XR-µCT for Earth material research

Thanks to the financial support from the Canada Foundation for Innovation, the Ontario Research Fund, and the Faculty of Science at Carleton University, we are running Canada's first high-resolution X-ray micro-computed tomography (XR-µCT) laboratory for Earth material research. The laboratory allows us to obtain quantitative microstructural and textural data that are essential to unravel fundamental atomic-scale processes that govern the formation of rocks. Because our instrument uses higher-energy X-rays and longer dosage times than conventional X-ray tomography facilities, we can non-destructively study the interior of solid matter at ultra-high resolution.

Figure 1: Calculated XR-µCT cross section of schist (Grt - garnet, Bt - biotite, Qtz- quartz, Ilm - ilmenite, Ms - muscovite, St - staurolite).

Figure 1: Calculated XR-µCT cross section of schist (Grt - garnet, Bt - biotite, Qtz- quartz, Ilm - ilmenite, Ms - muscovite, St - staurolite).

The key components of the XR-µCT system include (1) a 40-130 keV micro-focus (< 5 µm) X-ray source, (2) a distortion-free 2240 x 2240 pixel flat-panel X-ray sensor, (3) a micro-positioning sample stage that can handle also heavy (several kg) objects, and (4) a data acquisition, reconstruction and image processing system that renders a 3D image of the sample interior. While the sample is illuminated by an X-ray cone beam, the sample rotates around its vertical axis so that hundreds of angular views can be detected. Each view is a magnified projection image and corresponds to a calculated cross-section through the sample monitoring the details of its internal structure. These details reflect the 2D spatial distribution of X-ray attenuation of the sample interior which is directly related to variations in density and chemical composition.

Figure 1 is a XR-µCT cross-section through a rock cylinder drilled out of a garnet mica schist. The different grey values correspond to different degrees of X-ray attenuation and can be used to distinguish between garnet, biotite, ilmenite, muscovite, and quartz. Note that some muscovite grains pseudomorph staurolite. The diameter of this cross-section is ca. 3 cm, pixel size is ca. 15 µm.

Figure 2: Numerical model of the 3D distribution of garnet in the scanned schist. The matrix of the rock has been made transparent.

Figure 2: Numerical model of the 3D distribution of garnet in the scanned schist. The matrix of the rock has been made transparent.

Figure 2 is the numerical reconstruction of the scanned rock cylinder with garnet crystals shown in red. The rest of the rock has been replaced in this model by a transparent matrix. The animation in Figure 3 shows the largest garnet crystal of the scanned rock volume. Its position in the rock, as well as its shape (note that it does not exhibit isometric but hexagonal symmetry!) needs to be considered to prepare a physical cross section required for chemical, crystallographic or other analyses.

Figure 3: The largest garnet crystal of the scanned rock volume. Its position and (hexagonal!) shape needs to be considered when preparing physical sections for chemical and other analyses.

Figure 3: The largest garnet crystal of the scanned rock volume. Its position and (hexagonal!) shape needs to be considered when preparing physical sections for chemical and other analyses.

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Besides rocks, XR-µCT can be used to study a wide range of decimeter-sized dense solids including fossils, bones, and engineered materials. The maximum length of a sample that can be scanned is 15 cm and the maximum scan diameter is 14 cm (max. sample size that fits into sample chamber: 20 cm x 14 cm). Smaller specimens can also be studied at a maximum resolution of less than 5 µm.

Please get in touch if you are interested to use XR-µCT. Applications from within and beyond Carleton University as well as from government agencies and industry are welcome. 

User fees cover expenses associated with data acquisition (including specimen mounting, instrument calibration and scanning) and data reconstruction (conversion of raw CT data into imaginary slices, artifact reduction, data transfer and storage). Note that additional image processing and analysis can be offered (including 3D rendering and texture quantification) but are not included in the standard services.

Academic - NSERCAcademic - none-NSERCGovernment/Industry
Data acquisition$145 per hour$175 per hour$205 per hour
Data reconstruction$25 per hour$35 per hour$45 per hour
Data processing (additional)$45 per hour$55 per hour$65 per hour

A project is considered collaborative, including co-authorship on publications, if the data obtained in the XR-µCT lab are scientific contributions through study design and analysis. Additional 20% on the rates given above are charged for non-collaborative projects. Rates for large-scale projects can be negotiated. Free test scans (less than 1 hour scanning time) and pilot work can be offered to help determine whether XR-µCT may be beneficial to the research intended, and to assist in potential applications for project funding.