Atomic percent

Natural abundance. The natural abundances listed are on an atom percent basis for the stable nuclides present in naturally occurring elements in the earth s crust. 

Several features of ISS quantitative analysis should be noted. First of all, the relative sensitivities for the elements increase monotonically with mass. Essentially none of the other surface spectroscopies exhibit this simplicity. Because of this simple relationship, it is possible to mathematically manipulate the entire ISS spectrum such that the signal intensity is a direct quantitative representation of the surface. This is illustrated in Figure 5, which shows a depth profile of clean electrical connector pins. Atomic concentration can be read roughly as atomic percent direcdy from the approximate scale at the left. 

The relative natural abundance of a. stable i.sotope i.s important becau.se, in tracer studies, die amount of stable i.sotope is typically expres.sed in terms of atoms percent excess over the natural abundance of die i.sotope. 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

The presence of a few atomic percent of oxygen in tantalum increases electrical resistivity, hardness, tensile strength, and modulus of elasticity, but decreases elongation and reduction of area, magnetic susceptibility, and corrosion resistance to HF . 

As it happens, naturally occurring fluorine consists of a single isotope, ijF. It ibllows that the atomic mass of the element fluorine must be the same as that of F-19,19.00 amu. The situation with most elements is more complex, because they occur in nature as a mixture of two or more isotopes. To determine the atomic mass of such an element, it is necessary to know not only the masses of the individual isotopes but also their atom percents (isotopic abundances) in nature. 

Alloys of lead and thallium have a structure based upon cubic closest packing from 0 to about 87-5 atomic percent thallium. The variation of the lattice constant with composition gives strong indication that ordered structures PbTl, and PbTl, exist. In the intermediate ranges, solid solutions of the types Pb(Pb,Tl)a and Pb(Pb,Tl)TlB exist. Interpretation of interatomic distances indicates that thallium atoms present in low concentration in lead assume the same valence as lead, about 2-14, and that the valence of thallium increases with increase in the mole fraction of thallium present, having the same value, about 2-50, in PbTls and PbTl, as in pure thallium. A theory of the structure of the alloys is presented which explains the observed phase diagram,... 

The binary system lead-thallium shows an unusual type of phase diagram. Fig. 1, taken from Hansen (1936), represents in the main the results obtained by Kumakow Pushin (1907) and by Lewkonja (1907). The liquidus curve in the wide solid-solution region has a maximum at about 63 atomic percent thallium. The nature of this maximum has not previously been made clear. 

The diffraction patterns for the eighteen samples with between 0 and 87-8 atomic percent thallium correspond in positions and relative intensities of the lines to the A1 arrangement. The photographs for 93-4 and 96-9 atomic percent thallium show this pattern, and in addition the lines of the room-temperature modification of thallium, which has the A 3 structure. The sample of pure thallium shows only the latter pattern. 

For the alloys containing less than 70 atomic percent thallium the powder photographs showed the reflection 620. For the other alloys in the A1 phase the photographs contained reflections only as far as 600 and 442. The presence of the reflection 620 at Bragg angles varying from 80-7 to 85-5° significantly improves the... 

According to our interpretation the lead-thallium alloys in the range 0-75 atomic percent thallium have the structure Pb(Pb, Tl)3, and between 75 and 87-5 atomic percent thallium they have the structure Pb(Pb, TlJTlg. The values of a0 shown in Fig. 2 indicate that at 75 atomic percent thallium there is nearly complete order, corresponding to the compound PbTl3. 

In connection with a discussion of alloys of aluminum and zinc (Pauling, 1949) it was pointed out that an element present in very small quantity in solid solution in another element would have a tendency to assume the valence of the second element. The upper straight line in Fig. 2 is drawn between the value of the lattice constant for pure lead and that calculated for thallium with valence 2-14, equal to that of lead in the state of the pure element. It is seen that it passes through the experimental values of aQ for the alloys with 4-9 and 11-2 atomic percent thallium, thus supporting the suggestion that in these dilute alloys thallium has assumed the same valence as its solvent, lead. 

We have found it possible to formulate a simple treatment of the lead-thallium alloys that accounts satisfactorily for the existence of a maximum in melting-point displaced from the composition PbTls of the ordered structure, and that also accounts in a reasonably satisfactory way for the shapes of the liquidus and solidus curves throughout the range 0—75 atomic percent thallium (Fig. 1). The maximum in these curves occurs at a composition near that for a compound Pb2Tl3 or a compound PbTl2. If either of these compounds existed, it would have to be considered as forming solid solutions with lead and with thallium. The data, however, give no evidence for the existence of such compounds. 

The phase diagram constructed in this way, with the assumption that the difference in free energy of liquid lead and solid lead, Fo(l) — Fg(c), is a linear function of the temperature, and that the other parameters remain unchanged, is shown as Fig. 8. It is seen that it is qualitatively similar to the phase diagram for the lead-thallium system in the range 0-75 atomic percent thallium. 

There seem to be many binary metallic systems in which there are phases of this sort. In the sodium-lead system there are two such phases. One of them, based on the ideal structure Na3Pb, extends from 27 to 30 atomic percent lead, with its maximum at about 28 atomic percent lead and the other, corresponding to the ideal composition NaPb3, extends from 68 to 72 atomic percent lead, with maximum at about 70 atomic percent. The intensities of X-ray reflection have verified that in the second of these phases sodium atoms occupy the positions 0, 0, 0, and the other three positions in the unit cell are occupied by lead atoms isomorphously replaced to some extent by sodium atoms (Zintl Harder, 1931). These two phases are interesting in that the ranges of stability do not include the pure compounds Na8Pb and NaPb3. 

The synthesis [33] of magnesium ferrite (MgFe2C>4) from Fe203 and MgO for catalytic applications has been reported by the use of ultrasound of 20 kHz and power 100 W/cm2. Short range ordering of the alloy of Ni-(0.2-10.3) atomic percent in Cr solid could be affected by 17.5 Hz sound wave at liquid helium temperature (40 K) [34]. 

Figure 18 The elemental summary from the XPS multiplex analysis on Sample A shown in atomic percent.

Measurements of the EDS emission were limited to Cu and In edges since the EDS emissions for sulfur and molybdenum overlapped. SEM-EDS data on several regions on the film gave atomic percents representative of CuInS2 (Table 6.3), and no evidence of phosphorous could be detected under the typical detection limit of EDS (0.02 wt%), verifying that the precursor decomposes cleanly, as evidenced in EGA-TGA studies. 

Table 2 gives the compositions of the same four clay samples in atomic percent. The atomic percent is defined as the number of atoms of an element per unit volume divided by the number of atoms per unit volume of the substance containing the element. This is similar to mole fraction when the atomic percent is converted to fractional value. 

Interlaminar shear strength (ILSS), AES atomic percent, contact angle, 0, and surface energy, y, data for untreated and electrochemically oxidized pitch-based carbon hber"... 

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