Browsing by Author "Kletetschka, Karel"

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    3D Printing of Specialty Devices for Geochemical Investigations: Real-Time Studies of Goethite and Schwertmannite Formation
    Kletetschka, Karel (Virginia Tech, 2018-06-29)
    New types of laboratory reactors that are highly customizable, low-cost and easy to produce are needed to investigate low-temperature geochemical processes. We recently showed that desktop 3D printing stereolithography (SLA) can be used to efficiently fabricate a mixed flow reactor (MFR) with high dimensional accuracy comparable to traditional machining methods (Michel et al., 2018). We also showed that the SLA method allowed for the addition of complex features that are often beyond the capabilities of traditional methods. However, the stability of 3D printed parts at low-temperature geochemical conditions has not been fully evaluated. The objectives of this work were twofold: 1) to provide a framework for assessing the stability and compatibility of SLA printed materials at geochemically relevant conditions, and 2) to show how 3D printed specialty devices can enable new laboratory geochemical experiments. Part 1 of this Master's thesis presents findings for enhancing mechanical and solvent resistance properties of a commercial 3D printing material (Formlabs Clear) by UV post-curing procedures and also provide data showing its stability in aqueous solutions at pH 0, 5.7, and 12 for periods of up to 18 days. Thermal degradation patterns, mechanical analysis, and leachable fraction data are provided. Part 2 shows experiments coupling 3D printed reactors and flow devices for in situ small-angle x-ray scattering (SAXS). Schwertmannite (pH 2.7) and goethite (6.2) are precipitated from solution using various setups and observed differences in growth rates are discussed. The data show the potential of 3D printing for enabling novel laboratory geochemical experiments.
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    Establishing the suitability of 3D-printed devices for low-temperature geochemical experiments
    Kletetschka, Karel; Rimstidt, J. Donald; Long, Timothy E.; Michel, F. Marc (Elsevier, 2018-08-23)
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    Nanocomposite structure of two-line ferrihydrite powder from total scattering
    Funnell, Nicholas P.; Fulford, Maxwell F.; Inoue, Sayako; Kletetschka, Karel; Michel, F. Marc; Goodwin, Andrew L. (2020-02-21)
    Ferrihydrite is one of the most important iron-containing minerals on Earth. Yet determination of its atomic-scale structure has been frustrated by its intrinsically poor crystallinity. The key difficulty is that physically-different models can appear consistent with the same experimental data. Using X-ray total scattering and a nancomposite reverse Monte Carlo approach, we evaluate the two principal contending models-one a multi-phase system without tetrahedral iron(III), and the other a single phase with tetrahedral iron(III). Our methodology is unique in considering explicitly the complex nanocomposite structure the material adopts: namely, crystalline domains embedded in a poorly-ordered matrix. The multi-phase model requires unphysical structural rearrangements to fit the data, whereas the single-phase model accounts for the data straightforwardly. Hence the latter provides the more accurate description of the short- and intermediate-range order of ferrihydrite. We discuss how this approach might allow experiment-driven (in)validation of complex models for important nanostructured phases beyond ferrihydrite. Although a geologically important mineral, the atomic-scale structure of ferrihydrite remains unresolved. Here the authors combine X-ray total scattering and reverse Monto Carlo to evaluate the two principal contending models, explicitly considering the material's complex nanocomposite structure.