Analysis of Ancient Materials and their degradation – Lecture 3 CH-406 Prof. Dr. Claire Gervais

Content Introduction to Materials Introduction to ancient materials Materials: definitions, multidisciplinarity, challenges The triangle Structure-Property-Function Materials research: Why, What, How, Where? Introduction to ancient materials Diversity of ancient materials: paintings, archaological objects, fossils, ivory, ceramics. What is ancient? The concept of materials history and impact on their scientific study Typical reasearch topics in ancient materials Analyzing ancient materials: key concepts Heterogeneity in materials: a fuzzy concept with clear consequences. Too big or not too big? The art of adapting measurement scale to property scale. Sample preparation: bulk, cross-sections, thin-sections, porous materials. Example: Embedding techniques for thin sections of brittle paint samples.

Content Synchrotron techniques for ancient materials Synchrotron light: generation and specificities A specific synchrotron technique: X-ray absorption spectroscopy Example: Degradation of smalt pigment in paintings X-ray tomography techniques: Going to 3D and 4D imaging Materials through the X-ray beam: attenuation coefficients Acquiring a 3D image: Acquisition and reconstruction (principles) Basics of image processing: filtering, segmentation, labelization Example: Virtual unfolding of ancient manuscripts Physico-chemistry of materials degradation Reproducing and accelerating natural aging: limits of validity. In-situ analysis of degradation processes. Radiation damage: how to evaluate it and minimize it. Example: Radiation damage of Prussian blue paper artworks

Take-home lesson 1 & 2 Materials often designed/defined by the interest we have in them: multifunctional, synthetic, biogenic, composite, ancient, natural, raw..... Characterizing materials = characterizing a particular set of functions / properties / component structures, along with relationships between components (interface, distribution). Heterogeneity conditions the scale at which obtaining a correct measurement and requires adequate statistical processing. Correct characterization = Adapt the length scale of the measurement to that of the feature of interest.

Contents of the lecture Imaging techniques Examples: Catalyst and Eucalyptus Leaves A note on sample preparation A note on radiation damage

Materials characterization in a nutshell Define the research question: WHY / WHAT / WHERE (the most important part of the study) Choose the technique accordingly: HOW Sample preparation: sometimes 90% of the work! Measuring, imaging the sample Data processing (representativity, filtering, REV, statistics)

Your task for the exam

Your task for assignments and exam A. Locate the Why? What? Where? and How? Give lines and pages or highlight in color the pdf Answer to each with a short paragraph (if it is not clear in the publication, tell it!) B. Choice of technique Explain link between technique and question to answer e.g.: Technique X chosen because sensitivity to structural feature / spatial / non-destructive / ...etc. C. Statistics and representativity How did they handle statistical significance? Give lines and pages or highlight in color the pdf D. Explain one experiment From sample preparation to Data acquisition to Data processing

Your task for assignments and exam A. Locate the Why? What? Where? and How? Give lines and pages or highlight in color the pdf Answer to each with a short paragraph (if it is not clear in the publication, tell it!) Assignments (written) : 3-4 pages, in English, structured with these 4 blocks (A–D). Appendix: annotated pdf, images (if you want) Oral exam with the same structure B. Choice of technique Explain link between technique and question to answer e.g.: Technique X chosen because sensitivity to structural feature / spatial / non-destructive / ...etc. C. Statistics and representativity How did they handle statistical significance? Give lines and pages or highlight in color the pdf D. Explain one experiment From sample preparation to Data acquisition to Data processing

Imaging of Materials

What is imaging of materials? Definition: Visual representation of a volume/surface of the material that highlights the spatial distribution of the property, chemical element or phase of interest. Vocabulary: Representation of surface: 2D imaging (dimensionality) Representation of volume: 3D imaging or tomography (technique) Interest in element or chemical property: chemical imaging (property) Interest in morphology and micro-structure: micrograph (scale)

Imaging modalities Legrand, S. et al., ”Examination of historical paintings by state-of-the-art hyperspectral imaging methods: from scanning infra-red spectroscopy to computed X-ray laminography”, Heritage Science, 2014, 2:13

Imaging modalities – Full-field: an image is formed from interaction of the object with an extended beam FTIR-FPA imaging, X-ray tomography – Raster-scanning: the object is scanned in front of a focused beam Raman imaging, Scanning X-ray fluorescence Legrand, S. et al., ”Examination of historical paintings by state-of-the-art hyperspectral imaging methods: from scanning infra-red spectroscopy to computed X-ray laminography”, Heritage Science, 2014, 2:13

Raster scanning imaging

Example 1: Gold in leaves Cu Sr (oxalate crystals) Au 500μm 50μm Lintern et al. ”Natural gold particles in Eucalyptus leaves and their relevance to exploration for buried gold deposits”, Nature comm., 2013, 4, pp 2041.

Example 1: Gold in leaves Cu Sr (oxalate crystals) Au 50μm Lintern et al. ”Natural gold particles in Eucalyptus leaves and their relevance to exploration for buried gold deposits”, Nature comm., 2013, 4, pp 2041.

Example 1: Gold in leaves Exercise (facultative): Find out HOW these images were done. From sample preparation to data acquisition and image processing. (Part D of Exam). Draw or Text. 50μm Lintern et al. ”Natural gold particles in Eucalyptus leaves and their relevance to exploration for buried gold deposits”, Nature comm., 2013, 4, pp 2041.

Example 2: Nanoscale imaging of catalysts at work before treatment after 2hours in H2 after 4hours in gas 50μm De Smit et al., ”Nanoscale chemical imaging of a working catalyst by scanning transmission X-ray microscopy”, Nature Letters, 2008, 458, pp 222–225.

Example 2: Nanoscale imaging of catalysts at work Exercise (facultative): Find out the WHY/WHAT/WHERE in the introduction of the paper (Part A of Exam). Highlight in the text. 50μm De Smit et al., ”Nanoscale chemical imaging of a working catalyst by scanning transmission X-ray microscopy”, Nature Letters, 2008, 458, pp 222–225.

Sample preparation

Why preparing samples in imaging techniques? To access bulk/surface properties or phases To target specific features or phases For imaging techniques Air-glass interface (Optical Microscopy) Carbon Nanotube on carbon fiber (Scanning Electron Microscopy) Pharmaceutical (Raman mapping)

Importance of sample preparation – Very important step: ”bad” data cannot give beautiful results, even with excellent post-processing. – Sample preparation depends on technique specificities (scale, surface, bulk, imaging, quantification) and material properties (conducting, porous, brittle, layered). – Examples: Focusing techniques require flat surface to stay in focus. Full-field techniques require a sample in the field of view Tomography needs a sample thin enough to allow transmission Brittle samples need to be embedded

Importance of sample preparation With mechanical polishing With ion milling

Importance of sample preparation Sample not cleaned after polishing Sample thoroughly cleaned

Typical sample preparation pathway for imaging Cross-section preparation with mounting-polishing (but there are many, many other types of preparation techniques!) 1 Mounting / Embedding 2 Grinding 3 Polishing 4 (Etching)

1. Mounting / Embedding Goal: allow samples to be handled easily and protects them from mechanical damages (important for porous materials). Practical: Should not influence the specimen (chemically or mechanically) and should not interfere too much with the analysis. Most often: epoxy, acrylic or polyester resin.

2. Grinding Goal: Get a flat surface and remove scratches that may interfere with imaging. Practical 1: Done usually with silicon carbide papers of different grain sizes. Paper grit size: number of grains of silicon carbide per square inch (180 grit paper is coarser than 1200 – finest).

3. Polishing Goal: Get a flat and smooth surface suitable for imaging. Practical: Soft cloth impregnated with abrasive diamond particles (6μm and 1μm) and an oily lubricant. Usually need to wash but debris can remain at the surface. Electrochemical or chemical polishing can help in removing these debris.

4. Etching Goal: Enhance contrasts, for instance between metallic grains.

Example of optimal preparation Meirer, JAAS, 2013

Warning... High photon flux and micro/nanoscale can lead to radiation damage. Needs to be taken into account in the analytical pathway

Warning... High photon flux and micro/nanoscale can lead to radiation damage. Needs to be taken into account in the analytical pathway

Take-home lesson 1. Imaging techniques allow to keep track of heterogeneity in materials and get statistically relevant information 2. Imaging requires to take into account constraints due to both material and technique 3. Sample preparations may not be trivial but is very important (bad samples = bad data)