Nano-calorimetry: A New Tool for Materials Development
CME Department Seminar
March 6, 2020
2:00 PM - 3:00 PM
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Presenter: Prof. Joost J. Vlassak, School of Engineering and Applied Sciences, Harvard University
Abstract:
Calorimetry has long been used to study chemical reactions and phase transitions in materials. The technique finds its origin in the mid-18 th 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 10 5 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. 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 solid-state reactions in Zr/B and Zr/B 4 C multilayers and demonstrate that ultra-high temperature ceramics such as ZrB 2 and ZrB 2 /ZrC alloys can be synthesized at moderate temperatures. The formation reactions typically proceed in two distinct steps: inter-diffusion and amorphization, followed by crystallization. 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 Cu 50 Zr 50 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. Time permitting, a new isothermal device with applications in biophysics will be briefly discussed.
Bio:
Professor Vlassak studies the thermo-mechanical behavior of a broad range of engineering materials. He has developed experimental methods to characterize plastic deformation in thin films and coatings, elastic anisotropy in indentation, and fracture of coatings. Experimental research projects focus on the mechanical degradation of the electrodes in lithium ion batteries as a result of lithium insertion, on the swelling and fracture of hydrogels, and on the effects of microstructural length scales on the mechanical behavior of thin metal films. Recently, Professor Vlassak pioneered the use of combinatorial nanocalorimetry for the development and analysis of complex materials systems, including metallic glasses, ultra-high temperature ceramics, and high-temperature shape memory alloys.
Hosts: Dr. Sara Kadkhodaei and Dr. Matthew Daly
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Date posted
Mar 5, 2020
Date updated
Mar 5, 2020