Particle size refinement

Therefore, the rate at which chemical bonds break increases with elastic shear stressing of the material. The rupture of chemical bonds, hence fracture of material, leads to its fragmentation into particles. This reduces the average particle size in powder as fractured particles multiply into even smaller particles. Equation (1.24) points to the importance of elastic shear strains in mechanical activation of chemical bonds for particle size refinement and production of nanoparticles. 

Another method iavolves an electric-arc vaporizer which is >2000° C before burning (25,32). One of the features of the process is a rapid quench of the hot gas flow to yield very fine oxide particles (<0.15 nm). This product is quite reactive and imparts accelerated cure rates to mbber. Internally fired rotary kilns are used extensively ia Canada and Europe and, to a limited extent, ia the United States (24). The burning occurs ia the kiln and the heat is sufficient to melt and vaporize the ziac. Because of the lower temperatures, the particles are coarser than those produced ia the other processes. In a fourth process, ziac metal which is purified ia a vertical refining column is burned. In essence, the purification is a distillation and impure ziac can be used to make extremely pure oxide. Also, a wide range of particle sizes is possible (33). 

Modem 5-roU refiners with 2-m wide rollers can process 2200 kg of paste per hour. Output is dependent on particle size. 

For organic SEC separations the use of polystyrene/divinylbenzene (PS/ DVB) particles is almost universal throughout the industry. Polymer Laboratories PS/DVB material, PLgel, which is produced in a series of individual pore sizes, formed the basis for the original product line of SEC columns. Developments in the refinement of particle sizing introduced the benefits of smaller particle size and more efficient columns, which significantly reduced SEC analysis time through a reduction in the number of columns required for... 

Particle size distribution Polydisperse, requires refinement to give narrower fraction before use in column packing Monodisperse as produced in the reactor... 

The performance of a supported metal or metal sulfide catalyst depends on the details of its preparation and pretreatraent. For petroleum refining applications, these catalysts are activated by reduction and/or sulfidation of an oxide precursor. The amount of the catalytic component converted to the active ase cind the dispersion of the active component are important factors in determining the catalytic performance of these materials. This investigation examines the process of reduction and sulfidation on unsupported 00 04 and silica-supported CO3O4 catalysts with different C03O4 dispersions. The C03O4 particle sizes were determined with electron microscopy. X-ray diffraction (XRD), emd... 

The reactor system works nicely and two model systems were studied in detail catalytic hydrogenation of citral to citronellal and citronellol on Ni (application in perfumery industty) and ring opening of decalin on supported Ir and Pt catalysts (application in oil refining to get better diesel oil). Both systems represent very complex parallel-consecutive reaction schemes. Various temperatures, catalyst particle sizes and flow rates were thoroughly screened. 

For electrode manufacturing, powder of Ni(OH)2 was used, produced by H.C.Starck, USA. The product has mean particle size of d50 6p.n1. It was mixed with conductive additive, such as, for instance, refined graphite powder. 

Clay silicate minerals that also usually contain aluminum and have particle sizes less than 0.002 p.m used in separation methods as an adsorbent and in refining as a catalyst. 

Fig. 3.6b). It must be mentioned that both alanates NaAlH and LiAlH are extremely difficnlt to be effectively refined during ball milling. As can be seen the particle size redaction of LiAlH is only twofold after 20 h of milling. This can be compared with almost 40-fold particle size reduction of MgH milled for a mnch shorter time (Fig. 2.15 in Sect. 2.1.3). 

Figure 3.26 shows the scanning electron micrographs of the microstructure of composites after milling for 20 h. The microstructure of the composites after milling can be compared with the unmilled and milled LiAlH powder in Fig. 3.11. It is clear that up to 50 wt%FiAlH the milling refines the particle size of the composite quite effectively. However, at 70 wt%LiAlH the particle size becomes much coarser. This is confirmed in Fig. 3.27 which shows the dependence of average particle size (FCD) on the MgH content. It is clear that at a small fraction of MgH milling becomes less effective. As mentioned in Sect. 3.2.2 ball milling for 20 h of a pure FiAlH reduced its particle size from 10.5 4.8 to 5.2 4.3 pm which is marked in Fig. 3.27 at 0 wt%MgHj. At 50 wt%LiAIH the composite particle size is reduced to 1 pm.

---