Boron

Boron

Boron is a chemical element with chemical symbol B and atomic number 5. Because boron is produced entirely by cosmic ray spallation and not by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. Boron is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals. These are mined industrially as evaporites, such as borax and kernite.

Chemically uncombined boron, which is classed as a metalloid, is not found naturally on Earth. Industrially, very pure boron is produced with difficulty, as boron tends to form refractory materials containing small amounts of carbon or other elements. Several allotropes of boron exist: amorphous boron is a brown powder and crystalline boron is black, extremely hard (about 9.5 on the Mohs scale), and a poor conductor at room temperature. Elemental boron is used as a dopant in the semiconductor industry.
The major industrial-scale uses of boron compounds are in sodium perborate bleaches, and the borax component of fiberglass insulation. Boron polymers and ceramics play specialized roles as high-strength lightweight structural and refractory materials. Boron compounds are used in silica-based glasses and ceramics to give them resistance to thermal shock. Boron-containing reagents are used for as intermediates in the synthesis of organic fine chemicals. A few boron-containing organic pharmaceuticals are used, or are in study. Natural boron is composed of two stable isotopes, one of which (boron-10) has a number of uses as a neutron-capturing agent.

In biology, borates have low toxicity in mammals (similar to table salt), but are more toxic to arthropods and are used as insecticides. Boric acid is mildly antimicrobial, and a natural boron-containing organic antibiotic is known. Boron is essential to life. Small amounts of boron compounds play a strengthening role in the cell walls of all plants, making boron necessary in soils. Experiments indicate a role for boron as an ultratrace element in animals, but its role in animal physiology is unknown.

Symbol		B
Atomic Number		5
Atomic Weight		10.811
Oxidation States		+3
Electronegativity, Pauling		2.04
State at RT		Solid, Metalloid
Melting Point, K		2573
Boiling Point, K		3931

Discovery of Boron


Boron compounds such as borax (sodium tetraborate, Na2B4O7·10H2O) have been known and used by ancient cultures for thousands of years. Borax’s name comes from the Arabic buraq, meaning “white.”

Boron was first partially isolated in 1808 by French chemists Joseph L. Gay-Lussac and L. J. Thénard and independently by Sir Humphry Davy in London. Gay-Lussac & Thénard reacted boric acid with magnesium or sodium to yield boron, a gray solid. They believed it shared characteristics with sulfur and phosphorus and named it bore.

Davy first tried to produce boron by electrolysis of boric acid, but was not satisfied with the results.
He enjoyed greater success reacting boric acid with potassium in a hydrogen atmosphere.
The result was a powdery substance.

Davy commented the substance was, “of the darkest shades of olive. It is opake, very friable, and its powder does not scratch glass.” After carrying out a number of chemical reactions to verify the uniqueness of the substance, Davy wrote, “there is strong reason to consider the boracic basis as metallic in nature, and I venture to propose for it the name of boracium.”

Neither party had, in fact, produced pure boron. Their samples were only about 60% pure.

In 1909, American chemist Ezekiel Weintraub was able to produce 99% pure boron, by reducing boron halides with hydrogen.

Almost a century later, in 2004, Jiuhua Chen and Vladimir L. Solozhenko produced a new form of boron, but were uncertain of its structure.

In 2009, a team led by Artem Oganov was able to demonstrate the new form of boron contains two structures, B12 icosohedra and B2 pairs. Gamma-boron, as it has been called, is almost as hard as diamond and more heat-resistant than diamond.

Talking about boron’s part metal, part non-metal properties, Oganov said, “Boron is a truly schizophrenic element. It’s an element of complete frustration. It doesn’t know what it wants to do. The outcome is something horribly complicated.


Interesting Facts about Boron

• Boron is a tough element – very hard, and very resistant to heat. In its crystalline form it is the second hardest of all the elements on the mohs scale – only carbon (diamond) is harder. Only 11 elements have higher melting points than boron: these are C, W, Re, Os, Ta, Mo, Nb, Ir, Ru, Hf, and Tc. (As a challenge, how many of these elements can you name without looking them up?)
• Boron is an essential nutrient for all green plants.
• Boron in its crystalline form is very unreactive. Amorphous boron is reactive.
• Unusually, the universe’s atoms of boron were not made by nuclear fusion within stars and were not made in the big bang. They were made by nuclear fusion in cosmic-ray collisions. Most of the universe’s boron was made in this way before the formation of our solar system.
• Boron is an indispensable element in NIB magnets (Neodymium – Iron – Boron). NIB magnets are very powerful magnets invented in the early 1980s. They are used in computers, cell phones, medical equipment, toys, motors, wind turbines and audio systems.
• Boron is used to control nuclear reactions. It is an excellent neutron absorber. Alloyed with steel or reacted with carbon, titanium or zirconium, it is used in control rods for nuclear reactors.

Appearance and Characteristics

Harmful effects:

Elemental boron is not known to be toxic.

Characteristics:

• Boron is a metalloid, intermediate between metals and non-metals. It exists in many polymorphs (different crystal lattice structures), some more metallic than others. Metallic boron is extremely hard and has a very high melting point.
• Boron does not generally make ionic bonds, it forms stable covalent bonds.
• Boron can transmit portions of infrared light.
• Boron is a poor room temperature conductor of electricity but its conductivity improves markedly at higher temperatures.

Uses of Boron

• Boron is used to dope silicon and germanium semiconductors, modifying their electrical properties.
• Boron oxide (B2O3) is used in glassmaking and ceramics.
• Borax (Na2B4O7.10H2O) is used in making fiberglass, as a cleansing fluid, a water softener, insecticide, herbicide and disinfectant.
• Boric acid (H3BO3) is used as a mild antiseptic and as a flame retardant.
• Boron Nitride’s hardness is second only to diamond, but it has better thermal and chemical stability, hence boron nitride ceramics are used in high-temperature equipment.
• Boron nitride nanotubes can have a similar structure to carbon nanotubes. BN nanotubes are more thermally and chemically stable than carbon nanotubes and, unlike carbon nanotubes, boron nitride nanotubes are electrical insulators.
• Boron carbide (B4C) is used in tank armor and bullet proof vests.