Influence of Si Content on the Oxide Scale Formation of Ni-Based Alloy

2009 ◽  
Vol 79-82 ◽  
pp. 2239-2242
Author(s):  
Chu Lei ◽  
Li Xiang Chen ◽  
Ning Zhang ◽  
Yan Sheng Yin
Keyword(s):  
Oxide Scale ◽  
Effective Diffusion ◽  
Eutectic Structure ◽  
Fast Diffusion ◽  
Austenite Matrix ◽  
Metal Interface ◽  
Outward Diffusion ◽  
Diffusion Paths ◽  
Si Content ◽  
Kinetics Of

Effects of silicon concentrations in Ni-Cr-based alloys on the formation of oxide scales were examined in reduced atmosphere. The morphology and oxide scale were compared based on the Si content. The formation and growth kinetics of the oxide scale are rather sensitive to the alloy microstructures and their corresponding Si contents. Oxide ridges formed on the eutectic structure preferentially, while a thinner and homogeneous oxide scale grew from the austenite matrix. The thicknesses of the oxide ridges and the oxide layer on the austenite matrix are dependent of their corresponding Si contents. The ridge-like feature indicates that the austenite/carbide phase boundaries offer fast diffusion paths for metal atom outward diffusion. The formation of SiO2 sub-layer at the oxide scale/metal interface can act as an effective diffusion barrier for atom outward diffusion.

Structural Imperfections in thin Oxide Films Formed on Some Fe- and Ni-Base Alloys

1970 ◽  
Vol 28 ◽  
pp. 510-511
Author(s):  
L. P. Lemaire ◽  
D. E. Fornwalt ◽  
F. S. Pettit ◽  
B. H. Kear
Keyword(s):  
Oxide Scale ◽  
Oxidation Process ◽  
Short Circuit ◽  
Protective Oxide ◽  
Protective Oxide Scale ◽  
Thin Oxide Films ◽  
Diffusion Paths ◽  
Oxidation Resistant ◽  
Structural Imperfections ◽  
Short Circuit Diffusion

Oxidation resistant alloys depend on the formation of a continuous layer of protective oxide scale during the oxidation process. The initial stages of oxidation of multi-component alloys can be quite complex, since numerous metal oxides can be formed. For oxidation resistance, the composition is adjusted so that selective oxidation occurs of that element whose oxide affords the most protection. Ideally, the protective oxide scale should be i) structurally perfect, so as to avoid short-circuit diffusion paths, and ii) strongly adherent to the alloy substrate, which minimizes spalling in response to thermal cycling. Small concentrations (∼ 0.1%) of certain reactive elements, such as yttrium, markedly improve the adherence of oxide scales in many alloy systems.

Modelling of impregnation of γ-alumina with cobalt and molybdenum salts. CoCl2-(NH4)2MoO4-γ-Al2O3 (aluminate type) system

1987 ◽  
Vol 52 (3) ◽  
pp. 663-671 ◽  
Author(s):  
Jiří Hanika ◽  
Vladimír Janoušek ◽  
Karel Sporka
Keyword(s):  
Effective Diffusion ◽  
Type System ◽  
Catalyst Particle ◽  
Ammonium Molybdate ◽  
Active Components ◽  
Model Set ◽  
Cobalt Dichloride ◽  
Set Up ◽  
Electron Microanalysis ◽  
Kinetics Of

Adsorption data for the impregnation of alumina with an aqueous solution of cobalt dichloride and ammonium molybdate were treated in terms of the Langmuir adsorption isotherm and compared with a mathematical model set up to describe the kinetics of simultaneous impregnation of a support by two components. The effective diffusion coefficients of the two components at 25 °C in a cylindrical particle of alumina were obtained. The validity of the model used was verified qualitatively by comparing the numerical results with the experimental time dependent concentration profiles of the active components in a catalyst particle, measured by electron microanalysis technique.

scholarly journals Drying Kinetics of Noni Seeds

2019 ◽  
Vol 11 (5) ◽  
pp. 250 ◽  
Author(s):  
Wellytton Darci Quequeto ◽  
Osvaldo Resende ◽  
Patrícia Cardoso Silva ◽  
Fábio Adriano Santos e Silva ◽  
Lígia Campos de Moura Silva
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Diffusion Coefficient ◽  
Moisture Content ◽  
Mathematical Models ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Information Criterion ◽  
Drying Kinetics ◽  
Kinetics Of

Noni seeds have been used for years as an important medicinal source, with wide use in the pharmaceutical and food industry. Drying is a fundamental process in the post-harvest stages, where it enables the safe storage of the product. Therefore, the present study aimed to fit different mathematical models to experimental data of drying kinetics of noni seeds, determine the effective diffusion coefficient and obtain the activation energy for the process during drying under different conditions of air temperature. The experiment used noni seeds with initial moisture content of 0.46 (decimal, d.b.) and dehydrated up to equilibrium moisture content. Drying was conducted under different controlled conditions of temperature, 40; 50; 60; 70 and 80 ºC and relative humidity, 24.4; 16.0; 9.9; 5.7 and 3.3%, respectively. Eleven mathematical models were fitted to the experimental data. The parameters to evaluate the fitting of the mathematical models were mean relative error (P), mean estimated error (SE), coefficient of determination (R2), Chi-square test (c2), Akaike Information Criterion (AIC) and Schwarz’s Bayesian Information Criterion (BIC). Considering the fitting criteria, the model Two Terms was selected to describe the drying kinetics of noni seeds. Effective diffusion coefficient ranged from 8.70 to 23.71 × 10-10 m2 s-1 and its relationship with drying temperature can be described by the Arrhenius equation. The activation energy for noni seeds drying was 24.20 kJ mol-1 for the studied temperature range.

Structural analysis of calcium reactive hydride composite for solid state hydrogen storage

2014 ◽  
Vol 47 (1) ◽  
pp. 67-75 ◽  
Author(s):  
Fahim Karimi ◽  
P. Klaus Pranzas ◽  
Armin Hoell ◽  
Ulla Vainio ◽  
Edmund Welter ◽  
...  
Keyword(s):  
Hydrogen Storage ◽  
Composite System ◽  
Structural Investigation ◽  
Sorption Kinetics ◽  
Hydrogen Storage Material ◽  
X Ray ◽  
X Ray Scattering ◽  
Diffusion Paths ◽  
X Ray Absorption ◽  
Kinetics Of

Owing to a theoretical hydrogen storage capacity of 10.5 wt% H2, Ca(BH4)2+MgH2, the so-called calcium reactive hydride composite (Ca-RHC), has a great potential as a hydrogen storage material. However, its dehydrogenation temperature (∼623 K) is too high for any mobile applications. By addition of 10 mol% of NbF5into Ca(BH4)2+MgH2, a decrease of the dehydrogenation onset temperature by ∼120 K is observed. In order to understand the reasons behind this desorption temperature decrement two sets of samples [Ca(BH4)2+MgH2and Ca(BH4)2+MgH2+0.1NbF5] in different hydrogenation states, were prepared. The structural investigation of the above mentioned sets of samples by means of volumetric measurements, anomalous small-angle X-ray scattering (ASAXS) and X-ray absorption spectroscopy (XAS) is reported here. The XAS results show that after the milling procedure NbB2is formed and remains stable upon further de/rehydrogenation cycling. The results of Nb ASAXS point to nanometric spherical NbB2particles distributed in the hydride matrix, with a mean diameter of ∼10 nm. Results from Ca ASAXS indicate Ca-containing nanostructures in the Ca-RHC+0.1NbF5samples to be ∼50% finer compared to those without additive. Thus, a higher reaction surface area and shorter diffusion paths for the constituents are concluded to be important contributions to the catalytic effect of an NbF5additive on the hydrogen sorption kinetics of the Ca(BH4)2+MgH2composite system.

scholarly journals Steam Oxidation of Austenitic Heat-Resistant Steels TP347H and TP347HFG at 650–800 °C

Materials ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 577 ◽  
Author(s):  
Zhiyuan Liang ◽  
Qinxin Zhao
Keyword(s):  
Oxide Scale ◽  
Steam Oxidation ◽  
Oxidation Products ◽  
Oxide Scales ◽  
Metallic Ions ◽  
Breakaway Oxidation ◽  
Outward Diffusion ◽  
X Ray ◽  
Heat Resistant ◽  
Heat Resistant Steels

Steam oxidation of austenitic heat-resistant steels TP347H and TP347HFG at 650–800 °C was investigated. Comprehensive micro-characterization technologies containing Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) were employed to observe and analyze the oxidation products. Results show that breakaway oxidation behaviors were observed on TP347H at 700 °C and 800 °C. The oxidation kinetics of TP347HFG at 650–800 °C followed a parabolic law. The oxide scales formed on TP347HFG were composed of MnCr2O4 and Cr2O3. A thin and protective Cr-rich oxide scale was replaced by Fe2O3 nodules due to the insufficient outward migration of metallic ions, including Cr and Mn at the subsurface of coarse-grain TP347H. Smaller grain of TP347HFG promoted the formation of the compact Cr-rich oxide scales. At higher temperatures, the incubation period for breakaway oxidation of the Cr-rich oxide scale was much shorter because of quick evaporation of the Cr2O3 oxide scale and the slower outward diffusion of metallic ions via the grain boundaries.

Steam Oxidation Behaviour of Ni-Based Alloys

2009 ◽  
Vol 283-286 ◽  
pp. 117-122
Author(s):  
Hisao Fujikawa
Keyword(s):  
Oxide Scale ◽  
Oxidation Resistance ◽  
Industrial Applications ◽  
Steam Oxidation ◽  
Cr Content ◽  
Ni Alloys ◽  
Temperature Parameter ◽  
Time Parameters ◽  
Kinetics Of ◽  
Cr2o3 Layer

The steam oxidation behavior and the oxide scale structure of Ni-based alloys containing 20 to 25 mass% Cr content were studied. The oxidation test was carried out from 550 to 700°C at 50°C intervals for 100 hours in steam. All Ni-based alloys used showed good steam oxidation resistance; higher Cr containing alloys have a little better oxidation resistance than lower Cr containing alloys. The kinetics of the oxidation rate of all Ni-based alloys used was estimated as the temperature parameter in a 100 hour test and as the temperature and time parameters, respectively. These equations could be useful for industrial applications. The oxide scale of Alloy 625 was composed of two layers. The outer layer was composed of needle-like oxides and the inner layer was composed of isometric oxides. The oxide scale was composed of Cr2O3 type. The Cr/Ni ratio in the oxide scale at 700°C was by one order larger than that at 650°C. The oxidation resistance of Ni alloys is maintained by a uniform Cr2O3 layer which is composed of high Cr content.

The Influence of Tiw Barrier Layer on Reliability of AlCu and AlSiCu Interconnects

1995 ◽  
Vol 391 ◽  
Author(s):  
S. Kordic ◽  
R.A.M. Wolters ◽  
R.A. Augur ◽  
A.G. Dirks
Keyword(s):  
Stress Relaxation ◽  
Grain Boundaries ◽  
Barrier Layer ◽  
Void Formation ◽  
Diffusion Paths ◽  
Si Content

AbstractThe influence of a TiW barrier layer on the stress-voiding behavior of AlCu and AlSiCu interconnects is investigated. The results are compared to the same alloys deposited on SiO2- In both cases, AlCu exhibits a notably better voiding behavior compared to AlSiCu. In the case in which the alloys are directly deposited on the TiW barrier without breaking vacuum between TiW and Al(Si)Cu depositions, a significant improvement of the voiding behavior of both alloys is observed. Compared to AlCu, AlSiCu shows worse voiding behavior due to the presence of Si precipitates, which introduce significant extra dislocations and defects in the Al grains. These dislocations and defects are diffusion paths which assist stress relaxation and void formation. In the presence of a TiW barrier part of the Si content of the AlSiCu is consumed during the anneal by the Al-TiW interface, which results in a decreased number of dislocations and defects within the Al grains, and an improved voiding behavior compared to AlSiCu on SiO2-Furthermore, W and Ti diffuse into the grain boundaries of both alloys. The presence of W and Ti in the grain boundaries reduces the amount of Cu depletion from within the grains, which makes both alloys more resistant to stress voiding. The above is supported by Auger and TEM results. The electromigration results of the alloys in question are presented. These show that also with respect to electromigration AlCu is the preferred alloy both on TiW and SiO2.

The influence of water vapor on thermal transformation of boehmite

1992 ◽  
Vol 7 (2) ◽  
pp. 444-449 ◽  
Author(s):  
Zdenek Hrabe ◽  
Sridhar Komarneni ◽  
Ladislav Pach ◽  
Rustum Roy
Keyword(s):  
Water Vapor ◽  
Phase Transformations ◽  
Thermal Transformation ◽  
Nucleation And Growth ◽  
Furnace Atmosphere ◽  
Fast Diffusion ◽  
Thermally Activated ◽  
Activated Processes ◽  
Influence Of Water ◽  
Diffusion Paths

Boehmite compacts and boehmite gels (seeded and unseeded) were annealed at various temperatures in nitrogen and 1 atm water vapor to determine the influence of water vapor on boehmite transformation to new phases, changes in porosity, and morphology. Water vapor was found to accelerate the phase transformations markedly compared to dry N2 treatment. The catalyzing effect of water vapor may be due to its interactions on grain surfaces and generation of fast diffusion paths, resulting in nucleation and growth of new phases. This result shows that control of the furnace atmosphere is a useful variable in thermally activated processes.

Sign in / Sign up

Export Citation Format

Share Document