From Air Pump to Ultra-High Vacuum How the Vacuum Becomes the Pacemaker for High-tech
Evacuated space is a good place for research and manufacture. It has been a long journey though from a philosophical question in ancient times to today’s significance of the vacuum. It was Wolfgang Gaede who in the early 20th century laid the foundation for modern vacuum technology with his molecular pump.
Many modern analytics and production methods would not work without a vacuum. This insight is more important for today’s researchers, engineers and analysts in a wide variety of industries than the philosophical ponderings of ancient times whether “nothingness” exists. Strictly speaking, this question has still not been answered. The idea of an empty space (“vacuus” in Latin, meaning empty) in which the smallest particles move, was already a prominent part of the Epicurean world view. It was also highly controversial. “Vacuum sealed” products, like food in vacuum packaging, are in fact far removed from true “emptiness” and do not even achieve a low vacuum. More convincing were the experiments of Blaise Pascal and Otto von Guericke, the two great 17th century inventors, who made the idea of a vacuum respectable. Pascal's attempt regarding “Emptiness in emptiness” (in French “vide dans le vide”), but even more so the so-called Magdeburg hemispheres, in which von Guericke's simple piston pump generated negative pressure, as vividly demonstrated by the force of two teams of horses, made the existence of the vacuum plausible and disproved the idea of the “horror vacui”, nature’s supposed resistance to emptiness.
Von Guericke’s scientific curiosity in retrospective
Von Guericke’s experiment is with good cause still considered emblematic of scientific curiosity to this day. But his hemispheres would probably already have been forgotten had the vacuum not become so particularly important for modern technology.
As a matter of fact, for analytics, process engineering and many manufacturing techniques, vacuums are as essential as electricity - and ideally as readily available, at least as far as low vacuums (300 – 1 hPa), fine vacuums (1 – 10-3 hPa) or high vacuums (HV) (10-3 – 10-7 hPa) are concerned. For laboratories and factories, a loss of vacuum can be as devastating as a power outage. Therefore, today’s vacuum generation technology must above all be reliable in two respects: Users expect that they can quickly and easily generate a vacuum at any time and also increasingly that said vacuum is defined pure. When generating high and ultra-high vacuums (UHV) with a pressure of less than 10-7 hPa or between 1000 and 10 billion particles per cubic centimetre, a mechanical backing pump (like a slide vane rotary pump or a diaphragm pump) is first used to generate negative pressure. After this pre-evacuation, more powerful pumps are employed. For a long time, diffusion pumps used to be the first choice. Just like jet pumps, they work with a propellant, now usually a mineral or silicone oil, that is vaporised. Gas molecules diffuse through the oil vapour flowing from the nozzles system, and thus into an area outside of the evacuated body, where they are pumped out by the backing pump. Depending on the propellant’s vapour pressure, this method achieves ultimate pressures of up to 10-9 mbar.
Professor Gaede – A pioneer of vacuum technology
The first such diffusion pumps were operated with mercury. Their invention is attributed to physicist Wolfgang Gaede, today considered a pioneer of vacuum technology. He introduced a rotating mercury pump as early as 1905. Shortly after, he received a consulting contract from Cologne-based company E. Leybold’s Nachfolger - a collaboration that would prove highly significant for the company founded by merchant Martin Kothe in 1850. After the founder’s death, the company was acquired by the then 27-year old Ernst Leybold in 1851. Besides wine trading, the company also supplied pharmacies with medical containers and equipment. In 1859, Leybold promised in its catalogue that it would deliver all pharmaceutical, chemical, physical, mathematical and technical products not yet listed in the catalogue or yet to be invented precisely according to specifications or drawings and “as quickly and cheaply as possible.” So it probably safe to assume that Ernst Leybold was/had been very open to new inventions. At first, Leybold obtained all equipment from nearby craftsmen, until in 1867, he finally started his own production of scientific equipment in the centre of Cologne (Schildergasse). In the following years, schools and universities became important customers for the company's physics equipment. At the dawn of the 20th century, Leybold & Kothe had become E. Leybold’s Nachfolger (E. Leybold’s Successors) and was led by the Schmidt family. The company focused on physics equipment, laboratory furniture and power systems for universities, government agencies and other institutions. In 1906, the owner read a publication in the “Physikalische Zeitschrift” (Physical Journal) about a young physicist named Dr. Wolfgang Gaede. At that time, Gaede was already in negotiations with AEG and Siemens,
but E. Leybold’s Nachfolger agreed to his demand of a 25% licensing fee and thus secured not only the exclusive right to manufacture Gaede’s rotating mercury pump. The physicist would also have a huge impact on the future of the company. He constructed various other vacuum pumps and intensely worked in high vacuum research. At pressures where the mean path length of the remaining molecules matched the dimensions of the container, so that molecules would no longer collide, the traditional principles of physics no longer applied.