TY - GEN A1 - Heinemann, Robert A1 - Schmidt, Peer T1 - Crystal Growth by Chemical Vapor Transport: Process Screening by Complementary Modeling and Experiment T2 - Crystal Growth & Design N2 - Despite chemical vapor transport (CVT) being a widely used method for crystal growth of inorganic substances, detailed mechanistic studies on the course of the crystallization process are rather few. In this study, an elaborated experimental screening run combined with sophisticated modeling of the respective heterogeneous equilibria is presented: Crystal growth of germanium by vapor transport with the addition of iodine has been chosen as a model system for validation of the applied method spectrum. In order to record the course and the interplay of heterogeneous equilibrium and non-equilibrium reactions in the system Ge–I, the experimental setup of high-temperature gas-balance (HTGB) is applied. Additionally, the observed evaporation processes are compared with saturation curves of corresponding volatile substances and, thus, can be assigned to individual species within the system. In this experimental screening, a phase sequence means to examine how the condensed phases undergo iodine depletion and how the gaseous phase undergoes a germanium enrichment when the temperature is increased. This phase screening combined with annealing experiments in the course of the phase sequence helps to analyze stepwise non-equilibrium products and to identify the characteristic species. Subsequently, for the evaluation of the composition of the gaseous phase, and for the deduction of the vapor transport mechanism, thermodynamic modeling by the CalPhaD method is performed. For the reference system, it is confirmed that iodine does not act as the transport agent. Instead, GeI4 is responsible for the volatilization of germanium, forming GeI2. Nevertheless, investigations clearly illustrate how GeI4 forms naturally in the phase sequence in the system Ge–I, which makes direct addition of it unnecessary. The recommended temperature range for vapor transport of germanium spans from 460 to 800 °C. Modeling shows that migration rates for germanium reaches a maximum at a mean temperature between 540 and 550 °C. Finally, vapor transport experiments were performed from 565 to 515 °C and from 690 to 590 °C. By increasing the deposition temperature, a slight decrease of the migration rate was observed, though a positive impact on the crystal’s morphology was also found. KW - Crystal growth KW - Chemical vapor transport KW - High-temperature Gas-balance KW - Thermodynamic modeling KW - Phase barogram KW - Germanium Y1 - 2020 UR - https://pubs.acs.org/doi/abs/10.1021/acs.cgd.0c00679 U6 - https://doi.org/10.1021/acs.cgd.0c00679 SN - 1528-7505 SN - 1528-7483 VL - 20 IS - 9 SP - 5986 EP - 6000 ER - TY - GEN A1 - Jurischka, Christoph A1 - Dinter, Franziska A1 - Efimova, Anastasia A1 - Weiss, Romano A1 - Schiebel, Juliane A1 - Schulz, Christian A1 - Fayziev, Bekzodjon A1 - Schierack, Peter A1 - Fischer, Thomas A1 - Rödiger, Stefan T1 - An explorative study of polymers for 3D printing of bioanalytical test systems T2 - Clinical Hemorheology and Microcirculation N2 - Background: The 3D printing is relevant as a manufacturing technology of functional models for forensic, pharmaceutical and bioanalytical applications such as drug delivery systems, sample preparation and point-of-care tests. Objective: Melting behavior and autofluorescence of materials are decisive for optimal printing and applicability of the product which are influenced by varying unknown additives. Methods: We have produced devices for bioanalytical applications from commercially available thermoplastic polymers using a melt-layer process. We characterized them by differential scanning calorimetry, fluorescence spectroscopy and functional assays (DNA capture assay, model for cell adhesion, bacterial adhesion and biofilm formation test). Results: From 14 tested colored, transparent and black materials we found only deep black acrylonitrile-butadiene-styrene (ABS) and some black polylactic acid (PLA) useable for fluorescence-based assays, with low autofluorescence only in the short-wave range of 300-400 nm. PLA was suitable for standard bioanalytical purposes due to a glass transition temperature of approximately 60°C, resistance to common laboratory chemicals and easy print processing. For temperature-critical methods, such as hybridization reactions up to 90°C, ABS was better suited. Conclusions: Autofluorescence was not a disadvantage per se but can also be used as a reference signal in assays. The rapid development of individual protocols for sample processing and analysis required the availability of a material with consistent quality over time. For fluorescence-based assays, the use of commercial standard materials did not seem to meet this requirement. KW - Thermal analysis KW - 3D Printing Y1 - 2020 UR - https://pubmed.ncbi.nlm.nih.gov/31929149/ U6 - https://doi.org/10.3233/CH-190713 SN - 1875-8622 VL - 75 IS - 1 SP - 57 EP - 84 ER - TY - GEN A1 - Hansen, Felix A1 - Wels, Martin A1 - Froeschke, Samuel A1 - Popov, Alexey A1 - Wolf, Daniel A1 - Büchner, Bernd A1 - Schmidt, Peer A1 - Hampel, Silke T1 - Thermodynamic Evaluation and Chemical Vapor Transport of Few-Layer WTe2 T2 - Crystal Growth and Design N2 - Tungsten telluride WTe2 is the sole candidate of a group of two-dimensional layered transition metal dichalcogenides (TMDCs) MX2 with a thermodynamically stable 1T′-structure at room temperature. The binary system W/Te was audited with respect to a rational approach of planning and realization of a bottom-up synthesis of WTe2 nanostructures. Thus, the parameters of the synthesis via chemical vapor transports (CVT) were derived by thermodynamic simulations of the reaction pathway according to the Calphad method. Reflecting on the peritectic melting behavior at 1020 °C, the values of ΔfHm° (298 K) = −26.5 kJ·mol−1 and Sm° (298 K) = 132 J·mol−1 ·K−1 have been obtained. According to modeling, crystal growth by short time vapor transport is reasonable under the addition of bromine or TeBr4 in the temperature range between 650 and 750 °C. Experimental implementation of crystal growth of WTe2 nanosheets succeeded in a temperature gradient from 725 to 675 °C on yttria-stabilized zirconia (YSZ) (111) substrates, observing the deposition of single crystal sheets of high crystallinity with thicknesses of 15−20 nm (∼20−30 layers). The high crystallinity, pristine morphology, and overall quality of the deposited nanosheets is shown by means of atomic resolution transmission electron microscopy, selected area electron diffraction (SAED), and atomic force microscopy as well as profound double-polarized Raman spectroscopy. KW - Crystal growth KW - Chemical vapor transport KW - Thermodynamic modeling KW - 2D layered compounds KW - Chalcogenides KW - Phase diagram Y1 - 2020 UR - https://pubs.acs.org/doi/abs/10.1021/acs.cgd.0c01004 U6 - https://doi.org/10.1021/acs.cgd.0c01004 SN - 1528-7505 VL - 20 IS - 11 SP - 7341 EP - 7349 ER - TY - GEN A1 - Garai, Bikash A1 - Bon, Volodymyr A1 - Efimova, Anastasia A1 - Gerlach, Martin A1 - Senkovska, Irena A1 - Kaskel, Stefan T1 - Reversible switching between positive and negative thermal expansion in a metal–organic framework DUT-49 T2 - Journal of Materials Chemistry A N2 - Three-dimensional architectures constructed via coordination of organic ligands to metal ions (broadly termed metal–organic frameworks, MOFs), are highly interesting for many demanding applications such as gas adsorption, molecular separation, heterogeneous catalysis, molecular sensing, etc. Being constructed from heterogeneous components, such framework solids show characteristic features from both the individual components and framework-specific features. One such interesting physicochemical property is thermal expansion, which arises from thermal vibration from the organic linker and metal ions. Herein, we show a very unique example of thermal responsiveness for the DUT-49 framework, a MOF well-known for its distinctive negative gas adsorption (NGA) properties. In the guest-free form, the framework shows another counter-intuitive phenomenon of negative thermal expansion (NTE), i.e. the lattice size increases with decrease of temperature. However, in the solvated state, it shows both NTE and positive thermal expansion (i.e. lattice size decreases with lowering of temperature, PTE) based on a specific temperature range. When the solvent exists in the liquid form inside the MOF pore, it retains the pristine NTE nature of the bare framework. But freezing of the solvent inside the pores induces the strain, which causes a structural transformation through in-plane bending of the linker and this squeezes the framework by ∼10% of the unit cell volume. This effect has been verified using 3 different solvents where the structural contraction occurs immediately at the freezing point of the individual solvent. Furthermore, studies on a series of DUT-49(M) frameworks with varying metals confirm the general applicability of this mechanism. KW - Metal organic framework (MOF) KW - Thermal analysis KW - Crystal structure Y1 - 2020 UR - https://pubs.rsc.org/en/content/articlehtml/2020/ta/d0ta06830f U6 - https://doi.org/10.1039/D0TA06830F SN - 2050-7496 VL - 39 IS - 8 SP - 20420 EP - 20428 ER - TY - GEN A1 - Knorr, Monika A1 - Icker, Maik A1 - Efimova, Anastasia A1 - Schmidt, Peer T1 - Reactivity of Ionic Liquids: Studies on Thermal Decomposition Behavior of 1-Butyl-3-methylimidazolium Tetrafluoroborate T2 - Thermochimica Acta N2 - The Ionic Liquid 1-butyl-3-methylimidazolium tetrafluoroborate [C4C1im]BF4 serves as a commonly solvent in inorganic material synthesis and analytics. Nevertheless, its application is frequently associated with trial and error approaches. Thereupon, detailed knowledge on the thermal behavior is the key information for understanding the reactivity of [C4C1im]BF4. 1-butyl-3-methylimidazolium tetrafluoroborate behaves as a glass in the cold, its glass transition temperature being ϑg = −83 °C. During heating with 10 K·min−1 [C4C1im]BF4 appears to be stable above 350 °C with onset temperatures ϑonset, DSC = 375 °C, ϑonset, DTG = 422 °C, and ϑonset, TG = 437 °C. Thereby, thermal decomposition occurs in a single step reaction forming 1-methyl-1H-imidazole (CH3C3H3N2 or C4H6N2), but-1-ene (C4H8), fluoromethane (CH3F) and boron trifluoride (BF3) as main species, as determined by thermogravimetry coupled with mass spectrometry and FTIR spectroscopy. To be more specific in thermal behavior, the temperature and time dependent stability is evaluated here on the basis of the kinetic model of maximum operation temperature − MOT. Clearly, thermal stability rises with application time, thus being 193 °C for one hour, while reaching only 141 °C for one day, and 114 °C for one week. The incipient decomposition (≤ 1 %) at the calculated time dependent maximum operation temperature finally is verified by optical analysis, infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy. Y1 - 2020 UR - https://www.sciencedirect.com/science/article/pii/S0040603120307012?via%3Dihub#! U6 - https://doi.org/10.1016/j.tca.2020.178786 SN - 0040-6031 VL - Vol. 694 SP - 1 EP - 11 ER - TY - GEN A1 - Knorr, Monika A1 - Schmidt, Peer T1 - Reactivity of ionic liquids: Reductive effect of [C4C1im]BF4 to form particles of red amorphous selenium and Bi2Se3 from oxide precursors T2 - ChemistryOpen N2 - Temperature-induced change in reactivity of the frequently used ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([C4C1im]BF4) is presented as a prerequisite for the rational screening of reaction courses in material synthesis. [C4C1im]BF4 becomes active with oxidic precursor compounds in reduction reaction at ϑ > 200°C, even without the addition of an external reducing agent. The reaction mechanism of forming red amorphous selenium from SeO2 is investigated as a model system and can be described similarly to the Riley oxidation. The reactive species but-1-ene, which is formed during the decomposition of [C4C1im]BF4, reacts with SeO2 and form but-3-en-2-one, water, and selenium. Elucidation of the mechanism was achieved by thermoanalytical investigations. The mono-tropic phase transition of selenium was analyzed by the differential scanning calorimetry. Beyond, the suitability of the single source oxide precursor Bi2Se3O9 for the synthesis of Bi2Se3 particles was confirmed. Identification, characterization of formed solids succeeded by using light microscopy, XRD, SEM, and EDX. KW - Ionic liquid KW - Thermal analysis KW - Thermal decomposition KW - Chalcogenides KW - Selenium KW - Inorganic synthesis Y1 - 2021 UR - https://chemistry-europe.onlinelibrary.wiley.com/doi/epdf/10.1002/open.202000264 U6 - https://doi.org/10.1002/open.202000264 SN - 2191-1363 VL - 10 IS - 2 SP - 125 EP - 140 ER - TY - GEN A1 - Klepel, Olaf A1 - Utgenannt, Stephan A1 - Vormelchert, Carolin A1 - König, Mark A1 - Meißner, André A1 - Hansen, Felix A1 - Bölte, Jens-Henning Ingo Holger A1 - Sieber, Tim A1 - Heinemann, Robert A1 - Bron, Michael A1 - Rokicinska, Anna A1 - Jarczewski, Sebastian A1 - Kustrowski, Piotr T1 - Redox catalysts based on amorphous porous carbons T2 - Microporous Mesoporous Materials Y1 - 2021 U6 - https://doi.org/10.1016/j.micromeso.2021.111257 SN - 1387-1811 VL - 323 ER - TY - GEN A1 - Meißner, André A1 - Efimova, Anastasia A1 - Schmidt, Peer T1 - Impacts of TGA furnace parameters for prediction of long-term thermal stability of ionic liquids T2 - Thermochimica Acta N2 - The concept of maximum operation temperature is established for the prediction of the time dependent thermal stability of ionic liquids based on kinetic evaluation of thermogravimetric analysis. The influence of the furnace control parameters on the maximum operation temperature (MOT) is shown using the example of 1-methyl-3-propylimidazolium iodide ([C3C1im]I) with respect to three different parameter sets of a programmed proportional integral derivative (PID) controller of the TGA. Kinetics of thermal decomposition of [C3C1im]I have been investigated with the implementation of an improved kinetic model. The activation energy obtained using the Kissinger-Akahira-Sunose equation showed variations apparently due to the decomposition degree. The model compound is decomposed by a one-step kinetics, which results from pseudo zero order relationship of the activation energy to the conversion rate. The activation energy, pre-exponential factor, and the activation energy are strongly dependent on the parameters of TGA furnace controller. KW - Ionic liquid KW - Thermal analysis KW - Thermal decomposition Y1 - 2021 UR - https://www.sciencedirect.com/science/article/pii/S0040603121000587#! U6 - https://doi.org/10.1016/j.tca.2021.178917 VL - 704 SP - 178917-1 EP - 178917-7 ER - TY - GEN A1 - Ivshin, Kamil A1 - Metlushka, Kirill A1 - Zinnatullin, Ruzal A1 - Nikitina, Kristina A1 - Pashagin, Alexander A1 - Zakharychev, Dmitry V. A1 - Efimova, Anastasia A1 - Kiiamov, Airat A1 - Latypov, Shamil A1 - Kataeva, Olga T1 - Competitive Hydrogen Bonding and Unprecedented Polymorphism in Selected Chiral Phosphorylated Thioureas T2 - Crystal Growth Design N2 - New racemic and enantiopure N-phosphorylated thioureas bearing 1-phenylethyl or tetrahydronaphthalenyl fragments were synthesized. According to NMR data assisted by DFT calculations, the preferred conformation is stabilized by an intramolecular hydrogen bond. This form in solution is in equilibrium with dimeric N–H···S hydrogen-bonded associates, the population depending on the concentration. In the crystalline phase the low-energy conformation with an intramolecular H-bond is realized only in the racemic tetrahydronaphthalenyl derivative. In most crystals various types of intermolecular hydrogen bonding are observed, accompanied by the formation of infinite linear chains or helical structures. Due to the conformational lability of compounds and competitive intermolecular H-bonding, multiple polymorphic modifications are formed. Therefore, crystallization of enantiopure 1-phenylethyl derivatives from various solvents results in concomitant polymorphs at room temperature. One of them undergoes reversible two-step phase transitions from the high-symmetry I41 space group (Z′ = 1, no disorder) via the P41 space group (Z′ = 6) to the monoclinic P21 space group (Z′ = 16) accompanied by drastic concerted conformational changes. Notably, the optimization of the crystal packing is observed upon phase transitions with a gradual reduction of the void space in the unit cell from 4.5% to 0.8%. This is a rare case of several high-Z′ polymorphs for one compound, with chirality playing an important role. KW - Crystal growth KW - Crystal structure KW - Thermal analysis KW - Polymorphism Y1 - 2021 UR - https://pubs.acs.org/doi/10.1021/acs.cgd.1c00758 U6 - https://doi.org/10.1021/acs.cgd.1c00758 SN - 1528-7505 SN - 1528-7483 VL - 21 IS - 9 SP - 5460 EP - 5471 ER - TY - RPRT A1 - Schmidt, Peer A1 - Donath, Ines A1 - Wels, Martin A1 - Pinnau, Sebastian A1 - Grau Turuelo, Constantino A1 - Breitkopf, Cornelia A1 - Hack, Klaus A1 - Baben, Moritz to A1 - Reis, Bruno A1 - Müller, Michael A1 - Sergeev, Dmitry A1 - Qi, Jia T1 - PCM Screening - Evaluierung eutektischer Gemische für den Einsatz als PCM: thermodynamische Modellierung und experimentelle Methoden : Energie Speicher: PCM-Screening : Schlussbericht N2 - Ein wichtiges Ziel der Bundesregierung ist der Ausbau des Anteils erneuerbarer Energien an der gesamten Stromerzeugung. Die Entwicklung optimierter Wärme- und Kältespeicher stellt einen wichtigen Baustein bei der Erreichung dieser Zielstellung dar. Elektrisch betriebene Wärmepumpen und Kompressionskältemaschinen sowie dezentrale Klein-BHKW bieten in Verbindung mit entsprechend dimensionierten, thermischen Speichern ein großes Potential zum Lastmanagement in Smart Grids und somit zur Netzintegration von Strom aus erneuerbaren Energien. Die im Projekt entwickelte Methodik zur Suche nach neuen Latentspeichermedien kann für ein breites Anwendungsfeld von Heiz- und Kühlanwendungen in Gebäuden bis hin zur Kraftwerkstechnik eingesetzt werden. Innerhalb der Fördermaßnahme „Anwendungsorientierte Forschung und Entwicklung zur nichtnuklearen Energieforschung“ im 6. Energieforschungsprogramm der Bundesregierung wurde durch die Projektarbeiten das Schwerpunktthema Energiespeicher (3.8) adressiert, wobei der Aspekt der Entwicklung neuer Materialien mit reduzierten Kosten für einen wirtschaftlichen Betrieb im Vordergrund stand. Speziell wurden dabei die Unterpunkte 3.8.4 Thermische Speicher zur Weiterentwicklung, Optimierung und Erprobung von PCM sowie 3.8.5 Übergeordnete Themen mit Modellen und Simulationswerkzeugen für die Auswahl und Bewertung neuer Speichermaterialien adressiert. Die Projektergebnisse besitzen aber auch Berührungspunkte mit den Schwerpunkten 3.12 Energieeffizienz in Industrie, Gewerbe, Handel und Dienstleistungen sowie 3.4 Solarthermische Kraftwerke, da mit der entwickelten Screening-Methode für diese Anwendungsfälle neue Wärmespeichermaterialien auf der Basis wasserfreier Salze mit höheren Prozesstemperaturen gefunden werden können. Durch den Einsatz von Methoden zur Modellierung und Simulation von Prozessen erfolgt gleichermaßen die Umsetzung einer energie- und ressourcenschonenden Forschungstätigkeit. Das im Projekt entwickelte Vorgehen hilft dabei, einen äußerst sparsamen Einsatz von Chemikalien, eine niedrige Belastung der Umwelt durch verringerten Entsorgungsaufwand der verbrauchten Stoffe sowie einen deutlich geringeren Aufwand und Energieeinsatz für die Messtechnik zu ermöglichen. Damit wurde zugleich das Schwerpunktthema 3.8.5 Modelle und Simulationswerkzeuge für die Auswahl und Bewertung neuer Speichermaterialien angesprochen. KW - Latentwärmespeicher KW - Phase diagram KW - Thermodynamic modeling KW - Thermal analysis Y1 - 2021 UR - https://www.tib.eu/de/suchen/id/TIBKAT:177643451X/ U6 - https://doi.org/10.2314/KXP:177643451X PB - TIB – Leibniz-Informationszentrum Technik und Naturwissenschaften CY - Hannover ER -