Uniformity Of Layer Research Articles

Evaluation of compaction uniformity of the paving layer based on transverse and longitudinal measurements

ABSTRACT Compaction uniformity is essential to the successful performance of asphalt pavement. Therefore, understanding the characteristic and full evaluation on the overall density distribution in field construction is necessary. An available method capable to assess compaction uniformity of the hot paving layer was proposed by considering both longitudinal and transverse density distribution. Field tests of density distribution behind pavers and rollers were conducted on two test sections, respectively. Then, the quantitative evaluation indexes of uniformity (i.e. the range (R), coefficient of variation (CV), repeatability standard deviation in detection track (Sr), etc.) were used to analyse compaction uniformity and the severity of non-uniformity of the asphalt mat. Moreover, the uniformity variation from paving to rolling was evaluated through the tests and a compaction uniformity model. Results indicated that rolling compaction could intensify the degree of non-uniformity of the paving mat, although all the density after rollers is higher than the density behind pavers, and simulation analysis corresponds with the test results. The uniformity of density distribution in transverse is worse than in longitudinal. Tamper seemed to be more effective than other parameters at improving the initial density, while frequency of vibrator appeared to have the most impact on transverse compaction uniformity.

Processing of polycrystalline diamond surface by IR laser pulses without interior damage

A new approach to improve quality of diamond surface treatment by near IR short laser pulses is considered. The main problem being addressed is optical breakdown in diamond bulk occurred in the process of the surface ablation that causes multifold decrease of the machined surface transmittance. To eliminate laser-induced subsurface damaging, preliminary deposition of different absorbing coatings (titanium, graphite) on the diamond surface was proposed and experimentally tested. When the diamond surface is ablated by 10 ns laser pulses, both examined coatings significantly reduce the surface ablation threshold that makes possible to avoid completely the optical breakdowns in the diamond bulk. As a result, transmittance of the machined diamond drastically increases and surface roughness decreases. But the absorbing coatings have negligible influence on ablation of diamond by 1 ps pulses and don’t solve the problem of the interior damaging under these conditions. Other essential differences in processing of the polycrystalline diamond by the picosecond and nanosecond pulses are also analyzed including uniformity of laser-induced graphitized layer and surface roughening.

The influences of catalyst combination on the high temperature proton exchange membrane fuel cell

High temperature proton exchange membrane fuel cell (HT-PEMFC) is a green device which converts chemical energy to the electricity directly. A redox reaction occurs at the catalyst layers of fuel cell, where electrons separate from hydrogen molecule through the help of catalyst. The structure of catalyst is an important factor that affects the cell performance due to the consequences of chemical reaction area and thickness of the catalyst layer. SEM was used for structure investigating of different platinum and carbon ratios (Pt/C). At 0.7mg/cm2 Pt loading, 3 weight percentages, 10%, 20%, and 40% were compared to see the thickness differences of catalyst layer. The catalyst binder can affect the fuel cell performance as well. PTFE and PVDF were tested, and the results showed the former provided 50% higher current density than the latter at the same voltage output. The uniformity of catalyst layer provided better contact with the gas diffusion layer. It also induced thicker CL which results in more surface area for the chemical reactions. A catalyst combination of 10wt.% Pt/C and PTFE was able to reach 0.58A/cm2 at 0.278V.

Effect of various seed metals on uniformity of Ag layer formed by atmospheric plasma reduction on polyethylene terephthalate substrate: An application to electromagnetic interference shielding effectiveness

Dry plasma reduction under atmospheric pressure is a unique approach for stably, continuously, easily, and uniformly fabricating Ag layer on the metal seeds-polyethylene terephthalate (PET) substrate. In this study, effects of particle size, surface uniformity, surface coverage, and film thickness of metal seeds such as Ag, Cu, Fe and Ni on the formation of uniform Ag layer were studied on the basis of their surface free energies and critical radius, which further leads to variations in the sheet resistance levels of the silver layers. The root mean square roughness and sheet resistance of the Ag layer PET substrate were decreased with the deposition of metal seeds. Among the added seed metals, Ni seed has shown best uniformity. Furthermore, the fabricated films were applied for electromagnetic interference (EMI) shielding. Among the added seed metals, Ni has shown the highest electromagnetic interference shielding effectiveness. The present study will be useful for the development of various low-cost metal films in the field of EMI shielding.

Simulation for forming uniform inkjet-printed quantum dot layer

The quantum dot (QD) light emitting diode has emerged as one of the candidates for the next generation display technology with advantages such as tunable wavelength of emitted light and narrow bandwidth. For QD pixel patterning, inkjet-printing is superior to other methods in terms of material loss and process time. However, inkjet-printing has difficulty in controlling the uniformity of the QD layer. This is a serious issue considering that proper thickness and uniformity of the QD layer are important factors for high efficiency in displays. The main reason behind this problem is known to be the coffee ring effect (CRE), in which differential evaporation across a sessile droplet leads to an edge-ward flow of the fluid inside and causes suspending QDs to be concentrated at the perimeter of the droplet. Here, the possibility of improvement in layer uniformity by the reduction of the CRE is demonstrated. Mathematical simulation of the evaporation process of the QD colloidal solution droplet is conducted by solving partial differential equations (PDEs) numerically. The Navier-Stokes equation, continuity condition, and mathematical expressions of physical parameters including the evaporative flux are used for setting up the PDEs, which are then solved with the finite difference method. A filter is included in the process to suppress unwanted instability. Using this simulation, the whole evaporation process is analyzed by observing time evolution of parameters. As a result, various conditions for reducing the CRE are found: sufficient initial concentration, proper solvent type, small contact angle, and fast evaporation rate. The outcome appears to agree with experimental data.

Enhance the performance of ZnO-based perovskite solar cells under ambient conditions

The ETL layer is used to transport electrons and block holes in the perovskite solar cell (PSC), and the uniformity of the dense layer affects the open circuit voltage (Voc) of the battery. The PSC open circuit voltage prepared by the solution method was 0.68 V, and the open circuit voltage of the PSC prepared by the sol method was remarkably improved to 0.95 V. The quality of the perovskite layer is critical for obtaining high-performance perovskite solar cells (PSC). In the process of preparing PSC by sequential deposition, the MAI solution was formed by IPA-n-hexane instead of isopropyl alcohol (IPA) as a solvent to grow CH3NH3PbI3(MAPI). The MAPI prepared by the mixed solvent was characterized by scanning electron microscopy (SEM). The mixed solvent inhibited the Oswald ripening process, and the perovskite layer showed a uniform and dense morphology. The PL characterization implied that the MAPI film with low defect concentration, which prepared from the mixed solvent. Compared to the single solvent PSC (PCE = 4.2%), the efficiency was significantly improved by 1.5 times to 6.2%. This study provides the possibility to prepare ZnO-based high-efficiency solar cell devices in the air.

Ultrathin Al2O3 Coating on LiNi0.8Co0.1Mn0.1O2 Cathode Material for Enhanced Cycleability at Extended Voltage Ranges

Ni-rich LiNi0.8Co0.1Mn0.1O2 oxide has been modified by ultrathin Al2O3 coatings via atomic layer deposition (ALD) at a growth rate of 1.12 Å/cycle. All characterizations results including TEM, SEM, XRD and XPS together confirm high conformality and uniformity of the resultant Al2O3 layer on the surface of LiNi0.8Co0.1Mn0.1O2 particles. Coating thickness of the Al2O3 layer is optimized at ~2 nm, corresponding to 20 ALD cycles to enhance the electrochemical performance of Ni-rich cathode materials at extended voltage ranges. As a result, 20 Al2O3 ALD-coated LiNi0.8Co0.1Mn0.1O2 cathode material can deliver an initial discharge capacity of 212.8 mAh/g, and an associated coulombic efficiency of 84.0% at 0.1 C in a broad voltage range of 2.7–4.6 V vs. Li+/Li in the first cycle, which were both higher than 198.2 mAh/g and 76.1% of the pristine LiNi0.8Co0.1Mn0.1O2 without the Al2O3 protection. Comparative differential capacity (dQ/dV) profiles and electrochemical impedance spectra (EIS) recorded in the first and 100th cycles indicated significant Al2O3 ALD coating effects on suppressing phase transitions and electrochemical polarity of the Ni-rich LiNi0.8Co0.1Mn0.1O2 core during reversible lithiation/delithiation. This work offers oxide-based surface modifications with precise thickness control at an atomic level for enhanced electrochemical performance of Ni-rich cathode materials at extended voltage ranges.

Control Quality of Composite Materials by Using Subminiature Eddy Current Transducers

Based eddy current transducer (ECT), a probe has been designed to research composite materials. Defects inspection of composite materials is performed to determine the following standard defects: defect of the metallic and (or) polymer layer uniformity. The subminiature ECT of the original design is used as a sensor in this device, it is made according to a differential scheme of switching on of the coils of a transformer ECT and allowing to localize the control area up to 0.1-0.5 mm. The measurement procedure allowing one to detect defects in composite materials with a high accuracy is described. The sensor was tested on the composite material consisting of paper or low-density polyethylene and aluminum layers in which the model defect was placed. The dependences of the ECT signal on the defect in this structure are given. The determined dependence of electrical conductivity of composite materials on model defects make it possible to carry out defects inspection of composite materials.

Meniscus Guide Slot-Die Coating For Roll-to-Roll Perovskite Solar Cells

Abstract:Roll-to-roll slot-die coating with a meniscus guide is used to deposit several layers in a P-I-N perovskite solar cell stack, including the perovskite layer. The use of various length meniscus guides as part of the slot-die head allows controlled coating of these layers at a common coating speed. The length of meniscus guide used is optimised and related to the rheology of the coated ink and appropriate choice of meniscus guide length provides a way to avoid flooding of the coated area and improve coating definition. Initial coating trial results suggest the low-flow limit of slot-die coating is still applicable when using a meniscus guide, which is an important and previously unreported observation, application of this theory to meniscus guide coating provides a useful tool for rapidly determining the appropriate coating conditions that can be used as part of a manufacturing process. This is further explored through the deposition of perovskite solar cells by roll-to-roll slot-die coating. The perovskite layer is deposited using a sequential slot-die deposition process using a low toxicity dimethyl sulfoxide ink for the lead iodide layer, it is found that increasing the drying oven temperature and air flow rate can be used to improve the uniformity of the layer but this can also result in deformation of the plastic substrate. Functioning perovskite solar cells are demonstrated using this technique, but a large variation is found between device performances which is attributed to the poor uniformity of the perovskite layer and damage caused to the substrate by excessive heating.

Additive Manufacturing: Assessing Metal Powder Quality Through Characterizing Feedstock and Contaminants

The quality of powder feedstock for additive manufacturing (AM) metal powder bed fusion methods can significantly affect the quality of parts built from it. Particle size distribution (PSD) and shape factors influence flowability as well as the thickness and uniformity of each powder layer in the build box. For high-performance applications such as aerospace, medical, power generation and military, it becomes important to identify critical additional factors: the types, numbers and sizes of particulate contaminants that may be present in the powder. This is true for virgin, used and blended powders. Contaminants may be introduced during powder manufacture (e.g., ceramic insulation fragments from gas atomization equipment), handling (building insulation, talc) or possibly during the build process itself. Contaminants contained within a batch of powder can be physically built into an additive part when they are incorporated into the melt pool, and they can remain as discrete particulates or non-fused interfaces that act as stress concentrators. Their presence may decrease fatigue life by increasing the likelihood of fatigue crack initiation. This article describes three methods to rapidly and quantifiably characterize powder feedstock. (1) Computer-controlled scanning electron microscopy (CCSEM) provides quantitative size and shape parameters, as well as fine surface details from individual images on a particle-by-particle basis in large populations of powder. (2) Energy-dispersive spectroscopy (EDS) can be included, providing insights into variations within a batch of powder, as well as contaminant compositions. (3) For critical applications, the heavy liquid separation (HLS) method physically extracts low-density contaminants from a sample of powder metal down to part-per-billion detection limits to allow direct examination of contaminants and enhance identification and prevention of their sources. Altogether, these methods permit direct comparisons among powder metal samples. Better quantification of powder characteristics aids determination of suitability for end uses.

Overcoming intrinsic defects of the hole transport layer with optimized carbon nanorods for perovskite solar cells.

To overcome the intrinsic chemical-reduction-activity of highly p-doped PEDOT:PSS and improve the open-circuit voltage (Voc) of planar inverted perovskite solar cells, a kind of oxidized carbon nanorods (OCNRs) is developed by a ball-milling/chemical-oxidation method and incorporated into PEDOT:PSS hole transport layer (HTL). The incorporation of OCNRs can increase the work function of the PEDOT:PSS layer, which avoids the energy-level mismatch between the PEDOT:PSS HTL and the HOMO level of the CH3NH3PbI3 perovskite layer, leading to a relatively high Voc of 1.01 V (vs. 0.92 V for the PEDOT:PSS device). Moreover, the introduction of OCNRs into the PEDOT:PSS HTL increases the grain size and uniformity of the perovskite layer, accompanied by the improved charge transport ability. As a result, the fill factor of perovskite solar cells is increased from 75.4% to 81.7%, and the best power conversion efficiency of 19.02% is achieved.

Understanding Thickness Uniformity of Ga2O3 Thin Films Grown by Mist Chemical Vapor Deposition

α–Ga2O3 thin films were grown on a c–plane sapphire substrate by mist chemical vapor deposition in a horizontal furnace. The microstructure of the α–Ga2O3 grown layers was confirmed by X-ray diffraction. The effects of the temperature distribution and velocity field of the mist flow at the surface of the substrate on the uniformity of the epitaxy layers were revealed by numerical simulations and experimental measurements. The thickness uniformity of the thin film was found to be dependent on the position of the inlet and on the flow rate. The suggested configuration for obtaining highly uniform Ga2O3 epilayers is a low flow rate of less than 0.1 m/s and the flow directed from the bottom of the substrate to the top surface of the substrate.

Uncertainty of particle size measurements using dynamic image analysis

Metal powder particle size distribution (PSD) is a critical factor affecting powder layer density and uniformity in additive manufacturing processes. Among various existing measurement methods, dynamic image analysis (DIA) instruments are very appealing for measuring PSD. However, the ‘black box’ nature and complex measurement process inherent to DIA make quantification of uncertainty challenging. A method to establish DIA-based measurement uncertainty based on calibrated powder samples via a scanning electron microscope is described. Uncertainty analysis was performed taking into account uncertainties associated with the calibration of the sample as well as non-similarities of the calibrated sample and the measured sample.

Effect of Heat Treatments on the Anodizing Behavior of Additive Manufactured AlSi10Mg

In this work, the effect of heat treatments on the anodizing behavior of additive manufactured AlSi10Mg material is studied. Specimens are subjected to artificial aging or stress release heat treatments, followed by galvanostatic anodizing in sulfuric acid. Optical and scanning electron microscopy are employed to study the microstructure and the oxide layer characteristics. Upon applying the heat treatments, the microstructure shows a gradual evolution from a continuous 3D silicon network toward separate coarse silicon particles in an aluminum matrix. The morphology of the silicon phase is found to be a deciding factor as it determines the fraction of silicon that is oxidized during anodizing. This in turn is found to have a direct impact on the anodizing efficiency and oxide layer uniformity. Thicker and more uniform oxide layers are obtained for the additive manufacture AlSi10Mg specimens after the silicon network is broken up due to the heat treatments.

基于离子束溅射大口径光学元件平坦化层均匀性研究

基于离子束溅射大口径光学元件平坦化层均匀性研究

Fabrication of large scale PS monolayer colloidal crystal film by using a novel secondary self-assembly method for nanoimprint technique

PS microspheres emulsions with different PS diameters of 207 and 378 nm were prepared by using an emulsifier-free polymerization method. A novel secondary self-assembly method which combined the spin coating and the lifting-up method was used to prepare the close-packed PS MCC films. During the process, the PS MCC film was firstly assembled on a glass substrate by a spin coating technique. Secondly, the obtained PS MCC film was transferred on the air-water interface by immersing the PS glass substrate in water using a dip-coater. Thirdly, the floating close-packed PS MCC films on the air-water interface was transferred to a new glass substrate by using a lifting-up method. During the spin-coating and the self-assembly process, some SDS solution was added in the PS films to improve the uniformity of the PS layer. Effects of the spin-coating speeds, the SDS solution concentration and the lifting-up rates on the morphology of PS MCC films have been discussed. Scanning electron microscopy was used to observe the morphological properties of the PS colloidal crystal films. Results indicate that a relatively close-packed and large scale PS MCC films can be obtained when the spinning speed is 2000 rpm for 60 s, the SDS solution concentration is 2 wt% and the lifting-up rate is 2 mm/min. Furthermore, the polydimethylsiloxane soft mold was replicated from the-fabricated PS MCC films and was then imprinted onto the photosensitive hybrid film under UV-irradiation and thus the micro-lens arrays built in the photosensitive hybrid sol–gel film were obtained.

Measurement of the thickness of B4C layers deposited over metallic grids via multi-angle neutron radiography

At the present time, different kinds of thermal neutron detectors are under development at the European Spallation Source research facility, in order to overcome the well-known problem of the 3He shortage. One of these new systems relies on the use of a 3D neutron converter cathode that consists of a stack of aluminum grids, covered by a 0.9 µm 10B enriched boron carbide layer (10B4C). As the conversion efficiency is a function of the boron thickness and the mean free path of the charged particles produced in the neutron induced reaction, the characterization of the boron carbide layer uniformity over the grids becomes crucial. In this work, a non-destructive method to map the thickness distribution of the converter layer over the grids is shown. The measurements exploit the white-beam neutron radiography technique where the specimen is irradiated at different angles. This experiment has been performed at the IMAT beamline operating at the ISIS spallation neutron source (UK). The results confirm that this non-destructive, wide-ranging technique allows a reliable and fast sample characterization and that it may be exploited in similar analyses where equivalent requirements are requested.

Features of a zone thermal crystallization semiconductor thin films grown from a discrete liquid source

We studied the effect of the growth cell geometry on the temperature fields and the uniformity of semiconductor layers grown by thermal crystallization method from a discrete liquid source. Calculation results show that the radius of local sources practically does not change the temperature field of the substrate. When the radius of the local evaporators was changed from 2 to 6.5 mm, the observed increase in the maximum temperature did not exceed 2 K. However, increasing the distance between the substrate and the temperature screen fundamentally changes the temperature of the substrate. An increase in the distance from 2 to 25 mm caused a decrease in the substrate temperature by 20 K. It is shown that to achieve uniformity of better than 90% need to use a hexagonal arranged system of round local sources with the radius of r = 0.6 cm.

Enhanced magnetic properties and reduced core loss of intergranular insulating Fe-Si soft magnetic composites with three-shell SiO2-Fe2SiO4-SiO2 insulating layer

The intergranular insulating Fe-Si soft magnetic composites (SMCs) with uniform three-shell SiO2-Fe2SiO4-SiO2 insulating layer were prepared successfully via simple water oxidation combined with the spark plasma sintering process (SPS). The formation mechanism of the insulating layer and the magnetic properties of the Fe-Si SMCs have been studied systematically. Note that the simple water oxidation process could well ensure the uniformity of the oxide layer consisting of Si and Fe3O4. And then, the high temperature solid-state reactions during the SPS process would result in the conversion of the oxide layer (Si-Fe3O4) to the insulating layer with special three-shell structure (SiO2-Fe2SiO4-SiO2). As a consequent, the Fe-Si SMCs exhibit excellent performance suah as high saturation magnetization (181.9 emu/g), stable effective permeability (60.5) and very low core loss (7.8 W/kg at 50 kHz). The results indicate that the preparation method in this study is simple and effective to produce high performance Fe-Si SMCs used in the field of electromagnetic conversion equipment.

Critical influences of particle size and adhesion on the powder layer uniformity in metal additive manufacturing

The quality of powder layers, specifically their packing density and surface uniformity, is a critical factor influencing the quality of components produced by powder bed metal additive manufacturing (AM) processes, including selective laser melting, electron beam melting and binder jetting. The present work employs a computational model to study the critical influence of powder cohesiveness on the powder recoating process in AM. The model is based on the discrete element method (DEM) with particle-to-particle and particle-to-wall interactions involving frictional contact, rolling resistance and cohesive forces. Quantitative metrics, namely the spatial mean values and standard deviations of the packing fraction and surface profile field, are defined in order to evaluate powder layer quality. Based on these metrics, the size-dependent behavior of exemplary plasma-atomized Ti–6Al–4V powders during the recoating process is studied. It is found that decreased particle size (increased cohesiveness) leads to considerably decreased powder layer quality in terms of low, strongly varying packing fractions and highly non-uniform surface profiles. For relatively fine-grained powders (median particle diameter 17 μm), it is shown that cohesive forces dominate gravity forces by two orders of magnitude leading to low quality powder layers not suitable for subsequent laser melting without additional layer/surface finishing steps. Besides particle-to-particle adhesion, this contribution quantifies the influence of mechanical powder material properties, nominal layer thickness, blade velocity, as well as particle-to-wall adhesion. Finally, the implications of the resulting powder layer characteristics on the subsequent melting process are discussed and practical recommendations are given for the choice of powder recoating process parameters. While the present study focuses on a rigid blade recoating mechanism, the proposed simulation framework can be applied to systems using alternative recoating tools such as soft blades, rakes or rotating rollers.