TY - CONF A1 - Mieller, Björn T1 - Sintering and interconnecting thermoelectric oxides for energy applications N2 - Today, more than 12% of the primary energy is lost in the form of waste heat. Thermoelectric generators (TEGs) can convert waste heat directly into electrical power by utilizing the Seebeck effect. The performance of such a generator is defined by a dimensionless figure of merit ZT of the thermoelectric pairs and the resistance R of the metallic contacts between these pairs. The figure of merit of thermoelectric oxides is considerably smaller compared to semiconductors. Still, thermoelectric oxides like calcium cobaltite (Ca3Co4O9) are attractive for applications at elevated temperatures in air. In contrast to the established π-type architecture of common TEGs, tape casting and multilayer technology may be applied for cost-effective manufacturing of oxide TEGs. Promising demonstrations of multilayer TEGs have been published in the last years. Still, the development of reliable and scalable manufacturing processes and proper material combinations is necessary. The aim of our project is to evaluate the feasibility of low temperature co-fired ceramics (LTCC) technology for a practical manufacturing of oxide multilayer TEGs of Ca3Co4O9 (p-type) and calcium manganate (CaMnO3, n-type). Ca3Co4O9 exhibits an undesired phase decomposition at 926 °C. Because of that, the application of sintering strategies and interconnect concepts well known from LTCC technology is a promising approach. We present results of pressure-assisted sintering of Ca3Co4O9 multilayer at 900 °C and axial pressures of up to 7.5 MPa. Ca3Co4O9 was produced by solid state reaction of CaCO3 and cobalt(II,III)oxide at 900 °C. Green tapes were prepared by a doctor-blade process, manually stacked and laminated by uniaxial thermocompression. Sintering was conducted in a LTCC sintering press between SiC setter plates. The thickness shrinkage was recorded by an in-situ technique. After sintering under 7.5 MPa, the microstructure of the single phase material shows a high density of 95 % and an advantageous alignment of the platelet grains. This results in good electrical conductivity and a comparatively high ZT of 0.018 at room temperature. However, the lowering of CaMnO3 sintering temperature from above 1200 °C to below 920 °C remains a challenge. To select a proper metal paste for interconnections of an oxide TEG, several pastes have been investigated regarding contact resistance of internal and external (soldered) connections in a preliminary study. Commercial pastes containing Ag, Au, Au/Pt, Ag/Pd, and Ag/Pd/Bi were manually applied and post-fired on sintered test bars of Ca3Co4O9 and CaMnO3 at 900 °C for 2 h. All tested pastes formed mechanically stable metallization after firing. For resistance measurement, 4-wire method and a custom-made probe head were used. The contacts on Ca3Co4O9 exhibit significantly (2-sample t-test, α = 5%) higher resistance compared to contacts on CaMnO3. Pure silver paste exhibits the lowest resistance for internal contacts on both materials, lower than 5 mΩ on CaMnO3. Ag/Pd/Bi paste resulted in conspicuously high variance of resistance. EDX analyses clarified an enrichment of Bi in the thermoelectric material near the interface and thereby the formation of an oxide layer with probably high electrical resistance. The thickness of that layer varies with the thickness of metallization. In conclusion, the use of Bi containing pastes is not advisable. Pure Ag paste shows the best results regarding resistance and solderability. T2 - CICMT 2018 CY - Aveiro, Portugal DA - 18.04.2018 KW - Thermoelectric oxide KW - Thermoelectric generator KW - Multilayer technology KW - Pressure-assisted sintering PY - 2018 AN - OPUS4-44740 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kromm, Arne T1 - Residual stress formation in selective laser melted parts of alloy 718 N2 - Additive Manufacturing (AM) through the Selective Laser Melting (SLM) route offers ample scope for producing geometrically complex parts compared to the conventional subtractive manufacturing strategies. Nevertheless, the residual stresses which develop during the fabrication can limit application of the SLM components by reducing the load bearing capacity and by inducing unwanted distortion, depending on the boundary conditions specified during manufacturing. The present study aims at characterizing the residual stress states in the SLM parts using different diffraction methods. The material used is the nickel based superalloy Inconel 718. Microstructure as well as the surface and bulk residual stresses were characterized. For the residual stress analysis, X-ray, synchrotron and neutron diffraction methods were used. The measurements were performed at BAM, at the EDDI beamline of -BESSY II synchrotron- and the E3 line -BER II neutron reactor- of the Helmholtz-Zentrum für Materialien und Energie (HZB) Berlin. The results reveal significant differences in the residual stress states for the different characterization techniques employed, which indicates a dependence of the residual state on the penetration depth in the sample. For the surface residual stresses, longitudinal and transverse stress components from both X-ray and synchrotron agree well and the obtained values were around the yield strength of the material. Furthermore, synchrotron mapping disclosed gradients along the width and length of the sample for the longitudinal and transverse stress components. On the other hand, lower residual stresses were found in the bulk of the material measured using neutron diffraction. The longitudinal component was tensile and decreased towards the boundary of the sample. In contrast, the normal component was nearly constant and compressive in nature. The transversal component was almost negligible. The results indicate that a stress re-distribution takes place during the deposition of the consecutive layers. Further investigations are planned to study the phenomenon in detail. T2 - Forschungsseminar OvGU Magdeburg CY - Magdeburg, Germany DA - 15.11.2018 KW - Additive Manufacturing KW - Selective Laser Melting KW - Residual Stresses PY - 2018 AN - OPUS4-46876 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schröter, Felix T1 - Fluorescence? Not on my Shift! Excitation- Shifted UV Raman Microspectroscopy N2 - Spectroscopic analysis of samples provides elemental information, which is useful when the sample is homogenous. But many samples are not and consequently the creation of maps detailing the spatial composition of materials is needed. Raman microscopy can be used for this exact purpose but suffers a big drawback. The inherently weak Raman scattering results in long measurement times, especially when maps with many data points are created. This is due to the long exposure times needed when visible light lasers are used. A shift to UV-Lasers significantly increases the Raman intensity, as it scales with the fourth power of the inverse of the laser wavelength. But UV excitation often leads to fluorescence which can obscure the relatively weak Raman signal. Consequently, UV-Raman can only be used with specially prepared samples, for example through photo-bleaching, or with samples producing no fluorescence background in the measurement region. A solution is proposed that uses shifted-excitation Raman difference spectroscopy (SERDS) in a confocal microscope to obtain fluorescence-free Raman spectra. This is possible due to the collection of two Raman spectra at different excitation wavelengths. SERDS then allows for the calculation of just the Raman signal from the difference spectrum, which eliminates any fluorescence backgrounds, as they are not excitation wavelength dependent. The presented approach employs a polarized beamsplitter to irradiate the same spot with two lasers of different wavelengths which share the same beam path in the microscope. Consequently, a SERDS UV Raman Microscope is created, which utilizes the speed of UV-Raman without the drawbacks of possible broad fluorescence backgrounds. Here we present the instruments methodology and some first results. T2 - ANAKON 2025 CY - Leipzig, Germany DA - 10.03.2025 KW - UV Raman Spectroscopy KW - UV Raman Microspectroscopy KW - Confocal Microscopy KW - Excitation-Shifted Raman Spectroscopy PY - 2025 AN - OPUS4-62734 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Blume, Simon T1 - Exploiting Lithium Self-Absorption in a Laser-Induced Breakdown Plasma for Isotopic Analysis via Spatial Heterodyne Spectroscopy N2 - Lithium-ion batteries are ubiquitous in modern life. From powering consumer electronics to enabling electric mobility and energy storage, they are a key building block of a sustainable future. Determination of the ratio of the two naturally abundant stable isotopes, 7Li and 6Li, provides access to a wide variety of information, such as studying the aging processes of lithium-ion batteries or elucidating the isotopic fingerprinting of natural or recycled sources of lithium. However, accurately measuring the lithium isotope ratio in complex samples remains challenging, often requiring either extensive sample pretreatment or specialized equipment, thus impeding in-situ and high-throughput demands of global industries. Recognition and determination of the individual lithium isotopes with conventional laser-induced breakdown spectroscopy (LIBS) setups is nearly impossible. While LIBS offers several advantages, such as obviating time- and resource-intensive sample preparation and enabling rapid measurements, the high temperature (~20,000 K) of the plasma, as well as the Stark-broadening caused by the nascent free electrons spectrally broaden the atomic emission lines to such an extent that the isotopic shift of the lithium doublet at 670 nm cannot be resolved. Since, the excited state energy for this transition amounts to only 14,900 cm-1, lithium exhibits a pronounced self-absorption dip in the emission signal. This self-absorption dip is significantly less affected by the broadening effects, therefore, allowing for the resolution of the isotopic shift from its line shape. Spatial heterodyne spectroscopy (SHS) offers the superior resolution capabilities necessary to differentiate the individual isotopic contributions. To address the generally limited sensitivity of SHS, a high-repetition-rate (>10 kHz) laser allows the accumulation of more than 10,000 lasing events per spectral recording for a sufficient signal-to-noise ratio and gain statistical validity. Optical lithium fluoride serves as a model sample to showcase the analytical performance. Additionally, the impact of the laser parameters on the self-absorption will also be discussed. T2 - ANAKON 2025 CY - Leipzig, Germany DA - 10.03.2025 KW - Isotopic Analysis KW - Spatial Heterodyne Spectroscopy PY - 2025 AN - OPUS4-63559 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Sander, Luise T1 - Multi-Scale Analysis of Commercially Available Sodium-Ion Cells N2 - As the first commercial sodium-ion-batteries (SIBs) are available for purchase, it is possible to investigate material composition. Gaining an insight into the material composition of these SIBs is of interest not only for the classification of possible safety risks and hazards, but also in regards to recycling. Herein we report the preliminary investigations of the chemical and structural composition of first commercial SIB-cells. Two different SIB-cells with different specification were compared regarding electrode size, thickness and further parameters. Furthermore, the composition of the active materials and electrolyte was investigated and compared. T2 - Solid State Ionics (SSI) CY - London, United Kingdom DA - 15.07.2024 KW - Sodium Ion-Cells KW - Multi-Scale PY - 2024 AN - OPUS4-60764 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bresch, Sophie T1 - Lowering the sintering temperature of calcium manganate CaMnO3 for thermoelectric applications N2 - Thermoelectric materials can convert waste heat directly into electrical power by utilizing the Seebeck effect. Calcium cobaltite (p-type) and calcium manganate (n-type) are two of the most promising oxide thermoelectric materials. The development of cost-effective multilayer thermoelectric generators requires the co-firing of these materials and therefore the adjustment of sintering temperatures. Calcium manganate is conventionally sintered between 1200 °C and 1350 °C. Calcium cobaltite exhibits an undesired phase transition at 926 °C but can be sintered to high relative density of 95 % at 900 °C under axial pressure of 7.5 MPa. Hence, co-firing at 900 °C would be favourable. Therefore, strategies for lowering the sintering temperature of calcium manganate have been investigated. Basically, two approaches are common: i) addition of low melting additives like Bi2O3-ZnO-B2O3-SiO2 (BBSZ) glass or Bi2O3, and ii) addition of additives that form low-melting eutectics with the base material, for example CuO. In this study, several low melting additives including BBSZ glass and Bi2O3, as well as CuO were tested regarding their effect on calcium manganate densification. Bi2O3 did not improve the densification, whereas BBSZ glass led to 10 % higher relative density at 1200 °C. An addition of 4 wt% CuO decreases the temperature of maximum sinter rate from above 1200 °C to 1040 °C. By reducing the particle size of the raw materials from 2 μm to 0.7 μm the maximum sinter rate could be further shifted 20 K towards lower temperatures and the sinter begin decreased from 920 °C to 740 °C. It is shown that eutectic phase formation is more effective in lowering sintering temperature and accelerating densification than low-melting additives. T2 - 93. DKG-Jahrestagung und Symposium Hochleistungskeramik 2018 CY - Munich, Germany DA - 10.04.2018 KW - Thermoelectrics KW - Sinter additive PY - 2018 AN - OPUS4-44818 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - You, Yi T1 - Advanced Repetition-Rate Modulation and Computational Strategies for Background-Free LIBS Using Non-Gated Spectrometers N2 - Laser-induced breakdown spectroscopy (LIBS) is recognized for its rapid, direct elemental analysis capabilities. However, its general adoption is constrained by the reliance on expensive, high-power consumption, gated cameras such as intensified charge-coupled devices (CCDs). These devices, while sensitive, are expensive and possess low frame rates, limiting their efficacy in dynamic or challenging environments. Our study proposes an innovative approach that leverages non-gated spectrometers in conjunction with the framework of correlation spectroscopy to isolate analyte signals responsive to a specific repetition-rate modulation pattern, thereby yielding spectra with zero background. We utilized a diode-pumped solid-state laser, with repetition rates ranging from 10 Hz to 30 kHz, to induce plasma in aqueous solutions containing various alkaline and earth-alkaline metals. With a non-gated single-grating linear CCD spectrometer, we found that the continuum signal plateaued at approximately 7 kHz. In contrast, atomic emissions from the dissolved analytes showed continued increases. Notably, atomic emissions from the solvent (water) were observable only above 8.5 kHz, at a significant high rate of increase. Through computational synthesis of a modulation pattern, we determined an optimized scheme that effectively discriminates continuum and analyte signals; this pattern was optimized with a genetic algorithm. The spectral matrix correlating signal intensity with laser repetition rate and wavelength was used as the input of the model. Meanwhile, the fitness function that extracts the background-free spectra was built in-house and inspired by the Gardner transform, which exploits the power of Fourier transform, allowing for flagging and splitting analyte signal from other undesired features. This approach bypasses the limitations associated with gated cameras, while providing a cost-effective alternative for robust LIBS applications. This advancement is particularly relevant in field, portable and remote applications, aligning with the ongoing demand for accessible, high-performance analytical tools in diverse scientific fields. T2 - SCIX 2024 Conference CY - Raleigh, NC, USA DA - 20.10.2024 KW - LIBS KW - Data Processing KW - High Repetition Rate KW - Repetition Rate Modulation KW - Data-Oriented Experimental Design PY - 2024 AN - OPUS4-62137 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bruno, Giovanni T1 - Applications of X-ray refraction to non-destructive characterization of and composites T2 - 14th International Conference of the European Ceramic Society CY - Toledo, Spain DA - 2015-06-21 PY - 2015 AN - OPUS4-33974 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Mieller, Björn T1 - Tieftemperaturfügen mit Nano- und Submikronsilberpasten T2 - DKG-Symposium "Fügen von Keramik: Grundlagen - Verfahren - Anwendungen" CY - Erlangen, Germany DA - 2012-12-04 PY - 2012 N1 - Geburtsname von Mieller, Björn: Brandt, B. - Birth name of Mieller, Björn: Brandt, B. AN - OPUS4-27285 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Arlt, Tobias T1 - Tomographic methods for investigation for fuel cell materials T2 - Ulm Electro Chemical Talks CY - Ulm, Germany DA - 2010-06-15 PY - 2010 AN - OPUS4-21518 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -