Sodium tetraborate (borax) - Na2B4O7

Sodium tetraborate

(“borax”, “borax” (from Latin borax), sodium tetraborate) is an inorganic compound, sodium salt of boric acid with the chemical formula Na 2 B 4 O 7 {\displaystyle {\ce {Na2B4O7}}}, the most common and The boron compound used forms several crystalline hydrates and is widely used in industry.

Being in nature[ | ]

There are numerous minerals containing sodium tetraborate. These include:

• borax (borax, tinkal) - a mineral of the composition Na 2 B 4 O 7 ⋅ 10 H 2 O {\displaystyle {\ce {Na2B4O7.10H2O}}} - sodium tetraborate decahydrate;
• kernite - sodium tetraborate tetrahydrate - Na 2 B 4 O 7 ⋅ 4 H 2 O {\displaystyle {\ce {Na2B4O7.4H2O}}} ;
• numerous minerals of the borate class, which in addition to sodium and boron oxides contain other metals - calcium, magnesium, iron, etc.;
• Sodium tetraborate crystalline hydrates precipitate when some endorheic, seasonally dry salt lakes dry up, such as Lake Searles, located in the Mojave Desert in the United States, and some lakes in Turkey.

Tinkal

Tinkal, or “Borax” (sodium tetraborate decahydrate, Na2B4O7 10H2O) is a mineral of the monoclinic system, prismatic. “Tinkal” is a word of Sanskrit origin, which is synonymous with the more commonly used name for the mineral - “Borax” (from the Arabic “burak” - white). White color, glassy luster, hardness 2-2.5. Density 1.71. Cleavage is average in (100) and (110). It forms short-prismatic crystals, shaped like pyroxene crystals, as well as solid granular masses and veinlets in clayey rocks. A typical evaporite mineral. In air it collapses, losing water and becomes covered with a crust of tincalconite or kernite, or completely turns into them.

Chemical properties[ | ]

Solubility in water is 3.2 g / 100 ml (at 25 °C), 10.5 g / 100 ml (at 50 °C), in ethanol - 0.05 g / 100 g (at 25 °C), acetone - 0.006 g / 100 g (at 25 °C), insoluble in diethyl ether and glycerin. Reacts with methanol upon dissolution to form organoboron compounds[2].

Forms several crystalline hydrates with different water contents. These crystalline hydrates and anhydrous sodium tetraborate Na 2 B 4 O 7 {\displaystyle {\ce {Na2B4O7}}} are usually called “borax”. Examples of crystalline hydrates:

• pentahydrate (Na 2 B 4 O 7 ⋅ 5 H 2 O {\displaystyle {\ce {Na2B4O7.5H2O}}}), the so-called “jewelry borax”, is used in soldering jewelry;
• decahydrate ( Na 2 B 4 O 7 ⋅ 10 H 2 O {\displaystyle {\ce {Na2B4O7.10H2O}}} ).

However, the decahydrate Na 2 B 4 O 7 ⋅ 10 H 2 O {\displaystyle {\ce {Na2B4O7.10H2O}}} is most often called “brown”. This salt is transparent crystals with a molar mass of 381.43 g/mol, having good solubility in warm water [4]. When heated above 400 °C, it completely loses water of crystallization.

Since sodium tetraborate is a salt of a weak acid and a strong base, it hydrolyzes in water. An aqueous solution of sodium tetraborate has an alkaline reaction.

Reacts with strong acids, forming the corresponding salt and boric acid:

Na 2 B 4 O 7 ⋅ 10 H 2 O + 2 HCl ⟶ 4 H 3 BO 3 + 2 NaCl + 5 H 2 O {\displaystyle {\ce {Na2B4O7.10H2O + 2 HCl -> 4 H3BO3 + 2 NaCl + 5 H2O}}} .

Many metal salts of boric acid are insoluble in water and when their soluble salts react with sodium tetraborate in a solution, the resulting borates precipitate. This is the basis for the use of borax to “soften” water:

Ca ( aq ) 2 + + Na 2 B 4 O 7 ( aq ) ⟶ CaB 4 O 7 ( s ) + 2 Na ( aq ) + {\displaystyle {\ce {Ca^2+_{(aq)}\ + Na2B4O7_{(aq)}-> CaB4O7_{(s)}\ + 2 Na^+_{(aq)}}}}, Mg ( aq ) 2 + + Na 2 B 4 O 7 ( aq ) ⟶ MgB 4 O 7 ( s ) + 2 Na ( aq ) + {\displaystyle {\ce {Mg^{2}+_{(aq)}\ +Na2B4O7_{(}aq)->MgB4O7_{(s)}\ +2Na_{ (aq)}^{+}}}} .

When fused with the oxides of many transition metals, borax forms variously colored compounds - borates “borax pearls”. The color of the pearls can be used to judge the qualitative chemical composition of the sample.

The compound colors the burner flame green (a characteristic reaction to boron compounds)[4].

Flaws

• After use, a deposit of salts forms, which must be removed mechanically;
• It is necessary to choose storage areas that are free of moisture, since high humidity will cause the flux to deteriorate;
• To prepare the material for use, you need to spend time and choose the right proportion, which can lead to errors.

Varieties of Borax

There are two main varieties that relate to the appearance of the material. The first option is the solid form. Borax soldering flux is supplied in the form of a powder with fine solid fractions. Thanks to this, it is easy to lay it on the metal surface before soldering in the required quantity and it will not spread at the same time. This variety is supplied in a special box that protects the material hermetically from the penetration of moisture and other foreign factors. Fractions are white.

Soldering borax in powder form

The second type, which is more often used for lighter metals and their alloys, is diluted borax. In this case, you are offered the same material, but dissolved in liquid. Due to this, it can be used at lower soldering temperatures. Using this type is also easier, since small parts are simply dipped into the liquid, after which they can be soldered. This is used both in the jewelry industry and in other places where small items are worked. Contacts, wires and other types of equipment come into good contact with dissolved flux. Despite the fact that the principle of using borax for soldering in liquid form is somewhat different from the standard one, they have almost the same effect.

There are also varieties in the form of mixtures, when other fluxes are also used. This is necessary in cases where it is impossible to achieve the desired results using one substance. Proportions and composition depend on specific goals. Most often it is combined with boric acid.

Composition and physicochemical properties

The composition of borax for soldering includes sodium chloride and barium chloride, in some cases boric acid is added to it. It is not used in its pure form for all procedures, since this would require too high a melting point. Drill soldering powder is a high-temperature flux, so its main property is resistance to high temperatures. It is worth noting that the material perfectly retains its chemical properties even at a lower concentration than what is supplied. Thus, the flux solution has a fairly high level of dissolution of the oxides of all base metals for which it is used.

It can also dissolve fatty films and other unnecessary things that will interfere with the normal soldering of the material. Brown soldering protects against many types of defects that can occur in work.

Specifications

There are two main grades of the substance, which are defined according to GOST as grade A and grade B:

Soldering of metals is carried out by first removing traces of oxides from their surface. Fluxes are used for this. They should prevent oxidation when heated and encourage good flow of molten solder.

For soldering copper products, borax solder ideally meets all requirements. The substance has been known since the Middle Ages. It was mined in the lakes of India and Tibet, then transported to Europe, where it was used for processing fabrics and leather, and producing glass.

Borax is widely used for working with metals. When manufacturing or repairing metal products, borax soldering is carried out. First of all, the method is used for parts made of copper and brass. A special type of this flux is used when repairing jewelry.

Application[ | ]

Sodium tetraborate is used:

• as a raw material for the production of boric acid and various boron compounds[2];
• in the production of enamels, glazes, optical and colored glasses, various ceramics[2];
• when soldering and melting metals containing flux[2];
• when forging metals;
• in the paper and pharmaceutical industries;
• in the production of building materials as an antiseptic component for the production of cellulose insulation "Ecowool"
• as a disinfectant and preservative[2];
• for preparing buffer solutions;
• in analytical chemistry: as a standard substance for determining the concentration of acid solutions;
• for qualitative determination of metal oxides (by the color of pearls);

In 1977, global production of sodium tetraborate was 1.5 million tons[2].

Application of brass and copper powder

Practitioners often use flux that has been stored longer than expected. To solder with brass, the borax must be re-melted. The cooled powder should be placed in a jar with an airtight lid. Neglecting this procedure can ruin the work due to waste accumulated during storage.

At the beginning of soldering, the working area must be heated to a clearly visible red color . Heating should begin first at the edges, and then directly at the soldering site.

Then the heated area should be gradually sprinkled with flux, wait until it spreads in the form of a film along the edges of the part. At this point, the heated brass solder must be dipped into the molten borax so that it is covered with a hot flux film.

As experience shows, the soldering area is red in color, while the borax melt is colored bluish. You cannot keep solder in the flux for a very long time. Oxide residues may form.

Then you should warm up the work area again. The brass will take on an orange glowing appearance. You can proceed directly to soldering. If done correctly, the solder will fill all the gaps.

The soldering area will turn golden. When the process is completed, the hot zone should be sprinkled with borax powder and left to cool. Copper parts in a hot (200 ℃) state can be placed in a mixture containing equal parts acetone and water, or simply in water. It makes sense to immerse the cutters in hot sand.

A correctly made connection has a transparent film with a slight blue tint. There are no solder drops on it. If soldering is performed incorrectly, the seam becomes covered with a black porous crust.

The reason may be overheating of the working area, as a result of which slag is formed, or poor quality of borax-based flux. This is how brass and other copper-containing alloys are soldered.

Toxicity[ | ]

The substance is low toxic for warm-blooded animals, LD50 for rats is 2.66 g/kg. Dust can irritate mucous membranes and adversely affect the respiratory system.

There is evidence that the substance reduces fertility. According to European Union (EU) regulations, substances and mixtures imported into the EU containing borax must be labeled with the warnings “May cause harm to fertility” and “May cause harm to the unborn child” from July 2015[5].

It is also indicated that long-term, over 10-15 years, consumption of borax in the form of food additives can provoke cancer[6].

Mole

All substances are made up of atoms and molecules. In chemistry, it is important to accurately measure the mass of substances that react and are produced as a result. By definition, the mole is the SI unit of quantity of a substance. One mole contains exactly 6.02214076×10²³ elementary particles. This value is numerically equal to Avogadro's constant NA when expressed in units of mol⁻¹ and is called Avogadro's number. Amount of substance (symbol n

) of a system is a measure of the number of structural elements. A structural element can be an atom, molecule, ion, electron, or any particle or group of particles.

Avogadro's constant NA = 6.02214076×10²³ mol⁻¹. Avogadro's number is 6.02214076×10²³.

In other words, a mole is an amount of substance equal in mass to the sum of the atomic masses of atoms and molecules of the substance, multiplied by Avogadro’s number. The unit of quantity of a substance, the mole, is one of the seven basic SI units and is symbolized by the mole. Since the name of the unit and its symbol are the same, it should be noted that the symbol is not declined, unlike the name of the unit, which can be declined according to the usual rules of the Russian language. One mole of pure carbon-12 is equal to exactly 12 g.

Notes[ | ]

1. ↑ 12
   https://www.cdc.gov/niosh/npg/npgd0057.html
2. ↑ 12345678910
   Fedorov, 1992.
3. Franz v Bruchhausen, Siegfried Ebel, Eberhard Hackenthal, Ulrike Holzgrabe.
   Hagers Handbuch der Pharmazeutischen Praxis: Folgeband 5: Stoffe LZ. - Springer-Verlag, 2013. - 299 p. — ISBN 978-3-642-58388-9.
4. ↑ 123
   Ioffis, 1981.
5. Recommendation of the European Chemicals Agency of 1 July 2015 for the inclusion of substances in Annex XIV to REACH (List of Substances subject to Authorisation) Echa.europa.eu. Retrieved on July 6, 2015.
6. Watch Out For The Food We Consume (undefined)
   . Directorate of Consumer Protection, Jakarta, Indonesia (2006). Access date: February 10, 2009. Archived December 28, 2008.

Literature[ | ]

• Almedingen A. N.
  Bura, its falsification // Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg, 1890-1907.
• Herzenstein G. M.
  Bura, in medicine // Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg, 1890-1907.
• Sodium tetraborate // Photocinema technology: Encyclopedia / Ch. ed. E. A. Iofis. - M.: Soviet Encyclopedia, 1981. - P. 204. - 447 p.
• Levinson-Lessing F. Yu.
  Bura, being in nature // Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg, 1890-1907.
• Fedorov P.I.
  Sodium borates // Chemical Encyclopedia: in 5 volumes / Ch. ed. I. L. Knunyants. - M.: Great Russian Encyclopedia, 1992. - T. 3: Copper-Polymer. — P. 180-181. — 639 p. — 48,000 copies. — ISBN 5-85270-039-8.