Mechanochemical treatment

When polymerization proceeds in the presence of modifiers, the mechanochemical process enhances cross-linking and, correspondingly, improves the physicochemical properties of final plastics. For example, mechanochemical treatment of acrylonitrile butadiene styrene (ABS) plastic in the presence of tolnene diisocyanate improves thermal oxidative stability of the plastic (Chetverikov et al. 2002). 

A wide variety of instrumental techniques, including X-ray diffraction, thermal analysis, electron microscopy, MAS-NMR and infrared spectroscopy, have been employed at different levels of complexity to investigate the effects of mechanochemical treatment on kaolin. Unfortunately, vibrational spectroscopy has only been used at a superficial level in the study of milled kaolin despite the considerable contribution that it has made to the understanding of the structure and reactivity of kaolin itself. 

Figure 13.3.5 shows typical SEM photographs of the silica-coated polyethylene particles prepared by dry impact blending utilizing mechanochemical treatment and pollen grain of Clintonia udensis. 

S. Yariv, I. Lapides, The Effect of Mechanochemical Treatments on Clay Minerals and the Mechanochemical Adsorption of Organic Materials onto Clay Minerals, /. Mater. Synthesis Processing, 2000, 8 (3-4), 223. 

The investigation of hydrogen sorption properties of the MgH2-CNF composites, obtained by mechanochemical treatment of mixtures of the components, testifies about availability of use of carbon nanofibers for creation of hydrogen storage composite materials. 

Keywords Magnesium hydride Graphite Mechanochemical treatment Composite ... 

In the present work magnesium hydride as a starting material has been used for higher effectiveness of mechanochemical treatment. Magnesium hydride is less plastic and more fragile material as compared with metallic magnesium [3]. 

Keywords Alloy Composite Hydrogen Intermetallide Ternary eutectic Hydrogenation kinetics Mechanochemical treatment Hydrogen sorption... 

Boldyrev V.V., Khabibulhn A. Kh., Kosova N.V., Avvakumov E. G. Hydrothermal reactions under mechanochemical treatment. J. Mater. Synthesis and Processing 1996 4 377-81. 

Temuujin I., Mackenzie K.I.D. et al. Effect of mechanochemical treatment on the synthesis of calcium dialuminate. J. Mat. Chem. 2000 10 1019-23 Kvitkovsky A.K., Kosova N.V., Awakumov E.G. et al. Mechanochemical synthesis of calcium hydroaluminates. Chem Sustainable Development 2000 8 686-91. 

Temuujin J., Mackenzie K.l.D. Effect of mechanochemical treatment on the synthesis of calcium dialuminate. J. Materials Chemistry 2000 10 1019-23. 

Sasaki K., Masuda T., IshidaH., MitsudaT. Synthesis of calcium silicate hydrate with Ca/Si=2 by mechanochemical treatment. J. Am. Ceram. Soc. 1996 80 472-76. KosovaN.V., Avvakumov E.G., Malakhov V.V. et al. About nature ofphases formed in soft mechanochemical synthesis of calcium titanate. Doklady Akad. Nauk, 1997 356 350-53. 

In co-hydropyrolysis experiments without catalysts the degree of pine wood/ polyethylene mixture (1 1 weight ratio) conversion was 80% wt. and yield of the light liquid fraction - 23% wt. The addition of iron ore catalyst activated by mechanochemical treatment increased the degree of mixture conversion by 5-13%. This increase was mainly due to light liquid fraction formation. The variation of catalyst nature (pyrite, pyrrhotite, haematite) influences on the product composition. Pyirhotite catalyst yields the highest amount of the light fraction (about 40% wt.). 

Barothermal treatments were applied directly to catalyst extrudates. In the course of mechanochemical treatments, extrudates were physically milled, loaded into a planetary mill and extruded again after the treatment. 

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... 

It has been shown by us [9,10] that mechanochemical treatment is a perspective method to modify the properties of the precursor VOHPO4.O.5H2O and thus, to influence the catalyst prehistory. The present paper deals with the possibilities of mechanochemical and barothermal treatments applied at different stages of the catalyst synthesis the initial reactants, the precursor and the final catalyst. 

It has been established that mechanochemical treatment increases the specific surface area of V2O5 and produces V" ions. The latter phenomenon is indicated by an appearance of the low-energy contribution in the XPS spectrum of V 2p electrons. The STM study [13,14] showed that after the mechanochemical treatment in ethanol the change of V2O5 texture took place due to an anisotropic plastic shift deformation along the planes parallel to (001). This leads to an increase of the relative exposure... 

The change of V2O5 texture during its mechanochemical treatment in ethanol leads to the synthesis of VPO-El precursor with low specific surface area and unchanged texture. It can be... 

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). 

Continuation of the mechanochemical treatment leads to amorphization of the sample followed by the formation of vanadyl pyrophosphate phase. It should be however noted that even after 60 min. of the treatment this compound is not well crystallized and the specific surface area of the final catalyst is much smaller than that of a sample obtained by in situ activation of a precursor after 20 min of its mechanochemical treatment. 

It follows from the results presented in Table 4, that the samples obtained by mechanochemical treatment of the precursor become more active in the reaction of n-butane partial oxidation so that the hydrocarbon conversion and selectivity to maleic anhydride increase. The sample converted into vanadyl pyrophosphate by means of the mechanochemical treatment turned out to be more efficient than that activated with the reaction mixture. The most interesting is the sample after 30 min. treatment which is "half-activated" and consists of the amorphous phase. The active component forming directly in the catalytic mixture without long activation procedure gives rise to the most active and selective catalyst for n-butane oxidation. 

Recently [13, 16] we have shown the possibility of efficient promotion of VPO precursor with bismuth compounds. The present paper reports new results on promotion of VPBiO precursor with lanthanum compounds (previously a similar catalyst was shown to be active in tetrahydrofuran formation [17]). Table 5 compares the properties of traditionally prepared VPBiLaO sample (by simultaneous introduction of bismuth and lanthanum additives in the course of the synthesis of VPO precursor) with that (VPBiO-La-M) produced by the mechanochemical treatment of VPBiO precursor and lanthanum oxide powders. The treatment in the latter case was carried out for 10 min. in ethanol medium. 

The properties of vanadyl pyrophosphate after mechanochemical treatment... 

Figure 1. Transmission Scanning Microscope pictures of vanadyl phyrophosphate. a) initial, and after mechanochemical treatment b) in water, c) in ethanol and d) dry milling.

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). 

Additional Fe203 was added at the final stage of the mechanochemical treatment. 

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