Chromium Powder Manufacturing For Sputter Targets

The first step in converting Chrome ore into Electrolytic Chromium Metal is to dissolve the ore in a solution suitable for the electrolytic process. The two primary types of solution are a Chrome Alum Sulfate and Chromic Acid. The first is what is known as the Trivalent process and the second is the Hexavalent process. While the Trivalent process is much more efficient, the Hexavalent process makes a much higher purity metal.

If Chromium is needed for sputter targets where the purity must be over 99.9%, Electrolytic Chromium from the Hexavalent process must be used. While at times Chromium from the Trivalent process can exceed 99.9%, that purity cannot be reproduced on a regular basis.

During the electrolytic process the Hexavalent Chrome is completely converted to inert Chromium metal leaving no traces of any hazardous substances. Periodic tests are performed on the resulting metal to confirm the absence of any Hexavalent Chrome.

Oxygen and Sulfur levels are also very important in making Sputtering Target. Thus, in most cases the Electrolytic Chromium must be degassed by high temperature Hydrogen reduction. This can be accomplished with the Chromium in ‘flake’ form or as a pre-crushed powder. The ultimate application will determine the degree of degassing required.

Once the Chromium has been degassed, it is crushed in impact mills to the required particle size. Special materials of construction are used to minimize trace element contamination, particularly Iron contamination. If Oxygen levels are very critical, the milling process is carried out in an inert atmosphere.

The milling process should be designed to allow for a particle distribution that is consistent from one batch to another. This is to ensure that the targets made from one batch of powder perform the same as the targets made from another batch of targets. This is done by carefully controlling the milling/screening sequence.

Powder should also be blended into a homogeneous free flowing lot before samples are taken. Samples are then run for Particle Size Distribution, Tap Density, and full chemistry to ensure that the powder product meets the specifications of the sputter target manufacturer.

Powders are made in sizes from 1 mm for pressing into solid targets. Purities are generally greater than 99.8% but are commonly 99.9%, 99.95%, and higher.

Leave a Reply

Your email address will not be published. Required fields are marked *