Silica Coated Ultrafine Diamond And It’s Dispersion Stability In Multi-component Salt Solutions

The St?ber method was used to coat UFD with SiO₂ to make it have a strong hydrophilic property, it can improve the dispersion stability of the UFD multi-component salt solutions, so as to improve the microstructure uniformity and wear resistance of ultra-precision vitrified-bonded diamond wheels. The preparation process and dispersion stability in multi-component salt solutions of SiO₂ coated UFD（UFD/SiO₂） with different thickness were explored; efforts were also made to coat micron diamoND with SiO₂. These studies provide a theoretical guidance for the preparation of vitrified-bonded diamond wheels with good microstructure uniformity by polymer network gelmethod.Transmission electron microscope（TEM） and X-ray diffractometer（XRD） revealed that UFD/SiO₂ materials were core/shell structure with single diamond core and amorphous SiO₂ shell. The development of SiO₂ layer was investigated by adjusting the contents of ammonia, TEOS and reaction time.In this experiment, the SiO₂ shell thickness can be incrased by increasing the contents of ammonia and TEOS, more than 2.00 ml of ammonia or 1.00 ml of TEOS cuased free SiO₂ particles, and adding TEOS in multi times can significantly inhibit free SiO₂ particles. Under 25℃ and 2.00 ml of ammonia, 1.50 ml of TEOS can be basically completed converted to SiO₂ shell within 15 h. By hydrolysing 0.25 ml、0.50 ml and 1.00 ml of TEOS, UFD/SiO₂ materials with 10 nm、20 nmand 46 nm SiO₂ shell were prepared.Malvern Zetasizer was used to monitor the particle size distribution of the UFD/SiO₂ materials in 0.50 mol/L multi-component nitrate solutions. The DLS curves revealed that the dispension stability of UFD/SiO₂ in multicomponent nitrate solutions was much better than UFD, suspension of UFD/SiO₂ with 10 nm SiO₂ shell could stably stand more than 12 h without obviously stratification and sedimentation. UFD/SiO₂ dispersed easily when SiO₂ shell thickness increased, but the suspension stability reduced.It was found in the silica coating process of different grain size of diamond, ND were easily coated with SiO₂ due to its good suspension stability and high surface energy. However, the suspension stability and adsorption capacity of diamond with larger grain size were decreased. By increasing the stirring strength and slowing the hydrolysis, SiO₂ was deposited on the surface of larger diamond particles. The result showed that ultrasonic assisted method could coat 1.0 g ND and 0.5 g of UFD with SiO₂ shell in 50 ml of absolute ethanol solvent, which exhibited obvious advantages, compared with magnetic stirring method.