Preparation And Properties Of Monolithic Catalyst Carrier Orient To Green Monopropellant

Green monopropellant has attracted considerable attention in space propulsion fields because it has advantages of non-toxic,high density specific impulse,easy to store and use.The catalytic combustion condition of green monopropellant is a high-temperature,high-speed,water-vapor-containing environment,which brings forward rigorous demands for the catalyst carrier.In this work,the material and structure of catalyst carrier were considered overall,and a kind of monolithic catalyst carrier with a washcoat of Lanthanum zirconate?La₂Zr₂O₇,LZO?was prepared.The monolithic catalyst carrier with good loading percentage and mechanical stability was prepared by suspension method,using cordierite honeycomb ceramic as substrate material and LZO powder as washcoat material.In this work,the technological parameters were optimized,and the properties were studied.Details are as follows:The optimization and pretreatment of substrate material were studied.Cordierite honeycomb ceramic was chosen as substrate material because of its advantages,such as low pressure drop,high service temperature,good water-vapor-condition endurance,high combining strength with washcoat,low thermal expansivity and density.The loading percentage and mechanical stability of LZO washcoat were good when the base material was pretreated by 2h in 100?and 20wt%oxalic acid solution.Steady suspension was prepared by exploring the influence of ball millling time,solid content,pH and additive on stability of suspension,properties of LZO powder and washcoat.The best parameters were as follows:ball milling time was 1h,solid content was 20wt%,pH=6,and the content of PEG-4000 was 4wt%.In this case,partical size was 612nm,and the suspension was steady.A uniform LZO washcoat with good loading percentage and mechanical stability was prepared.The influence of impregnation time,calcine temperature and calcine time on the loading percentage and mechanical stability of washcoat was studied.The best parameters were as follows:coating 2min,calcining at 600?for 2h each time,and repeating for 3 times.In this case,LZO washcoat with loading percentage of 15.60wt%and drop ratio of 4.70wt%was prepared.The component,structure,and mechanical property were studied.When the calcine temperature was 600?,LZO had a low crystalline degree,and the washcoat was unsintered remaining porous structure.The monolithic catalyst carrier had a surface area of 5.36m²/g,and average pore size of 3.7nm,which depended mainly upon LZO washcoat.The compressive strength of the carrier depended upon substrate material.When the carrier was subjected to a compressive load,the channels were destroyed ply-by-ply.The compressive strength parallel to the channels was 1.86MPa,while it was 0.80MPa vertical to the channels.The high-temperature stability of the monolithic catalyst carrier was investigated.The size and phase of the carrier remained unchanged after calcining at 1000¹200?.After calcining at 1000?for 2h,the LZO washcoat remained unsintered,but the surface area of the carrier decreased to 2.42m²/g.However,after calcining at 1200?for 2h,the LZO washcoat sintered obviously.In this case,the surface area of the carrier decreased by 80.0%to 1.08m²/g,and the average pore size increased from 15.62nm to 86.10nm.So the micro-and mesoporous structure was destroyed severely.The thermal shock resistance of the carrier was studied.On the whole,the drop ratio increased when the temperature and times increase.The drop ratio was less than 8wt%after 10 times thermal shock when the temperature was 800¹400?and the carrier cooled down in air.In this case,the carrier had a good thermal shock resistance.However,when the carrier cooled down more quickly in water,and the temperature was higher than 1200?,the drop ratio increased to more than 15wt%.The water-vapor-condition endurance of the carrier was studied.The size and phase of the carrier remained unchanged after calcining at 1000¹200?in water-vapor-condition.After calcining at 1000?in water-vapor-condition for 30min,the LZO washcoat remained unsintered.However,after calcining at 1200?in water-vapor-condition for 30min,the LZO washcoat sintered obviously.The water vapor promoted the sintering of LZO washcoat.