Preparation And Properties Of Hierarchical Y Zeolite-based Molecular Adsorption-Thermal Control Coatings

In the high vacuum environment,organic molecular pollutants released by some spacecraft materials are easily deposited on the surface of some sensitive parts of the spacecraft,which will affect the performance and service life.The development of zeolite-based coatings with both molecular adsorption and thermal control functions can effectively solve the problem of in-orbit molecular pollution.In this work,the chemical dealumination method,chemical desiliconization method and surfactant-templating method were used to prepare hierarchical Y zeolite molecular sieves with different channel structures.Different hierarchical Y zeolite-based molecular adsorption-thermal control coatings were prepared and their properties were systematically studied.The main research conclusions are as follows:(1)The phase composition,morphology,pore structure,and toluene adsorption performance of different microporous zeolites such as 13X,NaY,β,and ZSM-5 are comparatively compared and studied.The NaY zeolite with the best molecular adsorption performance is preferred as the target material.NaY coatings with different thicknesses are prepared by spraying.It is confirmed that NaY coatings have excellent a lower ratio of solar absorption to emissivity(αs～0.15,εH>0.90)(2)The micropore zeolite has unique and narrow pore size,and it is difficult to adsorb the large diameter molecular pollutants.Hierarchical Y zeolites are prepared by the dealumination modification.The dealumination effect of some common acids is compared,and it is impossible to obtain modified zeolite samples with high crystallinity and high silicon to aluminum ratio.However,the hierarchical Y zeolite with high crystallinity(～80%)and suitable mesoporosity(0.3M NH4HF2-etched NaY,Vmeso:0.150 cm3/g,Vmeso rate:39.2%)is obtained using the acid fluoride salt represented by NH4HF2 as the dealumination agent and the dealumination mechanism is explored.In addition,the USY zeolite is prepared by the high-temperature hydrothermal method,and etched with NH4HF2 to further remove the non-framework aluminum.Then another hierarchical Y zeolite is obtained(0.3M NH4HF2-etched USY,Vmeso:0.133 cm3/g,Vmeso rate:35.8%).(3)In order to further improve the mesoporosity of the obtained hierarchical Y zeolite,NH4HF2-etched NaY and NH4HF2-etched USY samples are subjected to secondary etching modification by chemical desilication method,and the desilication mechanism of different bases is analyzed.It is confirmed that NaOH desilication can obtain the hierarchical zeolites with larger mesopore volume(NaOH/NH4HF2-etched NaY,Vmeso:0.284 cm3/g,Vmeso rate:46.7%,NaOH/NH4HF2-etched USY,Vmeso:0.234 cm3/g,Vmeso rate:43.1%),but the obtained hierarchical zeolite contains some super-sized mesopores(>30 nm).The NH4OH solution produces OH-at a slower rate,which has a certain regulation effect on the pore structure of the hierarchical zeolites and can improve the mesoporosity(NH4OH/NH4HF2-etched NaY,Vmeso:0.254 cm3/g,Vmeso rate:49.7%,NH4OH/NH4HF2-etched USY,Vmeso:0.184 cm3/g,Vmeso rate:42.3%).(4)In order to obtain more controllable mesopore,the hierarchical Y zeolite is prepared by the surfactant-templating process.The hierarchical NH4HF2-etched NaY and NH4HF2-etched USY zeolites are subjected to the surfactant-templating modification for obtaining smaller intracrystalline mesopores.The mechanism of the surfactant-templating process is elucidated.It has been proved that the surfactant-assisted desilication modification treatment can effectively reduce the number of large-sized mesopores,and increase the number of small intracrystalline mesopores(～4 nm).(5)The vacuum molecular adsorption properties and thermal radiation performances of different hierarchical Y zeolite coatings have been researched.Compared with the initial NaY,the vacuum molecular adsorption performance of different hierarchical Y zeolite coatings has been improved in a certain extent when the grey-skinned cables as the molecular contamination.Especially for the surfactant-templated Y zeolite coatings,its adsorption capacity is increased by～40 mg/g and adsorption performance is improved by～30%.At the same time,after adsorbing molecular pollutants,the surface color of different modified zeolite coatings is deepened,but zeolite coatings still have the lower ratio of solar absorption to emissivity.