ホウ砂

外観

無色澄明の液体

存在

日本では産出は知られていないが、インド・カシミールやチベット地方で塩湖堆積(たいせき)物として産し、厖大(ぼうだい)な鉱床を形成する。また温泉に関係した堆積物や乾燥気候地域の土壌の表面にいわゆる表成鉱物として産する。共存鉱物は岩塩、石膏(せっこう)、方解石、ボウ硝（テナール石）などホウ酸塩鉱物を欠くものと、カーン石、ウレクサイトulexite（化学式NaCa[B5O6(OH)6]・5H2O）などホウ酸塩鉱物を伴うものとがある。同定は可溶性、完全な一方向の劈開(へきかい)、加熱による膨張と白色粉末化、炎で加熱すると融解することなどであるが、ティンカルコナイトも同様の性質を示すので、形態が出ていないと識別はできない。なおティンカルコナイトは天然のものでは自形はきわめて微細な擬立方体で、肉眼で識別可能な大きさのものは報告されていない。英名はアラビア語の白を意味するbauraqに由来するとされる。

定義

本品は、ホウ酸のナトリウム塩であり、次の化学式で表される。

溶解性

水にやや溶けやすく、エタノールにほとんど溶けない。

解説

ナトリウム含有ホウ酸塩鉱物．理想的な組成は四ホウ酸ナトリウムNaB4O7･10H2Oである．単斜晶系．白色の粉末．硬度2～2.5．密度1.67～1.72 g cm－3．水に可溶で強アルカリ性を示す．水100 g に対する溶解度は1.3 g(0 ℃)，1.6 g(10 ℃)，201 g(100 ℃)．350～400 ℃ に加熱すると無水物となり，これをさらに878 ℃ まで加熱すると融解して無色透明なガラスとなる．融解したものはよく金属酸化物を溶かし，ほう砂球反応に用いられる．四水和物は天然にカーン石として産出する．ホウ素，ホウ酸塩の主要原料である．金属ろう付けの融剤，ガラス，うわぐすり，ほうろう，食品貯蔵用などの原料として用いられる．
森北出版「化学辞典（第2版）

解説

ホウ砂は，ホウ酸塩鉱物の一種。硼砂とも表記される。古くから東洋ではティンカルtincalとよばれていた。鉱物学的にはホウ砂はNa2[B4O5(OH)4]・8H2Oで、英名boraxであるが、ティンカルという名前はNa2[B4O5(OH)4]・3H2Oのティンカルコナイトtincalconiteに残されている。加熱すると無水物になり、731℃で融解する。また種々の金属を溶かし込んで特有の色を与える。これはいわゆるホウ砂球反応で、重金属の定性分析に応用される。報告されている自形は八角形の断面をもつ短柱状で、1個の底面と2個の錐面(すいめん)をもつ。頂部の面の発達がなければ、形状的には普通輝石にそっくりである。無色の軟らかい結晶あるいは粒状物質。風解性。比重 1.73。 320℃で無水物に変り，878℃で融解して無色透明のガラス状となり，金属酸化物を融解する。水に溶けるが，アルコールに不溶。水溶液は加水分解してアルカリ性を呈する。リン塩球反応用試薬，ガラス，釉，ほうろう原料，防腐剤，鋳造用潤滑剤などとして使用される。

用途

ほうろう鉄器、ガラス、金属ろう付

用途

汎用試薬、調製液原料、ほう酸緩衝液調製原料、防腐剤、写真材料。

用途

汎用試薬、緩衝液の調製原料、調製液の原料。

用途

ほうろう鉄器?ガラス?陶磁器?顔料原料、コンデンサー用電極材

用途

pH標準液(ほう塩標準液)及び緩衝液の調製原料。

化粧品の成分用途

pH調整剤

効能

眼科用消毒薬, アルカリ化剤

主な用途／役割

デンプン系接着剤の粘度調整に使用される。

商品名

ホウ砂 (健栄製薬); ホウ砂 (司生堂製薬); ホウ砂 (小堺製薬)

使用上の注意

空気中に放置すると風化して白い粉末となる。

化学的特性

White cryst. powder

物理的性質

White monoclinic crystal; density 1.73 g/cm³; decomposes at 75°C; soluble in water; the vapor pressure of the pure compound 1.6 torr at 20°C and that of a saturated solution 130 torr at 58°C; the pH of a 1% aqueous solution 9.24 (the pH is nearly independent of concentration); readily dissolves in alcohols.

天然物の起源

Borax decahydrate occurs in nature as mineral, borax (tincal). It is one of the most common sodium borate ores. The compound has several industrial applications. The refined material is mostly used in household cleaning products. It is used to make pyrex and other borosilicate glasses. Borax is added to fertilizers in small quantities as a source of boron, as a trace nutrient for plants. High purity grade borax is used in cosmetics, toilet products and electrolytic capacitors. It also is used in fire retardants, adhesives and herbicides.

使用

Sodium Tetraborate Decahydrate is used as a buffer in antigetn-retrieval procedure for bromodeoxyuridine immunolabeling with concurrent labeling of nuclear DNA and antigens damaged by hydrochloric acid pretreatment.

調製方法

Sodium borate can be prepared from minerals such as borosodium calcite, pandermite, or tinkal; these are natural sodium or calcium borates. Treatment of the mineral with sodium carbonate and sodium hydrogencarbonate yields the sodium borate decahydrate. In the USA, brine from salt lakes is also an important source of sodium borate.

危険性

Toxic by inhalation.

健康ハザード

Borates are irritants of the eyes, nose, and throat; at high concentrations ingestion of the compounds can result in gastrointestinal irritation, kidney injury, and even death from central nervous system depression or cardiovascular collapse.

応用例（製薬）

Sodium borate is used in pharmaceutical applications similarly to boric acid (see Boric Acid). It has been used externally as a mild astringent and as an emulsifying agent in creams. It has also been used in lozenges, mouthwashes, otic preparations (0.3% w/v), and ophthalmic solutions (0.03–1.0% w/v). Sodium borate has additionally been investigated in the prevention of crystal formation in freeze-dried solutions.
Preparations of sodium borate in honey have historically been used as paints for the throat, tongue, and mouth, but such use is now inadvisable because of concerns about toxicity in such applications. Sodium borate is also used in cosmetics such as moisturizers, deodorants, and shampoos.

农业用途

Solubor is a type of borate containing 20.3% boron. It is chemically a polyborate, similar to borax, and is represented as Na₂B₂O₇?5H₂O +Na₂B₁₀O₁₆?10H₂O. is a finely-ground, white product specially designed for foliar, liquid or dust applications, to correct boron deficiency.

安全性プロファイル

Experimental poison by subcutaneous route. Moderately toxic to humans by ingestion. Moderately toxic experimentally by ingestion, intravenous, and intraperitoneal routes. Experimental reproductive effects. Mutation data reported. Ingestion of 5-10 g of borax by children can cause severe vomiting, diarrhea, shock, death. Incompatible with acids, metallic salts. When heated to decomposition it emits toxic fumes of Na2O, boron. See also BORON COMPOUNDS. Used in ant poisons, for fly control around refuse and manure piles, as a larvicide, in manufacture of glazes, enamels, cleaning compounds, and in soldering metals.

安全性

Sodium borate has weak bacteriostatic and astringent properties. Historically, sodium borate has been used as a disinfectant in skin lotions and eye-, nose-, and mouthwashes. However, boric acid is easily absorbed via mucous membranes and damaged skin, and severe toxicity has been observed, especially in babies and children. Consequently, the use of sodium borate as a disinfectant is now considered somewhat obsolete and careful use is recommended. The toxic effects of sodium borate include vomiting, diarrhea, erythema, CNS depression, and kidney damage. The lethal oral intake is approximately 20 g in adults and 5 g in children.
LD50 (guinea pig, oral): 5.33 g/kg
LD50 (mouse, IP): 2.711 g/kg
LD50 (mouse, IV): 1.320 g/kg
LD50 (mouse, oral): 2.0 g/kg
LD50 (rat, oral): 2.66 g/kg

職業ばく露

Borax is used as a soldering flux, preservative against wood fungus; and as an antiseptic. Used in ant poisons, for fly control around refuse and manure piles, as a larvicide. It is used in the manufacture of enamels and glazes, fiberglass insulation; sodium perborate bleach; in tanning, cleaning compounds; for fireproofing fabrics and wood; and in artificial aging of wood.

発がん性

Sodium borate tested negatively in the Ames bioassay but was found to be cytotoxic to cultured human fibroblasts.

貯蔵

Sodium borate should be stored in a well-closed container in a cool, dry, place.

輸送方法

UN3077 Environmentally hazardous substances, solid, n.o.s., Hazard class: 9; Labels: 9—Miscellaneous hazardous material, Technical Name Required.

純化方法

Crystallise the borate from water (3.3mL/g), keeping below 55o to avoid formation of the pentahydrate. Filter it off at the pump, wash it with water and equilibrate it for several days in a desiccator containing an aqueous solution saturated with respect to sucrose and NaCl. Borax can be prepared more quickly (but its water content is somewhat variable) by washing the recrystallised material at the pump with water, followed by 95% EtOH, then Et2O, and dried in air at room temperature for 12-18hours on a clock glass. [Becher in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 794-795 1963.]

不和合性

Dissolves in water forming a basic solution. Boron dust may form explosive mixture with air. Contact with strong oxidizers may be violent. Boron is incompatible with ammonia, bromine tetrafluoride, cesium carbide, chlorine, fluorine, interhalogens, iodic acid, lead dioxide, nitric acid, nitric oxide, nitrosyl fluoride, nitrous oxide, potassium nitrite, rubidium carbide, silver fluoride.

廃棄物の処理

Borax, dehydrated: The material is diluted to the recommended provisional limit (0.10 mg/L) in water. The pH is adjusted to between 6.5 and 9.1 and then the material can be discharged into sewers or natural streams.

規制状況(Regulatory Status)

Accepted for use as a food additive in Europe. Included in the FDA Inactive Ingredients Database (otic preparations; ophthalmic solutions and suspensions). Included in nonparenteral medicines licensed in the UK, Italy, France, Germany, and Japan. Included in the Canadian List of Acceptable Non-medicinal Ingredients.