High Carrier Gas Flow Rates Research Articles

Deposition characteristics and tribological performance of atmospheric plasma sprayed diamond metal matrix composite (DMMC) coatings

Diamond-reinforced metal matrix composites (DMMC) have great potential for wear-resistance applications due to the superior hardness imparted by diamond. Atmospheric plasma spraying involving axial injection of suitable feedstock is a convenient pathway to fabricate DMMC coatings for tribological applications. In this paper, thick DMMC coatings were deposited by plasma spraying Ni–P clad diamond particles under varying spray conditions. It was found that the phase characteristics of DMMC coatings as well as extent of diamond retention and fragmentation were significantly influenced by spray conditions such as, stand-off distance (SOD) and carrier gas flow rate (CGFR). Mechanical characterization (by micro-indentation) on all DMMC coatings developed in this work showed that coatings sprayed with longer SOD and higher CGFR has relatively higher hardness than other two coatings. However, on nanoindentation, the diamond hardness was found overestimated due to effect of diamond roughness on fragmentation. Ball-on-disc wear testing showed excellent tribological properties in all cases, with enhanced wear performance being noted when more diamond is retained in the coating.

Real-time monitoring of atomic layer etching in Cl2/Ar pulsed gas, pulsed power plasmas by optical emission spectroscopy

Optical emission spectroscopy was used as a real-time monitor of the atomic layer etching (ALE) of Si in an Ar inductively coupled plasma (ICP). Pulses of Cl2 gas were repetitively injected into a continuous flow of Ar, followed by the ignition of the ICP and the application of substrate rf bias power (either continuous or rapidly modulated). Optical emissions from Si, SiCl, SiCl2, Ar, and Cl were monitored along a line parallel and close to the substrate surface as a function of time during the bias period, as well as in the ICP without bias power. From an analysis of the time dependencies of the decays of emissions during the modulated bias periods, it is argued that emissions at high Ar carrier gas flow rates are mainly from the primary products sputtered by the energetic Ar ions. Products decay with different, non-exponential time signatures. Cl and SiCl2 emissions decay to nearly undetectable levels toward the end of the bias period. SiCl emission follows a decay profile between that of Si and SiCl2. The time-integrated SiCl2 emission intensity scales linearly with time and correlates with etching rates measured by laser interferometry. The amount of Si etched per ALE cycle and the degree of self-limiting evolution of etching products is a sensitive function of the timing between the initiation and termination of Cl2 flow into the reactor and the application of ICP power. Spatially resolved optical emission is shown to be a useful in situ diagnosis, providing mechanistic insights, as well as process optimization for plasma-assisted atomic layer etching. It is also shown that the emission bands between 360 and 400 nm that are commonly observed during Si etching in a chlorine-containing plasma and are often ascribed to SiCl3 or SiCl3+ are instead most likely the A2Σ → X2Πr system of SiCl.

Highly sensitive detection of polystyrene by on-line splitless pyrolysis-gas chromatography/mass spectrometry with cryo-trapping of pyrolyzates and forced venting of carrier gas

Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) has been extensively used as a powerful tool for polymer analysis. In Py-GC/MS measurements, GC methods have usually employed split injection conditions for qualitative and quantitative analysis, but splitless injection of pyrolyzates to GC/MS has been reported to obtain higher sensitivity for small amount of analytes, since split ratio is inversely related to the amount of analyte entering the detection systems. However, the slower total carrier gas flow rate of splitless injection, which is necessary to keep the column flow rate at around a few mL/min, can increase residence time in the pyrolysis chamber, which can cause unfavorable secondary reactions of pyrolyzates such as decomposition and recombination in the pyrolyzer. In this study, we developed a new on-line splitless Py-GC/MS method called the Forced-Venting-and-Trap-Splitless (F-Splitless) method, based on cryo-trapping of pyrolyzates and forced venting of carrier gas under high carrier gas flow rate. Calibration curves measured by the F-Splitless method for polystyrene (PS) using the styrene monomer and trimer as key compounds show a good linearity over the concentration range from 0.01 ng to 100 ng. Limit of detection (LOD) and limit of quantification (LOQ) were 17 pg and 56 pg for the styrene monomer (S) based on the criterion of LOD: 3σ/a and LOQ: 10σ/a, where a is the slope of the calibration curve and σ is the standard deviation of the peak area of the minimum concentration, using the selected ion monitoring (SIM) mode. At a trace concentration level of PS, contamination from the environment was recognized. However, 100 pg of PS showed a signal to noise ratio (S/N) of 570 for S in SIM mode and 1.8 pg of PS could be quantified according to the criterion of LOQ based on signal to noise ratio (S/N), i.e., S/N = 10.

Low chlorine oil production through fast pyrolysis of mixed plastics combined with hydrothermal dechlorination pretreatment

Fast pyrolysis of the mixed plastics (PE: PP: PS: PVC = 0.5: 0.3: 0.15: 0.05) with and without hydrothermal dechlorination pretreatment were investigated in a fixed bed reactor to determine the effects of pyrolysis parameters (temperature, carrier gas flow rate and particle size) on the distribution and the quality of the products. The results showed that high pyrolysis temperature, high carrier gas flow rate and small particle size promoted the migration of organic chlorine in condensable products to inorganic chlorine in gas products. And the optimal conditions for fast pyrolysis of mixed plastics to produce oil were the pyrolysis temperature of 500 °C, carrier gas flow rate of 40 ml/min and particle size of 0.1–0.15 mm with the maximum oil yield of 67.88 wt%. Hydrothermal pretreatment of mixed plastics has shown an excellent dechlorination efficiency of 99.9 %. Furthermore, the total yield of oil and wax was increased by 7.06 wt%, meanwhile the content of C5-C9 components in the pyrolysis oil showed an upward trend when compared with fast pyrolysis without pretreatment. Besides, the concentration of methane achieved 50.68 % due to the possible weakening effect of hydrothermal pretreatment on CC bond energy of β-position.

Analysis of Gas-Solid Multi-Phase Flow Around a Deposit in Directed Energy Deposition

Although metal additive manufacturing (AM) gathers attention from various industries, the process stability in metal AM still remains in an important issue for ensuring the production quality. In particular, powder-based directed energy deposition (DED) is difficult to stabilize because large amount of metal is contentiously molten with a high-power heat source. Furthermore, the material powder flow needs to be precisely converged on the meltpool; otherwise the considerable amount of materials would be wasted. Against these challenges, this study aims to analyze the turbulent flow in the fabrication space for converging the powder trajectories on the meltpool stably and accurately. By constructing a gas-solid multiphase-flow simulation for the coaxial nozzle for DED, the influence of carrier and shield gases on the powder flow is numerically calculated. According to the estimated particle distribution, the particle concentration on the top surface of deposit decrea ses in the higher-layer deposition. Moreover, the particle-flow convergence is enhanced with higher carrier gas-flow rate. These analyses highly agree with the experimental results on powder distribution measured with a laser light sheet system. As a conclusion, it is clarified that the carrier gas supply should be higher at higher layer deposition to keep the powder convergence stable in DED.

Pyrolysing Horse Manure via Microwave-Induced Heating for Bioenergy Recovery

Transforming waste to energy is essential in view of the need to search for greener and more sustainable energy sources. Such transformation of energy is also aligned with the aim of reducing excessive waste generation whilst creating potential biofuel pathways for power generation. In the present study, animal waste in the form of horse manure is being used as feedstock to undergo microwave-induced pyrolysis via a fixed-bed pyrolysis rig. The relationship of the pyrolysis parameters such as pyrolysis temperature of 350 and 550 ?C, carrier gas flow rate of 0.5 and 1.5 L/min and ratio of horse manure to activated carbon blend of 1:2 and 1:1, with the yield of pyrolysed products is studied. The derived pyrolysis products in the form of solid, liquid and gaseous are characterised and quantified. Result shows that the highest yield of solid, liquid and gaseous products obtained are 78.8 wt%, 24.7 wt% and 34.2 wt%. Solid yield is observed to decrease with increasing pyrolysis temperature while gaseous yield shows a reverse trend. Higher carrier gas flow rate is observed to lower the generation of gaseous and liquid yield while increasing the solid yield. Higher amount of activated carbon within the feedstock is seen to lower the solid yield but increase the gaseous and liquid yields. The liquid yield is found to contain 55.78 wt% of phenolic compounds while gaseous product consists of up to 55 vol% of syngas. The control of the operating conditions in pyrolysis rig enables the production of pyrolysis end products in different phases, generating useful bioenergy and biofertilizer products in the context of circular economy.

Pyrolysis behavior of xylan-based hemicellulose in a fixed bed reactor

Investigation on the biomass components pyrolysis behaviors in a lab-scale reactor is a necessary step before its industrialization due to the poor transportability of the findings obtained from the micro-scale pyrolyzer which often neglects the heat and mass transfer effect. In present study, the pyrolysis behavior of xylan-based hemicellulose in a fixed bed reactor was investigated. The residue evolution and bio-oil composition of xylan, xylose, arabinose and glucose show the close relationship of pyrolysis characteristics between xylan and its components. It is noteworthy that the xylan and those mono-sugar units melted during pyrolysis, and many bubbles formed. Investigation of the effect of temperature, material thickness and carrier gas flow rate on the products distribution and bio-oil composition indicates that high temperature promotes the xylan conversion and increases the yield of bio-oil, however, if the temperature is too high (>500°C), violent decomposition of xylan occurs and leads to the formation of low molecular weight compounds (such as hydroxyl acetaldehyde, acetic acid and 1-hydroxyl-2-propaone etc.). And interestingly, the bio-oil yield increases monotonically with the material thickness, and thick material layer can increase the content of furfural in bio-oil. Carrier gas flow rate has a little influence on the xylan char yield, and relative high carrier gas flow rate (>2.55L/min) could decrease the secondary decomposition of primary didehydrated pentose but reduce the bio-oil yield.

Effect of Gas Flow Rates on Quality of Aerosol Jet Printed Traces With Nanoparticle Conducting Ink

AbstractThis paper focuses on the influence of carrier gas flow rate (CGFR) and sheath gas flow rate (SGFR) on the quality of conductive traces printed with nanoparticle inks using aerosol jet printing (AJP). This investigation was motivated by previous results of two AJP specimens that were printed at different gas flow rates and yielded significantly different thermal cycling durability lifetimes. A parametric sensitivity study was executed by printing and examining serpentine trace structures at 15 different combinations of CGFRs and SGFRs. The analysis included quantifying the trace's macroscale geometry, electrical properties, and micromorphological features. Interesting macroscale results include an increase in effective conductivity with increasing CGFR. At the microscale, image processing of high magnification scanning electron microscope (SEM) images of the printed traces revealed that agglomerations of silver clusters on the surface of traces became coarser at higher CGFR and also that agglomerates in the bulk were finer than those on the surface. Crystalline silver deposits were observed at all flow rates. In addition, cross sectioning of the printed traces showed higher incidences of buried cohesive cracking at higher gas flow rates. These cohesive cracks reduce the robustness of the traces but may not always be visible from the surface. The degree of cohesive cracking was seen to be broadly correlated with the coarseness of the surface agglomerates, thus suggesting that the coarseness of surface agglomerates may provide a visible surrogate measure of the print quality. The results of this study suggest that print quality may degrade as gas flow rates increase.

Atomic Layer Deposition on Porous Materials: Problems with Conventional Approaches to Catalyst and Fuel Cell Electrode Preparation

Atomic layer deposition (ALD) offers exciting possibilities for controlling the structure and composition of surfaces on the atomic scale in heterogeneous catalysts and solid oxide fuel cell (SOFC) electrodes. However, while ALD procedures and equipment are well developed for applications involving flat surfaces, the conditions required for ALD in porous materials with a large surface area need to be very different. The materials (e.g., rare earths and other functional oxides) that are of interest for catalytic applications will also be different. For flat surfaces, rapid cycling, enabled by high carrier-gas flow rates, is necessary in order to rapidly grow thicker films. By contrast, ALD films in porous materials rarely need to be more than 1 nm thick. The elimination of diffusion gradients, efficient use of precursors, and ligand removal with less reactive precursors are the major factors that need to be controlled. In this review, criteria will be outlined for the successful use of ALD in porous materials. Examples of opportunities for using ALD to modify heterogeneous catalysts and SOFC electrodes will be given.

Production of Syngas from Controlled Microwave-Assisted Pyrolysis of Crude Glycerol

Conversion of crude glycerol into synthesis gas was studied by using controlled microwave-assisted pyrolysis method. Pyrolysis of crude glycerol in the presence of carbonaceous catalyst was performed in a fixed bed reactor under oxygen-deficient environment using a domestic microwave. The effects of inert carrier gas flow rate and pyrolysis temperature on the product yield were investigated. Characterisation of the gaseous product showed that hydrogen, methane and carbon dioxide are the main components in the gaseous product. High temperature and low inert carrier gas flow rate are effective in pyrolysing crude glycerol due to sufficient energy and residence time for complete cracking of vapour into small gaseous molecules. Peak hydrogen yield of 35.2% by volume was obtained at the carrier gas flow rate of 100 mL/min and 600 °C.

Atomic Layer Deposition Process Modeling and Experimental Investigation for Sustainable Manufacturing of Nano Thin Films

This paper studies the adverse environmental impacts of atomic layer deposition (ALD) nanotechnology on manufacturing of Al2O3 nanoscale thin films. Numerical simulations with detailed ALD surface reaction mechanism developed based on density functional theory (DFT) and atomic-level calculations are performed to investigate the effects of four process parameters including process temperature, pulse time, purge time, and carrier gas flow rate on ALD film deposition rate, process emissions, and wastes. Full-cycle ALD simulations reveal that the depositions of nano thin films in ALD are in essence the chemisorption of the gaseous species and the conversion of surface species. Methane emissions are positively proportional to the film deposition process. The studies show that process temperature fundamentally affects the ALD chemical process by changing the energy states of the surface species. Pulse time is directly related to the precursor dosage. Purge time influences the ALD process by changing the gas–surface interaction time, and a higher carrier gas flow rate can alter the ALD flow field by accelerating the convective heat and mass transfer in ALD process.

Controlled vapour-phase deposition synthesis and growth mechanism of Bi2Te3 nanostructures

This work presents a study on the controlled growth and the growth mechanism of vapour-phase deposited two-dimensional Bi2Te3 nanostructures by investigating the influence of growth conditions on the morphology of Bi2Te3 nanostructures. The formation of a hexagonal plate geometry for Bi2Te3 nanostructures is a consequence of the large difference in growth rate between crystal facets along 〈0001〉 and 〈112¯0〉 directions. Under low Ar carrier gas flow rates (60–100 sccm), the growth of Bi2Te3 nanoplates occurs in the mass-transport limited regime, whereas under high carrier gas flow rates (130 sccm), the growth of Bi2Te3 nanoplates is in the surface-reaction limited regime. This leads to an increase in the lateral size of Bi2Te3 nanoplates with increasing the Ar carrier gas flow rate from 60 to 100 sccm, and a decrease in size for a flow rate of 130 sccm. In addition, the lateral size of Bi2Te3 nanoplates was found to increase with increasing growth time due to the kinetic characteristics of material growth. The proposed growth model provides an effective guide for achieving controlled growth of Bi2Te3 nanoplates, as well as other two dimensional nanomaterials.

Characterization of core-shell structured Ni@GDC anode materials synthesized by ultrasonic spray pyrolysis for solid oxide fuel cells

Core-shell structured NiO@GDC powders with NiO cores and GDC shells were synthesized by ultrasonic spray pyrolysis (USP) with a four-zone furnace. The morphology of the as-synthesized powders can be modified by controlling parameters such as the precursor pH, carrier gas flow rate, and zone temperature. At high carrier gas flow rates, the as-synthesized core-shell structured NiO@GDC powders have raisin-like morphology with a rough surface; this is due to fast gas exhaustion and insufficient particle ordering. The core-shell structured Ni@GDC anode showed considerable electrochemical performance enhancement compared to the conventionally-mixed Ni-GDC anode. The polarization resistance (Rp) of conventionally-mixed Ni-GDC anodes increases gradually as a function of the operation time. Alternatively, the core-shell structured Ni@GDC anode synthesized by USP does not exhibit any significant performance degradation, even after 500h of operation. This is the case because the rigid GDC ceramic shell in the core-shell structured Ni@GDC may restrain Ni aggregation.

Fast gas chromatographic residue analysis in animal feed using split injection and atmospheric pressure chemical ionisation tandem mass spectrometry

Significant speed improvement for instrumental runtime would make GC–MS much more attractive for determination of pesticides and contaminants and as complementary technique to LC–MS. This was the trigger to develop a fast method (time between injections less than 10min) for the determination of pesticides and PCBs that are not (or less) amenable to LC–MS. A key factor in achieving shorter analysis time was the use of split injection (1:10) which allowed the use of a much higher initial GC oven temperature. A shorter column (15m), higher temperature ramp, and higher carrier gas flow rate (6mL/min) further contributed to analysis-time reduction. Chromatographic resolution was slightly compromised but still well fit-for-purpose. Due to the high sensitivity of the technique used (GC–APCI-triple quadrupole MS/MS), quantification and identification were still possible down to the 10μg/kg level, which was demonstrated by successful validation of the method for complex feed matrices according to EU guidelines. Other advantages of the method included a better compatibility of acetonitrile extracts (e.g. QuEChERS) with GC, and a reduced transfer of co-extractants into the GC column and mass spectrometer.

Growth of InAs nanowires with the morphology and crystal structure controlled by carrier gas flow rate

We report on the growth of single crystal InAs nanowires on Si/SiOx substrates by chemical vapor deposition (CVD). Both pure zincblende InAs nanowires and twin superlattice InAs nanowires are produced. We demonstrate that the morphology and crystal structure of these nanowires can be controlled by tuning the H2 carrier gas flow rate in a CVD furnace and show that highly selected growth of twin superlattice nanowires are achieved at high carrier gas flow rates. Our work provides a new route to grow and phase-engineer single crystal InAs nanowires for a wide range of potential applications.

Hot-wire assisted ALD of tungsten films:In-situstudy of the interplay between CVD, etching, and ALD modes

In this work, we investigated an approach of hot-wire assisted ALD (HWALD), utilizing a hot (up to 2000 °C) tungsten (W) wire. Tungsten films were deposited by this method using alternating pulses of WF6 gas and atomic hydrogen (at-H). The latter was generated by catalytic dissociation of molecular hydrogen (H2) upon the hot-wire. The W films were grown on a 100-nm thick thermal SiO2. The growth process was monitored in real time by an in-situ spectroscopic ellipsometer (SE). The real-time SE monitoring revealed the coexistence of three processes: CVD, etching, and ALD of the W film. WF6 could back-stream diffuse to the hot-wire, resulting in WF6 decomposition and generation of a flux of fluorine (F). The latter caused etching of the grown W film and the filament, and provided extra tungsten supply, which might cause CVD. Higher pressure and higher carrier gas flow rate were found to largely suppress the back-stream diffusion of WF6, which efficiently limited CVD. By controlling the dose of WF6 and process pressure, the etching had also been minimized. X-ray photoelectron spectroscopy of optimized HWALD grown W revealed 99 at% of W; concentrations of oxygen and fluorine were lower than 1%, below the detection limit.

PEMBUATAN NANOPARTIKEL SENG OKSIDA (ZNO)MENGGUNAKAN PROSES FLAME ASSISTED SPRAY PYROLYSIS (FASP)

<p>Abstract: ZnO nanoparticles have been succesfully produced using Flame Assisted Spray<br />Pyrolysis (FASP) method. Burner type was a premixed flame reactor that used LPG as a fuel<br />and air as oxidizer because of an economical point of view. Zn(NO<br />3<br />)2<br />was used as a precursor<br />source for ZnO nanoparticles production. The flow rates of carrier gas during ZnO nanoparticles<br />fabrication were 5 L/menit, 7 L/menit, and 9 L/menit. To get the information about size and<br />shape of ZnO nanoparticles was characterized using Scanning Electron Microscope (SEM) and<br />X-Ray Diffractometry (XRD). The results showed that the higher carrier gas flow rate, the bigger<br />size of ZnO nanoparticles. By using the flow rate of carrier gas at 5 L/min, the mean size of ZnO<br />nanoparticles was about 80 nm. ZnO nanoparticles at carrier gas of 5 L/min were hexagonal<br />zincite crystalline structure and XRD were about 30,62 nm<br />Keywords: Flame Assisted Spray Pyrolysis, nanoparticles, ZnO, LPG, SEM, XRD</p>

Evaluation of TiO<sub>2</sub> Films Fabricated by Aerosol Deposition

Films of titanium dioxide (TiO2) were deposited by aerosol deposition at room temperature. Anatase TiO2 powders were used. The crystal structure of these films was a mixture of the anatase and brookite TiO2 phases, while the rutile TiO2 phase was observed at high carrier gas flow rates. The TiO2 film thickness increased in proportion with the scan time and the carrier gas flow rate. Film thickness was constant at constant total deposition times. Flake-like and mesh-like surface morphologies were observed on the films. The direct-current resistivity was estimated from the dielectric constant and the loss tangent; it was found to be much smaller than that of bulk TiO2. We speculate that this low resistivity is due to reduction of TiO2 particles during room-temperature impact consolidation in a N2 atmosphere.

Membrane Interface Probe Protocol for Contaminants in Low‐Permeability Zones

Accurate characterization of contaminant mass in zones of low hydraulic conductivity (low k) is essential for site management because this difficult-to-treat mass can be a long-term secondary source. This study developed a protocol for the membrane interface probe (MIP) as a low-cost, rapid data-acquisition tool for qualitatively evaluating the location and relative distribution of mass in low-k zones. MIP operating parameters were varied systematically at high and low concentration locations at a contaminated site to evaluate the impact of the parameters on data quality relative to a detailed adjacent profile of soil concentrations. Evaluation of the relative location of maximum concentrations and the shape of the MIP vs. soil profiles led to a standard operating procedure (SOP) for the MIP to delineate contamination in low-k zones. This includes recommendations for: (1) preferred detector (ECD for low concentration zones, PID or ECD for higher concentration zones); (2) combining downlogged and uplogged data to reduce carryover; and (3) higher carrier gas flow rate in high concentration zones. Linear regression indicated scatter in all MIP-to-soil comparisons, including R(2) values using the SOP of 0.32 in the low concentration boring and 0.49 in the high concentration boring. In contrast, a control dataset with soil-to-soil correlations from borings 1-m apart exhibited an R(2) of ≥ 0.88, highlighting the uncertainty in predicting soil concentrations using MIP data. This study demonstrates that the MIP provides lower-precision contaminant distribution and heterogeneity data compared to more intensive high-resolution characterization methods. This is consistent with its use as a complementary screening tool.

Hydrodeoxygenation of Guaiacol, A Surrogate of Lignin Pyrolysis Vapors, Over Iron Based Catalysts: Kinetics and Modeling of the Lignin to Aromatics Integrated Process

Biosourced aromatics (BTX (benzene, toluene, xylene) and phenols) could be produced by lignin pyrolysis coupled with catalytic hydrodeoxygenation (HDO) of uncondensed pyrolysis vapors. Guaiacol is used as a model compound to study the catalytic HDO over Fe/SiO2 catalyst. Experiments were conducted in a fixed bed reactor operated at 673 K (1 atm) with a gas mixture (guaiacol, H2, H2O, CO, CO2) that mimics the real gas composition from lignin pyrolysis. Fe/SiO2 catalyst was shown to be selective for guaiacol HDO into benzene and phenols because it does not catalyze the aromatic ring hydrogenation. Major and minor products are modeled by a semidetailed kinetic mechanism. A deactivation law is also determined. The kinetic model is then included in an Aspen Plus model of lignin to BTX process. Aspen Plus model handles (1) pyrolysis of lignin, including char, oligomers, gases and aromatic yields, (2) catalytic conversion of aromatics by the kinetic model, (3) heat exchangers, and (4) BTX vapors recovery by scrubbing with 1-methyl-naphthalene. Mass and carbon balances, heat demand, and selectivity in desired products are given for the overall process. The effect of gas dilution from pyrolysis reactor on BTX losses, heat demand, and scrubbing solvent flow rate is highlighted. High carrier gas flow rates (as required for biomass pyrolysis in fluidized bed) lead to the entrainment of fines and oligomers, dilute the products, and impact considerably the process intensification.