The first step in converting Chrome ore into Electrolytic Chromium Metal is to dissolve Chrome ore in a solution suitable for the electrolytic process. The two most common types of solution are 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. Some interesting articles on this subject can be found at: https://link.springer.com/article/10.1007/s40094-014-0129-5 .
And https://www.emsdiasum.com/microscopy/technical/datasheet/sputter_coating.aspx .
During the electrolytic process the hexavalent Chrome is completely converted to inert Chromium metal leaving virtually no traces of any other metals.
Oxygen and Sulfur levels are also very important in making sputter targets. Thus, in most cases the Electrolytic Chromium must be degassed by high temperature Hydrogen reduction.
Exotech is a primary manufacturer of Chromium powder. This is accomplished using Chromium in ‘flake’ form, pure Chromium ‘eggs’ or used Chromium sputter targets. The ultimate application and customer specification will determine the input Chromium metal to be used.
A source of very pure Chromium is used high purity Chromium sputter targets. Since generally only about 25-30% of a target is consumed in sputtering, the remaining material is available to be recycled by crushing back into powder.
Exotech has developed a special process to insure that the powder made from used Chromium sputter targets is virtually unchanged from the powder that originally made the target.
Exotech crushes the flakes and used targets in uniquely designed impact mills to the required particle size. Special materials of construction are used by Exotech to minimize trace element contamination, particularly Iron contamination. If Oxygen levels are very critical, the milling process is carried out in an inert atmosphere.
Exotech’s milling process is 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. By carefully controlling the milling/screening sequence, a very uniform batch to batch product is produced.
Exotech’s powder is then 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 customer. Exotech’s Chromium Powder is known for excellent uniformity in chemistry and size.
Powders are made in sizes from 0.5 mm to <45 µm for pressing into solid targets. Purities of Exotech powder are generally greater than 99.8% but are commonly 99.9%, 99.95%, and higher.
Mark Gussack, B. S. Ch. E., is the former President of Exotech, Inc. Exotech, is a manufacturer of high purity Chromium powder and a processor and recycler of exotic metals. Typical metals processed are Chromium, Tantalum, Niobium, Molybdenum, Tungsten, Germanium, Zirconium, Vanadium, Cobalt, Hafnium, and Indium. Exotech’s offices and manufacturing are located at 1851 Blount Road, Pompano Beach, FL 33069.