Title

Potential applications of supercritical carbon dioxide extraction and impregnation for the stabilization and conservation of industrial heritage artifacts

Document Type

Technical Report

Publication Date

2016

Abstract

An interdisciplinary team of students from Michigan Technological University completed a series of tests using Supercritical Carbon Dioxide (SC-C02) to extract water and volatile compounds from samples of corroded archaeological iron artifacts. Test samples were then cracked and examined using backscatter SEM. Qualitative visual inspection showed that pores and microfissures were clear and opened after SC-C02 extraction. Another SC-CO2 treatment then impregnated the test objects with an environmentally-benign polymer (Acryloid/ParaloidTM B-72) to consolidate fragile structures and seal objects against future water absorption. Following treatment, these samples were also cracked and examined with SEM. Chemical traces of the polymer demonstrated the complete diffusion of the B72 into the pores and microfissures of the sample. These tests were paralleled by the design and execution of traditional conservation plans for twenty ferrous metal artifacts. The project team developed essential comparative perspectives on existing techniques, while being engaged in considerations of professional ethics, practicality, and economic value. This study showed that the emerging application of Supercritical Fluid (SCF) Extraction can be used to rapidly stabilize batches of corroded ferrous metal artifacts, including cast and wrought iron and steel, as well as composite artifacts. This will allow labs to avoid or safely delay traditional electrochemical techniques that can require months of expert treatment. This technique works as a batch operation, allowing groups of small artifacts to be quickly stabilized and consolidated, potentially even in field settings. The process may also be tailored to treat objects from sites with soil contamination or materials from heritage collections, where potentially hazardous chemicals are also extracted during dewatering. While critically important questions remain to be addressed before the technique can be made systematically operational, particularly those surrounding chloride salts, the technique has tremendous potential to improve best practices in metals conservation. Our proof-of-concept experiments allowed us to improve our procedures for the next phase of development. Students and faculty disseminated their findings at four separate archaeological and conservation conferences where results could be disseminated to different professional communities. Team members also prepared blog posts about their experiments targeted to public audiences. The project established a sustained collaborative relationship between the Departments of Social Sciences, Materials Science and Engineering, and Chemical Engineering at Michigan Technological University. Project scientists also developed professional connections with practicing conservators for future collaborations.