Kirsch Bradley L, Riley Andrew E, Gross Adam F, Tolbert Sarah H
Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, USA.
Langmuir. 2004 Dec 7;20(25):11247-54. doi: 10.1021/la048343o.
In this work, we examine the phase stability of both uncoated and alumina-coated zirconia nanoparticles using in-situ X-ray diffraction. By tracking structural changes in these particles, we seek to understand how changing interfacial bonding affects the kinetics of amorphous zirconia crystallization and the kinetics of grain growth in both initially amorphous and initially crystalline zirconia nanocrystals. Activation energies associated with crystallization are calculated using nonisothermal kinetic methods. The crystallization of the uncoated amorphous zirconia colloids has an activation energy of 117 +/- 13 kJ/mol, while that for the alumina-coated amorphous colloids is 185 +/- 28 kJ/mol. This increase in activation energy is attributed to inhibition of atomic rearrangement imparted by the alumina coating. The kinetics of grain growth are also studied with nonisothermal kinetic methods. The alumina coating again dramatically affects the activation energies. For colloids that were coated with alumina when they were in an amorphous structure, the coating imparts a 5x increase in the activation energy for grain growth (33 +/- 8 versus 150 +/- 30 kJ/mol). This increase shows that the alumina coating inhibits zirconia cores from coarsening. When the colloids are synthesized in the tetragonal phase and then coated with alumina, the effect of surface coating on coarsening kinetics is even more dramatic. In this case, a 10x increase in activation energies, from 28 +/- 3 kJ/mol for the uncoated particles to 300 +/- 25 kJ/mol for the alumina-coated crystallites, is found. The results show that one can alter phase stability in colloidal systems by using surface coatings and interfacial energy to dramatically change the kinetic barriers to structural rearrangement.
在这项工作中，我们使用原位X射线衍射研究了未涂层和氧化铝涂层氧化锆纳米颗粒的相稳定性。通过追踪这些颗粒的结构变化，我们试图了解界面键合的变化如何影响非晶态氧化锆结晶动力学以及初始非晶态和初始晶态氧化锆纳米晶体中的晶粒生长动力学。使用非等温动力学方法计算与结晶相关的活化能。未涂层的非晶态氧化锆胶体的结晶活化能为117±13kJ/mol，而氧化铝涂层的非晶态胶体的结晶活化能为185±28kJ/mol。活化能的这种增加归因于氧化铝涂层对原子重排的抑制。还使用非等温动力学方法研究了晶粒生长动力学。氧化铝涂层再次显著影响活化能。对于在非晶态结构时涂有氧化铝的胶体，涂层使晶粒生长的活化能增加了5倍（33±8对150±30kJ/mol）。这种增加表明氧化铝涂层抑制了氧化锆核的粗化。当胶体在四方相中合成然后涂覆氧化铝时，表面涂层对粗化动力学的影响更加显著。在这种情况下，发现活化能增加了10倍，从未涂层颗粒的28±3kJ/mol增加到氧化铝涂层微晶的300±25kJ/mol。结果表明，通过使用表面涂层和界面能来显著改变结构重排的动力学障碍，可以改变胶体系统中的相稳定性。
