Mechanochemical dispersion

Chen, C.-W., Oakes, C.S., Byrappa, K., Riman, R.E., Brown, K., TenHuisen, K. S. and Janas, V.F. (2004) Synthesis, characterization, and dispersion properties of hydroxyapatite prepared by mechanochemical-hydrothermal... 

Well-dispersed and long-term stable carbon nanotubes/polyol dispersions can also be prepared by a mechanochemical approach with the aid of a dispersing agent (Tang and Xu, 1999). Good dispersion of CNTs in polymer matrix can be achieved by means of high-power dispersion, compatibilizer, polymer-assisted blending, and surfactants (Cochet et al., 2001). 

The fundamental task, in our opinion, is to correlate the principles and methods of the proposed synthesis with those of mechanochemical synthesis. Thus, besides the destruction processes and mechanochemical synthesis discussed in the literature, other lands of transformations sometimes occur as side reactions, or even as major processes. These include chemical fixation of small molecules (methyl chloride or butyl alcohol) on mechanically activated macromolecular backbones grafting of inorganic surfaces (quartz, metals, metallic oxides, inorganic salts, etc.) dispersed by vibratory milling on polymerized fragments synthesized from monomers present in the reaction medium, and activated by centers on the inorganic surface (14) and the possibility of some reactions (such as nitration), achieved so far on macromolecular supports and only as side reactions. 

Propagation of the reaction front causes intense dispersion of the frozen matrix of the monomer, and the temperature profile of the wave preserves all qualitative features characteristic of the mechanochemical wave of a solid-state conversion. 

Lithium aluminates. The compounds Li0H-2Al(0H)3-mH20 and LiCl-2Al(0H)3-mH20 (here m = 0.5 1.0 2.0) are easily synthesized under very low mechanical loading (blade mixer) in stoichiometric Al(0H)3+Li0H H20 and Al(0H)3+LiCl H20 mixtures [1,2]. It was stated that the dispersion of the initial aluminium hydroxide strongly influenced on the kinetics of mechanochemical interaction. The interaction rate increases linearly with the specific surface of the initial hydroxide. Fig. 6.1 shows the data on reactivity of initial hydroxide with different specific surface area (6 and 2 mVg, respectively). 

A detailed investigation of soft mechanochemical synthesis of aluminium titanate was described in [60]. The data obtained in this study are the evidence of the formation of amorphous hydrated aluminium titanium compounds at the initial stages. These compounds are stable till 450-700°C at higher temperature they decompose to give aluminium and titanium oxides which form dispersed aluminium titanate at 1340°C. 

In [94-98] mechanochemical method was nsed for the synthesis of high disperse stoichiometric and nonstoichiometric Li,Mn 04 spinel starting from different manganese (Mn02, Mh203, MnO) and lithium (LiOH. Li0H-H20, LiiCOi) compounds. 

Here, a new method for the preparation of an aqueous, well-dispersed sol of HAp nano particles directly via a mechanochemical route is described. It should be noted, that such products are very suitable for usual ceramic purposes as well. 

While stndying the mechanism of mechanochemical synthesis of magnesinm silicate, it was shovra that the components are dissolved in the liqnid phase and interact with each other [33]. At first, the precipitation of hydrosilicates from the solntion in fine disperse and X-ray amorphons state occnrs. Then the growth of larger crystals takes place. Therefore, the prodncts are not detected directly after mechanical activation some exposnre is necessary for them to be crystallized. 

Mechanochemical treatment of VPBiO sample (Dl) suspended in water and in the absence of any dispersant did not lead to important changes in phase composition. During the catalyst treatment in ethanol in the presence of hydrazine some visible changes occurred in its XRD pattern. Thus, for the sample treated for 40 min (D1-M40) the weak peaks at d = 0.386 and 0.313 nm attributed to the (VO)2P207 phase appear against a significant halo-effect. The... 

Previously we showed [13,16] that the nature of dispersant had a quite remarkable effect on the properties of VPBiO precursor which was subjected to a short-time mechanochemical treatment (up to 10 min.) and the best result was obtained when ethanol was used. Here we will describe the influence of the time of treatment on the properties of VPO precursor (PA = 1.07). 

The evidence of the polymer adsorption on the surface of pigment particles and the formation of protective layers has been obtained by ESA method by experiments on measuring the -potential of the TiC>2 surface in aqueous dispersions in the presence of EFIEC (Table 2). It can be seen from the table that -potential becomes less negative in the presence of EHEC and still more approaches zero as a result of the treatment of dispersions in an ultrasonic field. This indicates the activation of polymer adsorption and the formation of stabilizing layers due to mechanochemical modification of particles. From the table it is also seen that as a consequence of mechanochemical treatment, the size of pigment particles in dispersions decreases, and dispersion becomes structurally more uniform, which leads to an increase of its stability even at increased temperature (experiment 4). 

For aqueous dispersions of CuPc, a mechanochemical modification of surface results in the elimination of the problem of wetting and the obtaining of intensively coloured stable aqueous dispersions of this pigment. 

In our concluding remarks we can emphasize that depending on the nature of interactions between the components that constitute the medium and the solid, as well as on a combination of external conditions, one may observe the effects of various types and intensity. These include the facilitation of plastic flow of solids, or, alternatively, brittle fracture due to the action of lowered stresses mechanochemical phenomena in the zone of contact mechanically activated corrosion (the stress corrosion) the processes that are close to the spontaneous dispersion (the so-called quasi-spontaneous dispersion), and the true spontaneous dispersion, leading to the formation of thermodynamically stable lyophilic system. A great variety of types of interactions that exist between the stressed solids and the medium in contact with it requires careful and thorough examination of conditions under which... 

To lower the friction and mechanochemical wear in friction joints it is possible to use solid lubricants [71] containing fuming-oxides (FO) as an active modifier of nonferrous metals. The solid lubricants represent fine-dispersed sublimation products of lead smelting slag. 

These reactions can be carried out in solution or in dispersion or by reaction in the solid phase (Cunneen and Porter, 1965) in the last case it is again dilHcult to differentiate the Prins reaction from mechanochemical reactions initiated by chain rupture during mastication. 

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