Preparation And Characterization Of Silica Nanoparticles And Silica Nanoglass

Silica glasses are widely applied in many fields due to their unique properties such as high hardness,high strength and high transparency;but their brittleness limits their wider applications.Nanoglass is a new kind of glassy materials that exhibits a microstructure consisting of nanometer-sized glassy regions connected by glass/glass interfaces with an enhanced free volume(relative to the free volume in the glassy regions).The nanometer-sized glassy regions have high hardness,and the glass/glass interfaces have high toughness.Nanoglass may have good toughness and other properties because of the microstructure.Silica nanoglass may overcome the brittleness of the silica glasses and have important applications in many fields,the synthesis and characterization of silica nanoglass are thus of important significance.In order to prepare silica nanoglass,usually,disperse fine spherical silica nanoparticles have to be prepared in advance.And the silica nanoglass will prepared by ultrahigh vacuum/high pressure mechanical sintering the silica nanoparticles.Therefore,in this thesis,I mainly studied the preparation process of silica nanoparticles and used the prepared silica nanoparticles to produce nanoglasses.It mainly includes:(1)The synthesis of fine silica nanoparticles via a sol-gel method.Disperse fine amorphous silica nanoparticles were synthesized using TEOS as silicon source,ammonia as catalyst,ethanol as solvent,and polyethylene glycol 1000(PEG 1000)as surfactant via a sonochemical sol-gel process and subsequent calcination.And we discussed the hybrid mode,aging time and temperature,addition amount of TEOS,addition amount of ammonia,addition amount of water,calcination temperature,type and addition amount of surfactants to clarifying the influence on the final dispersity,shape,and size of the nanoparticles.By optimizing the preparation conditions,silica nanoparticles were synthesized at 6.3 m L TEOS,1 m L ammonia,1.3 mL water,and0.025 g PEG 1000 via ultrasonic stirring and aging 3 days under 60°C after calcination at 800°C for 10 h.The amorphous silica nanoparticles obtained are completely disperse without any agglomeration and equiaxed in shape and have a narrow size distribution of 4–18 nm and a fine average size of 9 nm.(2)The synthesis of spherical silica nanoparticles via a modified sol-gel method:Disperse fine spherical amorphous silica nanoparticles were synthesized using TEOS as silicon source,slow-hydrolysis catalyst as catalyst,water as solvent via a modified sol-gel process and subsequent calcination.We discussed the type and amount of slow-hydrolysis catalyst to clarifying the influence on the dispersion,shape and average particle size of the amorphous silica nanoparticles.With the optimized catalyst of 5 m L tetraethylammonium hydroxide and after calcination,the spherical amorphous silica nanoparticles obtained are disperse,narrow with a size distribution of 7–20 nm,and fine with an average size of 13 nm.This silica nanoparticles have special characteristics including good dispersion,spherical shape,and a fine average particle size.Silica nanoglass can be prepared from these dispersed spherical amorphous silica nanoparticles.(3)Silica nanoglass was prepared from the dispersed spherical amorphous silica nanoparticles with an average size of 13 nm.The largest vacuum of the ultrahigh vacuum/high pressure presser is 10~-77 Pa and its highest pressure is 2.5 GPa.We discussed the different compacting schemes to clarify their influence on the silica nanoglass to optimize the compacting schemes.First,the cracked silica nanoglass with a relative density of 96%was prepared through repeated compaction of silica nanoparticles for 55 min under the highest pressure.Second,the silica nanoglass with a relative density of 90%was prepared through slow pressure,slow decompression and constant pressure of silica nanoparticles for 60 min under the highest pressure.The obtaine nanoglass samples are monolithic without visible cracks.The results show that the compacting schemes have significant influence on the density of silica nanoglass.The microhardness of the cracked silica nanoglass with a relative density of 96%was6.71 GPa,and the nanoglass have favorable toughness.