96 nanomaterials nanopowder

Bulk Nanomaterials One of the most effective ways to densify nanopowders into bulk nanomaterials is SPS (spark plasma sintering). The powder is compressed and a high density current is passed through it in order to heat it up to the... 

In this chapter we described some of the industrial aspects of ceramics. Ceramics make money. Unfortunately obtaining the raw materials can have some undesirable environmental and societal impacts. The environmental impact of nanomaterials is an issue that has not yet significantly concerned the ceramics industry because no one knows exactly what that impact is. But as the market for ceramic nanopowders and other nanostructures (such as wires and tubes) increases the environmental concerns will have to be addressed. Many of the grand challenges we face as a society, such as energy, the enviromnent, and health care, will require innovative technological solutions. Ceramics can play an important role in these areas, e.g., nuclear waste immobilization, catalytic conversion, and viral nanosensors. 

Let us start with nanopowders. The measurements were carried out by XRD method. In Fig. 2.2, the lattice constants a and c, measured on tetragonal BaTiOs nanopowder, are shown at room temperature [17]. One can see that at average particle size about 50 nm c = a, so that the symmetry becomes cubic and ferroelectric phase transforms into paraelectric one at room temperature. To estimate the average nanoparticle size, where the ferroelectric phase becomes unstable and transforms into paraelectric one, the Scherrer formula has been used. This formula relates the particle size to the XRD lines half-width. The average particle size leading to the symmetry breaking is called critical size and constitutes the important characteristic of nanomaterials. It turns out, that the critical size measured on different samples can be essentially different. To illustrate this, on Fig. 2.3 we report the ratio c/a at room temperature for BaTiOs nanopowder obtained in Ref. [18]. It is seen that ratio c/a= 1 was obtained in the samples with average size 120 nm. The difference between the critical sizes in the papers [17] and [18] can be related to the... 

Here we consider the EPR and NMR spectra of oxide nanomaterials in the form of nanopowders and nanogranular ceramics on the base of the results obtained in Refs. [100-102]. 

While nanomaterials are in existence for quite some time in products such as catalysts, carbon black, pigments and other simple oxide nanopowders, in today s developing nanoceramic materials industry the emergence of low-cost, high-volume, novel manufacturing processes offer the chance of complex compositions with a level of precision and a range of properties that were, in the past, either too difficult to achieve or economically not feasible. 

Particle characterization can be studied on materials in solution or suspension and as the dry nanopowders, and a characterization profile of the nanomaterial recovered after exposures to in vitro or in vivo test systems... 

As represented in Figure 6.3, the resulting particle size distribution of reaerosolized bulk nanomaterials depends not only upon the bulk nanopowder properties formed by controlling the process inputs, but also upon the parameters used in reaerosolization process, including reaerosolization method, pressures, and forces and not necessarily upon the original process conditions used to synthesize the nanomaterials prior to collection as bulk nanopowder. 

Another problem limiting the application of nanociystalline materials is prep>aration of nanocrystalline alloys. Currently, the bulk metallic nanomaterials can only be prepared at the laboratory scale, usually by compacting prepared nanocrystalline powders. However, consolidation of the nanopowders into bulk materials needs high temperature and pressure which may considerably coarsen the structure. Because of this difficulty, surface nanocoating has been considered a potential industry application. Nanocrystalline costing are often prepared by chemical vapour deposition (CVD), physical vapour deposition (PVD), electrochemical deposition, electro-spark deposition, and laser and electron beam surface treatment. 

Gas-phase methods are widely used for the industrial production of the metal oxide nanopowders with diverse particle sizes that are often used as feedstocks in the preparation of ceramics. The stabilization of such powders has provend difficult task, however, and many of today s in vivo applications of nanomaterials rely on solution-based methods, based on much better possibilities of functionalization and manipulation. Comminution has also begun to be accepted for the production of nanoscale powders, although its use for high-purity zirconia nanomaterials, as required for biomedical use, is severely hampered by the extreme hardness of Zr02-... 

Ai, J., Rezaei-Tavirani, M., Biazar, E., Heidari, K.S., Jahandideh, R., 2011. Mechanical properties of chitosan-starch composite filled hydroxyapatite micro-and nanopowders. Journal of Nanomaterials 2011 16. 

When dealing with nanomaterials one has also to pay a particular attention to moisture, since these compounds can be very hygroscopic. Moisture is known to react with the electrol5d e and form HF which can seriously lower battery life. It is also more difficult to remove moisture from nanopowders when compared to micron sized particles. For instance it has been demonstrated that two days of drying at 120°C under vacuum is necessary to obtain optimal impedance of acethylene black and LiFeP04 when only half a day under the same condition is enough for micron sized nickel cobalt aluminium (NCA) cathode. 

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