Thermal and Environmental Effects on Ceramic Fibres

Karlsson, S; Lundberg, Robert; Carlsson, Roger

doi:10.1051/jphyscol:1986189

Cited by 1 publication

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“…Under conditions where boron rich oxides may form, their continuing growth can be explained by the rapid diffusion of boron in the alloy as an interstitial specie (Table 4). At 1050 8C the boron diffusivity is 3-4 orders of magnitude faster than those of the major alloying additions Ni, Cr, and Al [12,30]. The continuing oxidation of boron results in the lowering of its concentration in the bulk alloy which, according to the ICP-MS measurements, drops in Rene 80 from 100 to about 5 ppm within just 20 h oxidation at 1050 8C.…”

Section: Boron Oxidation and Depletionmentioning

confidence: 99%

“…Although the boron enrichment at 850 8C differs quantitatively from that during oxidation at 1050 8C, the Table 4. Solute diffusion for Ni, Cr, Al [30], and B [12] in Ni (D 0 is the preexponential term, Q the activation energy, and D the diffusion coefficient at 1050 8C) D 0 (m 2 /s) Q (kJ/mole) D (at 1050 8C) Ni 1.7 Á 10 À4 285 9.41 Á 10 À16 Cr 1.1 Á 10 À4 274 1.73 Á 10 À15 Al 1.0 Á 10 À4 260 5.42 Á 10 À15 B 2.0 Á 10 À7 106 1.29 Á 10 À11 qualitative similarity of the GD-OES profiles in Fig. 23 and 13 indicates that formation of the scale and its incorporation of boron are not fundamentally different from that at 1050 8C.…”

Section: Boron Depletion At Lower Temperaturementioning

confidence: 99%

“…Formation of the mixed B/Cr oxide resulted in fast boron depletion from the alloy. This was attributed to the high thermodynamic stability of boron containing oxides in combination with rapid interstitial diffusion of boron in the alloy matrix [5,12].…”

Section: Introductionmentioning

confidence: 99%

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Cover: High temperature corrosion attack of the surface of a heat resistant high-alloy steel for boiler tubes (DMV304HCu) after exposure to a chlorine-free coal-power-plant ash at 625 °C for 1000 hours (cross section/false colors): Coal-power-plant ash containing sulphur, sodium, potassium, calcium and iron-rich oxides (dark red and violet); outer iron-rich oxide scale (yellow); inward growing chromia scale containing sulphur (turquoise); small chromium sulphides at the corrosion front in the metal subsurface zone (pink). The corrosion test was conducted within a project of DECHEMA-Forschungsinstitut to investigate accelerated hot-corrosion through co-fi ring of "green fuels" in conventional coal-fi red power plants. The project was funded by Federal Ministry for Economic Affairs and Energy (BMWi) under contract No. 03ET7012D. More detailed information on the project can be found at http://dechema-dfi .de/en/L%C3%BCbkorr.html Aim of the study is to develop a simulation software for the prediction of internal corrosion during high-temperature applications. Within this study, the cellular automata approach was used to describe TiN formation in Ni-20Cr-2Ti, MnO formation in a Mn-steel containing 3.7 wt% Mn and intergranular Al 2 O 3 formation in Inconel 625Si. It is shown that experimental and simulated results are in good agreement. EFC-Workshop: Insight, mechanisms and modelling in high temperature corrosion M. Schütze and W. J. Quadakkers As a fi rst step toward multicomponent simulations of oxidation, simulations of oxidation of pure iron has been performed. The simulations were performed using a modifi ed version of the homogenization model as implemented in Dictra using Calphad databases. A reasonable agreement with experimental data has been obtained. An alumina forming austenitic steel is exposed in a nitriding atmosphere. The internal nitridation is compared with thermodynamic and kinetic modelling. The order of appearing nitrides from the surface of the sample is predicted by the modelling. However, the cubic chromium nitride was not detected in the sample and the experimental nitridation depth is smaller than the modelled nitridation depth. Isothermal, 500 h exposures at 750 °C in 1-300 bar CO 2 found little effect of pressure on the mass change or reaction rates for a group of chromia-and alumina-forming structural alloys. In addition to examining polished cross-sections, macroscopic evaluations via hardness and ex situ tensile properties did not reveal any evidence of signifi cant internal carburization under these conditions. During exposure of alloy 625 in wet air at 900-1000 °C chromium loss due to formation of volatile Cr species increases with increasing gas fl ow rate up to the maximum considered value of 6 m/s. Geometrical factors of the test specimen substantially affected the extent of volatile species formation; especially the specimen leading edge exhibited more extensive formation of volatile Cr species than other specimen areas. 159-170 Effect of gas fl ow rate on oxidation behaviour of al...

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Section: Boron Oxidation and Depletionmentioning

confidence: 99%

Section: Boron Depletion At Lower Temperaturementioning

confidence: 99%