Research On The Hydrogen Gas Sensing And Strain Properties Of The Nanocomposites Of Layered Molybdenum Compounds

The lightweight level of fuel tank which is the heaviest and largest part in cryogenic propulsion system of spacecrafts decides the key performance index of spacecrafts.Developing composites fuel tank is the important direction of research on cryogenic propulsion system of future spacecrafts.The development and manufacture of composites fuel tank involves in several key techniques.The nondestructive detection and health monitoring of the tank are two important contents of the key techniques.To guarantee the secure use of composites tank and considering the possible hazard brought in by the leakage of fuel,it's necessary to further progress the nondestructive detection and health monitoring techniques.Layered nanomaterials including Graphene,transition metal disulfide,transition metal oxides possess unique optical,electrical,mechanical properties which render them have a wide range of potential applications.Research interest on layered nanomaterials arise worldwidely.As in composites,layered nanomaterials can be used in electric conductive,thermal conductive,wear resisting and microwave absorpting composites.To furthering the application of layered nanomaterials in composites is one of the research hotspot in composites.This thesis carries out research from layered Mo compounds including MoO₃ and MoS₂ aiming at leakage detection and nondestructive strain detection during the development of composite tanks.On account of the hydrogen leakage problem of liquid hydrogen composite tank,we prepared MoO₃-x quantum dots?QDs?and Pd/MoO₃ nanocomposites,researched their room temperature H₂ gas sensing propertied,explained the mechanism of improved properties and pointed out the application prospect of these two sensing materials on leakage detection of liquid hydrogen composite tank.On account of the nondestructive strain detection of composites,we prepared ultrathin MoS₂ nanosheets and their resin based composites,researched the Raman shift of nanosheets in composites with the strain of matrix under uniaxial tensile tension,and pointed out their application prospect on nondestructive strain sensing of composite structures.Due to the fact that decreasing the grain sizes of gas sensing materials could remarkably improve their sensing properties,firstly,this thesis prepared the MoO₃-x QDs through exfoliating and cutting bulk MoO₃ by intercalating and thermal exfoliation method and photochemical method.And then the QDs were used as H₂ gas sensing material and their room temperature sensing properties were studied.N-butylamine was introduced into the layer space of MoO₃ through intercalation in the intercalating and thermal exfoliation method.The layers of MoO₃ were effectively exfoliated under instantaneous high pressure caused by the thermal decomposing of n-butylamine under high temperature.Simultaneously,defects were brought into the lattice structure during the thermal exfoliation process.QDs could be obtained after further sonication.Lattice structure deformation caused by H+ intercalation and photocorrosion caused by the accumulation of photoholes leaded to the etch of MoO₃ nanosheets in photochemical method and QDs were successfully prepared.The QDs showed much better gas sensing properties than MoO₃ nanosheets.The gas sensitivity of MoO₃-x QDs to 1000 ppm H₂ in room temperature was 9.02.And the response and recover time is 64 and71 s,respectively.According to that the dissociative adsorption of noble metal Pd to H₂ could obviously improve the gas sensing properties,this thesis prepared the nanocomposites of Pd nanoparticles decorated MoO₃ nanosheets through photochemical reduction method and in site reduction method.And then the gas sensing properties of the nanocomposites in room temperature were studied.Pd nanoparticles could be effectively decorated on the surface of MoO₃ nanosheets in photochemical reduction method.And the sizes of Pd nanoparticles prepared in photochemical reduction method were much more uniform than that in in site reduction method and could be tuned by adjusting the illumination time.The gas sensitivity of Pd/MoO₃ nanocomposites to 1000 ppm H₂ in room temperature was 12.48 and the response time is 24 s.In the meantime,the fact that Pd/MoO₃ nanocomposites showed prominent reversible chromism in H₂ atmosphere demonstrated that the optical signals of the nanocomposites could be further adopted in H₂ gas sensing which will be beneficial to the leakage detection of hydrogen composite tanks.Based on that the characteristic Raman peaks of MoS₂ nanosheets would shift under strain,this thesis prepared MoS₂ nanosheets and their resin based composites films.The Raman shifts of MoS₂ nanosheets in composites films under uniaxial tensile tension were researched to track the strain of matrix.Although the liquid exfoliation method could produce MoS₂ nanosheets in high yields,the size and thickness of the nanaosheets were nonuniform and uncontrollable.Ultrathin nanosheets could be prepared through further chemical exfoliating liquid exfoliated nanosheets by accurately control the dosage of oxidizing agent.Then chemical exfoliated ultrathin nanosheets were combined with PDMS to prepare composites.The characteristic Raman peaks of nanosheets shifted apparently under tensile tension.And that the shift rates of peaks of nanosheets sandwiched in PDMS were larger,indicating much more stronger interface interaction between matrix and nanosheets,than those of deposited on the surface of PDMS.The shift rates of peaks of E12 g and A1 g were-0.64 and 0.17 cm-1/%,respectively.The shifts of Raman peaks of MoS₂ were expectable to be adopted in the nondestructive strain sensing of composite tanks.