Ebonite

This article is about the type of rubber. For the manufacturer of bowling balls, see Ebonite International.

Ebonite is a brand name for very hard rubber first obtained by Charles Goodyear by vulcanizing rubber for prolonged periods. It is about 30% to 40% sulfur. Its name comes from its intended use as an artificial substitute for ebony wood. The material is known generically as hard rubber and has formerly been called "vulcanite", although that name now refers to the mineral vulcanite.

Applications

It is often used in bowling balls, electric plugs, smoking pipe mouthpieces, fountain pen bodies and nib feeds, and saxophone and clarinet mouthpieces. It is, rarely, used for the body of high quality clarinets. Hard rubber is also often seen as the wheel material in casters. It is also commonly used in physics classrooms to demonstrate static electricity.

Hard rubber was used in the cases of automobile batteries for years, thus establishing black as their traditional color even long after stronger modern plastics were substituted. It is used in hair combs made by Ace, part of Newell Rubbermaid, which survive, essentially unchanged, from the days of the US Civil War. Ebonite is used as an anticorrosive lining for various (mainly storage) vessels that contain hydrochloric acid. It forms bubbles when storing hydrofluoric acid at temperatures above room temperature, or for prolonged durations.

Properties

The material is brittle, which produces problems in its use in battery cases for example, where the integrity of the case is vital to prevent leakage of sulfuric acid. It has now been generally replaced by carbon black-filled polypropylene.

Contamination

Ebonite contamination was a big problem when it was used for electronics. The ebonite was rolled between metal foil sheets, which were peeled off, leaving traces of metal behind. For electronic use the surface was ground to remove metal particles.