Sensor for analysing oxidising gas, method for producing said gas and method for determining the concentration of the oxidising gas
An oxidizing gas and sensor technology, applied in the analysis of materials, material analysis by electromagnetic means, instruments, etc., can solve the problems of complex circuits and unstable output signals of measuring electrode potentials.
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Embodiment 1
[0062] The sensor consisted of a stainless steel housing, a 2.5 mm diameter platinum measuring electrode applied as a thin layer to a 30 μ thick PTFE gas diffusion membrane, a separator made of porous polypropylene, and electrolyte (0, 1 M KOH, pH=13). The counter electrode has a weight of 0.25g and is made of a commercial fabric (made of a specific surface of 1,200m 2 / g of activated carbon fiber), the fabric has not been subjected to any treatment, including oxidation. The virtually complete absence of electrochemically active surface compounds on the carbon fabrics used was confirmed by recording the charging curves in the region of the electric double layer. The resulting value of the integral capacitance 115 F / g was found to correspond to that of a carbon material substantially free of electrochemically active surface compounds. The initial counter electrode potential after impregnation was 830 mV for a hydrogen reference electrode in the same electrolyte. After sensor a...
Embodiment 2
[0064] The sensor was made as in Example 1 except that the counter electrode was made of activated carbon powder having a weight of 8 mg, ie 31 times lower than in Example 1. As an electrolyte, a 3M KOH solution (pH=14.5) was used. The starting and final potentials of carbon materials are more positive than 750mV.
[0065] A voltage of -700 mV for the counter electrode was applied to the measuring electrode. After 25 months of measurement, the weight of the counter electrode decreased by 2 mg. This weight loss indicates that the carbon material is mainly electrochemically oxidized to carbonate ions in the alkaline electrolyte according to reaction (5). The duration of continuous operation of the sensor as in Example 1 with a counter electrode weight of 0.25 g is lower than:
[0066] 25 months * 31=775 months (ie about 65 years).
Embodiment 3
[0068] The sensor has a fluoroplastic housing, a measuring electrode made of porous platinum with a diameter of 6 mm, an isolator made of porous polypropylene, and is composed of a specific surface of about 20m 2 A counter electrode made of graphite powder of 0.4 g weight per g, and an electrolyte (pH value is about zero) composed of 85% orthophosphoric acid.
[0069] After impregnation, the counter electrode potential was +280 mV, ie in the bilayer region of the potential. Before starting the analysis, the sensor had been exposed to air for 48 hours with a preset potential of -200 mV for the measuring electrode versus the counter electrode provided by an external voltage source. During 48 hours, the counter electrode potential shifted to 920 mV, ie to the anodized region. At the same time, a drop in the background current was observed in the sensor. The potential of the measuring electrode with respect to the counter electrode was then set to -500 mV and the analysis starte...
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