Roller atomization process

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... 

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. 

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. 

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. 

---