Basic introduction to silica
What is the role of SiO2?
Is SiO2 acidic or alkaline?
Usually manufacturing glass, ceramics and abrasives. Quartz is the second most common mineral in the earth's crust. Its chemical name is SiO2.
Is silica harmful to the human body?
There is no evidence that it is dangerous to replace it as a food additive, but further research on its role in the human body is needed. Long-term elimination of silica dust can cause lung disease.
Is SiO2 a tetrahedron?
In addition to the amorphous form,SiO2 also has many different crystal forms (polymorphs). With the exception of chabazite and fibrous silica, all crystal forms contain tetrahedral SiO4 units connected together by shared vertices.
Therefore, because silica does not contain oxide ions, it has no alkalinity. In fact, it is weakly acidic and will react with strong bases. Reacts with water: As thermodynamics is difficult to destroy its network covalent structure, silica does not react with water.
Why is SiO2 not sio4?
Because of the large size of silicon, it does not form double bonds with oxygen atoms. Therefore SiO2 is not linear. The electronegativity of carbon, silicon and oxygen atoms are 2.5, 1.7 and 3.5, respectively. The electronegativity difference between carbon atoms and oxygen atoms is 1, which meets the requirement of forming polar covalent bonds in CO2.
Is SiO2 ceramic?
Commonly used coating ceramic materials include SiC (silicon carbide), SiO2 (silicon dioxide) and Si3N4 (silicon nitride). You will end up with some of the characteristics of ceramic coatings, such as enhanced protection, durability and extreme water droplets.
Why is SiO2 insoluble in water?
All electrons are held tightly between atoms and cannot move freely. Insoluble in water and organic solvents. There is no possible attraction between solvent molecules and silicon or oxygen atoms to overcome the covalent bonds in the giant structure.
Study on the Heat Capacity and Viscosity Increase of the Mixture of SiO2 Nanoparticles and Binary Carbonate
The binary carbonate mixture (the molar ratio of Li2CO3-K2CO3 is 62:38) was mixed into SiO2 spherical nanoparticles with a concentration of 1% by weight. Differential calorimeter and rheometer were used to study the thermal and rheological properties of binary carbonate mixtures and nanofluids mixed with SiO2 nanoparticles. The results showed that the viscosity increased by 34.0-94.4% and the heat capacity increased by 19%. In addition, nanofluids exhibit significant non-Newtonian behavior (shear thinning). When nanoparticles have high aspect ratios (eg, rod-like structures, nanotubes, etc.) at high concentrations, nanofluids are known to exhibit non-Newtonian behavior. Literature studies have shown that salt mixtures can be micro-separated near the nanoparticles.The separated salt can crystallize on the surface of the nanoparticle and grow further to form a dendritic nanostructure. In order to verify the change of the nanostructure, we added a small amount of hydroxide (0.03 wt.%) to the nanofluid to destroy the change of the nanostructure, and measured its performance, as reported in the literature. The results show that the heat capacity enhancement is reduced from 19% to 9%. In addition, the viscosity decreased from 34.0% to 8.4% (at the highest shear rate) and 94.4% to 62.8% (at the lowest shear rate), respectively. In addition, the theoretical viscosity model can predict well at the highest shear rate (250 / s), where the effect of nanostructure changes is minimal, while at low shear rates, it cannot predict the increase in viscosity, while nanostructure changes are expected Will decrease. Lead the trend. Our experimental results support that dendritic salt nanostructures are mainly responsible for increasing the heat capacity and the shear thinning behavior of molten salt nanofluids.
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