Preparation And Sintering Behaviors Study Of ?-Al₂O₃ Nanoparticles With Narrow Size Distribution

Al₂O₃ ceramics are widely applied in mechanical materials,aerospace materials,electronic materials and medicine,which is attributed to its excellent physical performance and mechanical properties,such as high hardness?Mohs hardness 9?,good chemical stability which can be resistance to strong acid and alkali corrosion,high melting point above 2000°C and high temperature resistance.However,the common weakness of Al₂O₃ ceramics is the brittleness at low temperature,which is caused by its strong ionic bonds and few slip systems.When the grain size of Al₂O₃ ceramic with high-density?>99%?decreased to nanoscale,this nanocrystalline ceramic may exhibit good toughness and plasticity,which will greatly expand the application of Al₂O₃ ceramics in many fields.In order to prepare the Al₂O₃ nanocrystalline ceramics with small grain size and high density,the requirements of initial?-Al₂O₃ nanoparticles for sintering include fine,disperse,equiaxed,narrow size distribution,high-purity,high-yield,etc.However,conventional preparation methods usually cannot satisfy these conditions at the same time,especially in the demand of fine,narrow size distribution and high-purity,which are extremely unfavorable for the forming and densification of Al₂O₃ nanocrystalline ceramics.In addition,the sintering behaviors study on ultra-fine?-Al₂O₃nanoparticles with narrow size distribution is rarely reported.In this study,the wide size distribution?-Al₂O₃ nanoparticles with a higher percentage of smaller size?-Al₂O₃ nanoparticles were used as the particles to be separated and the electrolyte coagulation separation method was applied to extract small nanoparticles.The separation order was adjusted from low HCl concentration to high HCl concentration,which avoids the loss of small nanoparticles and the wide size distribution caused by the adsorption of small nanoparticles by larger nanoparticles of?-Al₂O₃ nanoparticles.Finally,the high-quality?-Al₂O₃ nanoparticles were obtained.This method has the advantages of low cost,simple operation and good repeatability.The prepared?-Al₂O₃ nanoparticles were pressed into a green body under uniaxial high pressure,and then it will be sintered with the two-step pressureless sintering method.The two-step sintering temperatures?T₁ and T₂?were explored to determine the optimized sintering temperatures for the preparation of Al₂O₃ nanocrystalline ceramics.This research was carried out in the following two parts:1)Preparation of?-Al₂O₃ nanoparticles with narrow size distribution:The wide size distribution?-Al₂O₃ particles with a higher percentage of smaller size?-Al₂O₃ nanoparticles were used as the particles to be separated.HCl solution was used as an electrolyte solution and the separation concentration interval is set at 0.2 mol/L.Larger Al₂O₃ particles were preferentially concentrated and separated at low concentration HCl.Finally,we determined the corresponding relationship of HCl concentration on the mean particle size,size distribution and yield of?-Al₂O₃nanoparticles.Experiments show that 0 mol/L HCl?deionized water?can preferentially remove large particles above 100 nm and the yield of?-Al₂O₃ nanoparticles less than 100 nm is approximately 11.75%;After separated at 1.0 mol/L HCl,?-Al₂O₃ nanoparticles smaller than 15 nm were obtained and the yield is 2.8%;The?-Al₂O₃ nanoparticles of<6 nm that separated with 3.0mol/L HCl meets all requirement for the preparation of Al₂O₃ nanocrystalline ceramics.The yield of the prepared nanoparticles is 0.46%,and about 126 mg?-Al₂O₃ nanoparticles can be obtained from 4 ball mill tanks;Finally,?-Al₂O₃ nanoparticles obtained in the supernatant at 4.0 mol/L HCl is completely dispersed,non-agglomerated,spherical shape and narrower size distribution?2-4 nm?with a mean particle size of only 2.9 nm.In order to ensure the number of powders in the sintering experiment,we firstly prepared?-Al₂O₃ nanoparticles according to a separation order of 0.6-1.0-2.0-3.0 mol/L HCl.The?-Al₂O₃ nanoparticles with a mean particle size of 3.4 nm and size distribution of 2-6 nm were obtained in the supernatant after separation of 3.0 mol/L HCl.2)Sintering of Al₂O₃ nanocrystalline ceramics:The?-Al₂O₃ nanoparticles with a mean particle size of 3.4 nm and size distribution of 2-6 nm were studied by two-step sintering.The morphology was characterized by scanning electron microscopy?SEM?and the relative density was measured by water boiling method based on the Archimedes'principle.After optimizing the sintering temperature,we successfully prepared Al₂O₃ nanocrystalline ceramics with a grain size distribution of 10-60 nm,a mean grain size of 30 nm and a relative density of 99.5%at T₁=1150°C and T₂=1000°C with a 40 h hold.In the above study,the wide size distribution?-Al₂O₃ nanoparticles with a higher percentage of smaller size?-Al₂O₃ nanoparticles were obtained by directly ball-milling high-purity?-Al₂O₃particles and were finely and systematically separated by the electrolyte coagulation separation method.The separation order was adjusted from low HCl concentration to high HCl concentration.This preparation method has obvious effects and its operation is simple and feasible,which effectively narrowing the size distribution of?-Al₂O₃ nanoparticles and reducing the mean particle size of?-Al₂O₃ nanoparticles.The sintering behaviors of?-Al₂O₃ nanoparticles with narrow size distribution were studied by two-step sintering.Moreover,Al₂O₃ nanocrystalline ceramics with fine grain size and high density were obtained finally.