Table of contents

The mechanism of formation and growth of calcium carbonate (CaCO₃) nanoparticles by bubbling carbon dioxide in aqueous suspensions of calcium hydroxide was investigated using time-resolved in situ synchrotron small-angle X-ray scattering (SAXS) and transmission electron microscopey (TEM). In situ SAXS showed a significant change in the particles size in the primary reaction. This suggests that the nucleus forms CaCO₃ at in this period. After the nucleation, the crystal grow with the reaction time to yield 40 nm CaCO₃ nanoparticles. TEM showed fibrous or chain-like intermediates formed by aggregation of fine particles of CaCO₃ as calcite. We propose that CaCO₃ crystal nuclei generated in the primary reaction grow to yield fibrous or chain-like CaCO₃ which then separates into individual particles to form CaCO₃ nanoparticles.

Two of the major problems related to nanoparticle dispersion with a conventional beads mill are re-agglomeration and damage to the crystalline structure of the particles. The Ultra Apex Mill was developed to solve these problems by enabling the use of ultra-small beads with a diameter of less than 0.1mm. The core of this breakthrough development is centrifugation technology which allows the use of beads as small as 0.015mm. When dispersing agglomerated nanoparticles the impulse of the small beads is very low which means there is little influence on the particles. The surface energy of the nanoparticles remains low so the properties are not likely to change. As a result, stable nanoparticle dispersions can be achieved without re-cohesion. The Ultra Apex Mill is superior to conventional beads mills that are limited to much larger bead sizes. The technology of the Ultra Apex Mill has pioneered practical applications for nanoparticles in various fields: composition materials for LCD screens, ink-jet printing, ceramic condensers and cosmetics.

This paper overviews recent studies on structural modification of metal oxide nanoparticles occurring in the process of chemical vapour condensation (CVC) and related peculiar properties. Hollow nanostructure is controlled at specific process conditions where the pressure in the reactor and the evaporation temperature play an important role in terms of kinematical equilibrium during particle formation and decomposition of precursors in the CVC reactor. As a natural consequence, particle properties also rely on a large surface area from the hollow nanostructure. In this review paper, phase transformation, chemical reactivity and microstructural evolution of nanoparticles are discussed based on hollow nanostructure.

A rich chemistry of ternary graphite intercalation compounds (GICs) containing alkali metal cations and amines or polyamines has been developed recently in our labs. Monolayer and bilayer structures for a range of amines and polyamines, including hexylamine, 1,2-diaminopropane, and diethylenetriamine, have been prepared chemically as stage 1 or 2 GICs. While these and related intercalates have been studied in detail with other layered host structures, there have been few reported analogs in graphite chemistry. However, our recent results indicate that under appropriate synthetic conditions the intercalation of amines into graphite may be comparable to that of other layered hosts, and may lead to an alternate chemical route to graphenes. The synthetic strategies employed and the structural and compositional details of the graphite intercalation compounds recently obtained (from XRD, NMR and thermal analysis) will be described.

Nematic and isotropic aqueous suspensions of beidellite clay sheets have been submitted to magnetic and a. c. electric fields. The nematic suspensions have positive anisotropy of magnetic susceptibility and negative anisotropy of electric susceptibility because the clay sheets orient their normals parallel to the magnetic field but perpendicular to the electric field. Moreover, the isotropic phase shows a large electric-field-induced birefringence. By dissolving acrylamide monomers in the clay suspensions and photopolymerization, clay/polymer composite gels could be elaborated. Aligned and patterned composites could be produced by application of an electric field during polymerization.

A foam-like graphene material can be prepared by freeze drying and thermal reduction of graphene oxide suspensions. The graphene foam has a much higher capacity then conventional graphite anode, and it possesses better rate capability comparing with powderlike graphene active materials reported previously. The influence of the annealing temperature on the charge-discharge performance of graphene foam has been investigated.

In this study, a new method has been developed to produce pure crystalline BaZrO₃ powders from Ba+Zr solution or weakly soluble reactants by using precipitation route in highly basic aqueous solution. The influence of several synthesis parameters is studied. At high OH⁻concentration ([NaOH] = 20 mol/l), it is possible to obtain the well-crystallized stoichiometric perovskite phase at relatively low temperature (∼80°C), after a short reaction time (15 minutes) and without requiring any precaution to avoid the presence of CO₂. This synthesis method yields spherical particles, whose size can be controlled by changing the concentration of the Ba+Zr solution. No calcination treatment is necessary since the precipitate is crystalline. Suitable choice of the synthesis parameters ([NaOH] = 20 mol/l, [Ba+Zr] = 1 mol/l, reaction time = 15 minutes) yields a sub-micron precipitate.

This paper demonstrated the effect of dispersibility in alumina slurry on the change in the distribution of orientation for the particle-oriented compact during a sintering process. The orientain was developed with increasing the sintering temperature. The variation of density and microstructure with sintering temparature clarified that both densification and grain growth contributed to development of the oriented structure. The difference in slurry dipersion affected the degree of orientation in sintered bodies. This result suggests that proper dispersion in slurry is necessary to obtain a material with highly oriented structure when it needs forming methods involving slurries and subsequent sintering.

Thanks to highly porous bone structure and three-dimensional nano-carbon networks in electrically conductive porous alumina (CPA) prepared by the combination of gel-casting and reductive sintering in inert atmosphere, recently a surge of increasing interest has been attracted to develop its various potential applications especially as catalyst support. In this work, CPA-based composites prepared by decoration with nickel and platinum nanoparticles indicate its potential applications especially as fuel cells. By uniformly dispersion of nickel and platinum nanoparticles with small sizes around 10 nm and 20 nm respectively on the surface of CPA, an increased electrochemical performance can be observed in 1 M NaOH solution. Raman spectroscopy, Field-emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS) have been employed to detect the changes of structure and morphology during modification. Moreover, electrochemical measurements results of cyclic voltammetry prove their improved electro-catalytic activities toward oxygen reductive reaction by comparing with the classical graphite electrode, which is mainly attributed to the unique structure and surface modification of CPA.

Anatase-type titania solid solutions co-doped with Nb⁵⁺ and cation M (M = Ga³⁺, Al³⁺, Sc³⁺) with composition Ti_1−2XNb_XM_XO₂ were directly formed as nanoparticles from precursor solutions of TiOSO₄, NbCl₅, and metal salts (Ga(SO₄)₃, Al(NO₃)₃, and Sc(NO₃)₃) under mild hydrothermal conditions at 180 °C for 5 h using the hydrolysis of urea. The effect of co-doped cation M on the formation and properties of anatase-type titania solid solutions was investigated. The region of anatse-type solid solution depended on the co-doped cation M. The composition range of anatase-type titania solid solution in the case of M = Sc³⁺ was much wider than that in the case of M = Ga³⁺ and Al³⁺. The increase in the amount of co-doped cation M = Ga³⁺, Al³⁺ enhanced the crystallite growth of anatase solid solutions under the hydrothermal conditions. The solid solutions co-doped with M = Al³⁺ showed the most improved photocatalytic activity in the three cations. The anatase-to-rutile phase transformation of solid solutions was promoted at lower temperature via the presence of co-doped cation M = Ga³⁺.

Thin films of synthesized TiO₂ nanoparticles were deposited by constant-current electrophoresis deposition in ethanol using colloid of various concentration of TiO₂ nanoparticles. Thin films deposited in colloid of high concentration had the high density, no apparent cracks and the higher optical transparency. The eficiency of the fabricated dye-sensitized solar cells was improved using thin film of TiO₂ nanoparticle deposited in colloid with high concentration. It was suggested that the thin film with high quality could be deposited by making the velocity of a TiO₂ nanoparticle low because the linkage between TiO₂ nanoparticles were promoted by oriented attachment mechanism.

Inner surface of microporous alumina tube was coated with nanoporous alumina layer using electrophoretic deposition (EPD) process. Polypyrrole (Ppy) film was formed on the inner wall of the porous tube to give electrical conductivity by chemical polymerization of pyrrole (Py). The nanoporous structure was controled using bimodal suspension of alumina powders with 0.6 μm and 30 nm in ethanol. The thickness of the coated layer was controlled by varying the processing parameters such as deposition time and DC applied voltage. After the deposition, the coated substrate was sintered at 1250°C for 2 h to bond the coated layer with the substrate.The microstructure of the substrate and the coated layer was observed by SEM. The results show the good interfacial joining between the substrate and the coated layer; they are not seperatated after the Ppy burnt-out. Crack-free and nanoporous layer on the microporous substrate was successfully fabricated.

Highly c-axis oriented Sr_0.6Ba_0.4Nb₂O₆ (SBN60) ceramics was prepared with the recent orientation method based on rotating magnetic field. Drastic improvement of piezoelectricity was noted by the c-axis orientation. The orientation increased in the sintering process through grain growth. Anisotropic microstructure was noted in the ceramics.

Non-uniform bulk or surface morphology of hollow particles has been an emerging interest because of the potential applications involving chemical storage, delivery and self-assembly for novel functional materials. There had been reports that experimental anisotropic (non-uniform) particles are much more difficult than synthesizing particles with uniform bulk and surface. Hence, this study reported a simple direct approach for the formation of unique hollow anisotropic amorphous silicate microparticles (10 to 20 μm). This was successfully prepared at room temperature via hydrolysis and condensation of tetraethylorthosilicate (TEOS), with ammonia water (NH₄OH) as catalyst, ethanol (EtOH) and inorganic micro-size calcium carbonate (CaCO₃) as template. The molar ratio used was 1.88:28.85:1:2.85 (CaCO₃: EtOH: TEOS: NH₄OH), mixed/stirred (at room temperature for 2 h), then filtered/washed by ethanol/water, after then dried and acid treated (3.0 mole/L) to obtained a micro-sized hollow SiO₂ particles. This simple approach for the formation of unique anisotropic shape hollow silicate micro-sized particles can be a good alternative for a possible application as large porous carrier for nanoparticles (large drug delivery (LPP's)).

Rutile-type TiO₂-SnO₂ solid solution nanoparticles were synthesized via "forced co-hydrolysis" of precursor solutions of TiCl₄ and SnCl₄ under hydrothermal conditions at 180∼240 °C for 10 h. The lattice parameters a₀ and c₀ of rutile (Ti, Sn)O₂ solid solutions changed according to the Vegard's Law. Rutile-type complete solid solutions in the system TiO₂-SnO₂ were directly formed in all composition ranges at 240 °C. The crystallite size of solid solutions containing more than 20 mol% SnO₂ was maintained in the range of 10 to14 nm by the control of crystallite growth of rutile-type solid solutions owing to the presence of SnO₂. The specific surface area of rutile-type solid solutions corresponded well to the change in crystallite size. The rutile-type solid solutions were metastable and decomposed into Ti and Sn rich phases via heat treatment at 1200 °C.

The ring-opening reactions of synthesized polycaprolactone/clay nanocomposites by way of swelling-agents-modified clays (organoclays) and caprolactone monomers were investigated with differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarized optical microscopy. Results show that the process is a two-stages reaction: the first stage happened at the lower temperatures which involved in situ initiating-polymerization caused by the caprolactone reacted with the active-functional groups of swelling agents, and the second stage took place at the higher temperature where the propagation of the active polycaprolatone chains progressed by a massive diffusion of caprolatone into among silicate layers to form the end-tethered polycaprolactone layered silicate nanocomposites.

We have examined the dispersion of barium titanate nanoparticles (BT-NPs) and have discussed the effect of air pressure supplied to the nozzle on the dispersion by using novel wet-type pulverizer utilized supersonic jet flow (SSJM). The aggregated particle size was decreased with increasing the air pressure and the collision times. In the optimized condition, almost the BT-NPs were dispersed with the primary particles, however, further excessive collision had caused reaggregations. The degree of dispersion has been affected by the air pressure. The injected droplets had formed almost the same diameter regardless of air pressure and the velocity was increased with increasing of the air pressure and reached 300 m/s. We have speculated that the shockwave dominates the dispersion of BT-NPs.

The mechanochemical activation processing has proved to be an effective technique to enhance a solid-state reaction at relatively low temperatures. In such a process, the mechanical effects of milling, such as reduction of particle size and mixture homogenization, are accompanied by chemical effects, such as partial decomposition of salts or hydroxides resulting in very active reactants. The objective of the present work is to obtain (ZrO₂)_0.97(Y₂O₃)_0.03 nanocrystalline tetragonal solid solution powders directly using a high energy milling on a mixture of the pure oxides. A second objective is to evaluate the efficiency of the processing proposed and to characterize both textural and structural evolution of the mixtures during the milling processes and throughout posterior low temperature treatments. The Textural and structural evolution were studied by XRD analysis, specific area measurements (BET) and SEM. Firstly a decrease of the crystallinity of the reactants was observed, followed by the disappearance of Y₂O₃ diffraction peaks and the partial appearance of the tetragonal phase at room temperature. The solid solution proportion was increased with the high energy milling time, obtaining complete stabilization of the tetragonal solid solution with long milling treatments (60 min).The obtained powders were uniaxially pressed and sintered at different temperatures (600-1400°C); the influence of the milling time was correlated with the sinterization degree and final crystalline composition of the materials. Finally, fully stabilized nanocrystalline zirconia materials were obtained satisfactorily by the proposed method.

Ba_1−xCa_xTiO₃, Ba_1−xSr_xTiO₃ and Sr_1−xCa_xTiO₃ (x = 0, 0.25, 0.50, 0.75 and 1) nanoparticles were synthesized using the microwave-assisted hydrothermal method. Samples were prepared for 40 minutes at 140°C under a pressure of 3 MPa using an adapted domestic microwave oven. The samples were characterized by X-Ray diffraction (XRD), scanning electron microscopy (FE-SEM), and Raman, photoluminescence (PL) and ultraviolet-visible (UV-Vis) spectroscopies. XRD data show that ceramic powders have crystalline phases associated with a short-range structural disorder. This structural disorder is confirmed by Raman spectral bands indicating multi-phonon processes and the presence of defects or impurities. Such defects account for a broad band in the photoluminescence spectrum in the green light (460 nm) region for all samples. Gap energy variation, obtained from UV-Vis spectra, suggest a non-uniform band structure of these titanates in accordance with the PL results. The morphology of each sample is changed with doping and varies from a spherical to cubic appearance for energy minimization.

SiC nanowires and nanotubes sheathed with BN were synthesized by annealing C-SiC and SiC nanotubes at 1600 °C for 5 h with BN powder in Ar gas. According to TEM observation, the BN coating was very thin and the layer number of BN coating was less than 15. The BN coating on the surface of SiC nanotubes was not produced by the heat treatment at 1500 °C. This result revealed that BN on the surface of SiC nanomaterials was produced by heat treatment of higher than 1600 °C.

Alumina nanoparticles were prepared by pulsed wire discharge (PWD) using aluminium wire in deionized water at relative energy of 2, which is the ratio of the charged energy of the capacitor and the vaporization energy of the wire. From voltage and current waveforms during PWD, calculated deposited energy of the wire was larger than the vaporization energy of the wire. Scanning electron microscopy images showed that the prepared Al₂O₃ nanoparticles were spherical particles with the median particle diameter of 103 nm and the geometric standard deviation of 2.3. The X-ray diffraction analyses indicated that the prepared nanoparticles were identified as γ-Al₂O₃. From these results, pure γ-Al₂O₃ with particle size of around 100 nm was successfully synthesized by PWD in water.

Calcium metaphosphate (CMP) nano-whiskers were produced by a chemical precipitation method. In order to produce nano-powders, CMP was prepared by the mixing of two precursors, calcium oxide (CaO) and phosphate acid (H₃PO₄). Sparingly soluble chemicals, the Ca/P ratio of the mixture was set to be 0.50 to produce stoichiometric CMP, were chemical agitated in phosphate acid solution. At least 3 hours of pre-hydrolysis of phosphorus precursor were required to obtain CMP phase. The CMP powders were dried in a drying oven at 60 °C for 7 days and then followed by a heat treatment at 390 °C for 8hours. The obtained powder was analyzed using XRD, XRF, FT-IR, SEM, TG-DTA, Zeta Potential Meter, Specific Surface Area, and Particle Size Analyzer. The results showed that obtained CMP nano-whiskers have a significantly powder characteristics.

Particles of Hydroxyapatite (HAp) were synthesized by means of chemical precipitation method, under atmosphere pressure. The starting solution with the Ca/P ratio of 1.67 was prepared by mixing 0.167 mol·dm⁻³ Ca(NO₃)₂·4H₂O, 0.100 mol·dm⁻³ (NH₄)₂HPO₄, 0.500 mol·dm⁻³ (NH₂)₂CO and 0.10 mol·dm⁻³ HNO3 aqueous solutions. The hydroxyapatite were prepared by heating the solution at 80 °C for 24 hour and then at 90°C for 72 hour. Then followed, the dry powers were heat treatment at 660°C temperatures for 8 hour. The obtained powder was analyzed using XRD, XRF, FT-IR, SEM, TG-DTA. The results showed that obtained HAp powers were greatly influenced by synthetic conditions. HAp powders with various morphologies, such as sphere, rod, layered, dumbbell, fibre, scaly, were obtained by controlling the synthetic conditions.

One of the ways for the production of ceramic materials with a fine-grained structure is the use of nanopowders. Different methods are used for the production of nanopowders. One of them is the method of plasmachemical synthesis. Different nanopowders of refractory materials can be obtained by this method. The preparation of nanosized powders of nitrides and oxides and their composites by the method of plasmachemical synthesis, the possibilities to receive nanopowders with different particle size and the potential advantages of nanopowders were investigated.