SILICON - Si - [silicium]
Properties of Silicon:
Nonmetal. Large crystals - dark gray, with metal gloss, very firm, very fragile, opaque, the semiconductor at the room temperature. Amorphous in the form of very small crystals - white (without impurity) or brown (with impurity). Melts with reduction of volume. It is steady on air (formation of a protective oxidic film). In a crystal form - small reactionary ability. Doesn't react with water, acids (including also fluoric acid), hydrogen.
In an amorphous form - more active. Reacts with the concentrated fluoric acid, alkalis (it is partially transferred to solution even in the alkalescent environment), absorbs significant amounts of various gases (including hydrogen). Is oxidized by oxygen and halogens. Reacts with hydrogen halides, ammonia, hydrogen sulfide, metals sulfides by heating. It is extremely active in the melted state, reacts with alkalis, alkaline earth metals and other metals. Alloyed (but doesn't react) with beryllium, aluminum, gallium, indium, tin, antimony, zinc, silver, gold. An alloy with iron - ferrosilicium (12-90% of Si) is industrially important. The second for prevalence (after oxygen) an element in Earth lithosphere.
| Molar mass | g/mol | 28.086 |
| Density | g/cm3 | 2.33 |
| Melting point | °C | 1415 |
| Boiling point | °C | 3250 |
Methods for the preparation of Silicon:
SiH4 = Si + 2H2 (400-1000°C).
SiO2 + 2Mg = 2MgO + Si (800-900°C, in atm. of argon).
SiO2 →(air, Mg, -MgO, -Mg3N2) → Si, Mg2Si (700-900°C).
SiO2 + 5C(coke) + CaO = Si + CaC2 + 3CO (800-1000°C).
SiCl4 + 2H2 = Si + 4HCl (800°C).
SiCl4 + Li[AlH4] = Si + LiCl + AlCl3 + 2H2 (over 450°C).
SiCl4 + 4M = Si(amorphous) + 4MCl (M = Na, K; 600-700°C).
3Na2[SiF6] + 4Al = 3Si + 2Na3[AlF6] + 2AlF3 (700°C).
Na2[SiF6] → Electrolysis → Si↓(on cathode) + 2F2↑(on anode) + 2NaF (in the liquid NaF).
Сhemical reactions with Silicon:
Si(amorphous) + 2H2O(steam) = SiO2 + 2H2 (400-500°C).
Si(amorphous) + 4NaOH(conc.) = Na4SiO4 + 2H2↑.
Si(amorphous) + 6HF(conc.) = H2[SiF6] + 2H2↑.
Si + 4HF(gas) = SiF4 + 2H2 (40-100°C).
3Si + 18HF(conc.) + 4HNO3(conc.) = 3H2[SiF6] + 4NO↑ + 8H2O.
3Si + 18HF(conc.) + 2KClO3 = 3H2[SiF6] + 2KCl + 6H2O.
Si + 6HF(conc.) + KNO3 = H2[SiF6] + 2KNO2 + 2H2O.
Si + O2 = SiO2 (1200-1300°C).
Si + 2F2 = SiF4 (normal temp., burning in the fluorine).
Si + 2Cl2 = SiCl4 (340-420°C, under argon).
Si + 2Br2 = SiBr4 (620-700°C, under argon).
Si + 2I2 = SiI4 (750-810°C, under argon).
Si + 4HI = SiI4 + 2H2 (400-500°C).
Si + S = SiS (650-700°C, pressure).
Si + 2S = SiS2 (250-600°C).
Si + 2E = SiE2(800°C, E = Se, Te; under argon).
3Si + 2N2 = Si3N4 (1200-1500°C).
Si + C(graphite) = SiC (1200-1300°C).
Si + M = MSi (by alloying, M = Na, K, Rb, Cs).
Si + 2M = M2Si (by alloying, M = Mg, Ca).
Si + M = MSi, MSi2 (by alloying, M = Ca, Sr, Ba).
2Si + M = MSi2 (by alloying, M = La, Th, Ti, Cr, Mo, Mn, Fe).
3Si + 4NH3 = Si3N4 + 6H2 (1300-1500°C).
Si + 2H2S = SiS2 + 2H2 (1200-1300°C).
