Силициды

Бориды of silicon.

2 chemical connections of silicon with бором B3Si and B6Si are known. The crystals B3Si have the form of rhombic plates of black colour with density 2520 kg /м3, B6Si is formed in the form of opaque grains of the wrong form with density 2470кг/м3. Бориды receive by restoration кремнезема in vacuum on reaction:

SiO2 + 8B B6Si + 2BO

Or way of hot pressing of a mix of powders бора and silicon at temperature 1600.. 1800 With. Бориды of silicon differ by high hardness and chemical stability(resistance). They плавятся at 2000 With slowly окисляются at very high temperatures.

The education of firm solutions бора in silicon results in sharp decrease(reduction) to electroresistance last. So the additive 0,0005%уменьгает specific resistance Si in 100 times, and additive 1 % in 1000 times. The additives to application from 0,01 up to 1 % бора cause it(him) дырочную conductivity. Semi-conductor properties of a firm solution бора in silicon is used at creation there of so-called solar batteries - photo cells serving for transformation of a solar energy in electrical. Are applied or силициды бора and to reception special высокоогнеупоров.

With the majority of metals the elementary silicon at high temperatures forms connections парообразного of structure representing crystal substances having metal shine and significant fragility.

Силициды are applied in metallurgy for раскисления of steel and reception кремневодородов, on reaction:

Mg2Si + 4HCl 2MgCl2 + SiH4

At processing силицида кальция the hydrochloric acid on a cold turns out гидраты of the lowest oxides of silicon - лейконы.

Силициды кальция are applied to clearing steel of sulfur and phosphorus. They turn out on reaction:

3СaO + 5 Si 2CaSi2 + CaSiO3

CaC2 + 2SiO2 + 2C CaSi2 + 4CO

2Si + CaO +C = CaSi2 + CO

Силициды кальция it is possible to receive and direct сплавлением Са and Si in an atmosphere of nitrogen or hydrogen. The large technical meaning(importance) in metallurgy have силициды of iron which is included in structure of a technical product - ферросилиций, received or in доменных furnaces or electrical furnaces.

The alloys of silicon with aluminium, are known under the name силуминов, as are applied in engineering as a material to manufacturing products of small densities and large durability.

Now more and more wide application in quality rather жароустойчивого of a material receives дисилицид молибдена, being as by an excellent heat resisting covering for products from a metal layer молибдена, generally speaking, chemically rather unstable at high temperatures.

Questions:

1. Lowest connections of silicon with oxygen. Силиконы and лейконы.

2. Кремнеорганические of connection:

диметилсилан (CH3) 2 SiH2

триметилсилан (CH3) Si (C2H5) 3

тримтилфенилсилан (CH3) 3Si (C6H5)

3. Features of structures силикатов also that lays to a basis of structure силикатов

4. What features of structures боридов, карбидов, нитридов and силицидов?