Atomization process and their types

                                                      Atomization

Atomization. Atomization, also called the spraying method, is a process in which molten metals are broken into small drops of liquid by high-speed fluids (gas as air or inert gas; liquid as water) or fluids with centrifugal force, and then solidified into powder.

There are types of Atomization process are:


1.1 Water Atomization

In the commercial production of metal powders water atomization is the pre-eminent mode; attendant capacity worldwide is at least 700000 tyr−1 with production rates up to 500 kg min−1. Water atomization is used primarily for ferrous compositions but can be used to produce a range of nonferrous alloys. It is lower in cost than other modes of atomization but limitations exist in relation to powder purity, particularly with reactive metals and alloys.
Nozzles used in water atomization are either in the form of discrete multiple nozzles or an annular slit concentric with the metal stream. Annular cone and V-shaped jet geometries are used widely. The “free-fall” configuration is common in which the liquid metal exits from the base of the tundish and falls under gravity before impingement by the jets of water.
Representative operating conditions in water atomization are summarized in Table 1 (Lawley 1992). Commercial water atomized powders are normally irregular in shape with a median particle size of about 100μm (Fig. 2(a)). Particle size of distributions are relatively broad (10–300 μm). Cooling rate is a function of particle size and is estimated to be >1×103 °Cs−1.

Table 1. Representative operating conditions in water atomization.
Metal flow rate (single nozzle)
4.5–90 kg min−1

Water flow rate
110–380 lmin−1

Water velocity (at nozzle exit)
70–230 ms−1

Water pressure (at nozzle exit)
5.5–21 MPa

Metal superheat
75–150 °C




1.2 Gas Atomization

In gas atomization, the stream of liquid metal is disrupted by a high velocity gas (air, nitrogen, argon, or helium). Worldwide annual tonnage of gas atomized powders is much less than that of water atomized powders: about 300,000 tyr−1 for air atomization and 50,000 tyr−1 for inert gas atomization of nonferrous alloys. Melt size and melt feed rate (<120 kg min−1) are lower than in water atomization.The nozzles used in gas atomization are either of the “free-fall” configuration or “confined.” The latter, used almost exclusively with annular nozzles, enhances the efficiency of the process since there is a rapid decay in gas velocity as the gas moves away from the jet. A schematic of a confined gas atomization nozzle is shown in Fig.
Representative operating conditions used in the gas atomization of a nickel base superalloy are summarized in Table 2 (Lawley 1992). Gas pressure is significantly lower than the water pressure in water atomization. Commercial gas atomized powders are normally spherical in shape with small satellites attached (Fig. 2(b)). Median particle size is in the range of 50 μm to 300 μm. For a given particle size, cooling rate is about one order of magnitude lower than in water atomization.

Table 2. Representative operating conditions in gas atomization.a
Metal flow rate
20 kg min−1

Gas pressure

2 MPa

Gas velocity
100 ms−1

Gas flow rate
8 m3min−1

Metal superheat
150 °C


 1.3 Centrifugal Atomization

The primary commercial adaptation of centrifugal atomization is the rotating electrode process.

The metal or alloy to be atomized, in the form of a consumable cylindrical electrode (65 mm diameter×1524 mm), is rotated at speeds of about 15000 rpm while the end of the electrode (anode) is melted by an arc.

The molten metal is ejected by centrifugal force in the form of droplets from the periphery of the bar.

 A transferred arc helium plasma torch (plasma rotating electrode process) is used in order to avoid contamination by tungsten, characteristic of earlier designs.

Helium gas in the working chamber enhances arc stability and convective cooling efficiency.


Powders atomized by this technique are of high purity since there is no containment of the molten metal. The powders are spherical and satellite free (Fig. 2(c)) and in the size range 50 μm to 400 μm with a median particle size of about 200 μm. Droplet cooling rates (<1×102 °Cs−1) are lower than in water or gas atomization.


1.4 Vacuum Atomization

When a molten metal, supersaturated with gas under pressure, is suddenly exposed to vacuum, the gas expands and comes out of solution with attendant atomization of the molten melt.

This principle is used in vacuum atomization, a commercial batch process. It is also termed soluble gas atomization or melt explosion atomization.

The method was developed primarily for the production of high purity nickel and cobalt base superalloy powders, but has also been used to atomize alloy powders of aluminum, copper and iron.






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