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 4 Monel 400, a decorative metal with a five-decade-long span of archi- tectural use in the first half of the 20th century, suffers from a two-fold predic- ament [1] . A victim of its own success, Monel’s anti-corrosive properties see the metal given short shrift by conser- vators, relegated to the back burner as more delicate materials demand imme- diate treatment, while the untold loss of proprietary research from the disband- ment of the International Nickel Com- pany has left a wide chasm in the body of knowledge. TESTING With an aim to begin the investiga- tion and establish potential cleaning av- enues for architectural conservators in the field, a range of testing was carried out on historic and modern samples of Monel towards the end of 2019. A quan- titative and qualitative two-stage pro- cess was formulated based on standard methods. The first stage utilized a por- table Bruker x-ray fluorescence (XRF) device and initially tested material in- side the historic preservation laborato- ry at Columbia University. Testing then migrated to three case studies, with the addition of x-ray diffraction (XRD), Ra- man spectroscopy, and gas chroma- tography–mass spectrometry (GC-MS) to help qualify corrosion compounds and identify, where possible, organic coatings. Samples in this testing session in- cluded two historic Monel sheets from the Metropolitan Museum and Battery Maritime Building’s roofs in New York City, one historic Monel rod from the Bryn Athyn Historic District, Pa., (see Fig. 1) and two modern Monel sheets, both provided courtesy of Special Met- als Corporation. The historic items had been fully exposed to the atmosphere and dated to themid-1930s. They exhib- ited different surface coatings that in- cluded corrosion product and apparent paint. Using the Alloy 2 setting provided by Bruker, calibration was verified with an iterative and comparative test using a laboratory ingot report. Percentage deviation was less than 0.1% for nickel, 0.5% for copper, and between 1-2% for low compositional elements such as manganese and iron. Tests were then carried out pre- clean, post-acetone, post paint strip- per (where required), and post-sanding back to bare metal. Silicon carbide pa- per was used for sanding. Surface was then cleaned with acetone to remove potential contaminants. In comparison to contemporary Monel, historic Monel averaged 1-1.5% more nickel and over HISTORIC MONEL—PART II: TESTING AND ANALYSIS OF ATMOSPHERIC CORROSION PRODUCTS A look at Monel after decades of exposure to the environment shows more work is needed to address the lack of scientific research and conservation literature. James E. Churchill,* Columbia University, New York and Kreilick Conservation, Pennsylvania *Member of ASM International