Scanning Auger Microscopy and X Ray Photoemission Spectroscopy Studies of Metallic Archaeomaterials
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E. PAPARAZZO, L. MORE'TO Istituto di Struttura della Materia del CNR Via E. Fermi 38, 00044 Frascati, Italy, [email protected] ABSTRACT We report on the surface microchemistry of a Roman iron object and of a Roman lead pipe 'fistula'. The original patina of the iron sample consists mainly of oxidic phases whose lateral distribution is imaged with a submicron spatial resolution. Metallic iron in the bare surface is covered with a Fe(lll)-Fe(ll) oxidic layer which is several times thicker than in a modern ferritic steel. We find that the presence of a flux minimizes lead oxidation in the joint of the fistula as well as in comparison, 'modern' lead soldered samples. In one of these comparison samples the lateral distribution of the chemical species present is imaged with a spatial resolution of about 1000 A. INTRODUCTION As part of a project focussed on the surface analysis of archaeomaterials [1-4], here we combine scanning Auger microscopy (SAM) techniques with x ray photoemission (XPS) techniques in order to study the surface microchemistry of a Roman iron object and a Roman lead pipe 'fistula'. In the former material we will attempt to highlight chemical inhomogeneities between the original patina and the bare surface. Also, we will compare the bare object with a modern ferritic steel as to the chemical nature and thickness of the ambient-induced layer present at the surface. Interest will be also placed on comparing the chemical composition of the joint region of the fistula with that of modern lead-to-lead soldered samples containing varying fluxes [5]. EXPERIMENT The Roman iron sample was cut from a ring-shaped object, about 5 cm in diameter, dating back to the third century B.C., found in an excavation carried out in Cars6li (Italy) in 1908 [6]. The original patina was completely removed by mechanical scraping in the specimen analyzed with XPS. Conversely, a region covered with the patina, about 2 square millimeters out of a total area of 1 square centimeter, was left on the specimen for SAM analysis. Comparison measurements were made on a sample of ferritic steel used in the automotive industry. The Roman fistula, of the third century A.D., was found in an excavation carried out at the 'Villa Palombara', Rome, in 1875 [7]. Analyses were performed in a cross section cut out from the joint region. Comparison measurements were done on three lead samples soldered by a professional plumber. A Pb-Sn alloy (containing - 30% w/w Sn), quite similar to the 'tertiarium' alloy described by Pliny [8], was used as a solder in all cases, whereas the flux varied. In the first sample, olive oil was used, i.e. the same flux used by the Romans for sealing fistulas [8]. Stearic wax [9], i.e. the flux commonly adopted in modern lead soldering, was used in the second, whereas no flux at all was employed in the third. Surface analysis experiments were performed in a Cameca 'Nanoscan 50' apparatus equipped with a W field-emission electron gun (primary energy = 10 keV), for SAM measurements, and an Alkoc source (hv= 148
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