Copper nanopowders

Reisee et al. [52] first described a pulsed electrodeposition and pulsed out-of-phase ultrasound to prepare copper nanopowders. Such an electrochemical method has since then employed to synthesize a variety of nanoparticles. Mancier et al. [53] have prepared Cu20 nanopowders (8 nm) with very high specific surface area of 2,000 m2/g by pulsed ultrasound assisted-electrochemistry. 

Typical dependencies of the friction coefficient on wear path length (time) by the example of copper nanopowder additive obtained in carbon dioxide are shown in Figure 5.2. The data in Figure 5.2(a) to (c) provide the evidence of improved friction conditions where the nanopowder additive has been used. It can be concluded that copper nanopowder additive to SAE 30 motor oil reduces friction most effectively at higher loads and higher sliding speeds. Based on these results, the researchers demonstrated the feasibility that nanoparticulate copper can adhere preferentially to steel friction pairs and reduce the friction. 

The copper nanopowder additive provides changes in worn surface topology and does not impair the lubrication characteristics of the motor oil. Local overheating caused by the direct contact of two surfaces initiates chemical deposition of copper on steel, providing a soft surface limited to the locality of the friction pairs. 

Figure 5.25 SEM images of worn surfaces after friction tests with copper nanopowder additive (x 1500). Reproduced by permission of Elsevier from Tarasov et al. [13], (2004) Elsevier...

Fievet et al. [225] have prepared and isolated metallic nanopowders of gold, palladium, iridium, osmium, copper, silver, nickel, cobalt, lead, and cadmium via polyol... 

Metal oxide nanocomposites were synthesized by electrical discharge method using a combination of aluminum and copper electrodes submerged into water. The crystal structure, lattice parameters and grain size of the nanopowders were determined by XRD using Cu K radiation (Fig. 3b). The XRD pattern exhibited the presence of cubic copper with a lattice constant of 0.3615 nm, as well as aluminum and copper oxide and hydroxide phases. The positions of all peaks were in agreement with the JCPDS standards. 

The average grainsize was determinedby means ofthe Sherrer s formula. Moreover, the nanopowders were investigated by means of transmission electron microscopy (TEM) (JEM 2010, JEOL). For the TEM studies the powders were dispersed in distilled water and a drop of suspension was placed on a copper grid with a transparent polymer and dried. Elemental analysis was performed by inductively coupled plasma (ICP) spectrometer, (Spectroflame Modula, Spectro). The in vitro test were performed leaving the nanopowders for 30 days in three different solutions distilled water, SBF (simulated body fluid [17]) and SBF added of citric acid (0.08 M), at 60°C. This temperature was chosen to better evaluate the powder behaviour under the most extreme conditions. 

The preparation of samples for the TEM investigations was carried out by putting a drop of the colloidal solution on a copper grid coated with an amorphous carbon film and letting the solution to become completely dry. Nanopowders for XRD measurements were obtained by evaporating the water from the colloidal solution. 

The sonochemical method has been applied to obtain nanoparticles of magnets such as Fe, Fc304, Fc203, cobalt ferrite and copper ferrite in Refs [259, 260, 267]. If the sonication occurs in the presence of oxygen, the oxide phases are obtained [267, 268]. In the case of Fc203, the sonolysis results in amorphous nanopowder,... 

Interestingly, Frizon et al. reported for the first time the synthesis and characterization of LC-based diselenides by couphng of aryl bromides with elemental selenium using a copper oxide nanopowder catalyst. These new structures, e.g., 42, which are characterized by the presence of 1,2,4-oxadiazole rings, exhibit a smectic A phase by POM and DSC, and showed weak blue fluorescence in solution (2012LC769 Figure 8). 

Bahsi ZB, Aslan MH, Ozer M, Oral AY. Sintering behavior of ZnO A1 ceramics fabricated by sol-gel derived nanocrystalline powders. Cryst Res Techn 2009 44 961-6. Athar T, et al. Wet synthesis of copper oxide nanopowder. Int J Green Nanotechnol 2009 1(2) M67-M73. 

The effect of the aluminum oxide layer is also known to reduce the propagation of thermite reactions since alumina is an effective absorber of thermal energy. A study by Weismiller et al. of a 49 % active aluminum nanopowder in a thermite with copper oxide supports the idea that too much oxide can actually reduce thermite performance. Table 13.4 shows Weismiller s data which indicates the negative effect of a thick oxide layer on aluminum nanoparticles. 

---