What is the bridgeman production method?

The method involves heating polycrystalline material in a container above its melting point and slowly cooling it from one end where a seed crystal is located. Single crystal material is progressively formed along the length of the container. The process can be carried out in a horizontal or vertical geometry.

It is a popular method of producing certain semiconductor crystals, such as gallium arsenide where the Czochralski process is more difficult.

There is a synopsis fo the method at the source below.

Cadmium single crystal 48Cd112.40

Discovered in 1817 by F. Stromeyer at Göttingen, Germany.

[Latin: cadmia = calamine]

French: cadmium

German: kadmium

Italian: cadmio

Spanish: cadmio

Description: Cadmium is a silvery metal that tarnishes in air, and is soluble in acids but not alkalis. It is used in rechargeable batteries, alloys and pigments, but because of its toxicity these uses are being phased out wherever possible.

Metal single crystal properties

State: single crystal

Crystal structure: rhombohedral

Production method: Bridgeman

Standard size: diameter 12mm

thickness 1-2mm

Orientation: (0001)

Orientation accuracy: <2°, <1°, <0.5° or <0.1°

Polishing: as cut, one or two sides electrochemical polished

Roughness of surface: <0.03µm

Purity: 99.999%

Further Materials properties

Crystal structure: (cell dimensions/pm), space group,

h.c.p. (a=297.94, c=561.86), P63/mmc

X-ray diffractions mass absorption coefficients: CuKa 231 (µ/r) / cm2g-1

MoKa 27.5 (µ/r) / cm2g-1

Neutron scattering length: 0.51 b/10-12 cm

Thermal neutron capture cross-section: 2450 sa / barns

Density: 8.65 g/cm3

Melting point: 320.95 °C / 594.1 °K

Boiling point: 764.85 °C / 1038 °K

Molar volume: 13.00 cm3

Thermal conductivity: 96.8 [300 K] Wm-1K-1

Coefficient of linear thermal expansion: 29.8 x 10-6 K-1

Electrical resistivity: 6.83x10-8 [273 K] Wm

Mass magnetic susceptibility: -2.21 x 10-9(s) kg-1m3

Young's modulus: 62.6 GPa

Rigidity modulus: 24.0 GPa

Bulk modulus: 51.0 GPa

Poisson's ratio: 0.30 GPa

Radii: Cd2+ 103; Cd+ 114; atomic 149; covalent 141

Electronegativity: 1.69 (Pauling); 1.46 (Allred); 4.33 eV (absolute)

Effective nuclear charge: 4.35 (Slater); 8.19 (Clementi); 11.58 (Froese-Fischer)

Number of Isotopes (incl. nuclear isomers): 31

Issotope mass range: 99 -> 124

Biological data

Biological role: None has been proved, although suspected. It is stimulatory

Toxicity

Toxic intake: 17 mg kg-1 (chloride, oral, rat)

Lethal intake: LD50 (chloride, oral, guinea pig) = 63 mg kg-1

Hazards: Cadmium is toxic but its emetic action means that little is absorbed, so fatal poisoning rarely occurs. Cadmium is carcinogenic and teratogenic.

Level in humans

Blood: 0.0052 mg dm-3

Bone: <1.8 p.p.m.

Liver: 2 - 22 p.p.m.

Muscle: 0.14 - 3.2 p.p.m.

Daily dietary intake : 0.007 - 3 mg

Total mass of element in average

[70 kg] person: 50 mg

Geological data

Minerals:

Mineral Formula Density Hardness Crystal apperance

Cadmoselite a-CdSe 5.6 n.a. hex., res./adam. black

Greenockite CdS 4.9 3 - 3.5 hex., yellow, tiny prisms

Otavite CdCO3 5.03 n.a. rhom., adam. white/brown

Chief ore: none as such, most cadmium is produced as a by-product of the smelting of zinc from its ore ZnS, in which CdS is a significant impurity.

World production: 13900 tonnes/year

Main mining areas: see zinc

Reserves: see zinc

Specimen: available as foil, granules, powder, rod, shot, stick ore wire. CARE !

Abundances

Sun: 71 (relative to H = 1 x 1012)

Earth's crust: 0.11 ppm

Seawater:

Atlantic surface: 1.1 x 10-6 p.p.m.

Atlantic deep: 38 x 10-6 p.p.m.

Pacific surface: 1.1 x 10-6 p.p.m.

Pacific deep: 100 x 10-6 p.p.m.

Residence time: 30 years

Classification: recycled

Oxidation state: II