Specialty Products: Mullite Edition
Alongside our flagship Virginia Kyanite® and Virginia Mullite®, KMC produces a range of specialty materials designed for highly specific applications. While they represent a small portion of our overall production, these products often deliver big results—helping customers solve challenges in refractories, ceramics, and investment casting.
In Part 2 of our Specialty Product Series, we’re highlighting Micronized Mullite, Stuccos, and Premium Grade Virginia Mullite®. First up, Micronized Mullite:
Micronized Mullite
What is it?
An ultra-fine version of our Virginia Mullite®, representing less than 1% of total sales. This product offers a pure source of alumina fines that remain partially unreacted, making it ideal for applications where micronized kyanite would not fully convert to mullite.
How is it made?
Instead of standard ball milling, micronized mullite (and micronized kyanite) are produced using an air-jet mill, where particles collide at high speed, reducing them to a d50 of around 5-10 microns—finer than our K325. It’s more challenging and costly to produce, but delivers unique performance benefits.
What is it used for?
Primarily in ceramic and refractory applications requiring a pure alumina source, especially when firing temperatures are too low for micronized kyanite. It also enhances thermal shock resistance.
Stuccos
What are they?
Coarse refractory grains used in the outer layers of investment casting shells to add strength, thickness, and high-temperature durability.
How are they made?
After calcination, our 35 mesh mullite is screened using multi-deck vibratory sieves to achieve precise mesh sizes of 20×50 mesh (coarser) and 50×100 mesh (finer). Oversized and undersized particles are removed and returned to the mill for further processing.
What are they used for?
Ideal when tighter control over particle size is needed or when eliminating nuisance dust in shell rooms. Fewer fines mean improved flowability and reduced water demand in the refractory. Stuccos are also used as grog in pottery.
20x50 is as coarse as we can produce our stucco—we start with 35 mesh as our feed material, which is the size we must grind the ore to remove impurities.
Premium Grade Virginia Mullite®
What is it?
Our newest specialty mullite, engineered with ultra-low iron oxide—reduced from a maximum of 0.75% to less than 0.2%—and lower titania (TiO2) for superior thermal stability. The result: improved creep resistance, dimensional stability, and casting yields.
How is it made?
Following our standard beneficiation process, the mullite undergoes additional passes through the magnet house to remove even more iron and titania. Our main Premium Grade size, known as Premium Grade F21, was developed through extensive R&D for use in investment casting slurries. The sizing provides ideal rheology to the slurry. Premium Grade Virginia Mullite is also available in 35 mesh and stucco sizes.
What is it used for?
Designed for investment casting shells and slurries requiring maximum purity to prevent creep and bulging. In some cases, it can replace zircon in shells and coatings, offering a more cost-effective alternative depending on metal type and temperature.
Learn even more about Premium Grade Virginia Mullite® here!
Special Considerations
Lead Time: Specialty runs are more time-intensive and less frequent—advance notice helps us plan production and ensure availability.
Custom Sizing: We can evaluate special screenings or sizes on a case-by-case basis.
Custom Products: We also produce many proprietary specialty materials under NDA for customers worldwide.
Have a challenge in mind? We’d be happy to discuss whether a specialty mullite could be the solution.
Get in Touch: sales@kyanite.com | +1 (434) 983-2043
If you missed it, explore Part 1: Specialty Kyanite Products
