Grain alumina

Steinfeld et al. [133] demonstrated the technical feasibility of solar decomposition of methane using a reactor with a fluidized bed of catalyst particulates. Experimentation was conducted at the Paul Scherrer Institute (PSI, Switzerland) solar furnace delivering up to 15 kW with a peak concentration ratio of 3500 sun. A quartz reactor (diameter 2 cm) with a fluidized bed of Ni (90%)/Al2O3 catalyst and alumina grains was positioned in the focus of the solar furnace. The direct irradiation of the catalyst provided effective heat transfer to the reaction zone. The temperature was maintained below 577°C to prevent rapid deactivation of the catalyst. The outlet gas composition corresponded to 40% conversion of methane to H2 in a single pass. Concentrated solar radiation was used as a source of high-temperature process heat for the production of hydrogen and filamentous... 

Lin, T.-F. and Wu, J.-K. (2001) Adsorption of arsenite and arsenate within activated alumina grains equilibrium and kinetics. Water Research, 35(8), 2049-57. 

SiC nanocomposite to abrasion with 45 pm diamond paste [9] (a) alumina, grain size 2.6 pm (b) alumina-11 vol% SiC, alumina grain size 2.6 pm. 

Electron microprobe analysis of concentration profiles across sections of the sintered samples revealed the existence of concentration gradients, the mullite content decreasing with increasing distance from the surface of the bodies [Marple Green, 1993], SEM examination also revealed a microstructural effect the alumina grain size tended to increase from the surface of the... 

Detailed HRTEM characterization of the specimens showed that all metal-ceramic interfaces in the two different nanocomposites had thin ( 1 nm thick) amorphous films (see Fig. 11.5). In addition, occluded particles were found inside the alumina grains which also had thin amorphous films at their interfaces with alumina. Analytical microscopy showed the films to contain Ca, Si, and Al.41 Hamaker coefficients were calculated for metal-ceramic interfaces in the presence of a Si02-based film, which indicated that a stronger attractive force is expected for intergranular films at metal-alumina interfaces,... 

Many clusters of Fe atoms are formed both inside and at the surface of each alumina grain and progressively grow. When the Fe nanoparticles located at the surface of the alumina grains reach a size around 0.7-2 nm, they immediately catalyze the decomposition of CH4 and the nucleation and growth of CNTs of very small diameter ... 

Susnitzky, D.W. and Carter, C.B., (1990), Structure of alumina grain boundaries prepared with and without a thin amorphous intergranular film , J. Am. Ceram. Soc., 73 (8), 2485-2493. 

Fig. 7.12 (a) A schematic representation of the pinning of grain boundaries by whiskers, (b) An example of the process shown in (a) in the fatigue crack tip region of the alumina/SiC composite subjected to fatigue fracture at 1400°C. From Ref. 61. A refers to alumina grains. 

The porous supports, in disc or tubular shaped form, were produced commercially (Velterop Company, Netherlands). The discs (25 mm in diameter and 2 mm in thickness) were available with different macropore sizes (0.08, 0.15, 2 and 9 pm). These macropores, which were formed between the sintered alumina grains are shown typically for a disc in Figure 1. The tubes with an outer diameter of 14 mm and a wall thickness of 3 mm were manufactured with pores of 2.5 pm and 9 pm. The macropore structure of these different types of supports was analysed by mercury porosimetry. Changes in the porosity which occurred after the hydrothermal treatment were also monitored. Figure 2 shows the highly uniform pore structure of a series of supports with different nominal pore sizes. 

Figure 7. Filamenteous carbon deposit on alumina grain in spent AZ-1 catalyst.

The effect of whisker-matrix interfaces on mechanical properties becomes clear when the same Al203-SiC materials are hot-pressed at different temperatures. While maintaining similar density, similar sizes of alumina grains, and identical whisker volumes, these composites have different fracture toughnesses as shown in Fig. 19. The differences in Klc values between A1203 with ACMC SC-9 SiC and A1203 with Tateho SCW... 

Figure 4.3 Microstructure of Biolox delta. 1, Alumina grains 2, Zirconia reinforcing grains and 3, Chromia elongated platelets as crack arresters. ( With permission of CeramTec GmbH, Plochingen, Germany.)...

Hydroxyapatite Coatings Cylindrical Ti6Al4V rods of 130 mm in length and diameters between 11 and 13 mm were grit blasted with alumina (grain size... 

It is also vital that a constant supply of aluminum is guaranteed through the diffusion from the substrate in order to ensure the surface is totally covered with alumina. Otherwise Cr203 and Fe-Cr spinel would be obtained mainly. The addition of the already mentioned RE in contents of less than 0.1% increase the resistance to oxidation of the Fe-Cr-Al alloys. Moreover the alumina grains are reduced in size. 

Not all sintered aluminas are tabular Al O, primarily because sintering aids, such as MgO compounds, are used to achieve densification at lower temperatures and the resultant a-Al O crystal size is not large enough to warrant the distinction of tabular Al O. Such dense sintered alumina grain exhibits poor thermal shock characteristics in comparison with tabular alumina. 

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