DETECTION OF METHANE BUTANE MIXTURES IN AIR BY A SET OF 2 MICROCALORIMETRIC SENSORS

Non-diffusion-limited microcalorimetric sensors with a platinum catalyst have been prepared. The methane response is proportional to its concentration, and the butane response can be described by a power law with the exponent 1.3. At concentrations near the stoichiometric ratio between the combustible gas and oxygen, the sensitivity increases markedly. This may be due to blocking of sites by an oxygen excess at low concentrations. In methane/butane mixtures the signals are not additive; the methane sensitivity is increased in the presence of butane. A moderate hexamethyldisiloxane (HMDS) treatment strongly reduces the methane sensitivity but the butane sensitivity remains nearly unchanged. A pair of sensors with and without HMDS treatment allows the composition of a methane/butane mixture in air to be determined.