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Frank Clemens
Empa - Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland

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Short Biography

Dr. Frank Clemens is Group Leader (Smart Ceramic Processing) in the Laboratory for High Performance Ceramics at Empa, Swiss Federal Laboratories for Materials Science and Technology, Switzerland. His scientific and applied research concerns the thermoplastic processing of powder-based sensors, actuators, and structural materials. He works with physicists, chemists, material scientists, and engineers together to investigate activation energies on different processing steps. Moreover, he develops new strategies for the processing of soft sensor materials and structures. Since 2003, he has been a lecturer at ETH Zurich and since 2010 a lecturer at ZHAW. He has published more than 125 peer-reviewed articles and patents.

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Journal article
Published: 06 August 2021 in Additive Manufacturing
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This study demonstrates the feasibility of fabricating large complex zirconia structures using a material extrusion-(MEX) based additive manufacturing process, called fused deposition modeling (FDM) or fused filament fabrication (FFF). For this purpose, a feedstock based on ethylene-vinyl acetate and stearic acid containing 45 vol.-% zirconia powder was extruded into filaments and used for printing on a consumer-grade FDM/FFF printer. To detect structural failures after each processing step, disks made out of 4 printed layers were selected. After printing, debinding and sintering a fractography analysis of the disks was evaluated using an optical and scanning electron microscope to identify the defects. To avoid defect formation during printing, a new approach, dynamic infill technique, was employed and resulted in void-free printed disks with a smooth top surface. This approach was essential to study the origin of failures in the post-processing steps. Model free-kinetic analysis was used to investigate the activation energy of the binder decomposition and to design a thermal debinding program with a constant 0.1%/min mass loss rate of the thermoplastic binder. Based on the kinetic studies it could be demonstrated that sufficient thermal binder burnout could be achieved by integration of solvent extraction and wicking debinding steps. Using ring-on-ring test it could be observed, that an edge-initiated failure resulted in low average strength (91 MPa) of the sintered disks. Finally, printed and defect-free sintered 120 mm high vase could be successfully achieved using the model free-kinetic designed debinding program.

ACS Style

Amir Hadian; Leonard Koch; Philipp Koberg; Fateme Sarraf; Antje Liersch; Tutu Sebastian; Frank Clemens. Material extrusion based additive manufacturing of large zirconia structures using filaments with ethylene vinyl acetate based binder composition. Additive Manufacturing 2021, 47, 102227 .

AMA Style

Amir Hadian, Leonard Koch, Philipp Koberg, Fateme Sarraf, Antje Liersch, Tutu Sebastian, Frank Clemens. Material extrusion based additive manufacturing of large zirconia structures using filaments with ethylene vinyl acetate based binder composition. Additive Manufacturing. 2021; 47 ():102227.

Chicago/Turabian Style

Amir Hadian; Leonard Koch; Philipp Koberg; Fateme Sarraf; Antje Liersch; Tutu Sebastian; Frank Clemens. 2021. "Material extrusion based additive manufacturing of large zirconia structures using filaments with ethylene vinyl acetate based binder composition." Additive Manufacturing 47, no. : 102227.

Journal article
Published: 11 June 2021 in Journal of the European Ceramic Society
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An optimized recipe for 3D printing of Mullite-based structures was used to investigate the effect of MgO sintering additive on the processing stages and final ceramic properties. To achieve dense 3:2 mullite, ceramic filaments were prepared based on an alumina powder, a methyl silicone resin, EVA elastomeric binder and MgO powder. Using 1 wt% MgO and a dwell time of 5 h at 1600 °C, a dense mullite structure could be obtained from filaments with a diameter of 1.75 mm. Ceramic structures with and without sintering additive were printed in vertical and horizontal direction, to investigate the effect of printing direction on mechanical strength after sintering. Using four-point bending test, it was demonstrated that by using MgO, the printing orientation did not affect the mechanical strength significantly anymore. The low Weibull modulus could be explained by the closed porosity that emerge during the degassing of the preceramic polymer due to cross-linking.

ACS Style

Fateme Sarraf; Edoardo Abbatinali; Lovro Gorjan; Tutu Sebastian; Paolo Colombo; Sergey V. Churakov; Frank Clemens. Effect of MgO sintering additive on mullite structures manufactured by fused deposition modeling (FDM) technology. Journal of the European Ceramic Society 2021, 41, 6677 -6686.

AMA Style

Fateme Sarraf, Edoardo Abbatinali, Lovro Gorjan, Tutu Sebastian, Paolo Colombo, Sergey V. Churakov, Frank Clemens. Effect of MgO sintering additive on mullite structures manufactured by fused deposition modeling (FDM) technology. Journal of the European Ceramic Society. 2021; 41 (13):6677-6686.

Chicago/Turabian Style

Fateme Sarraf; Edoardo Abbatinali; Lovro Gorjan; Tutu Sebastian; Paolo Colombo; Sergey V. Churakov; Frank Clemens. 2021. "Effect of MgO sintering additive on mullite structures manufactured by fused deposition modeling (FDM) technology." Journal of the European Ceramic Society 41, no. 13: 6677-6686.

Journal article
Published: 17 May 2021 in Engineering Proceedings
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In recent years, soft pneumatic actuators have come into the spotlight because of their simple control and the wide range of complex motions. To monitor the deformation of soft robotic systems, elastomer-based sensors are being used. However, the embedding of sensors into soft actuator modules by polymer casting is time consuming and difficult to upscale. In this study, it is shown how a pneumatic bending actuator with an integrated sensing element can be produced using an extrusion-based additive manufacturing method, e.g., fused deposition modeling (FDM). The advantage of FDM against direct printing or robocasting is the significantly higher resolution and the ability to print large objectives in a short amount of time. New, commercial launched, pellet-based FDM printers are able to 3D print thermoplastic elastomers of low shore hardness that are required for soft robotic applications, to avoid high pressure for activation. A soft pneumatic actuator with the in situ integrated piezoresistive sensor element was successfully printed using a commercial styrene-based thermoplastic elastomer (TPS) and a developed TPS/carbon black (CB) sensor composite. It has been demonstrated that the integrated sensing elements could monitor the deformation of the pneumatic soft robotic actuator. The findings of this study contribute to extending the applicability of additive manufacturing for integrated soft sensors in large soft robotic systems.

ACS Style

Antonia Georgopoulou; Lukas Egloff; Bram Vanderborght; Frank Clemens. A Soft Pneumatic Actuator with Integrated Deformation Sensing Elements Produced Exclusively with Extrusion Based Additive Manufacturing. Engineering Proceedings 2021, 6, 11 .

AMA Style

Antonia Georgopoulou, Lukas Egloff, Bram Vanderborght, Frank Clemens. A Soft Pneumatic Actuator with Integrated Deformation Sensing Elements Produced Exclusively with Extrusion Based Additive Manufacturing. Engineering Proceedings. 2021; 6 (1):11.

Chicago/Turabian Style

Antonia Georgopoulou; Lukas Egloff; Bram Vanderborght; Frank Clemens. 2021. "A Soft Pneumatic Actuator with Integrated Deformation Sensing Elements Produced Exclusively with Extrusion Based Additive Manufacturing." Engineering Proceedings 6, no. 1: 11.

Journal article
Published: 15 May 2021 in Polymers
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Magnetorheological elastomers (MRE) are increasing in popularity in many applications because of their ability to change stiffness by applying a magnetic field. Instead of liquid-based 1 K and 2 K silicone, thermoplastic elastomers (TPE), based on styrene-butadiene-styrene block copolymers, have been investigated as matrix material. Three different carbonyl iron particles (CIPs) with different surface treatments were used as magneto active filler material. For the sample fabrication, the thermoplastic pressing method was used, and the MR effect under static and dynamic load was investigated. We show that for filler contents above 40 vol.-%, the linear relationship between powder content and the magnetorheological effect is no longer valid. We showed how the SiO2 and phosphate coating of the CIPs affects the saturation magnetization and the shear modulus of MRE composites. A combined silica phosphate coating resulted in a higher shear modulus, and therefore, the MR effect decreased, while coating with SiO2 only improved the MR effect. The highest performance was achieved at low deformations; a static MR effect of 73% and a dynamic MR effect of 126% were recorded. It was also shown that a lower melting viscosity of the TPE matrix helps to increase the static MR effect of anisotropic MREs, while low shear modulus is crucial for achieving high dynamic MR. The knowledge from TPE-based magnetic composites will open up new opportunities for processing such as injection molding, extrusion, and fused deposition modeling (FDM).

ACS Style

Arturo Tagliabue; Fernando Eblagon; Frank Clemens. Analysis of Styrene-Butadiene Based Thermoplastic Magnetorheological Elastomers with Surface-Treated Iron Particles. Polymers 2021, 13, 1597 .

AMA Style

Arturo Tagliabue, Fernando Eblagon, Frank Clemens. Analysis of Styrene-Butadiene Based Thermoplastic Magnetorheological Elastomers with Surface-Treated Iron Particles. Polymers. 2021; 13 (10):1597.

Chicago/Turabian Style

Arturo Tagliabue; Fernando Eblagon; Frank Clemens. 2021. "Analysis of Styrene-Butadiene Based Thermoplastic Magnetorheological Elastomers with Surface-Treated Iron Particles." Polymers 13, no. 10: 1597.

Journal article
Published: 10 May 2021 in Actuators
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Soft pneumatic actuators with a channel network (pneu-net) based on thermoplastic elastomers are compatible with fused deposition modeling (FDM). However, conventional filament-based fused deposition modeling (FDM) printers are not well suited for thermoplastic elastomers with a shore hardness (Sh < 70A). Therefore, in this study, a pellet-based FDM printer was used to print pneumatic actuators with a shore hardness of Sh18A. Additionally, the method allowed the in situ integration of soft piezoresistive sensing elements during the fabrication. The integrated piezoresistive elements were based on conductive composites made of three different styrene-ethylene-butylene-styrene (SEBS) thermoplastic elastomers, each with a carbon black (CB) filler with a ratio of 1:1. The best sensor behavior was achieved by the SEBS material with a shore hardness of Sh50A. The dynamic and quasi-static sensor behavior were investigated on SEBS strips with integrated piezoresistive sensor composite material, and the results were compared with TPU strips from a previous study. Finally, the piezoresistive composite was used for the FDM printing of soft pneumatic actuators with a shore hardness of 18 A. It is worth mentioning that 3 h were needed for the fabrication of the soft pneumatic actuator with an integrated strain sensing element. In comparison to classical mold casting method, this is faster, since curing post-processing is not required and will help the industrialization of pneumatic actuator-based soft robotics.

ACS Style

Antonia Georgopoulou; Lukas Egloff; Bram Vanderborght; Frank Clemens. A Sensorized Soft Pneumatic Actuator Fabricated with Extrusion-Based Additive Manufacturing. Actuators 2021, 10, 102 .

AMA Style

Antonia Georgopoulou, Lukas Egloff, Bram Vanderborght, Frank Clemens. A Sensorized Soft Pneumatic Actuator Fabricated with Extrusion-Based Additive Manufacturing. Actuators. 2021; 10 (5):102.

Chicago/Turabian Style

Antonia Georgopoulou; Lukas Egloff; Bram Vanderborght; Frank Clemens. 2021. "A Sensorized Soft Pneumatic Actuator Fabricated with Extrusion-Based Additive Manufacturing." Actuators 10, no. 5: 102.

Journal article
Published: 10 April 2021 in Polymers
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Soft robotics and flexible electronics are rising in popularity and can be used in many applications. However, there is still a need for processing routes that allow the upscaling in production for functional soft robotic parts in an industrial scale. In this study, injection molding of liquid silicone is suggested as a fabrication method for sensorized robotic skin based on sensor fiber composites. Sensor fibers based on thermoplastic elastomers with two different shore hardness (50A and 70A) are combined with different silicone materials. A mathematical model is used to predict the mechanical load transfer from the silicone matrix to the fiber and shows that the matrix of the lowest shore hardness should not be combined with the stiffer fiber. The sensor fiber composites are fixed on a 3D printed robotic finger. The sensorized robotic skin based on the composite with the 50A fiber in combination with pre-straining gives good sensor performance as well as a large elasticity. It is proposed that a miss-match in the mechanical properties between fiber sensor and matrix should be avoided in order to achieve low drift and relaxation. These findings can be used as guidelines for material selection for future sensor integrated soft robotic systems.

ACS Style

Antonia Georgopoulou; Silvain Michel; Frank Clemens. Sensorized Robotic Skin Based on Piezoresistive Sensor Fiber Composites Produced with Injection Molding of Liquid Silicone. Polymers 2021, 13, 1226 .

AMA Style

Antonia Georgopoulou, Silvain Michel, Frank Clemens. Sensorized Robotic Skin Based on Piezoresistive Sensor Fiber Composites Produced with Injection Molding of Liquid Silicone. Polymers. 2021; 13 (8):1226.

Chicago/Turabian Style

Antonia Georgopoulou; Silvain Michel; Frank Clemens. 2021. "Sensorized Robotic Skin Based on Piezoresistive Sensor Fiber Composites Produced with Injection Molding of Liquid Silicone." Polymers 13, no. 8: 1226.

Journal article
Published: 24 February 2021 in IEEE Robotics and Automation Letters
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In this letter, we developed a piezoresistive auxetic sensor structure based on a silicone elastomer and carbon-based conductive thermoplastic elastomer fiber sensor (CTPE fiber). Liquid silicone has been used as the matrix material. In addition silicone has been mixed with silica filler to tailor the stiffness of an auxetic elastic structure that improved the sensor behavior of silicone-based CTPE fiber composites. The 2D auxetic structures with and without silica fillers have been successfully printed with the direct ink writing method. The piezoresistive fiber was integrated and the auxetic structure were embedded in the silicone matrix in a second step, via casting method. To detect the electrical signal behavior of the integrated fiber sensor, the hybrid manufactured auxetic fiber sensor composite was investigated using dynamic cycle testing between 0 and 20% strain. Using silicone with silica filler for the printing of the auxetic structure, the sensor behavior of the piezoresistive fiber elastomer composite was improved and a secondary peak of the sensor signal could be avoided at low strains. Unfortunately, a constant gauge factor between 0 and 20% strain could not be obtained by implementing the auxetic structure element inside the CTPE fiber composite. However, this structure can already be integrated into a watchband and used for gesture-controlled applications.

ACS Style

Frank Clemens; Mark Melnykowycz; Forian Bar; Daniel Goldenstein; Antonia Georgopoulou. 2D Printing of Piezoresistive Auxetic Silicone Sensor Structures. IEEE Robotics and Automation Letters 2021, 6, 2541 -2546.

AMA Style

Frank Clemens, Mark Melnykowycz, Forian Bar, Daniel Goldenstein, Antonia Georgopoulou. 2D Printing of Piezoresistive Auxetic Silicone Sensor Structures. IEEE Robotics and Automation Letters. 2021; 6 (2):2541-2546.

Chicago/Turabian Style

Frank Clemens; Mark Melnykowycz; Forian Bar; Daniel Goldenstein; Antonia Georgopoulou. 2021. "2D Printing of Piezoresistive Auxetic Silicone Sensor Structures." IEEE Robotics and Automation Letters 6, no. 2: 2541-2546.

Journal article
Published: 23 February 2021 in IEEE Robotics and Automation Letters
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Soft robotic sensors have been limited in their applications due to their highly nonlinear time variant behavior. Current studies are either looking into techniques to improve the mechano-electrical properties of these sensors or into modelling algorithms that account for the history of each sensor. Here, we present a method for combining multi-material soft strain sensors to obtain equivalent higher quality sensors; better than each of the individual strain sensors. The core idea behind this work is to use a combination of redundant and disjoint strain sensors to compensate for the time-variant hidden states of a soft-bodied system, to finally obtain the true strain state in a static manner using a learning-based approach. We provide methods to develop these variable sensors and metrics to estimate their dissimilarity and efficacy of each sensor combinations, which can double down as a benchmarking tool for soft robotic sensors. The proposed approach is experimentally validated on a pneumatic actuator with embedded soft strain sensors. Our results show that static data from a combination of nonlinear time variant strain sensors is sufficient to accurately estimate the strain state of a system.

ACS Style

Thomas George Thuruthel; Josie Hughes; Antonia Georgopoulou; Frank Clemens; Fumiya Iida. Using Redundant and Disjoint Time-Variant Soft Robotic Sensors for Accurate Static State Estimation. IEEE Robotics and Automation Letters 2021, 6, 2099 -2105.

AMA Style

Thomas George Thuruthel, Josie Hughes, Antonia Georgopoulou, Frank Clemens, Fumiya Iida. Using Redundant and Disjoint Time-Variant Soft Robotic Sensors for Accurate Static State Estimation. IEEE Robotics and Automation Letters. 2021; 6 (2):2099-2105.

Chicago/Turabian Style

Thomas George Thuruthel; Josie Hughes; Antonia Georgopoulou; Frank Clemens; Fumiya Iida. 2021. "Using Redundant and Disjoint Time-Variant Soft Robotic Sensors for Accurate Static State Estimation." IEEE Robotics and Automation Letters 6, no. 2: 2099-2105.

Journal article
Published: 02 December 2020 in Sensors and Actuators A: Physical
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Combining conductive fillers like carbon black with elastomers allows the development of soft elastomer strain sensors that can reach very large elongations, an important requirement for many robotic applications. However, when the conductive filler is introduced in the polymer, significant stiffening occurs, affecting the mechanical properties, e.g. Young’s Modulus, of the soft structure. In this attempt, single piezoresistive fiber composites were successfully fabricated, without drastically increasing the stiffness. Two silicone elastomers that are widely used in robotic applications were examined as matrix materials. Furthermore, modeling the stresses exerted on the fiber inside the composite was successfully used to predict the detachment of fiber inside the matrix, observed by visual inspection. For the PDMS based composite, pre-straining improved sensor properties, which could be confirmed for the monitoring of the movement of the crane robot. The results showed that the pre-strained piezoresistive sensor fiber-matrix composites positions of the robot crane can be monitored even at low strains.

ACS Style

Antonia Georgopoulou; Silvain Michel; Bram Vanderborght; Frank Clemens. Piezoresistive sensor fiber composites based on silicone elastomers for the monitoring of the position of a robot arm. Sensors and Actuators A: Physical 2020, 318, 112433 .

AMA Style

Antonia Georgopoulou, Silvain Michel, Bram Vanderborght, Frank Clemens. Piezoresistive sensor fiber composites based on silicone elastomers for the monitoring of the position of a robot arm. Sensors and Actuators A: Physical. 2020; 318 ():112433.

Chicago/Turabian Style

Antonia Georgopoulou; Silvain Michel; Bram Vanderborght; Frank Clemens. 2020. "Piezoresistive sensor fiber composites based on silicone elastomers for the monitoring of the position of a robot arm." Sensors and Actuators A: Physical 318, no. : 112433.

Conference paper
Published: 01 September 2020 in Industrializing Additive Manufacturing
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Shaping and thermal processing of ceramic structures with fused deposition modeling (FDM) is promising, but still a challenging technique. Achieving an optimal compromise between the thermoplastic feedstock properties in terms of 3D printing and debinding behavior is not trivial. In this paper aluminum oxide (Al2O3), zirconium oxide toughened aluminum oxide (ZTA) and ZrO2 (zirconium oxide) thermoplastic filaments were developed for multi-material printing of 2-2 and 3-3 composites using a Bowden extruder with 2.8 mm filament thickness. For all filaments, a thermoplastic binder based on Ethylene Vinyl Acetate (EVA) and stearic acid (SA) with a ceramic filler content of 45 vol.% were used. Increasing the SA content, it was possible to use the solvent debinding process and therefore the thickness of the printed structures could be increased up to 10 mm. After 2 h in acetone solvent, more than 40 wt% could be removed. With additional thermal partial debinding process at 240 °C for 8 h, up to 82 wt% of the thermoplastic binder could be removed successfully. The monolithic printed discs achieved a relative density of 98.2 and 99.1% for the ZTA and the ZrO2 samples, respectively. Finally, the mechanical properties were investigated by ring-on-ring bending test method based on ASTM standard. For ZrO2 discs a mechanical strength of 429 MPa could be achieved. By mixing 5% yttrium stabilized ZrO2 with Al2O3, the mechanical strength could be increased from 220 (pure Alumina) to 297 MPa (ZTA). For the 2-2 composite, a mechanical bending strength of 214 MPa could be achieved.

ACS Style

Frank Clemens; Josef Schulz; Lovro Gorjan; Antje Liersch; Tutu Sebastian; Fateme Sarraf. Debinding and Sintering of Dense Ceramic Structures Made with Fused Deposition Modeling. Industrializing Additive Manufacturing 2020, 293 -303.

AMA Style

Frank Clemens, Josef Schulz, Lovro Gorjan, Antje Liersch, Tutu Sebastian, Fateme Sarraf. Debinding and Sintering of Dense Ceramic Structures Made with Fused Deposition Modeling. Industrializing Additive Manufacturing. 2020; ():293-303.

Chicago/Turabian Style

Frank Clemens; Josef Schulz; Lovro Gorjan; Antje Liersch; Tutu Sebastian; Fateme Sarraf. 2020. "Debinding and Sintering of Dense Ceramic Structures Made with Fused Deposition Modeling." Industrializing Additive Manufacturing , no. : 293-303.

Journal article
Published: 06 August 2020 in Ceramics International
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In this study, two grades of high speed steel (HSS), having different carbon content and processing treatment (i.e. cryo-milling and atomization), were used as a metallic binder for NbC cemented carbides. Thermoanalytical methods were used to investigate the outgassing and sintering of the two NbC cemented carbides during heat treatment. For this mean, thermogravimetry (TG), differential scanning calorimetry (DSC) and evolved gas (EG) analysis during thermal heat treatment were carried out. The results indicated that the processing treatment has a great impact on the thermal behavior of the steel powders, which later can be traced in the thermal behavior of the compacts. Higher decarburization was traced during the thermal analysis on the powder prepared via cryo-milling compared to the one made by the atomization process. From the TG analysis of the green compacts, it was evident that intensive outgassing occurs at temperatures above 850 °C. This phenomenon is associated with the activation of several mechanism in NbC and steel above this temperature which was realized from the evaluation of the initial powders. To gain a deeper understanding on the basic reactions and the effect of carbon content on phase transformations during the thermal process, thermodynamic studies was performed using commercial software (Thermo-Calc). It was evident that decreasing the carbon content shifts the transformation temperatures (e.g. liquid formation) to higher levels. This is especially important in adjusting the sintering temperature in NbC-high speed steel system as sufficient portion of liquid phase should be presented during the sintering process in order to obtain a satisfactory sintering.

ACS Style

Amir Hadian; Cyrus Zamani; Claudia Schreiner; Renato Figi; Frank Jörg Clemens. Influence of carbon content and processing treatment of metallic binder on the outgassing and sintering of NbC based cemented carbide. Ceramics International 2020, 46, 28422 -28431.

AMA Style

Amir Hadian, Cyrus Zamani, Claudia Schreiner, Renato Figi, Frank Jörg Clemens. Influence of carbon content and processing treatment of metallic binder on the outgassing and sintering of NbC based cemented carbide. Ceramics International. 2020; 46 (18):28422-28431.

Chicago/Turabian Style

Amir Hadian; Cyrus Zamani; Claudia Schreiner; Renato Figi; Frank Jörg Clemens. 2020. "Influence of carbon content and processing treatment of metallic binder on the outgassing and sintering of NbC based cemented carbide." Ceramics International 46, no. 18: 28422-28431.

Communication
Published: 29 July 2020 in Advanced Materials Technologies
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Indium tin oxide (ITO) is a transparent conducting material that is widely used in devices where high transparency of the electrodes is required, such as flat panel and liquid crystal displays, touch panels, smart windows, and many others. ITO layers are deposited on a large scale by magnetron sputtering and then structured by lithography to define desired patterns of transparent electrodes. Here, a method for direct printing of transparent conductive patterns from ITO nanoparticle ink is communicated. The method combines inkjet printing with fast flash lamp annealing whereby the main novelty is to use an additional layer of a colored organic dye onto printed ITO to increase light absorption. The dye coating is instantly heated together with the underlying ITO layer by a light pulse, leading to an instant rise of the surface temperature, which is translated into improved optoelectronic properties of the ITO layers. Inkjet‐printed ITO patterns processed with the dye‐assisted flash lamp annealing exhibit a transmittance of up to 88% at 550 nm and resistivity of 3.1 × 10−3Ω cm. Transparent touch‐sensing trackpad and capacitive touch sensors are demonstrated based on the printed ITO patterns, which can be utilized in transparent security systems and other transparent Internet‐of‐Things devices.

ACS Style

Evgeniia Gilshtein; Sami Bolat; Galo Torres Sevilla; Antonio Cabas‐Vidani; Frank Clemens; Thomas Graule; Ayodhya N. Tiwari; Yaroslav E. Romanyuk. Inkjet‐Printed Conductive ITO Patterns for Transparent Security Systems. Advanced Materials Technologies 2020, 1 .

AMA Style

Evgeniia Gilshtein, Sami Bolat, Galo Torres Sevilla, Antonio Cabas‐Vidani, Frank Clemens, Thomas Graule, Ayodhya N. Tiwari, Yaroslav E. Romanyuk. Inkjet‐Printed Conductive ITO Patterns for Transparent Security Systems. Advanced Materials Technologies. 2020; ():1.

Chicago/Turabian Style

Evgeniia Gilshtein; Sami Bolat; Galo Torres Sevilla; Antonio Cabas‐Vidani; Frank Clemens; Thomas Graule; Ayodhya N. Tiwari; Yaroslav E. Romanyuk. 2020. "Inkjet‐Printed Conductive ITO Patterns for Transparent Security Systems." Advanced Materials Technologies , no. : 1.

Journal article
Published: 23 June 2020 in Additive Manufacturing
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Alumina ceramic feedstocks with ethylene vinyl acetate and stearic acid as an organic binder were prepared and shaped by a commercial 3D filament printer. Rheological properties and the ability of ceramic feedstocks to be processed into filaments and shaped by the fused deposition modeling/filament (FDM/FFF) technique were investigated. The addition of stearic acid affects the viscosity as a function of shear rate in a complex way. Analysis with rheological models shows that while using a small amount of stearic acid, a viscosity plateau at low shear rate (cross model) can be observed. At high stearic acid content, a yield point (Herschel-Bulkley model) occurs, as the stearic acid content surpasses the amount needed to cover the powder surface. The stearic acid also influences the properties of the solidified filament, making it more brittle and less flexible. Thin wall structures were printed, debinded and sintered to demonstrate the shape stability and fusion between the layers. Ring-on-ring bending tests of sintered discs show that the printing defects are the primary concerns that determine the strength of sintered samples.

ACS Style

Lovro Gorjan; Cristina Galusca; Marwah Sami; Tutu Sebastian; Frank Clemens. Effect of stearic acid on rheological properties and printability of ethylene vinyl acetate based feedstocks for fused filament fabrication of alumina. Additive Manufacturing 2020, 36, 101391 .

AMA Style

Lovro Gorjan, Cristina Galusca, Marwah Sami, Tutu Sebastian, Frank Clemens. Effect of stearic acid on rheological properties and printability of ethylene vinyl acetate based feedstocks for fused filament fabrication of alumina. Additive Manufacturing. 2020; 36 ():101391.

Chicago/Turabian Style

Lovro Gorjan; Cristina Galusca; Marwah Sami; Tutu Sebastian; Frank Clemens. 2020. "Effect of stearic acid on rheological properties and printability of ethylene vinyl acetate based feedstocks for fused filament fabrication of alumina." Additive Manufacturing 36, no. : 101391.

Journal article
Published: 10 June 2020 in Materials
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Safety workwear often requires antistatic protection to prevent the build-up of static electricity and sparks, which can be extremely dangerous in a working environment. In order to make synthetic antistatic fibers, electrically conducting materials such as carbon black are added to the fiber-forming polymer. This leads to unwanted dark colors in the respective melt-spun fibers. To attenuate the undesired dark color, we looked into various possibilities including the embedding of the conductive element inside a dull side-by-side bicomponent fiber. The bicomponent approach, with an antistatic compound as a minor element, also helped in preventing the severe loss of tenacity often caused by a high additive loading. We could melt-spin a bicomponent fiber with a specific resistance as low as 0.1 Ωm and apply it in a fabric that fulfills the requirements regarding the antistatic properties, luminance and flame retardancy of safety workwear.

ACS Style

Rudolf Hufenus; Ali Gooneie; Tutu Sebastian; Pietro Simonetti; Andreas Geiger; Dambarudhar Parida; Klaus Bender; Gunther Schäch; Frank Clemens. Antistatic Fibers for High-Visibility Workwear: Challenges of Melt-Spinning Industrial Fibers. Materials 2020, 13, 1 .

AMA Style

Rudolf Hufenus, Ali Gooneie, Tutu Sebastian, Pietro Simonetti, Andreas Geiger, Dambarudhar Parida, Klaus Bender, Gunther Schäch, Frank Clemens. Antistatic Fibers for High-Visibility Workwear: Challenges of Melt-Spinning Industrial Fibers. Materials. 2020; 13 (11):1.

Chicago/Turabian Style

Rudolf Hufenus; Ali Gooneie; Tutu Sebastian; Pietro Simonetti; Andreas Geiger; Dambarudhar Parida; Klaus Bender; Gunther Schäch; Frank Clemens. 2020. "Antistatic Fibers for High-Visibility Workwear: Challenges of Melt-Spinning Industrial Fibers." Materials 13, no. 11: 1.

Journal article
Published: 23 April 2020 in Sensors
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In this study, a thermoplastic elastomer sensor fiber was embedded in an elastomer matrix. The effect of the matrix material on the sensor properties and the piezoresistive behavior of the single fiber-matrix composite system was investigated. For all composites, cycling test (dynamic test) and the relaxation behavior at different strains (quasi-static test) were investigated. In all cases, dynamic properties and quasi-static significantly changed after embedding, compared to the pure fiber. The composite with the silicone elastomer PDMS (Polydimethylsiloxane) as matrix material exhibited deviation from linear response of the resistivity at low strains and proved an unsuitable choice compared to natural rubber. The addition of a spring construct in the embedded sensor fiber natural rubber composite improved the linearity at low strains but increased the mechanical and electrical hysteresis of the soft matter sensor composite. Using pre-vulcanized natural rubber improved linearity at low strains and reduced significantly the stress and relative resistance relaxation as well as the resistance hysteresis, especially if the resistance remained low. In both cases of the pre-vulcanized rubber and the spring structure, the piezoresistive behavior was improved, and at the same time, the stiffness of the system was increased indicating that using a stiffer matrix can be a strategy for improving the sensor properties.

ACS Style

Antonia Georgopoulou; Claudia Kummerlöwe; Frank Clemens. Effect of the Elastomer Matrix on Thermoplastic Elastomer-Based Strain Sensor Fiber Composites. Sensors 2020, 20, 2399 .

AMA Style

Antonia Georgopoulou, Claudia Kummerlöwe, Frank Clemens. Effect of the Elastomer Matrix on Thermoplastic Elastomer-Based Strain Sensor Fiber Composites. Sensors. 2020; 20 (8):2399.

Chicago/Turabian Style

Antonia Georgopoulou; Claudia Kummerlöwe; Frank Clemens. 2020. "Effect of the Elastomer Matrix on Thermoplastic Elastomer-Based Strain Sensor Fiber Composites." Sensors 20, no. 8: 2399.

Journal article
Published: 01 February 2020 in Journal of the European Ceramic Society
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Hydroxyapatite (HA) is considered as the most promising biomaterial candidate to replace and regenerate hard tissues. A small amount of β-tricalcium phosphate (β-TCP) phase is advantageous for rapid bonding of the artificial bones to natural ones due to its high solubility compared to hydroxyapatite. Synthesizing HA nanofibers from electrospinning of sol-gel is considered as a widely researched topic. Motivation of the current work was to investigate the influence of polymeric binder in the final phase evolution after heat treatment of electrospun nanofibers. Calcium phosphate nanofibers were fabricated by electrospinning sols using gelatine and polyvinylpyrrolidone as carrier polymers and subjected to heat treatment. It was realized that carrier polymers facilitate preferential calcium phosphate phase formation by forming hydroxyapatite as major phase while PVP was used and β-TCP with HA as secondary phase while gelatine was employed. XRD and thermal analyses were performed to ascertain the reason behind this interesting behaviour.

ACS Style

T. Sebastian; T.R. Preisker; L. Gorjan; T. Graule; C.G. Aneziris; F.J. Clemens. Synthesis of hydroxyapatite fibers using electrospinning: A study of phase evolution based on polymer matrix. Journal of the European Ceramic Society 2020, 40, 2489 -2496.

AMA Style

T. Sebastian, T.R. Preisker, L. Gorjan, T. Graule, C.G. Aneziris, F.J. Clemens. Synthesis of hydroxyapatite fibers using electrospinning: A study of phase evolution based on polymer matrix. Journal of the European Ceramic Society. 2020; 40 (6):2489-2496.

Chicago/Turabian Style

T. Sebastian; T.R. Preisker; L. Gorjan; T. Graule; C.G. Aneziris; F.J. Clemens. 2020. "Synthesis of hydroxyapatite fibers using electrospinning: A study of phase evolution based on polymer matrix." Journal of the European Ceramic Society 40, no. 6: 2489-2496.

Journal article
Published: 26 January 2019 in Ceramics International
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Densification behavior of NbC-12 wt.% M2 high speed steel (HSS) cemented carbide was studied using a thermo-mechanical analyzer. To be able to survey the complete sintering process, model-free and model-based kinetic analysis were combined. According to this approach, the sintering process was divided into two main parts. The first part is associated with high shrinkage and according to the model-free analysis, three steps can be identified in this part. In the second part, the presence of solution-reprecipitation can be identified according to the developed models for liquid phase sintering. By dividing the sintering behavior into two main parts, it is possible to overcome the effect of limited NbC solubility in Fe during the heating process. This effect can be observed in the densification curves as a slight expansion at the end of the first sintering part. It is assumed that poor wetting performance at low temperatures results in the outflow of the liquid phase to the surface of the compacts which results in a fake densification. It was evident that wetting performance improves significantly at elevated temperatures (above 1310 °C) inducing a re-infiltration of liquid drops on the surface inside the inner pores and the expansion in the shrinkage curve.

ACS Style

Amir Hadian; Cyrus Zamani; Frank Jörg Clemens. Sintering behavior of NbC based cemented carbides bonded with M2 high speed steel. Ceramics International 2019, 45, 8616 -8625.

AMA Style

Amir Hadian, Cyrus Zamani, Frank Jörg Clemens. Sintering behavior of NbC based cemented carbides bonded with M2 high speed steel. Ceramics International. 2019; 45 (7):8616-8625.

Chicago/Turabian Style

Amir Hadian; Cyrus Zamani; Frank Jörg Clemens. 2019. "Sintering behavior of NbC based cemented carbides bonded with M2 high speed steel." Ceramics International 45, no. 7: 8616-8625.

Research article
Published: 25 September 2018 in Advances in Materials Science and Engineering
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In this work, we investigated different short molecule polymer coatings in piezoelectric ceramic-polymer composites with low fibre volume contents. Modifying the interphase between the piezoelectric PZT (lead zirconate titanate) fibre and the epoxy matrix thus enhances the electromechanical coupling factor for 1–3 ultrasound transducers with low fibre contents. It is known that the electromechanical coupling factor can be increased by precoating a ceramic fibre with a soft interlayer polymer [1-1-3]. In this paper, we investigate the so-called 1-1-1-3 composites composed of a ferroelectric ceramic fibre (core), a soft polymer layer (e.g., fatty acids, amides, waxes, or oils), an epoxy resin shell, and an epoxy resin matrix. Some soft polymer layers allowed the free movement of the ferroelectric fibres reducing blocking or clamping by the inactive polymeric matrix, resulting in higher electromechanical coupling factors (kt) for composites with low fibre volume contents. Using an oil-based interlayer, the dielectric constant can be significantly increased. The lowest fibre push-out stress could be achieved with the paraffin interlayer; however, no correlation with the coupling factor could be observed.

ACS Style

Tony Lusiola; Sophie Oberle; Lovro Gorjan; Frank Clemens. Effect of Polymer-Ceramic Fibre Interphase Design on Coupling Factor in Low Fibre Volume Content Piezoelectric Composites. Advances in Materials Science and Engineering 2018, 2018, 1 -8.

AMA Style

Tony Lusiola, Sophie Oberle, Lovro Gorjan, Frank Clemens. Effect of Polymer-Ceramic Fibre Interphase Design on Coupling Factor in Low Fibre Volume Content Piezoelectric Composites. Advances in Materials Science and Engineering. 2018; 2018 ():1-8.

Chicago/Turabian Style

Tony Lusiola; Sophie Oberle; Lovro Gorjan; Frank Clemens. 2018. "Effect of Polymer-Ceramic Fibre Interphase Design on Coupling Factor in Low Fibre Volume Content Piezoelectric Composites." Advances in Materials Science and Engineering 2018, no. : 1-8.

Journal article
Published: 07 August 2018 in Phase Transitions
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ACS Style

L. Kozielski; M. Płońska; T. Sebastian; F. Clemens. Dielectric relaxation of Bi4Ti3O12 ceramics prepared by the low-temperature combustion synthesis. Phase Transitions 2018, 91, 1081 -1091.

AMA Style

L. Kozielski, M. Płońska, T. Sebastian, F. Clemens. Dielectric relaxation of Bi4Ti3O12 ceramics prepared by the low-temperature combustion synthesis. Phase Transitions. 2018; 91 (9-10):1081-1091.

Chicago/Turabian Style

L. Kozielski; M. Płońska; T. Sebastian; F. Clemens. 2018. "Dielectric relaxation of Bi4Ti3O12 ceramics prepared by the low-temperature combustion synthesis." Phase Transitions 91, no. 9-10: 1081-1091.

Journal article
Published: 07 August 2018 in Journal of Materials Processing Technology
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The aim of this study is to evaluate the thermoplastic processing on a new generation of hard metals based on NbC bonded with high speed steel. The conventional technique in producing cemented carbide parts is dry pressing with paraffin binder and post production. To overcome shape restriction in pressing and post production, thermoplastic shaping processes can be used. For this purpose, a previously known binder system for ceramic feedstocks containing paraffin wax and ethylene vinyl acetate was selected and used for the first time with cemented carbides. The stated organic binders were mixed with NbC-12 wt.% M2 high speed steel powder and feedstocks with solid loading content from 50 - 60 vol.% were obtained. The rheological behavior of the feedstocks as well as the critical solid loading content were assessed using a capillary rheometer. A model fitting approach was used for the first time in hardmetal feedstocks to estimate the critical solid loading. Experimental values were fitted to a model from Chong (1971) which is based on bimodally disperse powder mixtures and a critical powder loading of 70 vol.% could be calculated. However, based on the abrasion problems during mixing at high filler content, feedstock with 57.5 vol.% powder loading had the optimum processability characteristics, and was therefore selected for further shaping processes. Thermo gravimetric analysis on green samples was performed after shaping in order to develop an optimum thermal debinding profile. The thermal debinding program was adjusted with special attention on decomposition onset, maximum mass loss rate and decomposition offset temperatures. Initial trials using decomposition offset temperature as holding steps, resulted in fragmented samples after debinding. The final designed heating profile resulted in a consistent mass loss rate according to thermo gravimetric analysis which limited crack formation during debinding. Debinding under a forming gas (95N2-5H2) atmosphere using optimized heating cycles resulted in sound sintered bodies only when green parts were embedded in a powder bed during debinding.

ACS Style

Amir Hadian; Cyrus Zamani; Lovro Gorjan; Frank Jörg Clemens. Thermoplastic processing and debinding behavior of NbC-M2 high speed steel cemented carbide. Journal of Materials Processing Technology 2018, 263, 91 -100.

AMA Style

Amir Hadian, Cyrus Zamani, Lovro Gorjan, Frank Jörg Clemens. Thermoplastic processing and debinding behavior of NbC-M2 high speed steel cemented carbide. Journal of Materials Processing Technology. 2018; 263 ():91-100.

Chicago/Turabian Style

Amir Hadian; Cyrus Zamani; Lovro Gorjan; Frank Jörg Clemens. 2018. "Thermoplastic processing and debinding behavior of NbC-M2 high speed steel cemented carbide." Journal of Materials Processing Technology 263, no. : 91-100.