Diffusion Coefficient Of Nitrogen Research Articles

High nitrogen and argon diffusion in cyclic olefin copolymer foil versus temperature

Measurements of nitrogen and argon diffusion coefficient in cyclic olefin copolymer (COC) have been performed at different temperatures ranging between 21 °C and 101 °C. Optical transparent COC foils have been prepared with 10 μm thickness and total surface of about 25 cm2. The foils have exhibited high purity in composition. The morphology of the COC surface has been investigated by Scanning Electron and Atomic Force Microscopies. The room temperature measured diffusion coefficients, of about 6.56 × 10−3 cm2/s and 6.30 × 10−3 cm2/s for N2 and Ar, respectively, have been obtained with a home-made experimental set-up by measuring the gas pressure gradient reduction applied to the two faces of COC thin foils versus the time. The foils show a significant increase of the N2 and Ar diffusion coefficients with the temperature. The native amorphous nature, the obtained nano-porous structure, the damage suffered by the thin foils of COC under high applied pressure are responsible of the evaluated high diffusion coefficients for nitrogen and argon gases. The experimental apparatus to measure the diffusion coefficients vs. temperature, the obtained results, the COC sheets microstructure, the measurements comparison with the literature data and possible COC applications in biomedicine are presented and discussed.

Mechanisms of Growth and Hydrogen Permeation of Zirconium Nitride Film on Zirconium Hydride

Nitride film as a hydrogen permeation barrier on zirconium hydride has seldom been studied. In this work, the zirconium nitride films were prepared on zirconium hydride in an atmosphere of N2 and N2 + H2 at 500~800 °C, with a holding time of 5 h and 20 h, and the mechanisms of film growth and hydrogen permeation were analyzed. The results showed that the film growth was mostly influenced by the temperature, followed by the reaction atmosphere and the holding time. The hydrogen could increase the nitrogen diffusivity during the formation of zirconium nitride films. The in situ nitriding conditions were optimized as 800 °C, N2 + H2 atmosphere, and 5~20 h. The chemical composition of ZrN-based films was mainly comprised of Zr and N, with a minor content of O. In addition, the film exhibited a major phase of ZrN, accompanied by the coexistence of ZrO2, ZrO, ZrN(NH2), and ZrN0.36H0.8, as well as O-H and N-H bonds based on the XPS analysis. The as-prepared ZrN base films in the present study exhibited superior hydrogen permeation resistance to other ZrO2 films previously reported. The hydrogen permeation resistance of the films could be attributed to the following mechanisms, including the chemical capture of hydrogen by the above-mentioned compounds and bonds; the physical barrier of continuous and dense film incurred from the volume effect of different compounds based on Pilling-Bedworth model and the different nitrogen diffusion coefficients at different temperatures.

Mechanical Properties and Diffusion Studies in Wax–Cellulose Nanocomposite Packaging Material

This article focuses on the study related to the estimation of packaging material properties of cellulose–wax nanocomposite using molecular dynamics simulation (MDS). Cellulose based packaging material is gaining lot of importance due to its good material properties and low cost. Cellulose with small amount of plant-derived wax (nonacosane-10-ol and nonacosane-5,10-diol) offers higher mechanical strength and modulus of elasticity compared to the conventional synthetic polymer materials. In this article, in addition to the estimation of mechanical properties, the thermal stability of the proposed ecofriendly cellulose–wax composite is evaluated by estimating the glass transition temperature which essentially provides critical information on the glassy state and rubbery state of this biopolymer. The glass transition temperature of this composite changes significantly compared to that of pure cellulose (which also suffers from poor mechanical strength). Transport properties such as diffusion volume and diffusion coefficient of oxygen, nitrogen, and water are estimated using the results obtained from MDS. The diffusion coefficients of these species within the cellulose–wax composite are analyzed using the diffusion volume and interaction energies of these constituents with the wax and cellulose.

Model of growth kinetics of nitrided layer in the binary Fe–N system

Abstract The mathematical description of the kinetics of a layer development is subjectal to a continuous evolution connected with a growing amount of empirical data. Commencing with attempts to describe selected stages of this process, attempts are made at present to mathematically represent phenomena occurring in a gas atmosphere, on the boundary of gas-metal, and in a nitrided material, together with a description of mutual dependencies between these phenomena. The model proposed in this paper, which describes the growth of the zones of a layer nitrided in conditions of a diffusion quasi-equilibrium, is a simple and convenient tool allowing for both the determination of nitrogen diffusion coefficients in the layer’s monophase zones and for forecasting the growth of the layer’s zones as a function of the time of the process and the nitrogen potential.

Diffusion coefficients of carbon, oxygen and nitrogen in silicon melt

The carbon, oxygen and nitrogen are very important light impurities affecting the quality of silicon crystal used in photovoltaic and semiconductor industry. The diffusion coefficients are key parameters in determining the impurity distribution in the melt and crystal. Unfortunately, these parameters are rarely measured by experiments due to challenges of high temperature and complex flow in the melt during crystal growth. Nonetheless, the liquid diffusion coefficients exist as necessary input parameters in the continuum modelling work of mass transport. Here, we first reviewed the liquid state diffusion coefficients used in the continuum models and found out that they are far from consistency. Then, molecular dynamics simulations are employed to calculate the diffusion coefficients and migration barriers of the carbon, nitrogen and oxygen impurities in silicon melt based on various empirical interatomic potentials. The nitrogen diffusivity in silicon melt is reported for the first time. The calculated diffusion coefficients are generally lower than the values used in most continuum models although consistent across different potentials. This discrepancy is discussed in detail.

Reaction Model Taking into Account the Catalyst Morphology and Its Active Specific Surface in the Process of Catalytic Ammonia Decomposition.

Iron catalysts for ammonia synthesis/nanocrystalline iron promoted with oxides of potassium, aluminum and calcium were characterized by studying the nitriding process with ammonia in kinetic area of the reaction at temperature of 475 °C. Using the equations proposed by Crank, it was found that the process rate is limited by diffusion through the interface, and the estimated value of the nitrogen diffusion coefficient through the boundary layer is 0.1 nm2/s. The reaction rate can be described by Fick’s first equation. It was confirmed that nanocrystallites undergo a phase transformation in their entire volume after reaching the critical concentration, depending on the active specific surface of the nanocrystallite. Nanocrystallites transform from the α-Fe(N) phase to γ’-Fe4N when the total chemical potential of nitrogen compensates for the transformation potential of the iron crystal lattice from α to γ; thus, the nanocrystallites are transformed from the smallest to the largest in reverse order to their active specific surface area. Based on the results of measurements of the nitriding rate obtained for the samples after overheating in hydrogen in the temperature range of 500–700 °C, the probabilities of the density of distributions of the specific active surfaces of iron nanocrystallites of the tested samples were determined. The determined distributions are bimodal and can be described by the sum of two Gaussian distribution functions, where the largest nanocrystallite does not change in the overheating process, and the size of the smallest nanocrystallites increases with increasing recrystallization temperature. Parallel to the nitriding reaction, catalytic decomposition of ammonia takes place in direct proportion to the active surface of the iron nanocrystallite. Based on the ratio of the active iron surface to the specific surface, the degree of coverage of the catalyst surface with the promoters was determined.

Nitrogen diffusion in graphene oxide and reduced graphene oxide foils

Measurements of nitrogen diffusion coefficient in graphene oxide (GO) and reduced graphene oxide (rGO) have been performed at different temperatures ranging between 21 °C and 101 °C. GO and rGO foils have been prepared as thin foils with 15 μm in thickness, total surface of about 5 cm2 and active diffusion surface of about 20 mm2. The rGO foils have been obtained by thermal annealing at 170 °C for 30 min in air. The measured room temperature diffusion coefficients, of 3.43 × 10−4 cm2/s for GO and 5.1 × 10−4 cm2/s for rGO, and, at 101 °C, of 5.22 × 10−4 cm2/s for GO and 10.7 × 10−4 cm2/s for rGO, have been obtained with a simple experimental set-up measuring the gas pressure gradient applied to the two faces of the thin foils versus the time. The rGO foils show a significant increasing of the diffusion coefficients with respect to the pristine GO due to the removing of water and some functional oxygen groups which determines the aperture of nanochannels through which the N2 gas diffuses. The thermal activation energy of nitrogen diffusion is evaluated for the two investigated materials. The experimental apparatus to measure the diffusion coefficients, the obtained results, their correlation with the graphene sheets structure and the comparison with the literature data are presented and discussed.

Nitrogen diffusion in vacancy-rich ferrite and austenite, from first principles to applications

This work contains a systematic study of the diffusion of nitrogen in Ferrite (α-Fe) and Austenite (γ-Fe) from first principles, using a robust multiscale model which combines Density Functional Theory (DFT) and Kinetic Monte Carlo (KMC). Both ferromagnetic BCC Fe and non-magnetic FCC Fe are considered using DFT to drive a diffusion model, which shows strong agreement with experimental diffusion data in literature. Further, quantified predictions are calculated for nitrogen diffusion in iron crystals which are vacancy-rich. It was found that an extended diffusion coefficient of nitrogen can be expressed as a function of nitrogen and vacancy concentration by fitting polynomial coefficients. These are calculated within the 100∘C<T<1538∘C temperature range, and 0.1at.%<cN<1at.% nitrogen concentration range. Moreover, the error of extrapolating the diffusion coefficient outside of the calculated nitrogen concentration range was found to be small at some temperatures. Such insights in vacancy-rich crystals may be useful to nitriding manufacturers, as enhanced diffusion models are an important factor in improving existing processes and avoiding common manufacturing problems such as the egg-shell-effect.

TiO2 doped HKUST-1/CM film in the three-phase photocatalytic ammonia synthesis system

Photocatalytic synthesis of ammonia from N2 and H2O at room temperature and atmospheric pressure is considered to be a safe, clean and sustainable method. Due to the low solubility and diffusion coefficient of nitrogen in water, the rate of ammonia synthesis is significantly hindered. As a result, we develop a kind of thin film photocatalyst, which can be used in gas-liquid-solid three phase reaction system to solve this problem. The catalyst bases on HKUST-1 thin film with high nitrogen adsorption performance and supported with TiO2 nanoparticles with photocatalytic nitrogen fixation performance. The constructed binary composite photocatalyst has a stable structure under a 300 W xenon lamp, which exhibits good photoelectric conversion performance. While characterizing the structure and photoelectric performance of the material, the performance of photocatalytic ammonia synthesis was investigated. The highest ammonia synthesis efficiency was 0.048 μmol·h−1·cm−2, and its performance was 2.8 times that of TiO2/CM catalyst under the same conditions. The thin film catalyst does't contain any N substance and won't interfere with the ammonia synthesis reaction. The preparation process is simplified by directly using the copper source in the CM without additional metal reagent. Moreover, it provides a new idea for the design of photocatalytic catalysts for ammonia synthesis.

Nitriding of 4H-SiC by irradiation of fourth harmonics of Nd:YAG laser pulses in liquid nitrogen

This study presents surface nitriding of 4H-SiC by the irradiation of the fourth harmonics of Nd:YAG laser pulses in liquid nitrogen. A nitride layer with a depth of 1 μm is formed on the irradiated area. The irradiated area has a bumpy morphology. On the other hand, we also find a nitride layer with a smooth surface morphology in the outside of the irradiated area. The concentration of nitrogen is dependent on the laser fluence, and is 1–5%. The diffusion coefficient of nitrogen, which is deduced from the depth profile of the nitrogen number density, is much greater than the diffusion coefficient in solid SiC, suggesting the transport of nitrogen in melted SiC. Considering the fact that SiC does not have a melted state at the atmospheric pressure, it is revealed by the present work that the melted SiC is realized transiently with the help of the high pressure driven by the laser irradiation.

A pressure-decay method to determine influence of a surface-active agent on interface and internal resistances to gas–liquid mass transfer

When gas dissolves into a liquid, interface resistance can limit the mass flux. Increasing or decreasing interface resistance by means of surface-active agents is of interest in applications ranging from biomedicine to petroleum recovery. This paper describes a pressure-decay methodthat allows systematic investigation of both interface resistance and internal (diffusive) resistance during gas-to-liquid mass transfer; introduces a mathematical modeling approach that determines both resistances simultaneously; and provides experiments in which only the interface resistance varies. In the pressure decay method, the system pressure is recorded as gas transfers across the gas/liquid interface and diffuses within the liquid. It allows initiating the experiment at a prescribed pressure with high reproducibility, facilitating the interpretation of a series of experiments. The exact solution of the 1D resistance-in-series model is derived. An accurate approximation is further reported to analyze experiments conveniently. The interface resistance is systematically varied in a static nitrogen/water system by adding small concentrations of oleic acid. As the concentration of oleic acid increases, the mass transfer coefficient decreases or the interface resistance increases. The effect is significant: at a concentration of 2 ppm, at which concentration the interface resistance is almost four times greater than that for pure water. The oleic acid has little effect on the diffusion coefficient of nitrogen in water due to its low concentration. The model comparison indicates the range of Biot number when the interface resistance or internal resistance must be accounted for. The characteristic chart can effectively contribute to a qualitative analysis of the gas–liquid mass transfer process when the effect of surface-active agents is considered.

Nitrogen Diffusion in Vacancy-Rich Ferrite and Austenite, from First Principles to Applications

This work contains a systematic study of the diffusion of nitrogen in Ferrite (α Fe, BCC) and Austenite (γ Fe, FCC) from first principles, using a robust multi scale model which combines Density Functional Theory (DFT) and Kinetic Monte Carlo (KMC). Both ferromagnetic BCC and non-magnetic FCC iron are considered using DFT to drive a diffusion model, which shows strong agreement with experimental diffusion data in literature. Further, quantified predictions are calculated for nitrogen diffusion in iron crystals which are vacancy-rich. In particular, it was found that an extended diffusion coefficient of nitrogen can be expressed as a function of nitrogen and vacancy concentration by fitting polynomial coefficients. These are calculated within the 100◦C < T < 1500◦C temperature range, and 0.01 at.% < cN < 10.0 at.% nitrogen concentration range. Such insights in vacancy-rich crystals may be useful to nitriding manufacturers, as enhanced diffusion models are an important factor in improving existing processes and avoiding common manufacturing problems such as the egg-shell-effect.

Digital holography interferometry for measuring the mass diffusion coefficients of N2 in RP-3 and RP-5 jet fuels

Purpose The purpose of this study is to measure the mass diffusion coefficient of nitrogen in jet fuel using digital holography interferometry for cost-effective designing and modeling of the aircraft tank inerting system. Design/methodology/approach The mass diffusion coefficients of N2 in RP-3 and RP-5 jet fuels were measured by digital holography interferometry at temperatures ranging from 278.15 to 343.15 K. The Arrhenius equation is used to adequately describe the relationship between mass diffusion coefficients and temperature. The viscosities of RP-3 and RP-5 jet fuels were also measured to examine the accuracy of the Stokes–Einstein model in calculating mass diffusion coefficients. Findings As temperature increases from 278.15 to 343.15 K, the mass diffusion coefficients increase 4.23-fold for N2 in RP-3 jet fuel and 5.13-fold for N2 in RP-5 jet fuel. The value of Dµ/T is not constant as the Stokes–Einstein equation expressed, but is a weak linear function of temperature. Practical implications A more accurate diffusion model is proposed by fitting the measured Dµ/T with the temperature and calculating the mass diffusion coefficients of N2 in RP-3 and RP-5 jet fuels within 10 per cent relative deviation. Originality/value A measurement system for mass diffusion coefficients of N2 in RP-3 and RP-5 jet fuels was constructed based on the digital holography interferometry. The mass diffusion coefficient can be expressed by a uniform polynomial function of temperature and viscosity.

Solubilities and diffusion coefficients of carbon dioxide and nitrogen in poly(methyl methacrylate) at high temperatures and pressures

The solubilities and diffusion coefficients of carbon dioxide (CO2) and nitrogen (N2) in poly(methyl methacrylate) (PMMA) were studied at temperatures of 373 K–473 K and pressures of up to 20 MPa. The solubilities and diffusivities were measured by the gravimetric method using a magnetic suspension balance. The dissolution of CO2 and N2 in PMMA obeyed Henry’s law, with the solubilities of the two gases exhibiting different temperature dependences. Further, the solubility data could be fitted using the Sanchez–Lacombe equation of state. The Henry’s constants for the dissolution of the gases in PMMA indicated that their temperature dependences were similar to those of the gases in polystyrene. Finally, the diffusion coefficients of CO2 and N2 with model analysis suggested that, for both gases, the solubility has a determining effect on the diffusivity. The diffusion coefficients of both gases could be described using the free volume theory.

The enhancement effect of salt bath preoxidation on salt bath nitriding for AISI 1045 steel

A rapid salt bath nitriding technology was primarily developed by conducting salt bath pre-oxidation (SPO) instead of conventional air pre-oxidation (APO). Characterization of the modified surface layer was made by means of optical microscopy, scanning electron microscope (SEM), micro-hardness tester and x-ray diffraction (XRD). The results showed that salt bath pre-oxidation could significantly enhance the nitriding efficiency than conventional air pre-oxidation. Under the same salt bath nitriding parameters, the thickness of compound layer is only 13.3 μm treated by air pre-oxidation, and it is increased to 20.8 μm by salt bath pre-oxidation, more than 60% increased. While nitrided at 560 °C for 120 min, higher cross-section hardness and thicker effective hardening layer are obtained by salt bath pre-oxidation. In addition, kinetics analysis shows that the nitrogen diffusion coefficients were increased significantly by salt bath pre-oxidation and the activation energy of nitrogen atom diffusion (Q) was decreased from 216 kJ·mol−1 and 158 kJ·mol−1, and the enhancement mechanism of salt bath pre-oxidation for salt bath nitriding was discussed.

Experimental investigation of nitrogenation process for heavy rare earth nitrides from their hydrides

We experimentally investigated the nitrogenation process of heavy rare earth (Gd, Tb, Dy, Ho and Er) hydrides dynamically by thermal analysis. The onset temperature of nitrogenation and the absolute value of nitrogenation enthalpy increased as the atomic number of the heavy rare earth elements increased and the onset temperature of nitrogenation with a sharp exothermic peak exhibited a large gap between Tb (406 °C) and Dy (806 °C). The reaction route R→RHx→RN has been done at a relatively low temperature and atmospheric pressure, indicating that the diffusion coefficient of nitrogen into the rare earth hydride is much higher than that of nitrogen into the rare earth metal and/or the activation energy of RHx→RN is lower than that of R→RN. For complete nitriding, ErN requires the highest nitrogenation temperature of at most 1000 °C in N2 flow from ErHx. We obtained the magnetic entropy change ΔS of -14 J/kg K (144 kJ/m3 K, calculated by using the theoretical density of 10.3 g/cm3) at ΔH = 2 T for HoN prepared at the nitrogenation temperature of 1000 °C. This value reached the reported value, indicates that this simple synthesis route without any toxic compounds as a precursor and with normal equipment of an atmospheric furnace without high temperature and pressure can adequately exploit the ability of the rare earth nitride as a magnetic refrigerant for magnetic refrigeration.

Molecular Dynamics Study on Mechanical Properties of Cellulose with Air/Nitrogen Diffusion Behavior

Two hybrid models of cellulose and heat transfer media were designed to simulate changes of cellulose and gas during the heat treatment of wood. The chosen heat transfer media were air and nitrogen, and the range of selected simulation temperature was from 450 to 510 K. The diffusion coefficients of air and nitrogen both increased as the temperature increased, and the diffusion coefficient and amplification of air were larger than that of nitrogen. In addition, the calculation of free volume (fraction) confirmed this conclusion. The mechanical parameters of cellulose were analyzed in terms of the Young's modulus, Poisson's ratio, and the ratio of bulk modulus to shear modulus (K/G), which were affected by the temperature and heat transfer medium. Compared with the nitrogen model, the cellulose in the air model decreased in the Young's modulus and K/G as the temperature increased, while the Poisson's ratio increased. Young's modulus and K/G were larger when the heat transfer medium was nitrogen, and the Poisson's ratio was superior to nitrogen in the air environment. The rate of change of mechanical parameters of cellulose in the air system was greater than that of nitrogen, which was related to the larger diffusion coefficient of air.

Kinetics comparison between plasma oxynitriding and plasma nitriding and the application for AISI 1045 steel

ABSTRACTPlasma oxynitriding (PON) and plasma nitriding (PN) were carried out for AISI 1045 steel, and kinetics of the two cases were analysed and compared. Kinetics equations of and were obtained for PON and PN, respectively, which illustrates that much higher nitrogen diffusion coefficient and much lower activation energy for PON. Meanwhile, the reliability of obtained kinetics equations were verified by checking the agreement between the calculated compound layer thickness and those measured from the cross-sectional microstructures. The results confirmed the practicability of the kinetics equations.

Time-varying diffusion characteristics of different gases in coal particles

Based on the analytical solution of gas diffusion in spherical coal particles with a constant diffusion coefficient, a calculation method of time-varying diffusion coefficient is proposed by constructing objective function. The time-varying diffusion behavior of methane, nitrogen and carbon dioxide in the coal particles was studied. The results show that with the increase of diffusion time, the diffusion coefficients of methane, nitrogen and carbon dioxide gas in the coal particles exhibit an attenuation characteristic, eventually approaching a limit value individually. The diffusion coefficient of carbon dioxide is larger than methane, and the diffusion coefficient of nitrogen is smallest. Significant phenomenon of limited diffusion was observed for coal of strong adsorption capability. Through the analysis of the diffusion coefficient of gases at different diffusion time, a mathematical model describing the time-varying diffusion characteristic of gases is obtained. The implementation of mixed gases to replace coal bed methane has a very important practical significance.

Nitrogen Diffusion and Stresses during Expanded Austenite Formation in Nitriding

Low-temperature nitriding of austenitic stainless steels or chromium containing alloys can produce expanded austenite, known as S-phase, with combined improvement in wear and corrosion resistance. In the paper a critical review of various models for nitrogen diffusion during nitriding is presented. A special attention is paid to the expanded austenite growth. A new model based on bi-velocity method and including stresses is presented. Basic equations and boundary conditions are discussed. Composition dependent nitrogen diffusion coefficient is assumed. Numerical solutions are obtained for the growth of the S-phase layer in steel. The results are compared with previous experiment and calculations.