| 1. |
- Käll, Per-Olov, et al.
(författare)
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Nonparabolic Oxidation Kinetics of Advanced Ceramics
- 1993
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Ingår i: Proc. NATO Conf. on Corrosion of Advanced Materials. - Dordrecht, The Netherlands : Kluwer Academic Publishers. ; , s. 73-94
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Konferensbidrag (refereegranskat)
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| 2. |
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| 3. |
- Persson, Jeanette, et al.
(författare)
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Interpretation of the Parabolic and Non-Parabolic Oxidation Behaviour of Silicon Oxynitride
- 1992
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Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 75:12, s. 3377-3384
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation process of Si2N2O, prepared by a hot isostatic pressing technique, has been studied by the thermogravimetric method. The oxidation has been performed in oxygen for 20 h in the temperature range 1300° to 1600°C, producing oxide scales of amorphous SiO2 and α-cristobalite. The weight gain for T 1350°C does not begin to follow a parabolic rate law, until a certain time, t0. The A0 parameter in the parabolic rate law, (Δw/A0)2=Kpt+B, represents the cross section area, A, through which the oxygen diffuses; in the derivation of this law A is assumed to be constant during the experiment. If crystallization occurs during the oxidation process, A will decrease with time. A function, A(t), describing the time dependence, has been developed and incorporated into the parabolic rate law, yielding a new rate law, which reads ΔW/A0=a arctan √bt+c√t. This new rate law is valid in the time interval t < t0, whereas, for t > t0, the oxidation process follows the equation (Δw/A0)2=K°pt+B0. The relation of the latter equation to the common parabolic rate law is described. All of the oxidation curves are described by these equations. The activation energy of the oxygen diffusion (and of the oxidation (Kp)) is found to be 245 ± 25 kJ/mol, which is consistent with literature values reported for oxygen diffusion.
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| 4. |
- Persson, Jeanette, et al.
(författare)
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Oxidation Behaviour and Mechanical Properties of β- and Mixed α-β Sialons Sintered with Additions of Y2O3 and Nd2O3
- 1993
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Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 11:4, s. 363-373
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Tidskriftsartikel (refereegranskat)abstract
- Sialon ceramics have been prepared from two different Si3N4 powders obtained from different commercial sources, using Y2O3 and/or Nd2O3 as sintering aid. Although both powders were high-purity and high-quality silicon nitrides, surprisingly different phase compositions were obtained for the same overall starting compositions upon sintering at 1825°C. The phase compositions, densities, microstructures and mechanical properties of the samples obtained from the two powders have been compared. The samples prepared from one of the powders were oxidized at 1350°C for 20 h in dry oxygen in a TG unit. The oxidation curves obtained have been interpreted within the framework of a new rate law. The new rate law covers the observation that the oxidation behaviour of Si3N4-based ceramics is often non-parabolic, probably as a result of crystallization processes and the formation of cracks and/or bubbles within the oxide scale or at the scale/matrix interface during oxidation.
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| 5. |
- Persson, Jeanette, et al.
(författare)
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Oxidation Behaviour of Si3N4-Based Ceramics; Studied by the Thermogravimetric Method
- 1993
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Ingår i: Thermochimica Acta. - : Elsevier BV. - 0040-6031. ; 214:1, s. 27-31
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation curves of three different Si3N4-based ceramics are presented. In most cases, the obtained weight gain curves do not follow the parabolic rate law (ΔW/Ao)2 = Kpt + B. If crystallization occurs in the formed oxide scale during the experiment, the amorphous cross section area, A, through which oxygen most easily diffuses will decrease with time. With a function A(t), which describes the time dependence of the decrease of A, incorporated into the parabolic rate law one obtains a new rate law which reads ΔW/Ao = aarctan√bt +c√t. It is shown that all oxidation curves can be explained within the framework of this rate law in combination with the parabolic rate law.
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| 6. |
- Persson, Jeanette, et al.
(författare)
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Oxidation Kinetics of Si2N2O Ceramics
- 1993
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Ingår i: Mat. Res. Soc. Symp. Proc. 287. ; , s. 521-526
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Konferensbidrag (refereegranskat)abstract
- Ceramics based on silicon nitride have been considered promising candidates for high temperature engineering applications due to their excellent refractory properties combined with high strength and good resistance to oxidation. It is well known, however, that the performance of ceramics varies considerably with chemical composition, for example with type and amount of intergranular phase. Especially the evaluation of the high temperature behavior of the ceramics under varying conditions is therefore important in increasing the knowledge of these materials. In previous articles we have interpreted the oxidation behavior of Si2N2O ceramics with use of the parabolic rate law, and a new rate law. In this article we further develop the arctan function, and also show that by an alternative mathematical approach the following rate equation can be obtained. In the following, few compare the oxidation behavior of two series of Si2N2O ceramics within the framework of the two rate laws.
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| 7. |
- Persson, Jeanette, et al.
(författare)
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Oxidation Studies of Si2N2O
- 1991
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Ingår i: Proc. 4th Internat. Symp. Ceramic Materials and Components for Engines. - London & New York : Elsevier Applied Science. ; , s. 1187-1194
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Konferensbidrag (refereegranskat)
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| 8. |
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| 9. |
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| 10. |
- Persson, Jeanette, et al.
(författare)
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Parabolic-Non-Parabolic Oxidation Kinetics of Si3N4
- 1993
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Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 12:3, s. 177-184
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Tidskriftsartikel (refereegranskat)abstract
- The isothermal oxidation behaviour of Si3N4, HIP sintered without additives, has been investigated thermogravimetrically in the temperature range 1250–1500°C. The formed oxide scales were found to be partly crystalline, and the obtained weight gain curves followed the parabolic rate law after a certain time, t0, but not during the entire oxidation experiment. In the time interval t<t0 the curves have been interpreted with the rate law , which is developed with the assumption that the cross-section area available for oxygen diffusion decreases during the experiment, due to a crystallization process and to formation of nitrogen bubbles within the oxide scale. The rate constants, Kp were calculated from the constants in the arctan function, and the activation energy could be determined to be 310±25 kJ/mol. The oxygen diffusion rates found are in fair agreement with those obtained for amorphous silica.
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