Calculations of parabolic reaction rate constants

a b s t r a c tSelf-propagating high-temperature synthesis (SHS) was previously proposed as alternative preparation route for FeeAl intermetallics. However, this process was not optimized and the mechanism and kinetics of the phases' formation was not fully clarified up to current days. In this work, in situ high energy X-ray diffraction analysis was carried out during the SHS process and the mechanism of the intermetallic' formation in FeAl25 powder mixture was described during rapid heating and isothermal annealing at 800 C as well as during a slower continuous heating to 900 C. During slower heating, the formation of Fe 2 Al 5 and FeAl 2 intermetallics starts below the melting point of aluminium. When the heating rate is high, intermetallics are created after melting of aluminium. During long-term annealing, all of the phases can be transformed to FeAl phase when fine powders were applied. Detailed mechanism is proposed in this paper and kinetics of the intermetallics' formation is described.

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“…When a process is controlled by diffusion of species through a reaction product, it is generally described by the parabolic law [31], written as:…”

Section: Methodsmentioning

confidence: 99%

On the formation of intermetallics in Fe–Al system – An in situ XRD study

et al. 2013

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“…We used the approach suggested by Pieraggi and plotted the metal losses vs. the square root of time (a parabolic plot) rather than alternative methods, such as log-log or squared metal loss vs. time plots. [16] This graphical approach clearly differentiates between parabolic kinetics and linear kinetics. Linear kinetics are identified on such a parabolic plot as data that increasingly diverge upward from a straight line as time increases.…”

Section: Corrosion Kineticsmentioning

confidence: 99%

Corrosion resistance of stainless steels during thermal cycling in alkali nitrate molten salts.

Bradshaw¹,

Goods²

2001

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Pr epar ed b y Sa ndi a N at i ona l La bor a tor i es Al buqu er qu e, N ew M exi c o 8 7185 and Li v er m o r e, C al i for n i a 9455 0 Sa nd i a i s a m u l ti pr ogr am l a bo r at or y o pe r at ed by S and i a C o r p or a ti on, a Lo ckh ee d M ar ti n C om p an y, fo r t he U n i t ed St ate s D ep ar tm e nt of En er gy un der C ont r a ct D E -AC 04 -94 AL 850 00 .Ap pr ov ed f or p ubl i c r e l eas e; f ur th er d i sse m i na ti on unl i m i t ed.Issued by Sandia National Laboratories, operated for the United States Department of Energy by Sandia Corporation.NOTICE: This report was prepared as an account of work sponsored by an agency o the United States Government.Neither the United States Government, nor any agency thereof, nor any of their employees, nor any of their contracto subcontractors, or their employees, make any warranty, express or implied, or ass any legal liability or responsibility for the accuracy, completeness, or usefulne information, apparatus, product, or process disclosed, or represent that its use not infringe privately owned rights. Reference herein to any specific commer product, process, or service by trade name, trademark, manufacturer, or otherwi does not necessarily constitute or imply its endorsement, recommendation, or favo by the United States Government, any agency thereof, or any of their contractor subcontractors. The views and opinions expressed herein do not necessarily stat reflect those of the United States Government, any agency thereof, or any of t contractors.Printed in the United States of America. This report has been reproduced direc from the best available copy. ABSTRACTThe corrosion behavior of three austenitic stainless steels was evaluated during thermal cycling in molten salt mixtures consisting of NaNO 3 and KNO 3 . Corrosion tests were conducted with Types 316, 316L and 304 stainless steels for more than 4000 hours and 500 thermal cycles at a maximum temperature of 565°C. Corrosion rates were determined by chemically descaling coupons. Metal losses ranged from 5 to 16 microns and thermal cycling resulted in moderately higher corrosion rates compared to isothermal conditions. Type 316 SS was somewhat more corrosion resistant than Type 304 SS in these tests. The effect of carbon content on corrosion resistance was small, as 316L SS corroded only slightly slower than 316 SS. The corrosion rates increased as the dissolved chloride content of the molten salt mixtures increased. Chloride concentrations approximating 1 wt.%, coupled with thermal cycling, resulted in linear weight loss kinetics, rather than parabolic kinetics, which described corrosion rates for all other conditions. Optical microscopy and electron microprobe analysis revealed that the corrosion products consisted of iron-chromium spinel, magnetite, and sodium ferrite, organized as separate layers. Microanalysis of the elemental composition of the corrosion products further demonstrated that the chromium content of the iron-chromium spinel layer was relatively high for conditions in whic...

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“…2, clearly demonstrating the temperature-dependent oxidation kinetics. The oxidation kinetics were evaluated using the [14,15]. The ΔW and k P values are summarized in Table 2.…”

Section: Resultsmentioning

confidence: 99%

High-Temperature Oxidation Behavior and Kinetics of Forged 12Cr-MoVW Steel

Kim

Oak²,

Bae

et al. 2017

Archives of Metallurgy and Materials

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The oxidation kinetics of forged 12Cr-MoVW steel was investigated in an air (N 2 +O 2 ) atmosphere at 873-1073 K (Δ50 K) using thermogravimetric analysis. The oxidized samples were characterized using X-ray diffraction, and the surface and crosssectional morphologies were examined using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The forged 12Cr-MoVW steel samples exhibited parabolic behavior and a low oxidation rate compared with their as-cast counterparts. A protective oxide layer was uniformly formed at relatively low temperature (≤973 K) for the forged samples, which thus exhibited better oxidation resistance than the as-cast ones. These oxides are considered solid-solution compounds such as (Fe, Cr) 2 O 3 .

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Calculations of parabolic reaction rate constants

Cited by 248 publications

References 5 publications

On the formation of intermetallics in Fe–Al system – An in situ XRD study

On the formation of intermetallics in Fe–Al system – An in situ XRD study

Corrosion resistance of stainless steels during thermal cycling in alkali nitrate molten salts.

High-Temperature Oxidation Behavior and Kinetics of Forged 12Cr-MoVW Steel

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