Roller atomization

Roller atomization is a mechanical atomization process. It was invented in the mid 1970 sJ188] In this process, as schematically depicted in Fig. 2.22, a stream of molten metal is fed into the gap between two counter-rotating rolls and forms a thin liquid sheet that subsequently disintegrates into droplets by the mechanical forces. In the original design, a pair of rollers of 100 mm in diameter are mounted in the same horizontal plane and rotate at speeds up to 1250 radians/s. The roll gap is about 50-100 pm, and the metal flow rate is up to 6 kg/min. 

To ensure that a liquid metal is completely disintegrated into droplets before the initiation of any solidification in the gap, the heat transfer between the liquid metal and the rolls must be minimized. Materials with low thermal conductivity and poor wetting properties have been found to have the most significant effect on reducing the heat transfer. Epoxy and phenolic resin coatings have been applied to 

Depending on operation conditions and metal properties, the shapes of the atomized particles may be spheroidal, flaky, acicular, or irregular, but spherical shape is predominant. The spheroidal particles are coarse. For example, roller-atomized Sn particles exhibited a mass median diameter of 220 to 680 pm. The large particle sizes and highly irregular particle shapes suggested that the disintegration process may be arrested either by the premature solidification or by the formation of a thick, viscous oxide layer on the liquid surface. The particle size distributions were found to closely follow a log-normal pattern even for non-uniform particle shapes. 

Process parameters of primary importance include roll speed, differential roll speed, roll gap, metal flow rate, metal stream velocity, and melt superheat. The mass median diameter of particles diminishes exponentially as the roll speed increases. It is possible to obtain a smaller mass median diameter when one of the rolls is kept stationary rather than rotating the two rolls at the same speed. Metal flow rate seems to have a negligible effect on the mass median diameter. However, the mass median diameter increases with increasing metal stream velocity, suggesting that the relative velocity of the metal stream to the periphery of the rolls may be a fundamental variable controlling the mass median diameter. The size distribution is approximately constant for the conditions studied. 

The roller atomization process has been applied to the atomization of many metals and alloys, such as lead, tin, aluminum, copper and steel. The production rate is potentially high, and the energy requirement is much lower than in commercial gas and water 

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Roller Atomization 220-680 Pb, Sn, Cu, Al, Steels Relatively low -4 — Low energy requirements Irregular, coarse particles... 

When two layers of the substance are displaced relative to one another, the nuclei of phase A, located between them, can be regarded as kind of a roller about which oscillations are executed. - - - when the two layers of phase AB are displaced relative to one another, they transport past the nucleus, in its immediate vicinity, a multiplicity of atoms of both kinds. - - - it follows that all the atoms A passing in the immediate vicinity of the nucieus have sufficient time to combine with the latter and this in fact may be the mechanism of the growth of the nuclei of the new phase. ... 

Fig. 2.14. Atomic level relative mass motion is an expected consequence of plastic deformation. Dremin and Breusov [68D01] have described a conceptual model of such behavior (called a Roller Model ) to explain submicrosecond structural and chemical transformations under shock compression.

Taylor DB, Kingston HM, Nogay DJ, Roller D, Hutton R (1996) J Anal Atom Spectrosc 11 187... 

Wilson, R.H., Terry, J.L Operation Roller Coaster, Defense Atomic Support Agency, PQR-2512 (WT-2512) (1968)... 

D. B. Taylor, H. M. Kingston, D. J. Nogay, D. Roller, R. Hutton, On-line solid-phase chelation for the determination of eight metals in environmental waters by ICP-MS, J. Anal. Atom. Chem., 11 (1996), 187D191. 

Remember that you didn t learn to roller-skate, or to ride a bicycle, until you could balance yourself on your feet. You cannot devise new chemical reactions until you can balance chemical equations. It s fun to mix things in a laboratory and to guess or predict the results. You may not always be correct in your predictions, nor will you always be correct in your mixing, but it will always be fun to account for every single atom involved in a chemical reaction. You will learn how to do this gradually, as you do the experiments in this book. 

Roller et al. (1994) have developed an empirical chemical-shift parameter which takes into account the bond length of the Na-0 coordination sphere and the bond valence Sy between two atoms i and j, defined as... 

A mechanistically different type of nitrosation was discovered by Keefer and Roller (1973), namely a nitrosation of secondary aliphatic amines with nitrite anions in alkaline solution, catalyzed by aldehydes. Although it is unlikely to be applicable to diazotization, i. e., to primary amines, it will be mentioned here because it is a good example of the fact that, in chemistry, particularly in organic chemistry, for a certain type of reaction, e. g., nitroso-de-protonation (which includes substitution of protons bonded to C, N, O, S, etc., atoms), practically all methods follow the same basic pattern (in the case of nitrosation substitution by an electrophilic nitrosating reagent). The Keefer-Roller nitrosation is apparently different if one looks at the stoichiometric equation (4-8). A careful kinetic investigation (Casado et al., 1981b, 1984 a) on the concentration and pH dependence of this reaction revealed that the nitrite anion and free amine base enter the substitution process and that formaldehyde is a true catalyst, as it is not required in equimolar amounts. 

The Keefer-Roller nitrosation is not such as case, however, if one includes the mechanistic role of the catalyst, as shown in the sequence given in (4-9, R = H for formaldehyde). The aldehyde reacts first with the amine, forming an iminium ion. The Hard and Soft Acid and Base principle of Pearson (1963, 1968 Parr and Pearson, 1983 see also Zollinger, 1994, Sect. 3.2) predicts that the reaction of one of the O-atoms of the nitrite ion with the aldehyde C-atom of the iminium ion is the most likely reaction. In the last step, this addition product rearranges through an NN bonded four-membered ring transition state or intermediate into the nitrosoamine and the aldehyde. This mechanism is consistent with Casado s kinetic results. 

Roller and Gillham reported on the thermomechanical behavior 1n nitrogen (19) and in air (20) of a systematic series of linear poly(carborane-siloxane) s containing icosahedral (-CB,qH,(,C-) cages in place of some of the chain oxygen atoms ... 

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