Nov_Dec_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 2 0 2 9 discovery of bunsenite and retgersite confirmed green and yellow coloration of the alloy is not solely due to the pres- ence of copper. The discovery of retger- site, the rare but natural mineral form of nickel sulfate was again novel for conservator literature. Its phase in Mo- nel would be revealed more clearly by pH diagrams. The noticeable difference in corrosion at the tenon joint also ex- posed the importance of work hard- ening and annealing on corrosion of historic metals with potential impurity issues. At the Statue of Liberty, for ex- ample, differences in weathering along edges of copper panels found soft- er annealed sheets corroded, where- as non-annealed sheets did not, due to smaller grain size, greater hardness, and reduced electric potential [9] . CONCLUSIONS Current literature for Monel gener- ally relies on dated information gleaned from original International Nickel Com- pany marketing materials and claims, among other things, Monel cannot be extruded, has green corrosion prod- uct due solely to copper content, and is still produced with a matte process that was halted from 1947. All of these statements have now been proven to be incorrect, yet remain widely dissemi- nated [10-11,4] . Surviving independent em- pirical data from the British Non-ferrous Metals Research Association (BNFMRA) and ASTM International is dated. The Atmospheric Corrosion Research Com- mittee largely operated in the 1920s for the BNFMRA and was dominated at the time by the work of W.H.J. Vernon and J.C. Hudson. ASTM performed multi- decade studies that took place between 1925-1964, 1957-1977, and 1976-1996. A modern quantitative analysis for Mo- nel on the oxides and sulfates, as well as thermodynamic, kinetic, and equilibri- um parameters on their formation is desirable. Potential pH and schematic diagrams that were started in the 1990s on nickel and similar work would help unravel the Monel corrosion matrix [12,13] . It is hoped this new research will just be the beginning of work to rediscover this most modern of American alloys. ~AM&P For more information: James E. Chur- chill, Conservator, Kreilick Conserva- tion, jchurchill@kreilickconservation. Fig. 4 — Visual and technical identification of the tower railing at Glencairn, Bryn Athyn.