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Metal injection moulding of miniaturized devices demands unique feedstock materials and mould designs with high dimensional accuracy. In this work, the influences of the powder size and powder content of 17–4 PH stainless steel feedstock and the influence of mould design on the successful production of micro-scaled structures were investigated. Ni mould inserts with high dimensional accuracy and texture sizes of 50–200 μm using a new microtexturing technique were manufactured. 17–4 PH stainless steel feedstocks with powder sizes (D90) of 10 and 22 μm and powder contents of 60 and 65 vol.-% were compounded. The rheological properties of the obtained feedstocks were characterized with a capillary rheometer to assess their flowability. The results showed that 10 μm sized particles caused a slight but not significant increase in the viscosity. The highest viscosity increase occurred when the powder content increased from 60 to 65 vol.-%. Feedstocks with the 10 μm powder particles ensured complete filling within microtextures for all mould variations. However, when using feedstocks with 22 μm particles, the filling capabilities of the 50 and 100 μm microtextures decreased with increasing powder content. The shape retention was better for those micropillars produced with mould inserts with 200 μm cavities than for the micropillars replicated with the inserts having cavities of 50 and 100 μm. The results indicated that the proposed mould insert preparation technique opens new possibilities for mass production using the μMIM process to create micro-scaled components using feedstocks without nanoparticles.

Antibacterial activity of electrodeposited copper and zinc both on flat and micropatterned hard metal tungsten carbide-cobalt (WC-Co) specimens was studied. Tribological wear was applied on electrodeposited specimens: coatings were completely removed from flat surfaces whereas only top of the micropillars was exposed to wear for the micropatterned specimens protecting the functional metal coating in between the micropillars. The growth of Staphylococcus aureus (S. aureus) Gram-positive bacterial species was studied on the specimens using a touch test mimicking bacterial transfer from the surfaces. Copper coated specimens prevented bacterial growth completely independent of wear or surface structure, i.e., even residual traces of copper were sufficient to prevent bacterial growth. Zinc significantly suppressed the bacterial growth both on flat and micropatterned specimens. However, adhesion of zinc was low resulting in an easy removal from the surface by wear. The micropatterned zinc specimens showed antibacterial activity as electrodeposited zinc remained intact on the sample surface between the micropillars. This was sufficient to suppress the growth of S. aureus. On the contrary, the flat zinc coated surfaces did not show any antibacterial activity after wear. Our results show that micropatterned hard metal specimens can be used to preserve antibacterial activity under tribological wear.

Although it is experimentally difficult to observe, PdSO4 is considered to be the culprit for the reduced activity of SO2-poisoned methane oxidation catalysts. Density functional theory (DFT) predi...

Solid lubrication in tribological applications was studied on hard metal specimens with micropits fabricated using metal injection molding (MIM). This study investigated synergy effects of paraffin wax mixed with 5 wt% MoS2 on the lubricating potential both under normal and elevated temperatures. Pin-on-plate sliding tests were performed on a CSM tribometer in which WC–Co pins oscillated against microstructured and flat reference WC–Co specimens under 10 N applied normal load. Surface morphology characterization of test specimens was carried out before and after tribological tests using scanning electron microscopy. Solid paraffin wax displayed enhanced lubrication compared to solid paraffin wax mixed with 5 wt% MoS2 on micropit specimens under normal temperature. On the contrary, under heating conditions, solid paraffin mixed with 5 wt% MoS2 significantly reduced the dynamic coefficient of friction (COF) values for both flat and micropit specimens. The results showed that the micropits in textured specimens can be used as a reservoir for the lubricant that can significantly reduce friction compared to flat reference specimens. Graphical Abstract

The main target in this study was to increase adhesion of unsaturated polyester (UP) adhesive to aluminum by structuring the aluminum surface on the microscale and nanoscale as well as by f...

The ice friction behavior of various microtextured polymer surfaces was studied with respect to ice temperature and applied load using a customized linear tribometer. Similar micropillar patterns were replicated on polypropylene and two rubber compounds, and when hierarchical micro–micro textures were present, all the materials exhibited superhydrophobicity. Taller protective micropillars were shown to be crucial for protecting the smaller microtextures from abrasive wear. The mechanical properties of the polymers affected the sliding friction of the microtextured surfaces on ice. High loading of hierarchical textures on rigid polypropylene or operation near the ice melting point tended to increase its adhesion tendency or resisting behavior. The sliding performance of the hard and soft rubber compounds was temperature-dependent, and the texture on the soft rubber influenced the sliding friction differently depending on the ice temperature. Consequently, textural modifications of the sliding surface enabled a certain degree of control over the sliding friction behavior on ice.

Natural gas as a fuel for heavy duty applications has advantages in terms of lower CO2 and PM compared to Diesel applications. This makes operating heavy duty applications on natural gas attractive. However, in terms of aftertreatment, the challenge becomes one of controlling methane emissions over a range of vehicle operating conditions. Methane light off occurs > 400 °C and requires highly loaded precious metal catalysts (Raj in Johnson Matthey Technol Rev 60:228–235, 2016). This temperature is manageable in stoichiometric applications. However, for lean operating applications, the exhaust temperature can be below this posing a significant challenge for CH4 control. When operating lean the NOx emissions also become a challenge hence the requirement for a dedicated NOx control system. As part of the EU funded HD GAS project, an aftertreatment system was developed to meet the challenges of both NOx and CH4 control for a lean operating natural gas heavy duty engine. Fundamental studies were performed by the academic partners focusing on CH4 and NOx control, with the implementation and calibration on the engine performed by the industrial partners. This paper will discuss the steps taken from fundamental catalyst characterisation and catalyst specification to full size catalyst implementation onto a newly developed natural gas engine in order to meet Euro VI emissions legislation.

Decomposition of PdSO4, a species responsible for the deactivation of Pd-based methane combustion catalysts, was studied using a PdSO4/Al2O3 model system. PdSO4 was observed to behave differently under different reaction conditions. The decomposition of PdSO4 under inert atmosphere probably involved only one reaction step and resulted in the formation of metallic palladium. Under H2-containing atmosphere, the decomposition of PdSO4 resulted eventually in the formation of Pd4S, which is probably one of the many possible sulfur-containing palladium species that can be formed during regeneration of a sulfur-poisoned Pd-rich methane combustion catalyst. The formation of Pd4S can provide a reasonable explanation to the threshold temperature of sulfur removal from the catalyst, as well as to the residual sulfur present in the catalyst after regeneration under reductive atmosphere. Overall, the results obtained in the study provide deeper insight into the regeneration process of Pd-based catalysts, possibly enabling development of a more efficient regeneration strategy.

New particulate matter (PM) filtering technologies are needed to meet the emission regulations for small combustion appliances. In this work, we investigate the performance of a novel electrical particle filtration system, the single needle shielded corona charger (SCC), which offers an advantageous solution for PM control in boilers by enhancing particulate deposition within existing boiler sections. Experiments under different operating conditions of a wood-fired boiler were performed, wherein the SCC was installed upstream of either a condensing heat exchanger (CHX) or a cyclone. PM reduction was found to be strongly affected by the SCC temperature and the following collection surface area, and reached its highest reduction efficiency of >90% at the temperature range of 400–500 °C when operating in combination with a CHX. The SCC–cyclone combination was less efficient, providing a 27% PM reduction, as a result of the low surface area and residence time in the cyclone. These results indicate that the SCC can feasibly provide particle filtration when combined with a CHX, wet scrubber, or a cyclone to meet the new emission regulation requirements. The system is best suited for small-scale boilers but can be scaled up to larger boilers by increasing the number of corona chargers.

In this study, halloysite nanotubes (HNTs) were modified with three xanthene dyes and subsequently utilized for the fabrication of luminescent polymer nanocomposites. Two different sets of dyes (rhodamine B, rhodamine 6G, and fluorescein) were chosen because of their ability to interact differently with HNTs. Rhodamines B and 6G were adsorbed on the negatively charged external surface of HNTs due to their cationic nature, while fluorescein was infiltrated into the positively charged nano-size lumen of HNTs. The influence of the HNTs substrate on photoluminescence (PL) of the dyes in the polystyrene matrix was investigated. An enhancement in the PL intensity of fluorescein by a factor of 8 was observed upon its encapsulation into lumens of HNTs. On the other hand, the adsorption of rhodamines on HNTs led to a decrease in their PL intensity. A homogenous dispersion of the dye molecules achieved at nanoscale introduced luminescence properties in the polymer nanocomposites. The robust protocol for the modification of halloysites with organic chromophores provides a straightforward way to distribute the dye molecules in a polymer matrix and to incorporate luminescent properties into different polymer matrices.

An awareness of increasing climate and health problems has driven the development of new functional and affordable soot-oxidation catalysts for stationary sources, such as fireplaces. In this study, Al(OH)3, water glass and acidic aluminium phosphate binder materials were mixed with soot-oxidation catalysts. The effect of the binder on the performance of the Ag/La-Al2O3 catalyst was examined, while the Pt/La-Al2O3 catalyst bound with Al(OH)3 was used as a reference. Soot was oxidised above 340 &deg, C on the Ag/La-Al2O3 catalyst, but at 310 &deg, C with same catalyst bound with Al(OH)3. The addition of water glass decreased the catalytic performance because large silver crystals and agglomeration resulted in a blockage of the support material&rsquo, s pores. Pt/La-Al2O3 bound with Al(OH)3 was ineffective in a fireplace environment. We believe that AgOx is the active form of silver in the catalyst. Hence, Ag/La-Al2O3 was shown to be compatible with the Al(OH)3 binder as an effective catalyst for fireplace soot oxidation.

Catalytic combustion of methane, the main component of natural gas, is a challenge under lean‐burn conditions and at low temperatures owing to sulfur poisoning of the Pd‐rich catalyst. This paper introduces a more sulfur‐resistant catalyst system that can be regenerated during operation. The developed catalyst system lowers the barrier that has restrained the use of liquefied natural gas as a fuel in energy production.

An increasing number of heavy-duty vehicles are using liquefied natural gas (LNG) as a fuel due to the expanding refuelling station network for LNG and lower overall emissions compared to diesel vehicles. The latest EURO VI regulation or natural gas fuelled vehicles set a limit for NH3 of 10 ppm, and N2O exhaust is expected to be restricted in Europe in the near future. Poisonous and corrosive NH3 and the greenhouse gas N2O are formed as by-products in a three-way catalyst used to minimize the emissions of stoichiometric heavy-duty engines. In this work, we studied how high temperature NH3 and N2O formed in modern, fresh and aged bimetallic Pd/Rh three-way catalysts in simulated exhaust gas. More precisely, the exhaust gas composition and temperature were examined. Decreases in NO concentration and increases in temperature lowered the formation of NH3 and N2O, whereas a decrease in CH4 concentration reduced only NH3 formation. According to Raman and powder X-ray diffraction experiments, the structure of the catalyst changed during the ageing, and this reputedly affected the function of cerium-zirconium mixed oxides and thus the formation of NH3 and N2O. Temperature programmed reduction (H2-TPR) measurements showed changes in cerium-zirconium mixed oxide performance after ageing supporting Raman spectroscopy findings. Catalyst ageing in oxidizing conditions increased the formation of N2O. This study showed that exhaust gas composition plays an important role in the formation of undesired NH3 and N2O emissions.

Zinc electroplating was used to enhance corrosion resistance of porous metal injection molded 440C stainless steel. Controlled porosity was achieved by the powder space holder technique and by using sodium chloride as a space holder material. The internal pore structure of porous 440C was deposited by zinc using electroplating with three different electrolytes of zinc acetate, zinc sulfate, and zinc chloride. Our results show that all zinc depositions on porous 440C samples significantly improved corrosion resistance. The lowest corrosion was observed with zinc acetate at 30 wt.% porosity. The developed zinc coated porous 440C samples have potential in applications in corrosive environments.

Air pollution emitted by residential biomass combustion (RBC) is a known cause of adverse health and climate effects. Currently, manufacturers of stoves and fireplaces are facing challenges due to tightening emission regulations, such as the Ecodesign Directive in the European Union. Consequently, there is a demand for new emission control solutions for RBC. Herein, a novel method has been introduced to reduce particulate emissions, namely: high-temperature electric soot collector (HiTESC). In this method, an electrically insulated high-voltage electrode is installed in a combustion chamber, which generates an electric field. Particles that acquire the electrical charges produced by flames are collected on the electrode surface and oxidized at high temperatures. A fine particle (PM1) reduction efficiency of 45% was achieved using this method in a logwood-fired masonry heater. The reduction efficiency of the method was found to be dependent on the combustion phase. The PM1 reduction was most efficient during the flaming conditions, when the PM emissions were the highest with the studied logwood appliance. The advantages of this method are its simple construction, low space requirement, and low energy consumption; further, it does not require a separate cleaning mechanism. The proposed method can be used in logwood-fired combustion appliances to achieve future emission regulation limits, without using costly exhaust after-treatment systems.

Surface texturing with lubricant mixtures was studied by dynamic coefficient of friction (COF) values on micropit and micropillar WC-Co hard metal specimens that were fabricated using a micro-working robot technique combined with metal injection molding (MIM). Lubricating grease mixed with MoS2 was investigated, and 40 wt% additive level of MoS2 reduced COF values by 45% down to 0.06 level on flat WC-Co specimens. The corresponding COF values for the micropit specimens were higher up to 0.10 that may result from the small contact area of the used pin. On the contrary, a reduction of COF values was observed for micropillar specimens compared to the flat WC-Co specimens induced by a load carrying structure of the micropillar specimen. A highly stable antiwear behavior was observed for specimens with micropits.

Utilization of natural gas fuels in heavy duty vehicles offers an effective solution to reduce global warming and improve urban air quality. However, there are problems related to catalyst durability and release of unburned methane (methane slip). Catalyst durability can be achieved through clever designs of both catalyst material and its regeneration process. In this paper, we studied extensively low temperature regeneration strategies of a commercial methane oxidation catalyst (MOC), a three-way catalyst (TWC) and a diesel oxidation catalyst (DOC) as well as two coupled catalysts; TWC-MOC and DOC-MOC. Methane and propane conversion along with NO2, NO, SO2, CO, N2O and NH3 formation were recorded and analyzed in a laboratory setup using a FTIR multigas analyzer. According to our findings, the MOC and the DOC can be regenerated under a broader range of O2 concentrations whereas the TWC requires a very low O2 concentration or anoxic conditions for efficient regeneration. The conversion increase ranged between 0 and 20 percentage points for methane and 0–45 percentage points for propane depending on the catalyst and regeneration technique. The coupled catalysts were highly effective in methane conversion and possessed higher tolerance against SO2 poisoning compared to single catalysts. The study further revealed that 10 ppm regulation limit of NH3 emission is plausible to exceed during the regeneration of a catalyst. By controlling the exhaust gas composition during the regeneration and length of the regeneration, the NH3 and N2O emissions can be minimized.

One way to lower CO2 and other harmful emissions of the transportation sector is the development of natural gas fueled vehicles. Availability of natural gas is good, and it is easy to apply to stoichiometric and lean-burn engines, which makes it ready-to-use technology. The main concern in the field is a sulfur poisoning of the exhaust gas after treatment system. We aim to clarify mechanisms of sulfur poisoning and regeneration of a lean-burn methane oxidation catalyst. Overall, it is concluded that sulfur itself is not the only reason for the deactivation of methane oxidation catalyst, but it is a joint effect of water vapor and sulfur species. The irreversible sulfur poisoning deteriorates oxygen mobility and hinders water desorption, which inhibits low temperature methane oxidation activity. The regeneration of sulfur poisoned catalyst takes place stepwise: PdSO4 → PdSO3 + 0.5O2 → Pd + SO2 + 0.5O2. The formation of metallic palladium makes the catalyst vulnerable for sintering, which leads to deactivation during long-term regeneration.

Conventional fabrication methods to obtain metal patterns on polymer substrates are restricted by high operating temperature and complex preparation steps. The present study demonstrates a simple yet versatile method for preparation of silver nanoparticle micropatterns on polymer substrates with various surface geometry. With the microworking robot technique, we were able not only to directly structure the surface, but also precisely deposit silver nanoparticle ink on the desired surface location with the minimum usage of ink material. The prepared silver nanoparticle ink, containing silver cations and polyethylene glycol (PEG) as a reducing agent, yields silver nanoparticle micropatterns on plastic substrates at low sintering temperature without any contamination. The influence of the ink behaviour was studied, such as substrate wettability, ink volume, and sintering temperature. The ultraviolet visible (UV–vis), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) measurements revealed the formation of micropatterns with uniformly distributed silver nanoparticles. The prepared patterns are expected to have a broad range of applications in optics, medicine, and sensor devices owing to the unique properties of silver. Furthermore, the deposition of a chemical compound, which is different from the substrate material, not only adds a fourth dimension to the prestructured three-dimensional (3D) surfaces, but also opens new application areas to the conventional surface structures.

Bimetallic Pd–Ir catalysts based on halogen free precursors supported on alumina and La-stabilized alumina were prepared and characterized. The influence of iridium co-metal loading on activity of supported palladium catalysts in CO and C3H6 oxidation was studied. In addition, the effect of thermal aging on the catalytic activity was discussed. The powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy combined with energy dispersive X-ray spectroscopy, thermogravimetric analysis were used for characterization of the catalysts. The catalytic activity of prepared catalysts was determined based on conversion of CO and C3H6 under stoichiometric condition. The activity tests showed that bimetallic catalyst with Pd:Ir molar ratio of 1.00:0.18 on both support materials has the lowest light-off temperature difference between the fresh and aged catalysts in CO and C3H6 oxidation. However, high Ir loading improved the activity of the catalysts only, if La-stabilized aluminum oxide was used as a support material. Lanthanum oxide promoted the activity of the fresh catalysts in CO and C3H6 oxidation. Overall, Ir is a promising co-metal candidate for Pd-based catalyst for improving CO and C3H6 oxidation activity of the catalyst under stoichiometric conditions.

The main target in the study of aluminum-epoxy resin joints was to enhance adhesion by increasing the surface area of aluminum substrates and by chemical functionalizing the aluminum surface to provide coupling points for epoxy resin. The surface area of the aluminum substrates was increased by fabricating microscale structures and hierarchical micro-microstructures by utilizing a micro-mesh printing technique and sandblasting. The effects of silanization with 3-glycidoxypropyltrimethoxysilane (GPTMS) and of oxygen plasma treatment were also investigated. Compared to a smooth surface, the micro-mesh structures improved shear strength by 33% and the hierarchical micro-microstructures by 116%. The utilization of the oxygen plasma treatment and especially the silane modification of the aluminum substrates were found to be effective in promoting adhesion. The specimens modified by combining the chemical or energetic modification method with surface texturing tended to fracture more cohesively than the specimens having a single modification. The hierarchically patterned and plasma and silane modified specimens had so high adhesion that the aluminum substrates started to deflect during the shear strength measurements, thus preventing the evaluation of their maximum strength.

The formation of hydrogen sulfide in car exhaust is undesirable due to unpleasant odor and toxicity of H2S gas. H2S release can be suppressed by the addition of a NiO scavenger to a three-way catalyst (TWC). In this work, Pd–Ni bimetallic catalysts were prepared by the co-addition of Pd and Ni to γ-Al2O3 or Al2O3-La2O3 support, by the impregnation method. Different concentrations of a propionic acid aqueous solution were used as the impregnation solvent. The structure of prepared catalysts was characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), and temperature-programmed reduction (TPR) techniques. Catalyst poisoning by SO2 was simulated under lean conditions and H2S release under rich conditions. XRD and TPR measurements revealed the effect of the impregnation solvent concentration on the ratio between NiO and NiAl2O4 spinel species and the reducibility of Ni species. Co-addition of Pd with Ni was proven to be beneficial for H2S suppression. Prepared bimetallic catalysts released considerably less H2S compared to physical mixtures of Pd/Al2O3 with NiO. The presence of bulk and well dispersed NiO on Pd–Ni catalysts assisted in sulfur release in the form of sulfur oxides rather than H2S. Bimetallic catalysts supported on Al2O3-La2O3 were found to release more H2S compared to catalysts on γ-Al2O3. The use of diluted solvent in bimetallic catalysts preparation decreased H2S release from Pd–Ni catalysts.

The purpose of this work is to study dry sliding frictional properties of a polymer pair consisting of two commonly used engineering polymers: polybutylene terephthalate (PBT) blended with PTFE and polyoxymethylene (POM). A reciprocating pin-on-flat tribometer was employed to measure the maximum initial and dynamic friction coefficients (COF). All the specimens were used as obtained from injection molding, without any abrasive pretreatment. A sufficient repeatability of the results was achieved by using a PBT pin with a spherical tip. The influence of the applied load (1, 5, 10 and 20 N) and the sliding speed (10, 30 and 50 mm/s) on the frictional performance of PBT+PTFE pin sliding against POM was examined. Frictional heating was measured with an infrared camera and the obtained temperature rises were compared with the values predicted by three analytical frictional heating models. The results showed that both the maximum initial and dynamic friction coefficients were strongly affected by the applied load. Up to 50% reduction in the values of COFs was observed by increasing load from 1 to 20 N. The electron microscopy results of the worn surfaces indicated that the decrease in friction at higher loads could be due to softening of the PBT pin by frictional heating.

Lignin is an important aromatic biopolymer with the structure based on phenolic units. Depolymerized lignin materials can be useful substitutes for phenol in phenol-formaldehyde resins. Our aim was to examine the potential of the base-catalyzed oxidation method to provide reactive oligomeric lignin fragments from softwood kraft lignin through the cleavage of the ether bonds. Three different bases, namely, NaOH, KOH, and NH4OH, were used as the catalyst in an aerobic oxidation, in which the influence of the reaction time was examined for 2 h and 6 h. Oxidized lignin materials were characterized with high-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and nuclear magnetic resonance spectroscopy (13C, 1H-13C HSQC, and 31P NMR). The presence of methanol in the oxidation gas phase and formation of carboxylic acids indicate that some of the lignin structures were degraded in the oxidation. Guaiacyl units, the major phenolic structure of softwood kraft lignin, survived the oxidation. The oxidatively depolymerized lignin materials showed a reactivity close to that of pristine lignin in a reaction with formaldehyde, as determined by differential scanning calorimetry (DSC). Overall, the FT-ICR MS, NMR, and DSC results proved that the oxidized lignin materials maintained their oligomeric nature and possess the reactivity with formaldehyde.

Computational study at level of density functional theory has been carried out in order to investigate the adhesion between rubber and brass plated steel cord, which has high importance in tire manufacturing. Adsorption of natural rubber based adsorbate models has been studied on zinc sulfide, ZnS(1 1 0), and copper sulfide, Cu 2 S(1 1 1) and CuS(0 0 1), surfaces as the corresponding phases are formed in adhesive interlayer during rubber vulcanization. Saturated hydrocarbons exhibited weak interactions, whereas unsaturated hydrocarbons and sulfur-containing adsorbates interacted with the metal atoms of sulfide surfaces more strongly. Sulfur-containing adsorbates interacted with ZnS(1 1 0) surface stronger than unsaturated hydrocarbons, whereras both Cu 2 S(1 1 1) and CuS(0 0 1) surfaces showed opposite adsorption preference as unsaturated hydrocarbons adsorbed stronger than sulfur-containing adsorbates. The different interaction strength order can play role in rubber–brass adhesion with different relative sulfide concentrations. Moreover, Cu 2 S(1 1 1) surface exhibits higher adsorption energies than CuS(0 0 1) surface, possibly indicating dominant role of Cu 2 S in the adhesion between rubber and brass.

Ni additive in the three-way catalyst (TWC) has been known for its high activity in H 2 S suppression. However, the effect of Ni on the activity of TWC in stoichiometric exhaust gas conversion is less studied. In the present work characterization of bimetallic Pd–Ni catalysts supported on γ-Al 2 O 3 or γ-Al 2 O 3 –La 2 O 3 for potential TWC application was performed. The catalysts were prepared by wet co-impregnation and impregnation-evaporation methods. Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), temperature-programmed reduction (TPR), UV–vis diffuse reflectance spectrometry (UV–vis DRS), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM) techniques were employed to confirm the effect of Ni addition on the catalysts structure. XRD, TPR, and STEM characterization was employed in order to evaluate the presence of Pd–Ni interaction. The activity of the catalysts was tested in the oxidation reaction of CO and C 3 H 6 under stoichiometric conditions. Based on the obtained results, we confirmed the structure of prepared catalysts and the effect of Pd–Ni interaction on the catalytic activity of Pd–Ni catalysts in CO and C 3 H 6 oxidation. XRD and TPR characterization suggested that Pd and Ni are competing for the support sites. The observed competition affected Pd-support and Ni-support interactions and consequently activity. Fresh bimetallic catalysts had higher catalytic activity compared to monometallic ones due to higher active metal loading and the presence of NiO phase. It was concluded that the catalytic activity of aged bimetallic catalysts is not affected by the addition of Ni. For that reason, addition of Ni as a second metal to Pd-based catalysts for TWC reactions can be considered in the future studies.

Macro-scale surface patterns are often used with tool and working surfaces to improve gripping, sliding or other working abilities. Polyacetal (POM) samples possessing micron-scale surface structures were examined to determine effects of micro-scale patterning on the sliding friction and wear rate of POM surfaces. The micro-patterned samples were manufactured via injection molding and their friction/wear behaviors were compared to those of identically micro-patterned polypropylene (PP) surfaces. Polymer surfaces were slid against polished steel using a reciprocating pin-on-disk type measuring system. The wear and friction properties of the patterned polymers were studied as functions of surface pressure, induced by loads and pattern densities applied. For both materials, the wear rate was found to diminish with increasing surface pressure and the wear mechanism to resemble extrusion, producing flake-like particles. Dynamic friction levels were found to correlate with surface pressure, the micro-pattern having a distinct effect on friction with low loads. Both POM and PP were found to possess a friction minimum in the surface pressure range of 0.5–1.0 MPa, which is attainable by adjusting either the used load or the density of micro-patterns.

In this paper, the results of exploiting self-organized sub-micron polystyrene (PS) wrinkle patterns possessing random orientation, in preparation of a nickel stamp for hot embossing purposes, are presented. Self-organized patterns were prepared employing a method in which a stiff cross-linked capping layer on the topmost part of the soft polystyrene layer was created by using reactive ion etching (RIE) device with mild conditions and argon as a process gas, and the wrin- kle formation was initiated thermally. Different surface patternings were obtained using silicon and stainless steel (SST) wafers as substrates. Prepared Ni-stamps were employed in hot embossing of polycarbonate (PC) and cyclo-olefin polymer (COP) films, using a nano-imprinting process. The replication quality of the self-organized wrinkle structures in PC and COP films was monitored by comparing the shape and dimensions of the original and final surface structures. The hot embossed sub-micron scale features, originally formed on stainless steel substrate, were found to have influence on the optical properties of the PC and COP films by lowering their reflectances.

While the conventional photomask technique gives only two-dimensional anisotropies, in this study we fabricated microstructured polymer surfaces with a selective three-dimensional anisotropy. With the applied removable mesh, we were able to confine the contacting area between the surface and photoinitiator and provide three-dimensional wettability anisotropies. Different types of meshes were used depending on the desired micropatterns shape, size and substrate material. The results revealed the three-dimensional anisotropic micropits pattern with depth profiles, which would be applicable for the confinement and patterning of cells and biomolecules. In addition, the proposed method is applicable for creating selectively activated polymer surface as a substrate for further atomic layer deposition. Moreover, we demonstrate a low cost and fast mass productive method for patterning a viscous polymer liquid in a micro-sized scale.

Self-organized pattern formation is a phenomenon that can be used for nanoscale pattering of large surface areas in a cost-effective manner. We exploit the phenomenon and fabricate sub-micron polystyrene wrinkle structures and demonstrate that after being coated with silver, they can be used as surface-enhanced Raman spectroscopy (SERS) substrates. We show that the signal enhancement generated by the wrinkles is 8 times higher in comparison to a flat reference while the measurement repeatability is simultaneously improved (variation reduced from 30 to 13%). The results indicate that self-organization could be further utilized in cost-effective, large-scale production of SERS substrates.

Successful applications of mesoporous materials often require different surface properties of internal pore walls and external surfaces. The different functional moieties on the different surfaces enable them to fulfill multiple application demands. In this study, we introduce a nanostopper approach to selectively functionalize the different surfaces of porous silicon (PSi). The external surface was functionalized with amine groups to further graft with folic acid (FA) and fluorescein isothiocyanate (FITC) for targeting and imaging, respectively. The pore walls were functionalized with carboxyl groups to obtain a higher loading degree of doxorubicin and realize a pH-triggered drug release. The engineered PSi drug carrier showed specific targeting against cancer cells and improved cell internalization due to the FA functionalization. Moreover, the PSi carrier presented an intracellular drug delivery with pH-triggered functionality. With the selective modification, the loading degree of the drug was increas...

Interaction of rubber models with dopant atoms on ZnS(110) and Cu2S(111) surfaces, present in rubber–brass adhesive interlayer, has been studied via computational approach using density functional theory. Carbon–carbon double bonds and thiol groups in rubber are generally responsible of the interaction with metal atoms of ZnS(110) and Cu2S(111) surfaces. Inclusion of a copper atom into a zinc sulfide environment weakens the interaction with rubber. The incorporation of cobalt atoms as additives on ZnS(110) and Cu2S(111) surfaces enhances the adsorption strength with rubber. The cobalt dopant increases the adsorption strength of all functional groups of rubber with zinc sulfide, while in doped copper sulfide only the carbon–carbon double bond interaction with rubber is enhanced. It is noteworthy that also the adsorption of saturated hydrocarbons on zinc sulfide is improved by cobalt doping indicating enhanced carbon–hydrogen bond interaction with the sulfide surface.

Fireplaces are one of the largest sources of soot emissions. One possible approach to reduce wood-based soot emission is to use catalysts that have been designed for fireplace applications. This study compares the activities of silver and platinum catalysts in the oxidation of real fireplace soot in different gas atmospheres. Another goal is to examine the effects of water on the catalyst activity depending on the moisture content in the reaction gas. The study shows that the gas feed composition affects the performance of the catalyst. Unlike platinum, the silver catalyst directly oxidizes the soot in the presence of air and NO. The addition of water into the air promotes the soot oxidation activity of both the silver and platinum catalysts. The catalysts improve their activity with the increase in water content. For both the silver and platinum catalysts, the partial dissociation of water with oxygen and the formation of hydroxyls are promoted, which oxidize soot. Thermal ageing shows that silver has a higher thermal stability and retains its oxidation activity for longer than platinum under all of the applied conditions. Silver is a more suitable option for the catalytic oxidation of soot emission of fireplaces., published version, peerReviewed

In a controlled assembly of gold nanorods (GNRs) into surface patterns the important factors are surface properties of the GNRs and the substrate as well as the immobilization time. Influence of chemical and physical interactions on assembly of positively charged, hexadecyltrimethylammonium bromide (CTAB) stabilized GNRs on silicon wafer and indium tin oxide (ITO) substrate surfaces were studied. The substrates were silanized with mercaptosilane to provide thiol groups for chemical bonding of nanorods. Effect of pH of the GNR solution was examined in assembly of nanorods using electrostatic and morphologic interactions. By using a higher pH and ITO surface, we have demonstrated that the controlled assembly of the GNRs can be guided with ring and line patterns fabricated by electron beam lithography.

A novel trimetallic nanocomposite was prepared at a temperature of around 220 °C using co-precipitation of their carbonates from aqueous solutions of the metal nitrates. The morphology of the composite was investigated with scanning electron microscopy (SEM). The X-ray, FTIR and SEM/EDS analyses data indicate that as-synthesized composite which was heated at around 220 °C exists in a nanosized form consisting of crystalline Zn6Al2(OH)16CO3·4H2O and CeO2. Annealing at temperatures between 400 and 920 °C converts the as-synthesized composite to CeO2·ZnO·ZnAl2O4 multi-metal oxide consisting of crystalline CeO2, ZnO and semicrystalline ZnAl2O4. Photoluminescence (PL) spectra of the as-synthesized sample showed emissions at 440 and 590 nm. PL spectra of CeO2·ZnO·ZnAl2O4 annealed at 920 °C was recorded and three sharp lines were observed at 627 nm (1.98 eV), 530 nm (2.34 eV) and 465 nm (2.67 eV) with broad peaks at 540 nm (2.3 eV) and 400 nm (3.1 eV). These sharp lines resemble to those of CeO2 and the broad peaks originate from ZnO. The indirect band gap of the as-synthesized composite was found to be 2.44 eV. The luminescence lifetime at 4 K was measured to be 38 μs.

Polypropylene/viscose fiber (PP/VF) composite with a surface pattern consisting of periodic, micro-scale cylindrical pillars were manufactured and the effect of fiber loading and micro-patterning on the friction and wear properties of the composites was studied. The micro-patterned viscose fiber composite surfaces were prepared via melt compounding and injection molding. SEM studies showed that the fiber dispersion within the micro-bumps was influenced by the fiber loading and high aspect ratio (300–1200) of viscose fibers. With higher fiber loadings the fiber content of the micro-bumps was prominently higher than with lower fiber loadings of the composites. The wear and friction behavior of the patterned composite series were evaluated by sliding the fabricated surfaces against rough and smooth steel surfaces with a pin-on-disc type tribometer. It was noted especially in the case of a smooth counter surface that while both high fiber content and sparse micro-bump coverage individually decreased the sliding friction, their synergetic effect produced a dramatic drop in friction coefficient.

A multi metal oxide, CuO·ZnO·ZnAl 2 O 4 , was prepared by co-precipitation of their carbonates from the aqueous solution of the metal nitrates. Sample was dried in an oven for 3 hours at 220 °C and then sintered at 600 °C for 6 h and 900 °C for 10 h to convert the carbonate of the sample into their oxides. The morphology and crystallinity of the particles were investigated with scanning electron microscopy, X-ray diffraction and TEM analysis. Photoluminescence spectra of CuO·ZnO·ZnAl 2 O 4 showed four peaks at 2.52, 2.70, 2.86 and 3.02 eV. The separation energy between adjacent peaks is about 0.16 eV. Huang-Rhys factor S, which indicates the strength of electron-phonon interaction for CuO·ZnO·ZnAl 2 O 4 was calculated to be 1.3. Solution emission spectra of CuO·ZnO·ZnAl 2 O 4 in acetone showed peaks at 2.68, 2.85, 3.00 and 3.17 eV with separation energy similar to that found for solid samples. Thermal stability and luminescence spectra-structure relations have been appraised.

Bioelectrode–skin contact impedances need to be minimized to enable high quality recordings of biopotentials. Low contact impedances can be achieved with large, effective bioelectrode–skin contact areas. In this study, novel dry microstructured electrodes based on electrically conductive liquid silicone rubber (LSR) were developed and characterized with electrical impedance spectroscopy (EIS) measurements. Two different micropillar structures with inter-pillar distances of 20 μm and 100 μm, respectively, were compared with smooth LSR electrodes, as such or coated with silver (Ag). A gelatin gel based skin model was used in EIS measurements to overcome the problems associated with real skin measurements. Both microstructurings were found to significantly decrease the contact impedance modulus. In addition, the Ag coating caused highly significant ( p

This study focuses on design and fabrication of new UV-curable polyurethane acrylate submicron-structured coatings that have anti-reflective and anti-wettable surface properties. The coatings were replicated on PMMA substrates with use of a pair of nickel molds containing complementary surface patterns of submicron-sized pillars or pits in a cubic grid. The period of the square-shaped mold features was 270nm and the height/depth of the grating features was 110nm. The influence of the chemical composition and the replication accuracy on optical properties was examined by UV-Vis spectroscopy and variable angle spectroscopic ellipsometry. The UV-cured coatings showed a 1.5% reflectance between 400 and 700nm of the visible spectral region. Transmittance was increased from 91% to 94% when the submicron-structure was copied onto the surface. Furthermore, the investigation of static and dynamic wetting of the coatings with water or oleic acid demonstrated that the sub-micron structure and chemical modification with fluoroalkylsilane significantly improved the water and oil resistance of the prepared coatings. Especially for pit-covered coatings, the static water contact angle increased to 146^o and the highest advancing/receding contact angles for water were 150^o/119^o.

Considerable attention is currently being devoted less to the question of whether it is possible to produce superhydrophobic polymer surfaces than to just how robust they can be made. The present study demonstrates a new route for improving the mechanical durability of water-repellent structured surfaces. The key idea is the protection of fragile fine-scale surface topographies against wear by larger scale sacrificial micropillars. A variety of surface patterns was manufactured on polypropylene using a microstructuring technique and injection molding. The surfaces subjected to mechanical pressure and abrasive wear were characterized by water contact and sliding angle measurements as well as by scanning electron microscopy and roughness analysis based on optical profilometry. The superhydrophobic polypropylene surfaces with protective structures were found to maintain their wetting properties in mechanical compression up to 20 MPa and in abrasive wear tests up to 120 kPa. For durable properties, the optimal surface density of the protective pillars was found to be about 15%. The present approach to the production of water-repellent polymer surfaces provides the advantages of mass production and mechanical robustness with practical applications of structurally functionalized surfaces.

We report results of preparation of wrinkled polystyrene (PS) surfaces on silicon substrate employing two different methods, solvent-assisted wrinkling (SAW) and thermal wrinkling (TW). In both methods an argon (Ar) plasma treatment of PS/silicon bi-layer by reactive ion etching (RIE) was used for creation of cross-linked PS layer acting as a capping layer. In SAW method the layered system was exposed after the plasma treatment to solvent vapor and in TW method the layered system was heated above the glass-transition temperature of PS employed. Wave-like patterns were achieved with the both initiation methods and using the two polystyrenes having different molar masses. The plasma treatment time was found to have influence on the wrinkle formation by affecting the thickness of the cross-linked part of PS layer, and influencing slightly the dimensions of the wrinkles. The molar mass of PS was found to have effect on overall size-scale of the forming patterns. Moreover, employing TW as a wrinkling method yielded somewhat higher wrinkles.

Molecular dynamics simulations were performed to study the embedding behavior on functionalized polypropylene surfaces with combined topographical and chemical anisotropies. Three different substrate structure types were constructed to give a periodic, non-polar, and hydrophobic functionality. The carboxyl thiol monolayer covered structure bottoms are polar and hydrophilic in nature. Both static wetting and dynamic impact of nano-sized water droplets together with temperature effect were considered. The results revealed unconventional wetting on the functionalized surfaces when comparing to the purely structured counterparts. Complete water embedding was achieved under suitable conditions varied with the substrate topography.

Emission regulations and legislation inside the European Union (EU) have a target to reduce tailpipe emissions in the transportation sector. Exhaust gas aftertreatment systems play a key role in low emission vehicles, particularly when natural gas or bio-methane is used as the fuel. The main question for methane operating vehicles is the durability of the palladium-rich aftertreatment system. To improve the durability of the catalysts, a regeneration method involving an efficient removal of sulfur species needs to be developed and implemented on the vehicle. This paper tackles the topic and its issues from a fundamental point of view. This study showed that Al2(SO4)3 over Al2O3 support material inhibits re-oxidation of Pd to PdO, and thus hinders the formation of the low-temperature active phase, PdOx. The presence of Al2(SO4)3 increases light-off temperature, which may be due to a blocking of active sites. Overall, this study showed that research should also focus on support material development, not only active phase inspection. An active catalyst can always be developed, but the catalyst should have the ability to be regenerated.