Zinc partial pressure

The zinc solubility in the matte is affected by the partial pressure of zinc and the temperature under a given matte composition. To compare the zinc solubility from one test to anodier, this must be normalized to a standard zinc partial pressure, say 0.1 atm, and a temperature. The normalized zinc solubility at 0.1 atm zinc partial pressure was calculated by dividing the measured zinc solubility by the corresponding zinc partial pressure and by 10, (Zn wt%) / (10 Pzi,). As discussed in the above section, an increase of SO C in temperature causes a 40-60% decrease in zinc solubility for a given matte composition. Thus, the normalized zinc solubility at Pzn= 0.1 atm and experimental temperature was converted to that at 13S0°C by considering the effect of temperature. These zinc solubility data is summarized in Table IV as normalized zinc solubility at Pzn = 0.1 atm and 1350"C. 

To compare the elemental distribution ratio betweoi the condoised zinc and the matte from the different tests, these were also normalized to Pzn = 0.1 atm for all tests by assuming (normalized distribution ratio at 0.1 atm zinc partial pressure) = (measured distribution ratio Pzn / 0.1) as listed in Table IV. In general, the scatter of the estimated distribution ratio is large. This is not surprising if we recognize the many sources of variation different temperatures, different degrees of splashing caused by different feed rates and gas flow rates, aiuilytical errors and even different matte compositions. 

The present test was done at Pzn= 0.34 atm. It is expected that zinc solubility in the Fe-S-0 matte would be even lower if the zinc partial pressure was controlled at 0.1 atm. 

This test was carried out to investigate the effect of the Fe/S ratio on the solubility of zinc in the Fe-S matte. The initial matte consisted of 6,718 g pyrrohite and 282 g iron which corresponds to 72 %Fe and 28 %S in the matte. The molten bath temperature was controlled to around 1325°C. The feed material consisted of 51.4% zinc concentrate, 39.9% iron ore and 8.7% charcoal. The feed mixture was injected into the bath at 51.1 g/min with 8 NL/min nitrogen. The zinc partial pressure was calculated to be 0.237 atm. 

The equilibrium conditions for each reaction may be expressed in terms of the partial pressure ratios of CO to CO2 and are illustrated in Eigure 5.1. As a simplification this assumes solid-gas reactions with unit activity of the solid oxide reactants. If in the molten phase, such as PbO dissolved in slag, the activity will be much lower and the eqnihbrinm ratios for COiCOj will be correspondingly higher. For partial pressure ratios of one or above, covering the bulk of the reactions zones of the shaft. Figure 5.1 indicates that PbO reduction should proceed readily, ZnO can be reduced to zinc vapour above 800°C, and iron oxides will be reduced primarily to FeO. In Figure 5.1 the ZnO reduction equilibrium is shown for a zinc vapour partial pressure of 0.01 atmospheres or one per cent in the gas stream. Zinc partial pressure will vary widely however, this serves only to illustrate that zinc vapour will be present at partial pressures of this order. 

Deliquescence and efflorescence. A substance is said to deliquesce (Latin to become liquid) when it forms a solution or liquid phase upon standing in the air. The essential condition is that the vapour pressure of the saturated solution of the highest hydrate at the ordinary temperature should be less than the partial pressure of the aqueous vapour in the atmosphere. Water will be absorbed by the substance, which gradually liquefies to a saturated solution water vapour will continue to be absorbed by the latter until an unsaturated solution, having the same vapour pressure as the partial pressure of water vapour in the air, is formed. In order that the vapour pressure of the saturated solution may be sufficiently low, the substance must be extremely soluble in water, and it is only such substances (e.g., calcium chloride, zinc chloride and potassium hydroxide) that deliquesce. 

One feature of oxides is drat, like all substances, they contain point defects which are most usually found on the cation lattice as interstitial ions, vacancies or ions with a higher charge than dre bulk of the cations, refened to as positive holes because their effect of oxygen partial pressure on dre electrical conductivity is dre opposite of that on free electron conductivity. The interstitial ions are usually considered to have a lower valency than the normal lattice ions, e.g. Zn+ interstitial ions in the zinc oxide ZnO structure. 

The metals can be separated by simple evaporation until the partial pressure of cadmium equals that of pure zinc, i.e. 

Next, let the example of vanadium, which, in the as-reduced condition, may contain a variety of impurities (including aluminum, calcium, chromium, copper, iron, molybdenum, nickel, lead, titanium, and zinc) be considered. Vanadium melts at 1910 °C, and at this temperature it is considerably less volatile than many of the impurity metals present in it. The vapor pressure of pure vanadium at this temperature is 0.02 torr, whereas those of the impurity elements in their pure states are the following aluminum 22 torr calcium 1 atm, chromium 6 torr copper 23 torr iron 2 torr molybdenum 6 1CT6 torr nickel 1 torr lead 1 torr titanium 0.1 torr and zinc 1 atm. However, since most of these impurities form a dilute solution in vanadium, their actual partial pressures over vanadium are considerably lower than the values indicated. Taking this into account, the vaporization rate, mA, of an element A (the evaporating species) can be approximated by the following free evaporation equation (Langmuir equation) ... 

Chemically, this can be expressed in terms of defect formation equations. Taking the partial pressure of the zinc as dominant, zinc-rich material can be formulated by the capture of zinc atoms from the gas phase ... 

In a natural gas fueled PAFC, water is condensed out of the fuel stream going to the fuel cell to increase the partial pressure of hydrogen. In a coal gasification MCFC, water often is added to the fuel stream prior to the fuel cell to prevent soot formation. The addition of excess steam not only prevents the soot formation, but also causes a voltage drop of approximately 2 mV per each percentage point increase in steam content (45). The use of zinc ferrite hot gas cleanup can aggravate the soot formation problem because of the catalytic effect of the sorbent on carbon formation, and requires even higher moisture levels (46). 

The chain transfer process whose rate depends only upon the alkylaluminum concentration (or upon the zinc-diethyl concentration) is, on the contrary, independent of the partial pressure of the olefin and may occur even if the polymerization stops for lack of monomer. 

In this case, the number of zinc ions in interstitial positions and the number of free electrons will be decreased by an increase in the partial pressure of oxygen. These disorder reactions result in a dependence of the electrical conductivity on the oxygen pressure. This effect is a well known phenomenon in the field of semiconductors (1). Complicated relations, however, will occur at lower temperatures, at which no equilibrium can be attained between the gas phase and the lattice defects in the whole... 

Zinc Chloride Hydrocracking—Batch Autoclave Work. All tests were made in a 316 stainless steel, 300-ml rocking autoclave. The equipment, the product work-up, analytical and calculational procedures used are all identical to those previously described (1). A constant hydrogen partial pressure was used in each run by monitoring it with a palladium-silver alloy probe within the authoclave. The sensitivity of the probe response was increased as compared with prior work by heat treating at... 

If the temperature and pressure are increased, then a vehicle is no longer necessary even with the sub-bituminous coal. A series of experiments was carried out without a vehicle using a hydrogen partial pressure of 205 atm and at temperatures ranging from 370° to 427°C. The zinc chloride/moisture free (MF) coal feed ratio and the reaction time were held constant at 2.5/1 and 60 min, respectively, in these runs. 

The electron concentration in donor-doped TCOs becomes compensated with increasing oxygen partial pressure. The nature of the compensating defect thereby depends on the material. As mentioned earlier, compensation of n-type doping in ZnO occurs by introduction of zinc vacancies. In contrast, compensation in 1 03 is accomplished by oxygen interstitials [117], Their importance in Sn-doped 1 03 has been already pointed out by Frank... 

Fig. 1.15. Electron concentration (dashed line) of Sn-doped indium oxide and Al-doped ZnO in dependence on oxygen partial pressure for a dopant concentration of 1 % [117]. With increasing oxygen partial pressure the donors become compensated by oxygen interstitials (In20s) or by zinc vacancies (ZnO). Reprinted with permission from [117]. Copyright (2007) by the American Physical Society...

Assuming that only the doubly charged zinc interstitials (or oxygen vacancies) contribute to the excess electrons leads to the following oxygen partial pressure dependence of the conductivity ... 

When film growth occurs under an excess of zinc, the influence of substrate temperature becomes significant. The expected steady decrease in deposition rate with increasing reactive gas partial pressure is only observed at low substrate temperatures - an increase in rate can already be seen at Ts = 200°C when the reactive gas partial pressure is increased. As a first approximation, the deposition rate in this region is directly proportional to the reactive gas partial pressure, so that for p(O2) = OmPa, no coating would result. 

Hydrogen gas, liberated from a reaction between hydrochloric acid and zinc, is bubbled through water and collected in an inverted graduated cylinder at 22°C. The pressure of the gas mixture is 765 mm Hg. The vapor pressure of water at 22°C is 20 mm Hg. What is the partial pressure of the hydrogen gas ... 

Denny and Whan (26) also reviewed various contrasting reports on the effects of C02 on the synthesis and emphasized that any complete kinetic expression should include a term involving the partial pressure of C02. A rate equation that does contain an empirical C02-dependent term for the copper-zinc oxide-alumina catalysts has been presented in 1980 by Andrew (27) in the form... 

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