Stoichiometry particle

Safe operation of ferromanganese furnaces requires careful control of raw material particle size, oxygen content of the ore blend, and charge stoichiometry (38). 

Kim et al. [601] investigated the influence of both temperature and the excess amount of sodium compared with the stoichiometry of the interaction. The molten system K2TaF7 - KC1 - KF was used for the experiments and the temperature varied in the range of 800-980°C. The excessive amount of sodium ranged from -10% to +10%. It was found that increasing either the temperature or the excess amount of added sodium led to an enhanced yield and increased the particle size of the tantalum powder. Optimal conditions were found to be 920°C and 5% excess reductant. 

A recent review relating the pyrotechnic reaction mechanism, particle size, stoichiometry, temp and compaction density to burning rate is Ref 66, and a study of the effect of multidimensional heat transfer on the rate of flame propagation is Ref 120, which showed that the material of the delay body has no effect on the performance of most delay compns, a finding which agrees with test data... 

To construct an overall rate law from a mechanism, write the rate law for each of the elementary reactions that have been proposed then combine them into an overall rate law. First, it is important to realize that the chemical equation for an elementary reaction is different from the balanced chemical equation for the overall reaction. The overall chemical equation gives the overall stoichiometry of the reaction, but tells us nothing about how the reaction occurs and so we must find the rate law experimentally. In contrast, an elementary step shows explicitly which particles and how many of each we propose come together in that step of the reaction. Because the elementary reaction shows how the reaction occurs, the rate of that step depends on the concentrations of those particles. Therefore, we can write the rate law for an elementary reaction (but not for the overall reaction) from its chemical equation, with each exponent in the rate law being the same as the number of particles of a given type participating in the reaction, as summarized in Table 13.3. 

The stoichiometry of the recharged DNA/PLL/SPLL particles was studied using sucrose-gradient ultracentrifugation of fluorescently labeled polyion complexes in 25 mM HEPES buffer. Rhodamine-labeled DNA (Rh-DNA) and either fluorescein-labeled PLL (Fl-PLL) or SPLL (Fl-SPLL) were used to determine their relative amounts within DNA... 

The number of surface atoms can be determined by chemisorption of probe molecules (H2, O2...), knowing the stoichiometry of the adsorbed species. As an example, in the case of Pt, the stoichiometry of irreversibly adsorbed hydrogen (H/Pts) and oxygen (0/Pts) at room temperature are both close to 1/1 [108-111]. Knowing the total number of atoms (elemental analysis) and the number of irreversibly adsorbed H and O, the dispersion of the particles (D = Pts/Pt) is then easily obtained. Note that the dispersion of these particles decreases when their size increases (Fig. 5). 

Fig. 7 Reaction of SnBu4 on Pt particles supported on silica at 50 °C evolution of the stoichiometry of surface organotin species as a function of coverage and reaction time (see time in square boxes)...

In practice there is a need for characterization of the dispersion, if it were only to estimate the efficiency of the catalytically active component. This can be done by chemisorption of a gas that adsorbs at the surface of the metal particles. H2, CO, O2, and N2O are applied most often. For the calculation of the dispersion it is of paramount importance that the stoichiometry of the adsorption reaction is known and that the reaction is limited to the surface. 

In some specific cases one would like to convert the chemisorption data into an averaged particle size. In that case, the number of surface atoms per unit surface area (density of surface atoms) is an essential parameter. Since this number depends on the type of the crystallographic plane, (see Table 3.7), one also needs information on the types of crystallographic planes exposed to the gas phase. This is also important for another reason the adsorption stoichiometry may depend on the crystallographic plane. 

The electroneutrality condition decreases the number of independent variables in the system by one these variables correspond to components whose concentration can be varied independently. In general, however, a number of further conditions must be maintained (e.g. stoichiometry and the dissociation equilibrium condition). In addition, because of the electroneutrality condition, the contributions of the anion and cation to a number of solution properties of the electrolyte cannot be separated (e.g. electrical conductivity, diffusion coefficient and decrease in vapour pressure) without assumptions about individual particles. Consequently, mean values have been defined for a number of cases. 

---