The process developed in the lab of Rice chemist James Tour exposes a precursor to rapid heating and cooling to produce two-dimensional materials. The lab’s latest development produced pure boron nitride and boron carbon nitride, compounds that have been difficult to create in bulk and nearly impossible to produce in easily soluble form.
The lab’s report in Advanced Materials details how flash Joule heating can be modified to prepare purified, microscopic flakes of boron nitride with varying degrees of carbon.
According to Rice, experiments with the material showed boron nitride flakes can be used as part of an anticorrosive coating.
“Boron nitride is a highly sought 2D material,” Tour said in a statement “To be able to make it in bulk, and now with mixed amounts of carbon, makes it even more versatile.”
At the nanoscale, boron nitride comes in several forms, including a hexagonal configuration that looks like graphene but with alternating boron and nitrogen atoms instead of carbon. Boron nitride is soft and often used as a lubricant and as an additive to cosmetics. It is also found in ceramics and metal compounds to improve their ability to handle high heat.
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Rice chemical engineer Michael Wong recently reported that boron nitride is an effective catalyst in helping to destroy PFAS, a “forever chemical” found in the environment and in humans.
Flash Joule heating involves filling source materials between two electrodes in a tube and sending a quick jolt of electricity through them.
In experiments led by Rice graduate student Weiyin Chen, ammonia borane (BH3NH3) was placed into the flash chamber with varying amounts of carbon black. The sample was then flashed in under a second with 200V to degas the sample of extraneous elements and again with 150V to complete the process.
Microscope images showed the flakes are turbostratic with weakened interactions between them, making the flakes easy to separate. They’re also soluble, which led to the anticorrosion experiments. The lab mixed flash boron nitride with polyvinyl alcohol (PVA), painted the compound on copper film and exposed the surface to electrochemical oxidation in sulphuric acid.
The flashed compound reportedly proved over 92 per cent better at protecting the copper than PVA alone or a similar compound with commercial hexagonal boron nitride. Microscopic images showed the compound created “tortuous diffusion pathways for corrosive electrolytes,” to reach the copper, and also prevented metal ions from migrating.
The conductivity of the precursor can be adjusted also with iron or tungsten.
“Precursors that have been used in other methods, such as hydrothermal and chemical vapor deposition, can be tried in our flash method to see if we can prepare more products with metastable features,” Chen said. “We’ve demonstrated flashing metastable phase metal carbides and transition metal dichalcogenides, and this part is worth more research.”
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