HF / Hydrofluoric Acid Dissolve Metal Oxides
Hydrofluoric acid (HF) is a solution of hydrogen fluoride in water.
It is a valued source of fluorine and is a precursor to numerous
pharmaceuticals such as fluoxetine (Prozac) and diverse materials
such as PTFE (Teflon).
Hydrofluoric acid is a highly corrosive acid, capable of dissolving
many materials, especially oxides. Its ability to dissolve glass
has been known since the 17th century, even before hydrofluoric
acid had been prepared in large quantities by Carl Wilhelm Scheele
in 1771. Because of its high reactivity toward glass and
moderate reactivity toward many metals, hydrofluoric acid is
usually stored in plasticcontainers (although PTFE is slightly
permeable to it).
Hydrogen fluoride gas is an acute poison that may immediately and
permanently damage lungs and the corneas of the eyes. Aqueous
hydrofluoric acid is a contact-poison with the potential for deep,
initially painless burns and ensuing tissue death. By interfering
with body calcium metabolism, the concentrated acid may also cause
systemic toxicity and eventual cardiac arrest and fatality, after
contact with as little as 160 cm2 (25 square inches) of skin.
In a standard oil refinery process known as alkylation, isobutane
is alkylated with low-molecular-weightalkenes (primarily a mixture
of propylene and butylene) in the presence of the strong acid
catalystderived from hydrofluoric acid. The catalyst protonates the
alkenes (propylene, butylene) to produce reactive carbocations,
which alkylate isobutane. The reaction is carried out at mild
temperatures (0 and 30 °C) in a two-phase reaction.
Production of organofluorine compounds
The principal use of hydrofluoric acid is in organofluorine
chemistry. Many organofluorine compoundsare prepared using HF as
the fluorine source, including Teflon, fluoropolymers,
fluorocarbons, andrefrigerants such as freon.
Production of fluorides
Most high-volume inorganic fluoride compounds are prepared from
hydrofluoric acid. Foremost are Na3AlF6, cryolite, and AlF3,
aluminium trifluoride. A molten mixture of these solids serves as a
high-temperature solvent for the production of metallic aluminium.
Given concerns about fluorides in the environment, alternative
technologies are being sought. Other inorganic fluorides prepared
from hydrofluoric acid include sodium fluoride and uranium
Etchant and cleaning agent
The ability of hydrofluoric acid to dissolve metal oxides is the
basis of several applications. It removes oxide impurities from
stainless steel, a process called pickling, and silicon wafers in
the semiconductor industry. In this regard it is also referred to
as BHF, (when Buffered with Ammonium Fluoride), and BOE (for
Buffered Oxide Etch). It is a significant constituent of Wright
Etch and the similar HNA (HF+Nitric+Acetic Acid) etch. In similar
manner, it is also used to etch glass. A 5% to 9% hydrofluoric acid
gel is also commonly used to etch all ceramic dental restorations
to improve bonding.For similar reasons, dilute hydrofluoric acid
is a component of household rust stain remover and in car washes in
"wheel cleaner" compounds.Hydrofluoric acid attacks glass by
reaction with silicon dioxide to form gaseous or water-soluble
silicon fluorides. This dissolution process proceeds as follows:
SiO2 + 4 HF → SiF4 (g) + 2 H2O
SiO2 + 6 HF → H2SiF6 + 2 H2O
Because of its ability to dissolve iron oxides as well as
silica-based contaminants, hydrofluoric acid is used in
pre-commissioning boilers that produce high-pressure steam.
Because of its ability to dissolve oxides, hydrofluoric acid is
useful for dissolving rock samples (usually powdered) prior to
analysis. In similar manner, this acid is used in acid macerations
to extract organic fossils from silicate rocks. Fossiliferous rock
may be immersed directly into the acid, or a cellulose nitrate film
may be applied (dissolved in amyl acetate), which adheres to the
organic component and allows the rock to be dissolved around it.
Diluted hydrofluoric acid (1 to 3 %wt.) is used in the petroleum
industry in a mixture with other acids (HCl or organic acids) in
order to stimulate the production of water, oil, and gas wells
specifically where sandstone is involved.
Hydrofluoric acid is also used by some collectors of antique glass
bottles to remove so-called 'sickness' from the glass, caused by
acids (usually in the soil the bottle was buried in) attacking the
soda content of the glass.
HF is dangerous cargo , we can deal well with all the problem of
transportation on land or sea.