Effects of Long-Term Aging in Arsenical Copper Alloys.
Archaeological materials present unique records on natural processes allowing the study of long-term material behaviors such as structural modifications and degradation mechanisms. The present work is focused on the chemical and microstructural characterization of four prehistoric arsenical copper artifacts. These artifacts were characterized by micro-energy dispersive X-ray fluorescence spectrometry, optical microscopy, scanning electron microscopy with X-ray microanalysis, micro-X-ray diffraction and synchrotron radiation micro-X-ray diffraction. Cu3As is the expected intermetallic arsenide in arsenical copper alloys, reported in the literature as exhibiting a hexagonal crystallographic structure. However, a cubic Cu3As phase was identified by X-ray diffraction in all of our analyzed archaeological artifacts, while the hexagonal Cu3As phase was clearly identified only in the artifact with higher arsenic content. Occurrence of the cubic arsenide in these particular objects, suggests that it was precipitated due to long-term aging at room temperature, which points to the need of a redefinition of the Cu-As equilibrium phase constitution. These results highlight the importance of understanding the impact of structural aging for the assessment of original properties of archaeological arsenical copper artifacts, such as hardness or color.
1CENIMAT/I3N,Departamento de Ciências dos Materiais,Faculdade de Ciências e Tecnologia,FCT,Universidade Nova de Lisboa,2829-516 Caparica,Portugal.
Filipa
F
Pereira
1CENIMAT/I3N,Departamento de Ciências dos Materiais,Faculdade de Ciências e Tecnologia,FCT,Universidade Nova de Lisboa,2829-516 Caparica,Portugal.
Rui J C
RJ
Silva
2Centro de Ciências e Tecnologias Nucleares (C2TN),Instituto Superior Técnico,Universidade de Lisboa,Estrada Nacional 10 (km 139.7),2695-066 Bobadela LRS,Portugal.
António M
AM
Monge Soares
2Centro de Ciências e Tecnologias Nucleares (C2TN),Instituto Superior Técnico,Universidade de Lisboa,Estrada Nacional 10 (km 139.7),2695-066 Bobadela LRS,Portugal.
Maria F
MF
Araújo
4Laboratório José de Figueiredo,Rua das Janelas Verdes 37,1249-018 Lisboa,Portugal.
Maria J
MJ
Oliveira
1CENIMAT/I3N,Departamento de Ciências dos Materiais,Faculdade de Ciências e Tecnologia,FCT,Universidade Nova de Lisboa,2829-516 Caparica,Portugal.
Rui M S
RM
Martins
7Helmholtz-Zentrum Geesthacht,Max-Planck-Str. 1,21502 Geesthacht,Germany.
Norberth
N
Schell
X-ray diffraction; arsenical copper alloys; chalcolithic; copper arsenide; domeykite; microstructural characterization