Composite powders, morphology

FIGURE 6.3 (a) Morphology of ball-milled NiO and SDC powders produced separately and (b) NiO-SDC composite powders coproduced by spray pyrolysis, showing a possible mechanism by which the composite powders retain a higher surface area resulting in a higher performance [19]. Reprinted from [19] with permission from Elsevier. 

Les] Lesnik, N.D., Minakova, R.V., Khomenko, E.V., Chromium-Copper System Adhesion Characteristics, Doping, the Structure of Phase Boundary and Composites , Powder Metall. Met. Ceram., 40(7-8), 432-440 (2001) (Experimental, Morphology, Phys. Prop., Interface Phenomena, 12)... 

The composition of the electrolyte, i.e., Ni VCo " ions ratio, influences polarization curves for Co-Ni alloy powders electrodeposition, as well as alloy powder composition and morphology. It is also concluded that the shape of the polarization curves in all cases is practically defined by the shape of the polarization curve for hydrogen evolution. In the case of Ni powder cauliflower and spongy-type particles are detected, while Co powder contains only spongy-type particles. Both types of particles are present in the Co-Ni alloy powders obtained at Ni /Co ions ratios 4.00, 1.50, and 0.67, while only spongy-type particles are detected in the Co-Ni alloy powder obtained at Ni VCo " ions ratio 0.25. In all cases of alloy powder electrodeposition anomalous type of codeposition is detected. 

Gas phase combustion is well proven method for the bulk production of fine powders. On the other hand it has scarcely been investigated from the fundamental perspective, of the chemistry and physics of particle formation and growth. Our interest is in the development of a more thorough understanding of how to control particle formation in order to enable the economical production of materials with unique and useful properties. With the increasing interest in composite powders, control of both morphology and chemistry take on greater importance. 

Combustion synthesis The reaction time is short and the process is simple Low cost technique Low heating temperature Used to prepare different t5rpes of materials (ceramic, intermetallic, composite) Varied morphology of the produced powder Lower contamination Agglomeration/aggregation can occm Low crystallinity... 

Once an oxide scale is established on the coupon or powder, its composition and morphology may be characterized by a variety of optical, electron optical, and X-ray diffraction techniques (XRD). In many cases the products are amorphous and other techniques are used to supplement XRD, such as chemical analyses of the scale alone. Scanning electron microscopy (SEM) has proven most useful, although transmission... 

The fundamental goal of nanoparticle research is to assemble atoms in a controllable way and design nanostructured materials with the desired physical and chemical properties. A major part of the research in the field of nanoscience is dedicated to the development of synthesis routes to nanoparticles and nanostructures. Conventionally, solid-state reactions between powders have successfully been employed for the low-cost production of bulk metal oxides. However, to obtain metal oxide nanoparticles with well-defined shape, size, and composition, these solid-state routes are unsuitable. In contrast to these high-temperature processes, liquid-phase synthesis routes, and in particular sol-gel routes, offer better possibility to control the variation of structural, compositional, and morphological features of the final nanomaterials [1,2]. 

Finally, a reduced sub-set of sites was considered to investigate variability of chemical features of soils sampled among different farms, within the same farm and as function of sampling depth. The aim is to establish the proper number of samples to be collected for each farm and the depths to investigate. This goal was achieved by the combined use of X-ray powder diffraction technique, which produces a fingerprint related to the composition and morphological structure of the soil and chemometrics [26]. 

Characterization. Ceramic bodies are characterized by density, mass, and physical dimensions. Other common techniques employed in characterizing include x-ray diffraction (XRD) and electron or petrographic microscopy to determine crystal species, stmcture, and size (100). Microscopy (qv) can be used to determine chemical constitution, crystal morphology, and pore size and morphology as well. Mercury porosknetry and gas adsorption are used to characterize pore size, pore size distribution, and surface area (100). A variety of techniques can be employed to characterize bulk chemical composition and the physical characteristics of a powder (100,101). 

The strong influence of morphology and mixing is well illustrated with the composite particle investigation. These particles were composed of a nickel shell coated on spherical aluminum particles by hydrogen reduction in aqueous metal salt solution. The overall ratio of material in a particle was about 80 wt% Ni and 20 wt% aluminum. With these particles, the ratio of reactants was approximately the same as in the mixed powders, but the morphology of the reactants is radically different. 

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