In this interview, Christine Fingar, application engineer at Master Bond Inc., highlights the critical importance of specialized adhesives for cryogenic environments.
When discussing cryogenic temperatures, what is the range we are talking about?
The Kelvin scale is commonly used when referring to cryogenic conditions, and cryogenic temperatures are typically below -153 °C, or 120 Kelvin (K). “High-temperature cryogenics” extends the definition to include temperatures ranging from the boiling point of liquid nitrogen -196 °C (77 K) up to -50 °C (223 K), which corresponds to the lowest temperature achieved by conventional single-cycle vapor-cycle cooling methods in refrigeration.
Why are specialized adhesives necessary at cryogenic temperatures?
The unpredictable effects of cryogenic temperatures on materials present various challenges in bonding, sealing, coating, or encapsulating assemblies intended for very low-temperature operations.
Adhesives are used to create composite structures, safeguard electronic components, and achieve hermetic sealing for optical components, for example. Like the materials they adhere to, extreme cold can cause certain adhesives to lose adhesion, become brittle, and fracture under high vibration or impact. This could result in failure modes such as delamination and leaks in the bond joint.
Specialized, cryogenically serviceable adhesives successfully resist such environments and prevent failure modes. They play a vital role by maintaining the necessary strength profile even at such temperatures.
What is the impact on the mechanical properties of adhesives at cryogenic temperatures?
For most epoxy adhesives, cryogenic conditions can increase the modulus and hardness, reduce the elongation, and, in some cases, increase the adhesion strength. Most silicone adhesives tend to become extremely brittle below their glass transition temperature, which is typically around -50 °C, with some specialized low-temperature silicones going down to –100 to –120 °C. However, service below this temperature for most silicone adhesives is not typical.
How do fillers modify an adhesive’s performance properties at cryogenic temperatures?
Epoxy systems can incorporate filler materials, which improve specific properties such as hardness, dimensional stability, chemical resistance, thermal and electrical conductivity, and more.
By carefully selecting filler materials, adjusting particle size, and controlling the percentage of filler loading by weight, manufacturers can tailor epoxies to exhibit the desired properties. Specialty fillers can be selected to reduce the coefficient of thermal expansion and enhance dimensional stability even under cryogenic conditions.
What are some examples of fillers used in cryogenically serviceable epoxies?
Some examples include aluminum oxide-filled epoxies, which are thermally conductive and electrically non-conductive, and silver-filled epoxies, which are both electrically and thermally conductive. For dissipative applications, graphite-filled epoxies can also be a good choice.
Where are cryogenically serviceable adhesives, sealants, and encapsulants most used?
Most cryogenically serviceable adhesives are used in spacecraft applications. In such situations, NASA low outgassing or ASTM E-595-rated adhesives are a prerequisite.
Space-borne applications pose unique challenges due to their rigorous conditions and mission-critical demands. Enduring the vacuum of space is just one aspect; space platforms also undergo extensive thermal cycling across a broad temperature spectrum. Whether it is for Earth-based simulations of space conditions or innovative ventures delving into unexplored territories, the demand for adhesives is wide and varying.
Cryogenic adhesives are widely utilized in applications such as cryogenic sensors, cryostats, superconducting magnets, cryopreservation assemblies, and medical devices. In medical device situations, USP Class VI biocompatibility rated and/or ISO 10993-5 non-cytotoxicity tested products tend to be needed.
About Christine Fingar
Christine Fingar is an Application Engineer at Master Bond. She is HAZMAT trained and actively involved in new product development testing and ensuring quality compliance with various Master Bond products. She has over seven years of experience in analyzing application-oriented issues and provides product solutions for companies in the aerospace, electronics, medical, optical, and oil/chemical industries. She received a Bachelor's Degree in Chemical Engineering from Rensselaer Polytechnic Institute (RPI) in 2017.
This information has been sourced, reviewed and adapted from materials provided by Master Bond Inc.
For more information on this source, please visit Master Bond Inc.
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