·
Linear Formula H3BO3
·
Molecular Weight 61.83
·
eCl@ss 38120104
Detailed d
It has the chemical
formula H3BO3 (sometimes
written B(OH)3), and exists in the form of colorless crystals or a
white powder that dissolves in water. When occurring as a mineral, it is
called sassolite.
Uses
Industrial
The primary industrial use of boric acid is in the
manufacture of monofilament fiberglass usually
referred to as textile fiberglass. Textile fiberglass is used to reinforce
plastics in applications that range from boats, to industrial piping to
computer circuit boards.[21]
In the jewelry industry, boric acid is often used in
combination with denatured alcohol to reduce
surface oxidation and firescale from forming
on metals during annealing and solderingoperations.
In electroplating,
boric acid is used as part of some proprietary formulas. One such known formula
calls for about a 1 to 10 ratio of H3BO3 to NiSO4, a very small
portion of sodium lauryl sulfate and a small portion of H2SO4.
Boric acid, mixed with borax (sodium tetraborate
decahydrate) at the weight ratio of 4:5, is highly soluble in water, though
they are not so soluble separately.[22] The solution
is used for fire retarding agent of wood by impregnation.[23]
It is also used in the manufacturing of ramming
mass, a fine silica-containing powder
used for producing induction furnace linings
and ceramics.
Boric acid is one of the most commonly used
substances that can neutralize active hydrofluoric acid (HF). It works
by forcing the free F− anions into complex salts. This process
defeats the extreme toxicity of hydrofluoric acid, particularly its ability to
sequester ionic calcium from blood serum which can lead to cardiac arrest and
bone decomposition; such an event can occur from just minor skin contact with
HF.[24]
Medical
Boric acid can be used as an antiseptic for minor
burns or cuts and is sometimes used in dressings or salves. Boric acid is
applied in a very dilute solution as an eye wash. Dilute boric acid can be used
as a vaginal douche to treat bacterial vaginosis due to excessive alkalinity,[28] as well
as candidiasis due to
non-albicans candida.[29] As an antibacterialcompound, boric acid
can also be used as an acne treatment. It
is also used as prevention of athlete's foot, by inserting
powder in the socks or stockings, and in alcohol solution can be used to treat
some kinds of otitis externa (ear
infection) in both humans and animals. The preservative in urine sample bottles in the UK is boric acid.
Boric acid solutions used as an eye wash or on
abraded skin are known to be toxic, particularly to infants, especially after
repeated use; this is because of its slow elimination rate.[30]
Insecticidal
Boric acid was first registered in the US as an
insecticide in 1948 for control of cockroaches, termites, fire ants, fleas, silverfish, and many
other insects. The product is
generally considered to be safe to use in household kitchens to control
cockroaches and ants.[31] It acts as a
stomach poison affecting the insects' metabolism, and the dry powder
is abrasiveto the
insects' exoskeletons.
Preservation
In combination with its use as an insecticide, boric
acid also prevents and destroys existing wet and dry rot in timbers. It can be
used in combination with an ethylene glycol carrier to
treat external wood against fungal and insect attack. It is possible to buy
borate-impregnated rods for insertion into wood via drill holes where dampness
and moisture is known to collect and sit. It is available in a gel form and
injectable paste form for treating rot affected wood without the need to
replace the timber. Concentrates of borate-based treatments can be used to
prevent slime, mycelium, and algae growth, even in marine environments.
Boric acid is added to salt in the curing of cattle
hides, calfskins, and sheepskins. This helps to
control bacteria development, and helps to control insects.
pH buffer
Boric acid in equilibrium with its conjugate base
the borate ion is widely used (in the concentration range 50 - 100 ppm
boron equivalents) as a primary or adjunct pH buffer system in swimming pools. Boric acid is a
weak acid, with pKa (the pH at which buffering is strongest because the free
acid and borate ion are in equal concentrations) of 9.24 in pure water at
25 °C. But apparent pKa is substantially lower in swimming pool or ocean
waters because of interactions with various other molecules in solution. It
will be around 9.0 in a salt-water pool. No matter which form of soluble boron
is added, within the acceptable range of pH and boron concentration for
swimming pools, boric acid is the predominant form in aqueous solution, as
shown in the accompanying figure. The boric acid - borate system can be useful
as a primary buffer system (substituting for the bicarbonate system with
pKa1 = 6.0 and pKa2 = 9.4 under typical salt-water pool conditions) in pools
with salt-water chlorine generators that tend to show upward drift in pH from a
working range of pH 7.5 - 8.2. Buffer capacity is greater
against rising pH (towards the pKa around 9.0), as illustrated in the
accompanying graph. The use of boric acid in this concentration range does not
allow any reduction in free HOCl concentration needed for pool sanitation, but
it may add marginally to the photo-protective effects of cyanuric acid and confer
other benefits through anti-corrosive activity or perceived water softness,
depending on overall pool solute composition.
Lubrication
Colloidal suspensions of nanoparticles of boric acid
dissolved in petroleum or vegetable oil can form a remarkable lubricant on
ceramic or metal surfaces[33] with a
coefficient of sliding friction that decreases with increasing pressure to a
value ranging from 0.10 to 0.02. Self-lubricating H3BO3 films
result from a spontaneous chemical reaction between water molecules and B2O3 coatings
in a humid environment. In bulk-scale, an inverse relationship exists between
friction coefficient and Hertzian contact pressure induced by applied load.
Nuclear power
Boric acid is used in some nuclear power plants as
a neutron poison.
The boron in boric acid reduces the probability of thermal fission by absorbing
some thermal neutrons. Fission chain reactions are generally driven by the
probability that free neutrons will result in fission and is determined by the
material and geometric properties of the reactor. Natural boron consists of
approximately 20% boron-10 and 80% boron-11 isotopes. Boron-10 has a high
cross-section for absorption of low energy (thermal) neutrons. By increasing
boric acid concentration in the reactor coolant, the probability that a neutron
will cause fission is reduced. Changes in boric acid concentration can
effectively regulate the rate of fission taking place in the reactor. Boric
acid is used only in pressurized water
reactors (PWRs) whereas boiling water reactors (BWRs) employ control rod pattern and coolant flow for
power control. BWRs use an aqueous solution of boric acid and borax or Sodium
Pentaborate for an emergency shut down system. Boric acid may be dissolved in
spent fuel pools used to store spent fuel elements. The concentration is high
enough to keep neutron multiplication at a minimum. Boric acid was dumped over
Reactor 4 of the Chernobyl Nuclear Power
Plant after its meltdown to prevent another reaction from occurring.
Pyrotechnics
Boron is used in pyrotechnics to prevent
the amide-forming reaction between aluminum and nitrates. A small amount of
boric acid is added to the composition to neutralize alkaline amides that can
react with the aluminum.
Boric acid can be used as a colorant to make fire
green. For example, when dissolved in methanol it is popularly
used by fire jugglers and fire
spinners to create a deep green flame.
Agriculture
Boric acid is used to treat or prevent boron deficiencies in plants. It is also used in preservation of grains such
as rice and wheat.[citation needed]
Recreational
For the game of carrom, boric acid is sprinkled onto the board of play to
act as a dry lubricant to increase
the speed of the pieces when struck.
$96.65/KG OR $43.93/KG
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