Current Research

    Piezoelectric materials are widely used as sensors and actuators. Dr. Viljoen's group is focusing on piezoelectric materials which can be used in high temperature, oxidizing environments. Important applications include vibratory measurements in combustion housings of turbines and burners, as well as acoustic probing of structures at high temperatures. An acoustic system to detect cracks in a cement-based composite is under development for a metals-processing company. The system is designed to monitor the vessel while it is in use, eliminating the need to take equipment out of commission for an evaluation.
Thin films are sputtered onto a variety of substrate materials. Substrates for high temperature applications include Ni and Cr alloys. Rapid thermal annealing (RTA) is used to improve crystallinity and hence signal performance. The optimum RTA protocol leads to dramatic improvements; peak to peak strength of signals as high as 400 mV has been measured for vibratory tests.
Another research focus is ultra-fast reactions of highly energetic materials. Classical SHS is associated with slow deflagrations. Experimental evidence exists that fast deflagrations and detonations in the solid phase are possible. Models are developed for the compaction of porous preforms by a shock wave and the initiation of reaction by compression, viscoplastic dissipation and reduction of ignition temperatures by elastic compression.
Research is funded by NRI, Globe Metallurgical Inc., and NCMN.

Recent Key Publications

B. R. Jooste and H. J. Viljoen "A Study of Orthorhombic Ta₂O₅," J. Mater. Res. 13 (2), 475 (1998).

H. J. Viljoen and V. Hlavacek, "Deflagration and Detonation in Solid-Solid Combustion," A.I.Ch.E. Journal 43 (11), 3085 (1997).