Material selection in a vacuum system is not based on mechanical strength alone. Outgassing, gas permeability, temperature capability, chemical compatibility, surface condition and cleanliness can all affect the pressure a system can reach and the quality of the process.

For the broader system view, see what vacuum technology is and where it is used.

What properties are important in vacuum materials?

Depending on the application, useful properties may include:

+ Low outgassing
+ Low gas permeability
+ Adequate mechanical strength
+ Chemical compatibility with process gases
+ Suitable temperature range
+ Cleanable surfaces
+ Compatibility with bake-out where required

As operating pressure decreases, materials inside the system can themselves become a significant source of gas.

Why is stainless steel widely used?

Stainless steel is one of the most common materials for vacuum chambers, manifolds, pipework and fittings.

Depending on grade and surface preparation, it can offer:

+ High mechanical strength
+ Good corrosion resistance
+ Weldability
+ Cleanable surfaces
+ Good suitability for many high-vacuum systems

Grades such as 304 and 316L are frequently encountered, although process chemistry and temperature still have to be considered.

Is aluminium used in vacuum systems?

Yes. Aluminium is used in selected chambers, pump components, instrument bodies and vacuum assemblies.

Its advantages can include:

+ Low weight
+ Good machinability
+ Good thermal conductivity

The alloy, surface treatment and process chemistry still matter, so aluminium is not automatically the best material for every chamber.

Where are copper, nickel and titanium used?

Copper is useful where electrical or thermal conductivity is important and is also widely used in certain metal vacuum seals.

Nickel and nickel alloys may be selected for more demanding chemical or temperature conditions.

Titanium can be useful where low mass, mechanical strength or specialised process compatibility is required.

Because material choice and process gas are closely related, gas compatibility is also part of vacuum pump selection.

Why are ceramics used in vacuum equipment?

Technical ceramics such as alumina can provide:

+ Electrical insulation
+ High-temperature capability
+ Chemical stability
+ Good vacuum compatibility when properly selected and processed

Ceramics are commonly found in electrical feedthroughs, sensor assemblies and high-voltage vacuum instrumentation.

For the materials used inside measuring devices themselves, see materials used in vacuum sensors.

Can glass be used under vacuum?

Yes. Borosilicate glass and other suitable glasses are used in laboratory vacuum systems, observation windows and specialised chambers.

Glass can provide:

+ Electrical insulation
+ Chemical resistance
+ Optical access to the chamber

Mechanical design remains critical because atmospheric pressure acts on the outside of an evacuated glass component.

Can plastics and polymers be used?

Yes, but polymers require more care as vacuum levels become deeper.

Materials such as PTFE, PEEK and other engineering polymers can be useful in suitable applications.

Important considerations include:

+ Outgassing
+ Gas permeation
+ Maximum temperature
+ Solvent resistance
+ Process-gas compatibility

A polymer that works well in a rough-vacuum machine may not be suitable for a high-vacuum or contamination-sensitive chamber.

The relationship between material gas release and chamber cleanliness is explained further under vacuum level, residual gases and outgassing.

Which materials are used for vacuum seals?

Elastomer O-rings are common in industrial vacuum systems.

Depending on temperature and process chemistry, seal materials may include:

+ FKM fluoroelastomers
+ EPDM
+ NBR
+ Other specialised elastomers

FKM materials, including products commonly known by trade names such as Viton, are used because they can provide useful temperature and chemical resistance in many applications.

However, no elastomer is suitable for every gas, temperature and pressure range.

For high and ultra-high vacuum, metal seals such as copper gaskets can be preferred where lower permeation and lower outgassing are required.

Why can elastomer seals limit high-vacuum performance?

Compared with metal seals, elastomers generally allow more gas permeation and can contribute more outgassing.

As the chamber pressure decreases, that additional gas load can become important.

This does not make elastomer seals “bad”; it means that seal technology must match the required vacuum level.

Are pump oils also part of vacuum material compatibility?

In an oil-sealed system, pump fluid is effectively another material that can interact with the process.

Its:

+ Vapour pressure
+ Chemical stability
+ Compatibility with process gas
+ Contamination condition

can influence both pump performance and chamber cleanliness.

This is why vacuum pump oil selection is also part of materials compatibility.

What is outgassing?

Materials can release gases that were adsorbed on their surfaces or absorbed within the material.

This release is called outgassing.

Common sources include:

+ Water and surface moisture
+ Plastics and elastomers
+ Oils and greases
+ Adhesives
+ Surface contamination

Outgassing can prevent a chamber from reaching lower pressure even when the vacuum pump is still operating normally.

Why does bake-out affect material selection?

Some high-vacuum systems are heated in a controlled way to accelerate removal of water vapour and other volatile material from internal surfaces.

This process is known as bake-out.

If bake-out is planned, all components must tolerate the required temperature, including:

+ Seals
+ Sensors
+ Cables
+ Adhesives
+ Electrical feedthroughs
+ Viewing windows

A chamber material may survive the temperature while a nearby O-ring, cable or sensor does not.

Why is cleanliness so important?

Even a good vacuum material can perform poorly if its surface is contaminated.

Fingerprints, machining fluid, grease, water or cleaning residues can become additional gas sources after pump-down.

In high-vacuum systems, performance therefore depends on:

+ Material selection
+ Surface cleaning
+ Assembly method
+ Lubricants used during assembly
+ Storage and handling

Why must chemical compatibility be checked?

A vacuum system may handle much more than ordinary air.

If corrosive, oxidising, solvent-containing or reactive gases are present, chamber, seal, pump and sensor materials must be evaluated together.

An incompatible material can:

+ Swell
+ Harden
+ Corrode
+ Lose sealing performance
+ Contaminate the process

This also becomes a safety issue, so material compatibility should be considered together with vacuum-system safety.

Does material choice change by industry?

Yes.

Semiconductor and high vacuum → low outgassing and high cleanliness

Chemical processes → chemical resistance and seal compatibility

Food and pharmaceutical processes → cleanability and process suitability

Vacuum furnaces → temperature capability

Machine automation → mechanical durability, cost and easy service

For a wider industry overview, see industries using vacuum technology.

New trends in vacuum materials

Modern vacuum engineering is not focused only on reaching lower pressure.

There is also increasing interest in:

+ Lower outgassing
+ Longer seal life
+ Cleaner process conditions
+ Reduced maintenance
+ Better chemical resistance

These developments are closely connected with new developments in vacuum technology.

Quick vacuum-material selection checklist

1. Define the required absolute pressure.
2. Identify the process gas or vapour.
3. Check minimum and maximum temperature.
4. Consider outgassing and permeation.
5. Match seals to the process chemistry.
6. If bake-out is required, check every component for temperature compatibility.
7. Consider cleaning, surface preparation and assembly conditions.

The key point is:

The best vacuum material is not necessarily the strongest or most expensive material. It is the material that matches the required pressure, temperature and process conditions.

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Related vacuum technology topics

What is vacuum technology? | Industries using vacuum | Vacuum innovations | Vacuum safety

Vacuum level and residual gases | Vacuum pump oils | Vacuum sensor materials

Main sections:
Vacuum Sensors | Vacuum Pumps | Vacuum FAQ

Vacuum materials should be selected by considering pressure, temperature, process chemistry, outgassing, permeation and cleanliness together.

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