Session: 02-01-06: 7th Annual Conference-Wide Symposium on Additive Manufacturing: Unique Applications II

Paper Number: 99884

99884 - Direct Ink Writing of Zno: Interparticle Force Measurements via Afm 

The additive manufacturing (AM) of ceramic materials has tremendous potential in a variety of electronics, energy, automotive, and aerospace applications. In order to facilitate broad commercial acceptance, however, a better understanding of how feedstock properties affect the resulting product are required. In addition, the development of validated computer models that can accurately simulate AM processes would aid in the design and optimization of AM ceramics. With this goal in mind we have chosen to investigate the direct ink writing (DIW) of ZnO, a common electronics ceramic, and employ atomic force microscopy (AFM) to directly measure interparticle forces of ZnO nanoparticles in the feedstock slurry for use in computational fluid dynamics and discrete element method simulations.

Spherical ZnO nanoparticles were synthesized using a polyol-mediated technique with zinc acetate dihydrate and diethylene glycol as precursors.  The nominal radius was 100 nm and ranged to greater than 1 µm as shown by small angle X-ray scattering. Custom colloidal probe AFM tips are constructed from Bruker Probe SAA-SPH-1µm cantilevers with a flexural stiffness of 0.25 N/m. ZnO nanoparticles are isolated, dried, and affixed to the AFM cantilever using an FEI Helios Nanolab 660 SEM and FIB with an Oxford Omniprobe 300 nanomanipulator attachment. ZnO particles are anchored within a FIB-milled socket at the AFM tip apex via Pt deposition from a MultiChem gas delivery system. Spectroscopic Force-Indentation AFM measurements between the custom colloidal probe tip and a polished polycrystalline ZnO counter surface are conducted both in air and in a closed fluid cell containing the aqueous slurry solution to best approximate the in-situ DIW environment. For experiments conducted in air, the pull off force is found to be on the order of 74.6 nN ± 5.8 nN at variable applied loads while the average snap-in distance was 2.7 nm ± 0.7 nm for a ZnO tip radius of 0.83 µm. Analysis of the fluid cell experimental data is underway. The experimentally measured pull-off forces and snap-in distances are analyzed utilizing the snap-in/pull-off Numerical Adhesion Parameter method (or SNAP method) developed by Carpick et al. This method allows for the numerical extraction of the intrinsic work of adhesion, W_ADH, and the characteristic length scale of the interaction, z₀. These two parameters describe the Lennard-Jones interaction potential and serve as inputs for Discrete Element Method (DEM) simulations. By performing DEM simulations using the experimentally determined potential parameters we can predict slurry rheological properties, compare our predictions to experiments, start to build the first direct quantitative link between particle interaction forces and suspension rheology, and inform controlled DIW 3D printing of ceramic objects.

Presenting Author: Brian Bush National Institute of Standards and Technology

Presenting Author Biography: Dr. Bush graduated with a B.S. in Chemical Engineering from the University of Delaware in 2003, and obtained his Ph.D. from the University of California - Berkeley in 2009. He currently works in the Nanomechanical Properties Group of the Materials Measurement Laboratory at the National Institute of Standards and Technology. His research interests include Atomic Force Microscopy (AFM) techniques for measuring the nanomechanical properties of Additive Manufactured materials, soft and biological materials, and reference material measurement and calibration.

Authors:

Brian Bush National Institute of Standards and Technology
Russell Maier National Institute of Standards and Technology
Abhay Goyal National Institute of Standards and Technology