Frank Clemens - Academia.edu (original) (raw)
Papers by Frank Clemens
Glass Science and Technology, 2004
The fabrication of silica glass fibres by thermoplastic extrusion of nanosize and micron SiO 2 po... more The fabrication of silica glass fibres by thermoplastic extrusion of nanosize and micron SiO 2 powders has been investigated. The powders were mixed with a binder system, compounded for 3 h at 150°C, and finally extruded through a die with a 500 μm-diameter die land. After debinding the green fibres at 500°C, these were sintered for 1 h at 1100°C under air to yield glassy and crack-free silica fibres with a final diameter of 400 um. The effect of the two different particle size distributions as well as the influence of varying powder loading (between 38 and 58 vol.%) on the rheological properties of the feedstocks were analysed using capillary rheometry. The debinding and sintering behaviour was also investigated using mercury intrusion porosimetry, thermal gravimetric analysis and dilatometry.
Glass Science and Technology, 2005
Silica glass fibers with triangular and rectangular cross-sections have been produced by two diff... more Silica glass fibers with triangular and rectangular cross-sections have been produced by two different means, namely preform drawing and powder extrusion. For the preform drawing method, silica glass rods were machined and polished to yield preforms with the desired cross-sections. These were then heated to temperatures in excess of 1600°C and drawn to fibers with approximately 265 μm × 265 μm X 265 μm triangular and 275 μm × 100 μm rectangular cross-sections exhibiting tensile strengths between 300 and 400 MPa and bending radii smaller than 50 mm. For the extrusion route, a silica nanopowder was compounded at 150°C with a polyethylene-based binder and extruded at similar temperatures through dies with the desired exit cross-section. The fibers were debound by thermally decomposing the binder and sintered at 1100°C to yield amorphous glass fibers with approximately 205 μm X 205 μm X 205 μm triangular and 275 μm X 90 μm rectangular cross-sections. Although the two manufacturing processes are radically different, both involve flow of a fluid with a temperature-dependent viscosity and this dictates that shape trueness (i.e. flat faces and sharp corners) is a function of the drawing and extrusion rates and the temperature during drawing and sintering.
Materials Research Bulletin, 2009
Composite fibers of polyvinyl pyrrolidone and titanium isopropoxide were prepared in this study u... more Composite fibers of polyvinyl pyrrolidone and titanium isopropoxide were prepared in this study using the electrospinning technique. Titanium oxide fibers were obtained after subsequent heat treatment at high temperatures. The photocatalytic activity of these fibers is reported herein. The fibers were characterized using the BET model, thermogravimetry, X-ray diffraction, and scanning electron microscopy. The photocatalytic activity of the titania fibers
Particulate Science and Technology, 2009
... a , AK Alves a * , CP Bergmann a , FJ Clemens b & T. Graule b pages 203-2... more ... a , AK Alves a * , CP Bergmann a , FJ Clemens b & T. Graule b pages 203-209. ... The specific surface area (S BET , m 2 /g) of the heat-treated fibers were measured using the standard Brunauer-Emmett-Teller (BET) technique with N 2 adsorption (Beckman Coulter SA3100). ...
Microporous and Mesoporous Materials, 2014
Microporous and Mesoporous Materials, 2012
Microstructure of diatomite-clay based granulates for fluidized bed reactors, heat treated at 800... more Microstructure of diatomite-clay based granulates for fluidized bed reactors, heat treated at 800 and 1300°C, were investigated by mercury porosimetry, nitrogen sorption using Barrett–Joyner–Halenda (BJH) model and scanning electron microscopy. Special considerations were made on characterisation of ink-bottle pores by performing a multi-cycle porosimetry. The comparison between extruded granulates and pure diatomite powders revealed that diatom structure is still intact
Microporous and Mesoporous Materials, 2013
Journal of the European Ceramic Society, 2014
Journal of Intelligent Material Systems and Structures, 2014
Ferroelectric fibers based on a commercial lead zirconium titanate powder were investigated by a ... more Ferroelectric fibers based on a commercial lead zirconium titanate powder were investigated by a new characterization method to measure single fiber properties, such as large signal polarization and longitudinal free strain, and small signal properties, such as piezoelectric constant. To verify the measurements, the free strain data were compared with dynamic mechanical analyzer measurements. For this investigation, lead zirconate titanate fibers were sintered in lead-rich atmosphere at different temperatures. Microstructure and phase composition were analyzed by scanning electron microscope and X-ray diffraction. By increasing the temperature from 1150°C to 1200°C, the electromechanical behavior of the fibers could be improved: an increase in remnant and saturation polarization occurred. A d33 as of ∼430 and ∼400 pm/V could be measured for 1150°C and 1200°C, respectively. These d33 values are very close to the one reported on the data sheet of the material.
Ceramics International, 2012
Ceramics International, 2011
Advances in Applied Ceramics, 2010
Jurnal Teknologi, 2012
Stearic acid (SA) was used as an additive in the process of metal injection moulding (MIM). It wa... more Stearic acid (SA) was used as an additive in the process of metal injection moulding (MIM). It was added to the wax/polymer mixture in order to modify the powder wetting, mould lubrication, mixture viscosity, residual stress and debinding behaviour. In this study, the effect of SA in feedstock formulation on mixing torque and rheological properties was investigated. Further, it’s correlation on the as-moulded and as-debound parts behaviour was also investigated. The results showed that addition of SA significantly reduced the mixing torque value and viscosity which correspond to decreasing in inter-particle friction. As a result, injection moulding could be carried out at a lower temperature to achieve sound moulded parts and increased the removal rate of binder during solvent extraction process. However, it seemed that increasing the SA had a little negative effect on the as-moulded density.
Batteries
An inorganic solid electrolyte is the most favorable candidate for replacing flammable liquid ele... more An inorganic solid electrolyte is the most favorable candidate for replacing flammable liquid electrolytes in lithium batteries. Lithium lanthanum zirconium oxide (LLZO) is considered a promising solid electrolyte due to its safe operating potential window (0–5 V) combined with its good electrochemical stability. In this work, 250 g batches of pre-sintered Ta-doped LLZO (Li7La3Zr1.6Ta0.4O12, Ta-LLZO) were synthesized for bulk production of a dense LLZO electrolyte. A simple two-step thermal treatment process was developed. The first thermal step at 950 °C initiates nucleation of LLZO, with carefully controlled process parameters such as heating atmosphere, temperature, and dopant concentration. In the second thermal step at 1150 °C, sintered discs were obtained as solid electrolytes, with relative densities of 96%. X-ray diffraction analysis confirmed the phase purity of the sintered Ta-LLZO disc, and refined data were used to calculate the lattice parameter (12.944 Å). Furthermore,...
Composites Part B: Engineering
Glass Science and Technology, 2004
The fabrication of silica glass fibres by thermoplastic extrusion of nanosize and micron SiO 2 po... more The fabrication of silica glass fibres by thermoplastic extrusion of nanosize and micron SiO 2 powders has been investigated. The powders were mixed with a binder system, compounded for 3 h at 150°C, and finally extruded through a die with a 500 μm-diameter die land. After debinding the green fibres at 500°C, these were sintered for 1 h at 1100°C under air to yield glassy and crack-free silica fibres with a final diameter of 400 um. The effect of the two different particle size distributions as well as the influence of varying powder loading (between 38 and 58 vol.%) on the rheological properties of the feedstocks were analysed using capillary rheometry. The debinding and sintering behaviour was also investigated using mercury intrusion porosimetry, thermal gravimetric analysis and dilatometry.
Glass Science and Technology, 2005
Silica glass fibers with triangular and rectangular cross-sections have been produced by two diff... more Silica glass fibers with triangular and rectangular cross-sections have been produced by two different means, namely preform drawing and powder extrusion. For the preform drawing method, silica glass rods were machined and polished to yield preforms with the desired cross-sections. These were then heated to temperatures in excess of 1600°C and drawn to fibers with approximately 265 μm × 265 μm X 265 μm triangular and 275 μm × 100 μm rectangular cross-sections exhibiting tensile strengths between 300 and 400 MPa and bending radii smaller than 50 mm. For the extrusion route, a silica nanopowder was compounded at 150°C with a polyethylene-based binder and extruded at similar temperatures through dies with the desired exit cross-section. The fibers were debound by thermally decomposing the binder and sintered at 1100°C to yield amorphous glass fibers with approximately 205 μm X 205 μm X 205 μm triangular and 275 μm X 90 μm rectangular cross-sections. Although the two manufacturing processes are radically different, both involve flow of a fluid with a temperature-dependent viscosity and this dictates that shape trueness (i.e. flat faces and sharp corners) is a function of the drawing and extrusion rates and the temperature during drawing and sintering.
Materials Research Bulletin, 2009
Composite fibers of polyvinyl pyrrolidone and titanium isopropoxide were prepared in this study u... more Composite fibers of polyvinyl pyrrolidone and titanium isopropoxide were prepared in this study using the electrospinning technique. Titanium oxide fibers were obtained after subsequent heat treatment at high temperatures. The photocatalytic activity of these fibers is reported herein. The fibers were characterized using the BET model, thermogravimetry, X-ray diffraction, and scanning electron microscopy. The photocatalytic activity of the titania fibers
Particulate Science and Technology, 2009
... a , AK Alves a * , CP Bergmann a , FJ Clemens b & T. Graule b pages 203-2... more ... a , AK Alves a * , CP Bergmann a , FJ Clemens b & T. Graule b pages 203-209. ... The specific surface area (S BET , m 2 /g) of the heat-treated fibers were measured using the standard Brunauer-Emmett-Teller (BET) technique with N 2 adsorption (Beckman Coulter SA3100). ...
Microporous and Mesoporous Materials, 2014
Microporous and Mesoporous Materials, 2012
Microstructure of diatomite-clay based granulates for fluidized bed reactors, heat treated at 800... more Microstructure of diatomite-clay based granulates for fluidized bed reactors, heat treated at 800 and 1300°C, were investigated by mercury porosimetry, nitrogen sorption using Barrett–Joyner–Halenda (BJH) model and scanning electron microscopy. Special considerations were made on characterisation of ink-bottle pores by performing a multi-cycle porosimetry. The comparison between extruded granulates and pure diatomite powders revealed that diatom structure is still intact
Microporous and Mesoporous Materials, 2013
Journal of the European Ceramic Society, 2014
Journal of Intelligent Material Systems and Structures, 2014
Ferroelectric fibers based on a commercial lead zirconium titanate powder were investigated by a ... more Ferroelectric fibers based on a commercial lead zirconium titanate powder were investigated by a new characterization method to measure single fiber properties, such as large signal polarization and longitudinal free strain, and small signal properties, such as piezoelectric constant. To verify the measurements, the free strain data were compared with dynamic mechanical analyzer measurements. For this investigation, lead zirconate titanate fibers were sintered in lead-rich atmosphere at different temperatures. Microstructure and phase composition were analyzed by scanning electron microscope and X-ray diffraction. By increasing the temperature from 1150°C to 1200°C, the electromechanical behavior of the fibers could be improved: an increase in remnant and saturation polarization occurred. A d33 as of ∼430 and ∼400 pm/V could be measured for 1150°C and 1200°C, respectively. These d33 values are very close to the one reported on the data sheet of the material.
Ceramics International, 2012
Ceramics International, 2011
Advances in Applied Ceramics, 2010
Jurnal Teknologi, 2012
Stearic acid (SA) was used as an additive in the process of metal injection moulding (MIM). It wa... more Stearic acid (SA) was used as an additive in the process of metal injection moulding (MIM). It was added to the wax/polymer mixture in order to modify the powder wetting, mould lubrication, mixture viscosity, residual stress and debinding behaviour. In this study, the effect of SA in feedstock formulation on mixing torque and rheological properties was investigated. Further, it’s correlation on the as-moulded and as-debound parts behaviour was also investigated. The results showed that addition of SA significantly reduced the mixing torque value and viscosity which correspond to decreasing in inter-particle friction. As a result, injection moulding could be carried out at a lower temperature to achieve sound moulded parts and increased the removal rate of binder during solvent extraction process. However, it seemed that increasing the SA had a little negative effect on the as-moulded density.
Batteries
An inorganic solid electrolyte is the most favorable candidate for replacing flammable liquid ele... more An inorganic solid electrolyte is the most favorable candidate for replacing flammable liquid electrolytes in lithium batteries. Lithium lanthanum zirconium oxide (LLZO) is considered a promising solid electrolyte due to its safe operating potential window (0–5 V) combined with its good electrochemical stability. In this work, 250 g batches of pre-sintered Ta-doped LLZO (Li7La3Zr1.6Ta0.4O12, Ta-LLZO) were synthesized for bulk production of a dense LLZO electrolyte. A simple two-step thermal treatment process was developed. The first thermal step at 950 °C initiates nucleation of LLZO, with carefully controlled process parameters such as heating atmosphere, temperature, and dopant concentration. In the second thermal step at 1150 °C, sintered discs were obtained as solid electrolytes, with relative densities of 96%. X-ray diffraction analysis confirmed the phase purity of the sintered Ta-LLZO disc, and refined data were used to calculate the lattice parameter (12.944 Å). Furthermore,...
Composites Part B: Engineering