Narrowing Size Distributions Of ?-Al₂O₃ Nanoparticles By Electrolyte Coagulation Separation

?-Al₂O₃ ceramics are typical of oxide ceramics with high temperature resistant,corrosion resistance,wear resistance,oxidation resistance,high hardness,high strength,high melting point and other excellent performances and are widely used in aerospace,electronics,metallurgy,medicine and so on.However,the brittleness of ?-Al₂O₃ ceramics materials limits its wide applications.Researchers found that the performance will be greatly changed when the grain size of the material reaches the nanometer level.The appear of nanocrystalline ceramics provide an efficient way to solve the brittleness of ceramic materials.As a result,it is of great significance to prepare high quality of ?-Al₂O₃ nanocrystalline ceramics.Disperse fine ?-Al₂O₃ nanoparticles?NPs?with narrow size distribution widths are the key for the preparation of ?-Al₂O₃ nanocrystalline ceramics with good performance.Study shows that the free energy of ?-Al₂O₃ is higher than that of ?-Al₂O₃ when the size of ?-Al₂O₃ NPs is less than 15 nm,so the thermodynamically stable phase of Al₂O₃ is ?-Al₂O₃ in this case.Therefore,it is difficult to prepare disperse fine ?-Al₂O₃ NPs with narrow size distribution widths,especially with particle size less than 15 nm by direct synthesis method.Mechanochemical method combining with acid corrosion and electrolyte coagulation separation can obtained disprese fine ?-Al₂O₃ NPs but their size distributions is wide.The presence of large ?-Al₂O₃ nanoparticles has a great effect on the coagulation separation of small?-Al₂O₃ nanoparticles,which results in the broad size distribution of ?-Al₂O₃ nanoparticles.In order to narrow the size distribution width of ?-Al₂O₃ NPs we have done the follows in this work:?1?Electrolyte coagulation separation with separate sequence from low to high concentration.This separation sequence prior separate large ?-Al₂O₃ NPs at low concentration,which can reduces the influence of large ?-Al₂O₃ NPs on the coagulation behavior of small ?-Al₂O₃ NPs thus to narrow the size distribution widths of small ?-Al₂O₃ NPs.The a-Al₂O₃ NPs separated at 0.0,0.2,0.4,0.6,0.8,1.0,1.2,1.4,1.6,1.8 and 2.0 mol/L HCl have average sizes?and size distributions?of79.0?41-260?,43.0?13-82?,30.0?10-57?,15.0?7-25?,12.0?6-21?,10.0?5-17?,9.0?5-13?,8.0?4-12?,7.2?3-11?,5.2?2-8?,3.5?2-6?nm respectively;?2?Selecting an intermediate separation concentration separate the ?-Al₂O₃ NPs to be two parts and then separate this two parts of ?-Al₂O₃ NPs in a different separation order.This method can narrow the size distribution of large ?-Al₂O₃ NPs while ensuring a narrow size distribution of small ?-Al₂O₃ NPs and then obtain disperse fine ?-Al₂O₃ NPs with narrow size distribution widths.The a-Al₂O₃ NPs separated at 0.0,0.2,0.4,0.6,0.8,1.2,1.4,1.6,1.8,2.0,2.2 and 2.4 mol/L HCl have average sizes?and size distributions?of 72.0?15-190?,20.8?8-43?,13.5?7-27?,12.8?6-22?,11.0?6-20?,10.0?6-16?,8.0?4-13?,7.8?4-12?,7.2?4-10?,6.4?3-10?,4.6?2-7?and 3.8?2-6?nmrespectively.Compared the results in this experimental to the results of electrolyte coagulation separation with separate sequence from high to low concentration method show that the two methods adopted in this work can achieve the purpose of narrow the size distributions of ?-Al₂O₃ NPs.