Surface sintering

The last failure mechanism involves defects in the underlying support layer that are transferred to the thin permselective layer. Examples include surface irregularities (such as pits or cracks), and particles on the support surface. Sintered stainless steel supports may be especially prone to residual particles of metal powder that can pierce the thin permselective metal layer during use. Shock and vibration may cause damage (such as cracking) to a ceramic support layer that then results in damage to, and failure of, the permselective layer. 

It is known that micronization of compounds can lead to the formation of regions with a degree of disorder which, because of their amorphous character, are more reactive compared to the pure crystalline substance. This is particularly true on exposure to moisture and can lead to problems with caking, which is detrimental to the performance of the product. It has been argued that these amorphous regions transform during moisture sorption, due to surface sintering and recrystallization at RHs well below the critical RH. 

Liu and Park concluded that the deactivation was probably due to either the formation of an impervious glaze layer on the washcoat surface, sintering and gluing the y-alumina particles by glassy phase in the washcoat, or simply poisoning from lead. 

Figure 3-8. The images of Sm-doped ceria film on Pt the cross section of the film sintered at 800°C (a) and AFM images of the film surface sintered at 800°C (b) and 1,000°C (c)...

A noteworthy statement is that the inception of a reaction coincides almost always with the temperature at which one or the other of the reactants undergoes recrystallization. This may occur by partial fusion on the surface (sintering) that can take place (as proved by Hedvall) below actual fusion temperature accompanied by diffiisicm processes, sintering, and recrystallization with consequent shrinkage. These observations appear to derive from ceramic mixtures but may be applicable to pyrochemical combinations. 

Svoboda, J., Riedel, H. and Zipse, H., Equilibrium pore surfaces, sintering stresses and constitutive equations for the intermediate and late stage of sintering — I. Computation of equilibrium surfaces, Acta Metall. Mater., 42, 435-43, 1994. 

Figure 9.4 Scanning electron microscope (SEM) micrograph of polished AIN ceramic surface sintered at 1785°C for 300 min containing 3.8 wt% of YjOj additive and with thermal conductivity of 250 Wm K . ...

In classifying deposits by structure, the adherent layer can be characterized as loose (ash and soot deposits), tacky, dense (sintered and cemented), or liquid. The properties of the adherent layer are determined by the particular stage at which the deposit formation process ends, this process consisting of the deposition of fly ash, adhesion of ash particles to the heating surface, sintering of the ash particles, and melting of the outer layer of deposits. We will be considering three types of deposits loose, tacky, and dense. 

Temperatures higher than 550 °C must be avoided as the reforming catalyst loses surface (sintering) and mechanical resistance above 550 °C (Le Page, 1978). The first reactor usually contains about 3 wt% coke and less than 1 wt% after regeneration. The coke content increases in the direction of flow as the content of aromatics (coke precursors) increase. In the last reactor, a content of 20% coke may be reached prior to regeneration. 

A well-defined increase of the effective electrolyte surface area can also be achieved by a structured electrolyte surface. Sintering separate 8YSZ particles onto the electrolyte substrate and covering the increased surface area by an electrochemically active thin porous film cathode via metal-organic-deposition... 

Better thermal contact between the subliming material and the heater can be obtained by forming the material in physical contact with the heater, by sintering powders around the heater, or by electroplating the material onto the heater surface. Sintering generally produces a porous material that has appreciable outgassing. Chromium is often electrodeposited onto a... 

Surface diffusion Surface Sintering neck Grain coarsening... 

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