Vapour pressure of zinc

AG=2.916 kJ/mol at 18°C. The vapour pressure of water is 15.48 mmHg at the same temperature. What is the vapour pressure of zinc sulphate heptahydrate in equilibrium with the hexahydrate at 18°C (Hint the water vapour pressure gives the free energy change for the vaporization process.)... 

The vapour pressure of zinc above a slag bath relates to the CO/CO, partial pressure ratio in the gas and the activity of ZnO in the slag according to Equation 8.4 ... 

Gibbs energies can be obtained by measuring the dissociation pressure directly for alloy systems with one or more volatile components. Taking again the example of brass by the determination of the vapour pressure of zinc above the alloy as well as above, say, liquid zinc, one obtains the partial molar Gibbs energy of solution, by means of the scheme ... 

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. 

An important element that must be recovered from zinc is cadmium, which is separated by distillation. The alloys of zinc with cadmium are regular solutions with a heat of mixing of 8300 Xcd fzn J gram-atom and the vapour pressures of the elements close to the boiling point of zinc (1180K) are... 

The first ALD thin films were deposited in the 1970s using elemental zinc and sulphur, reacting to form ZnS at 250-450 °C [44], Although metals as ALD precursors seems to be the most straightforward method of producing compound thin films, this type of process is limited by the generally low vapour pressure of elemental metals. Therefore only zinc and cadmium have been used as metal sources in ALD processes. However, some metalloids, e.g. selenium and tellurium, can be used as well. 

Calculate the vapour pressure of Zn over a Cu-Zn binary solution of Nz = 0.3 at 1,280K. The vapour pressure of pure liquid zinc is given by... 

There have been many theoretical determinations of the rates of distillation under vacuum, but none that appeared to be applicable to vacuum dezincing when its development was commenced at Port Pirie in 1946. Thus it was felt to be desirable to develop the theoretical side (37) simultaneously with the practical development, as a guide to understanding and possible later application to optimising of the process. Figure 7 illustrates the concept of the distillation process which was developed. It was necessary to discard some faulty ideas or misconceptions, which derived fix>m implicit notions associated with equilibrium, but not kinetic conditions. Carman (38), for example, assumed that the partial pressure of the vapour of the condensing species is equal to its partial pressure in the condenser. It is not, unless the condensation rate is zero. Richardson (6) assumed that the measured vacuum is equal to the distilling species, which it is not, but is instead the partial pressure of the inert atmosphere. Warner (40) assumed the partial pressure of zinc to be constant across the distillation space, which is not correct unless the distillation rate is zero. 

In this experiment for the formation of zinc aluminate, the prerequisites were fulfilled by suspending a number of equal-sized spheres of a-corundum in a ZnO crucible and bringing the system to the reaction temperature. The vapour pressure of ZnO is large enough to ensure... 

Liquid zinc cannot be formed in the slag unless the vapour pressure is above the saturation vapour pressure of liquid zinc at the operating temperature. The saturation vapour pressure is given by Equation 8.6, and under atmospheric pressure conditions at around 1200 to 1300°C the saturation vapour pressure well exceeds the vapour pressure derived from reduction. Hence liquid zinc cannot form in the slag bath. 

The equilibrium constant for zinc oxide reduction according to Equation 8.4 is given as a function of temperature in Table 8.1, together with the partial pressure of zinc vapour in equilibrium with a slag containing four per cent ZnO, as the end-point slag fumer composition, and a reduction gas ratio of C0 C02 of 2 1. Also shown is the saturation vapour pressure of liquid zinc metal according to Equation 8.6. 

As well as removing zinc, fuming will also remove most of the lead content of the slag and if this is recycled by return of zinc smelter residues to the lead smelting stage, then almost complete lead recovery can be achieved in an integrated operation. This ability of lead to fume is illustrated by the vapour pressure of lead compounds at 1250°C ... 

Vacuum distillation utilises the widening differences in vapour pressure between zinc and lead at lower temperatures, as shown in Table 12.3. The rate of mass transfer is also increased at reduced total pressure. 

We consider now the possibility of the presence of an additional phase, namely, liquid zinc. If the temperature of the reaction system is raised above T the pressure will rise above 1 atm. It is found that the displacement to the right in the chemical reactions causes the partial pressure of the zinc vapour to rise more rapidly, with increasing temperature, than the vapour pressure of liquid zinc. The vapour... 

The interest in a wide range of rare earth-based intermetallic compounds, each with individual physical and metallurgical properties, presents the crystal grower with problems over and above those already encountered in discussion of the elements themselves. The use of UHV-rated environments and crucible-less techniques to minimise contamination is of paramount importance in the preparation of high purity rare earth elements. Adoption of the same stringent criteria is not always possible in the production of rare earth intermetallic compounds. The preparation technique employed has to take into account not only the physical properties of the rare earth metal, but also those of the other constituent(s) which can present equally difficult problems, e.g. the vapour pressure of molten zinc or the reactivity of molten Fe with W, a commonly used crucible material. These other constituent(s) also provide an additional potential source of contamination which can influence the quality of the compound prepared. Frequently, the main... 

Solution According to Eq.(4.7b), the vapour pressure of liquid zinc may be expressed as... 

Although zinc has an appreciable vapour pressure at the temperatures of treatment, it is unlikely that zinc vapour plays any significant part in the diffusion process and it is generally accepted that the mechanism relies almost exclusively on intimate contact of hnely divided zinc dust with the steel surface. In spite of this requirement, coatings of even thickness and composition are obtained on the most intricate shapes, on fine threads, inside blind holes, and in the bore of small-diameter tubes. Large articles of uniform section, e.g. rods, tubes, etc. can be coated by this process. 

The results obtained in above experiments confirm the removal of chemisorbed particles in the process of immersion of the film with preliminary chemisorbed radicals in a liquid acetone. Note that at low pressures of acetone, the CHa-radicals absorbed on ZnO film could be removed only by heating the film to the temperature of 200 - 250°C. Moreover, if the film with adsorbed radicals is immersed in a nonpolar liquid (hexane, benzene, dioxane), or vapours of such a liquid are condensed on the surface of the film, then the effect of removal of chemisorbed radicals does not take place, as is seen from the absence of variation of electric conductivity of the ZnO film after it is immersed in liquid and methyl radicals are adsorbed anew onto its surface. We explain the null effect in this case by suggesting that the radicals adsorbed on the surface of the ZnO film in the first experiment remained intact after immersion in a nonpolar liquid and blocked all surface activity of the adsorbent (zinc oxide). 

Diammino-mercuric Iodide, [Hg(NH3)2]I2, behaves like the ammines of zinc and loses ammonia on exposure to air the mon-ammino derivative from examination of vapour-pressure measurements does not appear to exist. 

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