9. Physical and Chemical Properties
Structure :
Crystalline
Form :
Lump material.
Colour :
Silvery material.
Odour :
Odourless.
Solubility (Water) :
Insoluble/slightly soluble.
Melting Point (°C) :
Approx. 1410
Boiling Point :
Approx. 2355
Specific Gravity (water = 1) : Approx. 2.3
10. Stability and Reactivity
Silicon is insoluble in most acids, but dissolves in a mixture of hydrofluoric acid (HF) and nitric
acid (HNO3) evolving hazardous gases. Impurities present in silicon (e.g. Al and Ca) may react with
dilute acids evolving hazardous gases
(see below).
Silicon dissolves readily in dilute lye.
Conditions to avoid:
Avoid generating sparks or other ignition sources (e.g. welding) in areas with high dust
concentrations. Silicon-particles suspended in air at concentrations above 100 g/m3 can cause dust
explosions. Both ignition sensitivity and the violence of explosion increase with decreasing
particle size. Silicon dust with particle diameter > 40 mm probably entails no danger of
explosion. Ignition temperature (warm surface) > 800 °C.
Addition of wet material to molten metal may cause explosions.
Materials to avoid:
Acids (see below).
Hazardous decomposition products:
A reaction with hydrofluoric acid (HF) and nitric acid (HNO3) leads to the formation of toxic gases
such as silicon tetrafluoride (SiF4) or nitrous gases (NOx). Impurities in silicon may react with
dilute acids forming flammable and harmful gases such as hydrogen (H2) and silane (SiH4).
Wet product will form flammable hydrogen gas if added to molten metal, due to decomposition of water.
Wet product will form flammable hydrogen gas if added to molten metal, due to decomposition of water.
11. Toxicological Information
Acute effects:
Inhalation: Dust may irritate
and dehydrate mucous membranes.
Skin contact: Dust
may irritate and dehydrate skin.
Eye contact: Dust may irritate and lead to dryness.
Ingestion: Dust may
irritate and dehydrate mucous membranes.
Chronic effects: No chronic effects known.