Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

In recent years, near-nano (submicron) and nanostructured materials have attracted increasingly more attention from the materials community. Nanocrystalline materials are characterized by a microstructural length or grain size of up to about 100 nm. Materials having grain size of ∼0.1 to 0.3 μm are classified as submicron materials. Nanocrystalline materials exhibit various shapes or forms, and possess unique chemical, physical or mechanical properties. When the grain size is below a critical value (∼10–20 nm), more than 50 vol.% of atoms is associated with grain boundaries or interfacial boundaries. In this respect, dislocation pile-ups cannot form, and the Hall–Petch relationship for conventional coarse-grained materials is no longer valid. Therefore, grain boundaries play a major role in the deformation of nanocrystalline materials. Nanocrystalline materials exhibit creep and super plasticity at lower temperatures than conventional micro-grained counterparts. Similarly, plastic deformation of nanocrystalline coatings is considered to be associated with grain boundary sliding assisted by grain boundary diffusion or rotation. In this review paper, current developments in fabrication, microstructure, physical and mechanical properties of nanocrystalline materials and coatings will be addressed. Particular attention is paid to the properties of transition metal nitride nanocrystalline films formed by ion beam assisted deposition process.

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Nanocrystalline materials and coatings

Mechanisms of tetragonal phase stabilisation, at room temperature, in nanocrystalline ( 1 μm) are reviewed in detail. The merits, demerits and scope of each individual model are outlined. The analysis of the literature shows that, although the mechanism of tetragonal phase stabilisation in bulk ZrO2 is well understood, the room temperature tetragonal phase stabilisation mechanism in undoped, nanocrystalline ZrO2 is controversial. Various proposed models, based on surface energy (nanocrystallite size), strain energy, internal and external hydrostatic pressure, structural similarities, foreign surface oxides, anionic impurities, water vapour and lattice defects (oxygen ion vacancies), are discussed in detail. It is proposed that generation of excess oxygen ion vacancies within the nanocrystalline ZrO2 is primarily responsible for the room temperature tetragonal phase stabilisation, below a critical size. Hence, the mechanism of ...

Mechanisms of room temperature metastable tetragonal phase stabilisation in zirconia

Synthesis of uniform anatase TiO2 nanoparticles by gel-sol method. 3. Formation process and size control.

Synthesis of uniform anatase TiO2 nanoparticles by gel–sol method: 4. Shape control

Size and shape characterization of TiO2 aerogel nanocrystals

Three different precursor materials giving rise to contrasted nanostructures, xerogels, aerogels and precipitates, are prepared by a sol gel route in the Zrn -propoxide—acetylacetone—water—n-propanol system. Clear homogeneous gels are made by using a proper amount of acetylacetone and water. The gels are dried either by conventional processing (xerogels) or by supercritical evacuation of alcoholic solvent (aerogels). The complexation ratio (R = [acetylacetone]/[Zr(OR)4]) is the main parameter controlling the size of ZrO2 primary particles. WhenR = 0 , precipitates are obtained.

Early Stages of Crystallization in Gel Derived ZrO2 Precursors

Zirconia cordierite composite powders were fabricated by a sol-gel coating route. The crystallization of a deposited zirconia percursor thin layer and further phase transformation of tetragonal grains were shown to exhibit rather different behaviour from that of the free xerogel. The precursor layer and tetragonal zirconia grains were observed and imaged by transmission electron microscopy.

Sol-gel coating of ceramic powders

Nous avons realise un montage de diffraction des rayons X, destine a la caracterisation d'echantillons plans polycristallins, equipe d'un detecteur courbe a localisation. La geometrie de ce montage conduit a la realisation de diagrammes de diffraction sous incidence fixe. L'angle d'incidence, reglable au millieme de degre, varie d'une dizaine de degres lorsqu'il s'agit de caracteriser des echantillons massifs a quelques centiemes de degre pour l'etude de couches minces. L'objet du travail presente ici est de montrer que ce montage permet d'obtenir des diagrammes d'une qualite comparable a celle observee en reflexion symetrique (Bragg Brentano). Apres une analyse du probleme specifique du positionnement de l'echantillon, nous montrons les resultats obtenus sur ce montage en ce qui concerne d'une part la mesure des parametres de maille sur un echantillon standard international et d'autre part l'affinement structural de type Rietveld d'une zircone monoclinique qui a servi d'echantillon pour une campagne internationale de la commision de diffraction sur poudre. Nous utilisons ensuite cet equipement pour etudier trois problemes differents de caracterisation des materiaux.

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O. Masson

Papers

Size and shape characterization of TiO2 aerogel nanocrystals

Early Stages of Crystallization in Gel Derived ZrO2 Precursors

Sol-gel coating of ceramic powders

Diffraction des rayons X en réflexion sous incidence fixe. Mise en œuvre d'un détecteur courbe à localisation (CPS 120 Inel)