Study On Amine-Directed Synthesis Of Thermally Stabilized Lamellar Crystallin Zirconia

In this paper,the thermally stabilized lameller crystalline zirconia was prepared by"reflux-hydrothermal method"with zirconium oxychloride as zirconium source,sodium hydroxide as precipitating agent and the surfactant octadecylamine（ODA）as template agent,and the effect of calcium chloride doping on the product was explored.Then,the samples were characterized by XRD,FT-IR,SEM and TEM.Finally,the synthesis of mechanism was proposed according to the theory calculation of Dmol³ in Materials Studio and the Gibbs nucleation free energy.Firstly,the thermally stabilized lameller crystalline zirconia was synthesized under the guidance of ODA.The as-synthesized zirconias are composed of tetragonal（t）and monoclinic phases（m）,in which tetragonal phase was the main component.The zirconia has a 10 nm thick curved multi-sheet petals shaped morphology.The petals possessed ordered lamellar（1.2 nm）and piled to form irregular pore structures.The crystal phase,lamellar structure and morphology of zirconia did not change much after calcination,which indicate that the product had good thermal stability at 500^oC.Then,calcium chloride was added in experimental process to study the effect of calcium chloride doping on the thermally stabilized lameller crystalline zirconia.It was found that the doping of calcium chloride had two effects on the product:（1）The grain size of the doped zirconia was smaller than that of the undoped zirconia,and the morphology was gradually refined small particles from nanosheets with the increase in doping amount,which show that calcium chloride doping has the effect of preventing the two-dimensional growth of zirconia crystals;（2）The monoclinic phase of the product decreases and the tetragonal phase increases,this indicates that the incorporation of calcium chloride increases the stability of the tetragonal phase.Finally,the molecular-molecular model of CH₃（CH₂）_n1NH₂-ZrO²⁺,CH₃（CH₂）_n1NH₂-ZrO（OH）₂,CH₃（CH₂）_n1NH₂-ZrO₂（where n1=0-17）and crystal plane-molecular model of ZrO₂（111）-CH₃（CH₂）_n2NH₂,ZrO₂（110）-CH₃（CH₂）_n2NH₂,ZrO₂（100）-CH₃（CH₂）_n2NH₂（where n2=7-14）were established by using the Dmol³ software package of Materials Studio and structural optimized.It was found that with the increased number of C atoms in the primary amines,the adsorption energy was smaller,this means,octadecylamine was the best template agent in the primary amine of C₁-C_18.From the molecular-molecular model,it can be seen that the N in the template molecule and the Zr in the ZrO²⁺ions,ZrO（OH）₂ and ZrO₂ molecules form a stable complex through the Zr-N coordination bond in the process of ODA-directed synthesis of thermally stable lamellar crystalline zirconia.According to the crystal plane-molecular model,the adsorption capacity of zirconia crystal plane on primary amines was:（100）>（110）>（111）,namely the orientation role of octadecylamine on ZrO₂（100）is the best.Then,through the theory of Gibbs nucleation free energy,the mechanism of octadecylamine directed thermally stabilized lameller crystalline zirconia was successfully explained from the thermodynamic point of view.