Low Nitrogen Flow Rate Research Articles

Enhancing wear resistance: In-situ ceramic phase precipitation for strengthening and toughening FeCoNiCrNx high-entropy alloy films

FeCoNiCr high-entropy alloys have attracted widespread attention because of their excellent toughness; however, their insufficient hardness limits their application in wear-resistant films. The introduction of non-metallic elements is an effective method for strengthening high entropy alloys films. In this study, high-entropy alloy films of FeCoNiCrNx with varying nitrogen content were fabricated using reactive magnetron sputtering. The influence of nitrogen content on the structure, mechanical properties, and tribological behavior of these high-entropy alloy films was studied. With an increase in nitrogen content, the FeCoNiCrNx film undergoes amorphization and simultaneous precipitation of Cr2N phases. At lower nitrogen flow rates (0–4 sccm), the film exhibits lower hardness (8.51–10.97 GPa) and poor wear resistance. At moderate nitrogen flow rates (8 sccm), the film exhibits enhanced hardness (12.8 GPa) and toughness, leading to favorable wear resistance (4.04 × 10−6 mm3 N−1 m−1). A further increase in the nitrogen flow rates (12–16 sccm), while raising hardness (13.08–15.17 GPa), leads to a slight reduction in toughness and consequently, a mild decrease in wear resistance (4.37–5.09 × 10−6 mm3 N−1 m−1). A biphase structure design combining FeCoNiCr high entropy alloy and ceramic (Cr2N) improved the strength and toughness of FeCoNiCrNx and significantly enhanced its wear resistance, thus enhancing its application potential.

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.

An Advanced Thermal Decomposition Method to Produce Magnetic Nanoparticles with Ultrahigh Heating Efficiency for Systemic Magnetic Hyperthermia.

Due to the limited heating efficiency of available magnetic nanoparticles, it is difficult to achieve therapeutic temperatures above 44°C in relatively inaccessible tumors during magnetic hyperthermia following systemic administration of nanoparticles at clinical dosage (≤10mg kg-1 ). To address this, a method for the preparation of magnetic nanoparticles with ultrahigh heating capacity in the presence of an alternating magnetic field (AMF) is presented. The low nitrogen flow rate of 10mL min-1 during the thermal decomposition reaction results in cobalt-doped nanoparticles with a magnetite (Fe3 O4 ) core and a maghemite (γ-Fe2 O3 ) shell that exhibit the highest intrinsic loss power reported to date of 47.5 nH m2 kg-1 . The heating efficiency of these nanoparticles correlates positively with increasing shell thickness, which can be controlled by the flow rate of nitrogen. Intravenous injection of nanoparticles at a low dose of 4mg kg-1 elevates intratumoral temperatures to 50°C in mice-bearing subcutaneous and metastatic cancer grafts during exposure to AMF. This approach can also be applied to the synthesis of other metal-doped nanoparticles with core-shell structures. Consequently, this method can potentially be used for the development of novel nanoparticles with high heating performance, further advancing systemic magnetic hyperthermia for cancer treatment.

Titanium nitride, TiXN(1−X), coatings deposited by HiPIMS for corrosion resistance and wear protection properties

The effect of nitrogen content on the structural, mechanical and corrosion properties of titanium nitride (TixN1−x) coatings deposited by high power impulse magnetron sputtering (HiPIMS) is investigated. The XRD results showed a (111) oriented crystalline structure at low nitrogen flow rate Qv(N2), and a mixed (111) and (200) at high Qv(N2). The average grain size was derived from XRD results and was found to increase with increasing N2 flow. The hardness results showed a maximum with variation of nitrogen content. All coatings exhibited excellent protection efficiency in acidic media compared to the uncoated steel samples, with protection efficiency reaching up to 98.9%. For reference, direct current magnetron sputtered (dcMS) coatings were deposited and investigated, confirming the superior performance of the HiPIMS coatings.

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.

Thermally coupled processes in a composite granular mixture (Ni + Al)–(Ti + C)

For the first time combustion of a thermally conjugated granulated mixture consisting of the mixture of Ni + Al and Ti + C granules, differing in burning velocity and temperature has been investigated experimentally in co-current flows of argon and nitrogen. It has been established that in the whole investigated gas flow rates the ignition of Ni + Al granules occurs in the combustion front. The high efficiency of Ti + C donor granules energy usage has been shown, since the time of heat exchange between the granules does not depend on the sample size, but is determined only by the characteristics of internal heat transfer. A strong increase in the burning rate of the composite mixture at low nitrogen flow rates has been explained via interaction of aluminum with nitrogen and effective reduction of heat loss of the donor. The possibility of isolating the target synthesis product was shown even if its melting point is below the adiabatic temperature of combustion of the composite mixture.

Mechanical properties of titanium nitride films obtained by reactively sputtering with hot target

The mechanical properties and morphology of the surface of titanium nitride films deposited by reactive sputtering with a hot target have been investigated. It was founded that films synthesized at low nitrogen flow rate and at high discharge current density have the highest hardness (up to 30 GPa) and Young’s modulus (up to 300 GPa). The analysis of films surface images obtained by atomic force microscopy is carried out. The typical grain size and its shape were determined. Films with the greatest hardness have the largest grains.

Mechanical and Tribological Properties of TiTaBN Graded-Composite Coatings Deposited Using the CFUBMS Technique

ABSTRACTIn this study, TiTaBN graded-composite coatings were deposited utilizing different process parameters on D2 steel and glass substrates using pulsed DC closed-field unbalanced magnetron sputtering (CFUBMS). The morphology and structure of the coatings were analyzed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The hardness and critical load values of the coatings were determined using a microhardness tester and scratch tester, respectively. The tribological properties of the coatings were analyzed in different testing environments using a pin-on-disc tribometer. The properties of the coatings were found to be strongly affected by the coating parameters. The maximum thickness and hardness were obtained at the lowest nitrogen flow rate and highest frequency. Critical load values of coatings were increased with increased nitrogen flow rate. The low nitrogen flow rate and high frequency across the coatings resulted in enhanced tribological properties.

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.

Tribological Properties of the ZrN Coatings by DC Magnetron Sputtering

ZrN thin films were successfully deposited by DC magnetron sputtering on die steel substrates. The objective of this study was to investigate heat treatment on the microstructure, morphology, nanohardness properties determined by X-ray diffraction, field-emission scanning electron microscope (FE-SEM), nanoindentation, and pin-on-disk, respectively. The XRD result shows that ZrN has intensity of (111) and (200) peak after 400 °C for 1 h at lower nitrogen flow rates. The surface of coatings revealed smaller grains and smooth surface under heat treatment. ZrN coatings consisted of lower nitrogen flow rate had much lower friction coefficient, better mechanical properties by annealing treatment process.

Surface/interface analysis and optical properties of RF sputter-deposited nanocrystalline titanium nitride thin films

Titanium nitride (TiNx) thin films were grown by radio-frequency (RF) magnetron sputter deposition by varying the nitrogen content in the reactive gas mixture over a wide range. The effect of nitrogen gas flow rate on the surface and interface morphology, chemical composition and optical properties of TiN thin films was studied employing atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). Analysis of the optical properties probed with SE has shown that films deposited at low (0–5sccm) nitrogen flow rates have the highest absorption at energies <2eV. It was also shown that Lorentz oscillators with energy positions lower than 2eV can be distinguished from the Drude oscillator function during parameter fitting. AFM imaging analysis indicates that the roughness decreases and plateaus at approximately 1.5nm with the introduction of a small N2 flow rate, remaining consistent thereafter. SEM cross-sectional imaging analysis indicates the dense, columnar structure for the films grown at lower nitrogen flow rates. XPS analysis of atomic composition and the chemical states indicate that the atomic composition remained nearly constant while the chemical states varied significantly among the samples as a function of N2 flow rate. XPS analyses confirm the presence of TiNx, TiO2 and TiOxNy. These process–property relationships derived could be useful for defining and expanding the range of optical and electronic applications of titanium nitrides and (oxy)nitrides.

Structural State and Mechanical Characteristics of the ZrN Films Prepared by Sputtering

ZrN films were prepared by magnetron sputtering on die steel substrates. The objective of this study was to investigate the effect of nitrogen flow rate on the microstructure ,morphology, nanohardness properties determined by X-ray diffraction, field-emission scanning electron microscope, nanoindentation, and pin-on-disk, respectively. The XRD shows that ZrN has (111) and (200) preferred orientation under lower nitrogen flow rates. The surface of coatings revealed smaller grains and uniform dense under lower nitrogen flow rates. With increasing the nitrogen flow rates, this result showed ZrN films lead to poor mechanical properties and hardness values. However, films consisted of up high ernitrogen flow rate had much lower friction coefficient.

Fundamental properties of a-SiNx:H thin films deposited by ICP-PECVD for MEMS applications

In this study, the impact of deposition conditions on the properties of amorphous hydrogenated silicon nitride (a-SiNx:H) films using an inductively coupled plasma enhanced chemical vapor deposition technique (ICP-CVD) is evaluated. Due to the large number of experiments – even when taking only the most important synthesization parameters into account such as the total pressure in the deposition chamber, the substrate temperature, the ICP power and the flow rate ratio of N2/SiH4 – a design of experiments-based approach is chosen. As expected, the deposition rate strongly depends on the ICP power and the N2/SiH4 flow rate ratio, respectively. Films in the field of investigation deposited with a high flow rate of N2 labeled as Type I show relatively low mechanical stress values between −50 and +200MPa, but exhibit a strong drift behavior toward compressive stress. Layers deposited at low nitrogen flow rates (Type II), however, yield large compressive stress and are stable as a function of time. The wet etch rate in hydrofluoric acid shows a gap of over two orders of magnitude when comparing the two a-SiNx:H types, indicating strong differences in the chemical composition. Fourier-transform infrared measurements demonstrate that in Type I films the hydrogen is mainly bonded to nitrogen, in contrast to Type II films, where Si–H bonds dominate. Surface related X-ray photoelectron spectroscopy measurements show that Type II layers have higher relative silicon content, while depth profiles yield that the oxygen content Type I films is above 10at.%. This high oxygen content is proposed to be the result of diffusion of H2O into the layer, causing oxidation, and, as a consequence, the drifting behavior of the intrinsic film stress.

Synthesis of TiN/Ti3Al composite coatings on Ti6Al4V alloy by plasma spraying and laser nitriding

The aim of this paper was to develop an in situ method to synthesize the TiN reinforced Ti3Al intermetallic matrix composite (IMC) coatings on Ti6Al4V alloy substrate by using plasma spraying and laser nitriding. The microstructure and mechanical properties of TiN/Ti3Al IMC coatings synthesized at different nitrogen flow rates (NFRs) in laser nitriding were investigated. Results showed that the crack- and pore-free IMC coatings can be made through the proposed method. The morphology of TiN phase and mechanical properties of coatings were strongly dependent on nitrogen NFR in nitriding. The TiN phase exhibited dendrite-like and undeveloped morphology at low nitrogen NFR. At high NFR, the TiN phase showed granular-like morphology. With increasing NFR, the amount of TiN phase in the coating increased, leading to the increment of microhardness and elastic modulus and the decrement of fracture toughness of coating.

Effects of spray drying process parameters on the solubility behavior and physical stability of solid dispersions prepared using a laboratory-scale spray dryer

Purpose: The purpose of this study is to determine the process parameters of the laboratory-scale spray dryer affecting the solubility behavior and physical stability of solid dispersions.Methods: Solid dispersions of the model drug (nilvadipine or nifedipine) and hypromellose (HPMC) (w/w: 1/1) were prepared using the laboratory-scale spray dryer. As process parameters, nitrogen flow rate, sample concentration and pump speed were investigated. The samples were characterized by dissolution tests, powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), scanning electron microscope (SEM), and nanoscale thermal analysis (Nano-TA). The physical stability was monitored after 7 months storage at 25°C.Results: Solubility behavior and physical stability were improved by setting the low nitrogen flow rate and high sample concentration. DSC showed that the physical state depends on the spray drying conditions, whereas, every sample showed the similar morphology from SEM results. The difference of solubility behavior and physical stability were found to come from the microstructural phase separation of the spray dried particles using a novel analytical technique (Nano-TA).Conclusions: This study demonstrated that nitrogen flow rate and sample concentration should be the critical parameters for the enhancements of the solubility and physical stability of solid dispersions.

Exploring Key Parameters to Detect Subtle Ligand-Induced Protein Conformational Changes Using Traveling Wave Ion Mobility Mass Spectrometry

Evidencing subtle conformational transitions in proteins occurring upon small modulator binding usually requires atomic resolution techniques (X-ray crystallography or NMR). Recently, hyphenation of ion mobility and mass spectrometry (IM-MS) has greatly enlarged the potentials for biomolecular assembly structural characterization. Using the well 3D-characterized Bcl-xL/ABT-737 protein model, we explored in the present report whether IM-MS can be used to differentiate close conformers and monitor collision cross section (CCS) differences correlating with ligand-induced conformational changes. Because comparing CCS derived from IM-MS data with 3D-computed CCS is critical for thorough data interpretation, discussing pitfalls related to protein construct similarity and missing sequence sections in PDB files was of primary importance to avoid misinterpretation. The methodic exploration of instrument parameters showed enhanced IM separation of Bcl-xL conformers by combining high wave heights and velocities with low helium and nitrogen flow rates while keeping a high He/N(2) flow rate ratio (>3). The robustness of CCS measurements was eventually improved with a modified IM calibration method providing constant CCS values regardless of instrument settings. Altogether, optimized IM-MS settings allowed a 0.4 nm(2) increase (i.e., 2%) of Bcl-xL CCS to be evidenced upon ABT-737 binding.

Comparison of Oxidation and Microstructure of Warm-Sprayed and Cold-Sprayed Titanium Coatings

Thick titanium coatings were prepared by the warm spraying (WS) and cold spraying (CS) processes to investigate the oxidation and microstructure of the coating layers. Prior to the coating formations, the temperature and velocity of in-flight titanium powder particles were numerically calculated. Significant oxidation occurred in the WS process using higher gas temperature conditions with low nitrogen flow rate, which is mixed to the flame jet of a high velocity oxy-fuel (HVOF) spray gun in order to control the temperature of the propellant gas. Oxidation, however, decreased strikingly as the nitrogen flow rate increased. In the CS process using nitrogen or helium as a propellant gas, little oxidation was observed. Even when scanning electron microscopy or an x-ray diffraction method did not detect oxides in the coating layers produced by WS using a high nitrogen flow rate or by CS using helium, the inert gas fusion method revealed minor increases of oxygen content from 0.01 to 0.2 wt.%. Most of the cross-sections of the coating layers prepared by conventional mechanical polishing looked dense. However, the cross-sections prepared by an ion-milling method revealed the actual microstructures containing small pores and unbounded interfaces between deposited particles.

Role of Temperature and Nitrogen Flow Rate During the Carbothermic Synthesis of SiC/Si3N4 Nanocomposite Powder from Gel

This research article explores the synthesis of SiC/Si3N4 nanocomposite powder via a carbothermic reaction of silica xerogel under nitrogen atmosphere. The influence of both reaction temperature and nitrogen flow rate on the properties of the produced sample was thoroughly investigated. The results revealed that both reaction temperature and nitrogen flow rate played a very important role not only on the composition ratio of SiC/Si3N4 in the finally produced sample but also on the morphology of both phases. At 1300°C, spherical particles of 40 nm grain size for both phases (SiC and Si3N4) were produced, while silicon nitride is the predominant phase. With increasing the reaction temperature, the amount of SiC increased at the expense of the amount of Si3N4 till SiC becomes the predominant phase at 1500°C. At 1500°C, almost both phases have the shape of nanorods with different grain sizes. At low nitrogen flow rate and reaction temperature of 1500°C, SiC predominates while with increasing nitrogen flow rate the Si3N4 becomes the predominant phase. The photoluminescence spectra revealed that a strong emission was observed at 354 and 389 nm for the sample produced at low and high N2 flow rate, respectively. On the other hand, a high surface area of 578 and 471 m2/g were produced for samples prepared under low and high nitrogen flow rate, respectively. Also, the mechanism of formation of the SiC/Si3N4 nanocomposite powder was postulated.

Influence of Operating Variables on Solid Carbons Obtained by Low-Density Polyethylene Pyrolysis in a Semicontinuous Fast Heating Quartz Reactor

Low-density polyethylene (LDPE) was pyrolyzed in a quartz semicontinuous feed reactor with fast heating to obtain solid carbons. Two different carbons were obtained by pyrolysis: pyrolytic carbon deposited on the wall of the reactor and spherical carbon from gas-phase nucleation and growth in the inner part of the reactor. The spherical carbon constituted the major portion of the solid carbon product (95%−99%). A two-factorial experimental design was used to study the influence of pyrolysis variables (temperature, nitrogen flow rate, and LDPE feed rate) on morphology, solid carbon yield, and structure. The yield of LDPE to solid carbon was high (15.3%−49.4%) and increased as the temperature and residence time each increased. Solid carbons with more homogeneous morphology and a higher degree of structural order were obtained at higher temperatures as well as lower nitrogen flow rates and lower LDPE feed rates (both leading to a higher residence time of pyrolytic gases).

Effects of Temperature of In-flight Particles on Bonding and Microstructure in Warm-Sprayed Titanium Deposits

Micron-sized titanium particles were deposited on steel substrates by the warm spraying, which is a modified high velocity oxy-fuel (HVOF) spraying technique. In the process, nitrogen gas is mixed with the HVOF flame jet to lower the temperature of injected powder particles. Detailed observations of splats formed on polished substrates by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were conducted to investigate the effects of particle temperature on the bonding of splats with the substrate and the microstructure within the splats. At lower nitrogen flow rates, the particles observed were heavily deformed and exhibited diverse splat morphologies and microstructures. At higher nitrogen flow rates, most of the particles were impacted in the solid state and the oxidation of particles was remarkably less. The TEM observation revealed distinctively different microstructures within the splats as well as the splat/substrate interfaces depending on whether the particle was molten or solid before the impact.