Materials & Chemicals : Ceramics & glasses


Oxidation-Resistant Coatings for Ultra-High Temperature Ceramic-Based Materials

UW–Madison researchers have developed alumina coatings that form protective, oxidation-resistant scales on ceramic substrates at high temperatures. The method for coating the ceramic-based substrates involves a two-stage deposition process. This process comprises depositing a layer of molybdenum metal onto a surface of the substrate and subsequently co-depositing silicon and boron onto the layer of molybdenum in the presence of alumina to form a continuous MoSiB coating. Ceramic-based substrates that can be coated in accordance with this method include ultra-high temperature ceramics, fiber-reinforced matrix composites and refractory metal cermets.

Efficient Method of Producing Glass with Enhanced Stability

UW-Madison researchers have developed an efficient method of producing extremely stable amorphous material through vapor deposition of organic molecules. The key to their method involves controlling the substrate temperature used for film deposition to 50 K below the glass transition temperature (Tg) of the substance being deposited and depositing the material at a rate of less than 1 nm/s.

Current instrumentation used for vapor deposition typically does not provide a means of controlling the temperature of the substrate. As a result, the substrate generally stays at room temperature, which is not optimal for producing stable glasses. Film layers deposited on these relatively cold substrates “freeze” in place upon deposition with no opportunity to form a stable glass.

The inventors modified their instrument to provide a means of controlling the temperature of the substrate. When the substrate temperature is controlled to about 50 K below Tg and the material in each layer is deposited at a relatively slow rate, the molecules at the surfaces of each layer are mobile enough to pack efficiently with each other, creating a more integrated and therefore more stable glass film. 

Corrosion- and Wear-Resistant Coating for Vessels, Equipment and More

UW–Madison researchers and others have developed a new composite coating made of amorphous metal and ceramic particles. The coating can be applied to seagoing vessels, containers and any other surface to prevent corrosion.

Suitable metals for amorphous alloys may be iron-based and include other elements (yttrium, chromium, molybdenum, tungsten, boron or carbon). The ceramic particles are produced by a partial nanocrystallization reaction. They range in size from nanometers to microns, and are used to improve hardness and wear resistance while maintaining corrosion resistance.

The coating can be applied to surfaces by cold spray, thermal spray, physical vapor or other deposition technique.

Zirconium-Rich Bulk Metallic Glass Alloys

UW-Madison researchers have developed improved zirconium-rich bulk metallic glass alloys. The alloys contain zirconium, aluminum, titanium, copper and nickel, but do not require the addition of beryllium to provide high quality BMGs.

Machining of Lithium Niobate by Laser Fracturing

UW-Madison researchers have developed a method for rapidly dicing lithium niobate wafers into a variety of shapes, including curved shapes. The edges cut with this method are nearly atomically smooth, allowing direct attachment of fiber optic pigtails without further polishing.

The process uses a commercially available laser to create and guide a fracture through the wafer to cut it. Under different beam conditions, the same laser can also ablate features on the wafer surface, such as alignment marks, gratings and microwave and optical cavities. Model calculations have shown that ablated features can significantly improve the performance of devices, such as the traveling wave modulator.