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Material World
Application

Sealing and gasketing

Keeping fluids on the correct side of a joint — an unglamorous application that decides whether engines, buildings and spacecraft work.

A seal is a deliberately soft component placed between two hard ones, deformed on assembly so it fills every irregularity in both surfaces. The requirement is elastic recovery over years, over temperature cycles, and in contact with whatever fluid is being held back — which is why this is elastomer territory and why the choice of elastomer is almost entirely a chemical-compatibility question.

The failure mode is loss of elasticity rather than rupture. A gasket that has taken a permanent set no longer pushes back, and the joint leaks with the seal apparently intact.

Uses

O-rings and shaft seals throughout machinery; head gaskets and fuel-system seals in engines; window and door weatherstripping in buildings and vehicles; sanitary sealant around baths; and the pressure seals of aircraft and spacecraft.

Material selection is by fluid and temperature: nitrile for oil and fuel, EPDM for water, steam and brake fluid — and emphatically not for oil — silicone for extreme temperature range, fluoroelastomer where both aggressive chemistry and heat are present.

The *Challenger* accident in 1986 turned on this application: an O-ring that had lost its resilience at low temperature and did not seal in the seconds after ignition.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

uses

  • Silicone rubber — material · where the temperature range is the problem — from about −60 °C to 200 °C, and unbothered by sunlight
  • EPDM — material · water, steam, brake fluid and weather; emphatically not oil or fuel, which swell it until the seal fails
  • Neoprene — material · the generalist gasket, with moderate oil resistance and genuine flame retardancy
  • Butyl rubber — material · pharmaceutical vial stoppers, where nothing may pass in either direction through the closure
  • Polytetrafluoroethylene — material · where the chemistry defeats every elastomer, at the cost of having no elasticity to recover with
  • Rubber — material · and the choice within the class is a chemical-compatibility question rather than a mechanical one
  • Beeswax — material · wax seals, waxed thread, and the traditional water-resistant finish for wood — it does not crack the way a hard varnish does

Sources

  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Sealing and gasketing back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Sealing and gasketing → uses (water, steam, brake fluid and weather; emphatically not oil or fuel, which swell it until the seal fails) → EPDM → is produced by (ethylene and propylene copolymerised with a Ziegler-Natta catalyst, plus a few per cent of a diene to give vulcanisation something to work with) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite
  • Sealing and gasketing → uses (where the temperature range is the problem — from about −60 °C to 200 °C, and unbothered by sunlight) → Silicone rubber → is produced by (and it is not organic chemistry at all: the backbone is silicon and oxygen, which is why the temperature range is what it is) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite
  • Sealing and gasketing → uses (the generalist gasket, with moderate oil resistance and genuine flame retardancy) → Neoprene → is produced by (emulsion polymerisation of chloroprene) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite
  • Sealing and gasketing → uses (pharmaceutical vial stoppers, where nothing may pass in either direction through the closure) → Butyl rubber → is produced by (cationic polymerisation at around −95 °C, one of very few industrial polymerisations run that cold) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite
  • Sealing and gasketing → uses (where the chemistry defeats every elastomer, at the cost of having no elasticity to recover with) → Polytetrafluoroethylene → is produced by (found by accident when a cylinder of tetrafluoroethylene polymerised itself, and made deliberately the same way since) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite
  • Sealing and gasketing → uses (and the choice within the class is a chemical-compatibility question rather than a mechanical one) → Rubber → is sourced from (for the rest, and it is a plantation crop rather than a petrochemical) → Natural rubber

These are the most distinct paths back. Sealing and gasketing can be traced through others besides.