Fractionation element

We may now argue whether or not a silicate melt can fractionate elements of the same group. The question is rather important for REE, whose relative fraction-... 

We also know that processes that eject solar wind fractionate elements based on their first ionization potential, the energy necessary to ionize the element. Over time, ejection of solar wind that is fractionated relative to the bulk Sun changes the surface composition of the Sun, the part that we measure spectroscopically. There are theoretical models to account for this effect, but it introduces uncertainties into the inferred composition of the bulk Sun. 

The solar system formed from a well-mixed collection of gas and dust inherited from its parent molecular cloud. The bulk composition of this material, as best we can know it, is given by the solar system abundances of elements and isotopes (Tables 4.1 and 4.2). From this bulk material, the planets, asteroids, and comets formed, each with its own unique composition. The processes that produced these compositions separated, or fractionated, elements and isotopes from one another. By studying these elemental and isotopic fractionations, we can potentially identify the processes that separated the elements and can leam about the physical conditions involved. This is particularly important for understanding the early solar system, because its processes and conditions are not directly observable. 

Vapor-solid and vapor-liquid transformations (condensation of a gas, or its reverse, evaporation) can fractionate elements and sometimes isotopes. Each element condenses over a very limited temperature range, so one would expect the composition of the condensed phase and vapor phase to change as a function of the ambient temperature. Many of the chemical fractionations that took place in the early solar system are due, in one way or another, to this phenomenon. It is convenient to quantify volatility by use of the 50% condensation temperature, that is, the temperature by which 50% of the mass of a particular element has condensed from a gas of solar composition. Table 7.1 lists the 50% condensation temperatures for the solid elements in a gas of solar composition at a pressure of... 

In Chapter 1 and again above, we introduced the cosmochemical classification of elements based on their relative volatilities in a system of cosmic (solar) composition. In a cooling solar gas, elements condense in a certain order, depending on their volatility (Table 7.1). Condensation and evaporation partition elements between coexisting gas and solid (or liquid) phases, and the removal of one or the other of these phases can fractionate element abundances of the system as a whole from their original cosmic relative proportions. 

An evaluation of processes that have fractionated elements and isotopes in interstellar space, in the solar nebula, and within planetary bodies... 

Fraction Elements, arranged in decreasing order of their factor loadings Eigenvalue Part of total variance in %... 

The post-crystallization regime for Fe,Mg-rich chondrules is essentially quantitatively unconstrained. However, the presence of glassy mesostasis and fractionated element abundances within chondrule phases indicates that most chondrules definitively did not experience prolonged heating after they were cooled and quenched. 

The effect of volatility in fractionating elements is due to the ratio of the saturation vapor pressures, but as shown by Equation (6), the relative masses of the gas species and possible differences in the evaporation coefficients also affect the degree of chemical fractionation produced by evaporation. When Equation (6) is used in connection with isotope fractionation, it is generally assumed that isotopes of the same element have the same evaporation coefficient and that the ratio of the saturation vapor pressures is equal to the isotopic ratio at the surface of the evaporating material (i.e., no equilibrium fractionation). This results in the following equation for the relative flux of the isotopes ... 

Both models assume a single porosity at any height in the melting region and produce well mixed melts at the top. Thus, these models cannot fractionate elemental uranium from thorium and cannot produce... 

The present analysis uses t, the fractional elemental enrichment factor relative to the parent... 

Meier D. Larimer D R. Faix O. (1986) Direct liquefaction of different lignocellulosics and their constituents, 1. Fractionation, elemental composition,... 

Element present in coal Mass fraction, % Element present in eoal Mass fraction, %... 

The elements in each of these respective groups have similar chemicai propernes and for this reason are expected to show similar geochemic behaviour. This is not always the case, however, because geological processes can take advantage of subtle chemical differences and fractionate elements of a group one from the other. Thus one of the tasks of trace element geochemistry is to discover which geological processes may have this effect and to quantify the extent of a particular process. 

One of the oldest methods used the difference in solubility of RE-potassium sulfates. The oxide mixture was dissolved in acid and potassium sulfate was added. Double salts of elements in the cerium group. La, Ce, Pr, Nd and Sm, have a low solubility and were precipitated first. The double sulfates of the elements Eu, Gd and Tb are a little more soluble but precipitated as a medium fraction. Elements of the yttrium group, Y, Dy, Ho, Er, Tm, Yb and Lu, remained in solution. 

The use of fractional derivatives for the constitutive equation allows us to define a more general, rheological element (Bagley 1989). A high bandwidth fit is possible using fewer variables than Prony s method. The relation of stress T and strain S for the fractional element is defined as... 

In literature the use of the fractional element is sometimes referred to by the term spring-pot, as it behaves between a spring (i9 = 0) and a damper (5=1). It is visualized by a rhombus and defined by the proportional factor p and the fractional... 

Fig. 11 Improved model with fractional element, (a) Mechanical equivalent circuit, (b) Comparison of measurement and calculated mechanical impedance...

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