Aluminum - The Unsung Hero for Non-magnetic Vacuum Applications.
A variety of industries — semiconductor manufacturing, aerospace, precision metrology, and scientific research — require vacuum systems with minimal magnetic interference.
Classified as a paramagnetic material, aluminum does not exhibit ferromagnetism like iron, nickel, or cobalt. And when exposed to an external magnetic field, aluminum incurs limited magnetization that disappears almost instantly when the field is removed. Here’s a helpful example.
Aluminum Vacuum Chambers used in Lightweight, Non-magnetic UHV Suitcases
Atlas Technologies machined a vacuum chamber out of single, solid block of aluminum for enhanced vacuum integrity. Then Atlas bimetal aluminum-titanium flanges were welded to multiple ports of the chamber to allow connection to different vacuum systems. Volkvac fitted the chamber with passive and battery-powered vacuum pumps to maintain UHV pressure.
The result? A portable UHV vacuum system that’s ultralight and nonmagnetic too.
Magnetic Permeability of Aluminum Versus Stainless Steel
Magnetic permeability (μ) is a measure of a material's ability to form a magnetic field within itself, indicating the ease with which a material can be magnetized. It is expressed relative to the permeability of free space (μ0), known as relative permeability (μr).
- Aluminum has a relative permeability very close to 1 (μr 1.000022), meaning it behaves nearly the same as free space and does not significantly distort or concentrate magnetic fields.
- Austenitic stainless steels (such as 304 and 316 stainless steel) have a relative permeability μr of 1.003 and 1.05 when fully annealed but may exhibit weak magnetism due to cold working (machining) and may also contain ferritic patches which have extraordinarily high permeabilities, particularly in welds.
- Ferritic and martensitic stainless steels (such as 410 and 430 stainless steel) are magnetic with significantly higher permeability values, typically μr above 100.
Even in applications that don’t require extraordinarily low magnetic permeabilities, aluminum is often a more practical choice because its permeability is not changed during machining and welding operations. Austenitic stainless steels have a crystal structure that can be disturbed by machining, forming or welding, causing the crystal structure to become martensitic in nature.
This martensitic form of stainless steel is ferromagnetic and can have a magnetic permeability in the range of µr ~1.5–10+. The paramagnetic properties of stainless can often be restored by annealing. However, the high temperature process can affect the dimensional stability and accuracy of machined features.
Applications of Aluminum in Magnetic-Sensitive Environments
Particle Physics: In electron/proton beamlines and accelerators, magnetic fields can deflect charged particle beams. Non-magnetic chambers help maintain beam stability and precision.
Quantum Physics: Experiments like electric dipole moment (EDM) measurements or searches for new fundamental particles require extreme magnetic shielding and non-magnetic environments.
Precision Metrology: Instruments like atom interferometers, laser gyroscopes, and gravitational wave sensors operate in vacuum and are extremely sensitive to magnetic disturbances.
Semiconductor Manufacturing: Because the circuits are drawn by an electron beam, which is easily influenced by magnetics, a non-magnetic vacuum environment is critical.
Satellite Instrument Calibration: Space-bound sensors, especially magnetometers, are often tested in vacuum. A non-magnetic environment ensures accurate calibration.
Atomic Clocks: Many advanced atomic clocks operate in vacuum and require non-magnetic environments to maintain precision.
Medical Equipment: Magnetic Resonance Imaging (MRI) and Nuclear Magnetic Resonance (NMR) machines and other imaging devices benefit from aluminum’s low interaction with magnetic fields.
Choose Aluminum for Critical Vacuum Applications
Compared to stainless steel, especially the martensitic grades, aluminum exhibits limited interaction with magnetic fields making it an ideal vacuum material. Additional benefits include:
- Low hydrogen and carbon contamination
- Good thermal conductivity and diffusivity
- Excellent outgassing performance
- Fast and complete bakeouts
- Easy machinability and fabrication
- Lightweight
By understanding the differences in magnetic properties between aluminum and stainless steel, engineers and designers can make informed choices for material selection in critical applications.
Let us help you with your next engineering challenge
Atlas Technologies is a fully integrated US-based facility with on-site design, development, testing and manufacturing capabilities. We specialize in aluminum and titanium vacuum chambers and bimetal components to help solve engineering challenges everywhere—from space missions to particle colliders to semiconductor fabrication. For more information, visit www.atlasuhv.com or email [email protected].