Mechanochemical surface preparation

The most commonly employed mechanochemical surface preparation combines mechanical abrasion with chemical etching. The idea was to rely on the etching process to produce microroughness and the blasting process to produce macroroughness. Initial joint strength was good but durability was poor. 

The various surface preparations for improving joint durability can be broadly classified into mechanical, chemical, mechanochemical, and electrochemical. 

Abstract. Nanocarbon materials and method of their production, developed by TMSpetsmash Ltd. (Kyiv, Ukraine), are reviewed. Multiwall carbon nanotubes with surface area 200-500 m2/g are produced in industrial scale with use of CVD method. Ethylene is used as a source of carbon and Fe-Mo-Al- mixed oxides as catalysts. Fumed silica is used as a pseudo-liquid diluent in order to decrease aggregation of nanotubes and bulk density of the products. Porous carbon nanofibers with surface area near 300-500 m2/g are produced from acetylene with use of (Fe, Co, Sn)/C/Al203-Si02 catalysts prepared mechanochemically. High surface area microporous nanocarbon materials were prepared by activation of carbon nanofibers. Effective surface area of these nanomaterials reaches 4000-6000 m2/g (by argon desorption method). Such materials are prospective for electrochemical applications. Methods of catalysts synthesis for CVD of nanocarbon materials and mechanisms of catalytic CVD are discussed. 

Complex oxides with perovskite structure are prepared by means of mechanochemical synthesis. A mixture of initial oxides, hydroxides or carbonates are subjected to mechanical activation, then the powder is calcined at 600-800°C for 2-4 h. The specific surface area of thus prepared perovskites is 10-20mVg [35-37]. 

New method of dispersed perovskites synthesis based upon mechanochemical activation of the solid starting compounds is elaborated. The influence of defect structure of these compoimds as well as surface segregation on their catalytic properties is discussed. Basic stages of the monolith perovskite catalysts preparation are optimized. The experimental samples of monolith catalysts of various shapes are obtained, possessing high activity, thermal stability and resistance to catalytic poisons. 

The application of mechanochemistry for the construction of metal-ligand bonds can significantly improve the synthesis of porous MOFs, a class of materials with increasing technological importance. Different materials have been synthesized such as (HKUST-1) obtained by neat grinding or LAG of copper(II) acetate monohydrate with benzene-1,3,5-tricarboxylic acid that has shown comparable BET surface area to that of samples obtained by conventional solution-based routes [14]. Another example concerns a porous interpenetrated mixed ligand MOF Zn2(fma)2(bipy), prepared mechanochemically from Zn(0Ac)2 2H20, fumaric acid, and 4,4-bipyridine [15]. 

Composites or alloys of Sn and Cu can also be prepared by other methods, such as electrochemical coprecipitation, mechanochemical methods, and chemical reduction, and their electrochemical performance can be improved further. For example, the Cu-Sn composite (atomic ratio 3.83 1) obtained by electrochemical deposition has a reversible capacity of 200 mAh/g after 40 cycles. Incidentally, CugSns alloy can also be prepared by deposition of Sn on Cu surface followed by annealing and pyrolysis at high temperature. 

The series of MnOx-modified cordierite-like catalysts 2(Mgi xMnx)0-2Al203-5Si02 (x=0-l) was prepared by mechanochemical method. It was found that the increase of calcination time and temperature, the decrease of particle size duriug the mechanical treatment, the modification with manganese oxide (up to x=0.5) leads to better cordierite crystallization followed by reduction of specific surface area and internal pore volume of the samples. The fully substituted catalysts were shown to have the highest selectivity to NO at studied conditions, most probably, due to the higher content of Mn20s (active oxide) on the catalysts surface. 

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