Date of Award

Fall 1983

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

Abstract

The object of this dissertation is the study and characterization of a new method for applying carbide coatings to graphite furnaces used in atomic absorption spectroscopy. The proposed method consists of impregnating graphite furnaces, under reduced pressure, with a liquid metal chloride. After soaking in water to hydrolyze the metal chloride to metal oxide, the furnace is fired at high temperature to form the carbide. Three metal chlorides, TiCl(,4), MoCl(,5) and WCl(,6), were used to apply TiC, MoC and WC coatings, respectively. Experimental details of the coating procedures are given.

Characterization of the various coatings was carried out using ESCA, SEM, EDAX and X-ray diffraction. The TiC coating was found to be the best, as a result of more extensive surface coverage and superior penetration of the graphite than the other coatings. None of the coatings sealed the graphite surface completely. Some data was obtained indicating problems with the MoC coating due to intercalation of the MoCl(,5), limiting its usefulness for applying coatings. All of the coatings were found to be rugged, lasting in excess of 500 high temperature cycles. X-ray diffraction revealed the coatings to consist of metal carbides and some metal oxides.

The analytical performances of the coatings were compared with each other and also with uncoated and pyrolytically coated furnaces. None of the coatings significantly altered the current-temperature behavior of the furnaces. The higher sensitivity observed with the carbide coated furnace for some elements was found to last for the entire lifetime of the furnace. The coated furnaces also had a significantly longer lifetime than uncoated furnaces. The TiC coating was found to be the most reproducible coating, followed by the WC and MoC coatings. Using the carbide coated furnaces, signal enhancements for Al, As, Ba, Be, Sb, Si and Pb. No enhancements were observed for Co, Cu, Ni, Sb and Sr. Approximate sensitivities, detection limits and signal enhancements are reported. Measurements of atomization times ((tau)(,1)) indicated that signal enhancement may be due to increases rates of atomization from carbide coated furnaces.

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