Evaluation of a Conductive Polymer-Based Sensor for Detection of Hydrazines at the Part-Per-Billion Level

摘要

A conductive polymer-based hydrazine sensor (CPHS) was developed. During preliminary testing, the sensor showed promise as a dosimeter with the ability to detect hydrazine (N2H4) and unsymmetrical dimethylhydrazine (UDMH) at levels well below the proposed threshold limit value (TLV) of 10 part per billion (ppb). The original sensor demonstrated a minimum detectable dose of approximately I part per billion-hour (ppb-hr) and a saturation dose of approximately 250 ppb-hr in dry conditions, offering adequate coverage of the proposed TLV limit of 80 ppb-hr (8 hours at the proposed TLV level of .10 ppb). However, initial testing in a more realistic humidified environment (relative humidities to over 60 percent) indicated an increased sensor reactivity, yielding a saturation dose of only approximately 30 ppb-hr at humidities greater than 60 percent . A second version of the sensor (CPHS2) was fabricated utilizing a thicker polymer film in an attempt to increase the saturation dose back up to a level that would provide a better dynamic range. Initial tests of the CPHS2 at the NASA Toxic Vapor Detection Laboratory (RVDL) in November 1993 exhibited a minimum detectable dose in the range of 1 to 2 ppb-hr, an increase in the saturation dose to approximately 150 ppb-hr in humid conditions and a measurement accuracy of plus or minus 20 percent . The CPHS2 sensors are currently undergoing tests at the TVDL. The TVDL has the unique ability to generate calibrated sample vapor streams of N2H4 and UDMH over a range from less than 10 ppb to thousands of parts per million (ppm) with full environmental control of humidity (O to 90 percent) and temperature (O to 50 C). The polymer-based sensors will be subjected to extensive testing over a wide range of humidities at N2H4 and UDMH concentrations of 12.7 an 10.6 ppb respectively.