Search

Since the 1980s, catalytic antipollution systems for petrol-fuelled vehicles have considerably reduced emissions of CO, NOx, and unburnt hydrocarbons. They use precious metals as catalyst on a hybrid support made from alumina and a mixture of cerium oxide and zirconium oxide, sometimes doped. Cerium oxide is a key element in these systems, thanks to its triple role as redox agent (maintaining the stoichiometry of the mixture of gases to be processed and hence the efficiency of the precious metal), dispersing and stabilising agent for the nanoparticles of precious metal, and thermal stabiliser for the alumina. However, these systems could only be developed with the help of nanoscale textured powders, able to conserve very high specific surface areas at high temperatures, and hence maintain constant and adequate reactivity over the lifetime of the catalyst (several tens of thousands of kilometers). [ABSTRACT FROM AUTHOR]

Inorganic reinforcements are used in rubber, and in particular in tyre treads for light vehicles, in order to improve the compromise between three key features of tyres: road holding performance or road adherence, especially when the road is wet or snow-covered (road safety), roll resistance (petrol consumption), and resistance to wear (lifetime of the tyre). Over the last ten years, highly dispersible silicas (HDS) developed by Rhodia have been more and more widely used as a substitute for the traditionally used carbon black. The advantage with HDS materials is that they improve road holding and reduce roll resistance, while maintaining the same level of resistance to wear. [ABSTRACT FROM AUTHOR]

Inorganic nanoparticles provide an excellent example of the way size reduction can lead to novel or improved applications. Catalysis (supported precious metals), magnetic recording (nanoparticles of metal, iron oxide, or chromium oxide) and photography (silver halides), have all been transformed over the past ten years by the use of nanoparticles. New applications have come to light recently, for both complex fluid media and bulk materials, usually through a combination of properties resulting from size reduction, leading to an improved overall performance for the user. [ABSTRACT FROM AUTHOR]

Multilayer ceramic capacitors (MLCC) are the capacitors most commonly used in electronic circuits (television, radio, telephone, automobile, aeronautics, space, etc.). The main advantages are low cost, small size, a good level of chemical inertness, due to the fact that they are made from chemically very stable oxide ceramics, and hence good stability in time. [ABSTRACT FROM AUTHOR]

Our senses of smell and taste are able to recognise molecules selectively, to the point where they can even discriminate between different chiral states. This property, called molecular recognition, is essential to all forms of life [1]. It is based on the principle of a specific interaction between a receptor or host and a target molecule, which will be identified among a multitude of others, then selectively adsorbed. If the host is endowed with reactive functions, the attached molecule may be transported or transformed. Enzymes are the archetypal host molecules exploiting the idea of molecular recognition. Their complexation sites comprise a hydrophobic pocket with definite shape within which amino acid residues are located in a precisely defined way. The combined effect of these different characteristics underlies not only the affinity for some specific substrate, but also the transformation of this substrate into the desired product [2]. In fact, the phenomena actually brought into play are much more involved, being made up of an ensemble of physicochemical events that act together in a cooperative way, either simultaneously or sequentially, and in which the molecular processes are difficult to follow in detail. [ABSTRACT FROM AUTHOR]

This chapter is concerned with ways of synthesising nanoporous solids, and in particular materials with a very narrow pore size distribution. Two main families of solids are relevant here: crystalline microporous solids (0.3 < pore diameter < 1.4 nm) comprising zeolites and related solids (metallophosphates), and ordered mesoporous solids (2 < pore diameter < 30 nm) which, in contrast to the zeolites, possess amorphous inorganic walls (see Sect. 11.4). In both cases, these solids are obtained by introducing inorganic or organic cations, or again molecular assemblages (surfactant micelles) into the reaction medium. These species then act as molecular ‘templates' around which the inorganic matter crystallises or polycondenses. After synthesis, these are occluded within its pores and the porous material is obtained when they are extracted or eliminated by calcination. The structure-directing role of these template species will be discussed and illustrated by several examples, and the main mechanisms for forming this kind of nanoporous solid will be presented. X-ray and neutron scattering techniques, which have proved to be particularly well suited for characterising ordered mesoporous solids, will be discussed at the end of the chapter. [ABSTRACT FROM AUTHOR]

To make good use of the physical properties of nanoparticles (see Part II of this book), most applications require them to be incorporated within solid materials, such as glasses, ceramics, oxides, etc. The inclusions obtained in this way are thereby protected from chemical (e.g., oxidation) or mechanical (e.g., friction or wear) alteration due to the environment. They are also separated from one another from an electrical or magnetic point of view, which limits this kind of interaction between the particles. The dispersion of particles within solid materials can be achieved in the ordinary way by exploiting precipitation effects in the solid state (e.g., alloys hardened by dispersions of nanometric precipitates, Guinier-Preston zones), but also by a great many less direct methods. Which method is finally chosen depends on several factors such as the kind of matrix and size, shape and spatial organisation of the particles, but also on the volume of material to be produced, the cost, and the difficulty involved in the process. [ABSTRACT FROM AUTHOR]

In many branches of technology where surfaces are playing a growing role, the use of coatings is often the only way to provide surfaces with specific functional properties. For example, the austenitic stainless steels or titanium alloys exhibit poor resistance to wear and low hardness values, which limits the field of applications. The idea then is to develop new solutions which would improve the mechanical performance and durability of objects used in contact and subjected to mechanical forces in hostile gaseous or liquid environments. Hard coatings are generally much sought after to enhance the resistance to wear and corrosion. They are of particular importance because they constitute a class of protective coatings which is already widely used on an industrial scale to improve the hardness and lifetime of cutting tools. [ABSTRACT FROM AUTHOR]

In the last chapter, we saw how it is possible today to fabricate regular 2D and 3D lattices of magnetic nanoparticles [1-3]. The aim here is to study the specific properties of these systems that can be attributed to the magnetic properties of the particles. Such properties underlie several applications currently under development. We shall then discuss ferrofluids. Magnetic nanoparticles are deposited on a substrate by evaporation of ferrofluids. The properties of these fluids are essential for explaining the structures observed on nanometric and mesoscopic scales in the resulting deposits. Finally, we shall discuss the influence of a magnetic field on the deposition structures. [ABSTRACT FROM AUTHOR]

The terms nanomaterial, nanocrystal and nanoparticle all refer to objects with nanometric sizes. The main feature of nanomaterials is that they are made up of a small number of atoms, from a few hundred to a few thousand. Due to their small dimensions, the physical properties of these materials generally differ from those of bulk materials. Over the last few decades, this field of research has developed considerably, both theoretically and experimentally. This development has been particularly pronounced in the three areas where size effects are important, viz., metals (Au, Ag, etc.), semiconductors (CdSe, Ag2S, etc.), and magnetic materials (CO, Ni, etc.). [ABSTRACT FROM AUTHOR]

Sintering can be defined as the consolidation of a dispersed material under the action of heat, without total melting of the material. If part of the matter reaches its melting point during this densification, we speak of liquid-phase sintering; otherwise, it is called solid-state sintering. Moreover, if the material is chemically synthesised during sintering, this is called reactive sintering; otherwise, it is called non-reactive sintering. [ABSTRACT FROM AUTHOR]

Processes involving supercritical fluids have taken on a considerable importance over the last few years. Indeed, the physical and chemical characteristics of this kind of medium, together with its exceptional transport properties, promise a whole range of potential applications. In the field of nanomaterials, the use of supercritical fluids opens the way to new opportunities for synthesis. We shall restrict the discussion here to what is required for a good understanding of this particular context. Definitions are mentioned briefly, and the interested reader is directed to the literature for more detail. [ABSTRACT FROM AUTHOR]

Mechanical processing can be used to obtain metastable crystalline phases, e.g., phases that can only be reached at equilibrium using high temperatures and/or pressures, or even amorphous phases from crystalline phases that are stable at room temperature and pressure. Such transformations, also called mechanical alloying, can be produced by ball milling. [ABSTRACT FROM AUTHOR]

Over the last decade, the new category of materials formed by nanostructures has stimulated growing interest in the field of fundamental and applied research. However, before such structures can be studied and used, ways must first be found to actually make them. A great many chemical and physical techniques have been developed, including methods using colloidal solutions which have proved themselves extremely effective for controlling the size, but also also the shape of the resulting nanoparticles. [ABSTRACT FROM AUTHOR]

Nanometric particles of transition metals generally react very strongly with air. One solution for stabilising them is to disperse them in an oxide matrix, either to study them or to benefit from their properties in genuine nanocomposite materials. [ABSTRACT FROM AUTHOR]

The aim of gas phase synthesis is to achieve the condensation of nanopowders with maximal specific surface area (see below for the definition), or in other words, to obtain nanoparticles that are not connected by strong chemical bonds (intergrain regions called grain boundaries; see, for example, the discussion of mechanical grinding in Chap. 19). When the contact region is partial, it is called a neck or bridge, a term taken from the field of sintering (see Chap. 21). [ABSTRACT FROM AUTHOR]

It is no easy matter to make nanoscopic objects. In fact, starting from a macroscopic sample, as one does when making objects with centimeter or millimeter dimensions, one soon comes up against technical problems. As we shall see, there are techniques for overcoming them, but they require a certain art to implement them successfully. [ABSTRACT FROM AUTHOR]

Increase the Young's modulus of a glassy resin by a factor of ten without making it heavier, for a new ski design, for example? Triple the rupture strength of an elastomer? Improve the thermal behaviour of an object made from a thermoplastic polymer by 100 degrees, to make a car dashboard, for example, or a part for the engine? Double the fire resistance time for the sheath around an electricity cable? Reduce the oxygen permeability of a film by a factor of ten, to make long conservation food packaging? All these things have been made possible by incorporating a few percent of inorganic nanoparticles in a polymer matrix. Figures 14.1 and 14.2 illustrate two such nanocomposites: the first was obtained by incorporating lamellar clay particles, and the second by incorporating fibrous nanoparticles, in fact, carbon nanotubes. [ABSTRACT FROM AUTHOR]

Supramolecular chemistry is an interdisciplinary field of research, reaching across from chemistry to the physics and biology of chemical species more complex than the molecules themselves. These molecular structures are held together and organised by non-covalent intermolecular interaction forces. Supramolecular chemistry is rooted in the chemistry of organic synthesis for the construction of molecules, and in the field of coordination chemistry for the assembly of multimolecular entities. But it also extends to physical chemistry in the theoretical and experimental investigation of the interactions that come into play, and biochemistry via the biological processes of recognition and binding of a substrate which originally inspired its development, and finally the science of materials where one investigates the novel physicochemical properties of these new chemical species. [ABSTRACT FROM AUTHOR]

When a fluid is confined by solid surfaces, its equilibrium properties are modified by several mechanisms. One point is that surface effects become quantitatively significant compared with bulk effects, and for this reason, solid-fluid interactions begin to compete with fluid-fluid interactions in the determination of the phase diagram of the fluid. If the fluid-solid attraction is sufficient, confinement can stabilise a liquid phase that would have evaporated in the absence of the solid. The liquid-vapour transition is modified by confinement. The same goes for the melting-solidification transition. For high levels of confinement, such that the mean size of pores becomes of the same order of magnitude as density inhomogeneities in the fluid, the liquid can no longer be distinguished from its vapour: the critical point is modified by confinement, the critical temperature decreasing with pore size. Finally, for the ultimate confinement, in which pore sizes are comparable with the size of molecules in the fluid, the very notion of fluid is no longer applicable. In the following, we shall review these various degrees of confinement and the resulting modifications of physical properties. [ABSTRACT FROM AUTHOR]

Many natural materials are characterised by an inorganic framework, generally negatively charged, containing cavities, cages, or tunnels in which inorganic (charge-balancing) cations and/or water molecules are occluded. Among these materials, the zeolites form one large family of crystalline porous materials (from the Greek zein meaning ‘to boil' and lithos meaning ‘stone'). Pore sizes in these aluminosilicates are generally of nanometric order. Because of their specific properties, the synthesis of zeolites, and more generally, zeolitic materials (zeolites and related solids) has considerably increased over the last few years. Indeed, applications are many and varied. They are relevant not only to the chemical industry (or more precisely, the petrochemical industry), but also to our everyday lives (phosphate-free washing powders, double-glazing insulation, and many others). By virtue of their porous structure and the mobility of the cations and water molecules occluded within their porous structures, these materials can be used as highly selective cation exchangers and adsorbents. [ABSTRACT FROM AUTHOR]

This chapter will be concerned with the parameters governing interactions between metallic nanoparticles and a reactive surrounding material, and hence with the catalytic properties of such nanoparticles. Indeed, most industrial metal catalysts contain very costly metals, such as the precious metals at the end of the transition series and the noble metals, and must therefore have as large a surface-to-volume ratio as possible in order to economise the number of atoms required. This is the solution provided by nanoparticles. [ABSTRACT FROM AUTHOR]