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.
Valente WJ, Pienaar E, Fast A, Fluitt A, Whitney SE, Fenton RJ, Barletta RG, Chacon O, Viljoen HJ, "A Kinetic Study of In Vitro Lysis of Mycobacterium smegmatis." Chem. Eng. Sci. 64 pp1944-52 (2009).
Pienaar E, Whitney SE, and Viljoen HJ, "A model of the complex response of Staphylococcus aureus to methicillin." J. Theor. Biol. 257 pp438-445 (2009).
Mammedov T, Pienaar E, Whitney SE, TerMaat JR, Carvill G, Goliath R, Subramanian A, and Viljoen HJ, "A Fundamental Study of the PCR Amplification of GC-Rich DNA Templates." Comp. Biol. & Chem. 32 pp452-457 (2008).
Pienaar E and Viljoen HJ "The Tri-Frame Model" J. Theor. Biol. 251: pp616-627 (2008). Pubmed# 18237749.
Fluitt, A, Pienaar E and Viljoen, HJ, "Ribosome kinetics and aa-tRNA competition determine rate and fidelity of peptide synthesis," Comp. Biol. Chem. (2007).
Tarlan G Mamedov, T.G., Kotera C, Padhye, N., Viljoen, H.J. and A. Subramanian "Rational 'de novo' Synthesis of Genes by Rapid Polymerase Chain Assembly (PCA): Assembly and Expression of Endothelial Protein-C Receptor Genes." J. Biotech. (2007).
Whitney, S., R. Agupally, R, M. Nelson, and H.J.Viljoen, "Principles of the Polymerase Chain Reaction: Mathematical Modeling and Experimental Verification" Comp. Biol & Chem. 28 pp195-209 (2004).
Ebmeier, R., S. Whitney, R. Agupally, G. Gogos, R.M. Nelson, N. Padhye and H.J. Viljoen, "A Ranque-Hilsch Vortex Tube Based Thermocycler for DNA Amplification" Instr. Science & Tech. 32 : 567-571 (2004).
Ebmeier, R., S. Whitney, R. Agupally, G. Gogos, R.M. Nelson, N. Padhye and H.J. Viljoen, "A Ranque-Hilsch Vortex Tube Based Thermocycler for DNA Amplification" Rev. Sci. Instr. 75 pp5356-5359 (2004).
Viljoen, S.V., M. Griep, M. Nelson and H.J. Viljoen, "A Macroscopic Kinetic Model for DNA Polymerase Elongation and High Fidelity Nucleotide Selection, " Comp. Biol & Chem 29 pp101-110 (2005).
Griep M, Whitney S, Nelson M and Viljoen HJ "DNA Polymerase Chain Reaction: A Model of Error Frequencies and Extension Rates" AIChE J. 52 pp384-392 (2006).
Pienaar, E.M., Theron, M. Nelson and H.J. Viljoen, "A Quantitative Model of Error Accumulation During PCR Amplification," Comp. Biol. & Chem. 30 pp 102-111 (2006.)
Griep, M.A., Kotera, C.A., Nelson, R.M. and Viljoen, H.J. "Kinetics of the DNA Polymerase Pyrococcus Kodakaraensis." Chem. Eng. Sci. 61 pp 3885-3892 (2006)Reaction Engineering of Heterogeneous Systems
Gordopolov, A., O. Dzenis and H.J. Viljoen, "Compression of Powders in a Bridgman Anvil: Fracture and Reaction", Int. SHS J. 13 (3) pp233-243 (2004).
Gordopolov, A., H.J. Viljoen and N.F.J. van Rensburg, "Reaction of thermites in a Bridgman anvil Part I: The Pre-Explosion Phase." Chem. Phys. 24 (3), pp60-68 (2005).
Gordopolov, A. and H.J. Viljoen, "A Study in Mechano-chemistry: Pressure Induced Reactions and Non-equilibrium Phenomena" Int. SHS J. 14 (2005).
Gordopolov, A., O. Dzenis and H.J. Viljoen "Reaction of thermites in a Bridgman anvil Part II: Fracture and Reaction" Chem. Phys. 24 (4), pp61-65 (2005).
For additional publications, please click the Digital Commons link in the right column of the page.
2005 Multidisciplinary Research Award, University of Nebraska-Lincoln
Viljoen, H.J. and Jooste, B.R., "Piezoelectric Sensors/Actuators for use in refractory environments," U.S. Patent 6,057,628, issued May 2, 2000
Whitney, S., Viljoen, H.J., Padhye, N. and Nelson, M.R., "A gas jet process and apparatus for high-speed amplification of DNA." PCT Patent, issued in 2005 in 22 countries in Europe and Asia