Hermetic seal

A hermetic seal is a seal which, for practical purposes, is considered airtight. The term is often used to describe electronic parts that are designed and intended to secure against the entry of water vapor and foreign bodies in order to maintain the proper functioning and reliability of their contents.

Etymology and history

The word hermetic comes from the syncretism of the Greek god Hermes and the Egyptian Thoth; this figure was also a mythological alchemist known as Hermes Trismegistus. The latter has two books attributed to him, the Emerald Tablet and the Corpus Hermeticum. He was believed to possess a magic ability to seal treasure chests so that nothing could access their contents.

Alchemists also frequently used distillation in their experiments, and needed an airtight seal to improve the efficiency of their alembic stills. Most alchemists, though, were considered to be Hermetics for adopting the philosophy of the Emerald Tablet or the Corpus Hermeticum.

Examples and applications

Applications for hermetic sealing include semiconductor electronics, thermostats, optical devices, and switches.

In 1951, The U.S. Constitution, U.S. Declaration of Independence and U.S. Bill of Rights were hermetically sealed with helium gas in glass cases housed in the U.S. National Archives in Washington, DC. In 2003, they were moved to new glass cases hermetically sealed with argon.^[1]

Packaging

The food, chemical, and pharmaceutical industries all have applications for the use of barrier packaging, such as glass, Tin cans, metal foils, and high barrier plastics.

Standard test methods are available for measuring the moisture vapor transmission rate, oxygen transmission rate, etc of packaging materials. Completed packages, however, involve heat seals, joints, and closures which often reduce the effective barrier of the package. For example, the glass of a glass bottle may have an effective total barrier but the screw cap closure and the closure liner might not.

External links

See also

• Heat sealer
• Permeation

Notes