Germanium

Germanium has stable chemical properties and does not react with air or water vapor at room temperature. However, at 600 to 700 degrees Celsius, it quickly forms germanium dioxide. It does not react with hydrochloric acid or dilute sulfuric acid. When concentrated sulfuric acid is heated, germanium will dissolve slowly. Germanium is readily soluble in nitric acid and aqua regia. The interaction between alkaline solutions and germanium is very weak, but molten alkali in the air can cause germanium to dissolve rapidly. Germanium does not react with carbon, so when melted in a graphite crucible, it will not be contaminated by carbon.

Germanium oxidizes at higher temperatures and is accompanied by weight loss. The reason is that GeO is formed due to its strong volatility. Researchers studied the process of oxidation on the surface of germanium. First, they reduced germanium with CO at 600℃ to remove the bound oxygen or adsorbed oxygen on the surface of germanium. Germanium was oxidized at 25 to 400℃ under an oxygen pressure of 10 kpa, and the first oxide layer was formed in just 1 minute. When the temperature exceeds 250℃, the second layer of carbon dioxide forms quickly. When the temperature is raised further, the oxidation rate slows down significantly. After oxidation at 400℃ for 3 hours, a GeO2 film with a thickness of 1.75nm was formed.

The corrosion dissolution behavior of germanium varies in different solvents. The dissolution potential of N-type germanium is slightly more positive than that of P-type, so the dissolution rate of the former is faster in the same solution. Germanium is readily soluble in hot acids, hot bases and H2O2 with oxidants added. It is insoluble in dilute sulfuric acid, hydrochloric acid and cold alkaline solution. Germanium is insoluble in water at 100℃, while in water with saturated oxygen at room temperature, its dissolution rate approaches 1μg/(cm·h).

The extraction method of germanium is as follows: Firstly, the enriched germanium is chlorinated with concentrated hydrochloric acid to produce germanium tetrachloride. Then, the main impurity arsenic is removed by solvent extraction with hydrochloric acid. After that, it is purified twice through distillation in a quartz tower and washed with high-purity hydrochloric acid to obtain high-purity germanium tetrachloride. Finally, germanium tetrachloride is hydrolyzed with high-purity water to obtain high-purity germanium dioxide. Some impurities will enter the mother liquor of hydrolysis, so the hydrolysis process is also a purification process. Pure germanium dioxide is dried and calcined, and then reduced in the quartz tube of the reduction furnace with hydrogen at 650-680℃ to obtain metallic germanium. High-purity germanium (with impurities less than 1/1010) used in the semiconductor industry can be obtained by zone melting technology.

4HCl+GeO2→GeCl4+2H2O

GeCl4+(n+2)H2O→GeO2·nH2O+4HCl

GeO2+2H2→Ge+2H2O