This work was based on the need for a relatively small passive detector of maximum temperature reached by an object that can be visually inspected. The device requirements are to be hermetically sealed for contamination control, give a clear indication of maximum temperature achieved (non-reversible) with a ~10 °C resolution, have an essentially unlimited shelf-life and insensitivity to radiation, be passive without any electronics or mechanisms, provide good thermal conductivity, and be low-cost. Prior detectors have an unclear lifetime, contamination outgassing properties, and radiation tolerance. These could be used at much higher temperatures than plastic methods (>>100 °C), though out of scope for the tests performed to date.
A device that permanently records the maximum temperature reached (47-70 °C) was tested, though other temperatures are possible. The low-cost device is hermetically sealed with no possibility of organic contamination, has an essentially unlimited shelf-life, is impervious to radiation damage, can function in any orientation or gravity, is unpowered, and passive. The device is read by visual inspection after opening the seal.
This work provides a metallic, robust, simple, non-reversible thermometer. The device features a commercial off-the-shelf (COTS) ultra-high vacuum flange with COTS eutectic metals and COTS Kapton tape. The design is flexible for space or non-space extreme environments where the temperature can be read optically, and can be used at much higher temperatures.