Fig. 1 – Evangelista Torricelli, Italian scientist, and mathematician (1608-1647)
Vacuum brazing involves the removal of all gaseous atmosphere from the sealed chamber of a “furnace” used for high-temperature brazing, a “furnace” being defined as any enclosure that can be heated to a high enough temperature to accomplish a specific task, such as heating a home, or heating an atmosphere to a temperature that can melt particular substances, such as a solder or a brazing filler metal (BFM), etc. By removing the atmosphere from a furnace during brazing, oxidation risks are eliminated (or greatly reduced), and brazing success is enhanced greatly. Thus, brazing in a vacuum furnace continues to gain popularity in the brazing world every day, because of its ability to “create a vacuum”, i.e., significantly reduce the amount of atmosphere (thus, oxygen), inside the brazing furnace. But — where did our understanding of vacuum come from?
One of the first practical experiments with vacuum was conducted by Evangelista Torricelli, an Italian scientist, back in 1643. Torricelli was a great thinker and put into action many of his theories related to both physics and mathematics. A portrait of him is shown above.
He was also an assistant to Galileo at one time, and it was Galileo who suggested to Torricelli that mercury (Hg) be used, rather than water, in some of Torricelli’s barometric experiments. Prior to this, Torricelli had used a long tube of water (about 10-meters/34-feet tall) in his experiments, but because mercury is about 14-times more dense than water, he could use a much shorter glass tube (only a little more than 1 meter long, about four-foot long) for his mercury-barometer experiments. When the glass tube (filled with mercury) was inverted in a dish, as shown in Fig. 1, Torricelli found that a sustainable vacuum (known as a “Torricellian vacuum”) was created in the sealed end of the tube after some of the mercury (Hg) drained out of the tube into the dish.