Several allotropes of boron exist; amorphous boron is a brown powder, though crystalline boron is black, extremely hard (9.3 on Mohs' scale), and a weak conductor at room temperature. Elemental boron is used as a dopant in the semiconductor industry, while boron compounds play important roles as light structural materials, insecticides and preservatives, and reagents for chemical synthesis.
Boron is an essential plant nutrient, although high soil concentrations of boron may also be toxic to plants. As an ultratrace element, boron is necessary for the optimal health of rats and presumably other mammals, though its physiological role in animals is poorly understood.
Brown amorphous boron is a product of certain chemical reactions. It contains boron icosahedra that are randomly bonded to each other without long range order. Crystalline boron is a very hard, black material with a high melting point. It exists in four major polymorphs: α, ß, γ and T. The tetragonal (T) boron phase contains 192 atoms per unit cell and has density 2.46 g/cm3. The γ-phase can be described as a NaCl-type arrangement of two types of clusters, B12 icosahedra and B2 pairs. It can be produced by compressing other boron phases to 12-20 GPa, heating to 1500-1800 0C and is quenchable to ambient conditions.
There is evidence of significant charge transfer from B2 pairs to the B12 icosahedra in this structure; in particular, lattice dynamics suggests the presence of significant long-range electrostatic interactions. Compressing boron above 160 GPa produces a boron phase with an as yet unknown structure, and this phase is a superconductor at temperatures 6-12 K
The base value of each unit of ranges between 1 and 10Ð per unit, with up to 4 units being found at any one time.
Presence on Mars: Common
|Group 1 | Group 2 | Group 3 | Group 4 | Group 5 | Group 6|
|Group 1|||Aluminum | Arsenic | Beryllium | Boron | Calcium | Cantite | Carbon | Chlorine | Chromium | Cobalt | Copper | Flourine | Helium| | Hydrogen | Iron | Lithium | Magnesium | Manganese | Nickel | Oxygen | Phosphorus | Plesium | Potassium | Silicon | Sodium||