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 5 2% less copper. Silicon, cobalt, and sul- fur averaged 0.75%, 0.51%, and 0.17%, respectively, in historic Monel versus nil or trace amounts in contemporary Mo- nel. The silicon reading was skewed by the historic rod at 1.57%, likely a cast- ing grade of Monel, sold from the 1910s. The author has uncovered at least 17 types of Monel that were utilized be- fore their eventual phasing out from the 1980s. See Table 1 for further de- tails and compositional content. Most interestingly, contemporary Monel reg- istered 0.48% chromium versus trace amounts in historic. Claimed as residu- al due to production bleed, the propri- etary nature of the alloy and modern tolerances leave question marks. Chro- mium was verified as effective in main- taining sheen in nickel as early as the 1920s. In W.H.J. Vernon’s seminal work “The ‘Fogging’ of Nickel,” W.R. Barclay notes experiments under Mond circa 1927 found just 2.5% chromium had a marked effect on nickel, while another article by W.A. Wesley noted chromium plating of as little as ten millionths of an inch stopped the fogging effect [2,3] . CASE STUDIES Three case studies were chosen based on weathering, location, and his- toric significance. Two of the sites at Woodlawn cemetery in New York are 700-feet apart, built in the same work- shop within three months of one an- other, yet are remarkably different in weathering and coloring. The third, the Bryn Athyn historic district, north- east of Philadelphia, had notably var- iegated corrosion throughout. All sites were chosen as a conscious attempt to emulate previous studies in urban and rural environments. Jesse I. Straus Gate: Handcraft- ed by the Samuel Yellin workshop in 1929, the Straus gate, one of three for each heir to the Macy’s fortune, depicts a grape and leaf design. A glass infilled metal frame with ventilation was likely installed later. Visual examination re- vealed a relief flattened by friable tur- quoise corrosion, olive coloring along the upper row from a green top and red lower layer, and brownish gray on the base plate. XRF showed vastly different elemental readings. Turquoise areas registered copper up to 51%, nickel 37%, and sulfur 3%, versus the typical Monel readings at the base. A thinner turquoise layer on the interior saw cop- per dropping below 40%, showing the importance of exposure. XRD revealed major phases of cuprite and brochan- tite around the turquoise areas and possible chalcanthite, but the brown layer was non-scrapable and could not be identified. Samples were ana- lyzed using copper radiation tubes with scans run over the range of 5 to 80°, a step size of 0.0131° and an accumulat- ed counting time of 500 s/step. Such thin layers could likely only be studied through x-ray photoelectron spectros- copy, XANES or XAAFS but were beyond the scope of this study. A lack of iden- tification of the base metal, hydrates and hydroxides by the databases used showed the limitations of testing an un- der-researched alloy. James Norman Hill Gate: Worked in the same shop, the Hill gate, built for an heir of the Northern Pacific railroad fortune, depicts seed motifs topped by fleur-de-lis, ensconced in leaves. While alsohousing a glass infilledmetal frame, a lack of ventilation netting, in compar- ison to Straus, has impacted corrosion significantly on the rear side. Examina- tion revealed a waxy black coating over the majority of the exterior, spotty tur- quoise corrosion at the top, a yellow area around the high-traffic hand area, and gray at the base. Turquoise was dif- ficult to measure with the XRF due to a lack of flat surface, but the elements of the handle presented copper of 47% and nickel of 41%, while the black and Metropolitan MuseumMonel Side A Metropolitan MuseumMonel Side B Battery Maritime Building Monel Side A Battery Maritime Building Monel Side B Bryn Athyn Historic District Monel rod Fig. 1 — The three historic samples of Monel chosen for laboratory sampling using portable XRF.