In titanium sublimation pump (TSP), companies usually use an alloy of Ti 85% - Mo15% to produce the filaments. Instead, can we use pure Ti to make the filaments with the same diameter?
my guess is that the Ti-15Mo alloy will be more durable when heated than pure Ti, because its melting point is slightly higher, as shown on the phase diagram
But, from this phase diagram, the difference is not big between pure titanium and the alloy to only depend on the alloy!
The selection of a titanium sublimation source is determined by the requirements for both pumping speed and throughput. If the system always operates in the UHV range, and the throughput of gas is small, then the simplest type of device and manual control will give adequate life even at high pumping speeds. Where the throughput is substantial, then a device capable of dispensing appropriate quantities of titanium, preferably with automatic control of the sublimation rate, may prove essential.
When the titanium is deposited on a surface at room temperature, it provides maximum pumping speeds of the order of 3 and 9 liter/sec.cm^, for hydrogen and oxygen, respectively. Cooling the titanium film to liquid nitrogen temperature increases the pumping speeds by a factor between 2 and 5, depending on the
gas. Higher pumping speeds can be easily achieved by increasing the area on which the titanium is deposited, but note that a larger surface area will necessitate an increase in the rate of sublimation to maintain the higher rate of pumping. The maximum pumping speed is obtained when the titanium surface is clean.
In practical applications, the surface will always be partially covered by an adsorbed layer, so the pumping speed will be only some fraction of this maximum value, determined by the frequency at which the surface is replenished by sublimation. For the case where the pressure is very low, and periodic sublimation is used, it is necessary to assume some effective pumping speed of the titanium, which is less than the speed for the clean film [30], say 20 to 30%.
The required area of titanium in a particular system can be calculated from the Equation
Titanium area = Q/P x 5 cm2
Where
Q is the estimated influx of gas from all sources, including outgassing and leakage, in torr liter/sec
P is the requires pressure, in torr
S is the gettering speed per square centimeter of titanium for the gas
being pumped
Particular care must be taken to assure that the conductance between the pump and the vacuum chamber does not seriously limit the effective speed of the pump.
The sublimator is mounted inside the vacuum chamber so that the sublimed titanium film is deposited on the chamber walls, or on baffle plates, positioned to protect the working volume of the chamber from titanium deposits.
I think you miss understood my question. I am asking about the material selection to produce filaments not the requirement of a TSP.
Recrystallization behavior will be different. Pure Ti might develop very fast large grains. Do you see any risks with that?
Possibly....they will be softer....may be single crystals....what is the diameter? What is the max. Temperatue and the time?
the diameter is 2 mm and it should work for 1:45 min with maximum temperature 1550 C (45-48 Amps as a filament current).
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