Recent advances in aerosol generation of materials are reviewed Gas-to-particle and spray processes (spray pyrolysis) for powder generation and various routes for film generation are discussed from the experimental and theoretical perspectives The range of materials generated by these routes has increased in recent years to include fullerenes and ceramic superconductors Many metals and various oxide and nonoxide ceramics have also been added to the list of materials generated by gas-phase routes Established aerosol routes such as vapor condensation have found widespread applications for generation of nanophase materials The formation of quantum dots via aerosol approaches has also been demonstrated The theoretical understanding of gas-to-particle conversion routes has advanced to include the finite rate of particle fusion or sintering occurring after collisions of particles The modeling of spray pyrolysis systems has provided insight into the control of particle morphology and reactor design In th

https://www.tandfonline.com/doi/pdf/10.1080/02786829308959650

Aerosol Processing of Materials

In this overview, an attempt is made to assess the present and future research and development in thermal plasma processing of materials restricted to (1) thermal plasma coating technologies, (2) thermal plasma synthesis of fine powders, (3) thermal plasma waste destruction, and (4) thermal plasma spheroidization and densification. Since thermal plasma processing is, in general, governed by a large number of parameters, implementation of controls becomes mandatory. The lack of sufficient controls combined with economic drawbacks in some cases has been the main obstacle for the growth of thermal plasma technology. Present R&D efforts, however, address these problems.

Thermal Plasma Technology: Where Do We Stand and Where Are We Going?

Gel-glasses of various compositions in the xZrO 2 .(10-x)SiO 2 system were fabricated by the sol-gel process. Precipitation due to the different reactivities between tetraethyl orthosilicate (TEOS) and zirconium(IV) n-propoxide has been eliminated through the use of 2-methoxyethanol as a chelating agent. Thermal treatment of these gels produced crystalline ZrO 2 particles. While monoclinic is the stable crystalline phase of zirconia at low temperatures, the metastable tetragonal phase is usually the first crystalline phase formed on heat treatment. However, stability of the tetragonal phase is low, and it transforms to the monoclinic phase on further heat treatment. In this study, it has been found that the transformation temperature increases as the SiO 2 content in the ZrO 2 -SiO 2 binary oxide increases. The most significant results were from samples containing only 2 mol% SiO 2 , where the metastable tetragonal phase formed at low temperatures and remained stable over a broad temperature range. X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy were used to elucidate the structure of these binary oxides as a function of temperature.

Stabilization of Tetragonal ZrO2 in ZrO2–SiO2 Binary Oxides

Metastable tetragonal ZrO2 phase has been observed in ZrO2–SiO2 binary oxides prepared by the sol–gel method. There are many studies concerning the causes of ZrO2 tetragonal stabilization in binary oxides such as Y3O2–ZrO2, MgO–ZrO2, or CaO–ZrO2. In these binary oxides, oxygen vacancies cause changes or defects in the ZrO2 lattice parameters, which are responsible for tetragonal stabilization. Since oxygen vacancies are not expected in ZrO2–SiO2 binary oxides, tetragonal stabilization should just be due to the difficulty of zirconia particles growing in the silica matrix. Furthermore, changes in the tetragonal ZrO2 crystalline lattice parameters of these binary oxides have recently been reported in a previous paper. The changes of the zirconia crystalline lattice parameters must result from the chemical interactions at the silica–zirconia interface (e.g., formation of Si–O–Zr bonds or Si–O− groups). In this paper, FT-IR and 29Si NMR spectroscopy have been used to elucidate whether the presence of Si–O–Zr or Si–O− is responsible for tetragonal phase stabilization. Moreover, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy have also been used to study the crystalline characteristics of the samples.

Chemical Interactions Promoting the ZrO2 Tetragonal Stabilization in ZrO2–SiO2 Binary Oxides

Submicron sized ceramic particles are produced by combining a ceramic precursor with an organic or carbonaceous carrier material, and exposing droplets of the mixture to a temperature sufficient to cause combustion of the organic material and subsequent vaporization and nucleation, or diffusion and oxidation, of the ceramic precursor to form pure, crystalline, uniform nanophase ceramic particles.

Process for producing nanoscale ceramic powders

Ultrafine powders of the ZrO2-SiO2 system prepared by spraying aqueous mixed solutions of ZrO(NO3)2·2H2O and silicone oil into an ultrahigh temperature inductively coupled plasma (the spray-ICP technique) have been investigated in connection with particle growth and phase change caused by heat treatment. The prepared powders were composed of roundish ultrafine particles 10 to 20 nm in size, and their components were tetragonal ZrO2 (t-ZrO2) and amorphous SiO2 (a-SiO2).a-SiO2 alone did not crystallize below 1400° C, though the particles grew above 900° C.t-ZrO2 converted to monoclinic ZrO2 (m-ZrO2) above 400° C, also followed by particle growth. On the other hand composite powders oft-ZrO2 anda-SiO2 exhibited no particle growth below 1200° C. Above 1200° Ct-ZrO2 converted tom-ZrO2, and its amount decreased with an increase in SiO2 content. At 1400° C particle growth occurred, and the round particles of ZrO2 were dispersed in ana-SiO2 glass medium. These results indicate that ZrO2 and SiO2 mutually block particle growth, and that SiO2 contributes to the quenching oft-ZrO2 by keeping the particles of ZrO2 within the critical particle size oft-ZrO2.

Ultrafine particles of the ZrO2-SiO2 system prepared by the spray-ICP technique

Ultrafine powders of a trnary oxide system, Ba−Pb−Bi−O, were prepared by spraying aqueous mixed solutions of Ba(NO3)2, Pb(NO3)2, and Bi(NO3)3 into an argon inductively coupled plasma of ultrahigh temperature above 5000 K (the spray-ICP technique). Phases of the powders were largely dependent on the powder collectors enclosing the tail flame and its successive gas flow. In the water-cooled collector, mixtures of amorphous and crystalline materials were formed. In the collector where the gas flow was spontaneously maintained at about 550°C by ICP itself, ultrafine BaPb1−xBixO3 (BPBO) 10–40 nm in particle diameter was obtained. The BPBO thus obtained had a few wt.% of water and carbonate. They were lost by heat treatment up to 550°C, and a single-phase BPBO was formed. The as-prepared BPBO (x=0.25) showed no superconducting transition down to 1.5 K, but the one having a particle diameter of ∼ 1 μm formed by heating the as-prepared BPBO up to 1000°C had a superconducting transition temperature at 11.3 K.

Ultrafine BaPb1-xBixO3 powders prepared by the spray-ICP technique

Shock loading effect on the hexagonal δ-MoN prepared by nitriding metal molybdenum in ammonia gas was investigated. δ-MoN decomposed to form γ-Mo2N with increasing shock pressure. The porosity of the specimens showed no effect on the amount of the formed γ-Mo2N, indicating that the decomposition reaction is predominantly due to the pressure effect at shock compression. The specimens shocked to 39 GPa had new Tc's at 5.8 and 5.0 K besides 13 K of δ-MoN. At 50 GPa δ-MoN converted to γ-Mo2N completely and the lattice constant of γ-Mo2N became smaller, thus implying the release of nitrogen. No B1 type MoN was observed up to this pressure region.

Shock-Loading Effect on Molybdenum Nitride Prepared in Ammonia Gas

In recent years, development of a next generation high-density recording system has attracted an increasing attention with the improvement of the storage density One of the attractive technologies to overcome the limit of the storage density is near-field optical data storage The optical memory with high density and high data transfer rate is highly demanded to utilize an array of nano-scaled light sources for writing and reading bits formed on a recording medium We have fabricated a micro-translation-table to convey the recording medium to the near-field optical head The proposed micro-translation-table consists of the inverted scratch drive-actuators (SDAs) which are electrostatically driven The inverted SDA is powerful and precise due to the stepwise movement A long distance translation is achieved by repeating the stepwise movement Fast moving speed, high response and the positioning resolution of the order of 1 nanometer are possible The inverted SDA has been fabricated with silicon surface micromachining technology We have proposed a novel mechanism that the SDAs can be retracted to a substrate by applying the voltage between the SDA and a lower electrode Therefore, the SDAs used for the conveyance are stretched and others are retracted We have observed that a micro object is translated with the fabricated actuators by applying AC voltage of 600 V at 100 Hz

Fabrication of high accuracy micro-translation-table for near-field optical data storage actuated by inverted-scratch-drive-actuators

Micromachining is an extended IC fabrication based on photo-fabrication, deep etching, anodic bonding and other advanced process technologies This is used to produce MEMS (Micro Electro Mechanical Systems) featuring multi-functions, small size and low cost Nanostructures such as CNT (Carbon Nano Tube) can be also included in the MEMS by nanomachining MEMS are used as value added key components in systems Examples of application oriented MEMS developed with attention to packaging and circuit integration will be described below Silicon rotational gyroscope has been developed for the purpose of motion control and navigation The principle and the photograph are shown A 15 mm diameter silicon ring which is electrostatically levitated by digital control using capacitive position sensing and electrostatic actuation is rotated at 75,000 rpm The rotation is based on the principle of a variable capacitance motor A 5mum radial gap between the ring rotor and stator electrodes is formed using deep RIE (Reactive Ion Etching) of a silicon wafer The silicon is anodically bonded on both sides to glasses which have electrodes The chip is packaged in a vacuum cavity to prevent a viscous dumping This inertia measurement system can measure two axes rotation and three axes acceleration simultaneously with high precision (sensitivity 001 deg/s and 02mG respectively)

T. Ono

Papers

Ultrafine particles of the ZrO2-SiO2 system prepared by the spray-ICP technique

Ultrafine BaPb1-xBixO3 powders prepared by the spray-ICP technique

Shock-Loading Effect on Molybdenum Nitride Prepared in Ammonia Gas

Fabrication of high accuracy micro-translation-table for near-field optical data storage actuated by inverted-scratch-drive-actuators

Application Oriented Micro-Nano Electro Mechanical Systems