Surface area reduction effect

The susceptibility of metal oxides to reduction and dissolution depends on mineralogy, crystallinity, surface area, the effectiveness of reducing and chelating agents, and microbial activity. Early culture studies with Ee(Hl)-respiring bacteria demonstrated that Ee(lll) reduction rates vary with mineral form or crystallinity... 

Adult patients presenting a noninfected VLU and receiving effective compression therapy were enrolled in this randomised, controlled, double-blind trial. The VLUs were assessed every 2weeks for 8weeks. The primary study outcome was the relative wound area reduction (WAR in %), and the secondary objectives were absolute WAR, healing rate and percentage of wounds with >40% surface area reduction. A total of 187 patients were randomly allocated... 

Common metals often form mixed oxides with the support compounds. For that reason common metals are usually used as massive metal catalysts. In the case of massive metal catalysts, a few weight percent of a promoter is added. Some promoters make mixed oxides with the active element and influence the reduction process and the surface area (structural promoter). Others are deposited on the metal surface and have an electronic interaction with the surface (chemical effect). Ammonia activity on Fe is known to be enhanced by adding AI2O3 and K2O. It is believed that AI2O3 stabilizes the high surface area of Fe (structural effect) and K2O promotes the ammonia activity per Fe surface area (chemical effect). The structural effect is well studied on Fe single crystal surfaces, where Fe(lll) is the most active plane and Fe(llO) is the next and Fe(lOO) is the least active plane [93]. Such studies have been expanded to other catalysts such as Re, and will be reviewed in Section 3.2.4.2. 

We conclude that the beneficial effects of water are not necessarily limited to reactions that are characterised by a negative volume of activation. We infer that, apart from the retro Diels-Alder reaction also other reactions, in which no significant reduction or perhaps even an increase of solvent accessible surface area takes place, can be accelerated by water. A reduction of the nonpolar nature during the activation process is a prerequisite in these cases. 

Third, design constraints are imposed by the requirement for controlled cooling rates for NO reduction. The 1.5—2 s residence time required increases furnace volume and surface area. The physical processes involved in NO control, including the kinetics of NO chemistry, radiative heat transfer and gas cooling rates, fluid dynamics and boundary layer effects in the boiler, and final combustion of fuel-rich MHD generator exhaust gases, must be considered. 

The concentration of K2TaF7 in the initial melt is the main parameter controlling the particle size and surface area of the reduced primary powder [598]. Typically, the increased concentration of K2TaF7 leads to the formation of coarse tantalum powder. According to Yoon et al. [599], the diluent prevents a strong increase in the temperature of the melt that is caused due to the exothermic effect of the reduction process. Based on the investigation of the reduction process in a K2TaF7 - KC1 - KF system, it was shown that increased amounts of diluent lead to a decrease in particle size of the obtained tantalum powder. 

Based on available results, it can be summarized that the particle size of tantalum powder increases (specific charge decreases) with the increase in temperature, K2TaF7 concentration and excess sodium. In addition, an increase in the specific surface area of the melt and Na/K ratio also leads to the formation of coarser tantalum powder. The most important conclusion is that for the production of finer tantalum powders with higher specific charges, the concentration of K2TaF7 in the melt must be relatively low. This effect is the opposite of that observed in the electrochemical reduction of melts. 

Supported iron catalysts are notoriously difficult to reduce [6-8] and thus a substantial fraction of the iron can be expected to remain inactive for the catalysis of hydrogenation. Particular attention has therefore been paid to the preparation of Fe/MgO catalysts by several different methods and examination of their effectiveness in producing metallic iron of adequate specific surface area after reduction in hydrogen. The activity and selectivity for primary amine formation have been determined for the hydrogenation of ethanenitrile (acetonitrile) and propanenitrile. 

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