Probing the effects of interfacial chemistry on the kinetics of phase transitions in amorphous and tetragonal zirconia nanocrystals.
Probing the effects of interfacial chemistry on the kinetics of phase transitions in amorphous and tetragonal zirconia nanocrystals.
复制标题
探讨界面化学对非晶态和四方氧化锆纳米晶体相变动力学的影响。
作者：
B. L. Kirsch;A. Riley;A. F. Gross;S. Tolbert
在这项工作中，我们用原位X射线衍射法研究了未包覆和氧化铝包覆的氧化锆纳米粒子的相稳定性。通过跟踪这些颗粒的结构变化，我们试图了解界面结合的变化如何影响非晶态氧化锆晶化的动力学，以及初始非晶态和初始晶态的氧化锆纳米晶中的颗粒生长动力学。用非等温动力学方法计算了与结晶有关的活化能。未包覆的非晶态氧化锆胶的晶化活化能为117+/-13kJ/mol，包覆氧化铝的非晶态胶体的晶化活化能为185+/-28kJ/mol。这种激活能的增加归因于氧化铝涂层对原子重排的抑制。用非等温动力学方法研究了晶粒长大动力学。氧化铝涂层又一次显著影响了激活能。对于在无定形结构中被氧化铝包覆的胶体，涂层使颗粒生长的激活能增加了5倍(33+/-8比150+/-30kJ/mol)。这一增长表明氧化铝涂层抑制了氧化锆芯的粗化。当胶体在四方相中合成后再包覆氧化铝时，表面包覆对粗化动力学的影响更为显著。在这种情况下，活化能增加了10倍，从未包覆颗粒的28+/-3kJ/mol增加到包覆氧化铝微晶的300+/-25kJ/mol。结果表明，利用表面涂层和界面能显著改变结构重排的动力学势垒，可以改变胶体体系的相稳定性。
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.