Publication Date
2017
Document Type
Thesis
Committee Members
John Boeckl (Committee Member), Jason Deibel (Committee Member), Gregory Kozlowski (Committee Chair), Zafer Turgut (Committee Member)
Degree Name
Master of Science (MS)
Abstract
Covetics are hybrid materials fabricated by fusing carbon with metals in an induction furnace. There is an indication that covetics have better thermal and electrical proper-ties in comparison with pure metals. The main goal of this research is to study thermal transport in covetics measured by specific absorption rate using calorimetry. In addition, temperature distribution has been measured along the both metal and covetic wires carrying currents of 5 A and 10 A, respectively. The first set of copper covetic (Cu cov) samples with nominal content of 36 at% carbon were prepared by Third Millennium Materials Company (TMMC) in the induction furnace using ceramic mold. After cooling, these samples were subjected to cold rolling to make wires. To remove contamination, defused from ceramic molds into covetics, the samples were subjected to numerous remelting steps in the induction furnace. In addition to remove stresses, the samples were annealed at elevated temperature in argon. Overall four Cu cov samples: as-received, and 8 remelt, including annealing, were pre-pared by TMMC. The second set of six Cu cov including annealing samples with nominal contents of 0 at%, 5 at%, and 10 at% carbon were prepared in AFRL facilities using graphite mold. For comparison, four other silver covetic (Ag cov) samples with nominal con-tents of 0 at% and 36 at% carbon were prepared under three different cooling processes by the TMMC. The SAR measurements of all covetic samples were done in a calorimetric system at currents of 5 A, 10 A, and 15 A, and at 177 kHz of AC magnetic field. The experimental data show that covetic samples have mixed heating rates in comparison to the pure metals. For instance, all the silver and Cu cov samples show lower specific absorption rates than the corresponding host metals, except the annealed Cu cov and druzzy Ag cov (a molten Ag cov was slowly cooled and stirred with graphite) samples. Additionally, SAR was higher for all the samples when the temperature sensor was touching top of the samples than for the sensor 2 mm above the samples. Finally, we observed the temperature distribution along Cu cov wire which was significantly lower than pure copper wire. Our research have showed that Cu cov samples provided by AFRL with nominal atomic percent of C increased from 0 to 10 at% indicate gradual decrease in average values of SAR and heating rate. For example, average value of SAR including annealed samples changes from 348 W/g for pure Cu (5N) to 77 W/g for Cu cov with 10 at% C. This de-crease of SAR (or heating rate) can be easily explained by changes in heat carriers from electrons (metal) to phonons (carbon). In contrast to this result, the samples provided by TMMC characterized by heavy cold rolling (Cu cov wire or Cu cov as received (AR)) with initial value of SAR very low and related to that low thermal conductivity. It can explain the observed high ampacity in this system. However, the same samples subjected to annealing process show significant increase in the thermal conductivity or SAR value as a result of stress removal in the presence of impurities or voids that are uniformly distributed inside of Cu or Ag grains.
Page Count
99
Department or Program
Department of Physics
Year Degree Awarded
2017
Copyright
Copyright 2017, all rights reserved. My ETD will be available under the "Fair Use" terms of copyright law.
