NCER Assistance Agreement Annual Project Summary

Date of Report: October 3, 2008

EPA Agreement Number: X-83254101-1

Center: Center for Environmental and Energy Research (CEER)

Project Title: The Use of Fly Ash in the Production of SiAlON based Structural Ceramics

Investigator(s): James R. Varner

Institution(s) of PI(s): Alfred University

Research Category: Congressionally Mandated Center

Project Period: June 2007 – February 2009

Objective of Research: Recycle fly ash from power plants for use in the synthesis of SiAlON powder by carbothermal reduction and nitridation. The goal is to prepare low-cost SiAlON powder from fly ash, thereby reducing waste going to landfill sites.

Progress Summary/Accomplishments: Using a novel chemistry modification technique, a ternary functionality diagram for the synthesis of SiAlON powders from chemically complex oxide powders was constructed. Six coal fly ashes were obtained from three different sources with four of the ashes coming from the same source, but being byproducts from different reactors. These ashes have been characterized. To test the ternary functionality diagram, chemical modification was made to the fly ashes to satisfy a predetermined SiAlON phase composition. These modified powders were subjected to carbothermal reduction and nitridation to form SiAlON powders. Hydrochloric acid washing was performed for each of the SiAlON powders to eliminate iron silicide, a byproduct of a catalyst addition to enhance the carbothermal reduction and nitridation process. The sialon powders have been characterized, including lattice refinements by X-ray diffraction to determine the phase composition, which matched well with the theoretical phase composition that was predetermined from the ternary functionality diagram.

Sintering trials have begun using predetermined sintering parameters. The amount of yttria necessary for maximum densification was determined. The shrinkage of a sintered specimen was determined to aid in the design of a die-press mold for near-net-shape forming of test bars for fracture toughness measurements. The die is currently being made.

Progress on the graduate research report first draft has been made. The introduction has been completed. The sections on experimental procedures and results and discussion are completed for the work up to SiAlON powder characterization.

Publications/Presentations: A poster presentation was given at the Materials Research Society Poster Contest at Alfred University, Mar 2008, Alfred, NY. A draft for publication is underway and is entitled: “Novel Chemistry Modification Approach for Synthesis of SiAlON from Fly Ash”.

Future Activities: When the test bar die is finished, thirty test specimens will be pressed using uniaxial pressing followed by cold isostatic pressing. The weight and dimensions of the green specimens will be noted. Sintering of the test bars will be performed. Shrinkage and weight loss due to decomposition will be determined. These test specimens will be machined according to ASTM standards for fracture toughness measurements, which will be statistically analyzed. Besides fracture toughness measurements, pulse-echo determination of Young’s modulus, Vickers hardness, Archimedes density, and phase analysis by X-ray diffraction will be performed. A second publication draft is expected on the results of the statistical analyses of the mechanical properties of the SiAlONs made from fly ash.

Supplemental Key Words: Fly ash, SiAlON, silicon aluminum oxynitride, carbothermal reduction and nitridation, mechanical properties, hardness, fracture toughness

Relevant Web Sites: http://ceer.alfred.edu/Abstracts/AbstrVarnerEarlFlyAsh.htm