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The formation of accretion layers within the waste heat boiler is a serious operational concern as it can potentially increase boiler downtime and, hence, limit continuous production. In previous Computational Fluid Dynamics studies, the accretion formation was predicted for an industrial-scale waste heat boiler, using a dust stickiness sub-routine of the model. In this study, a dust sampling campaign was used to validate this stickiness sub-routine. Furthermore, various sticking and reaction mechanisms of flue dust were investigated and compared to thermodynamic predictions. While the results suggest that the sub-routine is valid, the comparison of thermodynamics and species in the samples showed that the chemical reactions of the flue dust did not reach the thermodynamic equilibrium. Graphical Abstract

The standard method to determine chemical oxygen demand (COD) with K2Cr2O6 uses harmful chemicals, has a long analysis time, and cannot be used for on-site online monitoring. It is therefore necessary to find a fast, cheap, and harmless alternative. The amperometric determination of COD on boron-doped diamond (BDD) electrodes is a promising approach. However, to be a suitable alternative, the electrochemical method must at least be able to determine the COD of water samples independently of the contained substances. Therefore, the current signal as a function of various organic materials was investigated for the first time. It was shown that the height of the signal current depended on the type of organic matter in single-substance solutions and that this substance dependency increases with the amount of COD. Those findings could be explained by the mechanism proposed for this reaction, showing that the selectivity of the reaction depends on the ratio of the concentration of hydroxyl radicals and organic species. We give an outlook on how to improve the method in order to increase the linear working range and avoid signal variance and how to further explain the signal variance.

Hydrogen in aluminum causes the formation of detrimental hydrogen porosity in castings. In order to reduce the formation of hydrogen pores, an approach was targeted using lithium as target for hydrogen. This approach utilizes the affinity of lithium for hydrogen, whereby spodumene (a lithium aluminum silicate) and lithium aluminate were used as lithium providers. Within the scope of this study, the preparation of ceramic foam filters with a coating of lithium-containing raw materials (spodumene) was investigated. Those investigations revealed that the spodumene coating has a detrimental influence on the bending strength of the foams when a certain level of spodumene is exceeded. This observation might be explainable by the intrusion of the spodumene into the alumina matrix of the skeleton foam. Two wetting tests at different temperatures were conducted, verifying the significant influence of the temperature on the reaction between the spodumene and AlSi7Mg. Furthermore, test filters coated with raw materials exhibiting different amounts of lithium were conducted. The hydrogen pores were evaluated by light microscopy and computed tomography. The analyzed pore size distribution in the aluminum did not elucidate the proximate influence of the lithium-coating on the ceramic foam filter on the hydrogen porosity in the aluminum.

The Flash Smelting Furnace (FSF) is one of the most common reactors for the primary smelting of copper concentrates. Its smooth operation depends on the availability and performance of the downstream Waste Heat Boiler (WHB). The WHB is especially sensitive to problems with its flue dust handling, such as the formation of accretions, which can lead to downtime and equipment failures. Due to the limited accessibility and the harsh conditions of the WHB, experimental studies are challenging. Therefore, CFD simulations can be a promising option to increase knowledge and evaluate a range of options. The present study investigates the physical behavior of flue dust in an industrial-scale WHB via a three-dimensional CFD model. Size-dependent particle sedimentation and the risk areas for flue dust accretions are predicted, finding good agreement with industrial experience and data from the literature. To make the evaluation of accretion risk zones possible, a new sticking function for flue dust is developed. The results are validated against dust samples. Finally, operational recommendations for minimizing flue dust accretions are derived.

Li-ion batteries often use transition metal oxide (TMO) positive electrodes. Sodium-based analogs are also an excellent option for all-solid-state sodium-based batteries. However, combining TMOs with solid electrolytes is challenging, both being rigid in nature. In this work, we use a polymeric secondary electrolyte to combine a sodium manganese oxide composite positive electrode with a sodium-beta alumina solid electrolyte (BASE) to an all-solid-state sodium battery. The composite electrode exhibits intimate interface contact with the solid electrolyte and well-established intra-electrode conduction pathways because mechanical flexible poly(ethylene oxide) acts as an ionically conducting auxiliary agent. The composite electrode shows an ionic conductivity of 5.5·10−6 S cm−1 at 80 °C. The careful co-treatment of the Na|BASE interface, resulting in a superior cycling stability of 1000 h at 0.35 mA cm−2 in a symmetric cell, enhances sodium’s wettability to the BASE surface. The full cell achieves an initial discharge capacity of 80 mAh g−1 at an average voltage of 2.78 V vs Na+/Na, corresponding to a specific energy of 155 Wh kg−1 (positive electrode). Hence, we provide a proof-of-concept for all-solid-state cells, which paves the way for numerous combinations of well-conducting polymeric secondary electrolytes with TMO active materials and BASE.

Among the numerous techniques for water remediation, disinfection, and hydrogen generation, only pyrocatalysis has the potential to harvest and utilize energy from the environment as well as industrial processes in the form of temperature differences. In this work, our purpose was to reach a drastic improvement of the pyrocatalytic activity of BaTiO3 powders (BT) by decreasing the particle size in combination with catalyst annealing at temperatures between RT and 1000 °C. In the end, we reached our goal for a BT with a nominal particle diameter of 50 nm via low-temperature annealing at temperatures of only 300 °C. The activity boost was demonstrated for the dichlorofluorescein (DCF) oxidation assay (+585 %), the degradation of 4-hexylresorcinol (+1150 %) and, for the first time, the successful degradation of the micropollutant bisphenol A (+460 %). Using material characterization in combination with in-depth literature comparisons, we elucidated the underlying mechanism. It deviates strongly from our original assumptions as it includes the generation of oxygen vacancies. Based on our findings, several strategies for further improving pyrocatalysis were derived to enable an effective catalyst design. This will help pyrocatalysis to take the next step on its way towards an energy-efficient technique for water remediation.

Local and climate-driven challenges combined with an increasing anthropogenic pollution of the water compartment all around the world make a sustainable handling of wastewater imperative. New additional treatment methods are under examination, including cavitation-based advanced oxidation processes. To quantify structural influences on chemical processes, quantitative structure-property relationship (QSPR) modelling can be used, which calculates a correlation between a defined endpoint and structural properties expressed by molecular descriptors. In this study, QSPR modelling has been applied to investigate the structural influence on the degradability of organic micropollutants with high-frequency sonolysis. The dataset of a previous study on 32 phenol derivates was expanded by 60 mostly aromatic compounds, whose kinetic degradation constants were obtained in a standardized experimental setup. QSPR modelling was conducted using the software PaDEL for descriptor calculation and QSARINS for the modelling process using a multiple linear regression approach and genetic algorithm. All five OECD-requirements for applicable QSPR models were respected. The obtained model included 12 model descriptors, was evaluated with numerous statistical quality parameters, and shows good regression abilities as well as robustness and predictability (R2 = 0.8651, CCCtr = 0.9277, Q2loo = 0.8010, R2ext = 0.7836, CCCext = 0.8838, Q2F1 = 0.7697). The interpretation of selected model descriptors showed interesting connections between the model results and the experimental background. A strong influence of the polarity of organic compounds on their degradability with high-frequency sonolysis could been quantified, as more nonpolar molecules are degraded faster. Additionally, the impact of specific fingerprints, including for example substituents with heteroatoms, the number of fused and non-fused aromatic rings as well as the numerical appearance of secondary carbon could be identified as relevant for this cavitation-based treatment method.

Sodium based batteries are promising post lithium ion technologies because sodium offers a specific capacity of 1166 amp; 8197;mAh amp; 8201;g amp; 8722;1 and a potential of amp; 8722;2.71 amp; 8197;V vs. the standard hydrogen electrode. The solid electrolyte sodium beta alumina shows a unique combination of properties because it exhibits high ionic conductivity, as well as mechanical stability and chemical stability against sodium. Pairing a sodium negative electrode and sodium beta alumina with Na ion type positive electrodes, therefore, results in a promising solid state cell concept. This review highlights the opportunities and challenges of using sodium beta alumina in batteries operating from medium to low temperatures 200 amp; 8201; C 20 amp; 8201; C . Firstly, the recent progress in sodium beta alumina fabrication and doping methods are summarized. We discuss strategies for modifying the interfaces between sodium beta alumina and both the positive and negative electrodes. Secondly, recent achievements in designing full cells with sodium beta alumina are summarized and compared. The review concludes with an outlook on future research directions. Overall, this review shows the promising prospects of using sodium beta alumina for the development of solid state batteries

In industrial applications, filter materials are often chosen according to cost as well as their processing and thermomechanical properties, but rarely in terms of their behavior during filtration, which is largely due to there being insufficient information available on the influence of filter materials and surface quality on filtration behavior. In this study, the manufacture of functionalized Al2O3 nanofilters was investigated, along with their filtration performance in short- and long-term filtration trials. In addition, sessile drop tests were performed to measure the contact angle of the nanofunctionalized materials, and yielded an approximately 10 deg (11 pct) higher contact angle for nanocoated materials sintered at 800 °C and 1250 °C than for those sintered at 1600 °C and an approximately 23 deg (23 pct) higher contact angle compared to surfaces without a nanocoating. The filtration mechanism was assessed by means of Porous Disk Filtration Analysis (PoDFA) and Liquid Metal Cleanliness Analyzer (LiMCA) monitoring systems, as well as by analysis of the used and infiltrated filters using Scanning Electron Microscopy and Energy Dispersive X-ray analysis (SEM/EDX) technology. Both short-term and long-term filtration trials showed that the filtration behaviors of the reference and nanocoated filters were comparable. It was therefore determined that nanocoating of such filters with Al2O3 does not provide any improvement with regard to filtration performance.

Sustainable and low-cost technologies for carbon-based nanomaterials are required for wastewater treatment. Two graphitic precursors (graphite flakes and graphite powder) were tested to synthesize graphene-related materials using mechanochemical treatment. For comparison, chemical graphite oxide (GO imp) was synthesized. The pristine and final products were characterized by SEM-EDX, particle size distribution, elemental analysis, surface area, DTA-TG and Raman spectra. Oxygen/carbon ratios of the mechanochemical and chemical routes were detected by EDX and confirmed using elemental analysis. The surface area increased from ~1 up to 666 and 328 m2 g−1 for graphite flakes and graphite powder at 24 h of mechanochemical treatment, respectively. However, the surface area for GO imp reached 157 m2 g−1. The removal of methylene blue, acid orange 7 and bisphenol A with the mechanochemical synthesized graphite oxides reached >93.8% at 30 min. The adsorption mechanism is mainly governed by π − π interactions and hydrogen bonding.

Pyrocatalysis is an emerging advanced oxidation process for wastewater remediation with the potential for thermal energy harvesting and utilization. Although several studies explored the potential of new pyrocatalyst materials to degrade harmful organic water pollutants, the role of important material properties and electric poling procedures on the pyrocatalytic activity is still unclear. In this work, we investigate the interdependence between particle size, electric poling and pyrocatalytic activity of BaTiO3 powders with nominal particle sizes of 100, 200 and 500 nm by using the dichlorofluorescein redox assay. Depending on the particle size, the influence of surface area or phase composition on the pyrocatalytic activity predominates. Moreover, we demonstrate that poling of pyrocatalysts leads to a strong size-dependent increase of pyrocatalytic activity. This poling effect increases with particle size up to +247% and can be explained with size-dependent changes in phase composition and domain structure. Combining all results, the progression of the pyrocatalytic activity as a function of particle size was derived and a future strategy for maximizing the catalytic performance of pyrocatalysts was developed. This study greatly improves the understanding about the role of important material properties and electric poling on pyrocatalytic activity, thus enabling an effective catalyst design. With the help of highly active catalysts, the pyrocatalytic process can take the next step in its development into a new and energy-efficient advanced oxidation process for water remediation.

The state-of-the-art technology of raw silver refining in a silver nitrate-based electrorefining process (Moebius-electrolysis) is accompanied by several disadvantages, both from a technological and from an ecological point of view. In addition, increasing concentrations of critical impurities from secondary sources, like palladium, in raw silver are a further challenge for the future of silver refining. Thus, there is strong motivation for the development of an adequate, alternative process of raw silver refining to substitute the existing Moebius-electrolysis. Due to its less environmentally toxic character and the high aqueous solubility of its silver salt, methanesulfonic acid (MSA) is a possible base chemical for the design of an efficient refining method based on leaching of raw silver followed by electrowinning, with less ecological and technological complications. In this paper the results of some fundamental investigations on the leaching of raw silver granules, containing approx. 94% silver, with methanesulfonic acid and hydrogen peroxide as an oxidation agent are presented. Agitation leaching experiments were conducted on a laboratory scale and the effects of the solid concentration, the hydrogen peroxide dosage and the temperature as leaching parameters were studied. The obtained results indicate that silver leaching yields of more than 90% are achievable with leaching at elevated temperatures of 65 °C or 80 °C, solid concentrations of 500 g/L and at a stoichiometric H2O2:Ag-ratio of 3:1. Increased solid concentrations greater than 500 g/L and elevated temperatures of 65 °C or 80 °C additionally improved the selectivity of the process regarding the leaching of Pd.

Na-β″-alumina is the commercially most successful solid electrolyte due to its application in ZEBRA and NAS® batteries. In this work, Li-stabilized Na-β″-alumina electrolytes were doped with 3d transition metal oxides, namely TiO2, Mn3O4, and NiO, in order to improve their ionic conductivity and fracture strength. Due to XRD and EDX measurements, it was concluded that Mn- and Ni-ions are incorporated into the crystal lattice of Na-β″-alumina. In contrast, TiO2 doping results in the formation of secondary phases that enable liquid-assisted sintering at temperatures as low as 1500 °C. All dopants increased the characteristic fracture strength of the electrolytes, 1.5 wt% of NiO doping proved to be most efficient and led to a maximal characteristic fracture strength of 296 MPa. Regarding the ionic conductivity, TiO2 doping showed the uppermost value of up to 0.30 S cm−1 at 300 °C. In contrast to the other dopants, TiO2 doping lowered the sintering temperature needed to obtain a dense, stable, and highly conductive Na-β″-alumina electrolyte suitable for applications in Na based batteries.

The increasing environmental problems due to various organic micropollutants in water cause the search of suitable additional water treatment methods. Gaining experimental data for the large amount and variety of pollutants would consume a lot of time as well as economic and ecologic resources. An alternative approach is predictive quantitative structure-property relationship (QSPR) modeling, which establishes a correlation between the structural properties of a molecules with a biological, physical, or chemical property. Therefore, in this study, QSPR modeling has been conducted using extensive validation techniques and statistical test to investigate the structural influence on the degradability of organic micropollutants with ozonation. In contrast to most of the other studies, the underlying dataset - rate constants for 92 organic molecules - were obtained under standardized conditions with defined experimental parameters. QSPR modeling was executed using a combination of the software PaDEL for descriptor calculation and QSARINS for the modeling process respecting all five OECD-requirements for applicable QSAR/QSPR-models. The final model was selected using a multi-criteria decision-making tool to evaluate the model quality based on all calculated statistical quality parameters. The model included 10 selected descriptors and fingerprints and showed good regression abilities, predictive power, and stability (R=0.8221, CCCtr=0.9024, Qloo=0.7436, Rext=0.8420, QF1=0.8104). The applicability domain of the QSPR model was defined and an interpretation of selected model descriptors has been connected to previous experimental studies. A significant influence of the interpretable descriptors was put into experimental context and compared with previous studies and models. For example, the molar refractivity as a measure of size and polarizability of a molecule and the occurrence of important substructures such as a formamide group seem to decrease the removal rate constant. The contribution of lone electrons entering into resonance as well as the occurrence of fused rings were identified as influences for the increase of the degradability of micropollutants by ozonation.

The results of solidification experiments with gallium in a square-based 220 x 220 mm 2 container under the influence of alternating and travelling magnetic fields are presented. Such experiments are relevant for the growth of multi-crystalline silicon ingots for solar cells using directional solidification. The time-dependent magnetic fields are generated by a system of two inductors supplied with alternating current. The axial temperature field for solidification is established by thermostat-controlled heat exchangers at the top and the bottom of the container. A new approach for a reproducible directional solidification process using a special seeding technique is presented. The melt flow and interface positions are measured in-situ during solidification by using ultrasound sensor arrays for a 2D flow mapping, and single ultrasound transducers for interface detection. The experiments reveal significant changes of the flow structure and the interface shape with decreasing melt height. The results are compared with numerical simulation and a setup-independent categorization of the observed flow structures is proposed. Conclusions for silicon growth processes are discussed.

Sodium-ion conductive Li+-stabilized Na-β″-alumina was synthesized by calcinating a mixture of AlO(OH), Na2CO3 and Li2CO3. For additional improvement of the characteristics the ceramic powder was doped with various amounts of TiO2 and sintered at 1400, 1500 and 1600 °C. The effects of doping and sintering temperature were evaluated by measuring fracture strength, ionic conductivity, density, morphology and phase composition. The conductivity was raised from 0.2 to 0.3 S cm−1 at 300 °C by adding 1.5 wt.-% TiO2 to the Na-β″-alumina. By adding 1 wt.-% of TiO2 to the electrolyte material, the characteristic fracture strength σ0 was increased from 188 to 277 MPa. Aside from that, changes in the microstructure, due to doping were observed. The altered properties of the ceramic were mainly assigned to changes in the microstructure.

The contact angles of two different systems, molten silicon and a eutectic Si-8 at. pct Zr alloy and their evolution over timeon vitreous carbon and polycrystalline silicon carbide (SiC) substrates were investigated at 1500°C under vacuum, as well as in argon using the sessile drop technique. The contact angle and microstructure of the liquid droplet/solid substrate interface were studied to understand fundamental features of reactive wetting as it pertains to the infiltration process of silicon and silicon alloys into carbon or C/SiC preforms. Both pure Si and theeutectic alloy showed good wettability onvitreous carbon and SiC characterized by equilibrium contact angles between 29° and 39°. Theeutectic alloy showed a higher initial contact angle and slower spreading as compared to that of pure Si. On vitreous carbon bothsilicon and the eutecticalloy formed SiC at the interface, while no reaction was observed on the SiC substrates.

The pyro-electro-catalytic induced generation of hydrogen gas is an environmentally friendly and sustainable way to convert excess thermal energy into a storable form. The main idea is to make use of spontaneous polarization of pyroelectric materials that can be altered by temperature changes. Thus, surface potential changes and subsequent electron exchange with surrounding molecules can be induced. In this work, a fundamental model to describe the behavior of a thermally excited pyroelectric material in pure water is developed. The model combines the fields of pyroelectricity, electrochemistry, diffusion and semiconductor theory. After derivation, it was used to explore some basic questions on pyro-electro-catalytic hydrogen production and the accuracy was tested with experimental data. The results show that p/εr has to be balanced depending on the temperature gradient to maximize the hydrogen production. The validation of the experimental data revealed good agreement.

A new preparation concept of a partially porous solid-state bilayer electrolyte (BE) for high-temperature sodium-ion batteries has been developed. The porous layer provides mechanical strength and is infiltrated with liquid and highly conductive NaAlCl4 salt, while the dense layer prevents short circuits. Both layers consist, at least partially, of Na-β-alumina. The BEs are synthesized by a three-step procedure, including a sol-gel synthesis, the preparation of porous, calcined bulk material, and spin coating to deposit a dense layer. A detailed study is carried out to investigate the effect of polyethylene oxide (PEO) concentration on pore size and crystallization of the bulk material. The microstructure and crystallographic composition are verified for all steps via mercury intrusion, X-ray diffraction, and scanning electron microscopy. The porous bulk material exhibits an unprecedented open porosity for a NaxAlOy bilayer-system of ≤57% with a pore size of ≈200–300 nm and pore volume of ≤0.3 cm3∙g−1. It contains high shares of crystalline α-Al2O3 and Na-β-alumina. The BEs are characterized by impedance spectroscopy, which proved an increase of ionic conductivity with increasing porosity and increasing Na-β-alumina phase content in the bulk material. Ion conductivity of up to 0.10 S∙cm−1 at 300 °C is achieved.

Pyrocatalysis is an emerging advanced oxidation process for wastewater remediation with the potential for thermal energy harvesting and utilization. Although several studies explored the potential of new pyrocatalyst materials to degrade harmful organic water pollutants, the role of important material properties and electric poling procedures on the pyrocatalytic activity is still unclear. In this work, we investigate the interdependence between particle size, electric poling and pyrocatalytic activity of BaTiO3 powders with nominal particle sizes of 100, 200 and 500 nm by using the dichlorofluorescein redox assay. Depending on the particle size, the influence of surface area or phase composition on the pyrocatalytic activity predominates. Moreover, we demonstrate that poling of pyrocatalysts leads to a strong size-dependent increase of pyrocatalytic activity. This poling effect increases with particle size up to +247% and can be explained with size-dependent changes in phase composition and domain structure. Combining all results, the progression of the pyrocatalytic activity as a function of particle size was derived and a future strategy for maximizing the catalytic performance of pyrocatalysts was developed. This study greatly improves the understanding about the role of important material properties and electric poling on pyrocatalytic activity, thus enabling an effective catalyst design. With the help of highly active catalysts, the pyrocatalytic process can take the next step in its development into a new and energy-efficient advanced oxidation process for water remediation.

The wetting behavior was measured for Al2O3-C in contact with AlSi7Mg with a conventional sessile drop test (vacuum, 950 &deg, C and 180 min) and a sessile drop test with a capillary purification unit (vacuum, 730 &deg, C and 30 min). The conventional test yielded contact angles of around 92&deg, whereas the sessile drop measurement with capillary purification showed a strongly non-wetting behavior with a determined apparent contact angle of the rolling drop of 157&deg, Filtration tests, which were repeated twice, showed that the Al2O3-C filter possessed a better filtration behavior than the Al2O3 reference filter. For both filtration trials, the PoDFA (porous disc filtration analysis) index of the Al2O3-C filter sample was equal to half of the PoDFA index of the Al2O3 reference filter sample, indicating a significantly improved filtration performance when using Al2O3-C filter. Notable is the observation of a newly formed layer between the aluminum and the Al2O3-C coating. The layer possessed a thickness between 10 &micro, m up to 50 &micro, m and consisted of Al, C, and O, however, with different ratios than the original Al2O3-C coating. Thermodynamic calculations based on parameters of the wetting and filtration trials underline the possible formation of an Al4O4C-layer.

In this work we present a carbon free gas diffusion electrode (GDE) design. It is a first step towards improvement of technologies like alkaline fuel cells, some alkaline electrolyzes and metal-air-batteries by circumventing carbon degradation. A nickel-mesh was made hydrophobic and subsequently electrochemically coated with MnOx as electrocatalyst. By this, a carbon free GDE was prepared. The contact angle, specific surface area (BET), pore size distribution, crystal phase (XRD) and electrochemical properties were determined. The deposition scan rate (r scan) during dynamic MnOx deposition altered the macro surface structure, pore size distribution and deposited mass. High catalyst masses with high specific surface area were achieved by lower r scan, but hydrophobicity was decreased. Impedance spectroscopy showed that higher MnOx mass will increase the ohmic resistance, because of the low conductivity of oxides, such as MnOx. The diffusion of dissolved oxygen is the major contributor to the total resistance. However, the polarization resistance was reduced by increased specific surface area of MnOx. It was concluded that the ORR and OER are limited by diffusion in this design but nevertheless showed reasonable activity for ±10 mA cm−2 corresponding to ~8 O cm−2 while references exhibited ~3.5 O cm−2.

This paper describes recent developments of the high temperature vapor phase epitaxy (HTVPE) for the growth of GaN seed layers on sapphire substrates. The concept of a controlled coalescence of nucleation layers adopted from metal organic vapor phase epitaxy is used for the first time in HTVPE to reduce the density of threading dislocations of the seed layers. This concept implies a delay of coalescence by reducing the ammonia flow and increasing the admixture of hydrogen in the carrier gas. A series of nucleation and seed layers grown under different ammonia flows and hydrogen concentrations is presented. The layers are analyzed by X-ray diffraction as well as by optical and scanning electron microscopy. Microscopic investigations reveal that nucleation layers with large facetted growth islands are formed during the delayed coalescence. The measured rocking curves and estimated dislocation densities from the mosaicity model indicate a significant improvement of the crystal quality of the corresponding seed layers. The lowest dislocation densities are found to be in the range of 4-5 × 108 cm−2, compared with a dislocation density of about 1 × 109 cm−2 in a reference layer grown without an intentional delay of coalescence. A possible explanation is that the existence of large growth islands with extended pyramidal facets causes a preferred bunching and annihilation of dislocations.

A sustainable route to produce graphite oxide (GO) is presented using dry ball milling. The production method was based on pristine graphite flakes in a planetary ball mill. The prepared GO was characterized using UV–vis spectroscopy, BET surface area analysis, thermal analysis, SEM-EDX, TEM, XPS, elemental analysis, and Raman spectroscopy. The degree of graphite oxidation was controllable by the milling time and milling material, and the carbon-based yields ranged from 86 to 97%. The maximum oxygen/carbon ratios of the produced GOs were 0.16 and 0.15 after 24 h of ball milling with steel and zirconia balls, respectively. The BET surface area increased with increasing milling time from 1 m2 g–1 for pristine graphite up to 730 m2 g–1 for the ball-milled samples. Furthermore, the intensity ratios of the D and G bands (ID/IG) from the Raman spectra were 0.84 and 0.77 for GO produced with the steel and zirconia balls, respectively. The in-plane sp2 crystallite sizes (La) of graphite (168 nm) decreased to 20 (...

Ceramics of Ca0.96Gd0.04MnO3−δ are prepared via different soft chemistry methods and the solid state route. The phase formation processes of the synthesized powders are compared, and the effects of powder morphology and sintering behavior on the microstructure and thermoelectric properties of the ceramics are investigated. Ceramic powders with particle size of 110 nm are obtained from soft chemistry routes. These powders show excellent phase purity and shrink at lower temperatures compared to solid state route powders. Dense ceramics with 1 µm mean grain size, homogeneous dopant distribution and good thermoelectric properties are obtained after sintering at 1200 °C. Soft chemistry synthesized samples show a figure of merit ZT = 0.14 at 700 °C. This is higher than the figure of merit of solid state route ceramics, due to a more homogeneous microstructure, better densification and, hence, improved electrical properties. The soft chemistry synthesis methods provide ceramics with comparable thermoelectric performances.

This paper deals with technological development and investigation of the high temperature vapor phase epitaxy (HTVPE) for the growth of GaN films. A novel Ga evaporation cell designed for an optimal local temperature field and gas flow is described. The influence of the reactor pressure and the temperature of the Ga melt on the growth rate in HTVPE is studied. The experiments demonstrated growth rates up to 165 µm/h, which could be of potential interest for the deposition of thick GaN layers. Optical properties of the HTVPE layers, as well as typical process impurities are studied by PL, SIMS and GDMS, and discussed in detail. First experiments on a deposition of GaN films on sapphire substrates by HTVPE are presented.

This paper describes novel equipment for model experiments designed for detailed studies on electromagnetically driven flows as well as solidification and melting processes with low-melting metals in a square-based container. Such model experiments are relevant for a validation of numerical flow simulation, in particular in the field of directional solidification of multi-crystalline photovoltaic silicon ingots. The equipment includes two square-shaped electromagnetic coils and a melt container with a base of 220×220 mm 2 and thermostat-controlled heat exchangers at top and bottom. A system for dual-plane, spatial- and time-resolved flow measurements as well as for in-situ tracking of the solid-liquid interface is developed on the basis of the ultrasound Doppler velocimetry. The parameters of the model experiment are chosen to meet the scaling laws for a transfer of experimental results to real silicon growth processes. The eutectic GaInSn alloy and elemental gallium with melting points of 10.5 °C and 29.8 °C, respectively, are used as model substances. Results of experiments for testing the equipment are presented and discussed.

Carbon Nanotubes (CNTs) have been oxidized with ozone in the gas phase and different Advanced Oxidation Processes (AOPs) in the aqueous phase such as H2O2/UV, Fenton reaction and ozonation, in order to functionalize them. A significant difference between the amounts and types of oxygen containing groups were generated using different oxidants. To investigate the efficiency of the oxidation methods, we monitored the depletion of the oxidants, using a titration of H2O2 with KMnO4 and an ozone analyzer for the ozonolysis experiments. Furthermore, we investigated the formation of hydroxyl radicals during the oxidation experiments by decolorization of methylene blue and depletion of salicylic acid. Boehm titration, Raman spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, elemental analysis, temperature programmed desorption and thermogravimetric analysis have been utilized to characterize the CNTs. Our results demonstrate that direct ozonolysis with water vapor produces the highest amount of oxygen containing surface in comparison to the other oxidation methods, and this by using only a small amount of the available oxidant. With our results we confirm different previous assumptions about the oxidation mechanisms and theoretical calculations for oxidation processes practically.

NaNiCl2 batteries are member of the sodium metal halogenide battery family and represent a robust, save and environmentally friendly storage technology, which is in operation all over the world from small to large scale for decades. In particular, the high cycle stability, lifetime and the excellent safety predestine the technology for large scale stationary applications. Nevertheless, a significant marked penetration has so far failed to materialize. The dominating obstacle are the costs for conventional NaNiCl2 in competition with the dramatically falling prices for Li-Ion batteries. The energy intensive ceramic electrolyte manufacturing and the usually used high amount of nickel are mainly responsible. Beside this, some high power technical applications, such as peak shaving, are currently not accessible for NaNiCl2 batteries. The limited C-rates permit an economic operation of these business cases. To overcome these obstacles material scientific and engineering approaches are under development in workgroups all over the world. In the presentation, a technological review of new concepts for sodium metal halogenide batteries will be given. This will include new materials, designs and production methods along the battery value chain. The high economical impact from solid electrolyte manufacturing was tackled by lowering the sintering temperature by material doping. By 1.5 % TiO2 doping the sintering temperature for the Na-ß-alumina electrolyte was lowered by 150 °C. By optimizing the microstructure, an ionic conductivity of 0.25 S/cm and a mechanical toughness of 210 MPa were reached at the same time. Different cell designs matching different requirements in terms of power and energy will be presented. This will include 25 Ah plate cells and large tubular cells with high energy contents. Using the plate cell approximately, 100 % DoD can be discharged with an elevated current of 1 C which pushes NaNiCl2 close to Li-Ion cells. By a simple stacking of the cells, the capacity and the voltage level of a module can easily be adjusted to different applications. For high-energy applications tubular 100 Ah cells and 5 kWh battery packs were successfully developed. The simplification of the cell and module design with the simultaneous use of innovative production methods ended up in calculated costs of 300 to 400 €/kWh for a large scale production. An intermediate temperature NaNiCl2-like cell concept was developed. A fundamentally different cathode composition and a liquid sodium anode opens the door to a batteries with improved round trip efficiency, compared to high temperature NaNiCl2. Metal halogenid batteries have a high development potential. Away from the classic high temperature NaNiCl2 technology, a several approaches are under development and on the way to become a product in the near future. A successful implementation of the described approaches will yield in excellent batteries for large-scale stationary energy storage.