Quartz glassware is the secret ingredient to many scientific experiments. It handles heat and cold without cracking, remains inert to most chemicals and does not interact with light, a quality that makes it perfectly transparent. It doesn’t change shape and remains hard when cold, but becomes flexible when hot.
“Fused quartz implies crystals, but it’s a misnomer,” says Thomas McNulty, a material scientist at GE Global Research and a quartz expert. “Even though it has distinct properties like crystalline solids, the material is actually amorphous.”
McNulty says that producers manufacture fused quartz by heating ultra pure silica sand to temperatures exceeding 3,600 degrees Fahrenheit, higher than the melting point of steel. “The silica looks like bright, white beach sand,” McNulty says. “There are only a few places in the world where you can get it, including here in the U.S. in North Carolina.”
Because of the material’s high melting point, workers use furnaces made from tungsten and graphite. The resulting mass of fused quartz contains amorphous chains of pure silica molecules which give the material its prized properties. Like a faithful couple, “silicon and oxygen really like to be bonded to each other,” McNulty says. “Because they are so strongly bonded, they have low reactivity with most other elements.”
McNulty says that the amorphous structure also allows the material to keep its shape even when it’s exposed to thermal shocks. Fused quartz’s so-called “thermal expansion coefficient” is 100 times smaller than in most metals. “You can keep one end cold and another hot and it won’t crack,” McNulty says.
Glass workers initially shape the material into tubes and other basic forms and ship them to labs for further processing. GE Global Research labs in upstate New York employ two full-time employees who shape the tubes into custom reactors for chemists, muffle tubes for clean room furnaces, beakers and other lab ware designed for specific experiments.
The wonder material does have an Achilles heel. “Anytime you nick its surface, it loses its mechanical properties rather quickly,” McNulty says. “It’s a technical, not structural material. We need lots and lots of tubes.”
That’s where Bill Jones (above) comes in. He has been making bespoke glassware at GE for 33 years. Jones straps the quartz tubes inside graphite chucks on a special glass lathe, heats them with a semi-circle of gas torches to 3,000 degrees Fahrenheit where the materials becomes viscous like caramel, and shapes it with graphite paddles to the desired form. “There is no school for this,” McNulty says. “You learn it in the shop environment. It’s a bit of art.”
Filed Under: Materials • advanced