Radiation-Tolerant, High Thermal Conductivity Adhesives for High Energy Physics Detector Applications
High Energy Physics experiments utilize highly specialized detector systems that are dimensionally stable and have very low mass so that detected particle scattering is reduced. For this purpose, current detector systems make significant use of fiber-reinforced composites and adhesives; however, increasing the composite material’s though-thickness heat transfer is still desired. In particular, having a room temperature thermal conductivity above 4 W/m-K would greatly improve the overall system performance. For many applications, having both a low electrical conductivity in conjunction with high thermal conductivity is beneficial, creating a significant material design and formulation challenge. The objective of this Phase I SBIR effort was to develop a radiation tolerant resin system with high thermal conductivity that specifically addresses requirements unique to high energy physics detector applications. Specifically, the radiation length of the resulting resin system must be on the order of 20 cm in order to minimize scattering of the high energy particles being detected. In the Phase I program, Composite Technology Development, Inc. (CTD) sought to develop thermally conductive adhesive formulations with a radiation length appropriate for use in high energy physics detectors. Due to the radiation length requirement, the use of carbon-based fillers was favored over other options. The development of radiation-tolerant cyanate ester resins with low cure temperatures was also undertaken. Thermal modeling identified carbon nanotubes (CNT), with theoretical thermal conductivities on the order of 3000 W/m-K, as one of the most promising approach for increasing adhesive thermal conductivity while minimally affecting the radiation length of the adhesive. Despite not being oriented in the through thickness direction, it was demonstrated that the addition of even a small volume fraction of carbon nanotubes, either directly in the resin or in a mat carrier cloth offered a three-fold improvement in thermal conductivity over formulations containing graphite particles alone. It was further shown that a mixture of particle sizes and shapes provided the most enhancement to thermal conductivity; a three-fold increase in thermal conductivity relative to the unfilled adhesive system was realized. To explore the effect of using through-thickness alignment of CNT to enhance thermal conductivity, we evaluated the thermal conductivity of a composite laminate fabricated using a Z-direction enhanced carbon fabric. It was found that the Z-enhancement offered over 225% improvement in thermal conductivity, definitively demonstrating the value of aligned carbon for thermal conductivity enhancement. The milled carbon fibers here have more defects and smaller aspect ratios than carbon nanotubes, so it is expected that using aligned carbon nanotubes would provide significant improvements. Low temperature curing cyanate ester adhesives containing thermally conductive additives were also a target of this program. CTD successfully demonstrated a cyanate ester formulation capable of curing at 120°C both with and without thermally conductive fillers. Lap shear testing of adhesives based on this formulation exhibited bond strengths between 25 and 28 MPa, similar to that of the Hysol® EA9396 epoxy adhesive that is currently used in detector structural bonding applications. Overall, the results of the Phase I program demonstrated the potential for achieving high thermal conductivity in adhesive systems through the addition of carbon nanotubes. Additionally, potentially radiation-tolerant cyanate ester adhesives, with thermally conductive additives were developed and shown to have adhesive strengths comparable to that of the currently used Hysol® EA9396 system.
- Research Organization:
- Composite Technology Development, Inc., Lafayette, CO (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0019798
- OSTI ID:
- 1638506
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- DOE-CTD-19798; 7427
- Country of Publication:
- United States
- Language:
- English
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