Coffee filter - Al Alloy - Modern Times - France

Coffee filter - Al Alloy - Modern Times - France

Coffee filter

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 coffee filter,

Coffee filter with traces of use (deposits, deformation) and presence of local filiform corrosion (Fig. 1). Dimensions: ø.ext. = 10cm. 

Household implement

Château de Germolles, Mellecey, Bourgogne, France

Unknown

Modern Times

19th - 20th century

Outdoor 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 front and back sides of the coffee filter showing the location of Fig. 3,

Credit HE-Arc CR, J.Schröter.

Fig. 3: Detail of the back side of the coffee filter showing the location of the sampling area,

Stratigraphic representation: none.

Credit HE-Arc CR, J.Schröter.

Fig. 4: Micrograph of the cross-section showing the location of Figs. 6, 8 and 9, dark field,

Sample cut from the back side of the coffee filter (Fig. 3).

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

A second sample was taken and gave similar results.

Analyses performed: 
Metallography, SEM/EDS.

The metal is a relatively pure aluminium alloy with numerous elongated inclusions (Fig. 6). From their chemical composition they can be interpreted as Al3Fe intermetallic compounds (Fig. 7). Inter- and transgranular corrosion has developed so extensively that some grains (not elongated) are outlined (Fig. 8). 

Credit HEI Arc, S.Ramseyer.

Fig. 6: SEM image of the metal sample from Fig. 4 (detail), BSE-mode. We observe the presence of numerous elongated inclusions,

Credit HEI Arc, S.Ramseyer.

Fig. 7: EDS spectrum of the elongated inclusions of Fig. 6,

Credit HEI Arc, S.Ramseyer.

Fig. 8: SEM image of the metal sample from Fig. 4 (detail), BSE-mode. Extensive inter- and transgranular corrosion has developed within the metal,

None

Al

Fe

Complementary information

Nothing to report.

The average thickness of the corrosion layer (CP1) is about 50mm, but may be thinner or thicker depending on the area. Intergranular corrosion has developed locally to extend the whole thickness of the metal. Analysis by SEM-EDS indicates that the metal is, as expected, covered by an Al and O-rich layer containing chlorides (red spots on Fig. 9) and surprisingly Na (Figs. 10 and 11). Chlorides do not seem to form active corrosion. A new examination carried out after 4 months (Fig. 12) shows new forms of alteration with a local enrichment of Na, C and O (Na2CO3?).

Credit HEI Arc, S.Ramseyer.

Fig. 9: SEM picture (detail of Fig. 4 with location of EDS analyses of Fig. 10), BSE-mode. From bottom to top left: the metal (M1) in light grey, the corroded metal (CM1) and CP1. The mapped area of Fig. 11 is marked by a rectangle,

Credit HEI Arc, S.Ramseyer.

Fig. 10: EDS spectrum of red spots in Fig. 9,

Credit HEI Arc, S.Ramseyer.

Fig. 12: SEM image, BSE-mode, and elemental chemical distribution of the selected area of Fig. 9 after 4 months. Method of examination: SEM-EDS, Lab of Electronic Microscopy and Microanalysis, IMA (Néode), HEI Arc,

Credit HEI Arc, S.Ramseyer.

Fig. 11: SEM image, BSE-mode, and elemental chemical distribution of the selected area of Fig. 9. Method of examination: SEM-EDS, Lab of Electronic Microscopy and Microanalysis, IMA (Néode), HEI Arc,

Multiform - intergranular

None

Complementary information

Nothing to report.

Fig. 5: 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. The metal was stamped and punctured. It is covered by a relatively thick corrosion layer (probably aluminium oxide) due to filiform corrosion. Extensive intergranular corrosion has developed locally within the metal. Chlorides have been identified but the progress of the corrosion might be due to Na, C and O-rich compounds (Na2CO3?).

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.