Nano-scale additives

Various concentrations of nano-scale ZVl were run through the test columns to determine the optimal concentration to be employed during the field test. Groundwater samples were collected at regular intervals and analysed for the same contaminants as the baseline samples. In addition,... 

A key aspect of metal oxides is that they possess multiple functional properties acid-base, electron transfer and transport, chemisorption by a and 7i-bonding of hydrocarbons, O-insertion and H-abstraction, etc. This multi-functionality allows them to catalyze complex selective multistep transformations of hydrocarbons, as well as other catalytic reactions (NO,c conversion, for example). The control of the catalyst multi-functionality requires the ability to control not only the nanostructure, e.g. the nano-scale environment around the active site, " but also the nano-architecture, e.g. the 3D spatial organization of nano-entities. The active site is not the only relevant aspect for catalysis. The local area around the active site orients or assists the coordination of the reactants, and may induce sterical constrains on the transition state, and influences short-range transport (nano-scale level). Therefore, it plays a critical role in determining the reactivity and selectivity in multiple pathways of transformation. In addition, there are indications pointing out that the dynamics of adsorbed species, e.g. their mobility during the catalytic processes which is also an important factor determining the catalytic performances in complex surface reaction, " is influenced by the nanoarchitecture. 

Developments in modern CVD allow to improve the deposition of thin films and bulky coatings nevertheless, an additional major issue remains the building of nanostructured materials such as ultra-thin films or dispersed nanoparticles. For these applications, the control of the deposit at the atomic or nano-scale level is essential. Consequently, the role of surface chemistry occurring between the CVD precursor and the substrate, as well as the gas-phase main physical properties have to be indisputably clarified. 

In thermites using aluminum metal as the fuel, the passivation of the metal surface with oxide must be taken into account. For micrometer sized particles of aluminum, the oxide passivation layer is negligible, but on the nano-scale this passivation layer of alumina begins to account for a significant mass portion of the nanoparticles. In addition, the precise nature of the oxide layer is not the same for all manufacturers of aluminum nanoparticles, so the researcher must use TEM to measure oxide thickness to allow calculation of active aluminum content before stoichiometric calculations are carried out for the mixing of thermites. Table 13.3 shows details of some of the percentages of aluminum in aluminum nanoparticles and shows just how significant and inconsistent the oxide layer can be. 

Figure 2.57. Hydrogen absorption in different forms of LaNij a, polycrystalline b, nanocrystalline c, nanocrystalline with addition of catalyst. From A. Zaluska, L. Zaluski, J. Strom-Olsen (2001). Structure, catalysis and atomic reactions on the nano-scale a systematic approach to metal hydrides for hydrogen storage. Appl. Phys. A72, 157-165. Used by permission from Springer-Verlag.

Figure 32. Amperometric response of rotating Cat/NiO modified GC electrode to H202, conditions -0.3 V constant potential, pH 7.0 and rotation speed is 2000 rpm, (A) successive addition of lOOpM and (B ) 1 liM insets plot of chronoamperometric current vs, H202 concentration and linear calibration curve for determination of KM. Reprinted from Biophysical Chemistry, 125, A.Salimi, E. Sharifi, A. NoorBakhash, S. Soltanian, Direct electrochemistry and electrocatalytic activity of catalase immobilized onto electrodeposited nano-scale islands of nickel-oxide, 546, Copyright( 2007), with permission from Elsevier.

For scratch resistance improvement of organic surfaces also nano-composites are of interest. In a composite nano-scale boehmite or y-aluminia particles of about 15 nm diameter have been used as catalysts for epoxy groups linked to hydrolyseable and condensable silanes. Epoxy polymerization preferably takes place around the nanoparticles and additionally =Si-0-Al= bonds are formed between the silanes and the alumina surface [486]. It seems that the nano-particles, only 5% in volume fraction, are flexibly suspended in an inorganic-organic network. Such systems can be produced as transparent coatings and cured at relatively low temperatures of 90 to 120°C to high performance scratch resistant layers. 

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