“Incongruent Reduction (IR)” refers to a fluid/ solid reaction that results in the reduction of a solid compound via the formation of an inter-mediate solid product. IR reactions have been used by the PI’s to produce very high-melting, erosion-resistant, lightweight rocket nozzles (Fig. 1). Such novel processing is an attractive and cost-effective means of manufacturing advanced ceramic composites with complex 3-D shapes for aerospace, automotive, energy production, and defense industries.

This project is aimed at obtaining a basic understanding of the mechanism of IR in a model system: IR of Al2O3 by an Al-Mg melt,

which occurs via formation of spinel, MgAl2O4.

The spinel initially forms as oriented particles on an Al2O3 surface (Fig. 2). Further MgAl2O4

formation over time leads to a stack of continuous spinel layers on Al2O3 (Fig. 3). The

rate of layer thickening obeys a parabolic law (Fig. 4), which is consistent with solid-state diffusion as the rate-limiting step.

Mechanisms of Incongruent Reduction (DMR-0341010) K. H. Sandhage, R. L. Snyder, Georgia Institute of Technology

Fig. 1. Rocket nozzle via IR process (U.S. Patent No. 6,598,656, Sandhage, et al.)

Fig. 2. MgAl2O4 particles on an Al2O3 surface after immersion in Al-Mg(liq) for 0.5 h at 1100oC.

Fig. 3. MgAl2O4 layers on Al2O3 after immersion in Al-Mg(liq) for 168 h at 1000oC.

Fig. 4. MgAl2O4 thickness vs. reaction time at 1100oC.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 5 10 15 20 25

Time (104 sec)

(Lay

er T

hick

ness

)2 (X

10-1

1 m

2 )

1100oC

Cross-sectionof MgAl2O4

layers

Al2O3

This research has been (Ohio State University, OSU) and is being (Georgia Institute of Technology, GIT) integrated with education via activities such as:

Integration into classroom lectures:

“Principles of Materials Science and Engineering” (MSE 605, Snyder/OSU)

“Materials Characterization” (MSE 715, Snyder/OSU)

”High-Temperature Corrosion” (MSE 736, Sandhage/OSU)

“Introduction to Engineering” (MSE 1001, Sandhage/GIT)

“Chemical and Environmental Properties of Materials” (MSE 8003J, Sandhage/GIT)

Integration into undergraduate research projects/senior theses on incongruent reduction-based processing (6 undergraduates have been involved to date):

“Ceramic body armor” (Mr. Jason Zielsdorf, supervised by Sandhage/OSU)

“Bulk metallic glass composites” (Mr. Geoff Lofstrom, Mr. Alex Tsai, supervised by Sandhage/OSU)

“Rocket nozzle composites” (Ms. Erin Beatty, Ms. Wendy Fu, Mr. James Sinclair, supervised by Sandhage/GIT)

Mechanisms of Incongruent Reduction (DMR-0341010) K. H. Sandhage, R. L. Snyder, Georgia Institute of Technology