TY - JOUR A1 - Kojda, Danny A1 - Hofmann, Tommy A1 - Gostkowska-Lekner, Natalia Katarzyna A1 - Habicht, Klaus T1 - Characterization and modeling of the temperature-dependent thermal conductivity in sintered porous silicon-aluminum nanomaterials JF - Nano research N2 - Nanostructured silicon and silicon-aluminum compounds are synthesized by a novel synthesis strategy based on spark plasma sintering (SPS) of silicon nanopowder, mesoporous silicon (pSi), and aluminum nanopowder. The interplay of metal-assisted crystallization and inherent porosity is exploited to largely suppress thermal conductivity. Morphology and temperature-dependent thermal conductivity studies allow us to elucidate the impact of porosity and nanostructure on the macroscopic heat transport. Analytic electron microscopy along with quantitative image analysis is applied to characterize the sample morphology in terms of domain size and interpore distance distributions. We demonstrate that nanostructured domains and high porosity can be maintained in densified mesoporous silicon samples. In contrast, strong grain growth is observed for sintered nanopowders under similar sintering conditions. We observe that aluminum agglomerations induce local grain growth, while aluminum diffusion is observed in porous silicon and dispersed nanoparticles. A detailed analysis of the measured thermal conductivity between 300 and 773 K allows us to distinguish the effect of reduced thermal conductivity caused by porosity from the reduction induced by phonon scattering at nanosized domains. With a modified Landauer/Lundstrom approach the relative thermal conductivity and the scattering length are extracted. The relative thermal conductivity confirms the applicability of Kirkpatrick's effective medium theory. The extracted scattering lengths are in excellent agreement with the harmonic mean of log-normal distributed domain sizes and the interpore distances combined by Matthiessen's rule. KW - thermal conductivity KW - mesoporous silicon KW - porosity KW - spark plasma KW - sintering KW - nanoscale modeling Y1 - 2022 U6 - https://doi.org/10.1007/s12274-022-4123-y SN - 1998-0124 SN - 1998-0000 VL - 15 IS - 6 SP - 5663 EP - 5670 PB - Tsinghua Univ. Press CY - Beijing ER - TY - JOUR A1 - Zhang, Yan-qiu A1 - Guo, Zeng-hui A1 - Chen, Dai-zhao T1 - Porosity distribution in cyclic dolomites of the Lower Qiulitag Group (Upper Cambrian) in northwestern Tarim Basin, China JF - China geology N2 - Increasing interests in hydrocarbon resources at depths have drawn greater attentions to the deeply-buried carbonate reservoirs in the Tarim Basin in China. In this study, the cyclic dolomite rocks of Upper Cambrian Lower Qiulitag Group from four outcrop sections in northwestern Tarim Basin were selected to investigate and evaluate the petrophysical properties in relation to depositional facies and cyclicity. The Lower Qiulitag Group includes ten lithofacies, which were deposited in intermediate to shallow subtidal, restricted shallow subtidal, intertidal, and supratidal environments on a carbonate ramp system. These lithofacies are vertically stacked into repeated shallowing-upward, meter-scale cycles which are further grouped into six third-order depositional sequences (Sq1 to Sq6). There are variable types of pore spaces in the Lower Qiulitag Group dolomite rocks, including interparticle, intraparticle, and fenestral pores of primary origin, inter crystal, and vuggy pores of late diagenetic modification. The porosity in the dolomites is generally facies-selective as that the microbially-originated thrombolites and stromatolites generally yield a relatively high porosity. In contrast, the high-energy ooidal grainstones generally have very low porosity. In this case, the microbialite-based peritidal cycles and peritidal cycle-dominated highstand (or regressive) successions have relatively high volumes of pore spaces, although highly fluctuating (or vertical inhomogeneous). Accordingly, the grainstone-based subtidal cycles and subtidal cycle-dominated transgressive successions generally yield extremely low porosity. This scenario indicates that porosity development and preservation in the thick dolomite successions are primarily controlled by depositional facies which were influenced by sea-level fluctuations of different orders and later diagenetic overprinting. KW - Dolomites KW - porosity KW - cyclicity KW - Upper Cambrian KW - stromatolite KW - microbial KW - build up KW - oil-gas basin KW - oil-gas exploration engineering KW - Tarim Basin KW - China Y1 - 2020 UR - http://en.cgsjournals.com/zgdzdcqkw-data/zgdzyw/2020/3/PDF/cg2020026.pdf SN - 2096-5192 SN - 2589-9430 VL - 3 IS - 3 SP - 425 EP - 444 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Behl, Marc A1 - Zhao, Qian A1 - Lendlein, Andreas T1 - Glucose-responsive shape-memory cryogels JF - Journal of materials research : JMR N2 - Boronic ester bonds can be reversibly formed between phenylboronic acid (PBA) and triol moieties. Here, we aim at a glucose-induced shape-memory effect by implementing such bonds as temporary netpoints, which are cleavable by glucose and by minimizing the volume change upon stimulation by a porous cryogel structure. The polymer system consisted of a semi-interpenetrating network (semi-IPN) architecture, in which the triol moieties were part of the permanent network and the PBA moieties were located in the linear polymer diffused into the semi-IPN. In an alkaline medium (pH = 10), the swelling ratio was approximately 35, independent of C-glu varied between 0 and 300 mg/dL. In bending experiments, shape fixity R-f approximate to 80% and shape recovery R-r approximate to 100% from five programming/recovery cycles could be determined. R-r was a function of C-glu in the range from 0 to 300 mg/dL, which accords with the fluctuation range of C-glu in human blood. In this way, the shape-memory hydrogels could play a role in future diabetes treatment options. KW - shape memory KW - polymer KW - porosity Y1 - 2020 U6 - https://doi.org/10.1557/jmr.2020.204 SN - 0884-2914 SN - 2044-5326 VL - 35 IS - 18 SP - 2396 EP - 2404 PB - Springer CY - Berlin ER - TY - JOUR A1 - Léonard, Fabien A1 - Zhang, Zhen A1 - Krebs, Holger A1 - Bruno, Giovanni T1 - Structural and morphological quantitative 3D characterisation of ammonium nitrate prills by X-ray computed tomography JF - Materials N2 - The mixture of ammonium nitrate (AN) prills and fuel oil (FO), usually referred to as ANFO, is extensively used in the mining industry as a bulk explosive. One of the major performance predictors of ANFO mixtures is the fuel oil retention, which is itself governed by the complex pore structure of the AN prills. In this study, we present how X-ray computed tomography (XCT), and the associated advanced data processing workflow, can be used to fully characterise the structure and morphology of AN prills. We show that structural parameters such as volume fraction of the different phases and morphological parameters such as specific surface area and shape factor can be reliably extracted from the XCT data, and that there is a good agreement with the measured oil retention values. Importantly, oil retention measurements (qualifying the efficiency of ANFO as explosives) correlate well with the specific surface area determined by XCT. XCT can therefore be employed non-destructively; it can accurately evaluate and characterise porosity in ammonium nitrate prills, and even predict their efficiency. KW - ANFO KW - explosives KW - specific surface area KW - porosity KW - XCT KW - data processing Y1 - 2020 U6 - https://doi.org/10.3390/ma13051230 SN - 1996-1944 VL - 13 IS - 5 PB - MDPI CY - Basel ER -