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Atlas Technologies' Emissivac surface treatment creates highly polished aluminum surfaces that are UHV and XHV compatible. Our Emissivac Grade 3 finish holds an RMS level of <8 micro-inches and approaches a mirror-like finish on the interior walls of vacuum chambers.

Atlas Aluminum Emissivac UHV/XHV Surface Polish:

On its own, aluminum boasts superior thermal emissivity and outgassing rates when compared to stainless steel. Atlas Emissivac smooth, polished surfaces reduce surface irregularities, further reducing thermal emissivity and improving vacuum performance.

Aluminum is typically polished with compounds that are incompatible with UHV and XHV due to high outgassing rates. This can spoil the vacuum and present a source of contamination. An alternative application, electropolishing, doesn’t produce a reflective surface comparable to Atlas Emissivac. In short, Atlas Emissivac surfaces both radiate and absorb less heat than alternative methods.

Reduce Heat Transfer

Atlas Emissivac polished surfaces have a considerably lower thermal emissivity than both unpolished aluminum surfaces and polished stainless steel surfaces. Emissivac vacuum chamber surfaces can insulate the cold portions of cryostats and dewars. Emissivac is also utilized to minimize the heat loss from objects in vacuum.

Heat Flux radiated from hot surface absorbed by a colder surface:
Q = σƐA(Th4 – Tc4)
Q = heater transfer per unit time
σ = 5.6703 10-8 (W/m2K4) – The Stefan-Boltzmann Constant
Ɛ = emissivity
Th = hot body absolute temperature (K)
Tc = cold surroundings absolute temperature (K)

Emissivity (Ɛ) of Aluminum & Stainless Steel at 300K1:
Weathered Stainless: .85
Rough Aluminum: .07
Polished Stainless Steel: .075-.162
Polished Aluminum: .039-.057


Improve Vacuum Performance

At extreme and ultra high vacuum, surface irregularities begin to play a larger role in affecting the quality of vacuum chamber performance. The Atlas Emissivac process reduces surface irregularities on the micro-scale. As the unevenness of the surface becomes smoother, the microscopic surface irregularities (which affect thermal outgassing and diffusion rates) decrease as a factor (f), know as the Darcy friction factor. This factor f seems to influence the vacuum quality by about 1 order of magnitude from one extreme to the other. Atlas Emissivac surfaces approach a factor of 1, meaning an exceptionally smooth surface.

Ultimate pressure:
p∞ = Q/S = ((qT + qd)Af + Qh + QST )/S
p∞ = Ultimate pressure
Q = Total outgassing rate
S = Pumping speed
qT = Thermal outgassing per unit area
qd = Diffusion rate per unit area
A = Surface area
f = Surface roughness factor

Atlas Vacuum Surface Passivation:

Aluminum is produced with a heavy mill scale and a rough, porous oxide layer— a surface not well suited for vacuum because it absorbs water vapor and other contaminants. After removing this rough layer, Atlas cleans all metal surfaces before, during, and after completing the fabrication process. Atlas’ proprietary vacuum surface passivation process replaces thick, porous oxide layers with a quality thin and dense oxide surface. Treating aluminum in this manner effectively reduces surface area, contamination, and desorption.

Conventional Non-UHV Aluminum Surface Diagram

Conventional Non-UHV Aluminum Surface Diagram

Atlas Aluminum UHV Surface Passivation

Atlas Aluminum UHV Surface Passivation

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