Synthesis and microstructure of boron-doped alumina membranes prepared by the sol-gel method

Pure and boron-doped gamma -Al2O3 membranes have been synthesized by the so l-gel method. The thermal stability of the unsupported alumina membrane was studied by determining the pore structure (including average pore size, po re volume and BET surface area). The average pore size of the pure alumina membrane increased sharply after sintering at temperatures higher than 1000 degreesC. Addition of 16% boron can considerably stabilize the pore struct ure of the unsupported alumina membrane. The pore diameter for the B-doped membrane was stabilized within 13 run after sintering at 1200 degreesC for 5 h. The substantial increase in the pore size for the pure alumina membran e at the sintering temperature of 1000-1200 degreesC was accompanied by the phase transformation from gamma -Al2O3 to alpha -Al2O3. The addition of bo ron can raise the temperature of this phase transformation significantly an d, thus, improves the thermal stability of the membranes. (C) 2001 Elsevier Science B.V. All rights reserved.