Study On Fabrication, Growth Mechanism And Microstructure Of K₂Ti₆O₁₃ Whisker

Potassium hexatitanate(K₂Ti₆O₁₃) whisker has excellent mechanical properties and exhibits unique physical characteristics, such as high thermal insulating ability and chemical stability, due to its particular unique tunnel structure. It can find wide applications in many fields including aerospace & aviation, automobile, mechano- electronics, building materials, and armament, etc. The present work was aimed at in-situ studies of temperature and time induced phase transition, morphologic evolution, growth mechanism, microstructure, and growth crystallography during the reaction synthesis of K₂Ti₆O₁₃ whiskers using high-temperature X-ray diffractometer (HTXRD), scanning electron microscopy(SEM), and transmission electron microscopy(TEM). Based on the phenomena of"nano-cracking effect","crystal seed synthesis"; and"vapour assistance"found in this study, new technology was developed to prepare K₂Ti₆O₁₃ whiskers with high quality and low cost.Dynamic analysis of phase transition and observation of morphologic evolution show that the growth of K₂Ti₆O₁₃ whisker is quite sensitive to calcination temperature accompanying with fulminous growth at given temperature, but after that the growth became slow. Charge at the experimental temperature and air-cooling should be adopted for the synthesis of whisker so as to shorten the production periods and reduce the cost.We proposed concatenation-parallel growth model and diffusion-crack growth model on the basis of the dynamic phase analysis and morphologic evolution to elucidate the growth process of K₂Ti₆O₁₃ whisker. As to the whisker synthesized by concatenation-parallel model, small tandem steps and large parallel steps forms along the axis of the whiskers, and amorphous growth layer also emerges at the surface during the growth of the whisker; but there is not any growth step and amorphous layer on the whisker synthesized by diffusion-crack model. The above models have been proved thoroughly to be tenable by the microstructure observation.Selected area electron diffraction(SAED) analysis and high resolution transmission electron microscopy(HRTEM) observation indicates that the growth direction of the K₂Ti₆O₁₃ whisker axis is parallel to the [010] direction despite the different growth models, and the whisker fracture originated from the exfoliation along [010] direction and parallel to (-201) planes.The growth modes of K₂Ti₆O₁₃ whisker depends on the size of the starting TiO₂ particles,whose criterion of critical size are as follows: (1) the whisker growth follows concatenation-parallel model when TiO₂ particle size is smaller than the critical size of 160nm; (2) the whisker growth first follows diffusion-crack model when TiO₂ particle size is larger than the critical size, and then follows concatenation-parallel model to grow up further.Based on the diffusion-crack model, TiO₂ powder with particle size of 200nm, which is a little larger than the critical size, has been used as the starting material to prepare nanometer K₂Ti₆O₁₃ whiskers successfully. The nano-cracking effect greatly reduced the calcination temperature with a maximum magnitude of 200℃and remarkably shortened the calcinations time. Based on the concatenation-parallel model, nanometer K₂Ti₆O₁₃ whiskers have also been fabricated using 10nm-TiO₂ particles as the starting material.The high quality K₂Ti₆O₁₃ whiskers have been fabricated successfully at lower temperature with less time in virtue of cracking nano-effect and vapour assistance for 200nm-type TiO₂ raw material and crystal seeds and vapour assistance for 120nm-type TiO₂ reagent as raw material. As a result, the production cost will be decreased greatly.