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  MSE / Research / Projects / Rapid Investigations of Ultra-high Temperature ceramics

Rapid Investigations of Ultra-high Temperature ceramics
Materials: Composites Ceramics
Application: Structural
Technique: Processing Characterization

Ultrahigh temperature materials are receiving more attention due to an increase need for materials for extreme environments. Researches have shown the ultra high temperature ceramic (UHTC) composites ZrB2-SiC and HfB2/SiC have the most promise for use at ultrahigh temperatures due to their high melting temperatures, and high hardness, and chemical stability at elevated temperatures. To develop these materials, we must characterize the oxidation behavior and physical properties at temperatures around 2500oC. This is a challenge due to the difficulty in achieving the necessary high temperatures in the laboratory in a conventional furnace, making experiments difficult and expensive. There is also a challenge in the specimen fabrication, and there exists a difficulty of characterizing the oxidation process, due to the primary analysis being the room-temperature microstructure of the specimen after oxidation.
Our solution to this problem is the design of a self-supporting, self-heated miniature specimen along with a simple table-top apparatus. The specimen is prepared so it is a “matchstick”, a 2-mm square cross section and 20 mm long. In the center of the specimen the thickness is reduced to 0.35 mm to make a ribbon-like hot zone. A power supply is used to pass a modest current into the “thick” ends of the matchstick which will stay relatively cool, while the ribbon hot zone can reach desired temperature. The oxidizing ribbon is supported by the thicker ends of the matchstick i.e. self-supportive. The temperature is sensed with an optical pyrometer, which provides input to the control circuit to adjust the current to maintain the desired temperature.
The small size of the specimen enables us to reach high temperatures quickly without creating a difficult-to-manage heat load in the surroundings. Also, the small heat load enables diagnostics to be brought close to the hot specimen during testing, e.g. in-situ optical microscopy imaging.
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