Mechanical mixture

Potassium Chloride. The principal ore encountered in the U.S. and Canadian mines is sylvinite [12174-64-0] a mechanical mixture of KCl and NaCl. Three beneficiation methods used for producing fertilizer grades of KCl ate thermal dissolution, heavy media separation, and flotation (qv). The choice of method depends on factors such as grade and type of ore, local energy sources, amount of clay present, and local fuel and water availabiUty and costs. 

Crystallization methods are widely used for the separation, or resolution, of enantiomer pairs. Enantiomer mixtures may essentially crystallize in two different ways. In around 8 per cent of cases, each enantiomer crystallizes separately, giving rise to a mechanical mixture of crystals of the two forms, known as a conglomerate. Conglomerates may usually be separated by physical methods... 

Biol.) (Mause-Einheit) mouse unit. Mechanik,/. mechanics, mechsnism. Mechaniker, m. mechanician, mechanisch, a. mechanical, mechanic. — adv. mechsnically. — mechanisches Gemenge, mechanical mixture, mechanisieren, v.t. mechanize. 

Modern composite solid propellant is a mechanical mixture of the powder-like chemicals and a binding resin. The propellant used for the Space Shuttle solid rocket boosters (SRBs) is a typical example of such mixture ... 

Free nitrenes exist as mixtures of singlet and triplet forms and, since the triplet is simultaneously more thermodynamically stable and unable to react by a one-step mechanism, mixtures of cis and trans isomers invariably resulted from the early methods (Scheme 4.8). 

The partial molar entropy of a component may be measured from the temperature dependence of the activity at constant composition the partial molar enthalpy is then determined as a difference between the partial molar Gibbs free energy and the product of temperature and partial molar entropy. As a consequence, entropy and enthalpy data derived from equilibrium measurements generally have much larger errors than do the data for the free energy. Calorimetric techniques should be used whenever possible to measure the enthalpy of solution. Such techniques are relatively easy for liquid metallic solutions, but decidedly difficult for solid solutions. The most accurate data on solid metallic solutions have been obtained by the indirect method of measuring the heats of dissolution of both the alloy and the mechanical mixture of the components into a liquid metal solvent.05... 

For a fixed filling ratio, the degree of crystallinity and mean crystallite size are somewhat higher in PFCM than in mechanical mixtures of similar composition and similar matrix characteristics [299, 300]. 

In polymer regions of PFCM bordering on the filler one typically observes the formation of crystallites as tape-like structures orientated perpendicularly to the filler surface [295, 305, 306]. In real fact these are transcrystallite structures. A morphology of this kind can appear in a mechanical mixture as well [305, 306], but there the layer thickness will be much smaller [306, 307]. 

Using calorimetry to estimate the degree of filler-polymer interaction as described in [99] the authors of [318, 319] determined that the filler reaction with PVC is exothermic, which is indicative of a stronger bond in the polymer-filler system. No thermal effect was noted for mechanical mixtures, except for a few cases where it was endothermal. 

In [324] it was noted that in case of polyethylene-based PFCM it is the MM which is the parameter controlling the composite viscosity. For a fixed MM, the viscosity of the melt increases symbatically with the filling percentage by mass. The nature of the viscosity versus MM relationship is similar for both PFCM and mechanical mixtures, that is, in terms of rheology the two systems are practically identical. 

Fig. 2. Relationship of conductivity of polypropylene-based polymer composites and filler concentration (natural graphite) 1 — polymerization filling 2 — mechanical mixture [24]...

Decomposition of Ag20. Dubinin et al. [642] have shown that the induction period to Ag20 decomposition at 603 K is reduced and the initial reaction rate is increased by the deposition of a thin film of Ag (or of Ni) on the reactant surface. Close contact between reactant and additive must be established for the effective promotion of salt breakdown since no activating influence was detected during reactions of mechanical mixtures of Ag20 and Ag. 

The mathematical model was found to describe well the observed activity increase for numerous mechanical mixtures of a-Sb204/Mo03 at different oxygen partial pressures and temperatures.73... 

MASSECUITE A mechanical mixture of crystals in mother liquor (molasses or heavy syrup), produced in a vacuum pan. The suspension of sugar crystals in mother liquor produced during the early stages of crystallization. 

Promotional effects of sulfide can evidently be explained, because exposure of reduced metals Is Increased on reduced sulfided catalysts. The role of cobalt Is less clear. It Is normally not fully reduced. It apparently does not promote greater exposure of Mo In any form detected, either In the presence or absence of sulfide. On the contrary. It evidently only decreases the concentration of exposed Mo atoms, although, at concentrations typically used, most. Mo atoms are unaffected by Co. Either some property of Co alone or some local cooperative effect of adjacent Co and Mo must explain promotion. Simple mechanical mixtures will not give the synergism observed, however (1-4). 

No new peaks were observed in the mechanical mixtures. The binding energies of all elements were the same in the pure phases and in the mixtures [14]. Figure 1 shows the apparent atomic percentages of molybdenum and cobalt, as given by XPS, on the surface of the sulfided pure phases and mechanical mixtures. In both cases, the experimental results are close to the theoretical values calculated according to Equation 2. 

Figure 2 shows the conversions obtained with the three series studied, as a function of the mechanical mixtures composition, one hour after the beginning of the reaction and at the steady-state. Each series presents a maximum of activity, but at a different composition. SA6 series has a maximum between R , values of 50 and 75, whereas SA12 series has a maximum around = 50, and SA60 series near R , = 75. The dashed lines on the figures represent the sum of the individual contributions of the pure phases, calculated according to Equation 3. A very important synergetic effect is observed in all series, i.e., the activity of the mixtures is... 

Pure silica-aluminas are strongly deactivated, losing about 80% of their activity before reaching the steady-state. The loss in pure CoMo/Si02 catalyst is much less pronounced (about 15%). Mechanical mixtures represent an intermediate case they lose between 35% and 50% of their activity. 

Table 1 shows the experimental carbon contents of the used samples, compared to the theoretical values obtained by adding the contributions of the individual pure phases, taking into account their proportions in the mixtures. All mechanical mixtures present experimental carbon contents considerably lower than these calculated values. 

Figure 2. DPM conversion as a function of the mechanical mixtures composition, after 1 h ( ) of reaction and at the steady-state ( ), compared to the theoretical values calculated by Equation 3 (dashed lines).

Figure 3 shows the amount of Bronsted sites, as measured by the surface of the characteristic IR peak at 1540 cm after outgassing at 523 K, as a function of the composition of the mechanical mixtures. The dashed lines represent the addition of the contribution of the pure phases, calculated as in Equation 3. An enhancement of the amount of Bronsted sites on the mixtures, when compared to the theoretical values, is observed. This effect is not very clear in SA6 series, but it is more evident in SA12 and SA60 series. The reproducibility of the experiments has been checked the variation between different wafers of the same sample was always inferior to 10%. 

This interpretation of the experimental data is supported by the differences observed in the deactivation patterns and carbon contents after test, since one notorious effect of Hjp is the capacity to diminish the deactivation caused by coke deposition on the active sites [21,22]. This is supposed to be due to a reaction with the coke precursors, very likely a hydrogenolysis. In pure silica-aluminas, where no source of spillover is present, no special protection against deactivation should be observed. Indeed, the silica-aluminas lose most of their activity (about 80%) before reaching the steady-state and present the highest carbon contents after catalytic test. On the other hand, in the case of the mechanical mixtures, where spillover hydrogen is continuously produced by the CoMo/Si02 phase and can migrate to the silica-alumina surface, the predicted protection effect is noticed. The relative losses of activity are much lower... 

Reduction temperature 1 h with H,. Maximum NO to N, conversion. Hvlaximum NO conversitni temperature. CH to COj conversion Light-oflf temperamre selectivity. "Mechanical mixture. 

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