Study On Preparing Silica Aerogel And Nano-silica From Rice Husk

Silica aerogel, namely precipitate SiO₂, has the characteristics of highpurification, low density, high specific surface area and fine decentralization, and alsohas high optics and mechanism capability, so it has been widely used in many fields,such as rubber, plastics, medicines, paints, household chemicals, activator carriers,compound materials of macromolecule, electronic encapsulation materials and fineceramic materials. In recent years, silica is more and more used in technology ofmilitary affairs, communications, electron and laser.China is a major rice-producing country, rice husks as major products after riceprocessed were discarded and less than 10% as a primary fuel use. This is aremendous waste of resources, and has caused great environmental pollution.Comprehensive utilization of rice husk has been one of significant subjects peoplewant to study. Husks containing 16%～20% of the amorphous hydrated silica,silica main components of combustion. Contamination few other minerals, so ricehusk is an ideal production of fine chemical products silica materials.The project researched a new method of preparing silica aerogel from Rice Huskdirectly without producing water glass as intermediate product for the first time. Byboiling in dilute hydrochloric acid, drying and then calcining at a certain temperature,rice husk could manufacture high quality silica aerogel, the quality of products wasover the national standards. The optimal reaction conditions was determined: theconcentration of hydrochloric acid was 3% to 5%, boiling time was four hours,calcination temperature was 550℃. The white degree of products could reach 93%,and the content of SiO₂ reach 98% under these conditions. The special surface area ofproducts reached 235m²/g, the X-ray diffraction (XRD) and infrared spectra (IR)analysis showed silica aerogel were amorphous structure.At the same time, nano-silica and active carbon can be made from carbon ricehull ash by reacting with sodium hydroxide. The factors influencing condition wasstudied in this paper. In order to promote the qualities of productions, we have studiedmany methods which can give better results. The optimal technology parameters forreaction were NaOH concentration of 2.5mol/L; time 4 hour; the reaction temperatureof 100℃. And in this condition, 90% silicon oxide can be solved out, the white degreeof silica aerogel is above 90%, and the value of active carbon adsorption of methylene blue is 12 ml/0.1g. If rice hull can been treated by proportion way before burn, thequalities of productions would be improved. The reaction of sodium silicate solutionand ammonium chloride can prepare nano-silica, and glycol -6000 for surfactant.Prepared nano-silica is completely consistent with the national standard. Through theresearch, we find nano-silica is wadding-like precipitation. Analysis of X-raydiffraction shows that nano-silica is amorphous substance. Under TEM, the particle isspherical with average size of about 50 nm. Infrared absorption spectrum analysisshows nano-silica is the amorphous hydrated silica.