Aluminum Vacuum Chambers
Atlas Technologies specializes in aluminum vacuum chambers. Our research confirms that aluminum is a superior vacuum material to stainless steel for many applications. Take a look at the information below, and you'll see why the high and ultra high vacuum industry is rapidly embracing this versatile material.
For most applications, aluminum is a superior UHV chamber material, with 10,000,000x (7 orders of magnitude) less hydrogen permeation than stainless steel. Consequently, aluminum chambers have far less H2, H2O, and hydrocarbon vapor at HV and UHV levels. In addition, aluminum has less carbon contamination than stainless steel, and this reduces the amount of carbon-based gas contamination in vacuum.
Atlas manufactures UHV aluminum chambers with a thin, dense aluminum oxide coating. This serves as a resistive barrier, reducing diffusion and desorption of HV and UHV contaminates (hydrogen, oxygen and carbon). Once baked, Atlas’ aluminum vacuum chambers typically cycle to HV and UHV levels faster than stainless steel chambers and require less pumping.
Consider the superior vacuum properties of aluminum:
- 7 orders of magnitude less H2 than stainless for ultra pure vacuum
- Less carbon for reduced contamination
- 10x the thermal conductivity and 21x the thermal diffusivity for efficient bake outs and unmatched thermal performance
- Outgassing rates of less than 1 x 10-13 Torr liter/sec cm2 (suitable for extreme high vacuum)
- High resistance to a variety of chemicals
- The option to be anodized for electrical or chemical resistance
- Low Z (low nuclear activation) for less residual radiation
- Non-magnetic for applications that require it
- High vibration dampening (low Young’s modulus) for increased absorption
- 1/3rd the weight for superior manageability
- Lower material and operations cost for an improved bottom line
- Machinability up to 10x faster than stainless steel for lower manufacturing costs
The following physical properties of aluminum describe why it is an excellent vacuum material:
Outgassing Properties
One of the most important properties of a vacuum material is the outgassing rate as this determines the ultimate pressure that may be obtained in the vacuum chamber. Repeatable outgassing rates of <1 x 10-13 Torr liter/sec cm2 are attainable in aluminum UHV systems, comparable to the best outgassing rates obtainable with stainless steel. This improvement in outgassing performance makes aluminum a competitive material for the construction of UHV systems.
Thermal Conductivity
Depending on the alloy, aluminum’s thermal conductivity ranges between 170 W/mK and 230 W/mK. Stainless steels, by contrast, have thermal conductivities that are between 14 W/mK and 16 W/mK, so aluminum’s thermal conductivity is roughly 10x that of stainless steel. High thermal conductivity is an advantage when designing systems that require temperature cycling. This is the case for vacuum systems that must be baked to reach UHV levels. An aluminum chamber may be baked and then cooled much more rapidly than a stainless steel chamber. In addition, aluminum's high conductivity allows a complete bakeout without re-condensation of gases on local cool spots, a common problem in stainless steel systems.
Due to aluminum’s superior thermal conductivity, aluminum vacuum chambers:
- bake more uniformly even at lower temperatures (150 C).
- bake-out faster - aluminum chambers need only bake at 150 C for 24 hours to obtain the same level of baking as stainless at 250C for 48 hours
Weight
Aluminum is roughly 1/3 the weight of stainless steel (2.8 g/cm3 [Al] vs. 8.0 g/cm3 [stainless steel alloys]). The cost burden associated with excess weight begins when the raw materials are handled and progresses throughout the manufacturing process. It affects all production steps, including shipping, installation, and even the architectural engineering and construction of the environment surrounding the chamber.
Magnetic Properties
Aluminum is not magnetic, whereas stainless steel, being essentially an alloy of iron, exhibits residual magnetism. The absence of magnetic properties in aluminum is advantageous for applications involving charged particle beams because the vacuum chamber will not modify the fields created from the beam control magnets.
Radioactivity
Aluminum has a more rapid (better) decay of induced radioactivity than stainless steel. If both materials are bombarded with the same flux of charged particles, the residual radioactivity will typically be one to two orders of magnitude less for an aluminum sample than for an identically shaped stainless steel sample. The nuclear half-life of elements that make up stainless steel suggests that alpha-particle contamination is always present in stainless steel and a possible source of circuit damage.
Corrosion
The corrosion of both aluminum and stainless steel alloys in reactive gasses is complicated. Experimental work performed on various alloys in different reactive gaseous environments shows that both aluminum and stainless steel are subject to attack by reactive gasses. Halogen containing samples are typically the most damaging, and the corrosion of any given compound is usually no worse than that of its halogen component alone.
Aluminum is no worse with regard to corrosion than stainless steel. It simply has different reaction dynamics that do not serve as a source of iron and nickel contamination, one of the most significant yield-limiting factors for silicon IC production.
The special properties of aluminum make it the clear choice for many applications. Aluminum chambers can be dependably sealed with conventional CF flanges using Atlas CFBI and ATCR bimetallic flanges found in our standard fitting and flanges sections.
Atlas aluminum vacuum chamber production techniques, chamber configurations, or combinations thereof, employed by Atlas include:
HOW CAN WE ASSIST IN YOUR PRODUCT DEVELOPMENT NEEDS?
From our first custom aluminum vacuum chamber, to our recent niobium to stainless steel fittings for satellite delivery rockets, to our standard bimetal and titanium flanges and fittings, Atlas Technologies has been the solution of choice for mission critical projects around the world. Whether you have a rough sketch, a full-fledged design, or just need a handful of our US-manufactured bimetal products, we can help.
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