Range Of Few Micrometers Research Articles

On the correlation between pre-processing workflow and dimensional accuracy of 3D printed parts in high-precision Material Jetting

Material Jetting (MJ) is distinguished in the additive manufacturing field for its ability to create accurate multi-material functional objects with features in the range of few micrometers. Analyzing the impact of each step in MJ from virtual design to 3D printed object on the process response is essential for optimizing the technology’s capabilities. The current state-of-the-art reveals a gap in MJ regarding the fundamental understanding of the correlation between the pre-processing workflow and the geometrical and dimensional accuracy. This study aims to bridge this gap by examining factors such as utilization of different CAD software with diverse working principles, part-based versus assembly-based design, alternative 3D model formats (STL, OBJ, 3MF, AMF, STP), and slicing approaches (using open-source slicers). Two test specimens, each containing ten elements (either cylinders or hemispheres) with diameters ranging from 254 µm to 12.7 mm are examined. The results demonstrate the significant influence of the aforementioned factors on geometrical and dimensional accuracy, except for 3D model formats. Specifically, for large elements, the achievable accuracy depends on the tessellation approach of the CAD system, while for very small elements, the rasterization process is defining, and designing in assembly mode can further enhance accuracy. The handling of the 3D model by the slicer particularly affects geometrical accuracy. Experimental validation confirms the impact of the pre-processing workflow, though the data-related dimensional deviation for the base layer is masked by the wetting behavior of the dispensed droplets on the substrate.

Laser Assisted Electrodeposition of Metals and Alloys

Laser sources are extensively used in surface engineering technology and in materials processing. Their high energy density, excellent directionality and monochromaticity makes them ideal for a wealth of potential uses that require the concentration of a significant amount of energy in a small area. From the electrochemical point of view, one of the most interesting applications for lasers is Laser Assisted Electrodeposition (LAE). Indeed, the high energy density transferred by a laser can locally change the electrochemical state of a surface by inducing photo-electrochemical or thermal-electrochemical effects, triggering thus metal reduction. In addition, it is also possible to pattern the deposited metal layer by scanning the surface of the substrate with the laser, usually with spatial resolution in the range of few micrometers. From the applicative point of view, LAE can be exploited for the selective deposition of metal layers for both decorative and functional uses.LAE can be intended in two ways: the laser can be used to enhance a standard electrolytic deposition process [1, 2], increasing deposition rates by focusing the radiation on the cathode, or it can be used to trigger electrodeposition on freestanding metal surfaces in total absence of any external polarization [1]. The latter approach is the most interesting due to the reduced complexity of the setup required and is made possible by the localized variation of the rest potential induced in the zone of the substrate hit by the light [1]. As a consequence of this variation, metallic ions can be reduced in correspondence of the illuminated zone. The occurrence of this phenomenon, which allows metal deposition without any external power source, has been demonstrated for Cu [1, 3], Ni [3] and Au [4].Despite the work carried out by many research groups, still many aspects of LAE in absence of external polarization remain poorly understood. The aim of the present work is to investigate the possibility to perform LAE with some significant metal-substrate couples. The deposition mechanism is rationalized considering the specific electrochemical properties of the metals involved. In addition to this fundamental characterization, the work also aims at evaluating the industrial applicability of LAE. To this extent, patterned layers of precious metals are deposited on metallic substrates for decorative purposes. Finally, LAE is applied here for the first time to the deposition of alloys.[1] J. C. Puippe et al., J. Electrochem. Soc. 128(12), 2539-2545 (1981)[2] Z. Zhang et al., MDPI Materials 13, 3560 (2020)[3] R. J. von Gutfeid et al., IBM J. Res. Develop. 26(2), 136-144 (1982)[4] Khan et al., NASF Surface Technology White Papers 84(3), 6-13 (2019)

Natural protein-based electrospun nanofibers for advanced healthcare applications: progress and challenges.

Electrospinning is an electrostatic fiber fabrication technique that operates by the application of a strong electric field on polymer solution or melts. It is used to fabricate fibers whose size lies in the range of few microns to the nanometer range. Historic development of electrospinning has evinced attention due to its outstanding attributes such as small diameter, excellent pore inter-connectivity, high porosity, and high surface-to-volume ratio. This review aims to highlight the theory behind electrospinning and the machine setup with a detailed discussion about the processing parameters. It discusses the latest innovations in natural protein-based electrospun nanofibers for health care applications. Various plant- and animal-based proteins have been discussed with detailed sample preparation and corresponding processing parameters. The usage of these electrospun nanofibers in regenerative medicine and drug delivery has also been discussed. Some technical innovations in electrospinning techniques such as emulsion electrospinning and coaxial electrospinning have been highlighted. Coaxial electrospun core-shell nanofibers have the potential to be utilized as an advanced nano-architecture for sustained release targeted delivery as well as for regenerative medicine. Healthcare applications of nanofibers formed via emulsion and coaxial electrospinning have been discussed briefly. Electrospun nanofibers have still much scope for commercialization on large scale. Some of the available wound-dressing materials have been discussed in brief.

Contribution of fission products to displacement damage in fast reactor fuel cladding

The number of Displacement per Atom (DPA) in the fuel cladding is a key quantity for determining the operation lifetime of fuel assemblies in Sodium-cooled Fast Reactor (SFR). Since the cladding is directly irradiated by Fission Products (FPs), the present work evaluates the FPs-induced atomic displacements in the Fe-14Cr cladding. Three degrees of freedom (the yields of FPs, energy distribution, and angular distribution of each FP) are reduced using the assumptions proposed in this paper. Two additional approximations are proposed to obtain the reasonable upper and lower limits of DPA in the cladding so that the computation burden is largely reduced. Numerical results show that the proposed approximations can give a reasonable estimate of the FPs-induced DPA in the fuel cladding. The FPs-induced damage is limited in the range of few microns but can be 5 times more important than the neutron-induced one in the cladding of ASTRID inner core. Along with the depth in the cladding, the FPs-induced damage rate becomes less important than the neutron-induced one at penetration deeper than 5 μm and smaller than 1/10 of neutron-induced DPA at penetration larger than 7 μm. A subsequent question of whether the FPs-induced damage should be taken into account in the cladding needs to be discussed for SFRs.

Electrochemical recovery of hydrogen and elemental sulfur from hydrogen sulfide gas by two-cell system

ABSTRACT In spite of industries making huge investments, for a viable energy saving, still the methods for conservation of energy are lagging and the industries are still in search for alternatives. The major concern that persists with the oil and gas operations is emission of hydrogen sulfide, frequently or inadvertently, during the initial or later stages of the process. Hence, this study focuses on the indirect electrolysis toward the recovery of sulfur and hydrogen from hydrogen sulfide using graphite as both anode and cathode with calomel as reference electrode. The recovered sulfur was analyzed using high-resolution scanning electron microscope was in range of few microns that was in agreement with the X-ray diffraction analysis confirming the crystalline orthorhombic structure of sulfur (JCPDS Card no.89–2600). The cyclic voltammetry experiment was carried out by sweeping the potential between −1.2 and +1.2 V at a scan rate of 50 mVs−1 obtaining a maximum current density of 0.41 A/cm2. Maximum deposition of sulfur observed at pH 13 with a current density of 0.23 A/cm2 and temperature 80°C. The quantity of sulfur recovered by indirect electrolysis was in the range of 2.9 mg with efficiency of 90.44%.Thus an effective method using indirect electrolysis method was successfully used to achieve crystalline sulfur and hydrogen from H2S.

Hydrogen storage properties of Ti2FeV BCC solid solution

This paper deals with hydrogen storage properties of Ti-V based BCC solid solution incorporated with Fe. The alloy with composition Ti2FeV was prepared by arc melting method. X-ray diffraction (XRD) and energy dispersive X-ray analysis studies confirmed formation of solid solution phase with uniform composition and BCC structure. SEM studies revealed the formation of irregular shaped particles with size in the range of few microns up on hydrogenation of the parent alloy. The alloy shows maximum hydrogen storage capacity of 3.41 wt.% at 20 bar and 303 K and the thermodynamic parameters established near room temperature suitability of the alloy for solid state hydrogen storage applications. Hydrogenation kinetics is found to be quite fast and detailed kinetic analysis were done to underscore the hydrogenation mechanism. Activation energy during the initial stage of hydrogenation is found to be 30.8 kJ/mol. The value decreases to 14.4 kJ/mol for extended duration of hydrogenation, and this is explained based on difference in rate determining steps existing at different time scales. Extent of hydrogen absorption as a function of temperature and time for Ti2FeV alloy.

Fabrication of Biodegradable Poly(naringin) Particles with Antioxidant Activity and Low Toxicity

Naringin (NR, 4′,5,7 trihydrocyflavanone-7-O-rhamnoglucoside) is a flavanone found in citrus fruit that is composed of a phenolic compound, naringenin, and a disaccharide, neohesperidose. Poly(NR) [p(NR)] particles in the size range of few micrometers to few hundred nanometers were prepared from highly purified NR and subsequently characterized using UV/visible spectroscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, thermogravimetric analysis, and zeta potential measurements. The hydrolytic degradation of p(NR) particles at 37.5 °C was investigated at pHs 5.4, 7.4, and 9.0. The particles degraded most rapidly at pH 7.4, with >90% degradation after 5 h. The cytotoxicity was assessed by growing COS-1 fibroblasts for 5 days in the presence of increasing concentrations of NR or eluates from the p(NR) particles. Both NR and p(NR) particles were nontoxic for these mammalian fibroblasts; at the highest concentration tested (571 μg/mL), the per...

Tangential traction instability in fretting contact below fully developed friction load

Fretting experiments were run below fully developed friction load levels, and the stability of friction was investigated. It was observed that stable friction behavior can be achieved if friction load per normal load is limited to maximum of about 0.5. Exceeding this value leads to increasing instability in friction until gross sliding is achieved. Minute surface sliding, in range of few micrometers, occurred even at these load levels, which may contribute to friction instabilities.

Single step poly(l-Lysine) microgel synthesis, characterization and biocompatibility tests

In this study, an amino acid microgel from l-Lysine as poly(l-Lysine) (L1) was prepared in a single step for the first time via microemulsion polymerization/crosslinking technique using tetrakis (hydroxymethyl)phosphium chloride (THPC) as crosslinking agent. The spherical L1 microgels with size range of few micrometers revealed by SEM images, were readily modifiable in terms of surface charges upon simple treatment with HCl and NaOH to obtain L2 and L3 forms of the microgel due to protonation of amine groups and deprotonation of carboxylic acid groups to provide tunable surface charge on synthesized L1 microgels. The zeta potential of L1 microgels increased to +29.6 mV with HCl treatment and decreased to -41.8 mV with NaOH treatment from -19.1 mV for L1 microgels. Moreover, the biocompatibility tests of the prepared microgels interestingly showed L3>L2>L1 with over 85% biocompatibility up to 300 μg/mL particle concentration. Furthermore, the blood compatibility tests revealed that L1 and L3 microgels have high hemocompatibility with 5.12 ± 0.58% and 0.55 ± 0.27% hemolysis ratios, and effective hemostatic properties with 96.17 ± 2.15 and 99.63 ± 0.17 blood clotting indices, respectively; whereas L2 particles were found to be non-blood compatible due to their highly positively charged nature. Therefore, poly(l-Lysine) microgels possess great potential and may be readily used in vivo for biomedical purposes.

Microelectrodes As Effective Tools to Evaluate Biodiesel Corrosiveness By Electrochemical Techniques

Corrosion is one of the main concerns for using biodiesel as an alternative fuel. Nowadays, the vast majority of studies are done by immersion tests and the monitoring of its physicochemical properties during degradation reactions. The low conductivity of biodiesel and the development of high ohmic drops has restricted the use of electrochemical techniques for understanding the mechanisms involved in the corrosion processes. The addition of supporting electrolytes is often used to increase the conductivity and reduce the ohmic drop. In organic media as biodiesel, unfortunately, it is suspected that supporting electrolytes are not inert and can give misleading results. Microelectrodes are sensors with at least one dimension in the range of few micrometers (~50) and its geometry mostly depend on its application. Due to the small currents registered in microelectrodes, the effects of the ohmic drop become insignificant, even in very resistive electrolytes as biodiesel. In this work, we propose the use of microelectrodes as a methodology to evaluate the corrosion rate of metals, particularly copper, by EIS without any addition of supporting electrolytes (water or other contaminants). Two different types of microelectrodes (i.e. single classic and array) with disk geometry were constructed and characterized by different techniques (optical microscopy, SEM and cyclic voltammetry). Single classic microelectrodes were constructed manually by introducing a metallic wire (working electrode) into a capillary glass. The arrays with sixteen and twenty-five microelectrodes were constructed by photolithography technique. The impedance measurements were done in a Gamry ref. 600 potentiostat/galvanostat using a two electrode cell configuration were a Pt foil was used simultaneously as counter and reference electrode (i.e. short-circuited to the corresponding inlets of the potentiostat) and the microelectrode was the working electrode. The frequency range was from 100 kHz to 5 mHz, with an amplitude of potential perturbation of 30 mV rms (with lower perturbation of potential no response is obtained). For both types of microelectrodes, two time constants were observed, one at high frequencies and the other at low frequencies. The former corresponds to the electrolyte and the latter to interfacial phenomena between the electrolyte and the metal surface. Both hypothesis were corroborated using three different types of experiments. In the first case, another quality of biodiesel was used. Degraded biodiesel was obtained by introducing a copper foil, increasing the temperature and bubbling air during 5 days. With degraded biodiesel a reduction in the impedance at high frequencies was observed in both types of microelectrodes, as a result of the higher conductivity of the electrolyte. In the second case, an inert metal (Pt) was used as a microelectrode (single classic) and it was observed an increase in the impedance with respect to copper, due to the low activity that Pt has in biodiesel. Additionally, an array of copper with 25 microelectrodes was left in contact with degraded biodiesel during 60 h. Every 12 h the impedance was monitored and recorded. The results showed an increase in this parameter as a consequence of the growth in the corrosion layer formed on the surface of the metal in contact with the biofuel. As the corrosion layer growths the rate of the electron transfer reactions at the interface is reduced. In all cases, the second semicircle observed in Nyquist diagrams started at 0.3 – 0.1 Hz. A decrease in the phase angle at medium frequencies (1-0.1 Hz) was observed when the number of microelectrodes increased as a result of a higher kinetic for the change transfer process, due to the higher area and the interfacial character of the signal. Figure 1

Performance assessment of thermal sensors during short-duration convective surface heating measurements

The determination of convective surface heating is a very crucial parameter in high speed flow environment. Most of the ground based facilities in this domain have short duration experimental time scale (~milliseconds) of measurements. In these facilities, the calorimetric heat transfer sensors such as thin film gauges (TFGs) and coaxial surface junction thermocouple (CSJT) are quite effective temperature detectors. They have thickness in the range of few microns and have capability of responding in microsecond time scale. The temperature coefficient of resistance (TCR) and the sensitivity are calibration parameter indicators that show the linear change in the resistance of the gauge as a function of temperature. In the present investigation, three of types of heat transfer gauges are fabricated in the laboratory namely, TFG made out of platinum, TFG made out of platinum mixed with CNT and chromel–alumel surface junction coaxial thermocouple (K-type). The calibration parameters of the gauges are determined though oil-bath experiments. The average value TCR and sensitivity of platinum TFG is found to be 0.0024 K−1 and 465 μV/K, while similar values of CSJT are obtained as, 0.064 K−1 and 40.5 μV/K, respectively. The TFG made out of platinum mixed with CNT (5 % by mass) shows the enhancement of TCR as well as sensitivity and the corresponding values are 0.0034 K−1 and 735 μV/K, respectively. The relative performances of heat transfer gauges are compared in a simple laboratory scale experiment in which the gauges are exposed to a sudden step heat load in convection mode for the time duration of 200 ms. The surface heat fluxes are predicted from the temperature history through one dimensional heat conduction modeling. While comparing the experimental results, it is seen that prediction of surface heat flux from all the heat transfer gauges are within the range of ±4 %.

Fast one-dimensional wave-front propagation for x-ray differential phase-contrast imaging.

Numerical wave-optical simulations of X-ray differential phase-contrast imaging using grating interferometry require the oversampling of gratings and object structures in the range of few micrometers. Consequently, fields of view of few millimeters already use large amounts of a computer's main memory to store the propagating wave front, limiting the scope of the investigations to only small-scale problems. In this study, we apply an approximation to the Fresnel-Kirchhoff diffraction theory to overcome these restrictions by dividing the two-dimensional wave front up into 1D lines, which are processed separately. The approach enables simulations with samples of clinically relevant dimensions by significantly reducing the memory footprint and the execution time and, thus, allows the qualitative comparison of different setup configurations. We analyze advantages as well as limitations and present the simulation of a virtual mammography phantom of several centimeters of size.

Two‐Photon polymerization for microfabrication of three‐dimensional scaffolds for tissue engineering application

AbstractIn natural tissues cells are embedded in a three‐dimensional fibrous network of biopolymers like collagen, hyaluronic acid etc. This extracellular matrix (ECM) influences the cell fate, the differentiation status, metabolic processes and provides structural integrity. For a three‐dimensional or physiological cell cultivation that are required in biomedical applications (e.g. tissue engineering, BioMEMS) scaffolds are needed. These scaffolds mimic the ECM according to their biocompatibility which comprises aspects of surface compatibility and importantly for tissue engineering applications aspects of structural compatibility. We have evaluated scaffold design parameters for the three‐dimensional cultivation of chondrocytes for the tissue engineering of artificial cartilage. Two‐photon polymerization is a powerful technique for fabrication of polymeric three‐dimensional micro‐ and submicro‐structures. The photoinitiation system for two‐photon polymerization is excited by simultaneous absorption of two photons leading to chemical polymerization reactions. Due to a tight confinement of the excitation volume around the focal point, this method can produce micrometer sized objects maintaining a high spatial resolution down to 100 nm. Two‐photon processes require very high photon densities which are provided by pulsed femtosecond lasers. The potential of this approach for microfabrication of scaffolds for tissue engineering is demonstrated by investigation of the cell response to microstructures with complex three‐dimensional geometry and feature sizes in the range of few micrometers.

Dispersion Polymerization of Methyl Methacrylate in Supercritical Carbon Dioxide Using a Pseudo-Graft Stabilizer: Role of Reactor Mixing

The free radical polymerization of methyl methacrylate (MMA) in supercritical carbon dioxide (scCO2) using a commercially available acid-terminated perfluoropolyether as a stabilizer (Krytox 157 FSL) is analyzed experimentally. A series of polymerizations were carried out under identical conditions; only the rate of stirring was varied. At each specific stirring rate, the complete evolution of conversion and molecular weight was obtained by repeated experiments quenched at different times. The results obtained indicate that the dispersion becomes unstable at a surprisingly moderate stirring rate (above 25 rpm). Clearly, the anchoring interaction of the Krytox stabilizer is relatively weak, and destabilization occurs at modest shear induced by the mechanical stirring. However, when stable conditions are achieved, normal kinetic behavior is observed, leading to a fluffy polymer, with uniform particle size in the range of few microns and relatively broad molecular weight distribution. A particular attraction of these stabilizers is that the anchoring interactions occur via a hydrogen-bonding mechanism which is reversible; thus, no residues of stabilizer are found in the final PMMA product, and the stabilizer is vented with CO2. Apart from the shift of the high molecular weights, likely due to diffusion limitations in the polymer particles at high conversion, this broad molecular weight distribution is a result of the combined action of two reaction loci: the polymer particles and the continuous phase. Even under stable conditions, although the polymer particles are clearly the dominant locus of polymerization, the contribution of the polymerization in the continuous phase cannot be neglected.

Low Cost (La,Sr)MnO3 Cathode Material with Excellent Electrochemical Properties

The main objectives of H. C. Starck's internal development program for powders used in SOFC applications are to meet the cost targets of the customers as well as the performance requirements during cell operation. Optimization of LSM-powder engineering process resulted in very homogenous powders with good crystallographic properties. The morphological properties can be adapted to customer requirements, the primary particle size can be varied in the range of few micrometers down to submicron powders. Electrochemical performance tests of electrolyte supported single cells with cathodes based on these LSM-powders were conducted at the IWE, Universitat Karlsruhe (TH). The single cells were characterized with respect to performance and long term behavior (> 1000 h) including load and thermal cycling. Current densities of 0.18 A/cm 2 (750°C), 0.43 A/cm 2 (850°C) and 0.7 AJcm 2 (950°C) were achieved at a cell voltage of 0.7 V. The long term stability and thermal cycling behavior was acceptable for mono-layer cathodes; and performance and degradation were in good agreement with the standard type cathode compositions and microstructure.

Terahertz near-field imaging

A near-field probe is described that enables high spatial resolution imaging with terahertz (THz) pulses. The spatial resolution capabilities of the system lie in the range of few microns and we demonstrate a resolution of 7 µm using broad-banded THz pulses with an intensity maximum near 0.5 THz. We present a study of the performance of the near-field probes in the collection mode configuration and discuss some image properties.

Nanohardness of copper in the vicinity of grain boundaries

The nanohardness in the vicinity of grain boundaries in high purity Cu was investigated. It was found that the nanohardness increases while approaching the grain boundary, the characteristic distance at which the grain boundary influences the nanohardness being in the range of few micrometers.

Amorphous phase formation during spray forming of Al 84Y 3Ni 8Co 4Zr 1 alloy

In this investigation the Al 84Y 3Ni 8Co 4Zr 1 alloy has been processed by spray forming to investigate the potential of achieving substantial fractions of the amorphous phase in the billet. The alloy was prepared by spray metal forming using the ratio of volumetric gas flow rate to mass of metal flow rate of 8.7 m 3/ kg . The resulting billet, weighting 2.1 kg, as well as the powders produced by the particles that had not hit the growing billet (overspray), were characterized by using X-ray diffractometry (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The powders had particles with spherical morphology in the size range of few microns to 100 μm with the median particle diameters about 20±1 μ m. The resulting billet contained only crystalline phases nevertheless the powder was composed of about 40% volume fraction of amorphous phase. This result indicates that the heating of the billet, by the heat release during solidification of the liquid and semi-solid particles was at temperature and for time enough for crystallization.

Collection-mode near-field imaging with 0.5-THz pulses

High spatial resolution imaging with terahertz pulses is implemented with a novel collection-mode near-field probe. The spatial resolution capabilities of the system are in the range of few micrometers. We demonstrate resolution of 7 /spl mu/m using 0.5-THz pulses and discuss performance of the collection-mode near-field probes and image properties.

Incorporation of aerosol particles between 25 and 850 nm into cloud elements: measurements with a new complementary sampling system

The interpretation of the physico-chemical processes in clouds is facilitated by segregating in situ cloud elements from their carrier gas and small particles (interstitial aerosol). Thus, the present study focuses on the quantitative phase segregation of interstitial air from cloud phase by two complementary samplers with microphysical on-line analysis of the separated phases. An improved counterflow virtual impactor (CVI) was developed for the collection and subsequent evaporation of the condensed phase, releasing dissolved gaseous material and residual particles. This sampler operates in the size range of few micrometers up to 50 μm in cloud element diameter and is matched by an interstitial Round Jet Impactor sampling the gas phase with interstitial particles. Calibrations of both samplers verified the calculated cut sizes D 50 of 4, 5, and 6 μm and quantified the slope of the collection efficiency curves. Until this study no direct CVI measurements of the residual particle sizes far below the diameter of 0.1 μm were available. For the first time a CVI was connected to a Differential Mobility Particle Sizer (DMPS) scanning between 25 nm and 850 nm, thus, including the entire Aitken mode in the residual size analysis. Cloud studies on the Puy de Dôme, France, revealed residual particle sizes including Aitken mode (diameter D<100 nm) and accumulation mode ( D>100 nm). A major feature of the CVI data is expressed by the fact that despite incomplete incorporation of accumulation mode particles in cloud elements there are contributions of particles with diameters smaller than 0.1 μm to the number of residual particles. Cloud entrainment from height levels above the maximum supersaturation as wells as the size-dependent chemical composition of the aerosol population most likely produced the S-shaped size-dependent partitioning of residual particles. Compared to earlier studies the 50% partitioning diameters dropped significantly below 100 nm to roughly 70 nm.