Preparation Of 5A Molecular Sieve Composites With High Thermal Conductivity And The Performance On Hydrogen Isotopes Adsorption

As a sustainable and clean energy,nuclear fusion power offers an effective means to solve the increasingly serious energy crisis and environmental pollution,which can meet the requirements of highly developed industrialization in future.Hydrogen isotope separation is one of the most important segments during the fuel cycling in fusion energy projects.Efficient separation of hydrogen isotopes contributes to achieving fuel self-sustainment and reducing operating costs.Notably,most of current work has been focused on tailoring the structure of materials for improving the adsorption and separation for hydrogen isotopes,while the heat management during the process is usually ignored.Herein,commercial 5A molecular sieve is selected for the research of the effect of fillers types(boron nitride,graphite,graphene and polysiloxane),contents and the thermal networks on the thermal conductivity and hydrogen isotope adsorption and separation of 5A composites on the basis of the theory of porous material adsorption,separation as well as thermal conduction.The coupling relations between thermal conductivity and hydrogen isotope adsorption and separation in the composites are explored carefully.Then the tailoring methods on material design-thermal conductivity,hydrogen isotope adsorption and separation are proposed.The details are displayed as following:(1)To improve the thermal conductivity of 5A molecular sieves,boron nitride sheets(BNs)and graphite flakes(contents:0 wt%?30 wt%)are selected as thermally conductive fillers for preparing 5A/BNs and 5A/graphite composites by powder mixing method,compression molding and sintering process.XRD,SEM and FT-IR techniques are used to characterize the structure and morphology of the composite materials.The thermal conductivity test instrument and infrared thermal imager are utilized to study the effect of filler types and contents on the thermal conductivity of composites.The hydrogen adsorption is determined using a hydrogen storage performance test instrument.The results show that the higher content of filler in the composites contributes to forming stable thermally conductive networks,which immediately improves the thermal conductivity.Compared with BNs,graphite flakes play more positive role in the improvements in thermal conductivity and thermal response of 5 A composites.The thermal conductivity of composite with 30 wt%graphite flakes display 0.97 W/mK,which is 5.1 times than that of pure 5A molecular sieve.Compared with pure 5A,the normalized hydrogen adsorption capacity of 5A composite with 30 wt%graphite flakes has increased by 15.6 ml/g.It indicates the increased thermal conductivity may change the hydrogen adsorption behavior of 5A composites during the process.Then the relationship between thermal conductivity and hydrogen adsorption of the composites is tried to discusse.(2)To increase the hydrogen isotope adsorption per unit volume of 5A molecular sieve,graphene with high thermal conductivity is selected as thermally conductive filler for preparing 5A composites(GE,0 to 8 wt%)with the same route.The structure and morphology of the composites are characterized using XRD,Raman spectroscopy,SEM and other techniques.The thermal conductivity and thermal response of the composites are evaluated using a thermal conductivity test instrument and an infrared thermal imager.Hydrogen storage test instrument is used to monitor the hydrogen isotopes adsorption behavior.A thermally conductive network is observed in the 5A/GE8 composite,which significantly improves the thermal conductivity and thermal response of 5A molecular sieve.The thermal conductivity increases from 0.19 W/mK of pure 5 A to 1.23 W/mK with about 547%of increase.Second,5A/GE2 displays the maximum adsorption capacity of H2 and D2 among the composites.Particularly,the adsorption capacity of D2 is higher than that of pure 5A.5A shows the normalized 4.996 mmol/g of H2 and 5.125 mmol/g of D2 adsorption capacity,while 5A/GE2 shows the normalized 5.150 mmol/g of H2 and 5.505 mmol/g of D2 adsorption capacity,respectively.The D2/H2 adsorption molar ratios are approximately 1.026 of 5 A and 1.069 of 5A/GE2,respectively.Then an importance is attached to the relationship between thermal conductivity and hydrogen isotope adsorption of the composites.Finally,coupling relation between morphology-thermal conductivity/hydrogen adsorption is established.(3)To avoid the solid-phase inorganic filler from occupying the space of the 5A molecular sieve,a fluid organic filler polysiloxane is selected to fill the voids between the 5A particles via“void filling”.5A/polysiloxane composites are prepared with the same route for reducing the weight differences of 5A particles between pure 5A and 5A composites.It contributes to not only improving thermal conductivity but also enhancing excellent hydrogen isotope separation of 5A composites.The structure,morphology,thermal conductivity and hydrogen isotope adsorption of 5A composites are studied in details.The results show that 5A particles are bonded and the voids between 5A particles are occupied with an amorphous SiOC network.It is beneficial to improve the heat transfer of composites.0.74 W/mK of the optimal thermal conductivity is detected at 10 wt%of polysiloxane content,which is about 290%higher than that of pure 5 A.Significantly increased H2 and D2 adsorption capacities of the composite with 10 wt%polysiloxane occur,especially the normalized value of D2 adsorption capacity from 5.123 mmol/g to 5.799 mmol/g.And the D2/H2 adsorption molar ratio approximately increases by 0.028,indicating that 5A/SIOC10 has better hydrogen isotope adsorption capacity.(4)On the basis of the above,the fluid organic filler polysiloxane and solid inorganic filler graphene were selected at the same time.The 5A/polysiloxane/graphene composites are prepared with the same route to achieve high thermal conductivity and excellent hydrogen isotope adsorption and separation.The structure,morphology,thermal conductivity and hydrogen isotope adsorption of the composites are studied in detail.The results show that rich heat-conducting networks composed of SiOC and GE can be seen in the composites.5A/SIOC/GE8 has excellent thermal conductivity and thermal response behavior.1.47 W/mK of thermal conductivity and 674%of enhancement indicate that a synergistic effect with SiOC and GE tends to improve the thermal conductivity of 5A molecular sieve.Finally,high thermal response contributes to excellent hydrogen adsorption of 5A molecular sieve.The normalized D2 adsorption capacity increases from 5.123 mmol/g of pure 5A to 5.828 mmol/g of 5A/SIOC/GE2.And D2/H2 adsorption molar ratio is about 1.025 of 5A and 1.141 of 5A/SIOC/GE2,respectively.