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- carbon nanofibers, platinum electrodeposition, ele ctrochemical surface area (1)
- AEM-Electrolysis (1)
- Additive manufacturing Directed energy deposition-arc 316L stainless steel Corrosion behavior Electrochemical corrosion (1)
- Cavitation; Corrosion; Laser remelting; Self-fluxing alloys; Stellite 6 (1)
- Electrodeposition (1)
- Erneuerbare Energien (1)
- Hydraulic compression, Carbon Nano Fibers, PEM Fuel Cells, Catalyst utilization (1)
- Hydrogen evolution reaction (1)
- Kohlenstoff-Nanoröhre (1)
- Ni-Mo alloy Catalyst (1)
- NiCrBSi coatings; flame spraying; induction remelting; wear resistance (1)
- PEM fuel cell electrocatalysts, Carbon nanofibers, Oxygen plasma activation, Pulsed electroplating. (1)
- PEM water electrolysis (1)
- Polymer-Elektrolytmembran-Brennstoffzelle (1)
- Powder feed rate HVOF Cermet Wear Corrosion (1)
- PtCoMn (1)
- Stellite 6; HVOF-spraying; Laser remelting; Cavitation erosion; Coatings (1)
- Ternary alloy catalyst preparation (1)
- Thermal Performance (1)
- Titanium; Al2O3–TiO2 coatings; Nanoindentation (1)
- additive manufacturing; polylactic acid (PLA); fused filament fabrication (FFF); fused deposition modeling (FDM); printing temperature; filament color; dimensional accuracy; tensile strength; friction performance; wear (1)
- carbon nanofibers, platinum electrodeposition, electrocatalysts (1)
- co-based alloys; hot corrosion; solid particle erosion; microstructure; brazing (1)
- corrosion; self-fluxing alloys; NiCrBSi; WC-12Co; cavitation; hard metals (1)
- education; skills; competences; pandemic; online or face-to-face (1)
- fused deposition modeling (FDM); fused filament fabrication (FFF); polylactic acid (PLA); layer height; layer thickness; filament color; PLA color; dimensional accuracy; tensile strength (1)
- self-fluxing; ZrO2; NiCrBSi; vacuum post-treatment; thermal spraying (1)
Institut
The printing variable least addressed in previous research aiming to reveal the effect of the FFF process parameters on the printed PLA part’s quality and properties is the filament color. Moreover, the color of the PLA, as well as its manufacturer, are rarely mentioned when the experimental conditions for the printing of the samples are described, although current existing data reveal that their influence on the final characteristics of the print should not be neglected. In order to point out the importance of this influential parameter, a natural and a black-colored PLA filament, produced by the same manufacturer, were selected. The dimensional accuracy, tensile strength, and friction properties of the samples were analyzed and compared for printing temperatures ranging from 200 C up to 240 C. The experimental results clearly showed different characteristics depending on the polymer color of samples printed under the same conditions. Therefore, the optimization of the FFF process parameters for the 3D-printing of PLA should always start with the proper selection of the type of the PLA material, regarding both its color and the fabricant.
Among the FDM process variables, one of the less addressed in previous research is the filament color. Moreover, if not explicitly targeted, the filament color is usually not even mentioned.
Aiming to point out if, and to what extent, the color of the PLA filaments influences the dimensional precision and the mechanical strength of FDM prints, the authors of the present research carried out experiments on tensile specimens. The variable parameters were the layer height (0.05 mm, 0.10 mm, 0.15 mm, 0.20 mm) and the material color (natural, black, red, grey). The experimental results clearly showed that the filament color is an influential factor for the dimensional accuracy as well as for the tensile strength of the FDM printed PLA parts. Moreover, the two way ANOVA test performed revealed that the strongest effect on the tensile strength was exerted by the PLA color (2 = 97.3%), followed by the layer height (2 = 85.5%) and the interaction between the PLA color and the layer height (2 = 80.0%). Under the same printing conditions, the best dimensional accuracy was ensured by the black PLA (0.17% width deviations, respectively 5.48% height deviations), whilst the grey PLA showed the highest ultimate tensile strength values (between 57.10 MPa and 59.82 MPa).
A systematic method for obtaining a novel electrode structure based on PtCoMn ternary alloy catalyst supported on graphitic carbon nanofibers (CNF) for hydrogen evolution reaction (HER) in acidic media is proposed. Ternary alloy nanoparticles (Co0.6Mn0.4 Pt), with a mean crystallite diameter under 10 nm, were electrodeposited onto a graphitic support material using a two-step pulsed deposition technique. Initially, a surface functionalisation of the carbon nanofibers is performed with the aid of oxygen plasma. Subsequently, a short galvanostatic pulse electrodeposition technique is applied. It has been demonstrated that, if pulsing current is employed, compositionally controlled PtCoMn catalysts can be achieved. Variations of metal concentration ratios in the electrolyte and main deposition parameters, such as current density and pulse shape, led to electrodes with relevant catalytic activity towards HER. The samples were further characterised using several physico-chemical methods to reveal their morphology, structure, chemical and electrochemical properties. X-ray diffraction confirms the PtCoMn alloy formation on the graphitic support and energy dispersive X-ray spectroscopy highlights the presence of the three metallic components from the alloy structure. The preliminary tests regarding the electrocatalytic activity of the developed electrodes display promising results compared to commercial Pt/C catalysts. The PtCoMn/CNF electrode exhibits a decrease in hydrogen evolution overpotential of about 250 mV at 40 mA cm−2 in acidic solution (0.5 M H2SO4) when compared to similar platinum based electrodes (Pt/CNF) and a Tafel slope of around 120 mV dec−1, indicating that HER takes place under the Volmer-Heyrovsky mechanism.
Based on the fact that titanium and titanium alloys have poor fretting fatigue resistance and poor tribological properties, it is necessary to apply some surface engineering methods in order to increase the exploitation characteristics of these materials. One may either implement some surface treatment technologies or even deposit overlay coatings by thermal spraying.
The present study is focused on the achieved properties of the ceramic coatings (Al2O3 + 13 wt.% TiO2) deposited onto a titanium substrate using high velocity oxygen fuel (HVOF) and plasma spraying (APS) respectively.
The effect of the deposition method on the microstructure, phase constituents, and mechanical properties of the ceramic coatings was investigated by means of scanning electron microscopy (SEM), X-ray diffraction technique (XRD) and nanoindentation tests. The sliding wear performances of the Al2O3–TiO2 coatings were tested using a pin on disk wear tester.
Since the 1980’s, against the backdrop of global warming and the decline of conventional energy resources, low emission and renewable energy systems have gotten into the focus of politics as well as research and development. In order to decrease the emission of greenhouse gases Germany intents to generate 80% of its electrical energy from renewable and low emission sources by 2050. For low emission electricity generation hydrogen operated fuel cells are a potential solution. However, although fuel cell technology has been well known since the 19th century cost effective materials are needed to achieve a breakthrough in the market.
Proton Exchange Membrane Fuel Cells with Carbon Nanotubes as Electrode Material
At the Westphalian Energy Institute of the Wesphalian University of Applied Sciences one main focus is on the research of proton exchange membrane fuel cells (PEMFC). PEMFC membrane electrode assemblies (MEA) consist of a polymer membrane with electrolytic properties covered on both sides by a catalyst layer (CL) as well as a porous and electrical conductive gas diffusion layer (GDL).
For PEMFC carbon nanotubes (CNT) have ideal properties as electrode material concerning electrical conductivity, oxidation resistance and media transport. CNTs are suitable for the use as catalyst support material within the CL due to their large surface in comparison to conventional carbon supports. Furthermore, oxygen plasma treated CNTs show electrochemical activity referred to hydrogen adsorption and desorption, which has been shown by cyclic voltammetry in 0.5 M sulfuric acid solution. According to the PEMFCs anode a GDL coated with oxygen plasma activated CNTs has promising properties to significantly reduce catalyst content (e.g. platinum) of the anodic CL.
To further increase platinum utilisation in PEM fuel cells CNFs are investigated as catalyst support material due to the CNF’s high specific surface area. Furthermore, CNFs provide suitable properties concerning corrosion resistance as well as electrical conductivity in contrast to conventional carbon supports.
This work presents the results of an electrode preparation procedure based on O2 plasma activated CNFs. The plasma treatment leads to CNF dispersibility in alcohol/water for a spray coating process. Furthermore, O2 plasma activation enhances metal deposition on the CNF’s surface. Pulse plating procedure as well as wet chemical metal synthesis have been used for particle deposition. For pulse plating a potentiostat/galvanostat type MMates 510 AC from Materials Mates, Italy has been used. Electrode morphology has been determined in SEM type XL 30 ESEM from Philips, The Netherlands.
Optimization of the laser remelting process for HVOF-sprayed Stellite 6 wear resistant coatings
(2016)
Cobalt base alloys are used in all industrial areas due to their excellent wear resistance. Several studies have shown that Stellite 6 coatings are suitable not only for protection against sliding wear, but also in case of exposure to impact loading. In this respect, a possible application is the protection of hydropower plant components affected by cavitation. The main problem in connection with Stellite 6 is the deposition procedure of the protective layers, both welding and thermal spraying techniques requesting special measures in order to prevent the brittleness of the coating. In this study, Stellite 6 layers were HVOF thermally sprayed on a martensitic 13-4 stainless steel substrate, as usually used for hydraulic machinery components. In order to improve the microstructure of the HVOF-sprayed coatings and their adhesion to the substrate, laser remelting was applied, using a TRUMPF Laser type HL 124P LCU and different working parameters. The microstructure of the coatings, obtained for various remelting conditions, was evaluated by light microscopy, showing the optimal value of the pulse power, which provided a homogenous Stellite 6 layer with good adhesion to the substrate.
Platinum nanoparticles electrodeposition on carbon nanofibers (CNF) support has been performed with the purpose to obtain electrodes that can be further used especially in a polymer electrolyte membrane fuel cell (PEMFC). A pretreatment of CNF is required in order to enhance the surface energy, which simultaneously improves handling and wettability as well as interaction with the platinum cations. This step was performed using oxygen plasma functionalization. To produce CNF supported Pt catalysts, an electrochemical method was applied and the deposition parameters were adjusted to obtain nanosized platinum particles with a good distribution onto the graphitic surface. The morphology and structure of the obtained particles were investigated by scanning electron microscopy combined with energy dispersive X-Ray spectroscopy. The amount of deposited platinum was established using thermogravimetrical measurements. Cyclic voltammetry performed in 0.5 M H2SO4 solution was applied for determining the electrochemical surface area (ECSA) of the obtained electrodes.The functionalization degree of the CNF outer surface has a strong influence on the structure, distribution and amount of platinum particles. Moreover, the current densities, which were set for the deposition process influenced not only the particles size but also the platinum amount. Applying an oxygen plasma treatment of 80 W for 1800 s, the necessary degree of surface functionalization is achieved in order to deposit the catalyst particles. The best electrodes were prepared using a current density of 50 mA cm-2 during the deposition process that leads to a homogenous platinum distribution with particles size under 80 nm and ECSA over 6 cm2
Flame-sprayed NiCrBSi/WC-12Co composite coatings were deposited in different ratios on the surface of stainless steel. Oxyacetylene flame remelting treatment was applied to surfaces for refinement of the morphology of the layers and improvement of the coating/substrate adhesion.
The performance of the coated specimens to cavitation erosion and electrochemical corrosion was evaluated by an ultrasonic vibratory method and, respectively, by polarization measurements. The microstructure was investigated by means of scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX). The obtained results demonstrated that the addition of 15 wt.% WC-12Co to the self-fluxing alloy improves the resistance to cavitation erosion (the terminal erosion rate (Vs) decreased with 15% related to that of the NiCrBSi coating) without influencing the good corrosion resistance in NaCl solution. However, a further increase in WC-Co content led to a deterioration of these coating properties (the Vs has doubled related to that of the NiCrBSi coating).
Moreover, the corrosion behavior of the latter composite coating was negatively influenced, a fact confirmed by increased values for the corrosion current density (icorr). Based on the achieved experimental results, one may summarize that NiCrBSi/WC-Co composite coatings are able to increase the life cycle of expensive, high-performance components exposed to severe cavitation conditions.
In polymer electrolyte membrane fuel cells (PEMFC) noble metal nano particles are deposited on graphitic supports serving as electrocatalysts for devices with high power density. In this study anodes are analysed with low platinum loading of about 0.1 mg cm-2. These electrodes are prepared by carbon nano fibres (CNF) decorated with platinum nano particles. For electrode manufacturing two sorts of fibres, which are produced in an industrial scale, are used with different graphitisation degree and surface area. CNF layers are applied on commercially available graphitic substrate by spray coating which leads to a porous structure with high surface area. Subsequently, platinum deposition is achieved by pulsed electroplating for an improved platinum utilisation in PEMFC electrodes. Spray coating and platinum deposition are assisted by a previous oxygen plasma activation process. Prepared anode material is characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), X-ray fluorescence spectroscopy (XRF) and thermogravimetry (TGA). Electrochemical analyses (cyclic voltammetry and corrosion test) are carried out in 0.5 M sulphuric acid. The effect of graphitisation degree of carbon nano fibres on the performance of prepared electrodes is investigated in-situ in a PEM fuel cell test bench.
In this study, the characteristics of HVOF sprayed WC/Co-Cr and WC/Cr3C2/Ni coatings were investigated in correlation with the variation of the powder feed rate. For this purpose, the mass flow was adjusted to four different levels. The other process parameters were all kept constant. The morphological and mechanical properties as well as the electrochemical corrosion behaviour were investigated and associated with the achieved microstructure.
Both scanning electron microscopy and confocal laser scanning microscopical images of the cross sections demonstrated a good correlation between the selected powder feed rate and the degree of internal porosity produced, which can be attributed to the deposition process. The coatings which fulfilled the requirements of the pre-qualification step were selected for further hardness measurements, tribological tests and electrochemical corrosion measurements in a 3.5 wt% NaCl aqueous solution.
It was found that the powder feed rate strongly influenced the characteristics of the HVOF-sprayed cermet coatings. The tendency to crack formation, especially at the interface coating/substrate, was lower for the samples coated with a lower mass flow rate. These studies have shown that the applied powder feed rates had an important influence on the coatings microstructure and implicitly on the sliding wear behavior respectively on the electrochemical corrosion resistance of the investigated cermet coatings.
In this experimental work polymer electrolyte membrane fuel cell (PEMFC) electrodes are analysed, which are prepared by the use of two sorts of carbon nano fibres (CNF) serving as support material for platinum nano particles. Those CNFs, which are heat treated subsequently to their production, have a higher graphitisation degree than fibres as produced. The improved graphitisation degree leads to higher electrical conductivity, which is favourably for the use in PEMFC electrodes. Samples have been analysed, in order to determine graphitisation degree, electrical conductivity, as well as morphology and loading of the prepared electro catalyst. Membrane electrode assemblies manufactured from prepared electrodes are analysed in-situ in a PEM fuel cell test environment. It has been determined that power output for samples containing CNFs with higher graphitisation degree is increased by about 13.5%.
This work deals with the preparation and investigation of PEM fuel cell electrodes, which are obtained using graphene related material (GRM) serving as catalyst support for platinum nanoparticles. Applied GRM are used for the preparation of suspensions in four distinct mixing ratios. Two sorts of GRM have been investigated: carbon nanofibers (CNF) and graphene oxide (GO). Utilized CNFs provide a superior graphitization degree of about 100%, which leads to both high corrosion resistance and low ohmic resistance in PEM fuel cells.
For electrode preparation a GRM containing layer serving as catalyst support is applied onto a gas diffusion layer (GDL). Prior to GRM suspension and deposition onto a GDL, the graphene structures are functionalized by plasma treatment. Due to this step, an improved hydrophilic behavior for facilitating suspension preparation is achieved. In addition, a subsequent platinum nanoparticle deposition by pulsed electrodeposition process is optimized.
Even though we live in a period when the word digitization is prevalent in many social areas, the COVID-19 pandemic has divided mankind into two main categories: some people have seen this crisis as an opportunity to move the activities online and, furthermore, to accelerate digitization in as many areas as possible, while others have been reluctant, keeping their preferences for face-to-face activities. The current work presents the results of an analysis on 249 students from 11 engineering faculties. The study aims to identify the impact of the COVID-19 pandemic on students’ educational experiences when switching from face-to-face to online education during a public health emergency or COVID 19-related state of alert. The overall conclusion was that, although the pandemic has brought adverse consequences on the health and life quality of many people, the challenges that humankind has been subjected to have led to personal and professional development and have opened up new perspectives for carrying out the everyday activities.