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Universitat Politècnica de Catalunya BarcelonaTech: Characterization of 3D Printing for Ceramic Fuel Cell Electrolytes

Albert Folch Alcaraz recently submitted a Master’s thesis to the Universitat Politècnica de Catalunya BarcelonaTech. In ‘Mechanical and Microstructural Characterization of 3D Printed Ceramic Fuel Cells Electrolytes,’ Alcaraz delves further into digital fabrication using ceramic as a versatile material for creating solid oxide fuel cells—electrochemical devices capable of transforming chemical energy to electrical energy.

Striving to ‘bring science and society closer together,’ Alcaraz aims to develop energy devices that offer better efficiency, as well as offering clean energy that can be generated with less effect on our environment. Fuel cells are categorized regarding the types of electrolytes contained within, from low temperature (the alkaline fuel cell (AFC), the proton exchange membrane fuel cell, and the phosphoric acid fuel cell (PAFC)) to high temperature (operating at 500 – 1000 oC as two different types, the molten carbonate fuel cell (MCFC) and the solid oxide fuel cell (SOFC)).

SOFCs are made from ceramic, comprised of an anode that oxidizes and then sends electrons to the external circuit—and the oxidant which feeds into the cathode, thus ‘accepting’ electrons and then undergoing a reduction reaction. Electricity is created via electron flow from the anode to the cathode.

Working schematisation of a SOFC

Solid ceramic electrolytes prevent corrosion, offer superior mechanical performance for smaller, lighter weight structures, but do still present some challenges in terms of processing and temperatures.

“In theory, any gases capable of being electrochemically oxidized and reduced can be used as fuel and oxidant in a fuel cell,” states Alcaraz.

Working scheme of a fuel cell

Physical and chemical characteristics of the four components of a SOFC

For suitable performance, fuel cells must contain the following

  • High conversion efficiency
  • Environmental compatibility
  • Modularity
  • Sitting flexibility
  • Multifuel capability

Different applications of fuel cells; a) Fuel cell in the Toyota Mirai model and, b) a fuel cell for ships as part of a maritime project for the U.S. Department of Energy

More traditional techniques for production with ceramic materials include uniaxial and isostatic pressing, tape casting, slip casting, extrusion, and ceramic injection molding. 3D printing has been used in connection with ceramics and a variety of different projects around the world, to include the use of ceramic brick structures in architecture, porous ceramics with bioinspired materials, and establishing parameters in quality assurance.

Techniques such as powder bed binder jet/inkjet 3D printing are popular with the use of ceramics.

“It must be mentioned that although printed material in plaster-based printers is a ceramic material, if impregnated with and adhesive, it will not be a pure ceramic but a polymer-ceramic composite. As no extreme heating is required during and after processing, colors can be added to the part,” stated Alcaraz.

Examples of powder bed binder jet/inkjet 3D printed parts

Other popular 3D printing methods include selective laser melting (SLM), stereolithography (SLA), and robocasting. Alcaraz noted, however, that 3D printed samples demonstrated 98 percent relative density in comparison to tradition methods—and especially when compared to cold isostatic pressing.

“It has been demonstrated that the 3D printing specimens present similar micro- and nano- mechanical properties with the sample fabricated by a conventional processing route. In terms of the Vickers Hardness, the 3D printed specimens presented higher values than the specimen produced by CIP,” concluded the researchers. “As far as for the nanoindentation hardness and elastic modulus, the 3DP parts presented similar values of hardness. Nevertheless, it has been found that the values found for the elastic modulus are sensitive to different aspects such as the porosity and the roughness of the parts, giving less concise values.

“Concerning the reduction of printing defects, it is recommended to treat the feedstock before printing in order to achieve an homogenous particle size of the powder and be able to use a nozzle with a smaller diameter in order to enhance the resolution of the final 3D printed part. Finally, it would be interesting to follow the investigation of microcompression of the printed samples in order to extract the compression elastic modulus value through a different experiment and compare it to the nanoindentation technique. Furthermore, in the compression stress-strain curve obtained for the 3D printed specimen it is clear to observe a densification process (serrated zone) due to the presence of internal porosity heterogeneously distributed along the entire specimen.”

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[Source / Images: ‘Mechanical and Microstructural Characterization of 3D Printed Ceramic Fuel Cells Electrolytes’]

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Brazil: 3D Printed Miniaturized Platform with Disposable Detector

Brazilian researchers from Instituto de Química explore miniaturized devices in the recently published ‘Design of novel, simple, and inexpensive 3D printing-based miniaturized electrochemical platform containing embedded disposable detector for analytical applications.’

While there are many different methods used today for detection in miniaturized devices, electrochemical methods are attractive to users for the following reasons:

  • Sensitivity
  • Simplicity
  • Ease in operation
  • Potential for miniaturization of instrumentation
  • Low environmental impact
  • Minimal power requirements

Steps for the fabrication of the electro-chemical platform: (A) CAD design of the 3D printed mold used for prototyping the PDMS devices. The internal relief structures were20 mm length × 600 μmwidth × 1 mm height; (B)PDMS device obtained using the 3D printed mold;(C) PDMS miniaturized cell with the integrated working,pseudo-reference and counter electrodes; (D) geometric area of the electrodes delimited with adhesive tape, and (E)electrochemical platform

These techniques are applicable to other applications too, like electrochemical sensors:

“These aspects make the electrochemical techniques affordable, very attractive, and a powerful tool for analytical sciences,” stated the researchers.

Here, pencil graphite was chosen as it is a good alternative to carbon, accessible and affordable, and effective. For this project, the researchers presented a platform with a ‘fully integrated electrochemical detector, fabricated via FDM 3D printing.’

SEM images of the pencil graphite lead surface obtained in different magnifications

For the proof of concept, the device created here was used in analyzing both dopamine DOPA and acetaminophen (AC). This allowed the researchers to evaluate the functionality of the device, as they assessed parameters. Urine sample results were found to be ‘quite satisfactory,’ with the device functioning via a structure containing microchannels with the pencil graphite leads inserted into them, resulting in working electrodes.

“This way, the results reported here testify the good analytical efficiency, precision, and stability of the proposed device, and enables its use for routine analytical procedures and determination of electroactive substances in real samples, even using simple and inexpensive materials. Moreover, the 3D printing-based fabrication protocol used here may be an interesting alternative to the most widely used soft lithography on the fabrication of PDMS-based structures,” concluded the research team.

“It is interesting since the configuration of the devices is easily adjusted and the molds might be fabricated in-house without the use of complex instrumentation and expensive facilities such as clean rooms. Moreover, the device presented here might be used as a detector in other analytical systems such as flow and microfluidic devices. It opens promising new possibilities for application of the approach described here.”

3D printing and miniaturization often accompany each other today, and especially as researchers around the world seek greater opportunity to innovate and push the limits for versatility in a multitude of different applications, using a variety of hardware, software, and materials. As the lab-on-a-chip concept becomes increasingly more popular for scientists and industrial users, other vehicles such as microfluidics and micro-mixers are becoming widely used, along with so many other new methods and materials.

What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

[Source / Images: ‘Design of novel, simple, and inexpensive 3D printing-based miniaturized electrochemical platform containing embedded disposable detector for analytical applications’]

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Researchers Complete Comprehensive Evaluation of Manufacturing Methods, Including 3D Printing, for Impellers

EDM and ECM finishing of near-net-shape turbo charger wheels produced by additive manufacturing and investment casting.

Combustion engines uses turbochargers to boost their performance. But, for multiple reasons, there isn’t a conventional process chain for economically manufacturing the component. A team of researchers from RWTH Aachen University and Robert Bosch GmbH recognized the need for a comprehensive evaluation of alternative manufacturing methods for impellers – 3D printing isn’t the only way – and set out to deliver. They published their results in a paper, titled “Technological and Economical Assessment of Alternative Process Chains for Turbocharger Impeller Manufacture.”

The abstract reads, “In this paper, different manufacturing chains consisting of pre-finishing and finishing of near-net-shape parts are compared to each other for a given example geometry. Electrochemical as well as Electrical Discharge Machining technologies are taken into account as alternatives for conventional milling and grinding processes for the finishing of cast blanks or samples produced by additive manufacturing. Based on a technological analysis a cost comparison is executed, which allows an economical assessment of the different process chains regarding given boundary conditions and varying production quantities.”

In addition to electrochemical (ECM) and electrical discharge machining (EDM) technologies, the team also looked at wire-based technology variants (WEDM/WECM) for outer straight geometries, and 3D-(Sinking)-based technologies for inner flow ones. They completed a cost comparison of the methods, based on technological analysis, which, as the researchers wrote, “allows an economical assessment of the different process chains regarding boundary conditions and production quantities.”

Turbocharger wheels – blank manufacturing by investment casting (near-net-shape and finish contour) or additive manufacturing and conventional finishing by milling and grinding

“In a first step a technological process analysis took place for both alternative primary shaping processes of turbocharger wheel blanks and for finish machining of near-net-shape geometries by conventional as well as unconventional advanced machining processes,” the researchers wrote. “Target values were a geometrical precision better than 0.05 mm and a minimum surface roughness of Rz = 4 µm.”

Fine investment casting can be used to manufacture a blank with defined material allowance, as well as electron beam melting (EBM) 3D printing, though the latter with require post processing because of insufficient geometrical precision and a rough surface. It’s possible to finish with 5-axis milling, but due to extensive tool wear, it will require a lot of effort. The team determined that abrasive flow machining and vibratory grinding would not work.

“All technological necessary efforts have been evaluated and aggregated in a production cost ratio relative to the standard investment casting process as basis,” the team wrote in the paper. “This includes tool costs (purchase costs and life time), raw material costs (melt / powder material), energy (average energy consumption) and working costs (salary and multiple machine work) as well as machine costs (investment, net book value, space, maintenance, machining time per part) for main and secondary process like hot isostatic pressing (HIP) – imperative for the EBM parts – and washing. Additional industrial boundary conditions were a yearly lot size of 150,000 parts and working time of 4,800 h. The earnings per worker amounts to 43.75 €/h, the energy price and monthly space costs are 0.128 €/kWh and 12 €/m² respectively. The imputed interest rate is 10 %.”

Production costs of different primary shaping and finish machining as well as handling processes relative to the investment casting process.

Alternative EDM- and ECM-based processes were also included in the diagram.

The researchers explained that the microstructures from 3D printing and casting processes had a major influence on the final surface roughness. In addition, the ECM-processed material was analyzed, and basic EDM research showed that for the TiAl material, the correct electrical polarity had to be clarified. By applying a new flushing concept based on WECM, the team was able to achieve higher ECM cutting rates in a “competitive order of magnitude of 20 mm²/min also for macroscopic workpiece heights.”

EDM and ECM applications for finishing turbo charger wheels.

It was determined that, under the boundary conditions laid down, 3D-EDM is not a competitive  or efficient single process, but 3D-ECM is, when compared to 5-axis milling. Additionally, WEDM and WECM showed low costs.

“It can be concluded that the process chains involving 3DEDM are not suitable as their cost ratios are higher than 300 % of the reference but the ECM variants reveal significant advantages due to much lower cost ratios. In addition for the basis costs, the AM produced raw blanks reveal lower cost ratios compared to the investment casted ones – even for the given series production,” the researchers wrote.

These results are due to the specific material properties of the TiAl material. Because of low costs for the outer geometry finishing, the contour casted samples also had higher cost ratios.

“As a conclusion – for the given boundary conditions – the process chain including 3DECM and WECM of AM produced blank wheels achieved the lowest costs and was therefore the most efficient one,” the researchers wrote. “Further work should include detailed studies on surface integrity for the different machining processes and appropriate positioning.”

Co-authors of the paper are A. Klink, M. Hlavac, T. Herrig, and M. Holsten.