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Element Boron, B, Metalloid

About Boron

Among the non-metallic elements, boron occupies a rather isolated position, since the elements most nearly related to it must be sought for among the metals, namely, among the earth metals. On account of the properties of the free element and of those of the compounds, it is, however, not expedient to give boron a place among the metals. It may best be classed along with silicon, from which it differs, however, in its typical compounds having a different composition.

Boron is a solid substance which is capable of existing in several different forms, one amorphous and at least one crystalline. Amorphous boron is obtained by passing the vapours of the chlorine compound over heated sodium, or, quite similarly to silicon, by igniting the oxygen compound with magnesium. After the removal of the admixtures, it forms a black powder of the density 2.5, which in many respects behaves similarly to charcoal, but is more easily oxidised; this occurs more especially by means of strongly oxidising solutions even at the room temperature.

By the fusion of boron trioxide (vide infra) with aluminium, crystallised boron is obtained, which, on account of its hardness, has been called " adamantine boron." It is not obtained quite pure in this way, but contains aluminium derived from its preparation. Since this metal is the element most nearly related to boron, the product is not to be looked upon as a compound, but as a mixture (possibly with a diamond-like form of aluminium isomorphous with boron, and not known by itself).

Boron containing carbon, and obtained from the two elements at a very high temperature, is of a similar character, and also possesses an adamantine hardness. This also ought most probably to be regarded as a solid solution, and not as a chemical compound.

The two forms probably stand to one another in the relation that amorphous boron is unstable with respect to the crystalline, as white phosphorus is with respect to red. In this case, however, the velocity of transformation at temperatures below a red-heat is apparently immeasurably small.

The combining weight of boron is B = 11.

Boron History

Compounds of boron (Arabic Buraq from Persian Burah from Turkish Bor) have been known of for thousands of years. Burah was used as flux agent for gold and silver soldering as well as to fluidify glass and glaze fluidity in glassmaking. In the beginning of 17th century a substance was disengaged from burah which was called boronic acid. In 1808, Joseph Louis Gay-Lussac, and Louis Jacques Thenard, and shown up 9 days later Sir Humphry Davy announced about the discovery of a new element. It was separated by the reduction of boric acid baking it with metal potassium which was discovered by Humphry Davy shortly before. After separating the element the French chemists called the new element le bore and Davy called it boron (from Latin Boron), the name which is used in English now. In the beginning of 19th century Russian chemists gave various names to it, however nowadays it is called "bor".

Boron Occurrence

According to A.P. Vinogradov the boron clarke in the Earth's crust is 1.2x10-3%, mostly in clays and clay-slates (1.1x10-2%), in phosphorites (1.3x10-2%), ferro-manganese-nodules (1.1x10-2%), kimberlites (1.9x10-2%) as well as in underground water of volcanically active areas, petroleum water, gypsum-anhydrite salt-bearing masses and mud volcanoes. Approximately 160 boron minerals are known at the present time; most of them are sodium, potassium, magnesium and calcium borates, also well-known borosilicates, boroalumosilicates and other mineral groups.

Boron may be deemed as a nominally essential microelement, because it is always present in human body even though in negligibly small amounts. In fact the biological significancy of boron is not fully understood. Some recent findings indicate that boron participates in the metabolism of calcium, magnesium and phosphorus, and the deficiency of boron and magnesium caused detrimental changes in the bones. However the daily requirement ofboron for human beings is not determined yet. Anyway the fact that there is no boron deficiency in human body is certainly comforting.


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