium patriminoniaux et classification de leurs forms de corrosion - projet EtICAL, rapport interne HE-Arc CR.