Shakoorioskooie Mahdieh, Granget Elodie, Cocen Ocson, Hovind Jan, Mannes David, Kaestner Anders, Brambilla Laura
PSI Center for Neutron and Muon Sciences, Forschungsstrasse 111, 5232 Villigen, Switzerland.
Haute Ecole Arc Conservation-Restauration, HES-SO University of Applied Sciences and Arts Western Switzerland, Espace de L'Europe 11, 2000 Neuchâtel, Switzerland.
Appl Phys A Mater Sci Process. 2024;130(11):849. doi: 10.1007/s00339-024-07990-x. Epub 2024 Nov 2.
This study presents a preliminary examination of the effects of environment changes post-excavation on heavily corroded archaeological Roman iron nails using neutron tomography and image registration techniques. Roman nails were exposed to either a high relative humidity environment, or fast thermal drying as primary experiments to show the power of this imaging technique to monitor and quantify the structural changes of corroded metal artifacts. This research employed a series of pre- and post-treatment tomography acquisitions (time-series) complemented by advanced image registration methods. Based on mutual information (MI) metrics, we performed rigid body and affine image registrations to meticulously account for sample repositioning challenges and variations in imaging parameters. Using non-affine local registration results, in a second step, we detected localized expansion and shrinkage in the samples attributable to imposed environmental changes. Specifically, we observed local shrinkage on the nail that was dried, mostly in their Transformed Medium (TM), the outer layer where corrosion products are cementing soil and sand particles. Conversely, the sample subjected to high relative humidity environment exhibited localized expansion, with varying degrees of change across different regions. This work highlights the efficacy of our registration techniques in accommodating manual removal or loss of extraneous material (loosely adhering soil and TM layers around the nails) post-initial tomography, successfully capturing local structural changes with high precision. Using differential analysis on the accurately registered samples we could also detect and volumetrically quantify the variation in moisture and detect changes in active corrosion sites (ACS) in the sample. These preliminary experiments allowed us to advance and optimize the application of a neutron tomography and image registration workflow for future, more advanced experiments such as humidity fluctuations, corrosion removal through micro-blasting, dechlorination and other stabilization treatments.
本研究利用中子断层扫描和图像配准技术，对挖掘后环境变化对严重腐蚀的古罗马铁钉的影响进行了初步研究。作为主要实验，将古罗马铁钉置于高相对湿度环境或快速热干燥环境中，以展示这种成像技术监测和量化腐蚀金属文物结构变化的能力。本研究采用了一系列预处理和后处理断层扫描采集（时间序列），并辅以先进的图像配准方法。基于互信息（MI）指标，我们进行了刚体和仿射图像配准，以精心应对样品重新定位挑战和成像参数变化。在第二步中，利用非仿射局部配准结果，我们检测了样品中由于环境变化导致的局部膨胀和收缩。具体而言，我们观察到干燥处理的钉子出现了局部收缩，主要集中在其转变介质（TM），即腐蚀产物粘结土壤和沙粒的外层。相反，处于高相对湿度环境的样品出现了局部膨胀，不同区域的变化程度各异。这项工作突出了我们的配准技术在适应初始断层扫描后手动去除或丢失外来物质（钉子周围松散附着的土壤和TM层）方面的有效性，成功高精度地捕捉了局部结构变化。通过对精确配准的样品进行差分分析，我们还能够检测并定量分析水分变化，以及检测样品中活性腐蚀位点（ACS）的变化。这些初步实验使我们能够推进和优化中子断层扫描和图像配准工作流程的应用，以用于未来更先进的实验，如湿度波动、通过微喷砂去除腐蚀、脱氯和其他稳定化处理。
