Polychlorinated biphenyls (PCBs) are a class of chlorinated compounds used as industrial coolants and lubricants. Waterless coolant is used as an alternative to conventional water and ethylene glycol coolants. Liquids have a variety of uses, as lubricants, solvents, and coolants. Waterless coolant is generally more expensive than traditional water and ethylene glycol-based coolants. Gas turbines designed with foil bearings and air-cooling operate without lubricating oil or coolants. Water or glycol coolants are used to keep engines from overheating. Other cooling methods include thermoelectric cooling and coolants. Inert gases are used as coolants in gas-cooled nuclear reactors. Freons are chemicals used as coolants in refrigerators and as a pressurizing agent in aerosols. Oils are used as coolants in oil cooling, for instance in electric transformers. The line includes engine oils, gear oils and coolants. Dielectric gases can also serve as coolants. HOAT coolants typically mix an OAT with a traditional inhibitor, usually silicates. It keeps the equipment protected against seepage of non-corrosive coolants, splashing, oil, and dripping. Si-OAT coolants mix silicates with HOAT.