Nano-calorimetry: A centuries-old technique applied at the nano-scale
Event details
| Date | 24.08.2017 |
| Hour | 10:00 |
| Speaker | Prof. Joost J. Vlassak, Harvard |
| Location | |
| Category | Conferences - Seminars |
An IMT Talk
Calorimetry has long been used to study chemical reactions and phase transitions in materials. The technique finds its origin in the mid-18th century when Scottish physician Joseph Black discovered the notion of latent heat and Lavoisier developed an ice calorimeter to measure the amount of heat given off during combustion of carbon or respiration of living organisms. Since then calorimetry has developed into a sophisticated technique indispensable in chemistry and materials science.
In this seminar, I will show how the same technique can be used to make measurements at the nano-scale. We use micromachining to fabricate arrays of calorimetric sensors that can perform measurements on samples as thin as a few nanometers at rates varying from isothermal to 105 K/s. The sensor arrays are ideally suited to explore complex materials systems in a combinatorial approach based on thin-film composition spreads. This methodology is illustrated using high-temperature Ni-Ti-based shape memory alloys, where the effects of composition, sample length scale, heat treatment, and thermal fatigue on the shape memory properties are revealed. Because of its large dynamic range, nanocalorimetry is also ideal for studying the kinetics of solid-state and solid-gas reactions. We use nano-calorimetry to evaluate the kinetics of the solid-state reactions in Zr/B and Zr/B4C multilayers at temperatures up to 1,400K. We demonstrate that ultra-high temperature ceramics such as ZrB2 and ZrB2/ZrC alloys can be synthesized at moderate temperature using reactive multilayers.
The formation reactions typically proceed in two distinct steps: inter-diffusion and amorphization, followed by crystallization. Kinetics measurements show that the activation energies for both processes are very different. First-principles calculations provide insight in the amorphization processes in the reactive multilayers and confirm the relatively low activation energies associated with the amorphization process. Finally, I will present some results on the crystallization kinetics of Cu50Zr50 metallic glass. Measurements over a wide range of scanning rates reveal that crystallization upon heating does not follow Arrhenius kinetics. Instead, the behavior is well described by a fragility-based model of growth-controlled kinetics that takes into account breakdown of the Stokes-Einstein relationship between diffusivity and viscosity as a result of the heterogeneous structure that develops in the undercooled liquid state.
Bio: Professor Vlassak studies the thermo-mechanical behavior of a broad range of engineering materials. He has developed experimental methods for the characterization of phase transitions and solid-state reactions in thin films, plastic deformation in coatings, elastic anisotropy in indentation, and fracture. Current projects focus on the mechanical behavior of hydrogels and the use of hydrogels as ionic conductors in 3D printed devices. Professor Vlassak has pioneered the use of combinatorial nanocalorimetry for the analysis of complex materials systems, including metallic glasses, ultra-high temperature ceramics, and shape memory alloys. He has authored more than 140 journal publications.
Calorimetry has long been used to study chemical reactions and phase transitions in materials. The technique finds its origin in the mid-18th century when Scottish physician Joseph Black discovered the notion of latent heat and Lavoisier developed an ice calorimeter to measure the amount of heat given off during combustion of carbon or respiration of living organisms. Since then calorimetry has developed into a sophisticated technique indispensable in chemistry and materials science.
In this seminar, I will show how the same technique can be used to make measurements at the nano-scale. We use micromachining to fabricate arrays of calorimetric sensors that can perform measurements on samples as thin as a few nanometers at rates varying from isothermal to 105 K/s. The sensor arrays are ideally suited to explore complex materials systems in a combinatorial approach based on thin-film composition spreads. This methodology is illustrated using high-temperature Ni-Ti-based shape memory alloys, where the effects of composition, sample length scale, heat treatment, and thermal fatigue on the shape memory properties are revealed. Because of its large dynamic range, nanocalorimetry is also ideal for studying the kinetics of solid-state and solid-gas reactions. We use nano-calorimetry to evaluate the kinetics of the solid-state reactions in Zr/B and Zr/B4C multilayers at temperatures up to 1,400K. We demonstrate that ultra-high temperature ceramics such as ZrB2 and ZrB2/ZrC alloys can be synthesized at moderate temperature using reactive multilayers.
The formation reactions typically proceed in two distinct steps: inter-diffusion and amorphization, followed by crystallization. Kinetics measurements show that the activation energies for both processes are very different. First-principles calculations provide insight in the amorphization processes in the reactive multilayers and confirm the relatively low activation energies associated with the amorphization process. Finally, I will present some results on the crystallization kinetics of Cu50Zr50 metallic glass. Measurements over a wide range of scanning rates reveal that crystallization upon heating does not follow Arrhenius kinetics. Instead, the behavior is well described by a fragility-based model of growth-controlled kinetics that takes into account breakdown of the Stokes-Einstein relationship between diffusivity and viscosity as a result of the heterogeneous structure that develops in the undercooled liquid state.
Bio: Professor Vlassak studies the thermo-mechanical behavior of a broad range of engineering materials. He has developed experimental methods for the characterization of phase transitions and solid-state reactions in thin films, plastic deformation in coatings, elastic anisotropy in indentation, and fracture. Current projects focus on the mechanical behavior of hydrogels and the use of hydrogels as ionic conductors in 3D printed devices. Professor Vlassak has pioneered the use of combinatorial nanocalorimetry for the analysis of complex materials systems, including metallic glasses, ultra-high temperature ceramics, and shape memory alloys. He has authored more than 140 journal publications.
Practical information
- General public
- Free
Organizer
- IMT
Contact
- Lysiane Bourquin