Precisely measuring and observing the properties of new materials requires samples of the purest crystal form of the compound that can be achieved. While there are many methods of producing crystals of new compounds, solution growth is one of the best for discovery and characterization. When compounds have two, three, four or more elements that don’t all solidify at the same temperature, extracting solid crystal compounds out of them can be a challenge; that’s where solution growth comes in. The process also requires crucibles— the heat-resistant ceramic containers in which the elements of the desired compound are combined, heated and then cooled to produce a crystal, and spun to separate the newly formed crystal from remaining liquid elements. It was with these small cups and filters that one of Ames Laboratory’s materials experts, Paul Canfield, a condensed matter physicist, felt improvements could be made.
In a traditional solution growth experiment, elements are combined in a growth crucible, and topped with a second crucible filled with silica wool, which will act like “a coffee pot with a filter,” said Canfield, straining the liquids from the solids. The entire capsule is then sealed in a glass tube and placed in a furnace for heating and slow cooling. After the temperature is lowered, allowing the desired crystal to form, the assembly is then placed in a centrifuge, which spins any remaining liquid off into the catch crucible with the silica wool separating solid crystals from the remaining liquid metal. Whereas silica wool has worked well enough over the decades, it has several problems associated with its use as a filter material. An additional problem with the use of two crucibles and silica wool was the fact that the two crucibles were not physically attached or secured to each other. This could, in certain cases, lead to leakage of liquid or vapor during growth or separation steps.
The role of Ames Laboratory
With these concerns in mind, Canfield set about to design a better strainer, a single ceramic disc with holes (called a frit disc) that could be fitted in between the two crucibles. He reached out to LSP Industrial Ceramics, which offers custom-designed lab ceramic supplies. “Dr. Canfield came up with a design and asked me if it could be made,” said Frank Smith, CEO of LSP Industrial Ceramics. “We made a few changes to make it easier to produce, but it was his plan. We made it come to life.” While some initial attempts at threading the two crucibles together with the disc were successful, the item was very expensive to make, and the threads made the assembly difficult to take apart after the separation step. Canfield instead settled on a simple design of a step-edged disc between the two crucibles, so they nestled into each other and, if packed properly into the silica tube, would not misalign or shear apart in the centrifuge.
Canfield was so pleased with the performance of this new crucible design that he encouraged LSP to offer the crucible sets to other researchers who might want them. “I told him if this works, I’m pretty sure all of my friends and colleagues are going to want to use these,” said Canfield. When it came to naming the new item, “I told him that if Erlenmeyer could have his flasks, then Canfield could have his crucibles.” And so the Canfield Crucible Set was born.
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