High Nitrogen Flow Rate Research Articles

Microstructure and mechanical property of high-density 7075 Al alloy by compression molding of POM-based feedstock

Metal injection molding of aluminium alloy (MIM-Al) attracts attention, owing to the lightweight, corrosion resistance and good thermal conductivity. However, it is hard to fabricate high-quality MIM-Al due to the hard-to-sinter powder and poor mechanical properties. Here, we report a facile compression molding process for fabricating high-density 7075Al alloy parts using polyformaldehyde (POM)-based feedstock. Pressureless sintering with a high nitrogen flow rate was adopted to promote sintering densification process. The wetting behavior, rheological properties, and morphology of the feedstock were characterized, showcasing the shear-thinning behavior and suitable viscosity for POM-PP-SA binder. Through controlling the compact pressure, mold temperature and holding time, green gear part with good shape retention and dense microstructure was achieved. Influence of process factors and sintering temperature on the microstructure and mechanical properties of 7075Al alloy are investigated. Remarkably, the aluminum alloy components sintered at 610 °C exhibited excellent performance, with a relative density reaching 97.6 % and a tensile strength of 214.8 MPa. This achievement provides a foundation for the industrial application of complex-shaped aluminum alloy components through the compression molding process.

Thermal degradation of polyamide 66 and its model compound

Thermal degradation of N, N'-dibutyladipamide and polyamide 66 (PA66) was carried out in a large-scale experimental setup with nitrogen sweeping in order to collect elusive degradation intermediates. At a high nitrogen flow rate, 1-butylazepane-2,7-dione was identified as a major degradation product from the thermal decomposition of N, N'-dibutyladipamide. Upon heating, 1-butylazepane-2,7-dione produced cyclopentanone and its derivatives, dibutylurea and a nitrile that constituted the majority of degradation products of N, N'-dibutyladipamide, proving that the 7-membered heterocycle compound is a crucial primary degradation product as well as a precursor for the secondary degradation products of N, N'-dibutyladipamide. Subsequently, chemistry concerning the generation and decomposition of 1-butylazepane-2,7-dione was developed for the thermal decomposition of DBA. On the other hand, hexamethylenediamine, 1,8-diazacyclotetradecane-2,7-dione, cyclopentanone and its derivatives were collected as important degradation products from the thermal decomposition of PA66. In view of the structural similarity between DBA and PA66 and their comparable degradation products, a mechanism centering on the generation and decomposition of a 7-membered ring has ultimately been established for thermal degradation of PA66.

Development of maldistribution of humid nitrogen condensing flow and the blockage in parallel channels

Maldistribution in parallel flow fields reduces the performance of proton exchange membrane fuel cells (PEMFCs) and heat exchangers. In this study, a condensing flow experiment was conducted in which water vapor condensed while humid nitrogen flowed through a parallel flow field with eight channels. The flow maldistribution across channels and blockage in channels induced by condensed water were investigated by measuring the flow rates in the channels and the pressure drop across the flow field. The results show that the development of the condensing flow can be divided into developing and quasi-steady stages according to the evolution of the flow rate and pressure drop. At a high nitrogen flow rate, the maldistribution was more severe during the developing stage than during the quasi-steady stage. In contrast, at a low nitrogen flow rate, the maldistribution was more severe in the quasi-steady stage, which can be attributed to the complete blockage induced by liquid water in the channels in this stage. Finally, at low nitrogen flow rates, the extent of maldistribution and duration of complete blockage decreased remarkably with an increase in the water molar fraction.

Hydrogen peroxide sensing with nitrogen-doped carbon nanowalls

The fabrication of miniaturized, low-cost, enzyme-free sensors based on nanomaterials via high-performance techniques is expected to provide important benefits for applications in biological detection. In this work, nitrogen-doped carbon nanowalls (CNWs) were synthesized and used to fabricate electrochemical sensor for hydrogen peroxide (H2O2) sensing. The CNWs were grown on Ti\\SiO2\\Si substrates by radical-injection plasma-enhanced chemical vapor deposition (RI-PECVD) method with different nitrogen concentration. Structural and morphological properties of the obtained CNWs were analyzed using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron microscopy. Cyclic voltammetry and chronoamperometry were used to analyze the electrochemical properties of N-doped CNWs. This study demonstrates the effectiveness of CNWs doping with nitrogen during the synthesis process to improve the electrochemical characteristics of the sensor. It was shown that CNWs doped at high nitrogen flow rate (N2: 20 sccm) exhibited the highest amperometric response. Cyclic voltammetry results indicate that the CNWs doped at high nitrogen flow rate demonstrate excellent electrochemical activity for the reduction of H2O2. These results could pave the way for the development of easy-to-manufacture and highly efficient metal-free biosensors for H2O2 detection.

Effects of buffer gas on N-doped graphene in a non-thermal plasma process

A non-thermal plasma process based on a magnetically stabilized gliding arc discharge (MSGAD) at atmospheric pressure is developed for the synthesis of nitrogen-graphene nano-flakes (N-GNFs). Using propane as a precursor, N-GNFs with low relative amounts of bonded oxygen, large specific surface area (200–500 m2/g) and nitrogen doping level of 1–3% are produced by adjusting the buffer gas of the reaction system. N-doping is confirmed by X-ray photoelectron spectroscopy, Raman spectroscopy, and elemental CNHSO analysis. The effects of buffer gas on N-GNFs are investigated. It is found that the nitrogen configuration is always dominated by pyrrolic nitrogen. A high nitrogen flow rate with a total flow rate constant promotes a higher doping level of N, but more defects appear. The addition of NH3 or H2 further increases the nitrogen doping level, and eliminates some defects. Different buffer gases lead to different types and concentrations of active species, which is a key factor in the synthesis of nitrogen-doped graphene.

Growth and characterization of Rhenium Nitride coatings produced by reactive magnetron sputtering

In this work, thin rhenium nitride (ReNx) films were deposited by reactive radio frequency (R. F.) magnetron sputtering on H13 steel and polished silicon substrates. To improve adhesion to the substrates, a Ti/TiN bilayer was deposited before the ReNx films. Substrate temperature, R.F. power, Ar and N2 gas flow, negative bias voltage, and working pressure were varied in the experiments when synthesizing the ReNx coatings. It was found that lower process pressure and nitrogen flow rate negatively affect the stabilization of coatings and lead to their delamination after they are extracted from the vacuum chamber. Meanwhile, higher nitrogen flow rate and work pressure increase the stability of the coatings by up to several days. Additionally, when the nitrogen flow rate and the negative bias voltage were increased, changes in the crystalline structure of the coatings were observed. However, when the work pressure and N2/Ar ratio were increased and the bias voltage was decreased, the stability of ReNx coatings continued even several weeks after their deposition. X-ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD) measurements validated the formation of ReN compound. The more stable deposited rhenium nitride coatings exhibited lower hardness values than the theoretical predictions for this compound, possibly due to the presence of metallic rhenium and thereby rhenium oxides, as seen in the XRD and XPS characterizations.

The effect of step-wise surface nitrogen doping in MPECVD grown polycrystalline diamonds

Optical centres embedded via nitrogen doping in polycrystalline diamonds (PCDs) are becoming increasingly useful for several wide-area applications including magnetic field sensing. Therefore, investigating the effect of step-wise surface nitrogen doping in PCDs deposited at low pressure is essential. In this study, the influence of a step-wise surface nitrogen doping process on PCDs has been investigated to explain the dominance of neutral charged NV (NV0) centres in PCDs deposited at low pressure in a chemical vapour deposition (CVD) chamber. The surface properties of the films were probed using Raman spectroscopy, Photoluminescence spectroscopy (PL), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS) and Grazing Incidence X-ray Diffractogram (GIXRD). The results obtained from Raman analysis and corroborated by SEM micrographs show the formation of nanocrystalline diamonds (NCDs) with a large quantity of sp2/a-C (amorphous carbon) phases at low nitrogen flow rates on the surface of the doped PCDs. Conversely, increasing nitrogen flow rate ([N/C] > 0.0025) reduced the formation of nano-grains resulting in a decrease in the sp2/a-C contents in the grains and grain boundaries. The increase in the [N/C] ratio and a decrease in the sp2/a-C content at a high surface nitrogen flow rate (10 sccm) enhanced the formation of negatively charged nitrogen-vacancy (NV−) centres. Furthermore, it was shown that the occurrence of stable NV− centres in PCDs deposited at low pressure is also a function of the grain boundary line density: grain boundary line density increases at low surface nitrogen concentration thereby quenching the PL intensity of NV− centres. Samples doped with high surface nitrogen have surface roughness of less than 10 nm. The low surface roughness of highly doped films will optimize the performance of magnetometers that uses these diamond films as NV detectors. Our results give a better understanding of the formation of negatively charged NV centres in PCDs deposited at low pressure.

The Surface Morphology of a Ti–6Al–4V Fiber-Lasered Nitride Layer

A fiber laser was used to nitride Ti–6Al–4V titanium alloy the effect of the process parameters on the surface morphology was studied. The surface chemical composition of the nitride layer and the phase of black powder on the surface were analyzed, the two-dimensional and three-dimensional surface topography of the nitride layer surface were measured, and the cross-section microstructure of the nitride layer was photographed. The effects of laser power, laser scanning speed, nozzle distance, and nitrogen flow rate on the surface morphology were studied. The experiments show that the laser power mainly affects the surface oxidation, the laser scanning speed mainly affects the surface roughness, and the nozzle distance has a great influence on the surface morphology. The gas flow rate, however, had a slight effect on the surface morphology. A large heat input and a high nitrogen flow rate caused an increase in TiN and TiO2 black powders. Surface oxidation did not affect the formation of a continuous TiN layer nor surface roughness. Finally, the critical energy density leading to increased surface roughness was calculated.

SURFACE MORPHOLOGY OF SPUTTERED TITANIUM-ALUMINUM-NITRIDE COATINGS

A study on the surface morphology of sputtered TiAlN coatings is presented. The coatings were deposited by DC magnetron sputtering on tungsten carbide insert tools. The surface morphology was characterized by using Atomic Force Microscopy (AFM), and the surface roughness was indicated by RMS roughness value. It was observed that the TiAlN coating surface morphology was rough as the negative substrate bias and nitrogen flow rate are increased. The evolution of the sputtered TiAlN coatings surface morphology was due to the competition between particle diffusion and re-scattering effect during the sputtering process. At high negative substrate bias and nitrogen flow rate, the re-scattering effect was prominent, leading to the high roughness of the sputtered TiAlN coating surface.

GROWTH STRUCTURE EFFECT ON THE CORROSION RESISTANCE AND MECHANICAL PROPERTIES OF CrNx COATING

A new approach was adopted to improve the corrosion behavior of the chromium nitride (CrNx) hard coating through magnetron sputtering deposition at different nitrogen flow rates. The influence of the nitrogen flow rates on the chemical composition, microstructure, mechanical property and corrosion behavior in artificial seawater of the CrNx coatings was investigated. The results show that with the increase of the nitrogen flow rates, the growth structure of the coatings varied from dense granular growth to coarse columnar growth. Increasing the nitrogen flow rates was helpful to decrease the Cr/N ratio and induce the phase transforming from mixed hexagonal Cr2N and face-centered cubic CrN to single CrN. However, the coatings under different nitrogen flow rates significantly improved the corrosion resistance and hardness of the steel substrate. Furthermore, at high nitrogen flow rate, the coating had high corrosion velocity and low protective capability against the substrate corrosion due to the fast corrosion channels acted by the columnar grain boundaries. While at the middle nitrogen flow rate, the coating with CrN phase, densely granular growth structure and moderate grain size resulted in excellent corrosion resistance and highest hardness.

Changes of the Physical Properties of Sputtered InGaN Thin Films Under Small Nitrogen Gas Flow Variations

In this research work, InGaN triple compound was grown under low nitrogen gas flows by using the sputtering technique. The structural, optical and morphological characteristics of the InGaN compound have been studied in detail. X-ray diffraction (XRD) and Raman for structural analysis; absorption measurement technique for optical properties; scanning electron microscopy and atomic force microscopy (AFM) measurement techniques were used for the study of the morphological characteristics. In the XRD analysis, the film deposited at 0 sccm gas flow exhibits a (0002) peak of InN, (0002) and (10–11) peaks of GaN. Other films show dendritic structure. In the Raman analysis, the optical phonon modes of the InGaN compound are A1(LO) and E2(high). Optical band gaps are found to be 2.57 eV, 2.54 eV, 3.03 eV and 2.93 eV for 0–0.4–0.8–1.2 sccm, respectively. These changes are ascribed to the degraded crystallinity of the grown films at high nitrogen flow rates. The surface morphology of the InGaN films grown at 0 sccm displays clusters of near-spherical-shaped nanoparticles over the surface. In the results of the AFM, the surface topography of the InGaN thin films deposited with lower nitrogen content exhibited fewer grains on the surface, especially on 0.4 sccm gas flow rate. The number of grains increased with higher N2 gas flow rates. The surface roughness of the films decreased with increasing N2 gas flows. It is clear that surface morphology of the films depends on the gas flow rate very much. Due to their morphological properties, we can say that they are suitable structures for optoelectronic applications and friction applications in engineering. We can also say that films with a hexagonal crystal structure and different optical band gaps can be used in device applications such as LED, laser diode and power electronics.

Preparation of high-purity α-Si3N4 nano-powder by precursor-carbothermal reduction and nitridation

The high-purity α-Si3N4 nano-powder without any β-Si3N4 impurities was prepared by using a precursor-carbothermal reduction and nitridation method, and the detailed technical parameters were optimized. Using HNO3 and CO(NH2)2 as reaction raw materials, C6H12O6·H2O as carbon source and SiO2 as silicon source, a porous precursor was prepared at 350 °C, in which the SiO2 particles were uniformly distributed and in full contact with C. This precursor can be transformed into high-purity α-Si3N4 nano-powder under such optimal technical conditions as the nitriding temperature of 1500 °C, the nitriding duration of 1 h and the nitrogen flow rate of 1800 ml/min. As intermediate products, SiO and Si2N2O were considered to be involved in the carbothermal process, and the presence of SiO accelerated the carbothermal reaction. Furthermore, the higher nitrogen flow rate took more heat away from the reaction area, suppressing the transformation from α-Si3N4 to β-Si3N4, which might explain why the final products are mainly composed of high-purity α-Si3N4 powder.

The effect of nitrogen flow rate on Acrawax C decomposition and its removal during sintering of Alumix 431D grade powder

ABSTRACTAlumix 431D pre-alloyed powder (ECKA Granules GmbH) containing 1.5 mass% of Acrawax C was used to study the effect of nitrogen flow rate on delubrication and sintering evolution. Mass loss of compacts during heating was controlled by the TG method using a STA Netzsch apparatus coupled with a mass spectrometer. The latter was used to identify the volatile lubricant’s decomposition products. Macro- and microstructural observations of sintered compacts were also performed. The results documented a strong influence of nitrogen flow rate on delubrication and thus on the sintering behaviour of examined powder. High nitrogen flow rate is required to produce the desired sintered compacts. In contrast, at low nitrogen velocity, the lubricant removal is not complete, which leads to the formation of carbonaceous residuals in the form of soot, which in turn significantly impedes densification and deteriorates the sintered products.

Wettability, nanoscratch resistance and thermal stability of filtered cathodic vacuum arc grown nitrogenated amorphous carbon films

Abstract Composition, structure, surface energy, nanoscratch resistance and thermal stability of nitrogenated amorphous carbon films grown by filtered cathodic vacuum arc (FCVA) are studied in this paper. X-ray photoelectron spectroscopy and electron energy loss spectroscopy studies reveal that by controlling the nitrogen flow rate and substrate bias carbon films with different bonding structures and composition are formed. Higher nitrogen flow rate results in higher nitrogen content of the film and the stability of C N bonds. Increasing the nitrogen content of the films (0 to 16 at.%) increases the polar surface energy (10 to 22 mJ/m 2 ) of the films while the dispersive surface energy does not change significantly. Thermal stability of the films strongly depends on the composition and bonding structure. The films deposited at higher substrate bias (300 V) and containing higher nitrogen content undergo graphitization at lower annealing temperatures. There is no significant difference in the scratch resistance of the films at small scratch loads (up to 35 μN). Further increase in the scratch load results in larger scratch depth in the film deposited at high nitrogen flow rate (40 sccm).

Structure and Properties of Nanocrystalline (TiZr)xN1−xThin Films Deposited by DC Unbalanced Magnetron Sputtering

This study aims to investigate the effects of nitrogen flow rate (0–2.5 sccm) on the structure and properties of TiZrN films. Nanocrystalline TiZrN thin films were deposited on Si (001) substrates by unbalanced magnetron sputtering. The major effects of the nitrogen flow rate were on the phase, texture, N/(Ti + Zr) ratio, thickness, hardness, residual stress, and resistivity of the TiZrN films. The nitrogen content played an important role in the phase transition. With increasing nitrogen flow rate, the phase changed from mixed TiZr and TiZrN phases to a single TiZrN phase. The X-ray diffraction results indicated that (111) was the preferred orientation for all TiZrN specimens. The N/(Ti + Zr) ratio of the TiZrN films first increased with increasing nitrogen flow rate and then stabilized when the flow rate further increased. When the nitrogen flow rate increased from 0.4 to 1.0 sccm, the hardness and residual stress of the TiZrN thin film increased, whereas the electrical resistivity decreased. None of the properties of the TiZrN thin films changed with nitrogen flow rate above 1.0 sccm because the films contained a stable single phase (TiZrN). At high nitrogen flow rates (1.0–2.5 sccm), the average hardness and resistivity of the TiZrN thin films were approximately 36 GPa and 36.5 μΩ·cm, respectively.

Infuence of Nitrogen Gas Flow Rate on Nitrogenated Amorphous Carbon Film for Solar Cell Applications

In this paper, the effect of nitrogen gas flow rate on electrical and electronic properties of nitrogen doped amorphous carbon film (a-C:N) by the use of constant +50 V is presented. The flow-rate of nitrogen gas into the furnace was influenced the resistivity as well as conductivity a-C:N film. The resistivity and conductivity of a-C:N films deposited at high nitrogen flow-rate (200 mL/min) produced low resistivity and high conductivity under deposition condition used. The highest resistivity (4.97x107 Ω.cm) and lowest resistivity (2.81x101 Ω.cm) is found at 0 mL/min (undoped) and 200 mL/min. The fabricated solar cell device with the configuration of Au/n-C:N/p-Si/Au for undoped (0 mL/min) and nitrogen doped (200 mL/min) achieved efficiency (𝜂) 0.00111% and 0.00120 %, respectively.

Study of N-doped TiO2 thin films for photoelectrochemical hydrogen generation from water

Abstract The present work deals with nitrogen-doped stoichiometric TiO2:N and non-stoichiometric TiO2−x:N thin films deposited by means of dc-pulsed reactive sputtering for application as photoanodes for hydrogen generation from water, using solar energy. Stoichiometric thin films of TiO2 crystallize as a mixture of anatase and rutile while rutile phase predominates in TiO2:N at higher nitrogen flow rates as shown by X-ray diffraction at grazing incidence, XRD GID. Lack of bulk nitridation of stoichiometric TiO2:N is indicated by valence-to-core X-ray emission spectroscopy, XES, analysis. The energy band gap as well as flat band potential remain almost unaffected by increasing nitrogen flow rate in this case. In contrast to that, non-stoichiometric thin films of TiO2‑x:N demonstrate systematic evolution of the structural, morphological, optical and photolectrochemical properties upon increasing level of nitrogen doping. Pronounced changes in the growth pattern of non-stoichiometric TiO2-x:N upon varied nitrogen flow rate, demonstrated by scanning electron microscopy, SEM, can be easily correlated with the crystallographic properties studied by XRD GID. Relative positions of Kβ’’ XES lines of the TiO2-x:N thin films, which depend strongly on the nature of the ligands and their local coordination, change with the increasing nitrogen flow. Doping of nonstoichiometric titanium dioxide with nitrogen shifts the absorption spectrum towards the visible range and increases considerably the flat band potential which is beneficial for water photolysis.

Photocatalytic effects of reactively sputtered N-doped anatase upon irradiation at UV-A and UV-A/VIS threshold wavelengths

In biomedicine, light induced photocatalysis at implant surfaces has been gaining increasing interest during the last years. In the fields of biofilm attack at dental implant sites, photocatalytic decomposition of proteinaceous conditioning films could be shown recently on polycrystalline anatase coatings. However, for clinical treatments directly at the patient, the commonly applied UV-A is unwanted due to possible cell damage at host tissues. Therefore, in this study, anatase thin films were N-doped during reactive pulse magnetron sputtering, and the respective modifications were investigated for red-shifting, hydrophilization, and efficiency of photocatalytic organic decomposition upon UV-A compared to irradiation at the UV-A/VIS threshold around 400nm wavelengths. Generally, with increasing nitrogen flow during anatase sputtering, the ability of gaining superhydrophilicity or decomposing methylene blue decreased. Anatase sputtered under lowest nitrogen flow rates≤1sccm decomposed human serum albumin films more efficiently upon 405nm irradiation than anatase variants sputtered under higher nitrogen flow rates. Furthermore, undoped anatase could be activated similarly to low-doped variants even upon irradiation at 405nm peak wavelength enabling significant protein decomposition. These findings open the way for clinical applications of undoped and low-doped anatase modifications in cases where biocompatibility requires longer wavelengths than UV-A. Further research is still needed to clarify possible functional advantages of undoped and low-doped anatase modifications for specific biomedical applications at the UV-A/VIS threshold region around 400nm.

Effect of deposition conditions and post deposition anneal on reactively sputtered titanium nitride thin films

Titanium nitride (TiNx) was deposited by reactive sputtering using a titanium target in a nitrogen ambient. Nitrogen flow rate during deposition was varied in order to investigate its effect on film resistivity. Conductivity is found to improve with increasing nitrogen content. Films were then annealed, varying the time and temperature of the anneal. Resistivity was found to decrease with longer annealing time and higher temperature during post deposition annealing. TiNx films showed good thermal and electrical stability upon annealing and did not show any silicon diffusion. It was found that film orientation can influence the resistivity, with [111] oriented films more resistive than [200] oriented films. Moreover, re-crystallization effects brought on by post deposition annealing cause the resistivity to decrease. Films deposited above 20% nitrogen flow rates during deposition were all stoichiometric TiN. However, TiNx deposited at very high nitrogen flow rate was found to be electrically, thermally and morphologically more stable than the ones deposited at low nitrogen flow rates.

The Mechanical and Tribology Properties of Sputtered Titanium Aluminum Nitride Coating on the Tungsten Carbide Insert Tool in the Dry Turning of Tool Steel

The effect of the sputtering parameters on the mech anical tribology properties of Titanium Aluminum Nitride coating on the tungsten cabide insert tool in the dry turni ng of tool steel has been investigated. The coating was deposited using a Direct Current magnetron sputtering system with v arious substrate biases (-79 to -221 V) and nitroge n flow rates (30 to 72 sccm). The dry turning test was carried out o n a Computer Numeric Code machine using an optimum cutting parameter setting. The results show that the lowest flank wear (~0.4 mm) was achieved using a Titanium Aluminum Nitride-coated tool that was deposited at a high su bstrate bias (-200 V) and a high nitrogen flow rate (70 sccm). The lowest flank wear was attributed to high coating ha rdness.