Carbon and related materials for thermal and electrical applications
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High thermal stability has been attained in polyol ester by using a sterically half-hindered phenolic primary antioxidant and a thiopropionate secondary antioxidant. Carbon black and boron nitride (BN) serve as antioxidants in the presence of either primary antioxidant or secondary antioxidant at 200°C. BN paste shows an estimated 100°C lifetime of 19 years, compared to 1.3 years for the carbon black paste and 0.10 year for commercial silver paste. Phase-change materials (PCMs) with high thermal stability and high heat of fusion have been attained by using antioxidants (mainly hydrocarbons with linear segments). Their heat of fusion is much higher than those of commercial PCMs. The use of 98.0 wt.% thiopropionate antioxidant with 2.0 wt.% half-hindered phenolic antioxidant as the matrix and 16 vol.% BN particles gives 100°C lifetime indicator 5.3 years, in contrast to 0.95 year or less for the commercial PCMs. Carbon-based films with thickness 1-13 μm, electrical resistivity 6 × 10 -4 - 3 Ω.cm, and strong bonding to alumina, have been attained through the use of EPON SU 2.5 epoxy and an amine curing agent as the carbon precursor, and a carbonization temperature of 650°C. Nickel nanoparticles (filamentary) are more effective for enhancing the conductivity than silver nanoparticles (not filamentary) at the same volume fraction. Even the combined use of carbon nanotube and silver is less effective than nickel. A three-dimensional microstructure in the form of a microscale bridge on alumina has been attained by using a novel low-cost process that involves thermoplastic spacer (wax) evaporation during pyrolysis of an epoxy-based film that coats the spacer and a part of the substrate. Multiwalled carbon nanotube as a filler is effective for reducing cracking during pyrolysis. A bridge with a girder of length 90-300 μm, separated from the substrate by a height of 5-15 μm, has been attained.