Many alloys have rare earth additions to improve their surface properties at high temperatures. A new product, Minimox® Nanocrystalline Alloy Treatment, exploits this fact to protect a variety of alloys in extreme environmental conditions of elevated temperature and/or corrosive atmospheres. Thermal oxides that form after this treatment are different in structure and/or chemistry from the thermal oxides that form without pretreatment. The ultimate protective oxide is primarily a function of the alloy itself, not the rare earth material (Figure 1). In this way, the treatment helps the alloy become self-protective. The technology allows economical surface modification in the field and inside complex geometries using low concentrations of rare earth materials in a water-based solution.
Because Minimox® treatment is effective on a wide range of alloys (stainless steel, nickel, aluminum, magnesium and superalloys), the product can solve problems in diverse fields. These applications include pretreating stainless steel before heat treatment, protecting furnace components, lessening stainless and aluminum corrosion (Figure 2), decreasing spalling of utility plant fixtures, improving composite mechanical properties, reducing metal dusting failures, and magnesium alloy property improvement. The maximum temperature is set by the alloy, not the solution. Minimox® solution has provided astonishing protection in extreme environments, including over 1100°C.
The potential benefits are obvious. The cost of alloys that contain rare earth materials are typically 5X those that do not - Minimox® solution allows for lower cost alloys in place of expensive materials.
Demand for rare earths is anticipated to exceed supply in the near future. Using Minimox® alloy treatment, a low concentration of rare earth species is located only on the surface of the alloy - where it is needed - reducing the consumption of this valuable natural resource.
Minimox® nanocrystalline alloy treatment is water-based and has the appearance and viscosity of water - it is clear and nearly colorless (Figure 3). It is applied by either spray or dip methods without any special equipment. Protection of inside surfaces is obtained by pouring the solution in and pouring out the excess.
Applications of rare earth coatings via other methods include ion implantation and laser alloying, both expensive methods that cannot be done in the field. In contrast, the price for Minimox® protection is less than $0.18/square foot. Another method developed at National Energy Technology Laboratory (NETL) includes painting on a CeO2 slurry followed by heating in a vacuum furnace to 900°C and brushing off remaining loose powder. Clearly, this cannot be done in the field or on aluminum alloys. For the NETL process, it is the CeO2 coating that is doing the protecting. For the Minimox® process, the alloy is protecting itself through an improved thermal oxide.
Minimox® Nanocrystalline Alloy Treatment is an environmentally safe product that decreases material costs and reduces the use of natural resources of rare earth elements as well as alloy additions like chromium and nickel. The diversity of applications will drive a wide variety of new and improved products. Minimox® treatment is, quite simply, The Perfect Solution™ for aggressive environments.
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