BISMUTH

the hull's steel plates.

BISMUTH 

Bismuth is a chemical element with the symbol Bi and the atomic number 83. Bismuth, a pentavalent post-transition metal and one of thepnictogens, chemically resembles its lighter homologs arsenic and antimony. Elemental bismuth may occur naturally, although its sulphid and oxide form important commercial ores. The free element is 86% as dense as lead. It is a brittle metal with a silvery white colour when freshly produced but is often seen in air with a pink tinge owing to surface oxidation. Bismuth is the most naturally diamagnetic element, and has one of the lowest values of thermal conductivity among metals.

PROPERTIES:

Bismuth is a brittle metal with a white, silver-pink hue, often occurring in its native form, with aniridescent oxide tarnish 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 colourWhen burned in oxygen, bismuth burns with a blue flame and its oxide forms yellowfumes. Its toxicity is much lower than that of its neighbours in the periodic table, such as lead,antimony, and polonium.

MICROSTRUCTURE:

fracture stress capacity increased again9,11. These observations areimportant because it has been predicted that all elemental or randomsolid solution face-centered-cubic [001] tilt boundaries,such as those in copper, are constructed from a single arrangement of atoms. Because the separation of these structural units for tilt angles

between 23° and 67° is always less than 0.9 nm, and our micrographs

show that the Bi segregates to the centre of this structural unit we can

calculate the minimum amount of Bi that will embrittle copper.

We predict, based on the bicrystal studies9,11, that a Bi concentration of 8% of the atoms at the grain boundary plane (1.5 Bi atoms per nm2) is enough to cause catastrophic brittle fractures.

Bismuth-induced embrittlement of copper

grain boundaries

Bismuth is known to induce faceting of copper grainboundaries. It has also been shown that the grain-boundary facets disappear if the Bi is removed from the boundary. Sigleet al. have demonstrated a correlation between Bi segregation in a copper

bicrystal and boundary faceting.They found only a completely faceted

boundary exhibited extreme brittle behaviour and suggested that this

structural transition is a necessary prerequisite for grain-boundary

embrittlement.A key result of their study was to show brittle fracture (actually, boundary faceting) is the result of segregation of a sufficient amount of Bi to the grain boundary, which creates an easy crack path. However, these studies do not show how the segregated bismuth induces embrittlement. In the present study, we have concentrated on the electronic structure changes that result from Bi impurities in Cu. These changes are expected to occur even at single Bi atoms in bulk Cu.Butagain,brittle fracture will only occur if a sufficient amount of Bi segregates at a two-dimensional defect to form a crack path. A number of previous studies have found segregation levels of Bi to Cu grain boundaries greater than 1 monolayer.The work of Chang and  show that Bi enrichment at the boundaries increases for heat treatments in the two-phase (Cu-rich solid + Bi-rich liquid) region of the Cu–Bi phase diagram. It is possible that a different fracture mechanism exists when the Bi enrichment level becomes such that bismuth atoms become nearest neighbours. However,it has been shown in studies using special tilt angle bicrystalsthat very high Bi enrichment levels and the resulting faceting is not necessary to reduce.

One of the concequence of brittle fracture:

In brittle fracture, no apparent plastic deformation takes place before fracture. In brittle crystalline materials, fracture can occur bycleavage as the result of tensile stress acting normal to crystallographic planes with low bonding (cleavage planes). In amorphous solids, by contrast, the lack of a crystalline structure results in a conchoidal fracture, with cracks proceeding normal to the applied tension. The sinking of RMS Titanic in 1912 from an iceberg collision is widely reported to have been due to brittle fracture of