Particles aluminum oxide

Aluminum-containing propellants deflver less than the calculated impulse because of two-phase flow losses in the nozzle caused by aluminum oxide particles. Combustion of the aluminum must occur in the residence time in the chamber to meet impulse expectations. As the residence time increases, the unbumed metal decreases, and the specific impulse increases. The soHd reaction products also show a velocity lag during nozzle expansion, and may fail to attain thermal equiUbrium with the gas exhaust. An overall efficiency loss of 5 to 8% from theoretical may result from these phenomena. However, these losses are more than offset by the increase in energy produced by metal oxidation (85—87). 

Temperature of the fluidized bed is another parameter that could influence the heat transfer coefficient. Increasing bed temperature affects not only the physical properties of the gas and solid phases, but also increases radiative heat transfer. Yoshida et al. (1974) obtained measurements up to 1100°C for bubbling beds of aluminum oxide particles with 180 pm diameter. Their results, shown in Fig. 6, indicate an increase of over 100% in the heat transfer coefficient as the bed temperature increased from 500 to 1000°C. Very similar results were reported by Ozkaynak et al. (1983) who obtained measurements for bubbling beds of sand particles (dp = 1030 pm) at temperatures up to 800°C. 

Adsorption HPLC is the classification in which the highly polar silica particles are exposed (no adsorbed or bonded liquid phase). Aluminum oxide particles fit this description too and are also readily available as the stationary phase. As mentioned earlier, this classification can also be thought of as normal phase... 

A variation of this method was used to control the surface properties of aluminum oxide particles, particularly the surface density of Lewis acid sites. Instead of using a long-chain amine surfactant, the solution of aluminum alkoxide precursor was mixed with a small amine to convert the alkoxide dimer (or oligomer in general) into monomeric alkoxide-amine adduct. Controlled hydrolysis of this adduct produces an aluminum oxyhydroxide in which the surface A1 ions are coordinated to amine... 

When fine aluminum particles are incorporated into AP pyrolants, aluminum oxide (AI2O3) particles are formed when they bum. Dispersal of these aluminum oxide particles in the atmosphere generates white smoke even when the atmosphere is dry. The mass fraction of aluminum particles added is approximately 0.2 for the complete combustion of AP pyrolants. Though an excess of aluminum... 

Inorganics can also be synthesized and used as templates. Thus, controlled siloxane networks were formed when dispersions of alkoxysilanes (such as (MeO)3SiMe) are mixed with the suitable template matrixes. Ultrafine particles of metal oxides can be used as starting materials for the formation of metal oxide films. For instance, a mixture of a double-chained ammonium amphiphile and an aqueous solution of aluminum oxide particles (diameter about 10 100 nm) gives a multilayered aluminum oxide film when calcinated at over 300°C. 

Figure 6.4. Comparison of the surface area/volume ratio of macroscopic particles (marbles) and nanoscopic aluminum oxide particles. Since nanoparticules contain a proportionately large number of surface atoms, there are a significantly greater number of adsorption/reaction sites that are available to interact with the surrounding environment. Further, whereas bending of a bulk metal occurs via movement of grains in the >100nm size regime, metallic nanostructures will have extreme hardness, with significantly different malleability/ductility relative to the bulk material.

Niven S. E. H. and Moore R. M. (1993) Thorium sorption in seawater suspensions of aluminum oxide particles. Geochim. Cosmochim. Acta 57, 2169-2179. 

The effect of ultrasound on the hydrolysis of aluminum iso-propoxide has been studied [50]. The hydrolysis resulted in aluminum oxide particles whose size was 200-600 A. The reaction was accelerated 10-fold by sonication and the hydrolysis rate could be. increased further with increased ultrasonic intensity. This study provided a potential method for the preparation of ultrafme powders. 

Schlautman, M.A. and Morgan, J.J., Adsorption of aquatic humic substances on colloidal-size aluminum oxide particles Influence of solution chemistry, Geochim. Cosmochim. Acta, 58, 4293, 1994. 

A urease packed bed reactor combined with an ammonia electrode is being used in a blood urea nitrogen (BUN) analyzer marketed since 1976 by the Kimble Division of Owens-Illinois (USA). Urease is bound to aluminum oxide particles. The reaction is conducted at pH 7.5. In order to obtain a high sensitivity for the ammonia electrode, the product stream leaving the reactor is mixed with NaOH until a pH of 11 is attained (Watson and Keyes, 1976). 

Aggregation and fragmentation of colloidal particles has been investigated further employing natural polyelectrolytes like humic substances. Adsorption of humic acids on aluminum oxide was determined to resemble interfacial deposition on the basis of methods previously employed for the aluminum oxide/polyacrylic acid system [88]. Complexation by soluble aluminum ions produces pH drops that are very similar to that determined for polyacrylic acid, and essentially humic acids were determined to exert effects on the stability of colloidal aluminum oxide particles at pH 5 that are very similar to polyacrylic acid. 

Initial experiments demonstrated a dose-dependent induction of DNA adducts after exposure of alveolar epithelial cells (A 549) towards Pt and Pd particles. Furthermore, platinum attached to aluminum oxide particles also induced DNA adducts in A 549 cells after exposure, the formation of Pd-induced DNA adducts also being time-dependent. This is the first proof that PGM particles can be taken up by phagocytosis, enter the nucleus, and bind to DNA. However, as these are preliminary results further studies are necessary to estimate the genotoxicological potential of particulate PGM. Nonetheless, these findings are very important as between 11 and 36% of the particles emitted from automotive catalytic con-... 

From occupational studies it has been shown that the most significant health risk from Pt exposure is sensitization of the airways caused by soluble Pt compounds (Rosner and Merget 2000). Thus, for an assessment of the health effects of Pt it seems reasonable to distinguish between elemental Pt and halogenated Pt compounds. Pt is emitted from catalytic exhaust gas converters of cars in amounts which are in the ng km range, mainly as elemental Pt. The nanocrystalline Pt particles are attached to jm-sized aluminum oxide particles. Only very limited data are available from current studies showing that ultra-... 

The detection of airborne particles using piezocrystal devices was first reported by Chuan (6,7) who used an adhesive coated 10 MHz crystals to detect aluminum oxide particles and mass concentration as low as l g/m were detected. Particles were impacted by aerodynamics acceleration with reported sensitivity of 10" g. A portable continuous, direct reading instrument for measuring... 

Nanocomposites based on aluminum oxide, poly(pyrrole) (PPY), and PVK can be prepared by precipitating PVK in a suspension of PPY-coated aluminum oxide particles.A PPY/AI2O3 composite is added to an aqueous slurry of aluminum oxide powder, p5nrole, and anhydrous FeCls. 

Figure 4 shows exan les of mass spectra obtained for an individnal particle by a successful laser shot (a) for sodium chloride and (b) for aluminum oxide. The aluminum oxide particles were generated by heating aluminum nitrate particles in the furnace at 800 °C. No molecular species were observed, and multiply charged atomic ion peaks were present in both spectra. Quantitation of the conq>lete elemental conq>osition of particles is possible if the particle can be completely ablated and ionized. 

To adjust the height of the energy barrier in an aqueous suspension, it is simplest to alter pH by adding acid or alkali. The double layer of charge around each particle then changes systematically as shown in Fig. 10.11 for aluminum oxide particles, with no energy barrier at the point of zero charge. 

Microstmcture of Rodent after casting is composed of large grains/den-drites of the austenite matrix, which is the solid solution of nickel strengthened chromium and molybdenum. The matrix is additionally strengthened by dispersion of molybdenum silicide precipitates. A small number of carbide and aluminum oxide particles were also observed. The presence of eutectics y-P rather weakens the structure of the alloy. 

We see from these data that the electrical charges increase as the particle size diminishes, so that the electrical component of the adhesive forces also becomes greater. The same trend, but with a change in the size of the charge, was found when aluminum oxide particles were detached under the same conditions [28]. 

The aluminum oxide layer was applied to the inner walls of the glass capillary from an aqueous dispersion in the form of aluminum hydroxide and converted In situ into aluminum oxide by heat treatment. By varying heat treatment and by blocking unwanted activities with potassium chloride, adjustment to the desired separation characteristics can be achieved [55]. To prepare the coating suspension, aluminum oxide (particles <2 urn) obtained by calcination of hydroxide is heated for 24 h at 300 °C. 20 g of the alumina is mixed with 70 ml of 5% (w/w) Baymal solution (colloidal aluminum hydroxide) and with 0.3 ml of acetic acid (>96%) and stirred for about 10 min in an ultrasonic bath. Subsequently the mixture is filtered through a wire sieve of 300 mesh and allowed to stand for 24 h for aging. The suspension thus prepared shows thixotropic behavior. 

Use of an aluminum oxide colloidal solution allows preparation of a dispersion medium with an enhanced density and viscosity and thereby improves the suspension stability. Moreover, the colloidal aluminum oxide particles bind the large sorbent particles and additionally fix them on the capillary surface. 

Halasz and Heine [115] used this method for the preparation of aluminum oxide columns. To retain an open passage inside the column, a steel wire with a diameter of 1 mm was inserted into the initial tube. In the course of drawing the softened glass carried the aluminum oxide particles away. The obtained 2-m column represented an intermediate variant of packed and open capillary columns with a fairly high efficiency (3500 theoretical plates per meter) with respect to ethylene. 

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