Mechanical attrition

Catalyst performance depends on composition, the method of preparation, support, and calcination conditions. Other key properties include, in addition to chemical performance requkements, surface area, porosity, density, pore size distribution, hardness, strength, and resistance to mechanical attrition. 

Kuboi, R., Nienow, A.W. and Conti, R., 1984. Mechanical Attrition of Crystals in Stirred Vessels. In Industrial Crystallization 84. Eds. S.J. Jancic and E.J. de Jong, Amsterdam Elsevier Science Publishers B.V. 

Mechanical attrition is used to remove most of the spent binder. First, dry attrition or abrasion processes crush lumps to grain size. Mechanical abrasion is then used to separate the binder from the sand grains. Sometimes, sand is pneumatically propelled against a metal target plate. The impact of the sand on the plate scrubs off the clay and resin coating from the sand grains. Fines are separated and removed by dry classification. 

Particle attrition not due to thermal or chemical reaction effects (i.e., mechanical attrition) occurs much more rapidly in the grid region of fluidized beds than in the bulk of the bed. This is due to high-velocity gas... 

Since cross-linked polymers caruiot be re-formed or re-shaped it is necessary to synthesize them in the final physical form appropriate for each particular application. Particles in the size range 50-1000 pm are suitable for laboratory scale chemistry, while larger particles have advantages in large scale continuous processes. Irregularly shaped particles are susceptible to mechanical attrition and breakdown to fines , whereas the process of suspension polymerization [13] yields uniform spherical cross-linked polymer particles often referred to as beads, pearls or resins. These are much more mechanically robust and are widely exploited on both a small and large scale e. g. as the basis of ion exchange resins [14]. 

Fixed bed reactors still predominate for fuel processing. However, fixed beds are susceptible to vibrational and mechanical attrition. Recently, monolithic reactors, either metallic or ceramic, have attracted interest for reforming processes since they offer higher available active surface areas and better thermal conductivity than conventional fixed beds. Low-pressure drop and robustness of the structure are major advantages of monolithic reactors. 

Powder Formation. Metallic powders can be formed by any number of techniques, including the reduction of corresponding oxides and salts, the thermal dissociation of metal compounds, electrolysis, atomization, gas-phase synthesis or decomposition, or mechanical attrition. The atomization method is the one most commonly used, because it can produce powders from alloys as well as from pure metals. In the atomization process, a molten metal is forced through an orifice and the stream is broken up with a jet of water or gas. The molten metal forms droplets to minimize the surface area, which solidify very rapidly. Currently, iron-nickel-molybdenum alloys, stainless steels, tool steels, nickel alloys, titanium alloys, and aluminum alloys, as well as many pure metals, are manufactured by atomization processes. 

Mechanical methods of powder production, also known as mechanical attrition, typically require a brittle material, or at least one that becomes brittle during processing. There are various types of equipment that perform particle size reduction. 

Figure 7.14 Classification of equipment used in mechanical attrition. Reprinted, by permission from ASM Handbook, Vol. 7, Powder Metallurgy (1984), ASM International, Materials Park, OH 44073-0002. p. 70.

Nevertheless, the presented results indicate that if it is carefully distinguished between the process function (stress mode), the material function (material specific attrition mechanisms) and microscopic attrition mechanisms (attrition formation on the microscale) in the analysis of attrition processes, significant progress in the understanding of the complex phenomenon of attrition can be made. 

Several factors are responsible for the incorporation of chemical treatments in mechanical pulping including the high-energy demand of using only mechanical attrition and the limited utility of mechanically pulping many hardwood species. 

Tablet dosage forms have to satisfy a unique design compromise. The desired properties of rapid or controlled disintegration and dissolution of the primary constituent particles must be balanced with the manufacturability and esthetics of a solid compact resistant to mechanical attrition.

In the early days of development of continuous ion exchange processes the benefits to water treatment of high efficiency and low leakage were paralleled by the rapidly advancing designs of counterflow fixed bed plant. Thus the more complex hydrodynamic requirements of CIX, resin losses due to mechanical attrition, and perhaps a conservative attitude towards availability of plant during periods of unscheduled maintenance meant that, in the UK at least, the CIX... 

Silicon nanoparticles in a narrow range of sizes (25-50 nm) were obtained by mechanical attrition. ... 

Finally, mechanical attrition has been widely used to produce all forms of nano-... 

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