The high temperature corrosion resistance of α‐phase bronzes

Abstract

KurzfassungThe oxidation of Cu-Sn alloys containing up to 1 3 wt% Sn Die Oxidation von CuSn-Legierungen mit bis 13 Gew.-% in oxygen (1 atm) has been studied in the temperature range Zinn in puerstoff (1 atm) wurde im Fmperaturbereich 550 550 "Cto 800 "Cat 5 0 "Cintervals; the investigation involved the bis 800 C im Abstand von ieweils SO C untersucht; dabei study of the kinetics and of the morphology and structure of the scales by appropriate physical methods, with the aim o f correlating the two aspects of the oxidation behaviour. The oxidation rate of a 3 wt% Sn alloy is lower than f o r pure Cu at 550 and 600 "C, but higher above 600 "C. The effect o f the tin addition is related to the interplay o f many different factors affecting the reaction rate, the overall result depending on temperature. The rate o f oxidation o f the more concentrated alloys, however, is always lower than that o f pure Cu. This result is attributed to the formation o f an SnOz layer at the base of the scale which, although thin and usually discontinuous, slows down the outward diffusion of copper. The highest tin concentration allowed by its high temperature solubility in copper is not sufficient to produce a continuous thick healing layer o f SnO, at the alloy surface, but nevertheless it produces a pronounced decrease o f the oxidation rate.

Artificial patination in Early Iron Age Europe: an analytical case study of a unique bronze artefact

“…Another important observation of other scientists is that oxide layers consisting of cuprite and cassiterite with an outer layer of tenorite develop when tin bronzes are heated to temperatures of 300 C and above (Gesmundo et al 1979;Mathis, 2005, 76e94) (Fig. 13).…”

“…The fact that only few secondary corrosion products (i.e. malachite, azurite) are present in the browneblack patina indicates that these parts possessed a protective layer of copper and tin oxides before burial, thus, preventing severe natural alteration (Gesmundo et al 1979;Scott, 2002, 11;Piccardo et al 2007). Therefore, the dark patina has to be regarded as the original artificial corrosion layer that once perfectly contrasted with a yellowish and shiny metal colour of the stripes.…”

“…Similar conditions seem to apply to tin bronzes, although there are much less scientific data for the adherence of oxide scales on such alloys. Investigations carried out by Gesmundo et al (1979) and DeAsmundis et al (1983) revealed that oxide layers produced at elevated temperatures possess good adherence properties whereas Mathis (2005) has recognised their fragile character at lower temperatures. However, recent experiments by Binggeli and Krieg (2013) obtained durable oxide layers on high tin bronzes (11 wt.% tin) already at temperatures around 385 C and subsequent quenching.…”

“…Notwithstanding, the fragility and the mineral composition of the patina help to reconstruct the probable patination history of the artefact. Gesmundo et al (1979) and Mathis (2005) investigated the thermal oxidation of low and high tin bronzes and the composition, growth mechanism and microstructure of the resulting corrosion layers. Depending on the temperature (285e800 C) and the tin content they found variably composed and structured surface layers that are often quite fragile and not well adhered, even at low temperatures (Mathis, 2005).…”

Scaling and internal oxidation of α-CuSn alloy

“…The presence of tin in alloy leads to a decrease in the oxidation rates; this is associated with the formation of tin oxide in the oxidation layer. Gesmundo et al [1] and Mathis et al [2] showed that tin in CuSn alloys does not form a continuous protective layer of tin oxide as can be the case in Cu -Zn alloy in which a ZnO protective layer is formed [3]. Rather, tin forms some precipitates in the oxide layer as Ni and Si form in the Cu -Ni [4] and Cu -Si [5] alloys respectively, which slows down the outward diffusion of copper.…”