Physical characteristics

Bismuth is a brittle metal with a white, silver-pink hue, often occurring in its native form, with an iridescent oxidetarnish showing many colors from yellow to blue. The spiral, stair-stepped structure of bismuth crystals is the result of a higher growth rate around the outside edges than on the inside edges. The variations in the thickness of the oxide layer that forms on the surface of the crystal causes different wavelengths of light to interfere upon reflection, thus displaying a rainbow of colors. When burned in oxygen, bismuth burns with a blue flame and its oxide forms yellow fumes. Its toxicity is much lower than that of its neighbors in the periodic table, such as lead, antimony, and polonium.

No other metal is verified to be more naturally diamagnetic than bismuth. (Superdiamagnetism is a different physical phenomenon.) Of any metal, it has one of the lowest values of thermal conductivity (after manganese, and maybe neptunium and plutonium) and the highest Hall coefficient. It has a high electrical resistance. When deposited in sufficiently thin layers on a substrate, bismuth is a semiconductor, despite being a post-transition metal.

Elemental bismuth is denser in the liquid phase than the solid, a characteristic it shares with antimony, germanium, silicon and gallium. Bismuth expands 3.32% on solidification; therefore, it was long a component of low-melting typesetting alloys, where it compensated for the contraction of the other alloying components, to form almost isostatic bismuth-lead eutectic alloys.

Though virtually unseen in nature, high-purity bismuth can form distinctive, colorful hopper crystals. It is relatively nontoxic and has a low melting point just above 271 °C, so crystals may be grown using a household stove, although the resulting crystals will tend to be lower quality than lab-grown crystals.

At ambient conditions bismuth shares the same layered structure as the metallic forms of arsenic and antimony, crystallizing in the rhombohedral lattice (Pearson symbol hR6, space group R3m No. 166), which is often classed into trigonal or hexagonal crystal systems. When compressed at room temperature, this Bi-I structure changes first to the monoclinic Bi-II at 2.55 GPa, then to the tetragonal Bi-III at 2.7 GPa, and finally to the body-centered cubic Bi-IV at 7.7 GPa. The corresponding transitions can be monitored via changes in electrical conductivity; they are rather reproducible and abrupt, and are therefore used for calibration of high-pressure equipment.

Price

World mine production and annual averages of bismuth price (New York, not adjusted for inflation).

The price for pure bismuth metal has been relatively stable through most of the 20th century, except for a spike in the 1970s. Bismuth has always been produced mainly as a byproduct of lead refining, and thus the price, usually reflected the cost of recovery and the balance between production and demand.

Demand for bismuth was small prior to World War II and was pharmaceutical – bismuth compounds were used to treat such conditions as digestive disorders, sexually transmitted diseases and burns. Minor amounts of bismuth metal were consumed in fusible alloys for fire sprinklersystems and fuse wire. During World War II bismuth was considered a strategic material, used for solders, fusible alloys, medications and atomic research. To stabilize the market, the producers set the price at $1.25 per pound (2.75 $/kg) during the war and at $2.25 per pound (4.96 $/kg) from 1950 until 1964.

In the early 1970s, the price rose rapidly as a result of increasing demand for bismuth as a metallurgical additive to aluminium, iron and steel. This was followed by a decline owing to increased world production, stabilized consumption, and the recessions of 1980 and 1981–82. In 1984, the price began to climb as consumption increased worldwide, especially in the United States and Japan. In the early 1990s, research began on the evaluation of bismuth as a nontoxic replacement for lead in ceramic glazes, fishing sinkers, food-processing equipment, free-machining brasses for plumbing applications, lubricating greases, and shot for waterfowl hunting. Growth in these areas remained slow during the middle 1990s, in spite of the backing of lead replacement by the US Government, but intensified around 2005. This resulted in a rapid and continuing increase in price.