A solid freeform fabrication technique, freeze extrusion fabrication (FEF), was investigated for the creation of three-dimensional bioactive glass (13-93) scaffolds with pre-designed porosity and pore architecture. An aqueous mixture of bioactive glass particles and polymeric additives with a paste-like consistency was extruded through a narrow nozzle, and deposited layer-by-layer in a cold environment according to a computer-aided design (CAD) file. Following sublimation of the ice in a freeze dryer, the construct was heated according to a controlled schedule to burn out the polymeric additives (below ~500°C), and to densify the glass phase at higher temperature (1 h at 700°C). The sintered scaffolds had a grid-like microstructure of interconnected pores, with a porosity of ~50%, pore width of ~300 μm, and dense glass filaments (struts) with a diameter or width of ~300 μm. The scaffolds showed an elastic response during mechanical testing in compression, with an average compressive strength of 140 MPa and an elastic modulus of 5-6 GPa, comparable to the values for human cortical bone. These bioactive glass scaffolds created by the FEF method could have potential application in the repair of load-bearing bones.

Mullite powder with a nearly stoichiometric composition was hot-pressed at 1550°C to produce an almost fully dense microstructure of fine, nearly uniaxial grains. The grain growth of the dense mullite was investigated during subsequent annealing at temperatures in the range of 1550 -1750°C. Grain growth was relatively slow at 1550°C and the microstructure remained nearly equiaxial. Annealing at temperatures above the eutectic temperature (ϳ1590°C) produced fairly rapid anisotropic grain growth. At 1750°C, the anisotropic grain growth can be divided into two stages. In the first stage, the initial microstructure with an anisometric shape factor of 1.7 evolved rapidly into a microstructure with a shape factor of 2.7, consisting of a significant fraction of highly elongated grains. In the second stage, the microstructure evolved slowly into a system consisting of somewhat "blocky" grains with a shape factor of 2.2. The Al 2 O 3 content of the mullite grains increased slightly and reached an equilibrium value during the first stage of anisotropic grain growth. For the samples annealed at 1750°C, the indentation fracture toughness (2.5 ؎ 0.2 MPa ⅐ m 1/2 ) was almost independent of the anisometric shape factor. The interaction between the indentation cracks and the microstructure showed a predominantly transgranular mode of crack propagation. The data indicate that while a network of highly elongated grains can be developed by the present approach, some further manipulation of the grain boundary chemistry is required for an improvement of the fracture toughness.

The dispersion of ZrB2 particles 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 ζ potential of −50 mV at pH=9. The addition of a dispersant, either an ionic ammonium polyacrylate or a nonionic alkoxylated polyether, increased the ζ 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 with two different dispersants. The pastes had viscosities of 40–50 Pa·s which was acceptable for extrusion, and were used to fabricate three‐dimensional components from ZrB2.

A novel, environmentally friendly solid freeform fabrication method called freeze-form extrusion fabrication (FEF) has been developed for the fabrication of ceramic-based components. The method is based on deposition of ceramic pastes using water as the media. The ceramic solids loading can be 50 vol.% or higher and initial studies have focused on the use of aluminum oxide (Al 2 O 3 ). The FEF system components and their interaction are examined, and the main process parameters affecting part geometry defined. Three-dimensional 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.

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