Silica, chemical formula is SiO2. Naturally occurring silica called silica, it appears in three variants: quartz, tridymite, cristobalitex. The inert nature of silicon dioxide, hydrogen fluoride and hydrofluoric acid effect it. Hydrogen fluoride and hydrofluoric acid is the only acid can dissolve silicon dioxide, generate fluoride acid soluble in water.

Hydrofluoric acid is aqueous solution of hydrogen fluoride, transparent colorless to pale yellow liquid smoke. Irritating odor. Formula HF-H2O. The relative density of 1.15 to 1.18. Boiling point 112.2 ℃ (percentage by weight 38.2%). Typically commercially available concentration: about 47%. It is a weak acid. An aqueous solution of hydrogen fluoride, the solute mass fraction of up to 35.35%. Colorless solution, poisonous. When most concentrated density of 1.14g / cm3, the boiling point of 393.15K (120 ℃). Hair smoke. A weak acid, but the degree of ionization of concentrated time with the general weak electrolyte are different than dilute big. Corrosion of teeth, bone damage is more serious. Silicon compounds are highly corrosive. It should be kept in a sealed plastic bottle. Derived soluble in water with HF. For engraving glass, cleaning residue on the sand casting, controlled fermentation, power semiconductor wafer polishing and cleaning corrosion (with HNO3 mixed acid). Because between hydrogen atoms and fluorine atoms bonded relatively strong, hydrofluoric acid so that the water can not be completely dissociated.