Liquid petroleum gas (LPG): butane, propane or their mixture, is used as a fuel particularly in regions and activities where the usual utilities are missing. It is used commercially and domestically for space and water heating, cooking, lighting, and as an automotive fuel. It is sold and stored in refillable cylinders as a pressurised liquid. It is a clean versatile fuel (producing lower green house emissions than alternatives), but its flammability requires awareness and vigilant leak detection.

Zinc oxide (ZnO) or tin dioxide are common gas sensing materials usually with a thin layer of a noble metal (palladium (Pd) or platinum) to increase their catalytic activities and response times (1). Various methods are used to apply the catalyst layer to the substrate: salt decomposition, spraying, impregnation by salt solution, and CVD by sputtering or evaporation. Substrates have also been dipped into salt solution followed by evaporation. Optimisation of the noble metal catalyst layer and its properties is critical to the success of a detector.

Now, scientists in India have found some optimum values for catalyst layers in a wet-chemical process where a Pd oxide sensitiser layer was formed on a thin ZnO film for LPG detection (2).

They found a sensitised film with stable resistance was formed after 15 to 20 dippings of a ZnO film into a PdCl₂ suspension. The room temperature resistance was a function of the amount of Pd loading. Stable sensors were fabricated with optimised Pd loading, with a suitable operating temperature ∼ 250^C. A sensitivity of 88% was observed for 1.6 vol.% LPG in air with a 15 s response and 60 s recovery. The fast response and quick recovery provides a useful domestic LPG alarm.