Hot-pressing Sintering Of Ternary Layered Ceramic Mo₂ga₂c And Preparation Of Two-dimensional Mo₂c

Based on the method of preparing novel ternary layered MAX phase Mo₂Ga₂C,this thesis improved the process and explored the synthesis of Mo₂Ga₂C dense bulk with its electrical and thermal conductivity.Then the two-dimensional material Mo₂C MXene derived from Mo₂Ga₂C was studied.Etching method to obtain high pure samples was found and a series of characterizations of Mo₂C MXene was made.The synthesis of highly pure Mo₂Ga₂C is a prerequisite for subsequent experiments,especially for the etching of highly pure Mo₂C MXene.In this paper,the research group’s previous exploration was improved,and the process from raw material mixing to sintering was adjusted to improve the experimental efficiency,reduce raw material waste,and ensure the purity and output of Mo₂Ga₂C.The Mo₂Ga₂C bulk was obtained by hot pressing experiments.The density of the bulk samples varied according to different temperatures,different holding times and different pressures.Finally,a dense bulk with a density of 7.81g/cm³ was obtained,and the relative density reached 98.8%.After that,the sintering mechanism of Mo₂Ga₂C during hot pressing was discussed.The electrical and thermal conductivity of the bulk sample was then studied.It was found that the additional A layer made the thermal and electrical conductivity of Mo₂Ga₂C lower than that of most 211 phases.In particular,the low-temperature superconducting phenomenon of Mo₂Ga₂C was found at 5.1K,which not only verified the theoretical predictions of foreign scientists in the early stage,but also confirmed a new MAX phase as a superconductor.Based on the preparation of high-purity Mo₂Ga₂C,this article has carried out a detailed study on the preparation of Mo₂C MXene by etching Mo₂Ga₂C.The method of using an autoclave as a reactor and selecting HF（40%）as the etching solution has not only resulted in a favourable Mo₂C MXene,but the 7-day etching cycle was shortened to the current 1-day,which greatly shortened the synthesis cycle and improved the experimental efficiency.It paved the way well for subsequent performance tests of Mo₂C MXene.The prepared high-purity Mo₂C MXene was subsequently characterized.The XRD pattern showed that the high temperature and high pressure environment etched by using an autoclave as a reactor was favorable for the conversion of Mo₂Ga₂C into Mo₂C MXene.With increasing of the etching temperature,the characteristic peaks of Mo₂C MXene became more and more obvious.The main peaks of the precursor Mo₂Ga₂C almost disappeared when the temperature rose to 160℃.The SEM images showed the morphology of Mo₂C MXene.After etching,the size of the powders was reduced from micrometer to nanometer,and the sheets were adhered together by Van der Waals’force.The internal structure of the single-layer Mo₂C MXene was shown by TEM.On the premise of ensuring the conversion rate of Mo₂C MXene,there were no macro defects in the layer.The XPS spectrum revealed the existence and content of various components and surface functional groups of Mo₂C MXene obtained by this method.Together with EDS,it proved that the Ga element was completely removed,and there were a large number of O element on the surface of Mo₂C MXene.The low-F functional group content produced by this etching method is mainly due to the instability of the Mo-F bond caused by the high temperature and its replacement by-O and-OH.