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Parabolic ceramics

Fig. 33. Parabolic rate constant Kp of different Si3N4 ceramics [455], (SSN Mg/Al [465] SSN-Y/Al [466] HPSN Y/0.2 Al [466] HPSN Mg/Y [467] HPSN Y and HIPSN (no additives)... Fig. 33. Parabolic rate constant Kp of different Si3N4 ceramics [455], (SSN Mg/Al [465] SSN-Y/Al [466] HPSN Y/0.2 Al [466] HPSN Mg/Y [467] HPSN Y and HIPSN (no additives)...
Nordberg LO, Kail PO, Nygren M (1996) A Mathematical Analysis of the Non-Parabolic Oxidation Behaviour of /i-SiALON Matrices and Composites. In Fordham PJ, Baxter DJ, Graziani T (eds) Corrosion of Advanced Ceramics, Key Eng Mat 113. Trans Tech Publications, Switzerland, p 39... [Pg.162]

The oxidation of ceramic composites often obeys parabolic rate kinetics, implying diffusion control. Consider again the oxidation of alumina/SiC composites, one of the few ceramic composite materials for which oxidation data is available. Typical plots of (mass gain/area)2 are shown in Fig. 8.6 for alumina reinforced with different volume fractions of SiC. The parabolic rate constants can be defined by the relation... [Pg.272]

Flow FFF If the channel is constructed with porous walls (e.g., ceramic or metal frits covered with an appropriate membrane), a second flow stream can be pumped across the channel in order to drive the sample toward the accumulation wall (Figure 4C). On reaching the wall, back diffusion in the case of the Brownian mode or hydrodynamic lift forces for larger particles cause the sample components to take up their equilibrium positions. The parabolic fluid flow then causes selective migration along the channel. Molecules as small as IkDa and particles 1 nm in diameter can be separated in the Brownian mode. For small particles or macromolecules, elution depends entirely on the diffusion coefficient of the particles thus the hydrodynamic diameter can be determined, independent of density. [Pg.1235]

Parabolic oxidation behaviour of ceramics normally indicates that the rate-determining step is a diffusional process associated with the migration of ions . In the case of solid state sintered SiC, Luthra reviewed many studies on oxidation of SiC and concluded that, although most observed parabolic oxidation rate, mixed diffusion/reaction rate mechanism must be controlling the oxidation of SiC. On the basis of parabolic rate constants reported in Table III, we were able to determine the activation energy between 1200°C and 1500°C on the basis of the Arrhenius law ... [Pg.25]

Note that no yield-stress drop has been observed in these carbide ceramics (see Fig. 4.20). The curves are parabolic along the entire extension. [Pg.297]

Oxidation - Oxidation of a ceramic Is taken to be a surface effect governed by the parabolic diffusion law and a thermal activation process of constant activation energy, with an Arrhenius type of temperature dependence. By the assuming the Griffith flaw size to be proportional to the surface oxide thickness, we can structure the... [Pg.397]

In Fig. 11, a laboratory apparatus to test coupons of metallic alloys and ceramics is presented. The coupons are coated periodically with thin deposits of Na2S04 or a Na2S04"NaV03 mixture, and the gas composition is controlled to maintain the stability of the deposit [32], The specimens are removed at selected time intervals to examine the corrosion. Typical results obtained for AI2O3 [32,33] are presented in Figs. 12 and 13, showing a porous zone that developed in accordance with a parabolic rate. [Pg.462]

The thermal expansion of many glass ceramic materials shows a non-linear temperature dependence. As indicated in Fig. 3.23, Ceran glass ceramic cooktop panels exhibit a parabolic function. [Pg.83]

Most ceramic processes are carried out by intimately mixing fine powders. In 1927 Jander ( ) applied the parabolic rate law developed for planer interface reactions to powdered compacts. Jander s model is based on the following assumptions ... [Pg.424]

Figure 5. Effects of SiC and TaB incorporation on oxidation behaviour ofZrB ceramics at 130(FC. It can be clearly seen that incorporation of SiC changes the oxidation kinetics from severe linear to mild parabolic [Talmy, 2001]. Figure 5. Effects of SiC and TaB incorporation on oxidation behaviour ofZrB ceramics at 130(FC. It can be clearly seen that incorporation of SiC changes the oxidation kinetics from severe linear to mild parabolic [Talmy, 2001].
Studies on the oxidation behavior of dense SiCNO ceramic materials revealed the formation of a dense and continuous oxide layer with a sharp oxide/ceramic interface and parabolic kinetics from 800 °C to 1400 °C (Chollon, 2000). The parabolic constants and the activation energies were found to be similar with the values obtained for SiC and SijN. These results may be explained if oxidation of SiCNO PDCs is attributed to an oxidation mechanism involving the formation of an intermediate silicon oxynitride layer, which is also found for silicon nitride ceramics (Chollon, 2010). [Pg.221]


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