Vacuum: an Introduction to The Void of the Universe
Space has been a hot topic in recent weeks in the midst of Spacex’s successful launch of their Falcon 9 rocket, crewed by Bob and Doug aboard their Crew Dragon spaceship. While spaceships, space suits, and their related topics pique our interest, we here at Intlvac really perk up when the concept of vacuum comes up. A Latin term to describe 'The Void', the word 'Vacuum' is used to describe the boundless expanse of the cosmos. Yet while some work hard to get to it, we are adamant about bringing it to us. Let’s explore some of the basics and nuances of vacuum as a concept.
Vacuum can be defined as any particular volume with zero particles in it (or close to zero). That caveat is important, because the term vacuum is actually loosely defined. In most cases, having few enough particles in a given volume is ’good enough’ to be considered vacuum. This is true even in outer space. Particles are so few and far between that they become negligible. It’s actually impossible in practice to have a so-called ‘perfect vacuum’. Basically, even if every single atom was removed, which is as difficult as making a 100% pure material, neutrinos and photons would encroach upon the volume anyway.
Why does it interest us at Intlvac? Creating a vacuum environment is essential to cultivating the processes we and our customers conduct with our systems. Thin film coatings are micrometre, and often nanometre scale products. This means that they are very sensitive to small alterations and disturbances. Processes are precise to the atomic level. Likewise, testing and observation has to be able to pick up on the most minute changes. These main reasons obligate activities within this field to be performed under vacuum. It helps to standardize processes without the catastrophic fluctuations that the atmosphere would cause.
While experimental techniques fail at achieving the vacuum scale that outer space itself demonstrates which is about 1 proton/cm3, vacuum pumps can still arrive at impressive levels. The most Common pumps that are used to achieve this are cryopumps and turbomolecular pumps which can pump down to 10E-10 torr and 10E-11 torr respectively.
Cryopumps are as cool as they sound, freezing and condensing the air within the chamber, causing those particles to “stick” to the extremely cold plates. Turbomolecular pumps instead use a series of stacked blades to direct gas/fluid by exploiting the drag of the particles within imparting them with momentum. As the particles move through the stack, they reach the bottom where they are expelled.
We measure the atmosphere with the unit Torr, which is defined as the amount of pressure beyond the sea level equilibrium generated by 1 cubic mm of mercury. It was named after Evangelista Torricelli when he discovered vacuum by inverting a tube of mercury into an exposed basin filled with mercury. The atmospheric pressure pushing down on the exposed surface prevented the mercury within the tube from completely draining into the basin; essentially a barometer.
We arrive at the main challenge regarding high vacuum technology: what exactly is so difficult about removing particles from a volume? Why can’t you simply slap a pump to a chamber and tell it to pump down really quick? The answer is: outgassing. The truth is that removing the atmosphere from a volume doesn’t take particularly long, which is where the contributions from outgassing become a real problem. It describes the amount of gas leaving a surface area per unit time. While sublimation and evaporation are included within this, the real culprit is desorption, in which trapped particles simply expel themself from a surface as they please. Even pure and clean surfaces release trapped gases within their pores, which takes considerably longer to expel than if they were floating freely within the volume. Does this mean that almost all surfaces are ‘spongy’, with the means of trapping particles in them? Yes, it does.
While Bob and Doug’s mission sends them into the vacuum of space, Intlvac’s mission simulates the vacuum of space here on earth. This was a small look into the world of vacuum technology. Stay tuned as Intlvac dives deeper into this fascinating realm.
Photo source: Pixabay