The Preparation And Investigation Of Cl~- Storage-emission Material

Chlorine anion (Cl–) is a monovalent anion through the attachment of an electron to chlorine atom. It is potentially useful in many fields such as atmospheric & environment chemistry, anion mass spectrometry, material modifications, etching and biological chemistry, etc. This dissertation presents the synthesized of Cl– anions storage-emission material [Ca24Al28O64]4+·(Cl–)3.80(O2–)0.10 (C12A7–Cl^-). Its structural characteristics, anion-emission and storage features were observed. C12A7–Cl^- could be used as a Cl– anion source. The anion storage-emission mechanisms of C12A7–Cl^- material were further discussed. The C12A7–Cl^- material was also synthesized by the sol-gel self-propagating combustion (SGCS) method.The major conclusions have been summarized as follows:(1) Synthesis and structure characterization of C12A7–Cl^-. The C12A7–Cl^- material was synthesized by co-sintering CaCO3,γ-Al₂O₃ and CaCl2 under flowing argon atmosphere at 1350℃for 8 hours, then calcining at 700℃under flowing Cl2/Ar atmosphere for 10 hours. The field emission scanning electron microscopy (FESEM) and X-ray powder diffraction (XRD) results showed that C12A7–Cl^- material belongs to I 43d space group. Its lattice constant is 1.2015±0.0005 nm and the mean particle size is 50 nm.(2) Anions emission characteristics. The emission characteristics of C12A7?Cl^- material, including emission temperature effects, the anion emission branch ratio, the extraction electric field effects, and the anion emission stability have been investigated via time-of-flight mass spectrometry. The Cl^- anion is proved to be the dominant anion emitted from C12A7?Cl^- material, and its emission intensity increases with the increase of the emission temperature or the extraction electric field.(3) Cl^- emission current. The absolute current densities of different anions are calculated with emission branch ratios synchronously measured by TOF-MS spectra and the total emission current densities of the C12A7–Cl^- material. The Cl^- emission current density could reach 10μA/cm2 level. The apparent activation energies of anions derived from the current densities decrease with the increase of the extraction electric field,which accords with Schottky formula. When continuously supplying chlorine gas and electrons, an almost stable Cl– emission beam can be realized.(4) Anions storage characteristics. The electron paramagnetic resonance (EPR), ion chromatography (IC) and raman spectroscopy (RS) results showed that Cl– anions are the domiant anionic species stored in the C12A7?Cl^- material ((2.21±0.24)×1021 cm?3), accompanied by small amount of O2– and trace amount of O– and O2–.(5) Anions formation and emission mechanism. In the high-temperature sintering process, the Cl– and O2– anions are formed synchronously and during the following annealing process, the concentration of the encaged Cl– anions are increased by anion-molecule reactions. The Cl^- emission is origined from the encaged Cl^- anions stored in C12A7?Cl^- migrating from the bulk of sample onto the surface by field-enhanced thermal diffusion, and then desorbed to the gas phase. The weak electron and O? emission are mainly derived from the decomposition of anions stored in cages of the material.(6) Synthesize C12A7?Cl^- by SGCS method. The C12A7?Cl^- material was also prepared by SGCS method, the structural and storage features of material were investigated by various characterization methods. The anion emission was also observed by TOF-MS. The results show the SGCS method could be useful for synthesizing C12A7?Cl^- material.The above results showed that C12A7–Cl^- has the ability to store high-concentration of Cl^- anions and emit high-intensity and purity of Cl^- anions. Its stable emission via the electrical chemistry implantation method would be useful for the high-pure Cl^- source. The material could also be synthesized by sol-gel self-propagating combustion method successfully.