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Pure (semiconductive) Si.

SiCl4 + 2Zn Si + 2ZnCl2,

or

SiCl4 + 2Í2 = Si + ÍCl,

Crystals of semiconductive Si with required electrophysical and structural properties can be grown (the method of zone melting).

3. Especially pure silicon is produced by silane, SiH4, decomposition at 600-700°C:

SiÍ4 Si + 2Í2,

In a laboratory:

Dry sand with powdered magnesium mixture is ignited by Mg ribbon:

SiO2 + 2Mg = Si + 2MgO

After cooling, the mixture obtained is sequentially processed by HCl (to eliminate MgO) and HF (to dissolve excess SiO2).

Germanium. Firstly, GeCl4 is obtained that hydrolyzes further to GeO2. The latter is reduced by hydrogen:

GeO2 + 2H2 Ge + 2H2O

Annual production of Ge achieves several hundred tons. Semiconductor technologies are the major applications of Ge, satisfying the requirements for the extremely high purity (impurities should not exceed about 10-9 at. %).

Tin. Tin ore is initially concentrated by flotation and then reduced by coal (Al or Zn can be also used):

SnO2 + 2C = Sn + 2CO

Lead. In the extraction of lead, the sulfide ore is first roasted together with quartz in a current of air:

2PbS + 3O2 = 2PbO + 2SO2

¯6e ­2e•2

Any lead(II) sulfate formed in this process is converted to lead(II) silicate by reaction with the quartz. The oxide produced is then mixed with limestone and coke and heated in a blast furnace. The following reactions occur:

PbO +C =Pb +CO

PbO +CO =Pb +CO2

PbSiO3 +CaO +CO =Pb +CaSiO3 +CO2

Crude lead contains traces of anumber of metals.

Tin and lead of high purity are produced by electrorefining of these metals (during electrolysis SnSO4 and Pb[SiF6] solutions by making the crude metal the anode in an electrolytic bath). A smooth coherent deposit of lead is obtained on the pure lead cathode when the current is passed. The impurities here (i.e. all other metals) form a sludge in the electrolytic bath and are not deposited on the cathode.

 

The annual production of Sn and Pb in the world achieves hundreds thousands tons.


Date: 2016-01-03; view: 744


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