scholarly journals The Modeling of Nitrogen Mass Transport in CoCr Alloys

2016 ◽  
Vol 36 (331) ◽  
pp. 19-26
Author(s):  
Akvilė Petraitienė
Keyword(s):  
Diffusion Coefficient ◽  
Plasma Nitriding ◽  
Nitrogen Concentration ◽  
Nitrogen Adsorption ◽  
Nitrogen Diffusion ◽  
Depth Profiles ◽  
Swelling Rate ◽  
Cocr Alloy ◽  
Kinetics Of ◽  
Good Agreement

Abstract The kinetics of plasma nitriding of CoCr alloy below temperatures of nitrides formation and mechanisms of nitrogen penetration are analyzed by proposed kinetic modeling in this article. Proposed nitrogen diffusion model is based on the trapping – detrapping (TD) model and developed taking into account the effect of the concentration dependent diffusivity of nitrogen, nitrogen adsorption on the surface of alloy and surface swelling process. The model indicates the influence of chromium atoms to nitrogen atoms diffusivity. The model consists of time and depth dependent diffusion, which is described by a partial differential equation, and it is solved by using Crank – Nicolson finite difference method. By fitting of experimental nitrogen depth profiles, it is shown that nitrogen diffusion coefficient varies with nitrogen concentration according to Einstein-Smoluchowski relation. Nitrogen depth profiles in plasma nitrided medical grade CoCr alloy (ISO 5831 – 12) at T = 400 °C for 1, 4 and 20 hours calculated on the basis of this model are in good agreement with experimental nitrogen profiles. Furthermore, the swelling process is showed and analyzed, derived the dependency of swelling rate on nitriding duration – the swelling rate is inversely proportional to the square root of nitriding duration. The obtained diffusion coefficient value and the swelling process rates satisfy the experimental data form Ref. The derived model explains physical processes during plasma nitriding and allows obtaining nitrogen depth profiles for any requisite nitriding duration.

Effect of Pre-Shot Peening on Plasma Nitriding Kinetics of Austenitic Stainless Steel

2013 ◽  
Vol 634-638 ◽  
pp. 2955-2959 ◽  
Author(s):  
Lie Shen ◽  
Liang Wang ◽  
Jiu Jun Xu ◽  
Ying Chun Shan
Keyword(s):  
Stainless Steel ◽  
Surface Layer ◽  
Austenitic Stainless Steel ◽  
Shot Peening ◽  
Plasma Nitriding ◽  
Nitrogen Diffusion ◽  
X Ray Diffraction ◽  
304 Austenitic Stainless Steel ◽  
Strain Induced Martensite ◽  
Kinetics Of

The fine grains and strain-induced martensite were fabricated in the surface layer of AISI 304 austenitic stainless steel by shot peening treatment. The shot peening effects on the microstructure evolution and nitrogen diffusion kinetics in the plasma nitriding process were investigated by optical microscopy and X-ray diffraction. The results indicated that when nitriding treatments carried out at 450°C for times ranging from 0 to 36h, the strain-induced martensite transformed to supersaturated nitrogen solid solution (expanded austenite), and slip bands and grain boundaries induced by shot peening in the surface layer lowered the activation energy for nitrogen diffusion and evidently enhanced the nitriding efficiency of austenitic stainless steel.

The Effect of Hydrogen on the Kinetics of Solid Phase Epitaxy in Amorphous Silicon

1990 ◽  
Vol 205 ◽  
Author(s):  
J. A. Roth ◽  
G. L. Olson ◽  
D. C. Jacobson ◽  
J. M. Poate ◽  
C. Kirschbaum
Keyword(s):  
Growth Rate ◽  
Solid Phase ◽  
Intrinsic Value ◽  
Amorphous Layer ◽  
Inert Gas ◽  
Solid Phase Epitaxy ◽  
Depth Profiles ◽  
Kinetics Of ◽  
Crystal Interface ◽  
Good Agreement

AbstractThis paper discusses the intrusion of H into a-Si layers during solid phase epitaxy and the effect of this H on the growth kinetics. We show that during annealing in the presence of water vapor, H is continuously generated at the oxidizing a-Si surface and diffuses into the amorphous layer, where it causes a reduction in the epitaxial growth rate. The measured variation of growth rate with the depth of the amorphous/crystal interface is correlated with the concentration of H at the interface. The diffusion coefficient for H in a-Si is determined by comparing measured depth profiles with calculated values. Hydrogen intrusion is observed even in layers annealed in vacuum and in inert gas ambients. Thin (<;5000 Åthick) a-Si layers are especially susceptible to this effect, but we show that in spite of the presence of H the activation energy for SPE derived earlier from thin-layer data is in good agreement with the intrinsic value obtained from thick, hydrogen-free layers.

Influence of Diffusion through a Porous Film under Electrode Surface in Chronoamperometry Problems

2021 ◽  
Vol 413 ◽  
pp. 84-90
Author(s):  
Daniil Bograchev
Keyword(s):  
Diffusion Coefficient ◽  
Electrode Surface ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Electrode Reaction ◽  
Direct Numerical Simulations ◽  
High Porosity ◽  
Kinetics Of ◽  
Stationary Approximation ◽  
Good Agreement

In the presented work on chronoamperometry, the Cottrell model has been generalized by taking into account a thin porosity layer covering the surface of the electrode and Tafel kinetics of an electrode reaction. The effective diffusion coefficient inside a porosity layer is calculated by Bruggeman’s law. It is shown that in the quasi-stationary approximation of diffusion inside a thin porous layer, the chronoamperometry problem can be solved analytically. The obtained solution has been compared with the results of direct numerical simulations and a good agreement is shown. Limiting cases of the solution related to low and high porosity are considered.

Mechanism and Kinetics of Plasma Nitriding of the Nb-Alloyed PM Tool Steel

2007 ◽  
Vol 263 ◽  
pp. 87-92 ◽  
Author(s):  
Pavel Novák ◽  
Dalibor Vojtěch ◽  
Jan Šerák ◽  
Michal Novák ◽  
Barbora Bártová
Keyword(s):  
Tool Steel ◽  
Plasma Nitriding ◽  
Nitrided Layer ◽  
Hot Isostatic Pressing ◽  
Vanadium Content ◽  
Thin Layers ◽  
Nitrogen Diffusion ◽  
Mechanism And Kinetics ◽  
C 30 ◽  
Kinetics Of

The aim of this work was to describe the mechanism and kinetics of plasma nitriding of a Nb-containing PM (powder metallurgy) tool steel. Material containing 2.5 wt.% C, 3.3% Si, 6.2% Cr, 2.2% Mo, 2.6% V, 2.6% Nb and 1.0% W was prepared by nitrogen melt atomization and hot isostatic pressing. Heat-treated steel (quenching from 1100 °C, triple tempering at 550 °C for 1h) was plasma nitrided at temperatures ranging from 470 °C to 530 °C / 30 - 180 min. Light microscopy, TEM, SEM and WDS were used to study the nitrided steel. It has been shown, that nitriding at 470°C leads to the formation of thin layers composed only of a diffusion zone containing nitrogen-rich martensite and fine nitride precipitates, no layer of nitrides is formed on the surface. Nitriding is probably controlled by the nitrogen diffusion in martensite to the material or by the processes in the nitriding atmosphere at this temperature. Nitriding at the temperature of 500°C and more leads to the formation of a continuous layer of nitrides and carbonitrides on the surface that limits further nitrogen diffusion. Niobium, as a prospective element in tool steels, was not found to play a role in the formation of the nitrided layer directly. Niobium replaces vanadium in very thermodynamically stable primary MC carbides. This results in higher vanadium content in others less stable carbides and in the matrix. Due to this effect, higher portion of vanadium can precipitate as VC carbides and VN nitrides during heat treatment and nitriding, respectively.

Rapid Thermal Nitridation of Thin Oxides

1987 ◽  
Vol 92 ◽  
Author(s):  
D.K. Shih ◽  
S.K. Lee ◽  
Y.H. Ku ◽  
D.L. Kwong ◽  
S. Lee
Keyword(s):  
Diffusion Coefficient ◽  
Nitrogen Concentration ◽  
Chemical Properties ◽  
Oxide Surface ◽  
Replacement Reaction ◽  
Oxide Film Thickness ◽  
Pile Up ◽  
Thermal Nitridation ◽  
Kinetics Of ◽  
Nitridation Temperature

ABSTRACTIn this paper the kinetics of initial nitridation of thermal oxides is studied by using rapid thermal nitridation of thin oxides. FTIR and AES were used to investigate the chemical properties of nitrided oxide films. The amount of the nitrogenincorporated in and the oxygen escaped from 100Å oxides has been characterized quantitatively as a function of RTN conditions. Results show that RTN at 1100° for 120s incorporates about 85% and 12% of the maximum nitrogen concentration value at oxide surface and bulk, respectively. The nitrogen pile up peak at interface can be seen after RTN at 1100°C with the time as short as 5 s. Study of the effects of the nitridation temperature and the original oxide film thickness indicates that the reaction species has permeated through oxides before effective replacement reaction takes place. The diffusion coefficient of the permeating species is estimated of the value larger than 40−13cm2/s.

Diffusion model for deposition of epitaxial GaAs layers prepared by the MOCVD method

1991 ◽  
Vol 56 (10) ◽  
pp. 2020-2029
Author(s):  
Jindřich Leitner ◽  
Petr Voňka ◽  
Josef Stejskal ◽  
Přemysl Klíma ◽  
Rudolf Hladina
Keyword(s):  
Experimental Data ◽  
Growth Rate ◽  
Kinetic Model ◽  
Gas Phase ◽  
Substrate Surface ◽  
Deposition Process ◽  
Hydrogen Atmosphere ◽  
Epitaxial Gaas ◽  
Kinetics Of ◽  
Good Agreement

The authors proposed and treated quantitatively a kinetic model for deposition of epitaxial GaAs layers prepared by reaction of trimethylgallium with arsine in hydrogen atmosphere. The transport of gallium to the surface of the substrate is considered as the controlling process. The influence of the rate of chemical reactions in the gas phase and on the substrate surface on the kinetics of the deposition process is neglected. The calculated dependence of the growth rate of the layers on the conditions of the deposition is in a good agreement with experimental data in the temperature range from 600 to 800°C.

Point Contact Current Voltage Measurements of 4H-SiC Samples with Different Doping Profiles

2017 ◽  
Vol 897 ◽  
pp. 287-290 ◽  
Author(s):  
Matthias Kocher ◽  
Michael Niebauer ◽  
Mathias Rommel ◽  
Volker Haeublein ◽  
Anton J. Bauer
Keyword(s):  
Epitaxial Layer ◽  
Depth Profile ◽  
Point Contact ◽  
Surface Preparation ◽  
Epitaxial Layers ◽  
Depth Profiles ◽  
Current Voltage ◽  
Measured Resistance ◽  
Doping Profiles ◽  
Good Agreement

Point contact current voltage (PCIV) measurements were performed on 4H-SiC samples, both for n- an p-doped epitaxial layers as well as samples with rather shallow doping profiles realized by N- or Al-implantation in a range from 1016 cm-3 to 1019 cm-3. Surface preparation and measurement parameters were investigated in order to determine their influence on the measured resistance profiles. Furthermore depth profile measurements were performed on both an epitaxial layer as well as on implanted samples. These depth profiles could be measured reproducibly and showed good agreement with expected profiles for Al-implanted samples as well as for epitaxial layer whereas for N-implanted samples deviations between measured and expected profiles could be observed. It could be proven that PCIV profiling technique is a promising method for characterizing doped profiles in 4H-SiC, especially on Al-implanted samples.

Vulcanization of Elastomers. 23. The Chemical Kinetics of Vulcanization Reactions and The Physical Properties of The Vulcanizates. I

1960 ◽  
Vol 33 (2) ◽  
pp. 335-341
Author(s):  
Walter Scheele ◽  
Karl-Heinz Hillmer
Keyword(s):  
Activation Energy ◽  
Physical Properties ◽  
Chemical Kinetics ◽  
Kcal Mole ◽  
First Order ◽  
Equilibrium Swelling ◽  
Kinetics Of ◽  
Kinetics Of Vulcanization ◽  
Limiting Value ◽  
Good Agreement

Abstract As a complement to earlier investigations, and in order to examine more closely the connection between the chemical kinetics and the changes with vulcanization time of the physical properties in the case of vulcanization reactions, we used thiuram vulcanizations as an example, and concerned ourselves with the dependence of stress values (moduli) at different degrees of elongation and different vulcanization temperatures. We found: 1. Stress values attain a limiting value, dependent on the degree of elongation, but independent of the vulcanization temperature at constant elongation. 2. The rise in stress values with the vulcanization time is characterized by an initial delay, which, however, is practically nonexistent at higher temperatures. 3. The kinetics of the increase in stress values with vulcanization time are both qualitatively and quantitatively in accord with the dependence of the reciprocal equilibrium swelling on the vulcanization time; both processes, after a retardation, go according to the first order law and at the same rate. 4. From the temperature dependence of the rate constants of reciprocal equilibrium swelling, as well as of the increase in stress, an activation energy of 22 kcal/mole can be calculated, in good agreement with the activation energy of dithiocarbamate formation in thiuram vulcanizations.

Defect Structure of MEV Si Implantation in GaAs

1988 ◽  
Vol 126 ◽  
Author(s):  
S.-Tong Lee ◽  
G. Braunstein ◽  
Samuel Chen
Keyword(s):  
Free Surface ◽  
Defect Structure ◽  
Room Temperature ◽  
Surface Region ◽  
Peak Position ◽  
Lattice Disorder ◽  
Depth Profiles ◽  
Trim Calculation ◽  
Good Agreement

ABSTRACTThe defect and atomic profiles for MeV implantation of Si in GaAs were investigated using He++ channeling, TEM, and SIMS. Doses of 1–10 × 1015Si/cm2 at 1–3 MeV were used. MeV implantation at room temperature rendered only a small amount of lattice disorder in GaAs. Upon annealing at 400°C for 1 h or 800°C for 30 a, we observed a ‘defect-free’ surface region (- 1 μ for 3 MeV implant). Below this region, extensive secondary defects were formed in a band which was 0.7 μ wide and centered at 2 μ for 3 MeV implant. These defects were mostly dislocations lying in the [111] plane. SIMS depth profiles of Si implants showed the Si peak to be very close to the peak position of the defects. The experimental profiles of Si were compared to the TRIM calculation; generally good agreement existed among the peak positions.

Reaktionskinetik des Energietransportes zwischen Rekombinationszentren von Elektroluminophoren

1965 ◽  
Vol 20 (12) ◽  
pp. 1648-1654 ◽  
Author(s):  
I. Broser ◽  
H.-E. Gumlich ◽  
R. Moser
Keyword(s):  
Valence Band ◽  
Luminescence Quenching ◽  
Iron Group ◽  
Field Frequency ◽  
Kinetics Of ◽  
Good Agreement

The kinetics of holes in electroluminescence has been calculated by means of simple two- and three-level-models. As a result an equation is given which describes the ratio of intensity of different emission bands and the degree of luminescence quenching by iron group elements as a function of field frequency and temperature. The calculated curves are in good agreement with the values observed in ZnS containing Cu, Mn, Fe, Co, Ni respectively. The kinetics has been used to calculate the energetic separation of acceptor levels from the valence band and other constants.

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