Mineral oils are complex mixtures of hydrocarbons derived from crude oil. They are mostly used for lubricating machines. Mineral oils are also used as an ingredient in baby care products such as petroleum jelly. The various physical properties of mineral oils allow them to work well in these disparate applications.
Viscosity is a liquid's resistance to flow when it's poured on a surface. The viscosity of mineral oil increases as it's exposed to lower temperatures. The viscosity of mineral oil is also affected by the pressure applied to it. As the pressure increases, the oil molecules are squeezed together, increasing their interaction with each other and making the oil more viscous. In lubricating machines, the more viscous the oil is, the better the lubrication and thus the better the machine performance.
Density is the mass per unit volume of a substance. It determines how the mineral oil flows. The more dense mineral oil is, the higher its viscosity. This property is crucial in the making of baby care and beauty products. In petroleum jelly, for instance, mineral oil helps give the jelly high density and viscosity so that it sticks together.
A volume of a given mass of oil increases as the temperature rises. This makes the oil less dense and less viscous. The degree at which mineral oil expands is referred to as thermal expansion. This physical property is important both in the functionality of the mineral oil and in determining the size of the containers needed to store it.
Thermal conductivity is the rate at which heat is transferred through a substance. This property can determine how overheating can be controlled. Mineral oil with a high thermal conductivity lowers the temperatures of bearings. Thermal conductivity is therefore important to engineers who use machines with bearings.