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Boric
acid, บอริกแอซิด, กรดบอริก
กรดบอริก
เป็นสารใส ไม่มีสี ไม่มีกลิ่น เป็นผลึกหรือผงสีขาว บางครั้งเป็นเงาคล้ายไข่มุก
ละลายได้ดีในน้ำและแอลกอฮอล์ จะละลายได้ดียิ่งขึ้นในน้ำร้อนและกลีเซอรอล
กรดบอริกจะระเหยในไอน้ำเมื่อให้ความร้อนถึง 100 องศาเซลเซียส
จะสุญเสียน้ำและค่อยๆ เปลี่ยนเป็นเมตาบอริกแอซิด อุณหภูมิ 140 องศาเซลเซียส จะเปลี่ยนเป็นเตตราบอริกแอซิด และที่อุณหภูมิสูงๆ
จะเปลี่ยนเป็นโบรอนไตรออกไซด์ (boron trioxide, B2O3) กรดบอริก
(boric Acid) ใช้เป็นสารต้านจุลชีพ (antiseptic) เป็นวัตถุกันเสีย (preservative) และใช้เป็นตัวหยุดยั้งการเจริญของเชื้อรา
(mold) ในแป้งทาตัว ประกาศกระทรวงสาธารณสุขฉบับที่ 151
(พ.ศ. 2536) เรื่องวัตถุที่ห้ามใช้ในอาหารกรดบอริก
เป็นวัตถุที่ห้ามใช้ในอาหาร (prohibit substances) เป็นอันตรายในอาหาร
(food hazard) ประเภทอันตรายทางเคมี (chemical
hazard) ทั้งบอร์แรกซ์และกรดบอริกมีคุณสมบัติการดูดซึม การขับถ่าย
และพิษที่เกิดขึ้นคล้ายคลึงกัน บอริคแอซิ ด (H3BO3) : ช่วยในการเคลื่อนย้ายน้ำตาลไปยั
งส่วนต่างๆ ของพื ช ถ้ าขาดสารกลุ่มนี้ พืชจะโตผิดปกติ หรือหยุดการเจริ ญเติบโต Boric Acid (boracic
acid): White or colorless, smooth
crystals or powder, soluble in water, alcohol and glycerin. คุณประโยชน์:
เป็นสารเคมีที่ใช้ในอุสาหกรรมเซรามิก, ซิเมนต์, สารประกอบวัตถุกันเสียในอาหาร, เป็นสารสำหรับหนังรวมทั้งการตกแต่งและสารประกอบในการจัดทำหนังก่อนที่จะมีการฟอกหนัง,อัญมนีเทียม, อุตสาหกรรมสี สีเคลือบ, เคลือบกระดาษ, เครื่องสำอาง, สบุ่,ยา, สิ่งทอ
Boric
acid, also called hydrogen borate, boracic acid, orthoboric acid and acidum
boricum, is a weak acid of boron often used as an antiseptic, insecticide,
flame retardant, neutron absorber, or precursor to other chemical compounds. 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
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. As an antibacterial compound, 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 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.
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. It acts as a stomach poison affecting the insects'
metabolism, and the dry powder is abrasive to 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.
Lubrication
Colloidal
suspensions of nanoparticles of boric acid dissolved in petroleum or vegetable
oil can form a remarkable lubricant on ceramic or metal surfaces[19] 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.
Boric
acid is used to lubricate carrom and novuss boards, allowing for faster play.
Nuclear
power
Boric
acid is used in nuclear power plants as a neutron poison to slow down the rate
at which fission is occurring. Fission chain reactions are generally driven by
the amount of neutrons present (as products from previous fissions). Natural
boron is 20% boron-10 and about 80% boron-11. Boron-10 has a high cross-section
for absorption of low energy (thermal) neutrons. By adding more boric acid to
the reactor coolant which circulates through the reactor, the probability that
a neutron can survive to cause fission is reduced. Therefore, changes in boric
acid concentration effectively regulate the rate of fission taking place in the
reactor. This method is only used in pressurized water reactors (PWRs). Boron
is also dissolved into the spent fuel pools containing used uranium rods. 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.
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. 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 soldering operations.
Boric acid is used in the production of the glass in LCD flat panel displays.
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 H
2SO4. 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. The solution is used for fire
retarding agent of wood by impregnation. 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. Boric acid is added to borax for use as
welding flux by blacksmiths. Boric acid, in combination with silicone oil, is
used to manufacture Silly Putty. Boric acid, in combination with eighty other
chemicals, is used in Marcellus Shale hydraulic fracturing.
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.
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