publication . Thesis

Shiny helmets: investigation of tinning, manufacture and\ud corrosion of Greek helmets (7th-5th c. BC).

Manti, Panagiota;
Open Access English
  • Country: United Kingdom
Abstract
This thesis examines surface finishes and tinning on Archaic period (7th-5th c. BC) Greek\ud helmets. Experiments are designed to review and further understanding of what comprises\ud evidence of tinning on low-tin archaeological bronzes and to investigate the efficacy of\ud common and non-destructive methods for its detection. Methods examined include SEM,\ud XRD and neutron diffraction. Problems related to composition analysis are identified and the\ud thesis offers new data on the corrosion profiles of low tin bronzes, which adds to current\ud understanding. A ternary diagram to aid interpretation of compositional data is proposed. This\ud thesis also provide...
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free text keywords: CC
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.....................................................................................................................................................................221 Table 6.10: Summary of observations with regards to predominant deposit, physical nature of corrosion profiles and chemical composition in the outer corrosion zone.............................................222 Table 6.11: Pivot table showing analysis results from the outer corrosion zone (outer helmet side only) with corresponding chemical and physical corrosion profile (CP1 to CP3.2) and appearance group assigned based on macroscopic observation of the predominance of malachite or azurite. .................223 Figure 2.1: Type I corrosion or 'even' corrosion on archaeological bronzes that preserves the marker of original surface. Diagram redrawn based on Piccardo et al. 2007 fig. 14.1 and Robbiola et al.

1998a.............................................................................................................................................................10 Figure 2.2 (below): Above: Composition and commonly reported crystal structure of Cu-Sn phases.

Adopted from Saunders and Miodownik (1990), with calculated wt% values. Below: Phase Diagram of the Cu-Sn binary system at full equilibrium (Gale and Totemeier, 2004). .........................................13 Figure 2.3: Typical profile and intermetallics formed during tinning and species diffusion during annealing. A, B and C indicate moving directions of interfaces during solid-state diffusion at thermal aging (from Peng et al., 2007). Cu atoms diffuse from the substrate to be consumed at the Cu3Sn|Cu6Sn5 interface and Sn atoms can reach the Cu|Cu3Sn interface leading to growth of Cu3Sn.

The dotted line shows the original Cu|Cu6Sn5 interface before annealing. In cases were Cu is present at the tin coating (or solder), this is mainly consumed at the Cu6Sn5|Sn interface. .....................................17 Figure 3.1: Common experimental diffractometer geometries in angle dispersive systems. Left: BraggBrentano parafocusing diffractometer commonly used with a flat sample, a divergent beam and in reflection mode; Right: Debye Scherrer diffractometer commonly used with thin or capillary samples, with a parallel beam and in transmission mode. Figures from Anne, 2007. For applications and limitations of the different geometries (see Louer, 2002). ........................................................................41 Figure 3.2: Diffraction patterns obtained using ToF-ND (ROTAX diffractometer, ISIS) showing shifting of the major copper peaks (left) due to increasing amount of Sn in the bronze alloy and detail of the shape and position of the {111} αCu reflection (right). The bronzes are fully homogenised. The δ-phase has a distinct diffraction pattern and appeared at 16wt% Sn content. (From Siano et al., 2003).

BG1 (harness): corroded microstructure with lead inclusions and areas of unusually shaped α-bonze.

BOV (collar): wrought microstructure. Samples are polished but not etched. ........................................93 Figure 4.29: XRD pattern of fragment BG1 from the Brecon Gaer harness fitting. The pattern is dominated by η-Cu6Sn5 (PDF 65-2303). Alternative reference diffraction patterns are provided for comparison. ..................................................................................................................................................94 Figure 4.30: XRD pattern of fragment MB3 from the Manorbier skillet. Burkhardt's ε-Cu3Sn dominates the pattern...................................................................................................................................94 Figure 4.31: SEM-BSE images of samples from Ceredigion skillet. CER1: plan-view BSE image showing Cu6Sn5 scallops. CER2: BSE image showing scallops on the surface of the polished section.

Unetched samples. .......................................................................................................................................96 Figure 4.32: EDX maps of PbMβ, OKα, SnLα and CuKα X-ray lines of CER2 polished section seen above. The key indicates the counts of PbMβ . Unetched polished sample naturally corroded.............96 elemental distribution of PbMβ, OKα, SnLα and CuKα. The key indicates the counts of CuKα.

Details of plotted data are found in Table 5.3. The plot shows that sample thickness does not strictly depend on their position on a helmet........................................................................................................137 CORINTHIAN MIDDLE PHASE (II)

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