Atlas Technologies introduces a process that generates highly polished aluminum surfaces that is UHV and Extreme High Vacuum (XHV) compatible. 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.
On its own, aluminum boasts superior thermal emissivity and outgassing rates when compared to stainless steel. Atlas Emissivac smooth polished surfaces reduce surface irregularities and further enhance thermal emissivity and improve vacuum performance.
Typically, aluminum is polished with compounds that are incompatible with UHV and XHV due high out-gassing rates which spoil vacuum and present a source of contamination. An alternative application, electro-polishing, doesn’t produce the shine or reflective surface comparable to Atlas Emissivac. In short, Atlas Emissivac surfaces radiate and absorb less heat than the alternative application.
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 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 surface1:
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 quality of vacuum 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. This factor f seems to influence the vacuum quality by about 1 decade from one extreme to the other. Atlas Emissivac surfaces approach a factor of 1.
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
2, P.A. Redhead, http://www.chem.elte.hu/departments/altkem/vakuumtechnika/CERN17.pdf