All About Virginia Mullite
Everything you’ve ever wanted to know about Virginia Mullite!
What is Virginia Mullite?
Virginia Kyanite is converted to Mullite by calcining it at more than 1450°C in a rotary kiln. The resulting product, called Virginia Mullite, contains about 80% Mullite, 11% finely dispersed amorphous silica, 7% quartz, and less than 1% cristobalite. The alumina content of Virginia Mullite is between 56-61%. Virginia Mullite is different in particle shape and impurities than Mullite formed by calcining clay minerals. Because it is produced by calcining beneficiated Kyanite, not clay minerals, it retains a unique, acicular “blade-like” crystal structure and is very low in iron oxide and other impurities. These small, lenticular crystals promote high strength, even at very high temperatures.
How is Mullite used?
Our Mullite is used in applications where high creep resistance is critical. The low impurities in our Mullite makes it resist creep as well as mold metal reactions. Mullite can be used in refractory, ceramics, electrical insulators, heating elements, brake shoes, foundry sprays and washes, Mullite/cordierite kiln furniture, investment casting flours and stuccos, and more. It is used extensively in high-temperature applications for its high melting temperature, high hot strength, and excellent thermal shock and creep resistance.
How is KMC’s Mullite different from other Mullites on the market?
Our Mullite is made by calcining Kyanite. Other Mullites are typically created by calcining clay particles. Because of this, there are several differences in the physical properties as well as purity. When KMC makes Mullite, we have to purify the Kyanite from its orebody, and that purity transfers over to the Mullite. It also translates into a very different shape than typical Mullites. KMC’s Mullite is needle shaped and this aids in things like the strength of the refractory but changes the flowability/workability of the refractory castables/plastics. Additionally, the impurity level of our Mullite is generally lower than other Mullites.
What is the maximum size of KMC’s Mullite?
Unlike Mullites that are made from clay, our Mullite sizes cannot be larger than the largest size of Kyanite that we produce. We are limited in our maximum size to a 20x50 particle size because we need to eliminate the other minerals present in our orebodies to keep our purity as high as possible. We can then grind down our material to various sizes including 325 and finer for our customers.
More questions about Mullite? Reach out to us!
