Materials Research

EPA Grant Number: X83254101-0

Center: CEER at Alfred University

Investigators: Varner, James and Amarakoon, Vasantha

Institution: Alfred University

Project Period:  September 1, 2005 – December 31, 2006

Research Category: Congressionally Mandated Center

 

 

Description:

 

Objectives/Hypotheses:

SiAlON ceramics have been successfully produced from industrial wastes such as silicon sludge, aluminum dross and fly ash from power plants. One of the major limitations for assuring the reliability and lifetime of such ceramic materials is their inherent brittle nature and low fracture toughness. We propose to demonstrate through this project that the fracture toughness of the SiAlON based ceramics produced from silicon sludge can be improved by reinforcing secondary particles such as ZrO₂ into the SiAlON matrix. The anticipated benefits are high fracture toughness, low cost, reduced environmental pollution, significant energy saving due to microwave sintering and reduced emission due to the self-propagating exothermic synthesis reaction. The sintered products can be used for abrasives, corrosion resistant filters, and wear resistant materials below 1000° C.

 

The objectives of the project are:  1) Reduce the environment pollution due to silicon sludge produced in the semiconductor industry by recycling silicon sludge and convert into SiAlON ceramics by combustion synthesis process,  2) Reduce the energy requirement of the SiAlON ceramic processing by Microwave heating, and  3) Demonstrate that fracture toughness of SiAlON ceramics can be improved by transformation toughening of ZrO₂ secondary particles reinforcing into SiAlON matrix.

 

Approach:

Dried and pulverized sludge will be ignited in a pressured nitrogen atmosphere. The synthesized SiAlON powder will be coated with varying amounts of ZrO₂ and sintered using a 2.45 GHz microwave power without sintering aids over the  temperature range of 1400-1600 ^oC for varying times of 30min to 5 hours in a nitrogen atmosphere. Sintering will also be performed  in a conventional furnace for comparing experimental results. Polished sections will be used for microstructure characterization. The same polished specimens will be used for measurements of Vickers hardness and indentation fracture toughness. Once trends are established, bar specimens will be used to measure fracture toughness using a standard technique.

     
Expected Results:

The silicon sludge contains lots of ceramic abrasives such as Al₂O₃, ZrSiO₄, ZrO₂, coagulants (FeCl₂, polymers), grinding oils and water. It is disposed to reclaiming lands. If the silicon sludge is left outside and dried, there is some fear of pollution by diffusing out of fine powder in air. The recycling of this industrial waste to highly pure silicon is very costly. Our project can reduce the environmental pollution by recycling at least 1000 tons of the silicon sludge to low cost high performance SiAlON ceramics. Nitriding combustion of silicon sludge leaves a solid product of metal nitrides without discharging CO₂ like other combustion reactions, resulting reduced  environmental pollution.

 

Supplemental Keywords:

Transformation toughening, Self propagating Nitriding combustion, SiAlON, Recycling, Wastes, Microwave sintering