Vapour pressure of the elements

Hence, the evaporation rate of each element will only be in die proportion of the alloy composition at one composition, die congruently vaporizing composition. If drere is a large difference between the vapour pressures of the elements then the element having the higher vapour pressure could be completely evaporated hrst. 

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... 

Vapour pressures of the elements. I. group of the periodic system. 

The Handbook of Thermophysical Properties of Solid Materials covers results published in the period 1940—1957, and among other properties reports on melting temperatures, densities, enthalpies of transition, heat capacities, and vapour pressures of the elements. The information is presented on data sheets and also graphically. The work is intended for use by engineers and thus only materials melting above 1000 °F are listed. 

Nesmeyanov shows graphically all the results he has collected on the vapour pressures of the elements, together with his recommended values. The book also includes tables showing recommended values for the enthalpies of vaporization, the temperatures at which the elements exert pressures between 10 Torr and 1 atm, four-term equations, and vapour pressures at a number of rounded temperatures. Rand and Kubaschewski s Thermochemical Properties of Uranium Compounds contains many data, including heat capacity, solid transformations, melting temperature... 

In many spectroscopic techniques, e.g. in ABMR, atomic beams are employed [7.1]. Such beams are generated in a vacuum system by evaporation of atoms. Vacuum techniques are discu ed in [7.2, 7.3]. The energy of the atoms will be of the order of kT, normally corresponding to thermal velocities of a few himdred m/s. The temperatm e needed to produce an atomic beam is determined by the vapour pressure of the element [7.4, 7.5] (typically a value of 10 torr is used in the evaporating oven). In Fig. 7.2 vapour pressure data for different elements are given. 

The relationship of the vapour pressure of an element p, over a binary alloy, to the vapour pressure of the pure species p as determined by the thermodynamic activity, a, of the component in the alloy... 

Examples of this procedure for dilute solutions of copper, silicon and aluminium shows the widely different behaviour of these elements. The vapour pressures of the pure metals are 1.14 x 10, 8.63 x 10 and 1.51 x 10 amios at 1873 K, and the activity coefficients in solution in liquid iron are 8.0, 7 X 10 and 3 X 10 respectively. There are therefore two elements of relatively high and similar vapour pressures, Cu and Al, and two elements of approximately equal activity coefficients but widely differing vapour pressures. Si and Al. The right-hand side of the depletion equation has the values 1.89, 1.88 X 10- , and 1.44 X 10 respectively, and we may conclude that there will be depletion of copper only, widr insignificant evaporation of silicon and aluminium. The data for the boundaty layer were taken as 5 x lO cm s for the diffusion coefficient, and 10 cm for the boundary layer thickness in liquid iron. 

Some metals are soluble as atomic species in molten silicates, the most quantitative studies having been made with Ca0-Si02-Al203(37, 26, 27 mole per cent respectively). The results at 1800 K gave solubilities of 0.055, 0.16, 0.001 and 0.101 for the pure metals Cu, Ag, Au and Pb. When these metal solubilities were compared for metal alloys which produced 1 mm Hg pressure of each of these elements at this temperature, it was found that the solubility decreases as the atomic radius increases, i.e. when the difference in vapour pressure of the pure metals is removed by alloy formation. If the solution was subjected to a temperature cycle of about 20 K around the control temperature, the copper solution precipitated copper particles which grew with time. Thus the liquid metal drops, once precipitated, remained stable thereafter. 

A. N. Nesmayanov, Vapour Pressure of the Chemical Elements. Amsterdam, New York Elsevier, 1963 T. Boublik, F. Vojtech and H. Eduard, The Vapor Pressure of Pure Substances. Amsterdam, New York Elsevier Scientific, 1973. 

This expression, therefore, gives the correct value of the heat of formation. The heats of sublimation of elements can usually be determined directly, but are mostly derived from the change of vapour pressure of the solid with the change of temperature, making use of the Clapeyron equation which relates these quantities. 

Single, double and triple filaments have been broadly used in thermal ionization sources. In a single filament source, the evaporation and ionization process of the sample are carried out on the same filament surface. Using a double filament source, the sample is placed on one filament used for the evaporation while the second filament is left free for ionization. In this way, it is possible to set the sample evaporation rate and ionization temperature independently, thus separating the evaporation from the ionization process. This is interesting when the vapour pressure of the studied elements reaches high values before a suitable ionization temperature can be achieved. A triple filament source can be useful to obtain a direct comparison of two different samples under the same source conditions. 

Volatilization is usually utilized for separating individual trace elements from the sample before the determination. The methods based on volatilization are concerned mainly with non-metallic and amphoteric elements which have high vapour pressure in the elemental form (e.g., chlorine, bromine, sulphur), or in compounds with halogen, hydrogen, or oxygen. Other volatilization methods exist for the separation of certain elements, such as the distillation of boron as methyl borate. 

A. N. Nesmeyanov, Vapour Pressure of the Chemical Elements , Elsevier, Amsterdam,... 

In general, a weight loss of up to 20% observed as a result of decomposition for all the MAX phases can be attributed to the release of gaseous Al by sublimation during the decomposition process because the vapour pressures of the A elements exceed the ambient pressure of the furnace (i. e. < 5 x 10 torr) at > 1500°C. Since the vapor pressure of a substance increases non-linearly with temperature according to the Clausius-Clapeyron relation [25], the volatility of A elements will increase with any incremental increase in temperature. 

Mercury has been extensively used in instruments for laboratory tests. Carelessness with mercury may cause inhalation of mercury vapour in a concentration that may be a serious health risk. Mercury is the only metallic element that is liquid at room temperature at room temperature, the vapour pressure of the metal is so high that the air may contain hazardous concentrations of Hg. 

Nesemeyanov, A.N. (1963). Vapour pressures of the ehemioal elements. Elsevier, New York. 

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