不同氧化铝前驱体相转过程的研究

Phase Transition Process of Different Al_(2)O_(3) Precursors

以勃姆石(γ-AlOOH)、γ-Al_(2)O_(3)为前驱体,MgO为添加剂,采用扫描电子显微镜(SEM)、X射线衍射(XRD)、粒径分布等表征手段,对两种前驱体转变为α-Al_(2)O_(3)的相转过程进行了研究。研究发现,在未掺杂添加剂的情况下,γ-Al_(2)O_(3)、γ-AlOOH经煅烧转变为α-Al_(2)O_(3)时均经历了γ-Al_(2)O_(3)→θ-Al_(2)O_(3)→α-Al_(2)O_(3)的过程,完全转变为α-Al_(2)O_(3)的温度分别为1200℃和1100℃。MgO对Al_(2)O_(3)的相转过程有促进作用,MgO掺杂量适当(0.5%,质量分数)时促进作用最明显,掺杂量过高或过低对相转的促进作用均减弱。当MgO掺杂量为0.5%(质量分数)时,γ-Al_(2)O_(3)完成α相转的温度为1050℃,比没有掺杂MgO时温度降低了150℃。当MgO掺杂量为0.3%、0.5%时,γ-AlOOH完全转变为α-Al_(2)O_(3)的温度最低为1075℃,比没有掺杂MgO时温度降低了25℃。并对影响α-Al_(2)O_(3)相转温度的机理进行了分析。

Al_(2)O_(3)is widely used in the fields of machinery,chemical industry,electronics and other fields due to its excellent properties such as high hardness,ultra-high wear resistance,and chemical resistance.At present,most of the methods for preparingα-Al_(2)O_(3)powders use different precursors calcinated at a certain temperature.In this study,α-Al_(2)O_(3)was synthesized by usingγ-AlOOH andγ-Al_(2)O_(3)as precursor materials and using MgO as a doped additive.The phase transition process was characterized by SEM,XRD and particle size distribution.The results show that bothγ-Al_(2)O_(3)andγ-AlOOH undergoαphase transition process ofγ-Al_(2)O_(3)→θ-Al_(2)O_(3)→α-Al_(2)O_(3)during calcinations and pureα-Al_(2)O_(3)phases could be obtained at 1200°C and 1100°C,respectively.The temperature for pureα-Al_(2)O_(3)phase is affected by the particle size distribution ofγ-Al_(2)O_(3)formed during its calcination,and MgO doping additive can promote theα-Al_(2)O_(3)phase transition process.The promotion effect is most obvious when the doping amount is appropriate and it would be weakened when the doping amount is too high or too low.When the MgO doping amount(mass fraction)is0.5%,the temperature at whichγ-Al_(2)O_(3)completes theαphase transformation is 1050°C,which is 150°C lower than that without MgO.Whenγ-AlOOH is doped with 0.3%and 0.5%MgO,the temperature for complete transition toα-Al_(2)O_(3)is 1075°C,which is 25°C lower than that without MgO.The promotion effect of MgO on the phase transition of different precursors is affected by the size of the primary particles of the powder.