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Atomic number Atomic weight Isotopes and abundances (%) Mass No. 113 115
Metal Crystal structure Density (g/cm 3 ) Melting point CC) Boiling point (oC) Electron configuration Electrode potential for In 1 + (V) (In 1 + +e- = In° (H 2 = 0.0)) Electrode potential for In 1 + (V) (In3+ + 3e- = In° (H 2 = 0.0)) Ionic radius for In 3 + (pm) Ionization potential for In3+ (kJ/mol) Electronegativity (after Pauling) Ionic potential for In3+
49 114.82 4.8 95.72
tetragonal 7.31 156.61 2080
[Kr]4d 10 5s 2 5p 1 -0.18 -0.34 80 2704.0 1.7 3.8
Crystal chemistry and mineralogy Indium prefers covalent tetrahedral coordination in sulfide phases of the sphalerite-wurtzite type and octahedral com·dination in spinel-related structures such as Fein 2 S4 . The bond lengths of In-S and Sn-S are similar, facilitating higher temperature solid solutions of indium in tin bearing sulfides (e.g. stannite). In heteropolar structures, In3+ substitutes mainly for Fe 2 + (ionic radius 78 pm). Indium substitutes preferably for iron in phyllo- and ina-silicates. Indium occurs mostly as a trace constituent of other minerals. Indium minerals are rare, though not as rare as gallium minerals. Seven known mineral species are presented in Table I2, although the number of indium minerals is .likely to grow. Indium prefers tin minerals, especially cass1ter~te (up to 1%), hydrocassiterite (2%), kylindrite (1 %) and tealhte (0.3%), as well as minerals with tetrahedral covalent bonds, such as sphalerite, chalcopyrite and stannite (Table 13). Concentrations in silicates are low, frequently in the range of ppb. Indium is a rare element; the geochemical abundances are presented in Table I4. Its geochemistry is inadequately known due to the lack of suitable analytical methods for low concentrations. The chalcophile properties of indium significantly exceed any siderophilic or lithophilic tendencies.
Hypogene environment The distribution of indium in igneous rocks is more or less uniform. Significant concentration takes place only in the late Table 12 Indium minerals
Native indium Yixumite Roquesite Indite Sakuraiite Petrukite Dzahlindite
In Ptln? CuinS 2 (chalkopyrite group) Fe 2 + In 2 S4 (linnaeite group) (Cu,Zn,Fe) (In,Sn)S 4 (Cu,Fe,Zn,Ag)(Sn,In)S 4 In(OH) 3
340
INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY (ICP-MS)
Table 13 Abundances of indium (in ppb)
Cosmos Iron meteorites Carbonaceous chondrites Ordinary chondrites Hypersten chondrites Earth Crust Igneous rocks Ultrabasites Basalts Granites Shale Deep sea clay Seawater
0.184 atoms/10 6 Si 10
70
0.5
The indium content of shale corresponds with the average of the crust. Carbonate sediments have the lowest values of In. Data on the distribution of indium in continental water and seawater are limited.
Uses
70
Indium achieved economic importance in 1924; the growing production exceeds 100 !/year. The applications of indium metal and compounds are many: thin coatings on glass for digital displays, solar cells or heat-reflecting window coatings, electrical and electronic components, low melting all
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