Nanoparticles Find New Role in Process Control

New technique allows for restricting phase growth in advanced materials

Nanomaterials are different in many ways from their macro-scale counterparts. That’s why they are interesting and useful for new technology. Their unique properties also make it difficult to process them by conventional means. A new technique, however, actually uses  nanomaterials to control processing.

In a paper entitled, “Rapid control of phase growth by nanoparticles,” researchers at UCLA describe how the process works. “After phase nucleation, the nanoparticles spontaneously assemble, within a few milliseconds, as a thin coating on the growing phase to block/limit diffusion, resulting in a uniformly dispersed phase orders of magnitude smaller than samples without nanoparticles.”

The nanoparticles segregate to the surface and prevent coalescence, even under “harsh” conditions such as high temperature. This same general concept is actually used to create many types of nanoparticles which will agglomerate into larger particles quickly if not stopped by passivating them with  ligands, for example. In a bit of a plot twist, the particles are now serving in an analogous role to passivate larger phases.

As described in a related press release, the researchers examined the effect of nanoscale titanium carbonitride in the aluminum-bismuth system. Aluminum and bismuth are largely immiscible as they are cooled from the liquid state, and the two phases separate readily during processing (top of figure). To maintain a fine dispersion of bismuth (middle and bottom of figure), the nanoparticles were added to the molten mixture, ultrasonically dispersed and then segregated to the phase boundary during cooling which quickly suppresses the growth of bismuth nuclei.

The more uniform the dispersion of the immiscible phase is, the more uniform the properties will be. While the aluminum-bismuth alloys generated this way are useful for a variety of applications such as self-lubricating bearings, the concept goes beyond this alloy system and beyond alloys altogether.

This stabilization method can be applied to organic materials also, and the group demonstrated that methanol and cyclohexane could be treated similarly with boron carbide nanoparticles. This helps establish the universality of the technique. Many other materials (and associated technologies) may be aided by this approach as well.