9. What is coal tar? What are its uses?

Coal tar is a thick, dark liquid obtained as a byproduct during the process of coal gasification or the distillation of coal to produce coke. It is composed of numerous organic compounds, primarily aromatic hydrocarbons, along with small amounts of phenols, cresols, and other chemicals. Coal tar has a distinctive smell and a viscous consistency.

Uses of coal tar include:

1. Pavement Sealants: Coal tar is commonly used as a key ingredient in pavement sealants for asphalt surfaces. It helps to improve the durability and longevity of roads, driveways, and parking lots by providing a protective coating that seals out moisture, prevents oxidation, and enhances resistance to wear and tear.

2. Medicinal Products: Coal tar is used in various medicinal products, particularly in dermatology, due to its antiseptic, anti-inflammatory, and keratolytic properties. It is found in over-the-counter and prescription treatments for skin conditions such as psoriasis, eczema, dandruff, and seborrheic dermatitis.

3. Wood Preservation: Coal tar is employed in the preservation of wood and timber products. It is used as a wood preservative to protect against fungal decay, insect infestation, and weathering. Treated wood products, such as utility poles, railroad ties, and marine pilings, benefit from increased durability and resistance to environmental degradation.

4. Roofing Materials: Coal tar is a component of roofing materials, including built-up roofs (BUR) and modified bitumen membranes. It serves as a waterproofing agent and adhesive that helps to seal and protect roofs from water infiltration and damage.

5. Pesticides: Coal tar derivatives are used in the formulation of certain pesticides and herbicides to control pests, weeds, and fungal pathogens in agriculture, horticulture, and forestry.

6. Coal Tar Pitch: Coal tar pitch, a solid residue derived from coal tar, is used as a binder and adhesive in the production of carbon electrodes, graphite materials, and refractory products. It is also employed in the manufacturing of aluminum, steel, and other metals.

Despite its numerous industrial and commercial applications, coal tar contains several potentially harmful compounds, including polycyclic aromatic hydrocarbons (PAHs), which are known carcinogens and environmental pollutants. Therefore, proper handling and disposal practices are necessary to minimize human exposure and environmental contamination.