DENSIFICATION
AND SPHEROIDIZATION OF POWDERS
System description
Powder treatment by induction plasma processes is used to provide spheroidization and densification effects for the particles, which have important applications in the industry. Tekna has designed and implemented several industrial-scale systems for treating powders.
Industrial induction plasma system
The process systems developed by Tekna are characterized by their ability to melt relatively large particles and to operate with a wide range of gases. The latter offers a means of controlling powder chemistry. Thanks to our technology, our systems deliver a high-quality and stable powder treatment.
Some of the major features of the systems are:
Our control console monitors all vital system parameters and controls the operating parameters such as gas flow rate, water flow rate, temperature, gas pressure and water pressure. It incorporates the system interlocks that prevent the operation of the system under unsafe conditions. Its design features include:
Powder densification and spheroidization is one of the simplest and most widely accepted applications of induction plasma technology. It basically consists of in-flight heating and melting of feed material in the form of sintered or crushed powders. The thus-formed molten spherical droplets are gradually cooled under free fall conditions. Depending on the size and apparent density of the treated powder, their time of flight is controlled such that the molten droplets have ample 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.
The process is schematically represented in the attached figure. The heating of the particles is dependent on the proper balance between conductive and convective heat transfer from the plasma to the particle, and radiative heat losses from the particle surface and the vapor cloud surrounding the individual particles.
Examples of processed powders
Metallic powders before and after induction plasma melting and spheroidization
Electron micrographs of different
metallic and ceramic powders
spheroidized at Tekna using induction plasma technology
Silica powder spheroidization at Tekna in an open-air 100kW air induction plasma system
Applications
The plasma spheroidization process is an effective and economical process which can be used to significantly improve the physical and chemical properties of the treated powders in one or more of the following ways:
Improved powder
flowing properties
Spheroidized particles provide a more homogeneous 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 overall density of the powder is increased by having spherical 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.
Improved particle
surface finish
The sharp edges of individual particles are eliminated. The macroscopic surface
becomes smoother by improving microscopic smoothness levels. This principle
would benefit applications which require lower friction coefficients. The gas
transport of some non-spherical powder can cause a great deal of wear, which
leads to contamination and frequent parts replacement. In addition, a smoother
surface would decrease variability in the pigment mix recipes between production
lots, which would benefit paint manufacturers.
Enhanced
powder purification
The in-flight melting process can also be favourably used to enhance powder
purity through the selective/reactive vaporization of specific 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 required ppm or ppb levels in one or multiple passes
depending on the precursor's initial composition.