Dispersion and Stability Studies for Development of Ceramic Paste for Direct Ink Writing
Open Access
- Author:
- Fellabaum, Chloe
- Graduate Program:
- Materials Science and Engineering (MS)
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- February 19, 2024
- Committee Members:
- Richard Joseph Meyer, Jr., Thesis Advisor/Co-Advisor
James Hansell Adair, Committee Member
John Mauro, Program Head/Chair
Robert Allen Kimel, Committee Member
Mark Andrew Fanton, Special Signatory - Keywords:
- Direct Ink Writing (DIW)
Dispersion
Stability
Ceramic - Abstract:
- Tape casting is frequently utilized to manufacture ceramics with aligned microstructures, i.e. textured ceramics. The manufacturing method effectively aligns anisotropic particles called templates that, when sintered, act as seeds for grain growth, in a sintering process known as templated grain growth (TGG). However, this approach generates excess material that cannot be recycled, leading to significant material waste. Additionally, tape casting restricts design space for transducer materials and other applications. Direct Ink Writing (DIW) is an additive manufacturing technique that, if adopted, would reduce waste and thus production cost for identical designs, and provide greater design flexibility by enabling the formation of complex shapes in the green state. DIW also has the advantage of decreasing processing time as the minimal amount of additives decreases the binder burnout cycle time. While the DIW process itself has existed since the early 1990’s, there is no standard path for developing feedstock material for the process. The success of the print relies heavily on the rheological properties and stability of the feedstock material. Thus, in this paper, a series of tests are evaluated to determine their efficacy in guiding DIW feedstock development. The identified tests were not only evaluated based on their effectiveness for developing a DIW feedstock, but also their accessibility. These tests are meant for use in processing engineering where capabilities differ based on resources and parameters of interest. For DIW, the paste must be shear thinning for extrusion out of the syringe and have a quick recovery time in order to hold its shape once deposited. This requires the paste to be a stable suspension with the particles being well dispersed to avoid agglomerations that affect the viscosity and cause nozzle clogging during the extrusion. The experiments laid out in this paper determined the amount of dispersant required to fully coat and disperse the ceramic powder and the effect of pH on the dispersion of the powder. The ceramic powder used in the experiments is 2 mol% MnO2-doped 0.40Pb(Mg1/3Nb2/3)O3-0.25PbZrO3-0.35PbTiO3 (PMN-PZT), but the tests laid out are applicable to other ceramic systems. Ion leaching measurements were conducted to determine the concentration of lead ions leached from the particle surface at different pH values and where the leaching was at a minimum. This elucidated the pH range that minimized free ions in solution, which, if uncontrolled, could negatively impact rheological and chemical stability. It was determined that at a high pH, above pH 8, the lead ion concentration in solution was negligible. Settling tests and viscosity measurements were used to determine the minimum amount of dispersant required to coat the surface of the particles. Minimum dispersant content was found through the settling tests by adjusting the amount of dispersant and finding where the least amount of powder settled out of suspension. Similarly, viscosity measurements involved measuring the viscosity of slurries as a function of dispersant content. At some dispersant level, viscosity would reach a minimum, indicating the minimum amount of dispersant required to fully coat particles in the slurry. These tests were used to compare the results against each other and verify the results. Settling tests, X-ray sedimentation, viscosity, and zeta potential measurements were performed to determine and verify the stable pH range. The multitude of tests provided insight in each test’s accuracy and accessibility. In all tests the pH was adjusted between samples to determine the effect on the stability of the suspension. All tests for PMN-PZT showed that the suspension is most stable and well dispersed in the basic pH range, above pH 8, where the leaching was identified to be minimized also. At low pH ranges, the suspension showed gelling and powder began agglomerating. The tests’ results were applied to the formulation of a paste for DIW. Rheological testing was conducted to determine the viscosity, yield strength, and recovery time of the paste. The paste was then printed into a part, dried, burned out, and sintered to determine the printability. The green density and the sintered density were collected and compared to those formed through tape casting. The same series of tests were then applied to another ceramic powder, PbTiO3, to determine if they are applicable to other systems.