Doctoral Dissertations

Tieshu Huang

Keywords and Phrases

Aqueous dispersion; Freeze-form extrusion fabrication (FEF); Ultra-high temperature ceramic (UHTC)

Abstract

"A novel, environmentally friendly solid freeform fabrication method called Freeze-form Extrusion Fabrication (FEF) has been developed for the fabrication of high temperature and ultra-high temperature ceramic-based components. The method is based on deposition of ceramic pastes using water as the medium. The FEF system components and their interaction are examined, and the main process parameters affecting part geometry are defined. Three-dimensional (3D) shaped components have been fabricated by extrusion deposition of the ceramic paste in a layer-by-layer fashion. The feasibility of this process has been demonstrated by building components having a simple geometry, such as cylinders and solid or hollow cones. Hollow cones have also been fabricated to demonstrate the ability to build structures with sloped walls. Sintered samples have achieved 98% and 96% of their theoretical density for AI2O3 and ZrB2, respectively.

The dispersion of ZrB2 particles in an aqueous medium was investigated. In aqueous systems, the surface of ZrB2 consists of a thin layer of ZrO2 that controls the surface chemistry and surface charge. Measurements showed that the ZrB2 had an isoelectric point of pH = 4.7 and a maximum zeta potential of -50 mV at pH = 9. Either an ionic ammonium polyacrylate or a nonionic alkoxylated polyether increased the zeta potential of ZrB2 by as much as 60 mV, to -110 mV. Viscosity measurements were used to optimize dispersant concentrations. High solids loading (~45 vol.% ZrB2) aqueous pastes were prepared. The pastes had viscosities of 40 - 50 Pa·s-1 ,which was acceptable for extrusion. The pastes were used to fabricate 3-D components from ZrB2.

The microstructure of sintered ZrB2 consisted of equiaxed B4C with an average grain size of 4.3 μm and small equiaxed and large elongated ZrB2 grains with an average grain size of 40 μm. For longitude and transverse deposited samples, the elastic moduli were E = 435 and 417 GPa, the flexural strength σf = 353 and 230 MPa, and the Vickers’ hardness Hv = 18.74 and 18.50 GPa, respectively. The longitude deposited samples had an average fracture toughness of 3.09 MPa·m1/2. The ZrB2 component fabrication demonstrated the feasibility of using aqueous freeze-form extrusion fabrication technique"--Abstract, page iv.

Advisor(s)

Hilmas, Greg

Committee Member(s)

Leu, M. C. (Ming-Chuan)
Fahrenholtz, William
Liou, Frank W.
Newkirk, Joseph William

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Ceramic Engineering

Sponsor(s)

Air Force Research Laboratory (Wright-Patterson Air Force Base, Ohio). Materials and Manufacturing Directorate
Missouri University of Science and Technology. Center for Aerospace Manufacturing Technologies

Publisher

University of Missouri--Rolla

Publication Date

Spring 2007

Journal article titles appearing in thesis/dissertation

  • Solid freeform fabrication techniques of 3D-shaped ceramics
  • Freeze-form extrusion fabrication of ceramic parts
  • Aqueous paste freeze-form extrusion fabrication of alumina components
  • Dispersion of zirconium diboride in an aqueous, high solids paste
  • Microstructure and properties of ZrB₂ produced by freeze-form extrusion fabrication

Pagination

xiii, 179 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2007 Tieshu Huang, All rights reserved.

Document Type

Dissertation - Restricted Access

File Type

text

Language

English

Subject Headings

Extrusion processRapid prototyping

Thesis Number

T 9190

Print OCLC #

191050395

Electronic OCLC #

1079365836

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