Characterization and modelling of structure and transport properties of porous ceramics

A general scheme of material design and virtual testing of porous ceramics is presented, which provides new strategies for efficient development and optimisation of such materials. The development cycle contains three stages, which can be repeated, until the final targeted properties are reached. The first stage is the preparation of porous ceramics with properties in the region of interest and thorough 3D-investigation and characterization of the porous microstructure. In the second step, microstructure data either directly from real materials or indirectly from a virtual, stochastic model are fed into a numerical model to calculate the physical property of interest, e.g. permeability, diffusivity, thermal conductivity or electrical conductivity of pore fluids. Finally, an evaluation of data representing microstructure characteristics as well as macroscopic properties for a wide range of fabrication scenarios yields as a third step a validated model, which leads to the definition of optimised design guidelines. This optimisation cycle is then closed with the production of a porous ceramic material with improved physical properties. The successful implementation of such scheme is demonstrated here with the development of porous zirconia membranes as electric liquid junction for pH-sensors

Exploiting citation networks for large-scale author name disambiguation

We present a novel algorithm and validation method for disambiguating author names in very large bibliographic data sets and apply it to the full Web of Science (WoS) citation index. Our algorithm relies only upon the author and citation graphs available for the whole period covered by the WoS. A pair-wise publication similarity metric, which is based on common co-authors, self-citations, shared references and citations, is established to perform a two-step agglomerative clustering that first connects individual papers and then merges similar clusters. This parameterized model is optimized using an h-index based recall measure, favoring the correct assignment of well-cited publications, and a name-initials-based precision using WoS metadata and cross-referenced Google Scholar profiles. Despite the use of limited metadata, we reach a recall of 87% and a precision of 88% with a preference for researchers with high h-index values. 47 million articles of WoS can be disambiguated on a single machine in less than a day. We develop an h-index distribution model, confirming that the prediction is in excellent agreement with the empirical data, and yielding insight into the utility of the h-index in real academic ranking scenarios.Comment: 14 pages, 5 figure

Metal casting into NaCl molds fabricated by material extrusion 3D printing

Aluminum die casting is a well-established industrial process for mass producing aluminum parts with complex shapes, but design restrictions exclude some features like undercuts and hollow structures from being produced with this method. Water-soluble casting molds offer a promising solution to overcome those restrains, for example by hot pressing of salt cores or 3D printing of NaCl molds. Presently, 3D printing techniques available for NaCl are limited to direct ink writing (DIW) and photopolymerization. This study presents an approach to prepare NaCl parts by thermoplastic material extrusion (MEX) 3D printing. Firstly, a 3D printable feedstock is developed consisting of an organic binder, which is usually used for ceramic injection molding, and sodium chloride (NaCl) salt crystals. Various molds are then printed on a granulate-fed MEX printer. After thermal debinding and sintering at 690 °C, the 3D printed parts consist of pure NaCl. Furthermore, the same NaCl feedstock is used for injection molding. The bending strength of 3D printed samples with and without post-treatment are measured and compared to injection molded test specimens. Finally, metal casting in 3D printed NaCl molds is shown with tin or aluminum and the metal demonstrator parts with complex geometries such as gyroid structures and turbine wheels are released by dissolving the NaCl molds in water

Flexible interconnected ceramic parts 3D printed by two-component material extrusion with water-soluble support structures

Material extrusion (MEX) of complex thermoplastic structures often depends on the reliable printing of a water-soluble support structure. The material of choice is typically polyvinyl alcohol (PVA), which is not used in ceramic MEX printing due to a limited printing compatibility with most ceramic feedstocks (poor layer adhesion). Herein, a new thermoplastic feedstock was developed as temporary support material on the basis of NaCl mixed with a commercial injection molding binder system. The NaCl feedstock is fully compatible for MEX printing with ceramic feedstocks and showed excellent printing properties and high green body strength. The support structure is mostly dissolved in water and the rest can be removed manually or during thermal debinding. The NaCl support material was used to print flexible Al2O3 samples with hinges or chainmail samples. This strategy is an attractive way to introduce additional functionality and new applications which were so far inaccessible to technical ceramics

Water-soluble sacrificial 3D printed molds for fast prototyping in ceramic injection molding

Fabrication of steel molds is a major expense (time and cost) in ceramic injection molding research and development. 3D printed resin molds for fast prototyping are therefore highly attractive and have gained increasing attention. This paper reports strategies to use sacrificial molds 3D printed by fused deposition modeling (FDM) from PVA or digital light processing (DLP) from water soluble resin. Usage of sacrificial molds allows injection molding of complex geometries, which are not accessible for simple two-part molds. Ceramic heating elements in diverse geometries were injection molded using a composite feedstock containing MoSi2, Al2O3 and feldspar. More parts with various geometries were produced from Al2O3 feedstock. A comparison revealed that DLP printed molds are better suited for parts with very small structural features due to the higher resolution of the DLP process as compared to FDM. Finally, ceramic heaters were fabricated using two-component ceramic injection molding and successfully tested

3D printing of functional assemblies with integrated polymer-bonded magnets demonstrated with a prototype of a rotary blood pump

Conventional magnet manufacturing is a significant bottleneck in the development processes of products that use magnets, because every design adaption requires production steps with long lead times. Additive manufacturing of magnetic components delivers the opportunity to shift to agile and test-driven development in early prototyping stages, as well as new possibilities for complex designs. In an effort to simplify integration of magnetic components, the current work presents a method to directly print polymer-bonded hard magnets of arbitrary shape into thermoplastic parts by fused deposition modeling. This method was applied to an early prototype design of a rotary blood pump with magnetic bearing and magnetic drive coupling. Thermoplastics were compounded with 56 vol.% isotropic NdFeB powder to manufacture printable filament. With a powder loading of 56 vol.%, remanences of 350 mT and adequate mechanical flexibility for robust processability were achieved. This compound allowed us to print a prototype of a turbodynamic pump with integrated magnets in the impeller and housing in one piece on a low-cost, end-user 3D printer. Then, the magnetic components in the printed pump were fully magnetized in a pulsed Bitter coil. The pump impeller is driven by magnetic coupling to non-printed permanent magnets rotated by a brushless DC motor, resulting in a flow rate of 3 L/min at 1000 rpm. For the first time, an application of combined multi-material and magnet printing by fused deposition modeling was shown. The presented process significantly simplifies the prototyping of products that use magnets, such as rotary blood pumps, and opens the door for more complex and innovative designs. It will also help postpone the shift to conventional manufacturing methods to later phases of the development process

MoSi2/Al2O3/feldspar composites for injection‐molded ceramic heating elements

MoSi2 is an electrically conductive material with numerous applications mostly in high-temperature environments. Herein, the production of MoSi2-containing resistive heating elements by ceramic injection molding (CIM) is described. The sintered parts consist of MoSi2 particles embedded in a matrix of vitrified feldspar and Al2O3. The conductivity of sintered parts can be tuned precisely by varying the content of the conductive phase. For the development of the injection-molding feedstock, four binder systems are evaluated. The corresponding feedstocks are injection molded into different geometries in traditional molds as well as in additively manufactured, soluble molds. For each feedstock, a debinding and sintering routine is elaborated based on thermogravimetric measurements. Higher debinding temperature leads to more oxidation of MoSi2 and less conductive samples. Therefore, the conductivity as well as density of sintered parts is used to evaluate the applicability of the feedstocks. Finally, glow tests prove that MoSi2/Al2O3/feldspar composite parts can be used as heating elements and by combining infrared temperature measurement data with computational simulations important material data such as thermal and electrical conductivity and thermal capacity can be obtained reliably

Multi-parameter improvement method for (micro-) structural properties of high performance ceramics

Many pH-measurement electrodes rely on porous diaphragms to create a liquid electrolyte junction between reference-electrolyte and the fluid to be measured. In field applications, the diaphragm is required to meet partly contradictory improvement criteria. To minimize measurement errors and to ensure durability of the measurement device, the diaphragm is supposed to maximize electrolyte conductivity and reference-electrolyte outflow velocity, while simultaneously minimizing reference electrolyte flow rate. The task of optimizing the overall performance of this small piece of ceramics has lead to the development of a novel multi-parameter improvement scheme for its (micro-) structural design. The method encompasses the consideration of microscopic material design parameters, such as porosity, pore-tortuosity and constrictivity, macroscopic material parameters such as diaphragm diameter and length, as well as process parameters like internal electrode pressure or the electrolyte viscosity and specific resistivity. Comprising sets of design parameters to dimensionless groups, concrete design guidelines as well as the introduction of a three-dimensional improvement space concept are proposed. The novel design space concept allows the improvement of each possible diaphragm-based measurement set-up, by considering the simultaneous, dimensionless interaction of all relevant design parameters