AIST Stories No2

Impact in the following fields! Community life◦Apparel ◦Residential◦Household goods◦Information technology◦Eco products◦Environment, resources, energy◦IT and telecommunications◦Electronics◦Motor vehicles◦Materials◦ Medical welfare such as a denture and an artificial boneIndustryLeading the way AIST!3at a glanceTerminologybudget and started from a need for such technology but there was also interest from Akedo himself, a graduate in applied physics, who engaged in the development of a unique method for film-forming that entailed the layering of fine particles.Akedo tried a method that melted the fine particles and sprayed them in order to layer the fine metal oxide particles that form the ceramic material onto a substrate. In order for the fine particles to form a film on the substrate, they were deposited and sintered on a red-hot substrate or fused via heat from a plasma*2. However, the results weren’t quite as anticipated: the films peeled off or crumbled.Then one day during this time of trial and error, Akedo was cooling a substrate after an experiment and shutting down his apparatus when he mistakenly sprayed fine particles onto the substrate. “When I took a look, I saw some blackened residue had adhered to the edges of the substrate. It was dry and hard and wouldn’t crack even when I scraped it with sharp tweezers. This didn’t look like just residue. So what exactly was it? I felt that something just didn’t quite add up.”This was a trifling phenomenon that would have been so easy to overlook. Previously, Akedo had noted that a similar phenomenon had occurred occasionally but he hadn’t paid much attention to it. However, at the time he was coming to a dead end with his experiments so he decided to investigate what it was.If an organic substance had adhered, it should have melted at high temperature. However even after heating at 500–600°C overnight, the residue remained adhered to the substrate.“This certainly implied that ceramic particles had hardened at ambient temperature. I had a hunch that this was an important phenomenon and was in fact quite startled.” Akedo straight away used the same method to spray various ceramic particles onto substrates. He subsequently observed that other materials adhered to substrates at ambient temperature, forming hard films. This was the birth of an all-new coating technology called the Aerosol Deposition (AD) method for making ceramic films through the impact of collisions from spraying a mix of fine particles and gas.Does a ceramic solidify at room temperature?A groundbreaking discovery that confounds conventional wisdomStill, why do ceramic particles solidify in such a dense manner at room temperature? “I initially thought that the heat resulting from the collisions of fine particles with the substrate was enough to melt them. This is a common-sense explanation that can be derived from physics. Just like when cosmic dust is pulled by gravity to form planets, the energy from high-speed particle impacts heats up the particle surfaces and results in fusing. However, when I actually carried out measurements, in no way could I detect temperatures high enough to melt fine particles on the substrate surface. Whatever was happening, was happening at room temperature. Moreover, by raising the spraying velocity in order to raise the kinetic energy with the aim of *1 Piezoelectric thin film microactuator: A compact drive device that employs a piezoelectric material whose shape changes upon application of a voltage.*2 Plasma: Formed through electrical discharge in a gas, a gaseous state particle group that is comprised of positively charged particles (ions) and negatively charged electrons present in approximately the same ratio (electrically neutral) in ionized states.Aerosol deposition methodIn this technology, fine ceramic particles are mixed with gas and sprayed from a nozzle under reduced pressure. The resulting aerosol jet collides with the substrate and forms a film. Utilizing the room temperature impact consolidation phenomenon, dense, highly adhesive, and moreover hard ceramic films can be formed at room temperature on various substrate materials, including metal, glass and plastic. The rate of film formation is more than several tens of times faster than conventional thin film formation technology.▶ Transparent ceramic films can be fabricated at ambient temperature. This is an α-alumina (sapphire) film.▲ The film that forms on the substrate does not peel off even when scraped with sharp tweezers. NozzleCeramic filmSubstrateAerosol of fine ceramicparticles dispersed in a gasLarge area film forming viarelative oscillation of nozzleand substrateSpraying of aerosol containing fine ceramic particles