Research On Optical Fiber Sensing Materials And Devices For Hydrogen And Humidity Monitor In Hermetically-sealed Narrow Spaces

In special areas such as hermetically-sealed systems with narrow space,there is an urgent need for high-precision,high-reliability,long-term,real-time,and dynamic monitoring parameters of ambient atmosphere,temperature,and humidity.Traditional electrical and optical sensors are far from meeting all these requirements.In order to meet the rigorous requirements for atmospheric monitoring in these special fields,this dissertation,based on the specific films as well as powder materials,researches the method of preparing different types of sensitive materials on the end and sides of optical fibers,and the method of combining optical fibers with high-molecular polymers and powder materials,fabricates fiber optical atmosphere monitor systems which are nature safety,anti-electromagnetic interference,small-in-size,and long-term online monitoring.(1)A mesoporous WO₃/Pt powder synthesized by hydrothermal method is proposed to encapsulate Pt nanoparticles in mesopores and prevent agglomeration of Pt nanoparticles after multiple reactions.Mesoporous WO₃ with larger surface provides more activity position,making the limit of detection(LOD)of sensor is increased from400 to 100 ppm.The long-term stability of the fiber Brag grating(FBG)hydrogen sensor based on the powder has been greatly improved.The sensing system has a measurement range of 100 to 40000 ppm and a resolution of 30 ppm.It is suitable for a large-scale quasi-distributed hydrogen leakage real-time monitor network in the air.(2)The ion-intercalated MoO₃/Pt powders synthesized by hydrothermal method is also studied.Alkali metal ions are inserted between?-MoO₃ layers to improve the interlayer stability.When the ion concentration in the precursor solution utilized for intercalation is 1 mmol,Na⁺ion intercalation will maximize the long-term stability of the sensor.The FBG hydrogen sensing system based on this sensor has a measuring range from 400 to 40000 ppm and a resolution of 50 ppm,and is also suitable for a large-scale quasi-distributed hydrogen leakage real-time monitor network in the air.(3)A Pd alloy thin film is deposited on the side of the fiber based on the magnetron sputtering method,and this type of FBG hydrogen sensor and its system are studied.This type of sensor is suitable for the measurement of hydrogen in an oxygen-free environment with a measurement range from 500 to 10000 ppm and a resolution of 250ppm.In order to improve the performance of the system in harsh environments such as low temperature and high humidity,a closed-loop controlled light heating method is proposed to make the sensor working at an appropriate temperature,to improve the sensitivity and stability of the sensor.This system is not only suitable for hermetically-sealed systems atmosphere monitor,but also for the analysis of dissolved gas in transformer insulating oil.(4)WO₃/Pt film is deposited on the end face of the fiber by vacuum evaporation.A FBG hydrogen sensor suitable for accurate measurement of hydrogen concentration in an aerobic environment is developed.A fiber optical trace of hydrogen sensor system with optical-heated WO₃ film is proposed.In this way,the sensor is operated in a stable temperature field,thereby avoiding the interference of ambient temperature on sensitive materials,and achieving accurate on-line monitoring of hydrogen concentration on ppm level.The system has a measurement range from 5 to 5000 ppm and a resolution of 2 ppm,and is suitable for special areas such as such as hermetically-sealed systems atmosphere monitor which require high-level hydrogen concentration monitor.(5)Based on the accurate monitoring of hydrogen,the trace amounts of hydrogen optical fiber sensing system based on optical-heated WO₃ films is also simplified,and a photo-detection type optical fiber hydrogen sensing system based on WO₃ films is proposed.The simplified system has a measurement range from 20 to 5000 ppm and a resolution of 4 ppm,which fully meets the needs of the hydrogen energy industry for hydrogen leak alarms.At the same time,the system is low in cost,easy to carry,and more suitable for hydrogen detection by single-point leak.(6)In response to the needs of humidity monitoring in hermetically-sealed systems,fiber-end dielectric film interference-type fiber optical humidity sensing systems and polyimide-coated fiber grating humidity sensing systems are proposed.The former is suitable for accurate single point measurement of humidity.The system has a measurement range from 0 to 70%RH,a resolution of 1.5%RH,and a LOD as low as-50°C dew point(about 40 ppm V).The latter is suitable for a wide range of ambient humidity real-time monitoring network,which has a measurement range from1%to 100%RH,and a resolution of 1%RH.(7)The optical fiber sensors and systems developed for hermetically-sealed systems with narrow space are utilized in the scientific research and production of China Academy of Engineering Physics,including a corrosion-sensitized Pd alloy fiber optical hydrogen sensing system,a trace amounts of hydrogen optical fiber sensing system based on optical-heated WO₃ films,and a polyimide coated FBG humidity sensor system.The verification test oriented to hermetically-sealed systems was conducted in in Chinese Academy of Physical Engineering.Thereafter,three of all systems have been delivered to Chinese Institute of Physical Engineering and are monitoring the atmosphere of hermetically-sealed systems in progress,which provide new method for significant demand of national defense science and technology.