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.

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.

The effect of origin and physico-chemical properties on the kinetics of reduction of mixed NiO-Fe2O3 oxides with hydrogen

1986 ◽  
Vol 51 (10) ◽  
pp. 2098-2108 ◽  
Author(s):  
Milan Pospíšil ◽  
Jan Topinka
Keyword(s):  
Mixed Oxides ◽  
Mutual Influence ◽  
Spinel Phase ◽  
Chemical Properties ◽  
Inhibitory Effect ◽  
Chemical Parameters ◽  
Physico Chemical ◽  
Preliminary Annealing ◽  
Kinetics Of ◽  
Kinetics Of Reduction

We investigated the effect of origin and some physico-chemical parameters on the kinetics of reduction with hydrogen of two series of mixed NiO-Fe2O3 oxides differing by their composition, the character of their precursors (mixed crystalline nitrates and coprecipitated hydroxides) and their decomposition temperature.This effect manifested itself by different magnitudes of specific surfaces of the mixed oxides and coherent regions of present phases as well as by different oxidizing abilities of the surface and differences in morphology and phase composition of corresponding samples in both series investigated. Nonlinear or nonmonotonous composition dependences of physico-chemical parameters investigated point to a mutual influence of individual components, which is also a function of the system origin and which modifies its reactivity during its reduction with hydrogen. The kinetics of the reduction was studied thermogravimetrically at 320-410 °C. The reduction of oxides of the hydroxide origin is catalytically accelerated by primarily reduced nickel, whereas in corresponding samples of the nitrate series, the total NiO is bound to the spinel phase and the reduction is delayed. Experimental IR spectra, the effect of preliminary annealing and DTA of the mixed oxides point to an inhibitory effect of water, which is constitutionally bound in trace admixtures of the goethite phase, on the kinetics of reduction of samples in the hydroxide series.

Di-imide: Some Physical and Chemical Properties, and the Kinetics and Stoichiometry of the Gas-phase Decomposition

1973 ◽  
Vol 51 (21) ◽  
pp. 3605-3619 ◽  
Author(s):  
C. Willis ◽  
R. A. Back
Keyword(s):  
Gas Phase ◽  
Room Temperature ◽  
Chemical Properties ◽  
Phase Decomposition ◽  
Important Intermediate ◽  
Long Lifetime ◽  
Physical And Chemical ◽  
Text Formation ◽  
Kinetics Of

Preparation of di-imide by passing hydrazine vapor through a microwave discharge yields mixtures with NH3 containing typically about 15% N2H2, estimated from the gases evolved on decomposition. The behavior of the mixture (which melts at −65 °C) on warming from −196 to −30 °C suggests a strong interaction between the components. Measurements of magnetic susceptibility and e.p.r. experiments showed that N2H2 is not strongly paramagnetic, which with other observations points to a singlet rather than a triplet ground-state.Di-imide can be vaporized efficiently, together with NH3, by rapid warming, and the vapor is surprisingly long-lived, with a typical half-life of several minutes at room temperature. The near-u.v. (3200–4400 Å) absorption spectrum of the vapor was photographed; it shows well-defined but diffuse bands, with εmax = 6(± 3) at 3450 Å.Di-imide decomposes at room temperature in two ways:[Formula: see text][Formula: see text]Formation of NH3 was not observed but cannot be ruled out. The decomposition of the vapor is complicated by a sizeable and variable decomposition that occurs rapidly during the vaporization. The stoichiometry of this and the vapor-phase decomposition depends on total pressure and di-imide concentration. The kinetics of the decomposition of the vapor were studied from 22 to 200 °C by following the disappearance of N2H2 by absorption of light at 3450 Å, or the formation of N2H4 by absorption at 2400 Å, and by mass spectrometry. The kinetics are complex and can be either first- or second-order, or mixed, depending on surface conditions. The effect of olefin additives on the decomposition was studied, and is also complex.Mechanisms for the decomposition are discussed, including the possible role of trans-cis isomerization. The relatively long lifetime found for di-imide in the gas phase suggests that it may be an important intermediate in many reactions of hydronitrogen systems.

scholarly journals Unexpected Role of Electronic Coupling between Host Redox Centers in Transport Kinetics of Lithium Ions in Olivine Phosphate Materials

2021 ◽  
Author(s):  
Yu Gao ◽  
Jun Huang ◽  
Yuwen Liu ◽  
Shengli Chen
Keyword(s):  
Activation Energy ◽  
Diffusion Coefficient ◽  
Lithium Ion ◽  
Transport Kinetics ◽  
Electronic Coupling ◽  
Lithium Ions ◽  
Kinetics Of ◽  
Olivine Phosphate ◽  
Redox Centers

The discrepancy between the trend in the diffusion coefficient of lithium ion (DLi+) and that in the activation energy of ion hopping signals hidden factors determining ion transport kinetics in...

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.

scholarly journals Effect of Thermophysical Properties on Coupled Heat and Mass Transfer in Porous Material during Forced Convective Drying

2014 ◽  
Vol 6 ◽  
pp. 830387 ◽  
Author(s):  
Wei Cai ◽  
Lexian Zhu ◽  
Shilin Dong ◽  
Guozhen Xie ◽  
Junming Li
Keyword(s):  
Porous Medium ◽  
Diffusion Coefficient ◽  
Temperature Distribution ◽  
Moisture Content ◽  
Initial Conditions ◽  
Positive Impact ◽  
Soret Effect ◽  
Convective Drying ◽  
Large Temperature ◽  
Kinetics Of

The convective drying kinetics of porous medium was investigated numerically. A mathematical model for forced convective drying was established to estimate the evolution of moisture content and temperature inside multilayered porous medium. The set of coupled partial differential equations with the specified boundary and initial conditions were solved numerically using a MATLAB code. An experimental setup of convective drying had been constructed and validated the theoretical model. The temperature and moisture content of the potato samples were dynamically measured and recorded during the drying process. Results indicate that thermal diffusion coefficient has significant positive impact on temperature distribution and mass diffusion coefficient might directly affect the moisture content distribution. Soret effect has a significant impact on heat flux and temperature distribution in the presence of large temperature gradient.

Radiation damage in polyethylene as studied by electron spin resonance

1961 ◽  
Vol 262 (1309) ◽  
pp. 207-218 ◽  
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Alkyl Radical ◽  
Room Temperature ◽  
Chemical Properties ◽  
Resonance Method ◽  
Alkyl Radicals ◽  
Spin Resonance ◽  
Physical And Chemical ◽  
Kinetics Of

The electron spin resonance method was employed to study the nature, concentration and kinetics of the disappearance under varying conditions of radicals produced in polyethylene by fast electron irradiation at 77°K. The predominant radical species at 77°K is the alkyl radical —CH 2 —ĊH—CH 2 —. On being warmed to room temperature it disappears rapidly, revealing a more stable un­identified radical. The kinetics of the decay at room temperature of both radicals was observed. Their stabilities were found to vary in polyethylene samples of differing physical and chemical properties. G values for these radicals are given. Comparison was made with spectra obtained under similar conditions with two pure paraffins and a pure olefin to evaluate the effect of crystallinity branching, molecular weight and unsaturation. In the olefin there is evidence for a build-up of allyl radicals due to the encounter of an alkyl radical with main chain unsaturation. This supports the view that alkyl radicals are mobile, and cross-linking occurs when two such radicals meet.

scholarly journals The Formation of Barite and Celestite through the Replacement of Gypsum

Minerals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 189 ◽  
Author(s):  
Pablo Forjanes ◽  
José Astilleros ◽  
Lurdes Fernández-Díaz
Keyword(s):  
Solid Solution ◽  
Fluid Phase ◽  
Secondary Phase ◽  
Crystal Habit ◽  
Replacement Reaction ◽  
Random Orientation ◽  
End Members ◽  
Kinetics Of ◽  
Oriented Layer ◽  
Orientational Relationship

Barite (BaSO4) and celestite (SrSO4) are the end-members of a nearly ideal solid solution. Most of the exploitable deposits of celestite occur associated with evaporitic sediments which consist of gypsum (CaSO4·2H2O) or anhydrite (CaSO4). Barite, despite having a broader geological distribution is rarely present in these deposits. In this work, we present an experimental study of the interaction between gypsum crystals and aqueous solutions that bear Sr or Ba. This interaction leads to the development of dissolution-crystallization reactions that result in the pseudomorphic replacement of the gypsum crystals by aggregates of celestite or barite, respectively. The monitoring of both replacement reactions shows that they take place at very different rates. Millimeter-sized gypsum crystals in contact with a 0.5 M SrCl2 solution are completely replaced by celestite aggregates in less than 1 day. In contrast, only a thin barite rim replaces gypsum after seven days of interaction of the latter with a 0.5 M BaCl2 solution. We interpret that this marked difference in the kinetics of the two replacement reactions relates the different orientational relationship that exists between the crystals of the two replacing phases and the gypsum substrate. This influence is further modulated by the specific crystal habit of each secondary phase. Thus, the formation of a thin oriented layer of platy barite crystals effectively armors the gypsum surface and prevents its interaction with the Ba-bearing solution, thereby strongly hindering the progress of the replacement reaction. In contrast, the random orientation of celestite crystals with respect to gypsum guarantees that a significant volume of porosity contained in the celestite layer is interconnected, facilitating the continuous communication between the gypsum surface and the fluid phase and guaranteeing the progress of the gypsum-by-celestite replacement.

In vitro rumen gas production kinetics, hydrocyanic acid concentration and fermentation characteristics of fresh cassava root and feed block sulfur concentration

2020 ◽  
Vol 60 (5) ◽  
pp. 659 ◽  
Author(s):  
Gamonmas Dagaew ◽  
Anusorn Cherdthong ◽  
Metha Wanapat ◽  
Pin Chanjula
Keyword(s):  
Nitrogen Concentration ◽  
Gas Production ◽  
Nutrient Digestibility ◽  
Hydrocyanic Acid ◽  
In Vitro Digestibility ◽  
High Concentration ◽  
Cassava Root ◽  
Fermentation Liquor ◽  
Kinetics Of

Context Feeding ruminants with fresh cassava roots (FCR) is limited because they have a high concentration of hydrocyanic acid (HCN). Thus, it was hypothesised that receiving a feed block containing high sulfur (FBS) would reduce hydrocyanic acid (HCN) in FCR and improve rumen fermentation and nutrient digestibility in animals. Aims The goal of the present work was to study the influence of the ratio of FCR to rice straw (RS) together with FBS on kinetics of gas production, HCN concentration, fermentation characteristics and nutrient digestibility, using in vitro technique. Methods The experimental design was a 4 × 2 factorial arrangement in a completely randomised design, with three replications per treatment. Factor A was the FCR to RS ratio, which was 100:0, 60:40, 40:60 or 0:100. Factor B was sulfur, which was provided as two concentrations in FBS (2% and 4% DM). Gas production was recorded after incubation, at 0, 0.5, 1, 2, 4, 6, 8, 12, 18, 24, 48, 72 and 96 h. Fermentation liquor was collected and determined for kinetics of gas production, HCN concentration, fermentation characteristics and nutrient digestibility. Key results Cassava root to RS ratio influenced the cumulative gas production after 96 h. Inclusion of sulfur in the FBS at 4% increased the cumulative gas production, when compared with inclusion at 2%. The gas production from degradable fraction (b) and the rate of gas production (c) were significantly different among the treatments with different FCR:RS ratios, whereas there was no difference between using 2% and 4% sulfur in the FBS. The HCN concentration in fermentation liquor increased with an increasing proportion of FCR. Furthermore, inclusion of sulfur in the feed block at 4% reduced HCN concentration by 42.8%, when compared with inclusion at 2% (P < 0.05). Ammonia-nitrogen concentration was significantly different among the FCR:RS-ratio treatments and was reduced when the proportion of FCR was decreased (P < 0.05). In vitro digestibility was significantly increased with an increasing proportion of FCR. Increasing the proportion of FCR with 4% of sulfur in the FBS significantly increased in vitro DM digestibility, compared with 2% sulfur. Increasing the FCR:RS ratio with 4% of sulfur in the FBS increased the proportion of propionic acid (P < 0.05). Conclusions Using a high FCR:RS ratio (100:0 or 60:40) with 4% sulfur in the FBS enhanced kinetics of gas production, propionic molar proportion, nutrient digestibility, and HCN detoxification by rumen microbes in an in vitro trial. Implications An in vivo study should be encouraged to verify the results and obtain more data.

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