Technische Universität Bergakademie Freiberg
Recent publications
Blade design for a solar chimney power plant turbine is modeled geometrically. NACA 4412 blade is selected for its favorable lift to drag characteristics in the considered diameter range. The constructed model is integrated into a solar chimney plant and validated against existing examples in literature. A similar process is applied using a reverse fan model. Margins of discrepancies obtained from the turbine and reverse fan models are used as indicators for the total deviation expected from using the reverse fan model with a sloped collector plant. Here, the effect of turbine pressure change on the temperature rise and air flow are examined to set the upper limit of pressure drop and check the capacity of the system for power generation. The maximum air flow velocity at the center of the sloped collector reached 9.8 m/s. The highest achievable temperature difference was 37 °C. The favorable working zone for turbine operation inside the tower of a sloped collector solar chimney in terms of pressure drop and air flow rate is marked based on a constant efficiency.
Commercially available gray‐solidified cast iron exhibits reduced load‐carrying capacity under locally concentrated pressure with simultaneous sliding stress. Electron beam remelting dissolves the graphite near the surface, and the surface layer solidifies according to the metastable system. During subsequent gas nitriding, a dense compound layer forms on this white‐solidified, hard surface layer. The phase composition of the compound layer depends not only on the gas nitriding conditions, but also on the chemical composition of the cast iron. The effect of the individual processes of remelting and gas nitriding and their combination on the corrosion behavior of one ferritic and one pearlitic cast iron with different copper contents is investigated using potentiodynamic polarization measurements in 5% sodium chloride solution at room temperature. The remelted and nitrided surface layers exhibit the highest corrosion resistance. The proportion of iron carbonitrides γ ' and ε contained in the compound layer influences the corrosion behavior.
Die Biohydrometallurgie als Teilgebiet der Hydrometallurgie macht sich spezielle Stoffwechselleistungen von Mikroorganismen zur Metallgewinnung zu nutze. Biomining ist die angewandte Biolaugung zur Metallgewinnung aus sulfidischen Erzen. Für das Recycling, also die Metallgewinnung aus Abfall und Reststoffen, gibt es bisher noch keine angewandten biohydrometallurgischen Verfahren, aber vielversprechende Laborversuche zur Metallextraktion aus Feststoffen. In diesem Übersichtsartikel werden diese zusammenfassend dargestellt und Perspektiven aufgezeigt.
The title compound was prepared by reaction of the Schiff base ligand N-(2-hydroxy-1-naphthylidene)leucine with dichlorodimethylsilane in the presence of triethylamine as base. The resulting pentacoordinate silicon complex was characterized by NMR, IR, UV-Vis spectroscopy and melting point. The structure was confirmed by single-crystal X-ray diffraction data. It crystallizes in the monoclinic space group Ic with unit cell dimensions a = 7.2030(6), b = 22.9842(14), c = 10.8946(12) Å, β = 96.141(7)°, V = 1793.3(3) Å3, Z = 4.
The spatial analysis of horizontal stress orientation is important to study stress sources and understand tectonics and the deformation of the lithosphere. Additional to the stress sources, the geometry of stress fields depends on the underlying coordinate reference system, which causes spatial distortions that bias the analysis and interpretation of stresses. The bias can be avoided when the stress field is decomposed and transformed into the reference frame of its first-order stress source. We present a modified and extended theory based on the empirical link between the orientation of first-order stresses and the trajectories of lateral plate boundary forces. This link is applied to analyze the orientation of horizontal stresses, their patterns, and tectonic structures from the perspective of their first-order source or cause. By using only parameters for the relative motion between two neighboring plates, we model the first-order orientation of the maximum horizontal stress that statistically fits the orientation of ≥ 80% of the global stress data adjacent to plate boundaries. Considerable deviations of the observed stress from the predicted first-order stress direction can reveal the geometry of second-order stresses and confine areas where other stress sources dominate. The model’s simple assumptions, independence from the sample size, potential application to regional to global scale analysis, and compatibility with other spatial interpolation algorithms make it a powerful method for analyzing stress fields. For immediate use, the presented method is implemented in the free and open-source software package , which is written in the computer language R.
Plain Language Summary In 2022, western Europe recorded its hottest summer up to date since preindustrial times. At the same time, widespread dry conditions caused dramatic impacts on human health, water resources, crop yields and wildfires. This was partly enhanced by the human–caused cumulative emissions of greenhouse gases, but also potentially by large‐scale circulation anomalies that may also be triggered by global warming. By grouping distinct weather patterns, we find that many extreme hot days during the summer of 2022 over well‐defined parts of Europe were favored by anomalous transport of hot and dry air masses or persistent low‐wind conditions. These weather patterns were essential but not the dominant factor that led to the occurrence of extreme temperatures. Yet, they played a key role in enhancing the number of dry days. We also find that the weather patterns observed in summer 2022 will become more common in coming decades if greenhouse gas emissions remain without reduction. This would further worsen hot and dry extremes in summer over Europe.
Fe– x TiC in situ metal matrix composites (MMCs) are fabricated utilizing a cold crucible inductive melting (CCIM) technique with varying TiC amounts (2, 3.5, and 5 wt%). Steel blocks and pure Ti plates are remelted in a water‐cooled cupper crucible. The subsequent solidification of [Ti]‐ and [C]‐rich melt yields TiC reinforcement particles in an ingot. The holding time varies between 5 and 30 min, whereas the holding temperature alters depending on the amount of TiC, ranging from 1380 to 1620 °C for Fe‐5TiC and Fe‐2TiC, respectively. Alloying efficiency for TiC‐forming elements is estimated for all fabricated Fe– x TiC ingots by comparing [Ti] and [C] target values with measured ones. The lower TiC amounts and shorter holding times result in decreased [Ti] and [C] losses. SEM analysis of three cross‐section samples representing different TiC amounts reveals two distinct morphologies of TiC in situ reinforcements: primary blocky/cubic and eutectic plate‐like precipitates. The blocky precipitates appear slightly finer with a decrease in TiC amount (4.4 ± 1.2 μm for Fe‐5TiC and 3.8 ± 0.7 μm for Fe‐2TiC), whereas the length of plate‐like precipitates noticeably decreases in the samples with lower TiC amounts (11.0 ± 7.0 μm for Fe‐5TiC and 6.8 ± 3.6 μm for Fe‐2TiC).
Asymmetrically substituted s ‐triazine phosphonates with up to three different phosphonate groups C 3 N 3 RR'R” with R, R’, R”=PO(OR”’) and R”’=for example, methyl, ethyl, isopropyl or n ‐butyl are interesting as polymer additives like flame retardants. Typically, these compounds are obtained by multiple synthesis steps. However, this leads to high production costs, which are a disadvantage for commercial use. Here we report the one‐step synthesis of mixtures of asymmetrical s ‐triazine phosphonates which is an easy way to adjust the thermal behaviour and other properties such as viscosities of the compounds. The synthesis is based on a Michaelis–Arbuzov reaction. A complete conversion of the reactants to the target compounds is observed which was proofed by detailed ¹ H, ¹³ C and ³¹ P NMR investigations and elemental analysis. The thermal behaviour was compared with thermogravimetric analysis (TGA).
This study compares AZ91 with AZ31 to investigate the influence of a higher Al content on the resulting microstructure, mechanical properties, and hot deformation behavior. While AZ31 exhibits a globular structure after casting, AZ91 shows a fully developed dendritic structure due to the promotion of dendrites. A heat treatment helped to homogenize AZ31, dissolved a large part of the Mg-Al precipitations in AZ91, and formed globular grains in AZ91. Due to the impact of Al on constitutional supercooling, AZ91 exhibits smaller grains than AZ31. Because of the strengthening of the solid solution, AZ91 also exhibits higher strength and hardness compared to AZ31. Cylindric compression tests of the heat-treated samples were conducted at different temperatures (300–400 °C) and strain rates (0.1 × 10 s−1). The main dynamic recrystallization (DRX) mechanisms in AZ31 and AZ91 are twinning-induced DRX and discontinuous DRX. It was detected that Mg17Al12 precipitates at the grain boundaries in AZ91, which influences the grain size through pinning. Similar results could be conducted in rolling trials. Although both alloys have similar grain sizes after rolling, AZ91 exhibits higher strengths, while AZ31 shows higher ductility. This can be explained by the solid solution strengthening in AZ91 and less brittle Mg17Al12 precipitations in AZ31.
With the gradual transition towards assisted and automated driving, the car will transform into a more social environment where passengers and drivers engage in Non-Driving-Related Activities (NDRA). To support collaboration among occupants in future vehicles, research suggests interactive systems controlled by several users at once. In this paper, we explore five concepts for the collaborative performance of NDRA with the use-case of music playlist creation. While prior work investigated the effect on social connectedness, we expand insights towards team performance and fairness. Results from a mixed-subject experiment (N=27) show that the concepts have major consequences on team performance and fairness. Certain concepts can promote or hinder coordination effectiveness and, in turn, impact intra-vehicular collaboration. Our observations also indicate that fairness is key to fostering social collaboration in AVs, while it does not naturally define a high team performance. Subsequently, we provide recommendations to guide future designs of collaborative NDRAs in vehicles.
Geological energy is an abundant source of energy on Earth, encompassing both fossil and non-fossil forms such as oil, natural gas, coal, geothermal energy, shale gas, and coalbed methane [...]
To provide a better understanding of the contribution of specific constituents (i.e. proteoglycan, collagen, fluid) to the mechanical behavior of the superficial zone of articular cartilage, a complex biological tissue with several time-dependent properties, a finite element model was developed. Optimization was then used to fit the model to microindentation experiments. We used this model to compare superficial zone material properties of mature human vs. immature bovine articular cartilage. Non-linearity and stiffness of the fiber-reinforced component of the model differed between human and bovine tissue. This may be due to the more complex collagen architecture in mature tissue and is of interest to investigate in future work.
Climate change requires enhanced autonomous temperature monitoring during logistics/transport. A cheap approach comprises the use of temperature-sensitive copolymers that undergo temperature-induced irreversible coagulation. The synthesis/characterization of pentablock copolymers (PBCP) starting from poloxamer PEO130-b-PPO44-b-PEO130 (poly(ethylene oxide)130-b-poly(propylene oxide)44-b-poly(ethylene oxide)130) and adding two terminal qPDMAEMA85 (quaternized poly[(2-dimethylamino)ethyl methacrylate]85) blocks is presented. Mixing of PBCP solutions with hexacyanoferrate(III)/ferricyanide solutions leads to a reduction of the decane/water interfacial tension accompanied by a co/self-assembly toward flower-like micelles in cold water because of the formation of an insoluble/hydrophobic qPDMAEMA/ferricyanide complex. In cold water, the PEO/PPO blocks provide colloidal stability over months. In hot water, the temperature-responsive PPO block is dehydrated, leading to a pronounced temperature dependence of the oil-water interfacial tension. In solution, the sticky PPO segments exposed at the micellar corona cause a colloidal clustering above a certain threshold temperature, which follows Smoluchowski-type kinetics. This coagulation remains for months even after cooling, indicating the presence of a kinetically trapped nonequilibrium state for at least one of the observed micellar structures. Therefore, the system memorizes a previous suffering of heat. This phenomenon is linked to an exchange of qPDMAEMA-blocks bridging the micellar cores after PPO-induced clustering. The addition of ferrous ions hampers the exchange, leading to the reversible coagulation of Prussian blue loaded micelles. Hence, the Fe2+ addition causes a shift from history monitoring to the sensing of the present temperature. Presumably, the system can be adapted for different temperatures in order to monitor transport and storage in a simple way. Hence, these polymeric "flowers" could contribute to preventing waste and sustaining the quality of goods (e.g., food) by temperature-induced bouquet formation, where an irreversible exchange of "tentacles" between the flowers stabilizes the bouquet at other temperatures as well.
A series of mono- and dicationic 1,3,5-trisubstituted 2,4,6-triethylbenzenes containing pyridinium groups in combination with aminopyrimidine-/aminopyridine-based recognition units were synthesized and crystallographically studied. The combination of neutral and ionic building blocks represents a promising strategy for the development of effective and selective artificial receptors for anionic substrates. In the crystalline state, the investigated compounds show a tendency to bind the counterion PF6− in the cavity formed by the three functionalized side-arms. The intermolecular interactions with the PF6− ion comprise N-H∙∙∙F and C-H∙∙∙F bonds. Detailed analysis of various supramolecular motifs, including interactions with solvent molecules, provides deeper insights into the processes of molecular recognition. The information obtained is useful in the development of new receptor molecules for anions and in the selection of the most appropriate counterion.
Separate processes for shape setting and polishing of Nitinol workpieces are well investigated in scientific literature and adopted industrially. However, a simultaneous process for shape setting and polishing of Nitinol has not yet been reported. In this study, preliminary results of such process are presented, providing insights and directions for further research on post-processing shape memory materials. For this purpose, Nitinol wire samples with phase transformation temperatures Af = 4.5 °C, Af = 31 °C and Af = 61 °C were plasma electrolytic polished (PEP) while fitted in a specially designed sample holder at three electrolyte temperatures te = 50 °C, te = 65 °C and te = 80 °C. The PEP process duration was τPEP = 60 s, τPEP = 180 s and τPEP = 300 s. After the PEP processes, the samples were investigated for the shape memory effect (SME). The training effect, known to be present in shape memory alloys (SMA), was taken into account. The surface roughness of the investigated wires was measured before and after the PEP process. The obtained results demonstrate that both a phase transformation temperature and an electrolyte temperature have a strong effect on polishing and shape setting results.
The interaction of adsorbed water with the microstructure of cementitious materials leads to effects on macroscopic properties. However, precise quantitative correlation of adsorbed water with short‐term changes in macroscopic properties, such as dimensional changes, remains a challenge. We compare recent results from precise dual‐microscope‐based short‐term length change measurements and discuss differences in length‐change isotherms and adsorption isotherms arising from various cement types. Water vapor adsorption happens already at very low humidity in the interlayer space of the C‐S‐H gel. Adsorption and desorption on cement surfaces due to changing relative humidity induces strong forces in the cement gel, leading to detectable changes in dimensional stability for the hardened material. A significant hysteresis in the water desorption isotherm is often accompanied by hysteresis in dimensional change as well. For precise length change measurements, an optical method for tracking surface patterns on thin cement slices was applied. Short‐term length change results are compared to corresponding water vapor sorption isotherms and pore size measurements. Hypotheses and conclusions regarding microstructural changes and shrinkage mechanisms are discussed in order to understand the experimental data.
Young's modulus for ferritic and austenitic steel at high temperatures is typically acquired through acoustic emission tests. In this study, we applied an inverse solution method to consider the effect of a temperature gradient on samples under experimental conditions. Wachman model, Varshni models, and power model were used to describe the influence of temperature on the sound velocity of steel. The constants for these equations were acquired using an optimization scheme that minimized the error between calculated and measured travel times of sound in the samples. Using equations developed for the change in velocity under various temperatures, we calculated Young's modulus at low and high temperatures with acceptable accuracy.This method is non-destructive, and can be applied to measure Young's modulus at different temperatures using a single sample. The acquired Young's modulus values were compared with the results of a modified uniaxial tensile test that accurately measures strain at elevated temperatures. The results showed good agreement between Young's modulus values obtained using the two methods, demonstrating that incorporating the non-linear dependency of the sound velocity on temperature in Young's modulus calculations leads to higher accuracy at low and high temperatures.
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Nikolaus Klamerth
  • Institute of Geology
Hartmut Stöcker
  • Institute of Experimental Physics
Mohamed Sobh
  • Institute of Geophysics and Geoinformatics
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  • Institute of Business Computer Science / Information Economy
Oliver Wiche
  • Institute of Biosciences
09599, Freiberg, Germany