Spherical Powder

• Process description
• Applications

Process description

The most important aspect for industrial processes is the transformation of either agglomerated powders produced by spray drying or sintering techniques, as well as angular powders produced by conventional crushing methods, into spherical powder.

Powder densification and spheroidization is a widely accepted application of induction plasma technology. It basically consists of in-flight heating and melting of feed material followed by its subsequent cooling and solidification under controlled conditions.
Depending on the size and apparent density of the treated powder, their time of flight is controlled such that the molten droplets have sufficient time for complete solidification before reaching the bottom of the primary reactor chamber. Finer particles, entrained by the plasma gases, are recovered in a filter downstream of the primary chamber.

Industrial applications benefit already from the unique properties of Tekna’s spheroidization process. The process results in a considerable improvement of the properties of the powder in multiple aspects:
 

Improved powder flowing properties

Spheroidized particles provide a more homogeneous and stable flow while feeding. This allows flows to run at faster or slower rates without clogging problems.

Decreased powder porosity

Porosity is removed when the material is melted. This translates into better material to use in powder metallurgy applications and denser coatings.
 

Increased powder density

The tap density of the powder is increased by having spherical and dense particles, resulting in denser coating or parts.
 

Decreased powder friability

Wear on parts and coatings can be reduced by lowering the edging, crumbling, chipping or breakup of the powder used before being processed. The treatment removes internal fractures or weak internal bonds and its end effect is a longer life for the coated parts.
 

Enhanced powder purity

The in-flight melting process can also be favorably used to enhance powder purity through the selective/reactive vaporization of impurities. Tekna’s specialized equipment for purification enhancement can easily and rapidly increase the purity of the initial material by a factor of 10 to 100. Powder contaminant can be brought down to the ppm or ppb levels in one or multiple passes dependng on the precursor's initial composition.

The electron micrographs of the metallic powders shown in the following figure before and after plasma spheroidization show the drastic improvements of the powder quality.

Properties	Before Plasma Treatment	After Plasma Treatment
Particles	WC -100+400 Mesh   /   40-150 um	WC -100+400 Mesh   /   40-150 um
Tap Density	8.1 g/cm3	10.2 g/cm3
Hal Flow Test	19 sec/50g	7 sec/50g
Degree of spheroidization

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Applications

For many years, Tekna Plasma Systems has promoted and developed powder particle spheroidization/densification for commercial applications, using induction plasma technology.  The need for powder spheroidization comes from very different industrial fields ranging from powder metallurgy to thermal spray applications.   The most pressing need is for an industrial process to turn agglomerated powders, produced by spray drying or sintering techniques, and angular powders, produced by crushing of the process feed material, into perfectly free flowing spherical powders. Spherical powders are ideal for such applications as powder injection molding, and thermal spraying of coatings or near net shape parts.

Powder metallurgy Tekna’s plasma treated powders have superior properties in terms of spheroicity, tap density and purity, making them attractive precursors in many fields of the powder metallurgy.
Wear resistance application Spherical tungsten carbide (WC) is the base material of choice for hard surfacing application. It is well known that coating using spherical WC powders provides a better resistance to wearing and is less abrasive. Tekna’s unique spherical powder is being used for industrial applications such as: Centrifuges drums Drilling tools Nozzles Cutting edges
Electronic components The electronic industry benefits from the high purity spherical powders produced by Tekna’s induction plasma process for manufacturing high end electronic components such as piezoelectric devices, and hard drives.
Thermal spraying and laser cladding Plasma treated powder improves considerably the flowability of the powder which allows a better feeding and reflects in more uniform coating. The steady feeding is one of the most important parameters to achieve high quality thermally sprayed coating and laser cladding applications.

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Technology

• Plasma State Technology
• Nanopowder Synthesis
• Spherical Powder
• Plasma Spray Coating