HYDROFLUORIC ACID IS HISTORY

Sometimes a challenge can turn into a number of benefits. Heraeus Noblelight in Alzenau had been using hydrofluoric acid in the production of UV lamps. Because the highly corrosive substance presents a risk for employees and the environment, an interdisciplinary team searched for—and found—a better solution.

Acid Source: Herbert Naujoks, Stuttgart

Chemically speaking, quartz glass is a particularly durable material—it can withstand major fluctuations in temperature, allows UV radiation through, and has a high dielectric strength. These characteristics are highly prized by Heraeus Noblelight production in Alzenau, as quartz glass tubes are used as lamp bodies in the manufacture of UV lamps. But because the outer layer still may have a certain degree of impurities, the tubes must be cleaned before they can be used, which is a real challenge with such a resistant material.

Heraeus Noblelight previously only had one option for this, hydrofluoric acid (an aqueous solution of hydrogen fluoride). “Hydrofluoric acid is so corrosive that it etches away the top layers of the quartz glass, removing even the smallest impurity,” says Andreas Adam, a production engineer at Heraeus Noblelight. “Of course that also makes it an enormous safety risk.” Hydrofluoric acid is a contact poison and can be fatal even after a palm-sized chemical burn. Production has comprehensive security procedures to prevent serious accidents, but near accidents or even minor injuries cannot be ruled out when dealing with such a corrosive substance, according to Adam.

Something new on the horizon

Not only is hydrofluoric acid a potential danger to employees involved in the production process, but it also presents a risk to people and the environment when the waste acid is transported to the plant in Kleinostheim. A better solution had to be found. “Part of our job in Production Engineering is to question the status quo,” says Adam. “Just because something has always been done in a certain way, doesn’t necessarily mean that it’s good.” He and his coworker Martin Röhling began looking for an alternative to hydrofluoric acid. “We built a cross-functional team and banded together with some of our colleagues from Heraeus Quarzglas,” says Röhling. “Their expertise has been a big help to us.”

First they performed numerous tests using different types of cleaning agents. It quickly became clear that a single cleaning agent would not be sufficient. That’s how ultrasound came into play—it generates high-frequency sound waves that augment cleaning power. It took about nine months of testing until a suitable cleaning agent was found, the process combined with ultrasound and optimally adapted to the needs of the Heraeus Noblelight production.

Sustainable on all levels

“This intensive project also afforded us the opportunity to get to know and understand our production process better,” says Adam. Hydrofluoric acid is so corrosive that Production never had to think about the level of cleanliness that was actually needed.

This broad expertise then flowed into the development of the system needed for the new cleaning process, which is scheduled to be delivered and put into operation in fall 2019. The use of hydrofluoric acid will then decrease by about 95 percent. In addition, the fully automated cleaning process means that employees no longer have contact with the quartz glass tubes, which reduces the risk of cuts. Employees will no longer have to wear heavy protective clothing, and not as much training will be needed.

In addition to the obvious advantages for occupational safety, the new system will help protect the environment: waste acid will no longer be transported, and the system is smaller and uses less water. An additional drying process was integrated, reducing production time. Overall, the company is gaining an advantage over the competition while also saving about €120,000 per year.