Paraffin wax

Paraffin wax (or petroleum wax) is a soft, colorless solid made from petroleum, coal, or oil shale. It is made of hydrocarbon molecules that have between 20 and 40 carbon atoms. It is solid at room temperature. It begins to melt at about 37 °C (99 °F), and it boils at a temperature above 370 °C (698 °F).

People use paraffin wax for lubrication, electrical insulation, and candles. When it is colored with dye, it can be made into crayons.

Plain, unscented paraffin candles are odorless and bluish-white. Carl Reichenbach first made paraffin wax in Germany in 1830. This was a big step forward for candlemaking. Paraffin candles burned more cleanly and reliably than tallow candles, and they were cheaper to make.

In chemistry, the word paraffin means the same thing as alkane. Both words refer to hydrocarbons with the general formula C_nH_2n+2.

The name comes from Latin parum ("very little") and affinis, meaning "lacking affinity" or "lacking reactivity". This describes how paraffin does not easily react with other substances.

Properties

Paraffin wax is mostly a white, waxy solid. It has no smell and no taste. It melts at about 46 to 68 °C (115 to 154 °F). It does not dissolve in water, but it does dissolve in ether, benzene, and some esters. Most common reagents do not affect it, but it burns easily. Its heat of combustion is 42 MJ/kg.

Paraffin wax is a very good electrical insulator. This means it does not let electricity pass through it easily. It works better than almost all other materials, except some plastics, especially PTFE. It is also a useful neutron moderator. James Chadwick used it in his 1932 experiments to find the neutron. Paraffin wax is also very good at storing heat. Its specific heat capacity is 2.14–2.9 J⋅g⁻¹⋅K⁻¹ (joules per gram per kelvin), and its heat of fusion is 200–220 J⋅g⁻¹. It expands a lot when it melts. Because of this, it is used in wax element thermostats in factories, homes, and especially cars.

History

Paraffin wax was first made in 1830 by German chemist Carl Reichenbach. He was looking for a good way to separate and clean waxy substances found in petroleum. Paraffin helped candle-making a lot because it burned cleanly and cost less to make than other candle fuels, such as beeswax and tallow.

At first, paraffin wax melted at a low temperature, which was a problem. This was fixed by adding stearic acid. In the early 1900s, making paraffin wax grew a great deal. The oil and meatpacking industries were also growing, and they made paraffin and stearic acid as extra products.

Manufacturing

Paraffin wax starts from slack wax, a mixture of oil and wax. Slack wax is a leftover product from making lubricating oil. The first step is to take out the oil. This is done through a process called crystallization. The slack wax is heated and mixed with one or more solvents, such as a ketone. Then it is cooled. As it cools, the wax forms crystals and separates from the oil. The mixture is then filtered into two parts: a solid part, which is wax with some solvent, and a liquid part, which is oil and solvent. After the solvent is removed by distillation, the two products are called "product wax" (or "press wax") and "foots oil".

The less oil the wax contains, the purer it is considered to be. The product wax may be cleaned further to remove colors and smells. It may also be mixed with other materials to give it certain properties, such as its melting point and how it soaks in. Paraffin wax is sold as either a liquid or a solid.

Applications

In industry, makers often change the crystal structure of paraffin wax by adding branches to its carbon chain. They usually mix in additives such as EVA copolymers, microcrystalline wax, or forms of polyethylene. The changed wax is thicker, has smaller crystals, and behaves differently. Pure paraffin is rarely used to carve models for the lost wax process because it is brittle at room temperature and can chip or break. Softer waxes like beeswax may be preferred, but investment casting waxes, which are often paraffin-based, are made for this job. In a laboratory, paraffin wax is used to soak tissue before it is cut into thin slices on a microtome. Water is first removed with alcohol, and the alcohol is then cleared away with xylene. The tissue is placed in melted paraffin for several hours and then set in a mold to harden.

Paraffin wax has many other uses. It can stop fertilizers from clumping, keep out moisture, and coat dust. In rubber, blends act as antiozonant agents that help prevent cracking. They can also be a release agent that helps products come out of their mould. It is used to lubricate a bicycle chain, to coat waxed paper or waxed cotton, and as part of surfboard wax, ski wax, and skateboard wax. It is also used in crayons and candle-making. In food, it gives a shiny coating for candy-making, and it coats hard cheeses such as Edam cheese. It also seals jars, cans, and bottles, and is added to chewing gum. In forensic work, a nitrate test uses it to check a person's hand for certain chemicals. It fuels fire breathing, is used in investment casting and lava lamps, and helps make boiled leather armor and books. It also works as an expansion material in mechanical thermostats and actuators. As microwax, it is a glazing agent with E number E905. It is a moisturiser in toiletries and cosmetics such as Vaseline, and it helps shield against neutron radiation. It is a phase change material for thermal energy storage, and MESSENGER used it on the Mercury spacecraft. It is a phlegmatizing agent that makes high explosives such as RDX more stable. It is a potting material that encases electronic parts such as guitar pickups, transformers, and inductors. This keeps out moisture and reduces electromagnetically induced acoustic noise and microphonic effects. It also prevents oxidation on polished steel and iron, forms solid ink blocks for thermal printers, and serves as a solid fuel for hybrid rocket motors. It is used in textile making, such as for Eisengarn thread, and as a thickening agent in many paintballs. It is also used in wax baths for occupational and physical therapies and cosmetic treatments, in wax carving, and in wood finishing.

Occupational safety

People who work with paraffin can be exposed to it by breathing it in, or when it touches their skin and eyes. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) for paraffin wax fumes of 2 mg/m³ over an 8-hour workday.