Richard Fink | Applied Nanotech Inc: Can aerosol-jet printed refractory metals match the electronic properties and thermal stability of bulk materials?

Can printed thin-film thermocouples match the accuracy of standard wire sensors at extreme temperatures?

Evaluating printed Type K thermocouples (Chromel and Alumel) reveals promising alignment with traditional wire-based standards up to extreme temperatures. When sintered at 1300 degrees Celsius and tested in an argon atmosphere up to 1100 degrees Celsius, the printed device's temperature response closely tracks wire sensors with a slope of 1.04, representing just a 4 percent variance likely caused by spatial placement within the tube furnace. This demonstrates that printed metal inks can maintain accurate thermoelectric properties under inert, high-heat conditions.

Transitioning the testing environment to open air reveals critical material performance limits. Under atmospheric conditions, the printed sensor maintains a near-perfect 1-to-1 tracking ratio against wire controls up to 950 degrees Celsius, enduring an hour-long soak at 700 degrees Celsius during the ramp. However, failure occurs around 950 degrees Celsius due to severe oxidation of the printed tracks.

Post-failure analysis reveals distinct degradation paths for the two printed materials. The Alumel track oxidizes completely, flaking off as a non-conductive residue, whereas the Chromel track exhibits marginally better oxidation resistance, remaining intact but degrading into the megohm resistance range.

In this short video, you can learn:
* How printed Chromel and Alumel inks compare thermoelectrically to conventional wire thermocouples.
* The performance limits and behavior of printed thermoelectric sensors under inert argon versus open-air environments.
* The specific degradation mechanisms and failure modes of printed Type K materials at high temperatures.
📋 **Clip Abstract** This clip examines the performance of printed Chromel-Alumel (Type K) thermocouples tested up to 1100°C in argon and 950°C in air. The presenter details the sensor's high-temperature tracking accuracy and explains how open-air thermal failure is driven by the rapid oxidation and flaking of the Alumel trace.
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How do you stop refractory metal inks from bead-forming and losing adhesion during high-temperature sintering?

Molybdenum serves as an exceptional refractory conductor for extreme, high-neutron-flux environments, but adapting it into a printable ink presents severe thermodynamic challenges. When pure molybdenum ink is printed onto alumina and sintered at 1500 degrees Celsius, the material undergoes island growth. Because the internal cohesion of the sintering molybdenum particles is stronger than their adhesion to the ceramic substrate, the film breaks up into isolated, non-conductive droplets rather than forming a continuous path.

To overcome this fundamental physical limitation, the molybdenum ink must be doped with a small concentration of manganese. This metallurgical modification lowers interfacial energy and dramatically enhances the adhesion of the metallic phase to the alumina substrate. The doping process successfully suppresses the islanding effect, enabling a stable, continuous metallic film that remains bonded during extreme thermal processing.

Focused ion beam (FIB) cross-sectional analysis of the co-fired molybdenum-manganese film reveals its microstructural characteristics after sintering at 1500 degrees Celsius in an argon-hydrogen reducing atmosphere. Although the resulting film exhibits a degree of micro-porosity, the molybdenum particles are thoroughly fused and sintered together, establishing a robust, highly conductive, and well-adhered network.

In this short video, you can learn:
* The physical cause of island growth and dewetting during high-temperature sintering of pure refractory metal inks.
* How manganese doping alters interfacial energy to resolve adhesion and cohesion imbalances on ceramic substrates.
* The structural and network morphology of co-fired molybdenum inks analyzed via focused ion beam (FIB) cross-sections.
📋 **Clip Abstract** The presenter details the challenges of using molybdenum ink on alumina, focusing on the dewetting and island growth that occurs during 1500°C sintering. He explains how doping the formulation with manganese successfully resolves adhesion issues to yield a continuous, fused conductive path.
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