Untersuchungen zur Carboreduktion und Carboiodierung titanoxidhaltiger Edukte sowie zur Trennung von Iodidgemischen durch Sublimation

In der vorliegenden Arbeit wurden die grundlegenden Reaktionen eines Carboiodierungsprozesses und die fraktionierte Sublimation von Iodiden untersucht. Eine eingehende Literaturrecherche schuf die wissenschaftliche Ausgangsbasis für das Vorhaben und gab wichtige Hinweise auf die Reaktionsbedingungen und die chemisch-physikalischen Eigenschaften der Edukte. Zunächst wurde mit Reduktionsversuchen nach den optimalen Reaktionspartnern aus titanhaltigem Edukt und Kohlenstoffform gesucht. Dabei sollte bei möglichst niedriger Maximaltemperatur Ti2O3 als Produkt entstehen. Es zeigte sich, dass ein Gemisch aus reaktiv-gemahlenem Ilmenit und Holzkohle, das in einer Schwingmühle homogenisiert wurde, das beste Verhalten zeigte. Während bei den meisten Versuchen die Reduktion zu Ti2O3 erst bei über 1100 °C gelang, war es bei dem genannten Gemisch schon bei 950 °C möglich. In späteren Versuchen wurde dann gleichzeitig zur Reduktion Iod mit in den Reaktionsraum gegeben. Es zeigte sich, dass bei Anwesenheit von Iod schon ab 900 °C Reduktionsprodukte auftreten und Titantetraiodid gewonnen werden kann. Das beste Ergebnis konnte mit einem nano-Anatas-Thermolysekohlenstoff-Gemisch erzielt werden. Versuche mit Ilmenit zeigten etwas schlechtere Ergebnisse. Zwar fanden sich nach der Reaktion in der Komprette Phasen von teilreduzierten Titanoxiden, jedoch so gut wie kein Titantetraiodid als Sublimat am Kühlfinger der Reaktionsapparatur. Überraschend war, dass auch Titancarbid bei 950 °C mit Iod reagiert und Titantetraiodid bildet. Die Versuche zur fraktionierten Sublimation zeigten, dass sich ein Gemisch aus Iodiden, wie sie bei der Carboiodierung von unreinem Ilmenit auftreten können, zumindest grob auftrennen lässt. Die auftretenden Iodide können nach ihren Schmelzpunkten in zwei Gruppen eingeteilt werden. Einerseits lassen sich I2, TiI4, SiI4 und AlI3 gruppieren, da ihre Schmelzpunkte zwischen 100 und 200 °C liegen. Anderseits haben die Iodide FeI2, CaI2, MgI2 und MnI2 Schmelzpunkte zwischen 500 und 700 °C. Bei den Versuchen zeigte sich, dass sich die niedrig-sublimierenden Iodide gut von den hochsublimierenden Iodiden abtrennen lassen, da letztere bei der gewählten Temperatur von 200 °C keinen Dampfdruck aufweisen. Weiterhin zeigen auch die niedrig-sublimierenden Iodide untereinander eine grundsätzliche Trennbarkeit. Zwar konnten in den Versuchen nur selten reine Phasen nach der Sublimation gefunden werden. Jedoch waren die jeweiligen Sublimate aus unterschiedlichen Bereichen oft stark mit einem der gewählten Iodide angereichert. Die Optimierung der Reaktionsapparatur wird hier sicher zu einer höheren Trennwirkung führen. Insgesamt konnte gezeigt werden, dass die Carboiodierung als neuer Syntheseweg für Titantetraiodid im Labormaßstab geeignet ist. Es müssen weitere Untersuchungen und eine Ansatzvergrößerung folgen, um die Eignung als industrielles Verfahren belegen zu können. Die Sublimation als Trennverfahren für Iodidgemische hat sich als prinzipiell möglich gezeigt, jedoch verläuft der Prozess sehr langsam und die Trennwirkung war bislang noch nicht gut.In the present work, the basic reactions of a carboiodination process and fractional sublimation of iodides were investigated. A thorough literature survey provided the scientific basis for the project and gave important information on the reaction conditions and the physico-chemical properties of the reactants. First, a selection of optimal reaction candidates of titanium containing reactants and different carbon modifications was made with reduction experiments. The main objective was to obtain the product Ti2O3 at the lowest temperature possible. It was found that a mixture of reactive-milled ilmenite and charcoal, which was homogenized in a vibratory mill, showed the best performance. Although the reduction to Ti2O3 succeeded only at about 1100 °C in the most experiments, with the given mixture it was possible at 950 °C. In subsequent experiments iodine was added into the reaction chamber simultaneously with the reduction. It was found that in the presence of iodine starting at 900 °C reduction products occur and titanium tetraiodide can be obtained. The best result was achieved with a mixture of nano-anatase and thermolytic carbon. Experiments with ilmenite showed slightly worse results. While phases of partially reduced titanium oxides were found after the reaction, virtually no titanium tetraiodide occurred as a sublimate on the cooling finger of the reaction apparatus. Surprisingly, titanium carbide reacts with iodine at 950 °C and forms titanium tetraiodide. The experiments concerning the fractional sublimation showed that a mixture of iodides, which may occur in the carboiodination of technical ilmenite, at least can be roughly separated. The occurring oxides can be divided into two groups according to their melting points. On the one hand I2, TiI4, SiI4 and AlI3 can be grouped, because their melting points range from 100 to 200 °C. On the other hand, the melting points of FeI2, CaI2, MgI2 and MnI2 range from 500 to 700 °C. The experiments showed that the low-sublimating iodides can be separated well from the high-sublimating iodides, since the latter have no vapor pressure at the selected temperature of 200 °C. Furthermore, the low-sublimating iodides show a fundamental separability among themselves. Although pure phases were rarely found after sublimation, the respective sublimates from different areas were often highly rich of one of the selected iodides. The optimization of the reaction apparatus will certainly lead to a higher separation efficiency. Summarizing, it has been shown that the carboiodination is suitable as a new synthetic route for titanium tetraiodide in laboratory scale. Further investigations and an increase of the batch size have to follow in order to confirm the suitability as an industrial process. The sublimation as a separation method for iodide mixtures has shown to be possible in principle, but the process is very slow and the separation efficiency was not yet well

Electron Spin Resonance on the spin-1/2 triangular magnet NaYbS2

The delafossite structure of NaYbS2 contains a planar spin-1/2 triangular lattice of Yb3+ ions and features a possible realisation of a quantum spin-liquid state. We investigated the Yb3+ spin dynamics by Electron Spin Resonance (ESR) in single-crystalline samples of NaYbS2. Very clear spectra with a well-resolved and large anisotropy could be observed down to the lowest accessible temperature of 2.7 K. In contrast to the ESR properties of other known spin-liquid candidate systems, the resonance seen in NaYbS2 is accessible at low fields (< 1T) and is narrow enough for accurate characterisation of the relaxation rate as well as the g factor of the Yb3+ spins.Comment: 8 page

Discovery, Crystal Growth, and Characterization of Garnet Eu2PbSb2Zn3O12

Single crystal specimens of previously unknown garnet Eu2PbSb2Zn3O12 were grown in a reactive PbO:PbF2 flux medium. The crystals were characterized by a combination of X-ray crystallography, magnetization measurements, and the optical techniques of Raman, photoluminescence, and UV/Vis spectroscopy. The material exhibits Van Vleck paramagnetism associated with the J = 0 state of Eu3+, which was possible to accurately fit to a theoretical model. Band structure calculations were performed and compared to the experimental band gap of 1.98 eV. The crystals demonstrate photoluminescence associated with the 4f 6 configuration of the Eu3+ ions sitting at the distorted 8-coordinate garnet A site. The title compound represents a unique quinary contribution to a relatively unexplored area of rare earth bearing garnet crystal chemistry. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Supervised machine learning of environmental energy consumption types by AI algorithms targeting CO2 emission reduction and avoidance of bad air quality by giving recommendations

Behrens G, Schlender K, Brandt M, Kösling P. Supervised machine learning of environmental energy consumption types by AI algorithms targeting CO2 emission reduction and avoidance of bad air quality by giving recommendations. In: Schaldach R, Simon K-H, Weismüller J, Wohlgemuth V, eds. Environmental Informatics: Computational Sustainability. Skaker; 2019: 381 ff

Discovery, Crystal Growth, and Characterization of Garnet Eu 2

Single crystal specimens of previously unknown garnet Eu2PbSb2Zn3O12 were grown in a reactive PbO:PbF2 flux medium. The crystals were characterized by a combination of X-ray crystallography, magnetization measurements, and the optical techniques of Raman, photoluminescence, and UV/Vis spectroscopy. The material exhibits Van Vleck paramagnetism associated with the J = 0 state of Eu3+, which was possible to accurately fit to a theoretical model. Band structure calculations were performed and compared to the experimental band gap of 1.98 eV. The crystals demonstrate photoluminescence associated with the 4f 6 configuration of the Eu3+ ions sitting at the distorted 8-coordinate garnet A site. The title compound represents a unique quinary contribution to a relatively unexplored area of rare earth bearing garnet crystal chemistry. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Stripe-yz magnetic order in the triangular-lattice antiferromagnet KCeS2

Yb- and Ce-based delafossites were recently identified as effective spin-1/2 antiferromagnets on the triangular lattice. Several Yb-based systems, such as NaYbO2, NaYbS2, and NaYbSe2, exhibit no long-range order down to the lowest measured temperatures and therefore serve as putative candidates for the realization of a quantum spin liquid. However, their isostructural Ce-based counterpart KCeS2 exhibits magnetic order below TN = 400 mK, which was so far identified only in thermodynamic measurements. Here we reveal the magnetic structure of this long-range ordered phase using magnetic neutron diffraction. We show that it represents the so-called 'stripe-yz' type of antiferromagnetic order with spins lying approximately in the triangular-lattice planes orthogonal to the nearest-neighbor Ce–Ce bonds. No structural lattice distortions are revealed below TN, indicating that the triangular lattice of Ce3+ ions remains geometrically perfect down to the lowest temperatures. We propose an effective Hamiltonian for KCeS2, based on a fit to the results of ab initio calculations, and demonstrate that its magnetic ground state matches the experimental spin structure.This project was funded in part by the German Research Foundation (DFG) under the individual research Grant IN 209/9-1, via the project C03 of the Collaborative Research Center SFB 1143 (project-id 247310070) at the TU Dresden, and the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter—ct.qmat (EXC 2147, project-id 390858490). SA thanks A Popov (IFW, Dresden) and M Vojta (TU Dresden) for fruitful discussions and acknowledges financial support from the German Research Foundation (DFG) under Grant No. AV 169/3-1. We also acknowledge V Joyet and S Djellit for technical assistance and Institut Laue-Langevin, Grenoble (France) for providing neutron beam time.Peer reviewe

Stripe-yzmagnetic order in the triangular-lattice antiferromagnet KCeS2

Yb- and Ce-based delafossites were recently identified as effective spin-1/2 antiferromagnets on the triangular lattice. Several Yb-based systems, such as NaYbO2, NaYbS2, and NaYbSe2, exhibit no long-range order down to the lowest measured temperatures and therefore serve as putative candidates for the realization of a quantum spin liquid. However, their isostructural Ce-based counterpart KCeS2 exhibits magnetic order below TN = 400 mK, which was so far identified only in thermodynamic measurements. Here we reveal the magnetic structure of this long-range ordered phase using magnetic neutron diffraction. We show that it represents the so-called 'stripe-yz' type of antiferromagnetic order with spins lying approximately in the triangular-lattice planes orthogonal to the nearest-neighbor Ce–Ce bonds. No structural lattice distortions are revealed below TN, indicating that the triangular lattice of Ce3+ ions remains geometrically perfect down to the lowest temperatures. We propose an effective Hamiltonian for KCeS2, based on a fit to the results of ab initio calculations, and demonstrate that its magnetic ground state matches the experimental spin structure

Identification of behavior changes in energy consumption behavior with machine learning

Schlender K, Brandt M, Schmidt K, et al. Identification of behavior changes in energy consumption behavior with machine learning. In: Wohlgemuth V, Naumann S, Arndt H-K, Behrens G, eds. Environmental Informatics – A bogeyman or saviour to achieve the UN Sustainable Development Goals?. Shaker; 2021: 236 ff