Research & Development On Adsorbents For The Adsorption Of Water-vapor In Gaseous HF

The corrosive electronic gas HF is mainly used for etching and surface cleaning of silicon wafers in the semiconductor industry,and is one of the key gases in the manufacture of micro-nano electronics.With the development of advanced manufacturing,high integration,large size,narrow line width,high uniformity and integrity of the micro-nano electronic industry,the purity of HF electronic gas is increasingly demanded,Especially,more requirements are put on the content of moisture impurities,because the impure moisture not only causes defects in downstream products,but also induces and accelerates the corrosion of the contacted materials by HF gas,causing the release of secondary pollutants such as corrosion products and materials themselves,and reducing the purity of HF gas.Because CaF₂ has a synergistic corrosion resistance to HF and H₂O and can form a high binding energy with water molecules,it has broad application prospects in water removal from gaseous HF.However,the reported CaF₂ materials have small water-adsorption capacities.In this thesis the preparation methods and water adsorption properties of CaF₂ nanomaterials with different crystal morphologies and sizes were systematically investigated.The main research work is summarized as follows:1.CaF₂ nanoparticles and nanoflowers with uniform size and morphology were prepared by a hydrothermal method with sodium citrate as a complexing agent.The effects of fluorine source,calcium source,complexing agent dosage,and solution p H on the structure and morphology of resultant CaF₂ were investigated systematically.The techniques such as XRD,SEM,FT-IR,and N2 adsorption and desorption were used to characterize the synthesized materials.The results show that when the molar ratio of sodium citrate : CaCl₂ : KF in the synthesis solution is 15 : 1 : 2 and the p H in the synthesis solution is 10,and the morphology of the as-prepared CaF₂ nanoparticles is the most uniform and the average particle size is about 8 nm.Additionally,the synthesized CaF₂ particles gradually become larger and tend to form nanospheres with increasing the content of sodium citrate in the synthesis solution.When the molar ratio of sodium citrate : calcium acetate: NaBF₄ in the synthesis solution is 5 : 1 : 2 and the p H in the synthesis solution is 10,the synthesized CaF₂ is in the shape of nanoflower composed of multilayer nanosheets with a BET specific surface area of 94m²·g^-1,and its pore-size distribution is mainly concentrated at 4 nm.Furthermore,the nanoflower material has a good thermal stability.It is also found that the synthesized CaF₂ nanoparticles or nanoflowers are severely agglomerated,when the p H in the synthesis solution is 4 or 12 without changing other synthesis parameters.2.The adsorption isotherms of water vapor on the synthesized CaF₂ nanoflower and nanoparticles with different sizes were determined by a volumetric method.The results show that the CaF₂ nanoflower has the highest water-adsorption capacity under the same temperature and water vapor pressure and is obviously superior to the adsorption capacities of water vapor on the CaF₂ reported in the literature.Because the CaF₂ nanoflower composed of multi-layer nanosheets in this work has some excellent water-adsorption properties,it is anticipated that the synthesized CaF₂ nanoflower would be industrially applied in water removal from gaseous HF.