Graphite microparticles as coatings for quartz crystal microbalance-based gas sensors

The use of graphite particles (1-2 pm) as coatings on quartz crystal microb alances (QCMs) for detection and monitoring of toluene and other volatile o rganic compounds (VOCs) is described. Unlike the more commonly used polymer ic coatings with low glass transition temperatures (T-g) particulate graphi tic coatings are not as susceptible to loss of acoustic energy when coating thickness or operational temperature increases. This situation enables the use of relatively thick coatings, which increases the absolute amount of v apor sorbed in the coating and, consequently, lowers the level of detection and enhances operation over a wide temperature range. The use of small siz e particles also results in a coating with a more porous structure, which f acilitates uptake and release of VOCs incomparison to coatings made from hi gh T-g polymers, which have a lower porosity, These attributes, coupled wit h the inherent stability of graphitic materials, make particulate graphite coatings especially suitable for applications at high temperatures. The adv antages of using particulate graphite as a coating on QCMs are demonstrated by comparison to the performance of a few low-T-g polymers [i.e., poly(iso butylene) and poly(diphenoxyphosphazene)] and high-T-g polymers (i.e,, poly styrene).