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Sintering alumina

The continuous sintering is mainly a zone sintering process in which the electrolyte tube is passed rapidly through the hot zone at about 1700 °C. This hot zone is small (about 60 mm) in zone sintering, no encapsulation devices are employed. The sodium oxide vapor pressure in the furnace is apparently controlled by the tubes themselves. Due to the short residence time in the hot zone, the problem of soda loss on evaporation can be circumvented. A detailed description of / "-alumina sintering is given by Duncan et al. [22]. [Pg.580]

An unstabilized high surface area alumina sinters severely upon exposure to temperatures over 900°C. Sintering is a process by which the small internal pores in the particles coalesce and lose large fractions of the total surface area. This process is to be avoided because it occludes some of the precious metal catalyst sites. The network of small pores and passages for gas transfer collapses and restricts free gas exchange into and out of the activated catalyst layer resulting in thermal deactivation of the catalyst. [Pg.486]

Rasmussen et al. (2004) SAX Ni-alumina Sintering mechanism + + Distinction between coalescence and atomic migration... [Pg.323]

Richardson et al. (2004) SEM Ni-alumina Sintering role of structural promoters + + + Methane steam reforming... [Pg.324]

Ad Figure 2.1,2. Zeolite layers can be grown by hydrothermal synthesis onto porous supports (clay, alumina, sintered metal). Especially layers of MFI-type zeolite have been studied [e.g. 5-7]. Such MFI-layers were shown to survive template removal and subsequent thermal cycles up to 350 °C, which is taken as a strong indication for chemical bonding [8] at the support interface. To understand chemical attachment to metals one has to take into consideration that metals - by exposure to air - will be covered with a thin (1-2 nm) oxide film. Sometimes an intermediate mesoporous layer has been applied, e.g. a metakaolin film on clay or on zirconia [5] or metal wool on sintered metal [6]. [Pg.415]

Harris et al. [36] reported values of apparent activation energy based on decrease of surface area. Pure alumina sintering in hydrogen was found to have an apparent activation energy of ca 123 kJ/mol In steam, the value was reduced to ca 70 kJ/moL, The effect of steam was suggested to result both from the production of extra hydroxyl groups on the surface and from the possibility of an increase in the number of cation vacancies induced by steam in the trivalent aluminium lattice. However the evidence for either mechanism was sparse. [Pg.47]

Fig. 8 The microstructure of alumina sintered at 1450°C for 3 hr. The micrograph was taken by a scanning electron microscope. Grains, grain boundaries, and pores are evident in the nearly dense microstructure. The magnification bar is 10 pm, or about one-tenth the width of a human hair. Fig. 8 The microstructure of alumina sintered at 1450°C for 3 hr. The micrograph was taken by a scanning electron microscope. Grains, grain boundaries, and pores are evident in the nearly dense microstructure. The magnification bar is 10 pm, or about one-tenth the width of a human hair.
Figure 1 compares the time dependence of the density in undoped and Ti-doped aluminas fired in air at 1400°C. Under these conditions, Ti should be in the 4+ state. Pairs of data points for both the undoped and 500 ppm Ti-doped material represent measurements taken on different samples, not measurement error. It is evident that both the undoped and doped alumina sinter to... [Pg.327]

Limited attention has been focussed on the possibility of stabilising alumina under steam reforming conditions. Alumina sintering is also a problem in car exhaust catalysts, which are designed to operate up to about 1300 K [27,28]. [Pg.49]

Figure 10.6 (a-f) Microstructure development for an MgO-doped alumina sintered in air at 1600 "C as a function of time. [Pg.308]

Figure 35 Alumina sintering due to treatments at different temperatures. Wet air... Figure 35 Alumina sintering due to treatments at different temperatures. Wet air...
T.l.c. characteristics of nicotine on alumina sintered glass plates have been reported." Extraction of nicotine alkaloids using water vapour distillation" and fatty acids" has been studied. [Pg.62]

Fig. 4.44 SEM images (all scale bars 10 pm) of a EPD-formed alumina (from dispersion stabilized with polyacrylic acid at pH 5.4, fractured cross-section of green body with crack), b surface of EPD-deposited alumina sintered in air, and c surface of EPD-deposited alumina hot pressed on a piston-cylinder apparatus and sintered in air. Reproduced with permission from... Fig. 4.44 SEM images (all scale bars 10 pm) of a EPD-formed alumina (from dispersion stabilized with polyacrylic acid at pH 5.4, fractured cross-section of green body with crack), b surface of EPD-deposited alumina sintered in air, and c surface of EPD-deposited alumina hot pressed on a piston-cylinder apparatus and sintered in air. Reproduced with permission from...
Fig. 7.18 Microstructures of the alumina sintered at a heating rate of a 2 °C min and b 100 °C min . Reproduced with permission from [138]. Copyright 2009, Elsevier... Fig. 7.18 Microstructures of the alumina sintered at a heating rate of a 2 °C min and b 100 °C min . Reproduced with permission from [138]. Copyright 2009, Elsevier...
Alternately, an alumina-mullite matrix was developed in an effort to improve long-term thermal stability of porous-matrix CMCs. This matrix utilizes a bimodal mixture of mullite ( 1 jLm) and alumina ( 0.2 p,m) powders [4], The mullite exhibits relatively slow sintering that inhibits shrinkage and maintains the overall porous structure, while the fine alumina sinters more readily, cementing the mullite particles and providing strength to the porous matrix structure [66, 67]. Zirconia has also been studied as the primary phase, with mullite used to stabilize the matrix [68]. [Pg.387]

ALUMINA (fused) ALUMINA (SINGLE crystal) alumina (sintered) ALUMINA (tabular) CORUNDUM. Alumina Cement. See high-alumina CEMENT. [Pg.8]

The specimen was alumina sintered body with purity of 99.9%." The average grain size of as-received sample was 1.1 pm. It was annealed in air in three conditions for... [Pg.76]

The multitude of refractory aggregates (for example, calcined clay, flint clay, andalusite, mulhte, bauxite, fused white or brown alumina, sintered alumina, etc.) and the different grain sizes of these materials—in addition to the big variety of bonding agents, additives, and mixing liquids—enable endless combination possibihties in development work on unshaped refractory products. Therefore, a qualitative standardization is not really possible as it is the case for refractory bricks. As a result of the ENV 1402-1 standard, which now provides a more precise definition of the products, there will probably be adjustments on the market in the long run. If also considering economic aspects, suitable products will obviously be developed on the basis of all the available constituents. [Pg.306]

Yttria and alumina sintering-aids react in temperature with the silica layer covering the surface of silicon nitride powders to form a liquid phase that may accommodate the stress in the material due to external pressure during preparation of the CMC by SPS and, as a result, limits p>ossible fiber damage. [Pg.179]


See other pages where Sintering alumina is mentioned: [Pg.440]    [Pg.779]    [Pg.106]    [Pg.440]    [Pg.81]    [Pg.43]    [Pg.256]    [Pg.50]    [Pg.91]    [Pg.39]    [Pg.604]    [Pg.666]    [Pg.472]    [Pg.227]    [Pg.9]    [Pg.9]    [Pg.42]    [Pg.64]    [Pg.43]    [Pg.53]    [Pg.56]    [Pg.408]    [Pg.365]   
See also in sourсe #XX -- [ Pg.783 , Pg.788 , Pg.808 ]

See also in sourсe #XX -- [ Pg.116 ]




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