The physicochemical properties and preparation method of nano silica

[Physical and chemical properties] Nano silicon dioxide (SiO ₂ ) is an amorphous white powder, which is a non-toxic, odorless, and non-polluting non-metallic material

[Preparation method] (1) Preparation of nano-silica

The preparation process of nano-silica can be divided into two categories: dry method and wet method

①Gas phase method

The gas phase method mostly uses silicon tetrachloride as the raw material, and uses silicon tetrachloride gas to hydrolyze under the high temperature of hydrogen and oxygen flow to produce smoke-like silica

The nano SiO ₂ produced by the gas phase method is also called SiO ₂ aerogel.

Generally, the supercritical drying process is used to prepare SiO ₂ aerogels.

②Precipitation method

In the precipitation method, silicate is acidified to obtain loose, finely dispersed SiO ₂ crystals precipitated in a flocculent structure

CaSiO ₃ +2HCl→CaCl ₂ +SiO ₂ +2H ₂ O

③Gel method

The gel method is to add acid to reduce the alkalinity to induce the polymerization reaction of silicate, so that the particle size of the high polymer silicate ion in the form of colloidal particles in the system is continuously increased, forming a silica sol with opalescent characteristics

④Sol-gel method

The process is to stir silicate and absolute ethanol at a certain molar ratio to form a uniform mixed solution, slowly add an appropriate amount of deionized water under stirring, then adjust the pH value of the solution, and then add a suitable surfactant.

Dui Yuqiu et al.

⑤Microemulsion method

The microemulsion method can prepare nanoparticles with uniform particle size

⑥Supergravity method

The process is to filter a certain concentration of water glass solution and place it in a supergravity reactor.

⑦ Preparation of nano-silica from alkali metal silicate

Tang Fangqiong uses the surfactant to be dissolved in a non-polar organic solvent to form a solution; Rw (molar concentration ratio of water to surfactant) and Rsi (alkali metal silicate aqueous solution) required by the size of nano SiO ₂ particles And the molar concentration ratio of the surfactant) to prepare an aqueous solution of alkali metal silicate; this aqueous solution is added to the non-polar organic solvent solution of the surfactant under stirring to form a reverse micelle solution of alkali metal silicate The reverse micelle solution is added to the acidified polar organic solution dispersed phase, aged for a period of time, and centrifuged to prepare silica particles with a particle size of 5-100 nm