Particle processing technology

Abstract

In recent years, there has been strong demand for the development of novel devices and equipment that support advanced industries including IT/semiconductors, the environment, energy and aerospace along with the achievement of higher efficiency and reduced environmental impact. Many studies have been conducted on the fabrication of innovative inorganic materials with novel individual properties and/or multifunctional properties including electrical, dielectric, thermal, optical, chemical and mechanical properties through the development of particle processing. The fundamental technologies that are key to realizing such materials are (i) the synthesis of nanoparticles with uniform composition and controlled crystallite size, (ii) the arrangement/assembly and controlled dispersion of nanoparticles with controlled particle size, (iii) the precise structural control at all levels from micrometer to nanometer order and (iv) the nanostructural design based on theoretical/experimental studies of the correlation between the local structure and the functions of interest. In particular, it is now understood that the application of an external stimulus, such as magnetic energy, electrical energy and/or stress, to a reaction field is effective in realizing advanced particle processing[13].This special issue comprises 12 papers including three review papers. Among them, seven papers are concerned with phosphor particles, such as silicon, metals, Si3N4-related nitrides, rare-earth oxides, garnet oxides, rare-earth sulfur oxides and rare-earth hydroxides. In these papers, the effects of particle size, morphology, dispersion, surface states, dopant concentration and other factors on the optical properties of phosphor particles and their applications are discussed. These nanoparticles are classified as zero-dimensional materials. Carbon nanotubes (CNT) and graphene are well-known one-dimensional (1D) and two-dimensional (2D) materials, respectively. This special issue also includes two papers on the fabrication of mechanically reliable nanocomposites by dispersing graphene into a ceramic matrix, and on supercapacitors with high energy densities in a Co(OH)2 system decorated with graphene and carbon nanotubes. As a novel preparation method of oxide films, the fabrication of alumina films with laminated structures by ac anodization is reviewed. Moreover a new type of nanosheet has been fabricated by the exfoliation of layered, ternary transition-metal carbide and nitride compounds, known as Mn 11AXn phases (or MAX phases) where M is an early transition metal, such as Ti or Nb, A is an A group element, such as Si or Al, X is carbon and or nitrogen and n 113[4]. Among the MAX phases, those containing Mo have been theoretically calculated by first-principles calculations to be a source for obtaining Mo2C nanosheets with potentially unique properties. As an example of improving bulk ceramic properties, texturing by using a high magnetic field[5] and sintering by the electric current activated/assisted sintering (ECAS) technology[6] have been demonstrated for ultra-high temperature ceramics with high-temperature strength.A project on the development of materials and particle processing for the field of environment and energy has been ongoing at the National Institute for Materials Science since April 2011. This project employs various core competence technologies for particle processing such as ion beam irradiation for nanoparticle fabrication[7], fullerene nanomaterial processing using liquidliquid interface precipitation[8], a gas reduction nitridation process to obtain Si3N4-based phosphor materials[9], advanced phosphors via novel processing[10, 11], ultra-high pressure technology for processing and in situ analysis[12, 13], colloidal processing in a high magnetic field to obtain laminated, textured ceramics[1, 3, 5], the ECAS process for nanostructuring ceramics[6] and so forth. Here, I would like to introduce some research achievements that are not covered in this special issue.(1) The evolution of hydrogen by the reaction of fine metal particles such as Al[14] and Mg[15] with water; the specific surface area and surface modification are important factors.(2) The realization of new carbon related materials with 1D and 2D structures consisting of fullerenes prepared by liquid liquid interface precipitation: alkaline-doped superconductive nanotubes consisting of fullerenes[16], application to solar cells of fullerene/cobalt porphyrin hybrid nanosheets[17], etc.(3) The fabrication of textured films and bulk materials with excellent functional properties by colloidal processing methods such as slip casting[5], gel casting[18] and electrophoretic deposition[3, 19], in a high magnetic field, and with subsequent heating; examples of such materials include dye-sensitized TiO2 solar cells, thermoelectric materials and cathode materials for solid state Li-ion batteries and dielectric ceramics.(4) The fabrication of high-strength and high-toughness MAX phase ceramics[20, 21] inspired by the nacreous structure[22].(5) The modeling and development of the ECAS process[6]. This involves two-step pressure application[23] and high-pressure application above 400 MPa to fabricate transparent oxides[2426], and rapid heating to obtain dense nanocomposites of ceramic–CNT[27] and diamonds[28].(6) The contraction of ternary phase diagrams for oxide ion conductor systems such as zirconia[29] and apatite systems[30], leading to an increased understanding of the stability of such systems and assisting the search for high oxygen ion conductors.