A new idea for specific surface area standard reference materials (SRM) which are made of nonporous mono-disperse SiO2 spheres and the true specific surface area can be calculated accurately from their diameters is presented.Firstly,the mono-disperse SiO2 spheres were synthesized in bulk.Secondly,the spheres were modified to make them nonporous.Thirdly,the characteristic dimensions,such as the size,density of the spheres,were determined accurately.Finally,the specific surface areas were measured by using a static volumetric type Brunauer-Emmett-Teller (BET) (nitrogen gas) instrument.The experimental results showed that the micro-holes on the surface of mono-disperse SiO2 spheres were almost be sealed by calcining at the temperature of 1000℃ for three hours.The BET surface area was larger than the geometric specific surface area and the values of the deviation were 1.2 m2·g-1,2.0 m2·g-1 and 3.6 m2·g-1 for mono-disperse SiO2 spheres with diameters 1150 nm,453 nm and 269 nm respectively.In this case,the theoretical value can be used as reference for the determination of the specific surface area of nonporous mono-disperse SiO2 spheres SRMs.
The effect of inhomogeneity of particles on the band-gap of silica colloidal crystals(SCCs) fabricated by vertical deposition method was studied.The optical properties of the crystals were examined.The SEM images and transmission spectrum of the crystals showed that the inhomogeneity of particles not only affected the ordering,but also their mid-gap position.When the volume ratio of S particles(VS) to L particles(VL) in suspension was 1:1,the band-gap of silica colloidal crystals changed with the growth of particles.When the ratio was 2:1,the quality of SCCs on substrate was obviously improved simultaneously with the number decreasing of L particles.Especially,the quality of SCCs at the bottom of substrate was the best and its mid-gap(634 nm) was very close to that of theoretic value of S particles(636 nm).When the ratio was 3:1,the effect of L particles became smaller with the number decreasing of L particles in suspension.The mid-gap position(638 nm) of whole SCCs on substrate were all close to that of theoretic value of S particles(636 nm).
