As is well known, silica sol can remain stably suspended for a long time. However, there are still many factors in the environment that can affect its stability. In particular, some precautions need to be taken during the storage process; otherwise, irreversible damage may occur. Now, let's take a look at the five factors that affect the stability of silica sol.
Factor Affecting Stability 1: Freezing
Ordinary silica sol is an aqueous dispersion of nano-silica. When the storage or use temperature of the silica sol is too low, the silica sol will freeze. Once ordinary silica sol freezes, it will cause irreversible damage. Even if it is thawed again, phenomena such as flocculation and precipitation will occur in the silica sol. This is because when freezing occurs, during the formation of ice crystals, the nano-silica particles in the silica sol will be squeezed, causing them to agglomerate, thus destroying the stability of the silica sol.
Factor Affecting Stability 2: Electrolytes
Ordinary silica sol is an aqueous dispersion of nano-silica. The particles carry a negative charge on their surface, resulting in repulsive forces, so they do not agglomerate. This is the fundamental reason why the silica sol suspension system remains stable. Therefore, during the use process, polyvalent salts cannot be added to ordinary silica sol. This is because the silicate radicals on the surface of the silica sol will combine with polyvalent metal ions to form insoluble salts, which will destroy the surface charge structure and thus cause the silica sol to gel, flocculate, etc.
Factor Affecting Stability 3: Cationic Substances
Since the surface of the silica sol nanoparticles is negatively charged, adding cationic substances (such as cationic emulsifiers, polyvalent metal ions, etc.) to the silica sol system will cause the silica sol to flocculate, resulting in irreversible scrapping.
Factor Affecting Stability 4: Organic Macromolecules
If water-soluble organic macromolecules are added to the ordinary aqueous silica sol system, it will also cause the silica sol to gradually thicken or eventually gel. This is because organic macromolecules with too large a molecular weight will be adsorbed on the surface of the nanoparticles of the silica sol, covering their surface charges, weakening the charge repulsion between the particles of the silica sol, and thus causing the silica sol to gel.
Factor Affecting Stability 5: Open Container
During the use of silica sol, if the container remains open for a long time, the surface water will evaporate and silica crystals (in the shape of fine needles or sand grains) will precipitate out. Generally, this phenomenon will not affect the stability of the silica sol, but it may affect its use. When using it, these solid precipitates need to be filtered out with a very fine filter cloth.
