Borax
From Wikipedia, the free encyclopedia
Borax, also known as sodium borate, sodium tetraborate,
or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid.
Powdered borax is white, consisting of soft colorless crystals that dissolve
easily in water.
Borax has a wide variety of uses. It
is a component of many detergents, cosmetics, and enamel glazes.
It is also used to make buffer solutions
in biochemistry, as a fire retardant,
as an anti-fungal compound for fiberglass,
as a flux in metallurgy, neutron-capture shields for radioactive sources, a
texturing agent in cooking, and as a precursor for other boron compounds.
In artisanal
gold mining, the borax method is sometimes used as a substitute for toxic
mercury in the gold extraction process. Borax was reportedly used by gold
miners in parts of the Philippines in the 1900s.[2]
The term borax is used for a
number of closely related minerals or chemical compounds that differ in their crystal
water content, but usually refers to the decahydrate.
Commercially sold borax is usually partially dehydrated.
The word borax
is from Arabic būraq (بورق), meaning "white"; which is from Middle Persian
bwrk, which might have meant potassium nitrate or another fluxing agent, now
known as būrah (بوره). Another name for borax is tincal, from Sanskrit.[3]
Borax was first discovered in dry
lake beds in Tibet and was imported via the Silk Road
to Arabia.[3]
Borax first came into common use in the late 19th century when Francis Marion Smith's Pacific
Coast Borax Company began to market and popularize a
large variety of applications under the 20 Mule Team Borax trademark, named for the method by which borax was originally hauled
out of the California and Nevada deserts in large enough quantities to make it
cheap and commonly available.[4][5]
Contents
Chemistry
The term borax is often used
for a number of closely related minerals or chemical compounds that differ in
their crystal
water content:
- Anhydrous borax (Na2B4O7)
- Borax pentahydrate (Na2B4O7·5H2O)
- Borax decahydrate (Na2B4O7·10H2O)
Borax is generally described as Na2B4O7·10H2O.
However, it is better formulated as Na2[B4O5(OH)4]·8H2O,
since borax contains the [B4O5(OH)4]2−
ion. In this structure, there are two four-coordinate boron atoms (two BO4
tetrahedra) and two three-coordinate boron atoms (two BO3
triangles).
Borax is also easily converted to boric acid
and other borates, which
have many applications. Its reaction with hydrochloric acid to form boric acid
is:
Na2B4O7·10H2O +
2 HCl → 4 H3BO3 + 2 NaCl + 5 H2O
The "decahydrate" is
sufficiently stable to find use as a primary standard
for acid base titrimetry.[6]
When borax is added to a flame, it
produces a yellow green color.[7]
Borax is not used for this purpose in fireworks due to the overwhelming yellow
color of sodium. Boric acid is used to color methanol flames a transparent
green.
Etymology
The English word borax is
Latinized: The Middle English form was boras, from Old French
boras, bourras. That may have been from medieval Latin baurach
(another English spelling), borac(-/um/em), borax, or maybe directly
from the Arabic, along with Spanish borrax (> borraj) and
Italian borrace, in the 9th century. The Arabic was (is) بورق bauraq/būraq
"natron",
a word also used for borax. Traditional Arabic dictionaries say that it derives
from the verb "to glisten", which is also written بورق 〈bwrq〉, but it seems to actually derive from the Persian بوره būrah
"borax".[8]
The word tincal /ˈtɪŋkəl/ "tinkle", or tincar
/ˈtɪŋkər/ "tinker", refers to crude
borax, before it's purified, as mined from lake deposits in Tibet, Persia, and
other parts of Asia. The word was adopted in the 17th century from Malay tingkal
and from Urdu/Persian/Arabic تنکار tinkār/tankār; thus the two forms in
English. These all appear to be related to the Sanskrit टांकण ṭānkaṇa.[9]
Natural
sources
Borax occurs naturally in evaporite
deposits produced by the repeated evaporation of seasonal lakes.
The most commercially important deposits are found in Turkey; Boron, California;
and Searles Lake, California. Also, borax has been found at many other locations in the Southwestern
United States, the Atacama desert
in Chile, newly
discovered deposits in Bolivia, and in Tibet and Romania. Borax can also be produced synthetically from other boron
compounds. Naturally occurring Borax, (known by the trade name Rasorite – 46 in
USA and many other countries) is refined by a process of recrystallization.[10]
Uses
Household
products
Borax is used in various household
laundry and cleaning products,[11]
including the "20 Mule Team Borax" laundry booster and "Boraxo" powdered
hand soap. Despite its name, "Borateem" laundry bleach no longer
contains borax or other boron compounds. Borax is also present in some tooth bleaching
formulas.[12]
It is also an active ingredient in indoor and outdoor ant baits and killers.
pH
buffer
Sodium borate is used in biochemical
and chemical
laboratories to make buffers, e.g. for
gel electrophoresis of DNA, such as TBE or the
newer SB buffer
or BBS (borate buffered saline) in coating procedures. Borate buffers (usually at pH 8)
are also used as preferential equilibration solution in dimethyl pimelimidate (DMP) based crosslinking reactions.
Co-complexing
agent
Borax as a source of borate has been used to take advantage of the co-complexing
ability of borate with other agents in water to form complex ions with various
substances. Borate and a suitable polymer bed are
used to chromatograph non-glycosylated hemoglobin
differentially from glycosylated hemoglobin (chiefly HbA1c), which is an indicator of long term hyperglycemia
in diabetes mellitus.
Water-softening
agent
Borax alone does not have a high
affinity for the hardness cations, although it has been used for that
purpose. Its chemical equation for water-softening is given below:
The sodium ions introduced do not make water ‘hard’. This method is
suitable for removing both temporary and permanent types of hardness.
Flux
A mixture of borax and ammonium chloride
is used as a flux when welding iron and steel. It lowers the melting point of the unwanted iron oxide
(scale), allowing it to run off. Borax is also used mixed with water as
a flux when soldering jewelry metals such as gold or silver. It allows the molten solder to flow evenly over the joint in question. Borax is also a
good flux for "pre-tinning" tungsten with zinc
– making the tungsten soft-solderable.[13]
Small-scale
gold mining
Borax is replacing mercury as the
preferred method for extracting gold in small-scale mining facilities. The
method is called the borax method and is used in the Philippines.[14]
Flubber
A rubbery polymer sometimes called Slime,
Flubber, gluep or glurch (or erroneously called Silly Putty
which is based on silicone polymers, instead), can be made by cross linking
polyvinyl alcohol with borax. Making flubber from polyvinyl acetate
based glues, such as Elmer's Glue, and borax is a common elementary-science demonstration.[15][16]
Food
additive
Borax, given the E number E285,
is used as a food additive in some countries, but is banned in the US. As a
consequence, certain foods, such as caviar, produced for sale in the US contain higher levels of salt to assist preservation.[17]
Its use as a cooking ingredient is to add a firm rubbery texture to the food,
or as a preservative. In oriental cooking it is mostly used for its texturing
properties. In Asia, Borax (Chinese: 硼砂; pinyin: péng shā) or (Chinese: 月石; pinyin: yuè shí) was found to have been added to some
Chinese foods like hand-pulled noodles lamian
and some rice noodles like Shahe fen,
Kway Teow,
and Chee Cheong Fun recipes.[18]
In Indonesia
it is a common, but forbidden, additive to such foods as noodles, bakso (meatballs), and steamed rice. The country's Directorate of
Consumer Protection warns of the risk of liver cancer
with high consumption over a period of 5–10 years.[19]
Other
uses
- Ingredient in enamel
glazes
- Component of glass,
pottery,
and ceramics
- Borax can be used as an additive in ceramic slips and glazes
to improve fit on wet, greenware, and bisque.
- Fire retardant
- Anti-fungal
compound for fiberglass and cellulose
insulation
- Moth proofing 10% solution for wool[20]
- Pulvered for the prevention of stubborn pests (e.g. German cockroaches) intrusion in domestic deep closets, pipe and cable
inlets, wall panelling gaps, behind furniture and any hard to reach places
where bugs
would run through or gather but the ordinary pesticides
could emit toxic gases and would require replenishing
- Anti-fungal foot soak
- Precursor for sodium perborate monohydrate that is used in detergents,
as well as for boric acid and other borates
- Tackifier
ingredient in casein, starch and dextrin
based adhesives
- Precursor for boric acid,
a tackifier ingredient in polyvinyl acetate, polyvinyl alcohol based adhesives
- Fluoride
detoxification
- Treatment for thrush
in horses'
hooves
- Used to make indelible ink for dip pens
by dissolving shellac into heated borax
- Curing agent for snake
skins
- Curing agent for salmon
eggs, for use in sport fishing for salmon
- Swimming pool buffering agent
to control the pH
- Neutron absorber, used in nuclear
reactors and spent fuel pools to
control reactivity and to shut down a nuclear chain reaction
- As a micronutrient
fertilizer
to correct boron-deficient soils.[21]
- To clean the brain cavity of a skull
for mounting
- To color fires with a green tint[22]
- Was traditionally used to coat dry-cured meats such as
hams to protect them from becoming fly-blown during further storage.
- Is found in some commercial vitamin supplements
- For stopping car radiator
and engine block leaks[23]
- Used by the modern blacksmith
in the process of forge welding.
(Different from fabrication gas or electric style welding.)
Toxicity
Borax, sodium tetraborate
decahydrate, according to one study, is not acutely toxic.[24]
Sodium tetraborate decahydrate was once registered as an insecticide for a
brief period; however, the product was issued a "Danger" signal word
by the EPA. Registration was allowed to lapse after the initial one year
registration due to the fact the product could not be legally sold over the
counter as an insecticide due to the dangers the product posed to the general
public. Danger is the highest level signal word issued by the EPA. Its LD50 (median lethal dose) score is tested at 2.66 g/kg in rats:[25]
a significant dose of the chemical is needed to cause severe symptoms or death.
The lethal dose is not necessarily the same for humans.
Sufficient exposure to borax dust
can cause respiratory and skin irritation. Ingestion may cause gastrointestinal
distress including nausea, persistent vomiting, abdominal pain, and diarrhea. Effects
on the vascular system and brain include
headaches and lethargy, but are less frequent. "In severe poisonings, a
beefy red skin rash affecting palms, soles, buttocks and scrotum has been
described. With severe poisoning, erythematous
and exfoliative rash, unconsciousness, respiratory depression, and renal
failure."[26]
Borax was added to the Substance
of Very High Concern (SVHC) candidate
list on 16 December 2010. The SVHC candidate list is part of the EU Regulations on the Registration, Evaluation, Authorisation and Restriction of
Chemicals 2006 (REACH), and the addition was
based on the revised classification of Borax as toxic for reproduction
category 1B under the CLP Regulations.
Substances and mixtures imported into the EU which contain Borax are now
required to be labelled with the warnings "May damage fertility" and
"May damage the unborn child".[27]
No comments:
Post a Comment