Multifunctional dream ceramic matrix composites are born!
Osaka University scientists produce tough ceramic matrix composites that exhibit electrical conductivity and photocatalytic activity
Researchers at Osaka University produced composites consisting of alumina (Al 2 O 3 ) ceramics and titanium (Ti), namely Al 2 O 3 /Ti composites. They designed a percolation structure for forming a continuous conduction pathway by dispersing fine-sized Ti particles into an Al 2 O 3 matrix, optimizing the particle size of metallic Ti powder and sintering processes. They improved fracture toughness and electrical conductivity of Al 2 O 3 /Ti composites while simultaneously giving them photocatalytic ability through chemical and/or thermal treatment. (Figure 1)
Various types of metal-ceramic composites have been researched and developed, but their combination and fine structures were limited. In particular, the combination of ceramics such as alumina used as matrices and titanium, a biocompatible metal, has a problem in that the structure of composites is not uniform because of the high reactivity of titanium (oxidation happens and chemical compounds are produced) and the large particle size of commercially-available Ti powder (several tens of micrometers). Thus, it was difficult to produce composites that have advantages of both ceramics and metal: that is, composites in which metallic Ti powder is homogeneously dispersed in the matrix and has excellent mechanical properties.
The group prepared ball-milled titanium hydride (TiH 2 ) fine powder mixed with alumina powder, producing Al 2 O 3 /Ti composites using a method based on the in situ decomposition of TiH 2 to Ti and simultaneous sintering with Al 2 O 3 , which process inhibited Al 2 O 3 dissolution into Ti by diffusion through interfacial reaction between Al 2 O 3 and Ti during sintering. As a result, they minimized reactivity of Ti and Al 2 O 3 to disperse significantly finer and more homogeneous Ti (compared to those produced with conventional methods) in Al 2 O 3 , realizing composites with a percolation structure by controlling the content of added Ti.
In this way, the group improved fracture toughness of inherently brittle Al 2 O 3 through dispersion of fine Ti particles into Al 2 O 3 and, due to percolation of metallic Ti particles, contributing electrical conductivity to insulator ceramics Al 2 O 3 . They also demonstrated that Al 2 O 3 ceramics could be machined by electrical discharge machining like metals. (Usually, ceramics are not electrically conductive.) In addition, they formed a nano-porous- or nanorod- structured titania layer on the surface of the composite by selectively oxidizing Ti via NaOH treatment and/or heat treatment. Through this, they demonstrated that the photocatalytic ability to break down organic substances could also simultaneously be given to Al 2 O 3 /Ti composites.
Group leader Tohru Sekino says, “Al 2 O 3 /Ti composites will be used as ceramic matrix composites that have excellent mechanical properties and can be machined by electrical discharge machining. They will also be used for industrial products and biomaterials as new multi-functional composites that have an active surface layer with antibacterial properties and a photocatalytic ability to break down pollutants.”
(Upper left) Structure of Ti-dispersed Al 2 O 3 composites
(Lower left) Ti content dependency of fracture roughness and electrical resistivity
(Middle) Nanostructure of the surface of Al 2 O 3 composites produced via chemical and heat treatments
(Right) Discolored by the photocatalytic activity of Al 2 O 3 composites after chemical and heat treatments
The article, "Surface-morphology modification of ceramic-based composites for photocatalytic activity via simple chemical and heat treatments," was published in Journal of the Ceramic Society of Japan at DOI: https://doi.org/10.2109/jcersj2.18119 .
The article, "Formation of vertically grown 1D TiO2 nanorods on the surface of Al 2 O 3 /Ti composites by simple heat treatment and their photocatalytic performance," was published in Journal of the Ceramic Society of Japan at DOI: https://doi.org/10.2109/jcersj2.18133 .
The article, "Combinative effects of Y 2 O 3 and Ti on Al 2 O 3 ceramics for optimizing mechanical and electrical properties," was published in Ceramics International at DOI: https://doi.org/10.1016/j.ceramint.2018.07.054 .
The article, "Fine Ti-dispersed Al 2 O 3 composites and their mechanical and electrical properties," was published in Journal of the American Ceramic Society at DOI: https://doi.org/10.1111/jace.15472 .