Final Report: New Inert Anodes for Reduction of Perfluorocarbon Emissions

EPA Contract Number: 68D99044
Title: New Inert Anodes for Reduction of Perfluorocarbon Emissions
Investigators: Adamic, Kresimir J.
Small Business: Eltron Research & Development Inc.
EPA Contact:
Phase: I
Project Period: September 1, 1999 through March 1, 2000
Project Amount: $69,997
RFA: Small Business Innovation Research (SBIR) - Phase I (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , SBIR - Air Pollution , Small Business Innovation Research (SBIR)

Description:

This Phase I program addressed the development of inert anodes fabricated by reactive plasma surfacing and plasma spray deposition of metal oxide coatings onto metal or metal alloy supports. Phase I resulted in the fabrication and testing of tubular pressed ceramic anodes, the fabrication of a powder feeder, motion control system, and torchead modification for application of metal oxide films, and the testing of these metal oxide films in representative electrolyte media. The goal of the program was to fabricate these coated metal alloy anodes and demonstrate the efficacy of such anodes for oxygen evolution. Such an anode would not emit perfluorocarbons or other derivatives of carbon such as carbon monoxide or pyrenes, as is the case with the current generation of consumable carbon anodes. Ceramic tubular and metal oxide coated metal anodes were readily fabricated and found to perform well in electrolytic cells. Although it was not possible to assess corrosion resistance of these anodes over long run times, significant corrosion of anodes was not detected.

Summary/Accomplishments (Outputs/Outcomes):

Tubular ceramic anodes were fabricated from powders synthesized by the ceramic method. This consisted of thoroughly mixing the appropriate metal oxide starting materials, followed by calcination at appropriate temperatures to react the metal oxide starting materials. However, materials synthesized here were generally multi-phase. Generally, tubular anodes of most materials could be fabricated. Such an electrode construction proved to be less desirable because of the difficulty of current collection and the propensity of the electrode to separate from its holder. The absence of this problem is another attractive aspect of the metal oxide coated metal anodes.

The electronic properties of anode ceramic materials were evaluated. Tubular ceramic anodes were tested in cryolite melts modified with aluminum fluoride, calcium fluoride, and aluminum oxide. Overall performance was quantitated using a quality factor, Q, which allowed different anode materials to be compared. Materials containing Zr and Fe or Ce, Fe, and Zn were found to be the best candidates.

A powder feeder based on a piezoelectric shutter was fabricated and was found to effectively feed ceramic powder into an argon plasma. This enabled plasma spray of materials of fixed and definite stoichiometry to be performed. A device (X-Y-Rotational stage) for translating and rotating cylindrical metal supports was also fabricated, allowing for the even distribution of metal oxide on the cylindrical surface by the plasma approach.

Preferred ceramic powders were deposited onto metal or metal alloy supports. Initially, titanium, and then nickel alloy (Inconel 600) metal supports were coated by plasma spray. Anodes fabricated by the approach were tested at a realistic current density of 400mA/cm2. Deposition of the coatings resulted in a higher potential drop across the anodes than across uncoated metals. However, the performance of these anodes was superior to that of ceramic tubular anodes. The behavior of electrochemical cells containing the metal oxide coated metal cylinder anodes indicated some porosity of the metal coatings. This aspect must be improved during Phase II.

Conclusions:

The findings obtained here satisfy all of the Phase I technical objectives and demonstrated the feasibility of fabricating anodes by plasma coating of metal alloys. Results obtained here suggested that there is considerable merit to further development of the approach. Special accomplishments included the coating of metal and metal alloy bodies with metal oxide materials anticipated to both electrocatalyze the oxygen evolution reaction and to protect the metal surfaces from rapid dissolution. Phase II will consist of optimizing the coating process and improving the quality of metal oxide films. Additionally, testing of the anodes under a range of conditions (temperature, melt composition, etc.) and under long term operation will be preformed.

Supplemental Keywords:

inert anodes, plasma surfacing, perfluorocarbons, ceramic, metal oxide coatings, metal alloy supports, aluminum electrorefining., RFA, Scientific Discipline, Air, Toxics, Waste, Sustainable Industry/Business, air toxics, cleaner production/pollution prevention, Chemistry, HAPS, chemical mixtures, Technology for Sustainable Environment, Hazardous Waste, New/Innovative technologies, Engineering, Hazardous, Engineering, Chemistry, & Physics, cost reduction, air pollutants, clean technology, emissions, air pollution, alternative materials, carbon monoxide, carbon dioxide, perfluorocarbon, innovative technology, innovative technologies, industrial innovations, inert anodes, air emissions