Nanoporous Structure Morphological Evolution And Properties Of Dealloyed Cu-Al Eutectic Compounds

Nanoporous metal materials exhibit unique material properties such as ultra-high specific surface area,low density,and high strength,and have good application prospects in many fields.The dealloying method has become one of the important methods for preparing nanoporous materials due to its advantages of simple operation and low requirements for experimental equipment.Currently,the majority of dealloying preparation is thin strips and sheets,and there is little research on nanoporous particles.In terms of ultrasonic degradation and electrocatalysis,nanoporous particles exhibit unique advantages,so the preparation of nanoporous particles needs further exploration and research.In addition,the nanopores serving as corrosion exchange channels limit the dealloying rate to a certain range,which greatly prolongs the dealloying time of large-sized blocks,confirming the limitations of dealloying methods in the preparation of large-sized nanoporous blocks.Therefore,it is possible to prepare dealloyed precursors through powder sintering,and then combine them with the chemical dealloying method to prepare micro and nanoporous particles.The combination of the two methods is simple and fast,and the self-detachment phenomenon of the precursors can also meet the requirements of reaction intensity control.By adjusting the preparation and dealloying conditions of the precursor preparation,porous particles with different microstructure and adjustable ligament size can be obtained,It has good ultrasonic degradation and electrocatalytic performance.The secondary sintering of micro nanoporous particles can achieve the successful preparation of micro-nano porous blocks,greatly reducing the overall dealloying time.In this thesis,Cu-Al eutectic compound precursors were prepared by cold pressing and powder sintering,and nano-sized porous Cu/Cu₂O was prepared by etching in Na OH solution,and its ultrasonic degradation properties were studied.The reaction behavior during powder sintering was studied by TG-DSC.Among them,the precursor of eutectic component（C17A）undergoes reversible eutectic reaction,while the components of Hypoeutectic（C10A）and hypereutectic（C25A）undergo precipitation reaction in addition to eutectic reaction,which results in the formation of morphological features similar to hypoeutectic,eutectic and hypereutectic,respectively.The phase ratio and morphology characteristics of C17A are convenient for the dealloying reaction,so the obtained micro-nano porous Cu/Cu₂O particles（MNPC17）have the best nano ligament structure and overall morphology.The low and high Cu Al₂ phase in C10A and C25A will cause changes in yield and dealloying difficulty.The active substances produced by the"sonoluminescence"and"hot spot effect"caused by ultrasound can not be used for actual degradation,while the addition of MNPC can significantly improve the degradation rate of ultrasonic degradation of MO.During dealloying,the combination of dissolved oxygen and Cu elements will form part of Cu₂O,while the complex products of Cu and Cu₂O are easy to excite and generate electrons and holes,and rapidly transfer electrons to improve the degradation efficiency.Through the short time oxidation of MNPC17,the ratio of Cu and Cu₂O in the product can be adjusted to obtain the best degradation efficiency.The product oxidized at 120℃for 1 hour can degrade MO by 86%in 10 minutes,which is the result of the joint action of appropriate Cu/Cu₂O in the particle and the micro-nano double-layer pore structure.The effects of heating rate,etch concentration and temperature on phase distribution,microstructures and electrochemical properties of the prepared precursors were investigated.The results show that the phase distribution of precursors becomes more uniform as the heating rate decreases from 10℃/min to 2℃/min,but the independently accumulated particles melt together due to prolonged heating.The nano-ligaments become coarser during de-alloying,and the original micro-particles gradually become micron-sized fragments.On the other hand,the effect of corrosion solution concentration and temperature on the microstructure of particles was studied.At the concentration of 10 wt%,the dealloying time increased,and the residual Al element in the sample.At the concentration of 30 wt%,the dealloying reaction was too intense,which would not only coarsen the nano ligaments,but also destroy the pre-formed microstructure.At the concentration of 20 wt%,MNPC17 with good structure and complete morphology could be better obtained.The size of nanoligaments and the ratio of Cu/Cu₂O are greatly affected by the dealloying temperature.When the dealloying temperature is 80℃,the average size of nano ligaments is 58.76 nm.When the dealloying temperature is-20℃,the size of nano ligaments is refined by about 3.5times to 16.41 nm,which also makes the specific surface area of the sample increase from 11.44 m²·g^-1 to 21.13 m²·g^-1,and the Cu₂O in the product also increases with the decrease of temperature.Therefore,the sample dealloyed at-20℃can obtain better OER performance under the combined action of high specific surface area and high Cu₂O content.In addition,the short time of dealloying confirmed that during the corrosion processα（Al）is corroded before Cu Al₂.Based on nano-porous particles,the effect of sintering conditions on the mechanical properties of nano-porous blocks was studied by tubular furnace sintering and spark plasma sintering.The structure evolution of nano ligaments of particles in different atmospheres was studied by heat treatment of MNPC17 in vacuum,argon and hydrogen.The nanoligaments in vacuum atmosphere gradually coarsened with the increase of temperature.At 800℃,the phenomenon of sintering and merging occurred.Due to the pressure difference caused by vacuum atmosphere,the particles changed into the porous structure of micron solid edges at 1000℃.The argon and hydrogen atmosphere samples,due to the retention of gas and the generation of gas,respectively,play a role in pinning the grain boundaries and blocking the ligaments,so that the particles are transformed into large-grained micro-porous particles and coarsened micro-nano porous particles at 900℃.Through the heat treatment of the powder,select the appropriate atmosphere and temperature to prepare the micro-nano porous block,and then study the porosity and mechanical properties of the block under two kinds of atmosphere sintering.The total pore area of the block sintered at 700℃in vacuum for1 hour is far less than that of hydrogen sintering,and the overall compressive strength of the block is 73.36 MPa,which is slightly higher than 69.42 MPa of hydrogen sintering.In addition,micro-nano porous blocks can be rapidly prepared by spark plasma sintering,and the mechanical properties of the blocks prepared by two sintering methods are compared.This thesis includes 56 figures,7 tables and 106 references.