Rotating electrode atomization

Rotating electrode atomization process has been described in detail by many researchers.[183][184] As illustrated in Fig. 2.20, in the 

a rod of metal or alloy, referred to as a consumable electrode, is rotated at high speed about its longitudinal axis. Simultaneously, it is melted gradually at one of its ends by a heat source, such as an arc, a plasma, or an electron beam, etc. A thin film of the molten metal is detached from the rod end and ejected from the periphery of the rod by centrifugal force, forming spherical droplets. The atomization is conducted in an inert atmosphere, usually argon. Helium may be used to increase arc stability and convective cooling efficiency of droplets. 

In the DC circuit, the rotating consumable rod serves as an anode and the transfer arc plasma torch or a cooled tungsten tipped device as the permanent stationary cathode. As the anode is consumed, it is moved into the spray chamber. The chamber diameter may be as large as 2440 mm. 

Rotating electrode atomization may be applied to almost all metals and alloys since it does not require a crucible for melting and/ or pouring. In particular, high melting-temperature metals and alloys, such as Ti and Zr, are well suited for the process. However, the production cost is still a drawback associated with the process, since electrode production is generally more expensive than a metal melt. In addition, production rates are relatively low compared to other atomization processes such as gas atomization and water atomization. 

In a recently developed process, the consumable rods used in REP are replaced by disk-shaped electrodes, since such electrodes are easier to fabricate than long round rods. During atomization, a rotating consumable disk is melted at its periphery. 

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Numerous atomization techniques have evolved for the production of metal/alloy powders or as a step in spray forming processes. Atomization of melts may be achieved by a variety of means such as aerodynamic, hydrodynamic, mechanical, ultrasonic, electrostatic, electromagnetic, or pressure effect, or a combination of some of these effects. Some of the atomization techniques have been extensively developed and applied to commercial productions, including (a) two-fluid atomization using gas, water, or oil (i.e., gas atomization, water atomization, oil atomization), (b) vacuum atomization, and (c) rotating electrode atomization. Two-fluid atomization... 

Rotating Electrode Atomization (REP, PREP) -20 Standard deviation 1.3-1.5 Armco Fe, Cu, Al, Zn, Co-Cr, Ti, Zr, Ni alloys. Low carbon steels SlO2 1-10 -0.04 Spherical, very smooth, ultraclcan particles, Relatively high EE High cost, Low capacity and volume, D Relatively Coarse particles I... 

Droplet Formation in Centrifugal Atomization. The mechanisms of centrifugal atomization of liquid metals are quite similar to those for normal liquids. Three atomization modes have been identified in rotating electrode atomization process, i.e., (I) Direct Droplet Formation, (2) Ligament Disintegration, and (3) Film/Sheet Disintegration.1[189][32°] are aiso applicable to the centrifugal atomiza-... 

Table 4.20. Correlations for Droplet Sizes of Liquid Metals in Rotating Electrode Atomization (REP)...

In the VEP, currents used are between 600 and 1200 A at potentials between 30 and 60 V. The vibration frequency of the wire electrode is up to 500 Hz. The materials atomized via VEP include mild steel, Cr-Ni steel, Cu-Ni alloy and tungsten. The VEP is carried out in an inert atmosphere (typically argon) for most alloys, but the arc is struck under water for tungsten wire. Wire diameter is 1-4 mm, and its feed rate is 1.7-4.3 m/min. The feed rate and current density must be determined properly according to the relationship between these two variables. At lower current densities, the wire electrode tends to stick to the rotating electrode. At higher current densities, the wire electrode becomes overheated, causing it to bend or even rupture. 

This approximate relationship is similar to those for centrifugal atomization of normal liquids in both Direct Droplet and Ligament regimes. However, it is uncertain how accurately the model for K developed for normal liquid atomization could be applied to the estimation of droplet sizes of liquid metals Tombergl486 derived a semi-empirical correlation for rotating disk atomization or REP of liquid metals with the proportionality between the mean droplet size, rotational speed, and electrode or disk diameter similar to the above equation. Tornberg also presented the values of the constants in the correlation for some given operation conditions and material properties. 

Lukas et al. Spectro /nc.) describe an improvement made in rotating disc electrode atomic emission technology by incorporating a filter device in the rotrode, which enables to detect particles greater than 10 pm size. 

In order to reveal the mechanism of this molecular half-adder, the T(E) spectra of the molecule are presented in Fig. 26b. When perpendicular to the plane of the molecule, each NO2 contributes a very sharp resonance which does not participate in the overall conductance. When rotated by 90°, an NO2 introduces a supplementary resonance in the gap of the molecule. Due to its asymmetrical delocalization over the atomic orbitals, this resonance increase the conduction between the drive and the XOR electrode, but not between the drive and the AND electrode. This insures a 1 output for the former and a 0 for the latter. When the two NO2S are rotated, the two resonances they introduce create a deep interference between the drive and the XOR electrode. Located on the Fermi energy of the molecule, this interference leads to a low conductance state and a 0 logical output for the XOR gate. In contrast, the two resonances do not interfere destructively between the drive and the AND electrode, leading to a high conductance state and a 1 logical output. 

Oxidation of ketone phenylhydrazones generates a radical-cation centre on the nitrogen atom adjacent to the benzene ring. The radical-cation is delocalised by both the hydrazone group and the phenyl ring. Reactions of 1,3,5-triphenyl-A -pyazolines illustrate the properties of these radical-cations. Two one-electron waves are seen at a rotating disc electrode in acetonitrile and for 1,3.5-triphenyl-pyrazoline, Ey. = 0.82 and 1.68 V vs. see [33]. The delocalised radical-cation is... 

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