A coal tar, coal tar pitch is: coking products to pay, namely tar distillation residue after the black material in the distillation kettle. There were it with refined tar just physical properties, no clear boundaries, dividing method is generally prescribed softening point at 26.7 ℃ (cube method) for the following tar, 26.7 ℃ for asphalt. Coal tar pitch is mainly composed of anthracene, phenanthrene, difficult to volatilize pyrene. These toxic substances, the content of these different components, properties of coal tar pitch because they
But different. Great influence of temperature on coal tar pitch, winter easy to brittle fracture, summer easy softening. Heating with special odor; heating to 260 ℃ in 5 hours later, the content of anthracene, phenanthrene, pyrene and other components will be volatile out.
Two, petroleum asphalt: petroleum asphalt is a crude distillation residue. According to the degree of refining, at room temperature into the liquid, semi-solid or solid. Petroleum pitch green black and shiny, temperature sensing with high. Because it is in the production process was distilled to 400 ℃, the volatile components is very little, hydrocarbons but may still be a polymer without volatile out, these substances are more or less harmful to human health.
Three, natural asphalt: natural asphalt storage in underground, some of the formation of ore or piled up in the earth's crust. The pitch after natural evaporation, oxidation, generally do not contain any toxin.