Borax

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.

When borax is added to a flame, it produces a yellow green color. 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/bwrk ("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 būrah (بوره "borax"). The word borax is found in 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.

The word tincal /ˈtɪŋkəl/ "tinkle", or tincar /ˈtɪŋkər/ "tinker", refers to crude borax, before it is 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.

Household products

Borax is used in various household laundry and cleaning products, 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.

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:

Ca²⁺ _(aq) + Na₂B₄O_{7 (aq)} → CaB₄O_{7 (s)}↓ + 2 Na⁺ _(aq)Mg²⁺ _(aq) + Na₂B₄O_{7 (aq)} → MgB₄O_{7 (s)}↓ + 2 Na⁺ _(aq)

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. Borax is often used as a flux for forge welding.

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.

Flubber

A rubbery polymer sometimes called Slime, Flubber, gluep or glurch (or erroneously called Silly Putty, which is based on silicone polymers), 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.

Food additive

Borax, given the E number E285, is used as a food additive in some countries, but is banned in some countries, like the U.S., and Thailand. As a consequence, certain foods, such as caviar, produced for sale in the US contain higher levels of salt to assist preservation. 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. 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.

Other uses

Ingredient in enamel glazes

Component of glass, pottery, and ceramics

Used as an additive in ceramic slips and glazes to improve fit on wet, greenware, and bisque

Fire retardant

Anti-fungal compound for cellulose insulation

Moth proofing 10% solution for wool

Pulverized for the prevention of stubborn pests (e.g. German cockroaches) in closets, pipe and cable inlets, wall panelling gaps, and inaccessible locations where ordinary pesticides are undesirable

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

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 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.

Preservative in taxidermy

To clean the brain cavity of a skull for mounting

To color fires with a green tint

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

Used by blacksmiths in forge welding

Used as a woodworm treatment (diluted in water)

Used in the treatment or prevention of wood rot in classic wood boats

Toxicity

Borax, sodium tetraborate decahydrate, according to one study, is not acutely toxic. Its LD₅₀ (median lethal dose) score is tested at 2.66 g/kg in rats, meaning that a significant dose of the chemical is needed to cause severe symptoms or death. The lethal dose is not necessarily the same for humans. On pesticide information websites it is listed as a non-lethal compound and of no hazardous concerns.

First registered in 1946 by the EPA as an insecticide with various restrictions, all restrictions were removed in February 1986 due to the low toxicity of borax, as published in two EPA documents relating to boric acid and borax.

Although it cited inconclusive data, a re-evaluation in 2006 by the EPA still found that "There were no signs of toxicity observed during the study and no evidence of cytotoxicity to the target organ." In the reevaluation, a study of toxicity due to overexposure was checked and the findings were that "The residential handler inhalation risks due to boric acid and its sodium salts as active ingredients are not a risk concern and do not exceed the level of concern..." but that there could be some risk of irritation to children inhaling it if used as a powder for cleaning rugs.

Sodium tetraborate decahydrate has no known hazard issues.

Conditions defined as "over-exposure" to borax dust can cause respiratory irritation, while no skin irritation is known to exist due to borax. 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."

A draft risk assessment released by Health Canada in July 2016 has found that overexposure to boric acid has the potential to cause developmental and reproductive health effects. Since people are already exposed to boric acid naturally through their diets and water, Health Canada advised that exposure from other sources should be reduced as much as possible, especially for children and pregnant women. The concern is not with any one product, but rather multiple exposures from a variety of sources. With this in mind, the department also announced that registrations for certain pesticides that contain boric acid, which are commonly used in homes, will have their registrations cancelled and be phased out of the marketplace. As well, new, more protective label directions are being introduced for other boric acid pesticides that continue to be registered in Canada (for example, enclosed bait stations and spot treatments using gel formulations).

Possible carcinogen

The Indonesian Directorate of Consumer Protection warns of the risk of liver cancer with high consumption over a period of 5–10 years.

Risk to fertility and pregnancy

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". It was proposed for addition to REACH Annex XIV by the ECHA on 1 July 2015. If this recommendation is approved, all imports and uses of borax in the EU will have to be authorized by the ECHA. Review of the boron toxicity (as boric acid and borates) published 2012 in Journal of Toxicology and Environmental Health concluded: "It clearly appears that human B [boron] exposures, even in the highest exposed cohorts, are too low to reach the blood (and target tissue) concentrations that would be required to exert adverse effects on reproductive functions."