Preparation Of Sinterable Nanometer α-alumina Ceramics By Thermal Decomposition

a-phase alumina ceramics have high strength,high hardness,wear resistance,high temperature resistance,corrosion resistance,and excellent thermal conductivity.In chemical,mechanical,electronic,electrical,construction,medicine,precision ceramics have a wide range of applications.The nano-alumina ceramics are nano-scale due to their size,grain boundary width and pore size,which fundamentally changes the structure of alumina powders.Therefore,nano-alumina ceramics have better sintering performance than traditional alumina ceramics.However,the preparation of nano-alumina ceramics has been greatly challenged.Because the transformation temperature of a-alumina is very high,it usually reaches 1200℃or more,which causes the grain size to grow at a high temperature and it is difficult to reach the nanometer level.The preparation process is greatly hindered.This project has studied the relative best process for preparing nano alpha alumina by homogenous precipitation method and thermal decomposition method.The use of aluminum ammonium carbonate(AACH)as a precursor to prepare nano-alumina by thermal decomposition by adding α-Al2O3 seed and aluminum fluoride(AIF3),using TEM,BET,XRD,TG-DSC,FT-IR characterizes the product.The alumina prepared by this method has small particle size,good dispersion performance and high activity.The ceramic body made of the powder can be densely sintered at a temperature of 1350℃ to 1400℃,reaching a theoretical density of more than 97%,and has a high degree of compactness.The main results of the experiment:(1)The optimum process conditions for the synthesis of ammonium aluminum carbonate are:titration method:ammonium aluminum sulfate(AAS)to ammonium bicarbonate(AHC)solution;titration rate:5 mL/min;excess coefficient of AHC and AAS:1.3;pH is maintained at about 9;temperature:8℃,ammonium bicarbonate concentration is 1.7 mol/L,ammonium aluminum sulfate concentration is 0.3 mol/L,and PEG 2000 is 5%.(2)Using aluminum ammonium carbonate mixed with 10wt%α-Al2O3 seeds and 5wt%AlF3 for calcination,it can be totally converted to a-alumina at 900℃ with an average particle size of about 30nm.After the calcination,some regular rectangular shapes and hexagonalα-alumina.α-Al2O3 seeds and AIF3 mineralizers resulted in the disappearance of γ phase.α-Al2O3 seeds and AIF3 mineralizers significantly reduced the phase transformation fromθ-Al2O3 to α-Al2O3 to 900℃.which is 300℃ lower than that of aluminum ammonium carbonate without additives.(3)The nano-alumina powder prepared by the relatively optimal process is heated to 1400℃by pelletizing and ceramics made of 16 MPa,and the relative density is more than 99%after sintering for 4 hours.The crystals are completely dense.It is 200℃ lower than the theoretical temperature.