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Ebonite was 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.
It is often used in bowling balls, electric plugs, smoking pipe mouthpieces, fountain pen bodies and nib feeds, saxophone and clarinet mouthpieces as well as complete clarinets (barrels/upper & lower joints/bells). Hard rubber is 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 colour even long after stronger modern plastics were substituted. It was used famously for many decades in hair combs made by Ace, now part of Newell Rubbermaid, although the current models are known to be produced solely with plastics. (An easy way to identify a hard rubber comb is to rub part of its surface vigorously, then immediately smell the comb. Hard rubber's scent, resulting from the sulfur in the ebonite, can usually be detected temporarily. The same effect can often be produced by running the comb under hot tap water.) 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.
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.
Under the influence of daylight sulfuric acid is produced at the surface that will gradually discolor the surface gray green to white.
Ebonite contamination was problematic 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.
Charles Goodyear's brother Nelson Goodyear experimented with the chemistry of ebonite composites. In 1851 he used zinc oxide as a filler.
- Merriam-Webster (2002) , vulcanite, Webster's Third New International Dictionary, Unabridged (Springfield, Massachusetts, USA: Merriam-Webster).
- Seymour, Raymond Benedict; Deaning, Rudolph D. (1987). History of Polymeric Composites. VSP. p. 374.
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