Because zirconia oxygen sensors used for air/fuel mixture control in automobile engines can be fouled by silica (the oxidation product of low molecular weight volatile silicones in RTV gasketing), a precise new technique has been developed for the analysis of these silicones. The new method replaces an earlier General Motors standard procedure that centered on gas chromatographic (GC) identification and quantification of materials evolved from thermogravimetric analysis (TGA). Since the TGA/GC procedure is cumbersome, a simplified method involving solvent extraction of the cured elastomer was established with gas chromatography analysis of the extract. With evidence of excellent repeatability, the method has been adopted by GN as standard #GM9009-P.
SILICA, THE OXIDATION PRODUCT of low molecular weight silicones from room temperature vulcanized (RTV) gasketing, can foul zirconia oxygen sensors used for air-fuel mixture control in automobile engines. Malfunction of this sensor can cause decreased fuel economy and performance problems, indicating the need to carefully control the level of volatiles during sealant manufacture. To do so, a test method was required that would accurately identify and quantify the level of silicone volatiles present in sealants designed for this application.
The objectives of this paper are to outline the evaluation of the existing test method and detail the development of an efficient, reliable, new procedure to determine the volatiles content of RTV sealants used in the automotive industry. This development included examination of the method in a General Motors-sponsored, round-robin test.